Synthesis of modern synthetic oils based on dialkyl carbonates

A new two-stage process is elaborated to produce ester oils with dialkyl carbonate structure which show a very good characteristic in view of their use as lubricants. Di-2-ethylhexyl carbonate and di-3,5,5-trimethylhexyl carbonate were synthesized by transesterification of dimethyl carbonate with 2-ethylhexanol and 3,5,5-trimethylhexanol, respectively. Some oxides, hydroxides, and methoxides of sodium, magnesium, calcium, barium, and aluminum were studied as catalysts for this reaction. Calcium methoxide appeared to be the most suitable, due to its high activity and ease of separation from the reaction mixture. The reaction conditions were mild. The synthesis was carried out under atmospheric pressure at temperatures not higher than 120 degreesC reaching a relatively high yield of 65-70%. The synthesized oils were characterized by high purity (above 98%) and excellent physicochemical properties. They show a low pour point, a good miscibility with hydrocarbon oils, and a high thermal-oxidative stability.