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Abstract

The cyclization rate constants have been measured of substituted ethyl N-(phenylaminocarbonyl)-, N-(alkylaminocarbonyl)-, and N-(phenylaminothiocarbonyl)glycinates RNHCXNHCH₂CO₂.C₂H₅ (X = O, S). Logarithms of these constants increase with decreasing basicity of the amines down to the value of pK_a(RNH₂) = 5.5. The rate-limiting step of the reaction is formation of the tetrahedral intermediate. With ethyl N-(phenylaminocarbonyl)glycinates (whose pK_a(RNH₂) values are higher) this dependence, on the contrary, slightly decreases, and the acid-catalyzed splitting off of ethoxy group from the cyclic intermediate becomes rate-limiting. The cyclization rate of a series of ethyl N-(phenylaminothiocarbonyl)glycinates is practically independent of the pK_a(RNH₂) values, the change in the rate-limiting step would take place at pH about 9.