Sonolysis of the carbon-nitrogen bond

The bond energy is ca. 280 kj mol i for C-N single bonds and 240 kj mol i for diazomethane, i.e., somewhat lower than that of the carbon-halogen bond. The sonolysis should then be relatively easy, and is known in a few cases. The mechanism was not studied, but it is unlikely that sonolysis occurs in the bubble, since most of the substrates are much less volatile than the solvents. 

Extrusion of nitrogen from arylchlorodiazirines formally gives a carbene. In the presence of an olefin, a sonochemical cyclopropanation occurs smoothly under neutral conditions (Eq. 6). The authors state that the procedure is extraordinarily simple a diazirine and an olefin are sonicated in a bath in hexane at 40 C, a temperature at which the compounds are thermally stable.66 The reaction occurs in yields equivalent to the photochemical process, but with much greater ease. Good yields are obtained from allyl bromide, 2,3-dimethyl-2-butene, or diethyl 

By studying the stereospecificity of the reaction, it should be possible to determine if the carbene is generated in the singlet or triplet state, a question of interest to determine the sonolytic mechanism. 

The Amdt-Eistert transposition of diazomethylketones to carboxylic esters is run in methanol using silver benzoate-triethylamine as a soluble catalyst (Eq. 7). 

Under sonication at room temperature, the reaction takes place in high yields in a few minutes.67 xhe thermal procedure requires heating for several hours. The cleavage of the carbon-nitrogen bond in aromatic diazonium salts produces radicals which can be trapped by phenyl f-butyl nitrone (PBN). Besides the aryl radicals, species derived from the counter-anion were detected. 

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