Location: Bio-oils Research Unit
Title: Synthesis of formyl esters of vegetable oils: Milkweed, Pennycress and Soy Authors
Submitted to: Society of Tribologists and Lubrication Engineers
Publication Type: Abstract Only
Publication Acceptance Date: January 17, 2014
Publication Date: May 18, 2014
Citation: Harry O Kuru, R.E., Biresaw, G., Evangelista, R.L. 2014. Synthesis of formyl esters of vegetable oils: Milkweed, Pennycress and Soy [abstract]. Society of Tribologists and Lubrication Engineers Annual Meeting & Exhibition. p. 139. Technical Abstract: In a previous study of the characteristics of acyl derivatives of polyhydroxy milkweed oil (PHMWO), it was observed that the densities and viscosities of the respective derivatives decreased with increased chain length of the substituent acyl group. Thus, from the polyhydroxyl starting material, attenuation in viscosity of the derivatives relative to PHMWO was observed in the order: PHMWO>>PAcMWE>>PBuMWE>>PPMWE (2332:1733: 926.2: 489.4 cSt, respectively at 40°C); where PAcMWE, PBuMWE and PPMWE were the polyacetyl, polybutyroyl and polypentanoyl ester derivatives, respectively. Analogously corresponding densities also decreased with substituent chain-length increase although not as precipitously compared to the viscosity drop. By inference, derivatives of vegetable oils with short chain length substituents on the triglyceride would be attractive in lubricant applications in view of their higher densities and possibly higher viscosity indices. Such characteristics are important in lubrication applications as well as retention of the intrinsic biodegradability of the spent lubricant. Pursuant to this, we have explored the synthesis of formyl esters of three vegetable oils: milkweed, soy, and pennycress in order to examine the optimal density, viscosity and related physical characteristics for their suitability as lubricant candidates. In the absence of formic anhydride ready availability, we have employed epoxidized vegetable oils as substrates for polyformyl ester generation using glacial formic acid. The epoxy ring-opening process, though smooth, was counter intuitive here as the reaction did not stop at the traditional alpha-hydroxyl ester expected but was rather followed by a simultaneous condensation process of the putative alpha-hydroxyl formyl intermediate to yield vicinal diformyl esters from each oxirane unit. The mechanistic explanation would be that subsequent protonation of the putatively formed alpha-hydroxyl intermediate was followed by elimination of water assisted by a neighboring formate anion shown below. The presence of condensed water was ascertained in a subsequent ring-opening reaction when toluene was added to the reaction mixture and the azeotrope trapped in a Dean Stack setup. The reaction is presumably a general one as all three epoxidized vegetable oils used gave the corresponding vicinal polyformates. All three polyformates: milkweed, soy and pennycress derivatives exhibited low coefficient of friction and a correspondingly much lower wear scar in the 4-ball anti-wear tests compared to the longer chain acyl analogues earlier studied.