Comparison of two granulation processes with the view to reduce manufacturing cost
- Authors: Maclean, Aldritt Allister
- Date: 2004
- Subjects: Drugs -- Granulation , Tablets (Medicine) , Pharmaceutical industry
- Language: English
- Type: Thesis , Masters , MTech (Chemistry)
- Identifier: vital:10980 , http://hdl.handle.net/10948/210 , Drugs -- Granulation , Tablets (Medicine) , Pharmaceutical industry
- Description: Aspen Pharmacare, one of the leading pharmaceutical manufacturers in South Africa has embarked on a programme of improving the production processes currently employed at their Port Elizabeth site. With the introduction of new technology at the site and the move towards globalization, it became imperative that Aspen remain competitive in the market. The product of interest in this research, Degoran Plus tablets, is one of the company’s leading brand sellers. Upon investigation, it became apparent that this product created opportunity for process improvement using the new technology. The manufacture of Degoran Plus entails granulation, compression and coating of the product. Most opportunity for improvement was possible in the granulation stage because of the laborious nature of the present process. Degoran Plus tablets had a history of analytical failures, especially with regard to the dissolution rate of the final product, as well as other quality related issues. The product was not considered to be a “through-runner”, which resulted in bad production output, due to continual repeats of not only analysis but also reworks in production. A strategic decision was taken to manufacture Degoran Plus using the Collette Gral granulator as the equipment offered superior mixing capability when compared to the Bear planetary granulator. It was assumed that the granulation process would result in more uniform distribution of the actives. Upon producing a better granule, a final product of superior quality would be attained. The validation protocol stipulates that three samples be taken and tested from the powder mix. Nine samples taken from granulated bulk are treated in the same manner. The validation protocol further stipulates that the first three batches manufactured utilise the new process, and tested according to the protocol. The results obtained from the analysis are evaluated statistically and a conclusion and recommendation were derived based on the evaluation.
- Full Text:
- Date Issued: 2004
- Authors: Maclean, Aldritt Allister
- Date: 2004
- Subjects: Drugs -- Granulation , Tablets (Medicine) , Pharmaceutical industry
- Language: English
- Type: Thesis , Masters , MTech (Chemistry)
- Identifier: vital:10980 , http://hdl.handle.net/10948/210 , Drugs -- Granulation , Tablets (Medicine) , Pharmaceutical industry
- Description: Aspen Pharmacare, one of the leading pharmaceutical manufacturers in South Africa has embarked on a programme of improving the production processes currently employed at their Port Elizabeth site. With the introduction of new technology at the site and the move towards globalization, it became imperative that Aspen remain competitive in the market. The product of interest in this research, Degoran Plus tablets, is one of the company’s leading brand sellers. Upon investigation, it became apparent that this product created opportunity for process improvement using the new technology. The manufacture of Degoran Plus entails granulation, compression and coating of the product. Most opportunity for improvement was possible in the granulation stage because of the laborious nature of the present process. Degoran Plus tablets had a history of analytical failures, especially with regard to the dissolution rate of the final product, as well as other quality related issues. The product was not considered to be a “through-runner”, which resulted in bad production output, due to continual repeats of not only analysis but also reworks in production. A strategic decision was taken to manufacture Degoran Plus using the Collette Gral granulator as the equipment offered superior mixing capability when compared to the Bear planetary granulator. It was assumed that the granulation process would result in more uniform distribution of the actives. Upon producing a better granule, a final product of superior quality would be attained. The validation protocol stipulates that three samples be taken and tested from the powder mix. Nine samples taken from granulated bulk are treated in the same manner. The validation protocol further stipulates that the first three batches manufactured utilise the new process, and tested according to the protocol. The results obtained from the analysis are evaluated statistically and a conclusion and recommendation were derived based on the evaluation.
- Full Text:
- Date Issued: 2004
The use and performance of recycling polypropylene in lead-acid battery cases
- Authors: Rust, Nico
- Date: 2004
- Subjects: Polypropylene , Lead-acid batteries
- Language: English
- Type: Thesis , Masters , MTech (Chemistry)
- Identifier: vital:10978 , http://hdl.handle.net/10948/269 , Polypropylene , Lead-acid batteries
- Description: Polypropylene has proven to be the ideal material for the outer shell of the lead acid batteries. Due to its mold-ability and inert properties the material provides a capsule for the functioning components of the lead acid battery and can withstand a variety conditions encountered during its application, such as impact shock resistance, high and low temperatures and acid resistance. Polypropylene has however become of great concern with regards to environmental pollution since it is generally resistant to normal conditions of degradation and can only be properly disposed of by incineration. This factor has encouraged the industry to find ways to regenerate spent polypropylene. A good example of such a process is the recycling of lead acid batteries. This allows not only for the regeneration of lead, but also for the recycling of polypropylene in the manufacturing of battery cases. There are some cost advantages in using recycled polypropylene. However it does have its disadvantages in that the material does start to deteriorate after multiple processes. A common practice amongst battery manufacturers is to add virgin polypropylene to the recycled material in order to ensure performance consistency. The comparative study investigated the use of various ratios of virgin and recycled PP in the manufacturing of lead acid battery cases and their influence on the physical properties and performance of the final material. The degradation of PP was also investigated as the material was subjected to multiple manufacturing processes where the influence of stabilizers was further considered. A common technique of PP analysis such as MFI was shown to be an effective technique to maintain good quality control. The study further showed that it is important that the material grade of PP used in the manufacturing of the battery case and lid is compatible in order to allow for effective heating sealing of the two components. Polypropylene has a waxy surface finish and it is generally difficult to label or write on. Labels tend to fall off in application and make it difficult to maintain a track record of the manufactured batteries with time. This study showed successfully that a laser activated dye can be added to the PP without influencing its color or its performance. This allows for successful labeling of battery cases by various bar coding writers that can trace the battery through its manufacturing process. Lead acid batteries are often operated outside the specified temperature range that is determined by battery manufacturers resulting in premature failure. These failures can occur within the warranty period of the battery and result in illicit claims since the monitoring of the batteries in its application was not possible. A suitable temperature monitoring device was designed that would be incorporated into the vent cap or lid of the battery case. The device contained temperature sensitive indicators that would undergo a permanent color change at specified temperatures thereby giving the battery manufacturer an indication as to the maximum temperature the battery was exposed to.
- Full Text:
- Date Issued: 2004
- Authors: Rust, Nico
- Date: 2004
- Subjects: Polypropylene , Lead-acid batteries
- Language: English
- Type: Thesis , Masters , MTech (Chemistry)
- Identifier: vital:10978 , http://hdl.handle.net/10948/269 , Polypropylene , Lead-acid batteries
- Description: Polypropylene has proven to be the ideal material for the outer shell of the lead acid batteries. Due to its mold-ability and inert properties the material provides a capsule for the functioning components of the lead acid battery and can withstand a variety conditions encountered during its application, such as impact shock resistance, high and low temperatures and acid resistance. Polypropylene has however become of great concern with regards to environmental pollution since it is generally resistant to normal conditions of degradation and can only be properly disposed of by incineration. This factor has encouraged the industry to find ways to regenerate spent polypropylene. A good example of such a process is the recycling of lead acid batteries. This allows not only for the regeneration of lead, but also for the recycling of polypropylene in the manufacturing of battery cases. There are some cost advantages in using recycled polypropylene. However it does have its disadvantages in that the material does start to deteriorate after multiple processes. A common practice amongst battery manufacturers is to add virgin polypropylene to the recycled material in order to ensure performance consistency. The comparative study investigated the use of various ratios of virgin and recycled PP in the manufacturing of lead acid battery cases and their influence on the physical properties and performance of the final material. The degradation of PP was also investigated as the material was subjected to multiple manufacturing processes where the influence of stabilizers was further considered. A common technique of PP analysis such as MFI was shown to be an effective technique to maintain good quality control. The study further showed that it is important that the material grade of PP used in the manufacturing of the battery case and lid is compatible in order to allow for effective heating sealing of the two components. Polypropylene has a waxy surface finish and it is generally difficult to label or write on. Labels tend to fall off in application and make it difficult to maintain a track record of the manufactured batteries with time. This study showed successfully that a laser activated dye can be added to the PP without influencing its color or its performance. This allows for successful labeling of battery cases by various bar coding writers that can trace the battery through its manufacturing process. Lead acid batteries are often operated outside the specified temperature range that is determined by battery manufacturers resulting in premature failure. These failures can occur within the warranty period of the battery and result in illicit claims since the monitoring of the batteries in its application was not possible. A suitable temperature monitoring device was designed that would be incorporated into the vent cap or lid of the battery case. The device contained temperature sensitive indicators that would undergo a permanent color change at specified temperatures thereby giving the battery manufacturer an indication as to the maximum temperature the battery was exposed to.
