Methanol, ethanol, propanol, and butanol adsorb on alumina as stable alkoxyl groups. Above 150°in the presence of alcohol vapor or air these alkoxyl groups are converted to carboxyl groups. A kinetic analysis of this reaction using infrared spectroscopy showed that the surface reaction is pseudo-zero order. The presence of a Lewis acid site (A1+) is necessary in order that the gaseous alcohol or oxygen may adsorb and produce an oxygen-containing species. This species is mobile on the surface and reacts with the bonded alkoxyl groups to produce a bonded carboxyl group. Poisoning of the Lewis acid sites with pyridine strongly inhibits the reaction. Based upon the data a reaction mechanism is proposed.
Rates of the basic hydrolysis of 2-(4-chlorophenoxy)quinoxaline 1 were measured in aqueous cetyltrialkylammonium chlorides, C16H33NR3Cl, R ) Me (CTACl), Et (CTEACl), n-Pr (CTPACl), n-Bu (CTBACl). The shape of the rate versus surfactant concentration profiles depends on substrate concentration. At low substrate concentration, first-order rate constants go through maxima with increasing surfactant concentration, but at higher concentration, double-rate maxima are observed. The presence of single-or double-rate maxima is ascribed to reaction in micelles or in premicellar complexes. At low substrate concentration, micellar effects were analyzed by means of a mass-action model. Second-order rate constants, kM, for reactions in the micellar pseudophase increase with headgroup size.
The gas phase thermal decarbonylation of a,b-unsaturated aldehydes E-2-butenal and E-3-phenyl-2-methylpropenal was studied in a static system over the temperature range 380.5-490.0 8C and pressure range 55.5-150 Torr. The reactions are homogeneous and unimolecular and obey a first-order rate law. The rate coefficient is represented by the following Arrhenius equations:EÀ2ÀButenal : log k 1 ðs À1 Þ ¼ ð13:18 AE 0:16Þ À ð212:0 AE 2:0Þ kJ mol À1 ð2:303 RTÞ À1 EÀ3ÀphenylÀ2Àmethylpropenal : log k 1 ðs À1 Þ ¼ ð13:23 AE 0:22Þ À ð234:6 AE 3:2Þ kJ mol À1 ð2:303 RTÞ À1The elimination products of 2-butenal are propene and CO gas, while 3-phenyl-2-methylpropenal produces a-methylstyrene, cis-trans-b-methylstyrene, indan, and CO gas. Kinetic and thermodynamic parameters suggest these elimination reactions to proceed through a three-membered cyclic transition state type of mechanisms. However, a two steps mechanisms for the formation of a carbene type of intermediate through a four-membered cyclic transition structure can not be overlooked.
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