Benzoyl azide, Curtius rearrangement

Interest in the photochemical generation and fate of acyl nitrenes has again been expressed. In benzoyl, p-methoxybenzoyl, and m-fluorobenzoyl azides, Curtius rearrangement of the photochemically generated acyl nitrenes to the corresponding isocyanates competes with formation of insertion products in halogen-free solvents.78 In halogenomethanes, the yields of isocyanates are... 

The thermal Curtius rearrangement of formyl, acetyl, and benzoyl azides was studied by DFT.78 The authors conclude that the reaction occurs by a concerted mechanism and not by the alternative nitrene intermediate. 

Phenylethylamine has been made by a number of reactions, many of which are unsuitable for preparative purposes. Only the most important methods, from a preparative point of view, are given here. The present method is adapted from that of Adkins,1 which in turn was based upon those of Mignonac,2 von Braun and coworkers,3 and Mailhe.4 Benzyl cyanide has been converted to the amine by catalytic reduction with palladium on charcoal,5 with palladium on barium sulfate,6 and with Adams catalyst 7 by chemical reduction with sodium and alcohol,8 and with zinc dust and mineral acids.9 Hydrocinnamic acid has been converted to the azide and thence by the Curtius rearrangement to /3-phenyl-ethylamine 10 also the Hofmann degradation of hydrocinnamide has been used successfully.11 /3-Nitrostyrene,12 phenylthioaceta-mide,13 and the benzoyl derivative of mandelonitrile 14 all yield /3-phenylethylamine upon reduction. The amine has also been prepared by cleavage of N- (/3-phenylethyl) -phthalimide 15 with hydrazine by the Delepine synthesis from /3-phenylethyl iodide and hexamethylenetetramine 16 by the hydrolysis of the corre-... 

The Curtius rearrangement also occurs in the direct photolysis of acylazides, but additional products have been isolated and have been shown to arise from typical nitrene reactions . For example, Horner et have trapped benzoyl nitrene with a variety of scavengers. Similarly to the Wolff rearrangement (vide infra) it has been shown ° that the Curtius rearrangement occius via a singlet intermediate this intermediate can be a nitrene or an excited azide molecule in which a concerted decomposition leads to isocyanate derivatives. This reaction could occur in competition with nitrene formation or, alternatively, originate from a vibrationally-excited ground state azide molecule. 

A striking, but isolated, obsei vation was reported by Horner . He found that direct photolysis of benzoyl azide in ethanol or isopropanol led to the Curtius rearrangement (44%), to insertion (31%) and to some hydrogen abstraction (23%). However, in the presence of small concentrations of benzophenone the photoreaction produced exclusively benzamide, with a quantum yield far in excess of unity. The high yield indicated a chain reaction, benzophenone playing more the part of a photocatalyst than that of a convcndonal sensitizer. 

The reductive cleavage of benzoyl azide rans at low temperature with tetracarbonylhydridofeirate, [HFe(CO)4] and with diphosphorus tetraiodide in benzene under reflux. Curtius rearrangement side products are not observed. 

The thermal Curtius rearrangement of benzoyl azide in the presence of Lewis acids was studied using DFT. ... 

Other types of bonds undergo sonolysis, for instance the nitrogen-nitrogen bond of an azido group. The Curtius rearrangement of benzoyl azide is probably one of the first attempts to use sonication in an organic reaction. 3 phenyl isocyanate is... 

Figure 2 Rate constants and activation parameters for Curtius rearrangement of benzoyl azides...

In hot ethanol, benzoyl azide was converted to ethyl A-phenylcarbamate (1894). This Curtius rearrangement was recognized by its discoverer as a general method of degrading carboxylic acids to amines, whereas the intermediacy of isocyanates escaped him. 

Scheme 9.129. A representation of the formation of phenyUsocyanate (CjHsNCO) from the reaction between the acid chloride of benzenecarboxyhc acid (benzoyl chloride, CeHsCOCl) and sodium azide (NaNs) followed by rearrangement of the benzoylazide (C6H5CON3) (the Curtius reaction). ...

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