- Full Text:
- Date Issued: 2004
To investigate the effect of a change in hard gelatin capsule supplier on a phenytoin sodium capsule formulation
- Authors: Marx, Amor
- Date: 2004
- Subjects: Capsules (Pharmacy) , Phenytoin
- Language: English
- Type: Thesis , Masters , MTech (Chemistry)
- Identifier: vital:10984 , http://hdl.handle.net/10948/265 , Capsules (Pharmacy) , Phenytoin
- Description: Stability studies were undertaken at ambient (25ºC/60%RH) and accelerated conditions (40ºC/75%RH) to determine the effect of changing of hard gelatin capsule supplier on a phenytoin sodium (100 mg) capsule formulation. Three hard gelatin capsule suppliers: RP Scherer (Supplier A), Capsugel (supplier B) and Associated Caps (Supplier C) were used in the study. Capsules were analyzed just after filling of the capsules (T0), after 1 month (T1), after 2 months (T2) and after 3 months (T3) after being stored in securitainers under the above-mentioned conditions. The moisture content of the empty shells as well as the capsule contents were analysed at each time-point. The capsule disintegration time was recorded at each time point. Multi-point dissolution testing was performed at each time point to determine the release of the active substance in each case. Based on the achieved results, the best capsule shell supplier was recommended, and other suggestions were made to improve the capsule formulation.
- Full Text:
- Date Issued: 2004
- Authors: Marx, Amor
- Date: 2004
- Subjects: Capsules (Pharmacy) , Phenytoin
- Language: English
- Type: Thesis , Masters , MTech (Chemistry)
- Identifier: vital:10984 , http://hdl.handle.net/10948/265 , Capsules (Pharmacy) , Phenytoin
- Description: Stability studies were undertaken at ambient (25ºC/60%RH) and accelerated conditions (40ºC/75%RH) to determine the effect of changing of hard gelatin capsule supplier on a phenytoin sodium (100 mg) capsule formulation. Three hard gelatin capsule suppliers: RP Scherer (Supplier A), Capsugel (supplier B) and Associated Caps (Supplier C) were used in the study. Capsules were analyzed just after filling of the capsules (T0), after 1 month (T1), after 2 months (T2) and after 3 months (T3) after being stored in securitainers under the above-mentioned conditions. The moisture content of the empty shells as well as the capsule contents were analysed at each time-point. The capsule disintegration time was recorded at each time point. Multi-point dissolution testing was performed at each time point to determine the release of the active substance in each case. Based on the achieved results, the best capsule shell supplier was recommended, and other suggestions were made to improve the capsule formulation.
- Full Text:
- Date Issued: 2004
Evaluation of manufacturing processes for the production of atrazine
- Authors: Schaefer, Melissa Claire
- Date: 2002
- Subjects: Atrazine , Pesticides
- Language: English
- Type: Thesis , Masters , MTech (Chemistry)
- Identifier: vital:10960 , http://hdl.handle.net/10948/96 , Atrazine , Pesticides
- Description: This report describes the results of investigations carried out with the view to find an alternative for MIBK as solvent for the production of atrazine as currently practised by Dow AgroSciences in South Africa. The main motivating factors for the said investigation was: · to increase the yield of atrazine produced, · to reduce the amount of organics, consisting essentially of reaction solvent containing dissolved product, in the aqueous process effluent, and · to improve the properties of the solid (crystalline) product to enable easier product formulation. Synthetic reactions carried out in the absence of organic solvent, i.e. in essentially a 10% NaCl solution containing a surfactant, proved rather disappointing. Low yields of atrazine were obtained together with relatively large amounts of by-products such as propazine and simazine, irrespective of the nature of the surfactant. The reason for the low yield of atrazine and high yields of by-products were established in competing substitution reactions. In these reactions, IPA was reacted with an equimolar mixture of cyanuric chloride and mono-i (first reaction intermediate) in both aqueous medium and in toluene as reaction solvent. The results of these experiments indicated that in aqueous medium IPA reacts faster with mono-i than cyanuric chloride to give propazine as by-product. In toluene, however, the preferred reaction is with cyanuric chloride to give more mono-i as product. Toluene was investigated as an alternative organic solvent to MIBK in view of its desirable properties such as low solubility in water and ease of recovery and recycling. The synthesis of atrazine was optimised in terms of addition sequence and rates of amine reagents and base (HCl acceptor), both by means of benchscale reactions and reaction calorimetry. Reaction energy profiles indicated that both the reaction of secondary amine/NaOH and primary amine/NaOH were virtually instantaneous. This implies that the reaction can be performed under feed control conditions. Of particular importance in ensuring high yields of high purity product was accurate temperature control (since both reaction steps are highly exothermic) and mixing. The latter was important in view of the rapid reaction of amine/NaOH with cyanuric chloride, as well as the possible reaction of mono-i, the first reaction intermediate, with IPA in cases of local excesses of reagent. Under optimum conditions, a yield of atrazine > 97% could be achieved where the resultant product was well within stipulated product specifications. In view of the results obtained, the following recommendations regarding the synthesis of atrazine in toluene as reaction solvent can be made: · Use a reagent addition sequence that staggers the addition of amine and NaOH in such a manner that amine is added first for a short while, followed by the simultaneous addition of amine and NaOH, and ending with NaOH. Use two reaction vessels in series, one for the IPA addition reaction and one for the MEA addition reaction. In this manner the reaction can be run on a continuous basis since no lag time between amine additions is required. Also, smaller reactors may be used whilst maintaining high production rates. Smaller reactors will improve both temperature control and mixing of reagents.
