Decarbonylation chlorination reaction

A C(carbonyl)-C bond of aldehydes can be cleaved under oxidative reaction conditions [31]. For example, when a mixture of aldehyde 55 and aniline was treated with Mn(0Ac)3-2H20 under an oxygen atmosphere, formanilide was obtained, presumably through fragmentation of the 1,2-dioxetane intermediate 56 (Scheme 7.22). Treatment of the aldehyde 57 with KCl and HjOj in the presence of a vanadium peroxo complex promoted a decarbonylative chlorination reaction to produce aryl chloride 58 (Scheme 7.23) [32]. 

Acyl radicals can fragment with toss of carbon monoxide. Decarbonylation is slower than decarboxylation, but the rate also depends on the stability of the radical that is formed. For example, when reaction of isobutyraldehyde with carbon tetrachloride is initiated by t-butyl peroxide, both isopropyl chloride and isobutyroyl chloride are formed. Decarbonylation is competitive with the chlorine-atom abstraction. 

In contrast to this imide-based synthesis, amides of the type RC(0)NH2 are decarbonylated to primary amines (RNH2) with chlorine in the presence of base. This process, often called the Hofmann reaction, involves an intermediate isocyanate (R-N = C = 0) (Fieser and Fieser, 1961 Sandler and Karo, 1983). Aromatic oximes, lacking an a-hydrogen, react with chlorine to form intermediates that are converted to nitrile Af-oxides with base. (Nitrile N-oxides are highly reactive species.)... 

Lock (1933) found long ago that two classes of polychlorinated benzalde-hydes exist, distinguished by their behaviour toward ethanolic potassium hydroxide (1) benzaldehydes that undergo the Cannizzaro reaction and (2) benzaldehydes that decarbonylate. In the second class, the formyl group is invariably flanked by two o-chlorines. These results, which are analogous to the dealkylations, indicate likewise that, when the Cannizzaro reaction— which is known to be initiated by hydroxide-ion addition to the formyl... 

The kinetic study " " was performed on RhCl(PPh3)3 and the chlorine-bridged dimer, Rh2Cl2(PPh3)4, with a variety of aldehydes. The progress of the reaction was monitored by UV-VIS electronic absorption spectroscopy at 25 C, and decarbonylation products RhCl(CO)(PPh3)2 and alkane were analyzed. 

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