title: Ultrasonic evidence of hydrophobic interactions. Effect of ultrasound on benzoin condensation and some other reactions in aqueous ethanol.
abstract: The kinetics of KCN-catalyzed benzoin condensation of benzaldehyde in water and ethanol-water binary mixtures was investigated both under ultrasound at 22 kHz and without sonication. Thermodynamic activation parameters were calculated from kinetic data obtained at 35, 50, and 65 degrees C. Evidence that ultrasound can retard reactions is reported and hence a direct proof that sonochemical processes occur in the bulk solution. Former results and literature data for ester hydrolyses and tert-butyl chloride solvolysis are involved in the discussion. A quantitative relationship between sonication effects and the hydrophobicity of reagents is presented for the first time. Ultrasound affects hydrophobic interactions with the solvent, which are not manifested in conventional kinetics. When it suppresses the stabilization of the encounter complexes between reagents, sonication hinders the reaction but accelerates it when it perturbs the hydrophobic stabilization of the ground state of a reagent.
authors: Institute of Organic and Bioorganic Chemistry, University of Tartu, Jakobi 2, 51014 Tartu, Estonia. ants.tuulmets@ut.ee
authors: Ants
authors: A
authors: Tuulmets
authors: Hannes
authors: H
authors: Hagu
authors: Siim
authors: S
authors: Salmar
authors: Giancarlo
authors: G
authors: Cravotto
authors: Jaak
authors: J
authors: Järv
mesh_terms: D001547:Benzaldehydes / Q000737:chemistry; D001573:Benzoin / Q000737:chemistry*; D002384:Catalysis; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D000431:Ethanol / Q000737:chemistry*; D006868:Hydrolysis; D007700:Kinetics; D011190:Potassium Cyanide / Q000737:chemistry; D013696:Temperature; D013816:Thermodynamics; D014465:Ultrasonics; D014867:Water
chemical_list: D001547:Benzaldehydes; D014867:Water; D000431:Ethanol; D001573:Benzoin; D011190:Potassium Cyanide; C032175:benzaldehyde