Synthesis, characterization and application of novel acetals derived from Eucalyptus oil

Burger, Kirstin.

Title: Synthesis, characterization and application of novel acetals derived from Eucalyptus oil
Creator: Burger, Kirstin.
Subject: Plasticizers
Subject: Eucalyptus citriodora
Date Issued: 2018
Date: 2018
Type: Thesis
Type: Doctoral
Type: DPhil
Identifier: http://hdl.handle.net/10948/23548
Identifier: vital:30579
Description: The aim of the project was to develop new bio-plasticizer compounds which could be incorporated into infant plastics. Plasticizers increase flexibility of plastic. These plasticizer compounds were derived from crude natural oils such as Eucalyptus citriodora oil and virgin coconut oil. A reagent which could be synthesized from Eucalyptus citriodora oil was, para-menthane-3,8-diol (PMD) which was present in a 60:40 ratio of cis and trans isomers of the diol. A green procedure to synthesize the diol, where an environmentally friendly catalyst, citric acid was used. Optimal conditions were 7% aqueous citric acid as the catalyst and 12 hour reaction which resulted in a citronellal conversion of 88.4 ± 0.80% and PMD selectivity of 75.4 ± 1.22%. As the diol was present in isomers, it was of interest to separate the cis and trans isomers for characterization purposes and later for subsequent individual isomer acetalization reactions. Yields obtained for the reaction for cis and trans-PMD were 51% and 36%, respectively. The kinetics for PMD synthesis from Eucalyptus citriodora oil was determined as second order with a rate constant of 0.0008hr-1 and Ea of 15.77kJ/mol. The isomers of para-menthane-3,8-diol could be separated from the isomeric mixture by solvent extraction at -78°C with n-heptane. Individual rod-shaped crystals could be isolated with this procedure and was characterized by X-ray crystallography techniques and identified as cis-para-menthane-3,8-diol. The trans-para-menthane-3,8-diol was successfully separated, however adequate crystals were not grown for X-ray crystallography analysis. Another method of isomer separation was investigated for PMD by the formation of a complex where anhydrous copper chloride could only form a novel complex with cis-para-menthane-3,8-diol. The trans isomer remained unreacted in the filtrate. The cis-para-menthane-3,8-diol isomer could be freed from the complex to yield pure cis isomer. Aldehydes could be synthesized from virgin coconut oil with carboxylic acid extraction procedures of the crude oil. Subsequent synthesis reactions from carboxylic acid to form aldehydes were performed and octanal (85% yield), decanal (88% yield), dodecanal (86% yield) and tetradecanal (14% yield) could be successfully synthesized as precursors to the novel acetalization reactions. Eight novel cyclic acetals with a characteristic 1,3-dioxine ring were successfully synthesized. However, diastereoisomers of cis-acetal and trans-acetal were present and required separation for characterization 1H-NMR, 13C-NMR, FT-IR, GC-MS and optical rotation techniques. The eight novel acetals were further characterized according to their physical properties such as there was no data available for these compounds. The following properties were determined: molecular mass, molecular formula, density, viscosity, boiling point, refractive index, enthalpy of vaporization, flash point, UV-VIS compatibility, solubility’s, colour and odour determination. Yields of up to 97% were obtained for these acetal compounds. The synthesis of acetals was optimized with batch reactions and optimum conditions were determined where eight catalysts were screened. These catalysts included: scandium triflate, Zeolite, sulphuric acid, p-toluene-sulfonic acid, Amberlyst 15®, Amberlyst 36®, Amberlite® IRA-120 and formic acid. Optimal conditions were with Amberlyst 15® catalyst, 50 minute reaction time at 65°C reaction temperature. The kinetics of the reaction was determined as zero order with a rate constant of 11.92 hr-1 and Ea of 0.050 kJ/mol. The acetalization reaction was evaluated using a UniQsis FlowSyn continuous flow reactor. One of the eight acetals (hexanal acetal) was used for the optimization study and the remaining acetals were evaluated with the optimum flow conditions. The reaction was improved with the use of continuous flow chemistry techniques by lowering of the optimum batch conditions. Various