- Full Text:
- Date Issued: 2002
- Authors: Schaefer, Melissa Claire
- Date: 2002
- Subjects: Atrazine , Pesticides
- Language: English
- Type: Thesis , Masters , MTech (Chemistry)
- Identifier: vital:10960 , http://hdl.handle.net/10948/96 , Atrazine , Pesticides
- Description: This report describes the results of investigations carried out with the view to find an alternative for MIBK as solvent for the production of atrazine as currently practised by Dow AgroSciences in South Africa. The main motivating factors for the said investigation was: · to increase the yield of atrazine produced, · to reduce the amount of organics, consisting essentially of reaction solvent containing dissolved product, in the aqueous process effluent, and · to improve the properties of the solid (crystalline) product to enable easier product formulation. Synthetic reactions carried out in the absence of organic solvent, i.e. in essentially a 10% NaCl solution containing a surfactant, proved rather disappointing. Low yields of atrazine were obtained together with relatively large amounts of by-products such as propazine and simazine, irrespective of the nature of the surfactant. The reason for the low yield of atrazine and high yields of by-products were established in competing substitution reactions. In these reactions, IPA was reacted with an equimolar mixture of cyanuric chloride and mono-i (first reaction intermediate) in both aqueous medium and in toluene as reaction solvent. The results of these experiments indicated that in aqueous medium IPA reacts faster with mono-i than cyanuric chloride to give propazine as by-product. In toluene, however, the preferred reaction is with cyanuric chloride to give more mono-i as product. Toluene was investigated as an alternative organic solvent to MIBK in view of its desirable properties such as low solubility in water and ease of recovery and recycling. The synthesis of atrazine was optimised in terms of addition sequence and rates of amine reagents and base (HCl acceptor), both by means of benchscale reactions and reaction calorimetry. Reaction energy profiles indicated that both the reaction of secondary amine/NaOH and primary amine/NaOH were virtually instantaneous. This implies that the reaction can be performed under feed control conditions. Of particular importance in ensuring high yields of high purity product was accurate temperature control (since both reaction steps are highly exothermic) and mixing. The latter was important in view of the rapid reaction of amine/NaOH with cyanuric chloride, as well as the possible reaction of mono-i, the first reaction intermediate, with IPA in cases of local excesses of reagent. Under optimum conditions, a yield of atrazine > 97% could be achieved where the resultant product was well within stipulated product specifications. In view of the results obtained, the following recommendations regarding the synthesis of atrazine in toluene as reaction solvent can be made: · Use a reagent addition sequence that staggers the addition of amine and NaOH in such a manner that amine is added first for a short while, followed by the simultaneous addition of amine and NaOH, and ending with NaOH. Use two reaction vessels in series, one for the IPA addition reaction and one for the MEA addition reaction. In this manner the reaction can be run on a continuous basis since no lag time between amine additions is required. Also, smaller reactors may be used whilst maintaining high production rates. Smaller reactors will improve both temperature control and mixing of reagents.
- Full Text:
- Date Issued: 2002
Process for the preparation of vanillin from a mixed m-cresol/p-cresol stream
- Authors: Buddoo, Subash
- Date: 2002
- Subjects: Vanillin
- Language: English
- Type: Thesis , Masters , MTech (Chemistry)
- Identifier: vital:10968 , http://hdl.handle.net/10948/138 , Vanillin
- Description: The Vanillin project was undertaken by AECI as it was believed that with the raw materials available from SASOL i.e. cresols, it would be possible to develop a process that would be globally competitive. A process for preparing both vanillin and ethyl vanillin was developed by AECI’s Research and Development Department using a mixed m- and p-cresol stream as feed. The displacement of bromide by methoxide is very successful when using a dimethyl formamide (DMF)/alcohol solvent system and excellent conversions (>95%) and selectivities (>95%) may be obtained. However, the use of DMF, which poses a serious chronic health risk, is unacceptable in this process since the products are intended for use as food and flavouring chemicals. In view of the above the main objectives of this study were: · To find a suitable alternative solvent system, which could produce comparable results while still being economically viable; · To develop an appropriate experimental protocol in the laboratory based on the alternative solvent system; · To determine the important reaction variables by conducting statistically designed experiments; · To optimise the reaction to produce a reproducible and robust experimental protocol; and · To test the reaction thoroughly at bench-scale level and to obtain experimental data for scale-up to pilot plant The most promising alternative solvent system was a methanol/methyl acetate mixture, which produced satisfactory results in the preliminary assessment (conversion of 98.3% and selectivity of 92.0%). DMA and acetonitrile also produced promising results but were not considered for further investigation because of toxicity and cost issues. A set of statistically designed experiments was carried out on the methanol/methyl acetate solvent system where four variables were tested i.e., substrate concentration, temperature, catalyst loading, and methanol to methyl acetate volume ratio. The experimentally determined response surface model showed that the most important variable was catalyst loading (63.2%) for conversion. With respect to selectivity, the most important variables were catalyst loading (31.9%) and methanol to methyl acetate ratio (33.1%). The optimum reaction conditions were as follows: · Temperature: 120°C · Methanol:methyl acetate: 15:1 vol/vol · Catalyst loading: 8 mol % to substrate · Substrate concentration: 22 %m/m on solvent · Catalyst: Copper(I) bromide · Sodium Equivalents: 2.7 wrt substrate · Time: 3 hours The optimum conditions were tested for reproducibility in a 1 Labmax pressure reactor. Replicated reactions, two at a 10% and two at a 20% substrate concentration gave conversions and selectivities all greater than 90%. Although the reaction mixture was a slurry at these concentrations, the reactions were very fast and virtually complete within the first hour (~95% conversion). Initial scale-up studies were conducted in an 8 Parr reactor where five reactions were carried out using the optimum conditions described above. The conversion of substrate and vanillin selectivity was consistently high and compared favourably to the Labmax reactions. The average conversion was 97.3% (96.3 to 98.5%) at an average selectivity of 98.2% (97.4 to 99.1%). A study of the reaction kinetics confirmed that the reaction was first order with respect to the substrate as a plot of substrate concentration versus reaction rate gave a straight line. The rate constant was calculated as 1.1096 k(h-1). The reaction mechanism proposed for the copper assisted nucleophilic aromatic substitution involves the formation of an adduct between sodium methoxide, methyl acetate and copper(I) bromide. The formation of a transient intermediate with the substrate allows intramolecular delivery of the methoxide ion to the aryl moiety through a CuI – CuIII type cycle.
- Full Text:
- Date Issued: 2002
- Authors: Buddoo, Subash
- Date: 2002
- Subjects: Vanillin
- Language: English
- Type: Thesis , Masters , MTech (Chemistry)
- Identifier: vital:10968 , http://hdl.handle.net/10948/138 , Vanillin
- Description: The Vanillin project was undertaken by AECI as it was believed that with the raw materials available from SASOL i.e. cresols, it would be possible to develop a process that would be globally competitive. A process for preparing both vanillin and ethyl vanillin was developed by AECI’s Research and Development Department using a mixed m- and p-cresol stream as feed. The displacement of bromide by methoxide is very successful when using a dimethyl formamide (DMF)/alcohol solvent system and excellent conversions (>95%) and selectivities (>95%) may be obtained. However, the use of DMF, which poses a serious chronic health risk, is unacceptable in this process since the products are intended for use as food and flavouring chemicals. In view of the above the main objectives of this study were: · To find a suitable alternative solvent system, which could produce comparable results while still being economically viable; · To develop an appropriate experimental protocol in the laboratory based on the alternative solvent system; · To determine the important reaction variables by conducting statistically designed experiments; · To optimise the reaction to produce a reproducible and robust experimental protocol; and · To test the reaction thoroughly at bench-scale level and to obtain experimental data for scale-up to pilot plant The most promising alternative solvent system was a methanol/methyl acetate mixture, which produced satisfactory results in the preliminary assessment (conversion of 98.3% and selectivity of 92.0%). DMA and acetonitrile also produced promising results but were not considered for further investigation because of toxicity and cost issues. A set of statistically designed experiments was carried out on the methanol/methyl acetate solvent system where four variables were tested i.e., substrate concentration, temperature, catalyst loading, and methanol to methyl acetate volume ratio. The experimentally determined response surface model showed that the most important variable was catalyst loading (63.2%) for conversion. With respect to selectivity, the most important variables were catalyst loading (31.9%) and methanol to methyl acetate ratio (33.1%). The optimum reaction conditions were as follows: · Temperature: 120°C · Methanol:methyl acetate: 15:1 vol/vol · Catalyst loading: 8 mol % to substrate · Substrate concentration: 22 %m/m on solvent · Catalyst: Copper(I) bromide · Sodium Equivalents: 2.7 wrt substrate · Time: 3 hours The optimum conditions were tested for reproducibility in a 1 Labmax pressure reactor. Replicated reactions, two at a 10% and two at a 20% substrate concentration gave conversions and selectivities all greater than 90%. Although the reaction mixture was a slurry at these concentrations, the reactions were very fast and virtually complete within the first hour (~95% conversion). Initial scale-up studies were conducted in an 8 Parr reactor where five reactions were carried out using the optimum conditions described above. The conversion of substrate and vanillin selectivity was consistently high and compared favourably to the Labmax reactions. The average conversion was 97.3% (96.3 to 98.5%) at an average selectivity of 98.2% (97.4 to 99.1%). A study of the reaction kinetics confirmed that the reaction was first order with respect to the substrate as a plot of substrate concentration versus reaction rate gave a straight line. The rate constant was calculated as 1.1096 k(h-1). The reaction mechanism proposed for the copper assisted nucleophilic aromatic substitution involves the formation of an adduct between sodium methoxide, methyl acetate and copper(I) bromide. The formation of a transient intermediate with the substrate allows intramolecular delivery of the methoxide ion to the aryl moiety through a CuI – CuIII type cycle.
