Photochemistry of hydroxyalkanones in solution

Abstract

The photochemistry of α-hydroxyketones (1,3-dihydroxyacetone, 3-hydroxybutan-2-one, 3-hydroxy-3-methylbutan-2-one, and 5-hydroxyoctan-4-one), β-hydroxyketones (4-hydroxy-3-methylbutan-2-one and 4-hydroxy-4-methylpentan-2-one), and a γ-hydroxyketone (5-hydroxypentan-2-one) has been studied by traditional steady-state photolysis and product analysis. Triplet yields were evaluated by cis–trans penta-1,3-diene isomerization, singlet lifetimes by absorption and fluorescence measurements, and triplet lifetimes from product-quenching experiments employing 1,3-dienes as selective triplet quenchers. α-Hydroxyketones photodecompose by a Type I cleavage, presumably from the excited triplet. β-Hydroxyketones decompose by –O–H intramolecular hydrogen abstraction and subsequent reactions of the produced biradicals, both from the excited singlet and triplet states. 5-Hydroxypentan-2-one gives Type II products from the singlet state, but no acetone is produced from the excited triplet.