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 co nditions of intercalation in the anion-exchange clay, hydrotalcite. Ph otolysis 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 henc e became negligibly small when n greater than or equal to 6, in contra st with the photolysis of 1 in homogeneous aqueous solutions. The effe ct of coadsorbates was significant in the acceleration of the type II reaction, but the product distributions remained unchanged. These resu lts will be discussed in terms of the conformational flexibility of th e aromatic ketocarboxylate ions imposed by the interlayer space of hyd rotalcite clays. (C) 1997 Elsevier Science S.A. All rights reserved.