Meerwein-Ponndorf-Verley Reduction over Heterogeneous Catalysts

Abstract

The Meerwein-Ponndorf-Verley (MPV) transfer hydrogenation of aldehydes and ketones to the corresponding alcohols is distinguished by its exceptional chemoselectivity. This reaction is particularly suited for the reduction of unsaturated aldehydes and ketones, compared to catalytic reductions with molecular hydrogen using noble metal catalysts. The MPV reaction has traditionally been carried out using homogeneous catalysts like aluminium or titanium alkoxides. However, over the past two decades, an increasing number of reports on heterogeneous catalysts for the MPV reaction have been published. This interest is stimulated by the advantages of heterogeneous over homogeneous catalysis, particularly for larger-scale applications. The article provides a critical review of the recent literature on heterogeneous catalysts for the MPV reaction. The materials include hydrotalcites, metal oxides such as magnesium oxide, zirconia, silica and alumina, alkoxides of Al, La, Zr and Hf grafted to high surface area mesoporous materials, and zeolites. In particular, zeolite beta has been found to be a highly stereoselective catalyst in the MPV reduction of 4-tertbutylcyclohexanone, giving predominantly cis-4-tert-butylcyclohexanol rather than the thermodynamically stable transalcohol. The activity was improved with the incorporation of other metals such as Ti, Sn and Zr. These materials show good tolerance to moisture, lack of leaching and ease of regeneration, thus making them useful catalysts in MPV reduction. The activity of a catalyst depends on its ligand exchange capability with the reductant with a high ligand exchange rate enabling the use of catalytic amounts.

Reactivity of Alcohols in Chemoselective Transfer Hydrogenation of Acrolein over Magnesium Oxide as the Catalyst

“…In general it has been stated that the reactivity of acrolein as the hydrogen acceptor from alcohols in the presence of MgO is very low compared to the reactivities determined for saturated carbonyl compounds [17,18,23,[27][28][29]. At 473 K the conversion of acrolein (results not shown) did not exceed 10%, whereas for saturated carbonyl compounds the conversions higher than 60% have been reported [17,18,23,27,29].…”

“…Metal oxides, MgO [11,12], ZrO 2 [13], double layered hydroxides [14], MgO-B 2 O 3 [15], and Al 2 O 3 -AlPO 4 [16] have been used as catalysts. According to literature data, MgO is one of the most active catalysts in CTH [17,18].…”

Catalytic hydrogen transfer over magnesia. Part XXV. Liquid and vapor phase reduction of ketoesters

“…Catalyst synthesis and characterization Magnesium oxide was prepared by the thermal decomposition of Mg(OH) 2 (0.16-0.40 mm grain diameter) at 873 K for 1 h in a stream of dry air and for 5 h in a stream of dry deoxygenated nitrogen. The details of its preparation are described elsewhere [28].…”

“…Catalytic hydrogen transfer, also known as catalytic transfer hydrogenation (CTH), is a useful method for the reduction of many aldehydes and ketones to the corresponding alcohols under mild conditions [1,2]. This reduction can be performed either in vapor or liquid phase, depending on the acceptor reactivity, with alcohols as hydrogen donors.…”

“…Recently, the catalysts obtained from hydrotalcites have also been used in CTH [12,[19][20][21]. According to the published works, MgO is one of the most efficient oxide catalysts in the CTH of carbonyl compounds with alcohols [1,2].…”