Multiphase Catalytic Hydrogenation of p-Chloroacetophenone and Acetophenone. A Kinetic Study of the Reaction Selectivity toward the Reduction of Different Functional Groups

Abstract

A multiphase catalytic system consisting of hydrocarbon solvent and aqueous phase, phase-transfer (PT) agent (Aliquat 336), and supported Pt or Pd catalyst, bubbled with hydrogen at atmospheric pressure, affords the rapid and efficient hydrodechlorination and the selective reduction of the functional groups of p-chloroacetophenone and acetophenone at 50 • C and in moderate reaction times. The reaction gives quantitative yields of reduction products with variable selectivity, which can be controlled by varying some simple reaction conditions. Herein both halogen removal and carbonyl group or phenyl ring reductions are discussed. The composition of the aqueous phase, the nature of supported catalysts, the effect of various inorganic anions, and other reaction conditions have been studied kinetically to estimate the mechanistic aspects of the reaction selectivity. Emphasis is placed on the development of a novel synthetic tool, which allows control over the selectivity in the reduction of the carbonyl group and the phenyl ring. A number of kinetic models and the corresponding integral rate expressions were used, coupled with the "simultaneous nonlinear least-squares fitting" method, to estimate the rate constants for the formation of each particular reaction component. The kinetic monitoring allowed the accurate analysis of the reaction selectivity. Some mechanistic conclusions were drawn for the reaction under study that suggest that "softer" reduction conditions are attained in the presence of a PT agent and the aqueous phase.

Hydrodechlorination and Hydrogenation over Raney–Ni under Multiphase Conditions: Role of Multiphase Environment in Reaction Kinetics and Selectivity

“…We have previously reported on a number of applications of the multiphase conditions for hydrodechlorination (HDC) and hydrogenation (HG) reactions of various polyhalo- (1)(2)(3)(4)(5) and other functional aromatics (5)(6)(7)(8) over supported Pt (6)(7)(8) and Pd (1)(2)(3)(4)(5) catalysts. The multiphase system is made by a biphasic aqueous-organic medium, a heterogeneous catalyst, and a phase-transfer (PT) agent, and it operates at atmospheric pressure of hydrogen and 1 To whom correspondence should be addressed.…”

“…The presence of a base in the aqueous phase is also critical, especially for the HDC reaction, and its presence can also steer selectivity in the reduction of other functional groups, such as carbonyl, hydroxyl, and aromatic ring (6)(7)(8).…”

“…Particular attention is paid to the investigation of the roles played by the PT agent (Aliquat 336 R , tricaprylmethylammonium chloride) and the aqueous base, which are known to have a decisive role in the reaction selectivity (3)(4)(5)(6)(7)(8). A kinetic study of these reactions allows measuring the rate constants for the independent steps, which provide a straightforward estimation of the selectivity of the reaction.…”

Hydrogenation of Acetophenone in the Presence of Ru Catalysts Supported on Amine Groups Functionalized Polymer

“…An exception is Pt/TiO 2 catalyst which exhibit high and selective ability for C=O activation due to the presence of active centers formed as the result of strong metal support interactions [14][15][16]. Palladium supported catalysts, besides being highly reactive toward C=O hydrogenation to C-OH, they catalyze the hydrogenolysis of C-OH to give ethylbenzene as a final product [13,[17][18][19][20]. Ruthenium supported catalysts are also tested in hydrogenation of ACT because of their high ability to hydrogenate carbonyl group in the vicinity of conjugated and isolated double bonds [11,12,21,22].…”

Mild catalytic multiphase hydrogenolysis of benzyl ethers

“…9,10 Recently Raney-Ni was found to be active for hydrodehalogenation and hydrogenation reactions under multiphase conditions as well. 11 The multiphase system proves advantageous over monophasic ones, as demonstrated in a number of instances, 10 in particular for the case of Raney-Ni, where in the absence of A336, or of the alkaline aqueous phase, the reactions are inhibited. 11 From the green chemistry standpoint, heterogeneous catalysis is an attractive synthetic tool, particularly: when it allows to selectively (chemo-, regio-, stereo-) conduct different transformations by tuning some simple reactions parameters, when the reaction conditions are easily accessible (e.g.…”