residence times (3.46-17.30 minutes) and temperature range (25-85°C) were studied to obtain optimum conditions. This process was efficient and low maintenance, which produced high acetal product selectivity of Optimum continuous flow conditions were determined at 55°C and 17.30 minute residence time with the flow rate of 0.1 ml/min. Heterogeneous catalysts such as Amberlyst 15® and Zeolite were screened and Amberlyst 15® determined as most favourable. The effect of Amberlyst 15® catalyst loading (0.5-2 g) was investigated over a temperature range of 25-85°C. Optimum catalyst loading was determined at 1g. The 8 compounds were tested for potential as plasticizers. This included mechanical, thermal, migratory and aesthetic testing. The novel acetals had to be compared to known plasticizers. Therefore, their plasticizer properties were compared to two commercial plasticizers: DBP and Eastman 168. As the compounds were derived from natural resources, they would be classified as bio-plasticizers if they exhibited such properties. Therefore, it was of interest to compare the novel compounds to a known bio-plasticizer: PMD-citronellal acetal. This compound was also present as a diastereoisomers mixture of cis and trans isomers. Therefore, diastereoisomers of the 8 acetals were separated as cis and trans isomers in high yields for plasticizer testing purposes. All 11 compounds (8 novel acetals, PMD-citronellal acetal, DBP and Eastman 168) were formulated in PVC to produce plastic films. As previously stated, isomers were present for the acetal compounds and these individual isomers were formulated into PVC formulations to evaluate if there was an effect of stereochemistry in the plastic films. Studies on this phenomenon were limited and therefore of interest. For isomeric plasticizer testing, 9 acetals (8 novel acetals and PMD-citronellal acetal) were used in the testing. Therefore 18 test compounds were formulated in PVC films for isomer plasticizer testing. The effect of increasing the compound amount in the PVC formulation was investigated in the range of 3-12% (w/w). The following tests were evaluated for all PVC test films: elongation, stress to fracture, glass transition temperature, leaching rate, flexibility, gloss and opacity. To validate the data and observations made, statistical validation models were developed to justify experimental design and trends observed. All novel compounds had plasticizer properties and one acetal compound was concluded as superior to DBP and Eastman 168, within the testing scope of the research. It was observed that higher molecular mass acetal compounds had increased plasticizer properties. Isomers for all acetal compounds were concluded to affect plasticizer properties differently and were highly significant. As the novel acetal compounds could be synthesized from natural crude resources, it was interesting to investigate if the synthesized acetals retained their anti-bacterial properties which the precursor oils possessed. Anti-bacterial testing of isomeric mixtures of C5-C12 acetal was investigated and compared to PMD-citronellal acetal and the two commercial plasticizers: DBP and Eastman 168. As the scope of the research focussed on bio-plasticizers for infant plastic products, test bacterial strains were chosen based on the pathogenic strains which cause diseases in babies. Six strains of bacteria were evaluated. It was of interest to evaluate the potency of the compounds by determining the minimum concentration of the compounds which would be potent enough to inhibit the bacteria. The commercial plasticizers inhibited no bacteria within the scope of the research. The acetals retained their anti-bacterial properties where C12 acetal was superior in 4/6 strains of bacteria and PMD-citronellal acetal was superior in 2/6 strains of bacteria. This research is novel and there are presently no data available on this. It was concluded that 8 new bio-plasticizers were synthesized, optimized and tested, within the scope of this research. These compounds were comparable to industry standards in all tests and possessed anti-bacterial properties which the industrial standards don’t possess.
Format: 370 leaves
Format: pdf
Publisher: Nelson Mandela University
Publisher: Faculty of Science
Language: English
Rights: Nelson Mandela University

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