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The action of phosgene on N, N'-disubstituted ureas is described in literature as giving a variety of products depending upon the reaction conditions. However, in no instance has the formation of N, N', N''-trisubstituted guanidines been reported from the above reaction. A novel synthesis is now presented in which these aforementioned guanidines are obtained. This reaction involves the phosgenation of N, N'-dialkyl- or N-alkyl-N'-arylureas at temperatures between 110 and 120° in an inert solvent such as monochlorobenzene. In the case of symmetrically disubstituted alkylureas, the N, N', N''-trialkylguanidines in the form of their hydrochloride salts are obtained. Unsymmetrically substituted ureas upon phosgenation also give guanidines, the type of which, in terms of their substituents, is dependent upon the ability of the urea nitrogen to act as a nucleophile as well as the steric nature of the substituent itself. Thus, phosgenation of N-cyclohexyl-N'-phenylurea gives N, N'-dicyclohexyl-N''-phenylguanidine exclusively. In cases where the substituents on nitrogen atoms of the urea molecule are alike in electron-donating abilities, product distributions are obtained, as with Ncyclohexyl-N'-isopropylurea. Where one urea nitrogen is strongly deactivated, as with N-cyclohexyl-N'-trifluoroethylurea, there is no indication of guanadine formation. Different types of compounds are isolated from these reactions. A mechanism is proposed to account for these observed patterns. Copyright © 1967, American Chemical Society. All rights reserved.

15 citations (Crossref) [2023-10-31]