- Full Text:
- Date Issued: 2002
The electrochemical hydroxylation of aromatic substrates
- Authors: Rautenbach, Daniel
- Date: 2002
- Subjects: Aromatic compounds , Hydroxylation
- Language: English
- Type: Thesis , Masters , MTech (Chemistry)
- Identifier: vital:10959 , http://hdl.handle.net/10948/94 , Aromatic compounds , Hydroxylation
- Description: The electrochemical hydroxylation of aromatic substrates was investigated in some detail, with the view to develop a method, which could produce dihydroxybenzenes in acceptable yields. Of particular interest was the selectivity and yield of the 1,4-dihydroxybenzenes. Two distinctly different methods were investigated in order to achieve this goal, acyloxylation and direct electrochemical hydroxylation. Acyloxylation is the process where radical cations generated at the anode undergoes nucleophilic attack by acetate anions. The resulting aromatic acetates so produced can then be hydrolysed to the phenolic compounds. Two nucleophile systems were considered in the investigation, acetates (acetoxylation) and trifluoro-acetates (trifluoro-acetoxylation). These investigations were conducted under a variety of conditions using phenol and phenyl acetate as starting materials. From the results it was, however, concluded that the acetoxylation of these aromatic compounds occurs in unacceptable product and current yields. Trifluoro-acetoxylation on the other hand showed promise, but due to the nature and cost of the reagents it was deemed to be an impractical process. Direct electrochemical hydroxylation: in which the radical cations produced at the anode undergoes nucleophilic attack by water producing the corresponding dihydroxybenzenes. These dihydroxybenzenes are then further oxidised to the benzoquinones, which then undergo reduction at the cathode in order to produce the corresponding dihydroxybenzene. In this process phenol, 2-tert-butylphenol and 2,6-di-tert-butylphenol were investigated as substrates. The results indicated that the yield towards the 1,4-dihdroxybenzenes increased as the degree of substitution on the ring increased.
- Full Text:
- Date Issued: 2002
- Authors: Rautenbach, Daniel
- Date: 2002
- Subjects: Aromatic compounds , Hydroxylation
- Language: English
- Type: Thesis , Masters , MTech (Chemistry)
- Identifier: vital:10959 , http://hdl.handle.net/10948/94 , Aromatic compounds , Hydroxylation
- Description: The electrochemical hydroxylation of aromatic substrates was investigated in some detail, with the view to develop a method, which could produce dihydroxybenzenes in acceptable yields. Of particular interest was the selectivity and yield of the 1,4-dihydroxybenzenes. Two distinctly different methods were investigated in order to achieve this goal, acyloxylation and direct electrochemical hydroxylation. Acyloxylation is the process where radical cations generated at the anode undergoes nucleophilic attack by acetate anions. The resulting aromatic acetates so produced can then be hydrolysed to the phenolic compounds. Two nucleophile systems were considered in the investigation, acetates (acetoxylation) and trifluoro-acetates (trifluoro-acetoxylation). These investigations were conducted under a variety of conditions using phenol and phenyl acetate as starting materials. From the results it was, however, concluded that the acetoxylation of these aromatic compounds occurs in unacceptable product and current yields. Trifluoro-acetoxylation on the other hand showed promise, but due to the nature and cost of the reagents it was deemed to be an impractical process. Direct electrochemical hydroxylation: in which the radical cations produced at the anode undergoes nucleophilic attack by water producing the corresponding dihydroxybenzenes. These dihydroxybenzenes are then further oxidised to the benzoquinones, which then undergo reduction at the cathode in order to produce the corresponding dihydroxybenzene. In this process phenol, 2-tert-butylphenol and 2,6-di-tert-butylphenol were investigated as substrates. The results indicated that the yield towards the 1,4-dihdroxybenzenes increased as the degree of substitution on the ring increased.
- Full Text:
- Date Issued: 2002
The evaluation of waste minimization/waste treatment strategies for a commercial production process of 4-methyl-3-thiosemicarbazide
- Authors: Bennen, Wilroy
- Date: 2002
- Subjects: Hazardous wastes , Hazardous substances -- Analysis
- Language: English
- Type: Thesis , Masters , MTech (Chemistry)
- Identifier: vital:10951 , http://hdl.handle.net/10948/97 , Hazardous wastes , Hazardous substances -- Analysis
- Description: Chemical synthesis is closely related to waste minimization. There is no chemical process that does not produce waste. The methods used by industry to deal with this waste is a major environmental concern. This thesis describes the laboratory scale waste minimization and waste treatment strategies for the commercial production process of 4-methyl-3-thiosemicarbazide (MTSC). The production process of 4-methyl-3-thiosemicarbazide was investigated with the aim of increasing the isolated yield of MTSC and at the same time decrease the amount and toxicity of effluent obtained. During this study, parameters were investigated such as the use of excess DIPEA and the temperature of the reaction. Preliminary studies clearly showed that both factors have a significant influence on the final yield of the product. The next part of the investigation was to optimize the two parameters influencing the isolated yield of the MTSC. For this investigation, a multi factorial design was used to determine the optimum conditions in the MTSC yield response. From the results obtained, it was clear that the excess of DIPEA and the temperature of the reaction both need to be high to obtain high yields. These theoretical results were confirmed by results obtained practically, where yields of up 82 % were obtained, but it became clear that even higher yields could be obtained since chromatographic results showed yeilds as high as 90 %. The mass balance of the MTSC synthesis showed a loss of approximately 30 grams per reaction. This loss may have an influence on the final yield. The effluent obtained during the synthesis of MTSC was investigated and a waste treatment protocol was established to reduce the high COD value of the MTSC effluent. The protocol consists of two steps used for the clean up of the effluent. The first being a cooling step; the effluent was cooled at 0oC to induce precipitation of a solid, consisting mostly of MTSC. The second step is a high pressure wet oxidation of the effluent with oxygen in a high pressure reactor. The remaining compounds in the effluent were oxidized, resulting in another precipitate, consisting mostly of sulphur. After the oxidation the COD value of the effluent was decreased by 98 % to a value of 0.4 %. The MTSC present in the precipitate obtained after cooling could be isolated and purified, to add to the yield of the synthesis. The sulphur obtained during the oxidation could also be isolated and reused, or sold to prevent it from contaminating the environment.
