Synthesis, characterization and application of novel acetals derived from Eucalyptus oil
- Authors: Burger, Kirstin.
- Date: 2018
- Subjects: Plasticizers , Eucalyptus citriodora
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/23548 , 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.
- Full Text:
- Date Issued: 2018
Evaluation of eucalyptus citriodora derived p-menthane-3,8-diol-citronellal acetal as a bio-plasticizer for cosmetic application
- Authors: Burger, Kirstin
- Date: 2013
- Subjects: Plasticizers , Eucalyptus citriodora
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10420 , http://hdl.handle.net/10948/d1014080
- Description: Plasticizers are generally added to cosmetic and personal care products to improve the filmforming abilities of the product and increase flexibility of the film formed on the skin or hair surface. For example, plasticizers are present in perfumes to prolong the release of the specific scent, which is the ultimate goal in a good quality perfume. Plasticizers in nail varnishes prevent chipping, improve the aesthetics by adhering to the keratin in the nail which means the coating stays on for much longer, which is the ultimate goal in nail products. Plasticizers improve the gloss, resist chipping and allow quick drying time. Therefore it can be seen that plasticizers play a vital role in personal care products like perfumes and nail varnishes. Certain plasticizers e.g. phthalates, can cause problems associated with human health and can harm the environment. They are easily available and large volumes can be obtained at a low cost. These phthalates, for example, di-butyl phthalate (DBP) have been identified as carcinogenic. Nowadays the occurrence of cancer is rapidly increasing. The plasticizers present in a large number of consumer and personal care products, can possibly be linked to the ever increasing reports of cancer. Therefore a substitute to the traditional phthalate plasticizers must be investigated. The aim of this research is to produce a plasticizer derived from naturally occurring Eucalyptus oil, which can be used to replace the existing plasticizers in cosmetic formulations. Para-menthane-3,8-diol (PMD), occurring naturally in the oil from the tree, Eucalyptus citriodora, forms an acetal with citronellal (PMD, acetal, citronellal all occur naturally in the oil). It has been previously shown that PMD-citronellal acetal will exhibit plasticizing properties similar to conventional plasticizers. The objective was to enhance the formation of the acetal in the Eucalyptus oil by reacting it with excess PMD. An effective synthesis method for the PMD-citronellal acetal enriched oil (~73.8 percent) was determined from optimization experiments. The physical characterisation of the PMD-citronellal acetal enriched oil was done and compared with that of DBP. The acetal-enriched oil had a lower density, slightly higher solubility in water (at 25°C), lower refractive index (Brix percent) and a higher boiling point (350°C) than DBP. The physical characteristics of the Eucalyptus oil source and the acetal-enriched Eucalyptus oil were very similar. This can be expected as the Eucalyptus oil consists of ~84.3 percent Citronellal, ~ 1.3 percent PMD and 2.7 percent PMD-citronellal acetal. In this study the effectiveness of the acetal-enriched Eucalyptus oil (referred to from now on as the bio-plasticizer) was compared to a conventional plasticizer such as di-butyl phthalate (DBP), commonly used in cosmetic products. Two cosmetic formulations were produced: a nail varnish and a perfume formulation. Various tests were performed on these formulations to investigate the plasticizing properties of the bio-plasticizer. The objectives were to determine if the natural plasticizer is as effective as the potentially carcinogenic phthalate plasticizers and can be used as a substitute for the phthalates in personal care products. The results indicate that the bio-plasticizer does behave similarly to di-butyl phthalate, however, the effectiveness of the bio-plasticizer is lower than that of di-butyl phthalate. As the viscosity of the synthesized oil was high, this affected the overall consistency of the products. A more viscous nail varnish and perfume was produced in comparison to the DBP counterpart. The stability of the bio-plasticizer in the cosmetic formulations of nail varnish and perfume was also investigated. The cosmetic products were incubated at 0°C, 25°C and 40°C over a period of two months. Any changes in colour, odour, pH, refractive index, separation and plasticizer peak change in the gas chromatogram trace were recorded. It was determined that the PMD-citronellal acetal-enriched oil was relatively unstable under elevated temperatures and light intensity. Storage under higher temperatures (40°C) tends to increase the acidity. Therefore the bio-plasticizer must be placed in a closed, covered bottle and stored in an environment away from light and elevated temperatures. According to the gas chromatogram peaks, it was clear that both the bio-plasticizer and the DBP were more unstable in the perfume formulation than in the nail polish and were especially sensitive to light when in the perfume. This could possibly be due to the interaction with the fragrance molecule, p-anisaldehyde.
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- Date Issued: 2013