Production of isocyanates from esters of carbamic acids (urethanes)

A method for the production of isocyanates from esters or carbamic acids having the formula R(NHCOOR').sub.x or (RNHCOO).sub.x R' wherein R is a substituted or unsubstituted mono-, di- or trivalent organic radical selected from the group consisting of a saturated or monoolefinic unsaturated straight or branched chain aliphatic or cycloaliphatic radical containing not more than 32 carbon atoms, an alkoxyalkyl radical having not more than 32 carbon atoms, an aryl radical, an aralkyl radical, and an alkaryl radical containing 1 to 5 rings;

• R' is a substituted or unsubstituted mono-, di- or trivalent radical selected from the group consisting of a saturated or monoolefinic unsaturated straight or branched chain aliphatic or cycloaliphatic radical containing not more than 32 carbon atoms, an alkoxyalkyl having not more than 32 carbon atoms, an aryl radical, an aralkyl radical, and an alkaryl radical containing 1 to 3 rings;
• and x is 1, 2 or 3, and R and R' being the same or different, respectively, where x is 2 or 3, which comprises thermally decomposing said ester at a temperature in the range of from 175.degree.C. to 350.degree.C. while said ester is dissolved in an inert solvent to produce the isocyanate and alcohol, said solvent being characterized as a compound which is (a) a solvent for said ester, (b) liquid and stable at said reaction temperature and (c) non-reactive with said isocyanate produced in said thermal decomposition reaction and selected from the group consisting of aliphatic hydrocarbons having from 4 to 32 carbon atoms, the halo- and mono-nitro substituted derivatives of said aliphatic hydrocarbons, cycloaliphatic hydrocarbons, or aromatic hydrocarbons having from 1 to 3 rings, the alkyl benzenes having from 1 to 15 carbon atoms in the alkyl group, the halo- and mono-nitro substituted derivatives of said aromatic hydrocarbons, oxygenated compounds containing from 4 to 32 carbon atoms selected from the group consisting of ethers, ketones, and esters of organic carboxylic acids and sulfur analogues of said oxygenated compounds, and separately recovering said isocyanate and alcohol.