Crystals ketones, decarbonylation

The ketone (13) does not undergo loss of CO on irradiation in the crystalline phase. In benzene solution, however, decarbonylation does occur to give biradicals that disproportionate to yield (14) and (15). The more hindered ketone (16) behaves differently and decarbonylates in both the crystal and solution with different results. Thus (17) and (18) are formed in solution, while only the latter... 

Although the reports by Quinkert and Turro suggested the feasibility of the decarbonylation reaction in crystals and demonstrated a very high chemo- and stereoselectivity, the factors that may facilitate or impede solid-state reactivity remained unexplained. Recognizing that the efficient a-cleavage and rapid acyl-radical decarbonylation of ketones with radical stabilizing a- and a -phenyl substituents may determine the reactivity of ketones 54 to 57 and 64 (Schemes 15 and 17), Choi et al. carried out the first systematic search for a correlation between the reactivity of solids and the stability of the radicals involved in the reaction (Scheme 18). 

C3C3a bond is not possible in crystals, decarbonylation of BRl maybe slower than intersystem crossing to BRl which can go back to the starting ketone (Scheme 21). 

Decarbonylation reactions such as that of ketone 70 can be easily carried out in a multigram scale with microcrystalline samples and it may be possible to scale up the reaction further. Several decarbonylation reactions have been documented to trap CO gas within the crystal lattice and to proceed by phase-transition mechanisms. It has been suggested that reactions in solids occur heterogeneously with a reaction front determined by exposure to light. When product molecules begin to form, they go into a... 

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