Diphenyl diazomethane, decomposition

Kinetic studies of the thermolysis of diazomethane were carried out by various authors. These experiments demonstrated that the decomposition of diazomethane was a first order reaction 41-43) Similar investigations of the p5n olysis of diphenyl-diazomethane in xylene or 1-methylnaphthalene also showed that the disappearance of diphenyl-diazomethane is a first order process. It may be concluded that a free carbene is involved in these reactions, in accordance with the following scheme ). 

The triplet benzophenone-sensitization of diphenyldiazomethane at 77 °K induces a marked colour change and esr spectra of the intermediates have been reported in addition to the usual N2 -1-carbene decomposition, another, reversible path was proposed, involving a photochromic form of diphenyldiazomethane. The esr spectrum of triplet diphenylcarbene produced by the photolysis of diphenyl diazomethane in the solid state has been observed using 5250 A - and 2537 A radiation. 

As is well known, most diazoalkanes undergo a ready thermal decomposition. For the substrates considered in this section, no difficulty has been reported in distinguishing thermal and acid-catalysed reactions consequently, the thermal reaction is described in the case of diphenyl-diazomethane only. Compounds for which separation of the two reactions is less straightforward are considered in the final part of the review. 

When diaryldiazomethanes are decomposed by means of a metal salt in the presence of an alkene, 1,1-diaryIcyclopropanes are formed (see also Section 1.2.1.2.4.2.6.3.). A number of salts are able to promote the decomposition of the diazo compounds,but whatever the salt is, the cyclopropane is generally afforded in moderate to low yield due to formation of significant quantities of ketazine and benzophenone derivatives. Thus, decomposition of diphenyl-diazomethane by copper(II) sulfate in butyl vinyl ether gave l-butoxy-2,2-diphenylcyclo-propane (1) in 17% yield, benzophenone azine (2) in 14% yield and benzophenone (3) in 11% yield. ... 

By using a more stable system it is possible to isolate the initial reaction product, and study its decomposition. The reaction of diazomethane with thiobenzophenone at -78 °C (the Schdnberg reaction) yielded 2,2-diphenyl-1,3,4-thiodiazoline (167). The product was obtained as colourless crystals which, in the words of the authors, went pfft around -20 °C. At -30 °C in tetrahydrofuran solution the reaction proceeds more smoothly to give 2,2,3,3-tetraphenyl-l,4-dithiane (168) in a reaction which is probably dimerization of the ylide 169. Decomposition of the ylide can also proceed via 170 to 171, or it can be trapped by dipolarophiles. 

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