The cyclisation of N-substituted hydantoic acids involves general acid-base catalysed attack of urea nitrogen on the CO,H group. The variation of the Brsnsted exponents for the reactions of the Nmethyl and N-phenyl derivatives ( 2) and (3) allows a choice between kinetically equivalent mechanisms. Stereoelectronic effects o n the nucleophilic reactions of urea N H are considered, and a mechanism involving an initial rotation about the terminal C-N bond of the ureido group is suggested. * This value compares well with Guler and Moodie's figure of 0.47, based on a two-point Brsnsted plot, for the cyclisation of N-methylaminocarbony lglycine.
ChemInform Abstract (mechanism and Bronsted α-values for the buffer-catalyzed ring closure reactions of (Ia) (0.60) and (Ib) (0.27), respectively; kinetics of the reversible hydrolysis of (IIb)).
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