Intercalation and control of the Norrish type II reactions of aromatic ketocarboxylates in hydrotalcite clay interlayers

The Norrish type II reactions of a number of aromatic ketocarboxylate ions, p-CH3C6H4CO(CH2)(n)CO2- (1, n = 4-10), were studied under the conditions of intercalation in the anion-exchange clay, hydrotalcite. Photolysis of 1 adsorbed in aqueous hydrotalcite suspension yielded the type II products p-methylacetophenone and alkenecarboxylates (E), and/or cyclobutanols (C) in variable yields depending on the length of the alkyl chains (n). The ratios C/E decreased with increasing n and hence became negligibly small when n greater than or equal to 6, in contrast with the photolysis of 1 in homogeneous aqueous solutions. The effect of coadsorbates was significant in the acceleration of the type II reaction, but the product distributions remained unchanged. These results will be discussed in terms of the conformational flexibility of the aromatic ketocarboxylate ions imposed by the interlayer space of hydrotalcite clays. (C) 1997 Elsevier Science S.A. All rights reserved.