New Phosgene-Free Procedure for Preparation of Methyl N-Phenylcarbamate and Dimethyl Diphenylmethane Dicarbamate as Important Precursors for Producing Iso- and Diisocyanates

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Abstract
Methyl N-phenylcarbamate was prepared by reductive carbonylation of nitrobenzene in the presence of methanol and a new catalytic system composed of sulfur, vanadium pentoxide and a base - alkoxides of alkali metals or hydroxides of alkali metals or alkali earths - in good yields. Reaction mechanism of this process is discussed. Diphenylmethane dicarbamates were obtained by acid-catalyzed condensation of methyl N-phenylcarbamate with formaldehyde. Concentrated and dilute sulphuric acids, dilute hydrochloric acid, a mixture of hydrochloric and sulfuric acids, and bentonite were the catalysts investigated. The influence of the catalyst used, the molar ratio of methyl N-phenylcarbamate (MPC) to formaldehyde, temperature and reaction time of yields of dimethyl 4,4'-diphenylmethane dicarbamate and its higher homologues was examined. The condensation products were analysed by high-performance liquid chromatography on reversed phases (RP-HPLC) with a favourable chemically bonded octadecyl stationary phase and a mixed mobile phase water-methanol.

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