Solvent-free synthesis of di-esters of o-phthalic acid and sebacic acid for lubrication oil under microwave irradiation

Di-esters of lubricating oil are synthesized by the reaction of o-phthalic acid or sebacic acid with 2-ethylhexyl alcohol or dodecanol in the solvent-free conditions under microwave irradiation. Effect of catalyst amount, microwave power and reaction time on the yield was investigated. The results show that for microwave power of 280 w ~320 w, catalyst amount of 2.5% ~3.0% and 4.9~9 min the yields of di-esters are 96% ~ 99%. Their chromaticity and crystallization points are measured and the structures have been characterized by ¹H NMR% ¹³C NMR and IR spectra. Compared with conventional synthesis method, the solvent-free microwave method makes the yields of the di-esters increase by 3%~16% and the reaction times are shorted by a factor of 13.3-24.5. The present method offers several advantages such as simple, rapid, excellent yields and good chromaticity of production.