Abstract
Carbamoyl chlorides are important intermediates, both in the research laboratory and in industrial scale syntheses. The most studied and used are the disubstituted derivatives, incorporating either aryl or alkyl groups (Ar2NCOCl or R2NCOCl). Sometimes, the groups are tied back to give a ring and piperidino- and morpholino-derivatives are commonly encountered. Some studies have been made with two different groups attached. Solvolyses tend to occur at the carbonyl carbon, with replacement of the chloride ion. Studies of both rate and products are reviewed and the solvolysis reactions are usually SN1, although addition of an amine leads to a superimposable bimolecular component. Many of the studies under solvolytic conditions include the application of the extended Grunwald–Winstein equation. The monosubstituted derivatives (ArNHCOCl or RNHCOCl) are less studied. They are readily prepared by the addition of HCl to an isocyanate. In acetonitrile, they decompose to set up and reach equilibrium with the isocyanate (ArNCO or RNCO) and HCl. Considering that the structurally related formyl chloride (HOCOCl) is highly unstable (with formation of HCl + CO2), the unsubstituted carbamoyl chloride (H2NCOCl) is remarkably stable. Recommended synthetic procedures require it to survive reaction temperatures in the 300–400 °C range. There has been very little study of its reactions.
Highlights
In contrast to the parent acid of chloroformate esters (HOCOCl), where attempts to prepare it lead to carbon dioxide and hydrogen chloride [1], the corresponding parent structure for carbamoyl chlorides (H2NCOCl) is a stable molecule, even at quite high temperatures [2,3,4]
In Equation (2), k and ko are the specific rates of solvolysis in a given solvent and in the standard solvent (80% ethanol), l is the sensitivity towards changes in solvent nucleophilicity (NT), m is the sensitivity towards changes in solvent ionizing power YX, and c is a constant
When a rigid correlation analysis is carried out, the results show poor correlations with large standard errors for the sensitivity values
Summary
In contrast to the parent acid of chloroformate esters (HOCOCl), where attempts to prepare it lead to carbon dioxide and hydrogen chloride [1], the corresponding parent structure for carbamoyl chlorides (H2NCOCl) is a stable molecule, even at quite high temperatures [2,3,4]. The authors carried out a Taft Equation treatment involving a consideration of changes in the specific rate of ethanolysis in 100% ethanol as the σ* values, a measure of electronic effects, for the R group in R2NCOCl was varied This type of study is labor intensive since for each point in a Taft Equation treatment a new substrate is required. 0.72 [17] are often taken as typical values for addition-elimination reaction, with addition rate-determining, and for ionization with moderate assistance from nucleophilic solvation, respectively; d Multiple correlation coefficient; e Calculated using the original Y scale, which is based on the first-order rate coefficients for solvolyses of tert-butyl chloride; f With omission of the four 2,2,2-trifluoroethanol (TFE)-ethanol mixed solvents; g Morpholine with an N-chloroformyl substituent; h The 1-adamantyl group. Since the other group was an aryl group, this study will be discussed of this review
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