Die Kennzeichnung von Carbonsäuren als Ureide mit Hilfe der Carbodiimide (V. Mitteil.)

Advances in the Chemistry of Carbodiimides

“…Aliphatic carbodiimides and carboxylic acids normally yield disubstituted ureas together with acid anhydrides (5,495,856,858) but afford exclusively N-acylureas if organic bases (e.g., pyridine or triethylamine) are present (308,495,857). Thus, gradual addition of carboxylic acids to dicyclohexylcarbodiimide (628) in hot pyridine (which is claimed to accelerate the oxygen-to-nitrogen migration, CXXXII -* CXXXIII) (see mechanism, below), affords the acylurea as the main product (857) Frederick Ktjrzer and K. Douraghi-Zadeh two acylureas should theoretically be expected; in fact, only one isomer appears to be formed (336), the acyl group attaching itself on the less basic nitrogen (i.e., the one of lower electron density).…”

The Chemistry of Carbodiimides.

“…With aromatic carbodiimides reaction proceeds in most cases readily to form the acylureas (59, 92,93,96,97,101,102,103,104). A number of solvents can be employed for this reaction: e.g., ether, benzene, dioxane, pyridine, etc.…”

“…However, by employing reaction conditions which accelerate the oxygen-to-nitrogen migration (XIV -* XV) and perhaps hinder the attachment of the second proton (XVI), the formation of the "acylurea" (XV) can be made the main reaction. Thus, by carrying out the reaction in hot pyridine and adding the carboxylic acid in portions to dicyclohexylcarbodiimide, satisfactory yields of some acylureas were prepared (93).…”

4‐dimethylaminopyridine‐based organoactivation: From simple esterification to lactide ring‐opening “Living” polymerization

“…Initially used by Fredrich for the preparation of sugar derivatives,1 N,N ′‐dicyclohexylcarbodiimide (DCC) is known for more than 70 years for being one of the most efficient esterification agents. Initially limited to phenols and thiophenols and because of its tendency to generate undesirable N ‐acylureas during the esterification process,1, 2 Steglich‐associated DCC with the catalytic acylation action of the 4‐dimethylaminopyridine (DMAP) molecule concluding that: “… (the) addition of 3–10 mol % DMAP accelerates the DCC‐activated esterification of carboxylic acids with alcohols and thiols to such an extent that formation of side products is suppressed and even sterically demanding esters are formed in good yields at room temperature .”3…”