- Full Text:
- Date Issued: 2002
- Authors: Bennen, Wilroy
- Date: 2002
- Subjects: Hazardous wastes , Hazardous substances -- Analysis
- Language: English
- Type: Thesis , Masters , MTech (Chemistry)
- Identifier: vital:10951 , http://hdl.handle.net/10948/97 , Hazardous wastes , Hazardous substances -- Analysis
- Description: Chemical synthesis is closely related to waste minimization. There is no chemical process that does not produce waste. The methods used by industry to deal with this waste is a major environmental concern. This thesis describes the laboratory scale waste minimization and waste treatment strategies for the commercial production process of 4-methyl-3-thiosemicarbazide (MTSC). The production process of 4-methyl-3-thiosemicarbazide was investigated with the aim of increasing the isolated yield of MTSC and at the same time decrease the amount and toxicity of effluent obtained. During this study, parameters were investigated such as the use of excess DIPEA and the temperature of the reaction. Preliminary studies clearly showed that both factors have a significant influence on the final yield of the product. The next part of the investigation was to optimize the two parameters influencing the isolated yield of the MTSC. For this investigation, a multi factorial design was used to determine the optimum conditions in the MTSC yield response. From the results obtained, it was clear that the excess of DIPEA and the temperature of the reaction both need to be high to obtain high yields. These theoretical results were confirmed by results obtained practically, where yields of up 82 % were obtained, but it became clear that even higher yields could be obtained since chromatographic results showed yeilds as high as 90 %. The mass balance of the MTSC synthesis showed a loss of approximately 30 grams per reaction. This loss may have an influence on the final yield. The effluent obtained during the synthesis of MTSC was investigated and a waste treatment protocol was established to reduce the high COD value of the MTSC effluent. The protocol consists of two steps used for the clean up of the effluent. The first being a cooling step; the effluent was cooled at 0oC to induce precipitation of a solid, consisting mostly of MTSC. The second step is a high pressure wet oxidation of the effluent with oxygen in a high pressure reactor. The remaining compounds in the effluent were oxidized, resulting in another precipitate, consisting mostly of sulphur. After the oxidation the COD value of the effluent was decreased by 98 % to a value of 0.4 %. The MTSC present in the precipitate obtained after cooling could be isolated and purified, to add to the yield of the synthesis. The sulphur obtained during the oxidation could also be isolated and reused, or sold to prevent it from contaminating the environment.
- Full Text:
- Date Issued: 2002
The investigation of the hydrolysis reaction of m-phenylene to resorcinol
- Authors: Khaile, Thebeeapelo John
- Date: 2002
- Subjects: Resorcinol
- Language: English
- Type: Thesis , Masters , MTech (Chemistry)
- Identifier: vital:10961 , http://hdl.handle.net/10948/107 , Resorcinol
- Description: The purpose of this study was to characterise the resinous material formed during the acid catalysed hydrolysis of m-phenylenediamine (MPDA) to resorcinol, and to establish a reaction mechanism that could explain the formation of both resorcinol and the resinous materials in the reaction. A further objective was to determine reaction conditions that would lead to reduced formation of the resins during the hydrolysis reaction. The number of compounds present in a sample taken during the course of the hydrolysis reaction was determined by HPLC fitted with a photodiode array detector. Five main components were detected. These compounds were identified as mphenylenediamine, m-aminophenol, resorcinol, 3,3’-aminodiphenylamine and 3- amino-3’-hydroxydiphenylamine by means of GC-MS. 3,3’-Diaminodiphenylamine is formed by self-condensation of MPDA and 3-amino-3’-hydroxydiphenylamine is formed by the reaction of MPDA with resorcinol. The degree of formation of these intermediates is substantially reduced when MPDA is added dose-wise to phosphoric acid at a reaction temperature of 220oC. The reaction mechanism of the hydrolysis reaction was investigated by isotopic lable incorporation, followed by analysis by NMR. This was done by hydrolysing MPDA using deuterated phosphoric acid (D3PO4). D3PO4 was generated by dissolving phosphorus pentoxide in deuterium oxide. The resorcinol product obtained from the hydrolysis using D3PO4 was found to be deuterated on the C-2, C-4 and C-6 positions. This suggests that the hydrolysis reaction involves protonation of MPDA on these positions, and this results in the formation of an iminium ion as one of the resonance forms. Hydrolysis then occurs on the positively charged carbon of this species. Fertiliser grade phosphoric acid can be used in the hydrolysis reaction, provided sulphates are removed before the acid is used in the hydrolysis reaction. The hydrolysis reaction using either ammonium sulphate or sulphuric acid produces resorcinol in yields lower than 60% if the hydrolysis is conducted in one pass. If these catalysts are used in the hydrolysis reaction, the reaction mixture needs to be re-heated after removal of resorcinol in order to increase the yield. Hydrolysis of MPDA using zirconium phosphate as catalyst gave resorcinol yields in excess of 90% over 24 hours. These reactions were carried out at very low concentrations of MPDA (0.3%). The mode of catalysis in these reactions is unclear. There is a possibility that the reaction is catalysed by phosphoric acid that leaches out of zirconium phosphate at high temperatures. The reaction might therefore not differ mechanistically from the phosphoric acid catalysed reaction. Further studies are required to clarify this point.
- Full Text:
- Date Issued: 2002
- Authors: Khaile, Thebeeapelo John
- Date: 2002
- Subjects: Resorcinol
- Language: English
- Type: Thesis , Masters , MTech (Chemistry)
- Identifier: vital:10961 , http://hdl.handle.net/10948/107 , Resorcinol
- Description: The purpose of this study was to characterise the resinous material formed during the acid catalysed hydrolysis of m-phenylenediamine (MPDA) to resorcinol, and to establish a reaction mechanism that could explain the formation of both resorcinol and the resinous materials in the reaction. A further objective was to determine reaction conditions that would lead to reduced formation of the resins during the hydrolysis reaction. The number of compounds present in a sample taken during the course of the hydrolysis reaction was determined by HPLC fitted with a photodiode array detector. Five main components were detected. These compounds were identified as mphenylenediamine, m-aminophenol, resorcinol, 3,3’-aminodiphenylamine and 3- amino-3’-hydroxydiphenylamine by means of GC-MS. 3,3’-Diaminodiphenylamine is formed by self-condensation of MPDA and 3-amino-3’-hydroxydiphenylamine is formed by the reaction of MPDA with resorcinol. The degree of formation of these intermediates is substantially reduced when MPDA is added dose-wise to phosphoric acid at a reaction temperature of 220oC. The reaction mechanism of the hydrolysis reaction was investigated by isotopic lable incorporation, followed by analysis by NMR. This was done by hydrolysing MPDA using deuterated phosphoric acid (D3PO4). D3PO4 was generated by dissolving phosphorus pentoxide in deuterium oxide. The resorcinol product obtained from the hydrolysis using D3PO4 was found to be deuterated on the C-2, C-4 and C-6 positions. This suggests that the hydrolysis reaction involves protonation of MPDA on these positions, and this results in the formation of an iminium ion as one of the resonance forms. Hydrolysis then occurs on the positively charged carbon of this species. Fertiliser grade phosphoric acid can be used in the hydrolysis reaction, provided sulphates are removed before the acid is used in the hydrolysis reaction. The hydrolysis reaction using either ammonium sulphate or sulphuric acid produces resorcinol in yields lower than 60% if the hydrolysis is conducted in one pass. If these catalysts are used in the hydrolysis reaction, the reaction mixture needs to be re-heated after removal of resorcinol in order to increase the yield. Hydrolysis of MPDA using zirconium phosphate as catalyst gave resorcinol yields in excess of 90% over 24 hours. These reactions were carried out at very low concentrations of MPDA (0.3%). The mode of catalysis in these reactions is unclear. There is a possibility that the reaction is catalysed by phosphoric acid that leaches out of zirconium phosphate at high temperatures. The reaction might therefore not differ mechanistically from the phosphoric acid catalysed reaction. Further studies are required to clarify this point.
