Carbamoyl anions, formation

The existence of strong catalysis by some bivalent anions (carbonate, phosphate, succinate, maleate, citrate, phthalate) but not others (sulphate, oxalate, fumarate, isophthalate) has been claimed and attributed to the formation of carbamoyl derivatives of the anion. 

In the absence of n-butanol, the reaction between DBTDL and carbamoyl chloride was very slow (dotted curve). In the presence of n-butanol (solid curve) the completion of the reaction was very fast as can be seen from the disappearance of the carboxylate anion band ( 1600 cm l) and the formations of dimerized acid band (- 1700 cm l) and urethane bands ( 1700 cm-1, v(C=0) 1535 cm- (NH)). This reaction can be depicted as follows ... 

When carbon monoxide is bonded to a transition element, in a positively charged or even uncharged compound, the electrophilic capacity of carbon increases compared with the isolated molecule. Examples of nucleophilic attack are in equations (4) and (5). The reaction of methyl-lithium with W(CO)e giving the anionic acyl complex of equation (4a) is followed by alkylation to the carbene derivative of equation (4b). The formation of a carbamoyl complex with c/5-PtCl2(CO)2 is shown in equation (5). 

Ethyl carbamate in wine is formed (mostly at the end of fermentation) from urea. The intermediates of its degradation are probably cyanates and cyanic acid (HO-C=N), also known as hydrogen cyanate, which may isomerise to isocyanic acid (H-N=C=0). Iso-cyanic acid can also arise by protonation of the cyanate anion and nucleophilic addition of ethanol to isocyanic acid yields ethyl carbamate. Isocyanic acid also reacts with other nucleophilic reagents, such as water (with formation of ammonia and carbon dioxide), thiols and amino groups of proteins. By catalysis with ornithinecar-bamoyl transferase, citrulline is transformed into ornithine and carbamoyl phosphate, the ethanolysis of which yields ethyl carbamate (Figure 12.39). 

The formation of the resonance-stabilized anions RaN—C=S (147), by metallation of iViV-dialkylthioformamides, and their use as efficient thio-carbamoylation reagents, has been further elucidated. " Their reaction with... 

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