Aromatic urethans are prepared by reacting aromatic carbonates with aliphatic amines, within an organic solvent or not. It is preferred that a stoichiometric quantity of the amine be employed to prevent the formation of urea by-products which are likely to be formed if an excess of the amine is used. The temperature should not exceed 100.degree. C, the interval between 20.degree. and 40.degree. C being preferred. Nearly quantitative yields are obtained.
Continuous process for the preparation of isocyanates
申请人:ENICHEM SYNTHESIS S.p.A.
公开号:EP0492556A1
公开(公告)日:1992-07-01
Organic mono- and di-isocyanates are prepared by decomposition of the corresponding urethanes, by means of a continuous process in which:
(a) a urethane is continuously fed to a decomposition reactor containing a liquid mixture composed of a high boiling inert organic solvent, urethane and isocyanate, kept at the boiling point of the solvent and at a temperature suitable for decomposing the urethane and evaporating the alcohol which is the other product of the reaction;
(b) the liquid mixture is continuously withdrawn from the reactor of (a) and is fed to a flash evaporator kept at an operating temperature lower than the decomposition temperature of the urethane, where the isocyanate is partially evaporated and the residual liquid mixture is recycled to the reactor of (a); and
(c) the vapor generated in (b) is distilled to separate the isocyanate in pure of substantially pure form.