Photolysis of biacetyl in the presence of triethylborine

Abstract

When biacetyl is photolysed in admixture with triethylborine, the replacement of ethyl by the acetyl radical competes with its decomposition. This exchange can be represented by: CH₃CO +(C₂H₅)₃B = C₂H₅+ CH₃CO·B(C₂H₅)₂(A)

The acetyl–boron compounds were not identified in the system; the extent of reaction (A) was estimated from the number of ethyl radicals produced. When the rate of reaction (A) was related to that of the reaction CH₃CO = CH₃+ CO, the Arrhenius parameters found by changing the temperature from 316 to 413°K were log (A₄/A₅)= 1·6 ± 0·4 and (E₄–E₅)= 15·7 ± 0·7 kcal./mole. This points to a very low activation energy for reaction (A).