The photochemistry of butyric acid and some related compounds

Abstract n-Butyric acid, isobutyric acid, methyl butyrate and sodium butyrate have been photolyzed, and to provide a comparison the photosensitized decompositions of butyric acid, methyl butyrate and n-butyraldehyde have been examined. By photolysis in the vapour phase, in hydrocarbon and in aqueous solution, the primary reactions for n-butyric acid and methyl n-butyrate have been shown to be C3H7COOR + hv = C3H7CO + OR (Ia) = C3H7COO + R (Ib) = C2H4 + CH3COOR (II) Reaction (II) does not and cannot occur with isobutyrio acid. These reactions are analogous to the type (I) and (II) reactions which occur in the photolysis of the aldehydes and ketones. The studies in solution gave the activation energy for the reaction CH3 + C8H18 = CH4 + C8H17 to be 8⋅4 kcal/mole. Addition of argon and nitrogen to the mercury photosensitized decomposition showed that both of the excited states of mercury (2P1 + 2P0) react with butyric acid in reactions similar to (la) and (1b). The type (II) reaction does not occur on photosensitization. By comparison of the results from the photolysis and the photosensitized decomposition, and by application of the Wigner spin conservation rule, it has been possible to assign electronically excited states to these larger carbonyl compounds which are consistent with results obtained in the presence of oxygen.