- Full Text:
- Date Issued: 2002
Evaluation of Lewis acid catalysed and other nitration strategies for the selective nitration of cresols
- Van Niekerk, Rudolf Jacob Francois
- Authors: Van Niekerk, Rudolf Jacob Francois
- Date: 2001
- Subjects: Nitration
- Language: English
- Type: Thesis , Masters , MTech (Chemistry)
- Identifier: vital:10957 , http://hdl.handle.net/10948/60 , Nitration
- Description: The nitration of m- and p-cresol was investigated under mild reaction conditions in a number of solvents; the effects of certain nitration catalysts were also evaluated. These different reaction parameters were evaluated in terms of their effect on a number of important reaction responses. Other important factors that were investigated were the manipulation of the isomer ratios by changing reaction parameters, as well as important process chemistry information, such as product distribution, isolation and purification, identification of side products formed, and evaluation of the heat of reaction. Use was made of an experimental design system to evaluate the effect of reaction parameters on the chosen design responses. It was found that the ratio of para to ortho nitrocresol products could be influenced slightly by using low concentrations of nitric acid and low reaction temperatures. A different mechanism for the formation of 2-methyl-1,4-benzoquinone (from mcresol nitration) was proposed (compared with that previously reported), which could explain a “one mole nitric acid” pathway and the fact that only the pbenzoquinone isomer was observed. Reaction side products were identified and found to consist of dimers of cresol and nitrocresol, which were probably the result of oxidation of the cresol, subsequent formation of a quinomethide intermediate and reaction with either the product or the substrate. The heat of nitration was determined for various reaction systems and found to be governed by two factors, namely the actual nitration process and also an oxidation process, which is responsible for the formation of side products.
- Full Text:
- Date Issued: 2001
- Authors: Van Niekerk, Rudolf Jacob Francois
- Date: 2001
- Subjects: Nitration
- Language: English
- Type: Thesis , Masters , MTech (Chemistry)
- Identifier: vital:10957 , http://hdl.handle.net/10948/60 , Nitration
- Description: The nitration of m- and p-cresol was investigated under mild reaction conditions in a number of solvents; the effects of certain nitration catalysts were also evaluated. These different reaction parameters were evaluated in terms of their effect on a number of important reaction responses. Other important factors that were investigated were the manipulation of the isomer ratios by changing reaction parameters, as well as important process chemistry information, such as product distribution, isolation and purification, identification of side products formed, and evaluation of the heat of reaction. Use was made of an experimental design system to evaluate the effect of reaction parameters on the chosen design responses. It was found that the ratio of para to ortho nitrocresol products could be influenced slightly by using low concentrations of nitric acid and low reaction temperatures. A different mechanism for the formation of 2-methyl-1,4-benzoquinone (from mcresol nitration) was proposed (compared with that previously reported), which could explain a “one mole nitric acid” pathway and the fact that only the pbenzoquinone isomer was observed. Reaction side products were identified and found to consist of dimers of cresol and nitrocresol, which were probably the result of oxidation of the cresol, subsequent formation of a quinomethide intermediate and reaction with either the product or the substrate. The heat of nitration was determined for various reaction systems and found to be governed by two factors, namely the actual nitration process and also an oxidation process, which is responsible for the formation of side products.
- Full Text:
- Date Issued: 2001
Strategies for the improvement of the industrial oxidation of cymene
- Authors: Harmse, Nigel
- Date: 2001
- Subjects: Oxidation , Cymene
- Language: English
- Type: Thesis , Masters , MTech (Chemistry)
- Identifier: vital:10958 , http://hdl.handle.net/10948/73 , Oxidation , Cymene
- Description: The oxidation of cymene with dioxygen has been investigated in some detail with the view of establishing the feasibility of improving the efficiency of the oxidation process. Of particular interest were the rate of cymene oxidation and the selectivity of the oxidation process for the tertiary cymene hydroperoxide, especially at conversions above 15%. In order to be able to evaluate the selectivity of oxidation processes, a reliable method for analysis of the individual hydroperoxides had to be established. Two methods were investigated, namely reduction of the hydroperoxides to alcohols using ferrous sulphate and reduction using triphenylphosphine, and analysing the reduction products by gas chromatography. Of these two methods, the triphenylphosphine method proved to be superior to the ferrous sulphate method and was used as the method of choice for this investigation. A number of oxidation systems were evaluated in an initial screening experiment for the oxidation of p-cymene. The results of this screening experiment showed that three-phase oxidation systems, i.e. systems containing an organic phase, an aqueous phase and gas, gave significantly lower activities than two-phase oxidation systems. In addition, the use of a base in the aqueous layer does not improve the overall selectivity of the oxidation process, but improves the selectivity towards the tertiary hydroperoxide to some extent due to the decomposition and extraction of primary hydroperoxide into the basic aqueous phase. Oxidation systems using a non-autoxidation catalyst, i.e. a catalyst that does not catalyse the conventional autoxidation of organic compounds, gave by far the most promising results. These systems gave both a high selectivity as well as high reaction rate. From the initial screening experiment, and using multi-factorial statistical techniques, two catalyst systems were selected for investigation, namely vanadium phosphate and boron phosphate. The results of these investigations showed that these two catalysts are remarkably active and selective for the oxidation of p-cymene, giving the cymene tertiary hydroperoxide in selectivities exceeding 85% and at substrate conversions as high as 25%. These results are a considerable improvement over currently known oxidation systems and may offer opportunities for further commercial exploitation.
- Full Text:
- Date Issued: 2001
- Authors: Harmse, Nigel
- Date: 2001
- Subjects: Oxidation , Cymene
- Language: English
- Type: Thesis , Masters , MTech (Chemistry)
- Identifier: vital:10958 , http://hdl.handle.net/10948/73 , Oxidation , Cymene
- Description: The oxidation of cymene with dioxygen has been investigated in some detail with the view of establishing the feasibility of improving the efficiency of the oxidation process. Of particular interest were the rate of cymene oxidation and the selectivity of the oxidation process for the tertiary cymene hydroperoxide, especially at conversions above 15%. In order to be able to evaluate the selectivity of oxidation processes, a reliable method for analysis of the individual hydroperoxides had to be established. Two methods were investigated, namely reduction of the hydroperoxides to alcohols using ferrous sulphate and reduction using triphenylphosphine, and analysing the reduction products by gas chromatography. Of these two methods, the triphenylphosphine method proved to be superior to the ferrous sulphate method and was used as the method of choice for this investigation. A number of oxidation systems were evaluated in an initial screening experiment for the oxidation of p-cymene. The results of this screening experiment showed that three-phase oxidation systems, i.e. systems containing an organic phase, an aqueous phase and gas, gave significantly lower activities than two-phase oxidation systems. In addition, the use of a base in the aqueous layer does not improve the overall selectivity of the oxidation process, but improves the selectivity towards the tertiary hydroperoxide to some extent due to the decomposition and extraction of primary hydroperoxide into the basic aqueous phase. Oxidation systems using a non-autoxidation catalyst, i.e. a catalyst that does not catalyse the conventional autoxidation of organic compounds, gave by far the most promising results. These systems gave both a high selectivity as well as high reaction rate. From the initial screening experiment, and using multi-factorial statistical techniques, two catalyst systems were selected for investigation, namely vanadium phosphate and boron phosphate. The results of these investigations showed that these two catalysts are remarkably active and selective for the oxidation of p-cymene, giving the cymene tertiary hydroperoxide in selectivities exceeding 85% and at substrate conversions as high as 25%. These results are a considerable improvement over currently known oxidation systems and may offer opportunities for further commercial exploitation.
