| Abstract
| - A model halogenated aryl ketone (4-chloropropiophenone 1) was subjected to mild catalytichydrodehalogenation (p[H2] = 1 atm, T = 50 °C) in a multiphase system consisting of isooctaneand an alkaline aqueous phase, in the presence of onium salts as phase-transfer agents. Thechemoselectivity of the reaction was sharply influenced by the KOH concentration of the aqueousphase: thus, the formation of 1-phenyl-1-propanol 4 was favored in a highly alkaline pH range(>13.5 by 50% to 5% KOHaq). Instead, up to 95% selectivity toward phenyl ethyl ketone 2 wasobserved if the pH was controlled (8 < pH < 13) by adjusting the KOHaq concentration in therange between 5 and 1%. Further investigation of the pH effect indicated that an acidic aqueousphase directed the reaction chemoselectivity toward the formation of products arising from aromaticring reduction (i.e., cyclohexyl ethyl ketone 7 and 1-cyclohexyl-1-propanol 8) rather than fromcarbonyl hydrogenation or hydrogenolysis. Also aliphatic amines, used in place of the PT oniumsalt, afforded good selectivities toward 2, although not as high as the ones obtained with Aliquat336.
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