Synthesis And Properties Of Mono-estolide 2-Ethylhexyl Ester Derived From α-Hydroxyl Fatty Acid

Estolide is a new kind of oleochemicals with superior performances. As a functional fluid, it can be applied in lubricants, cosmetics, ink formulations, lipid-solubilizing auxiliary for drug delivery, food emulsifiers, pigment dispersants, plasticizers and other fields. There are mainly two synthetic methods, one is by the formation of a carbocation at the site of unsaturation that can undergo nucleophilic addition by another unsaturated fatty acid using acidic catalyst; the other is by multistage esterification reaction of unsaturated hydroxyl fatty acid under high temperature conditions or lipase-catalyzed. But lactones are generated easily by carbocation migration along the length of the chain under acid catalysis; it cost long time for enzymatic reactions and have low conversion rate. In both reaction pathways, multi-estolide linkage can be formed. Leading to obtain oligomeric fatty acid mixture consist of broad molecular weight distribution estolides.Because of low pour point, low viscosity, high viscosity index and other excellent properties, mono-estolide esters have become the research focus recently. Based on the above issues, a controllable synthesis was developed to prepare mono-estolide esters from α-hydroxyl fatty acids in order to improve the uncontrollability of estolides formation and avoid the unsaturated double bond from the source. Expected to obtain EN = 1, carbon atoms constant and fully saturated mono-estolide esters with high yield and selectivity. The physical properties of mono-estolide esters were investigated, the products were expected to have application potential used as bio-based lubricants and cosmetics base oil.The p-toluenesulfonic acid(Ts OH) was introduced in esterification of 2-ethylhexanol with α-HDA in the first step esterification for improving the degree of molecular branched. We explored two methods of dehydration including cyclohexane(CH) and vacuum. When using CH as a water entrainer, under the condition: n(2-EH) : n(α-HDA) : n(CH) : n(Ts OH) = 1.1 : 1.0 : 2.3 : 0.01, refluxing 1.5 h, esterification rate was up to 98.3%. Under the vacuum dehydration condition, the influence of α-HDA to 2-EH molar ratio, vacuum degree, the length of distillation column and reaction temperature on the esterification were investigated. When n(2-EH) : n(α-HDA) : n(Ts OH) = 2.1 : 1 : 0.01, vacuum 0.04 Mpa, distillation column length 20 cm, 95 oC, 2 h, esterification rate was up to 98.8%. Using DA as a capping fatty acid, esterified with 2-ethylhexyl α-hydroxyl dodecanoate(EHHD) to prepare mono-estolide 2-ethylhexyl ester. In an open and solvent-free system, n(DA) : n(EHHD) : n(Ts OH) = 1.5 : 1 : 0.015, nitrogen bubbling for dehydration, 140 oC, 4.5 h, esterification rate was up to 87.5%. The products were confirmed successfully obtained according to FT-IR, ESI-MS and 1H NMR.Further changed the carbon chain length of bifunctional α-HFA and capping fatty acid, designed the molecular ester to synthesize mono-estolide ester with different total number of carbon atoms. The intermediates and target products were identified by FT-IR, ESI-MS and 1H NMR. It proved the universality of this approach that using α-HFA as the raw materials to prepare mono-estolide esters controllably through two-step esterification reactions. This method can provide possibilities for preparing products according to different application requirements effectively.Melting point, thermal stability, dynamic viscosity, kinematic viscosity, surface tension and contact angle on paraffin were measured. The experimental data were separately analyzed from bio-based lubricant and cosmetic base oil. All synthesized mono-estolide esters possessed excellent low temperature properties(Tp <-10 oC); half-life temperatures were higher than 300 oC for products capped with DA, indicating that they had better thermal stability; lower viscosity can reduce the power loss in the course of using. Therefore, they had the potential to be used as bio-based lubricants or oil additives. Contrasted with the commonly used cosmetic base oils, the values of surface tension and contact angle were similar. Low viscosity made the products easily spread on the skin and possessed good wettability, which had great prospects as cosmetic base oil.In the work of this master thesis, we had successfully established a controllable synthesis to prepare mono-estolide esters from α-HFA. Improving the uncontrollability of estolide formation, avoiding the unsaturated double bond from the molecular structure and producing mono-estolide ester with branched-chain alcohol had been reached. Property test results showed that we had controllably synthesized new oleochemicals with thermal stability, low pour point and low viscosity.