- Full Text:
- Date Issued: 2001
The development and evaluation of procedures for the synthesis of phenolic ethers by Baeyer-Villiger oxidation
- Authors: Hoffmann, Petra
- Date: 2001
- Subjects: Ethers , Phenols
- Language: English
- Type: Thesis , Masters , MTech (Chemistry)
- Identifier: vital:10955 , http://hdl.handle.net/10948/51 , Ethers , Phenols
- Description: A novel preparative method has been discovered in our laboratories which produces hydroxy-substituted phenolic ethers in a simple one-pot process. Initially it was found that 4-hydroxyacetophenone, when oxidized in the presence of ammonium peroxydisulfate and concentrated sulfuric acid in methanol, resulted in 4- methoxyphenol as product in high yield. Being novel, no information about the method was available in the literature, and hence it was our task to study the reaction more extensively. The scope of the reaction was investigated in that different reagents and substrates, as well as alternative oxidants, catalysts and alcohols (or reagents which may be envisaged to behave similarly to alcohols) were used. The studies showed that 4- hydroxy-substituted benzaldehyde and acetophenone, vanillin, fuchsones and stilbenequinones as substrates all successfully afforded the phenolic ether. Other oxidants such as hydrogen peroxide, sodium perborate etc. also afforded the phenolic ether but were less effective. The use of other acids than sulfuric acid resulted in comparable or lower yields of the desired phenolic ether. When the use of alcohols or similar reagents was varied, it was found that methanol, ethanol, benzyl alcohol, allyl alcohol, but-3-en-1-ol, hex-5-en-1-ol and undec-10-en-1-ol all afforded the desired ethers in significant yields. In an investigation to determine how this method may be useful for industrial applications, it was observed that compounds such as 3,5-di-tert-butyl-4-hydroxysubstituted alkenyloxy phenols, having potential application as antioxidant precursors in the polymer industry, may be prepared. Results showed that the reaction became less efficient when the alkenyl chain length was increased. The use of different acids and oxidants, the change of the oxidant:substrate ratio and the addition of a potential lanthanide catalyst did not improve the yield of the desired ether. A mechanism for the reaction was proposed which involved an initial Baeyer-Villiger oxygen insertion step to afford an ester which was hydrolysed in situ to hydroquinone. The remaining oxidant was then involved in oxidizing some of the soformed hydroquinone to benzoquinone. It was then proposed that these two compounds, i.e., hydroquinone and benzoquinone, interacted with each other in solution, forming a charge-transfer complex. According to our proposal, the carbonyl group of the benzoquinone, when complexed with hydroquinone in solution, was then attacked by nucleophilic reagents such as alcohols. Etherification hence resulted as a consequence of this attack. A statistical experimental evaluation and optimization study was then performed which led to a system that produced the phenolic ether, 4-methoxyphenol, in an 86% yield. An analysis of the effects of the reaction parameters on the reaction showed that the reaction temperature and the oxidant:substrate ratio played a major role in deciding the effectiveness of the reaction, while the amount of substrate and acidic catalyst had a much smaller influence on the ether yields.
- Full Text:
- Date Issued: 2001
- Authors: Hoffmann, Petra
- Date: 2001
- Subjects: Ethers , Phenols
- Language: English
- Type: Thesis , Masters , MTech (Chemistry)
- Identifier: vital:10955 , http://hdl.handle.net/10948/51 , Ethers , Phenols
- Description: A novel preparative method has been discovered in our laboratories which produces hydroxy-substituted phenolic ethers in a simple one-pot process. Initially it was found that 4-hydroxyacetophenone, when oxidized in the presence of ammonium peroxydisulfate and concentrated sulfuric acid in methanol, resulted in 4- methoxyphenol as product in high yield. Being novel, no information about the method was available in the literature, and hence it was our task to study the reaction more extensively. The scope of the reaction was investigated in that different reagents and substrates, as well as alternative oxidants, catalysts and alcohols (or reagents which may be envisaged to behave similarly to alcohols) were used. The studies showed that 4- hydroxy-substituted benzaldehyde and acetophenone, vanillin, fuchsones and stilbenequinones as substrates all successfully afforded the phenolic ether. Other oxidants such as hydrogen peroxide, sodium perborate etc. also afforded the phenolic ether but were less effective. The use of other acids than sulfuric acid resulted in comparable or lower yields of the desired phenolic ether. When the use of alcohols or similar reagents was varied, it was found that methanol, ethanol, benzyl alcohol, allyl alcohol, but-3-en-1-ol, hex-5-en-1-ol and undec-10-en-1-ol all afforded the desired ethers in significant yields. In an investigation to determine how this method may be useful for industrial applications, it was observed that compounds such as 3,5-di-tert-butyl-4-hydroxysubstituted alkenyloxy phenols, having potential application as antioxidant precursors in the polymer industry, may be prepared. Results showed that the reaction became less efficient when the alkenyl chain length was increased. The use of different acids and oxidants, the change of the oxidant:substrate ratio and the addition of a potential lanthanide catalyst did not improve the yield of the desired ether. A mechanism for the reaction was proposed which involved an initial Baeyer-Villiger oxygen insertion step to afford an ester which was hydrolysed in situ to hydroquinone. The remaining oxidant was then involved in oxidizing some of the soformed hydroquinone to benzoquinone. It was then proposed that these two compounds, i.e., hydroquinone and benzoquinone, interacted with each other in solution, forming a charge-transfer complex. According to our proposal, the carbonyl group of the benzoquinone, when complexed with hydroquinone in solution, was then attacked by nucleophilic reagents such as alcohols. Etherification hence resulted as a consequence of this attack. A statistical experimental evaluation and optimization study was then performed which led to a system that produced the phenolic ether, 4-methoxyphenol, in an 86% yield. An analysis of the effects of the reaction parameters on the reaction showed that the reaction temperature and the oxidant:substrate ratio played a major role in deciding the effectiveness of the reaction, while the amount of substrate and acidic catalyst had a much smaller influence on the ether yields.
