Green synthesis of alkyl 8-(2-butyl-5-octyl-1,3-dioxolan-4-yl)octanoate derivatives as potential biolubricants from used frying oil

Three pentanal-derived acetal esters have been prepared using a sonochemical method employing the principles of green chemistry. As many as two steps were required to produce these esters of alkyl 9,10-dihydroxystearate in 67-85% yield. The green synthesis evaluation was carried out through a comparison between reflux and sonochemical methods, as well as homogeneous and solid acid catalysts. Activation of Indonesian natural bentonite was conducted by Bronsted acid-enabled dealumination to obtain a low-cost solid acid catalyst. It was found that sonochemical esterification of the acid-catalyzed by H-bentonite gave products in up to 70% yield in 3 times shorter reaction time than the reflux method, which is remarkable. The final acetalization step with n-pentanal in the presence of H-bentonite with sonochemical method afforded three pentanal-derived dioxolane derivatives in 69-85% yields, which are higher than the conventional method. Examination of the physicochemical properties of each product revealed that methyl 8-(2-butyl-5-octyl-1,3-dioxolan-4-yl)octanoate is the most suitable novel biolubricant to substitute currently commercial lubricant.