New synthesis of Dialkyl carbonates from alkylene carbonates and titanium alkoxides

Abstract

Dialkyl carbonates are used in industry as organic solvents, fuel additives, lubricants in refrigerating units, and heat carriers. A conventional procedure for the preparation of dialkyl carbonates is based on the reaction of alcohols with phosgene which is very toxic. Phosgene-free syntheses of organic carbonates are extensively developed; they include oxidative carbonylation of alcohols [1, 2], reactions of alcohols with urea [3, 4], reactions of oxiranes with carbon dioxide [5, 6], and reactions of inorganic carbonates with alkyl halides [5] or alcohols [7, 8]. Also, mutual transformations of alkyl carbonates are possible. We now propose a new phosgene-free synthesis of dialkyl carbonates via reaction of alkylene carbonates with titanium alkoxides. An advantage of the proposed procedure is that it ensures simultaneous preparation of two important products, dialkyl carbonate and alkyl titanate derivative [dialkyl alkanediyl titanate or bis(alkanediyl) titanate]. The latter can be used as curing agent for epoxy resins or as precursor for the synthesis of nanosized titanium dioxide. The titanium-containing residue can be decomposed by treatment with dilute sulfuric acid to regenerate the diol. The reactions were carried out with a number of alkyl titanates and alkylene carbonates. A mixture of 45.62 g (0.2 mol) of tetraethyl titanate and 40.8 g (0.4 mol) of propylene carbonate was slowly heated and distilled through a column, and a fraction boiling in the range from 120 to 130°C was collected. Yield of diethyl carbonate 40.59 g (86%), nD = 1.384 (published data [9]: nD = 1.384). Found, %: C 50.84; H 8.45. Calculated, %: C 50.85; H 8.47.