A Straightforward Synthesis of N-Substituted Ureas from Primary Amides
A direct and convenient method for the preparation of N-substituted ureas is achieved by treating primary amides with phenyliodine diacetate (PIDA) in the presence of an ammonia source (NH 3 or ammonium carbamate) in MeOH. The use of 2,2,2-trifluoroethanol (TFE) as the solvent increases the electrophilicity of the hypervalent iodine species and allows the synthesis of electron-poor carboxamides. This transformation involves a nucleophilic addition of ammonia on the isocyanate intermediate generated in situ by a Hofmann rearrangement of the starting amide.
A kinetic study of the denitrosation and hydrolysis reactions of N-nitrosophenylureas
The kinetics of the decomposition of N-nitroso-phenylurea in aqueous solution have been studied in the acidity range 0.035-0.36 mol.l-1-HCIO4 and in buffer solutions of pH 3.98-6.14.Below pH 3 the decomposition proceeds mainly by acid catalysed denitrosation, but a small uncatalysed contribution has also been detected.The general acid catalysis, the absence of nucleophilic catalysis by halides and the isotopic effect (kH:kD ca. 1.5) allow a mechanism to be proposed in which the protonation of N-nitrosophenylurea is the rate determining step.The results obtained on studying the denitrosation of some ring-derivatives of N-nitrosophenylurea show a little effect on reaction rate.The mechanism proposed for the hydrolysis reaction (studied at pH > 3.9) involves the formation of a nitrosourea hydrate under steady state conditions, which undergoes an OH(1-) catalysed reaction yielding benzenediazonium ion and an uncatalysed reaction yielding an unidentified product.This latter pathway is virtually negligible at the highest values of pH worked with.
Casado, Julio,Castro, Albino,Lorenzo, Francisco Manuel,Meijide, Francisco,Mosquera, Manuel
p. 597 - 601
(2007/10/02)
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