Mild catalytic multiphase hydrogenolysis of benzyl ethers

Abstract

A preliminary study was conducted on the multiphase (aqueous KOH-isooctane-Aliquat ® 336) hydrogenolysis of benzyl methyl ether using Pd/C, Pt/C and Raney-Ni as catalysts, under mild conditions (T = 50 °C, pH 2 = 1 atm). Using ethanol as solvent, the Pd/C system is very efficient, while the same catalyst under multiphase conditions is almost inactive. With Pt/C, the reaction is always sluggish, and ring hydrogenation kicks in under multiphase conditions. The Raney-Ni system has an opposite behavior, while debenzylation is slow in ethanol, under multiphase conditions the reaction is quite fast. Other O-benzyl protected substrates undergo debenzylation with Raney-Ni as well, with varying chemoselectivity.

Dechlorination of lindane in the multiphase catalytic reduction system with Pd/C, Pt/C and Raney-Ni

“…Previously, we have reported on a number of applications of the multiphase catalytic systems for various catalytic reduction reactions [18][19][20][21][22][23][24][25][26], in particular, for the HDC of chlorinated aromatics [22][23][24][25][26]. The multiphase system consists of a substrate solution in isooctane-water (alkaline or not), a metal catalyst and a PT agent, e.g.…”

Multiphasic Heterogeneous Catalysis Mediated by Catalyst‐Philic Liquid Phases

“…It proved to be a less active catalyst-not surprisingly-but it also showed high potential in the multiphasic system, since its activity was always strongly enhanced by ther presence of A336. 87 A striking example of this difference was shown in the case of the hydrogenolysis of benzyl methyl ether, where only Raney-Ni proved active enough to promote the C-O bond breaking reaction under the multiphasic conditions (table 2).…”

Enhanced Pd‐Catalyzed Hydrogenation of Olefins within Polymeric Microreactors under Organic/Aqueous Biphasic Conditions

“…To confirm this hypothesis, hydrogenation of styrene employing the reference catalyst of 4.1 nm Pd nanoparticles immobilized on the solid microsphere ( Figure S8 in the Supporting Information) under other similar conditions was tested, resulting in a much lower TOF than those of the microreactor (entry 5). Furthermore, the present microreactor used in hydrogenation under organic/aqueous biphasic conditions has an advantage that it avoids the bothersome separation of catalyst or the product purification, which is usually necessary in the batch hydrogenation employing a typical heterogeneous Pd catalysts, such as Pd/C [23] and Pd nanoparticles deposited on mesoporous silicas, [24][25][26] or in the hydrogenation under multiphasic condition employing a phase-transfer catalyst [27,28] ( Figure S9 in the Supporting Information). In the present experiment, after the hydrogenation is completed, the organic phase just contains the product, which can be separated simply by decantation and no further purification is needed; therefore it has possible practical application for continuous hydrogenation of olefins on technical scale (Figure S9 in the Supporting Information).…”