Branched saturated esters and diesters: Sustainable synthesis of excellent biolubricants

The enzymatic production of biolubricants with desirable properties such as high viscosity index and resistance to oxidation is investigated. These characteristics are ascribed to their branched structure and high molecular weight, as well as, to the absence of unsaturated bonds in the molecule. Solvent-free processes with moderate enzyme concentrations (up to 5% wt.) and reaching conversions of 95% or more, have been conducted. Firstly, up to fifteen branched esters and diesters, all of them saturated, are obtained from a branched acid, 2-methylhexanoic acid, and a variety of linear and branched alcohols and linear diols. Among them, three esters have viscosity indexes close to 200 or higher (1,10-decanediolyl 2-methylhexanoate, 1,12-dodecanediolyl 2-methylhexanoate and 2-octyl-1-dodecanoyl 2-methylhexanoate). For the synthesis of these compounds, optimization of biocatalyst concentration and temperature has been carried out, reaching conversions above 95% within operation times between 2 and 3.5 h. [Display omitted] •Fifteen new branched esters are obtained through an enzymatic solvent-free process.•The viscosity index shows that three of the obtained esters are excellent biolubricants.•These double branched esters can be successfully produced at 80 °C and 5% wt. catalyst.•Conversions above 95% are obtained in less than 3.5 h of reaction.•Other double branched esters could be synthesized using the proposed procedure.