- Full Text:
- Date Issued: 2001
The evaluation of autoxidation procedures for the selective oxidation of aliphatic alcohols
- Authors: Bacela, Siyabulela Mawande
- Date: 2001
- Subjects: Oxidation , Aliphatic compounds
- Language: English
- Type: Thesis , Masters , MTech (Chemistry)
- Identifier: vital:10950 , http://hdl.handle.net/10948/59 , Oxidation , Aliphatic compounds
- Description: The homogeneously catalyzed oxidation of 1-propanol by dioxygen in glacial acetic acid using cobalt(II)acetate and sodium bromide as the catalyst system has been investigated with the view of determining the significance of various experimental variables during the oxidation. The results of this investigation show unequivocally that a number of reaction variables have a direct influence upon catalytic activity and hence the reaction products. It is quite evident that the major product of this autoxidation reaction is propionic acid with the respective esters as side-products. This is an indication that the autoxidation mechanism occurs via a two-stage pathway, namely, the oxidation of 1-propanol to propionaldehyde as the primary product and, subsequently, the further oxidation of the propionaldehyde to propionic acid as the major product. Thus the esterification process of the propionic acid with the substrate 1-propanol could be termed as a side-reaction because its not facilitated by the catalyst system and it consumes the formed product. The catalyst activity has been demonstrated to depend on a number of factors, including the bromide concentration, the cobalt(II)acetate concentration, the water concentration, reaction temperature, and the presence of metal acetates as co-catalysts. There is an observed decrease in catalytic activity at high bromide concentration, which may be explained in terms of cobalt bromide complexes that form at these high concentrations. Subsequently, the same trend of catalyst activity reduction at high cobalt(II)acetate concentration may be ascribed to the “inactive” metal complexes that are susceptible to form at high metal ion concentrations. The catalytic activity increases with increase in total concentration and rapidly decreases at very high concentrations. This can be explained in terms of the observations made during the investigation of the effect of cobalt(II)acetate and bromide concentrations. The high increase in catalytic activity with increasing temperature is ascribed to the Arrhenius law, which relates the rate constant for a particular reaction to temperature. However, there is an observed loss of catalyst selectivity at high temperatures which maybe due to two possible factors. The first is simply related to an increased loss of volatile material from the reactor in the oxygen gas stream as the temperature is increased. The second relates to the increasing activity of the catalyst system for the selective decarboxylation of the carboxylic acid product. The addition of water to the reaction system rapidly reduces the catalyst activity. This detrimental effect is an indication that there is an effective competition by water with bromide for coordination sites on cobalt(II), thereby preventing the formation of the active catalyst species. The introduction of metal acetates as co-catalyst reduces the catalyst activity quite dramatically. This inhibition effect is suggested to relate to the redox potential of the respective metal ions. The results of statistical analysis of the experimentally derived response surface during the oxidation of 1-propanol, show no significant lack of fit, and the residuals obtained by applying the response surface to the design settings show that the data is normally distributed. The response surface is therefore reliable, but keeping in mind that the central composite design used is not rotatable so that its predictive power, especially outside the experimental domain investigated, is quite limited. However, several interesting observations were still possible The oxidative dehydrogenation of ethanol over supported noble-metal catalysts has been investigated with the view of identifying the most active supported noble-metal and also to compare this oxidation procedure with the autoxidation procedure. Secondly, the effect of an acidic resin as a co-catalyst was also investigated during the said oxidation. On the basis of results presented in this study during oxidative dehydrogenation of ethanol, catalysts no.2 (10% Pd/C), 8 (2% Pd/Al – Pb-promoted) and 9 (2% Pt/8% Pd/C) appear to be the most active in terms of relative rates, while catalysts 6 (10% Pd/C- Pbpromoted), 7 (5% Pd/C-shell reduced-Pb -promoted) and 10 (5% Pt 5% Pd on C) are more active based on the comparison of average rates. Two other observations are of interest. Firstly, the promotion of the Pd catalysts with lead appears to improve catalyst activity to some extent as shown by the comparisons between catalysts 1 and 5, 4 and 8, 2 and 6 and 3 and 7. Secondly, the introduction of Pt up to equal amounts with palladium seems to produce the most active catalysts. On its own, platinum appears to be a better catalyst than Pd when supported on activated carbon (catalysts 1 and 12). In comparison with the homogeneous, cobalt-bromide catalyzed oxidation of 1- propanol in the liquid-phase, oxidations over noble-metal catalysts in the liquid-phase appear to be significantly less active. The presence of the resin promoted the formation of ethyl acetate to some extent, the improvements are not as dramatic as expected.
- Full Text:
- Date Issued: 2001
- Authors: Bacela, Siyabulela Mawande
- Date: 2001
- Subjects: Oxidation , Aliphatic compounds
- Language: English
- Type: Thesis , Masters , MTech (Chemistry)
- Identifier: vital:10950 , http://hdl.handle.net/10948/59 , Oxidation , Aliphatic compounds
- Description: The homogeneously catalyzed oxidation of 1-propanol by dioxygen in glacial acetic acid using cobalt(II)acetate and sodium bromide as the catalyst system has been investigated with the view of determining the significance of various experimental variables during the oxidation. The results of this investigation show unequivocally that a number of reaction variables have a direct influence upon catalytic activity and hence the reaction products. It is quite evident that the major product of this autoxidation reaction is propionic acid with the respective esters as side-products. This is an indication that the autoxidation mechanism occurs via a two-stage pathway, namely, the oxidation of 1-propanol to propionaldehyde as the primary product and, subsequently, the further oxidation of the propionaldehyde to propionic acid as the major product. Thus the esterification process of the propionic acid with the substrate 1-propanol could be termed as a side-reaction because its not facilitated by the catalyst system and it consumes the formed product. The catalyst activity has been demonstrated to depend on a number of factors, including the bromide concentration, the cobalt(II)acetate concentration, the water concentration, reaction temperature, and the presence of metal acetates as co-catalysts. There is an observed decrease in catalytic activity at high bromide concentration, which may be explained in terms of cobalt bromide complexes that form at these high concentrations. Subsequently, the same trend of catalyst activity reduction at high cobalt(II)acetate concentration may be ascribed to the “inactive” metal complexes that are susceptible to form at high metal ion concentrations. The catalytic activity increases with increase in total concentration and rapidly decreases at very high concentrations. This can be explained in terms of the observations made during the investigation of the effect of cobalt(II)acetate and bromide concentrations. The high increase in catalytic activity with increasing temperature is ascribed to the Arrhenius law, which relates the rate constant for a particular reaction to temperature. However, there is an observed loss of catalyst selectivity at high temperatures which maybe due to two possible factors. The first is simply related to an increased loss of volatile material from the reactor in the oxygen gas stream as the temperature is increased. The second relates to the increasing activity of the catalyst system for the selective decarboxylation of the carboxylic acid product. The addition of water to the reaction system rapidly reduces the catalyst activity. This detrimental effect is an indication that there is an effective competition by water with bromide for coordination sites on cobalt(II), thereby preventing the formation of the active catalyst species. The introduction of metal acetates as co-catalyst reduces the catalyst activity quite dramatically. This inhibition effect is suggested to relate to the redox potential of the respective metal ions. The results of statistical analysis of the experimentally derived response surface during the oxidation of 1-propanol, show no significant lack of fit, and the residuals obtained by applying the response surface to the design settings show that the data is normally distributed. The response surface is therefore reliable, but keeping in mind that the central composite design used is not rotatable so that its predictive power, especially outside the experimental domain investigated, is quite limited. However, several interesting observations were still possible The oxidative dehydrogenation of ethanol over supported noble-metal catalysts has been investigated with the view of identifying the most active supported noble-metal and also to compare this oxidation procedure with the autoxidation procedure. Secondly, the effect of an acidic resin as a co-catalyst was also investigated during the said oxidation. On the basis of results presented in this study during oxidative dehydrogenation of ethanol, catalysts no.2 (10% Pd/C), 8 (2% Pd/Al – Pb-promoted) and 9 (2% Pt/8% Pd/C) appear to be the most active in terms of relative rates, while catalysts 6 (10% Pd/C- Pbpromoted), 7 (5% Pd/C-shell reduced-Pb -promoted) and 10 (5% Pt 5% Pd on C) are more active based on the comparison of average rates. Two other observations are of interest. Firstly, the promotion of the Pd catalysts with lead appears to improve catalyst activity to some extent as shown by the comparisons between catalysts 1 and 5, 4 and 8, 2 and 6 and 3 and 7. Secondly, the introduction of Pt up to equal amounts with palladium seems to produce the most active catalysts. On its own, platinum appears to be a better catalyst than Pd when supported on activated carbon (catalysts 1 and 12). In comparison with the homogeneous, cobalt-bromide catalyzed oxidation of 1- propanol in the liquid-phase, oxidations over noble-metal catalysts in the liquid-phase appear to be significantly less active. The presence of the resin promoted the formation of ethyl acetate to some extent, the improvements are not as dramatic as expected.
- Full Text:
- Date Issued: 2001
- «
- ‹
- 1
- ›
- »