The Meerwein-Ponndorf-Verley reaction

The hydride anion is derived from 2-propanol, which is first deprotonated to form an alkoxide. 

The equilibrium can be shifted to the (secondary) alcohol if die propanone is removed by distillation 

Lewis acids, such as Al(OR)3, are employed so as to facilitate hydride transfer by forming a complex with the alkoxide and carbonyl compound. 

The reverse reaction, involving the oxidation of the secondary alcohol to form a ketone, is known as the Oppenauer oxidation. In this case, the equilibrium is pushed to the ketone by using excess propanone. 

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Smis assisted version of this reduction has been reported. The Meerwein-Ponndorf-Verley reaction usually ... 

The Oppenauer Oxidation. When a ketone in the presence of base is used as the oxidizing agent (it is reduced to a secondary alcohol), the reaction is known as the Oppenauer oxidation. This is the reverse of the Meerwein-Ponndorf-Verley reaction (16-23), and the mechanism is also the reverse. The ketones most commonly used are acetone, butanone, and cyclohexanone. The most common base is aluminum r r/-butoxide. The chief advantage of the method is its high selectivity. Although the method is most often used for the... 

The Meerwein-Ponndorf-Verley reaction is a classic method for ketone/ aldehyde carbonyl group reduction, which involves at least 1 equivalent of aluminum alkoxide as a promoter. In this reaction, the hydrogen is transferred from isopropanol to the ketone/aldehyde substrate, so the reaction can also be referred to as a transfer hydrogenation reaction. 

The Meerwein-Ponndorf-Verley reaction usually321 involves a cyclic transition state 322... 

The Meerwein-Ponndorf-Verley reaction is a useful method for the reduction of carbonyl groups to alcohols. Most typically, aluminium isopropoxide is used as a reducing agent. The acetone produced can be easily removed by distillation, thus driving the equilibrium reaction in the desired direction. When the carbonyl compound was refluxed... 

Aramendia, M. A., Borau, V., Jimenez, C., Marinas, J. M., Ruiz, J. R. and Urbano, F. J. Activity of basic catalysts in the Meerwein-Ponndorf-Verley reaction of benzaldehyde with ethanol, J. Colloid Interface Sci., 2001, 238, 385-389. 

Both the Meerwein-Ponndorf-Verley reaction and the Cannizzaro reaction are hydride transfers in which a carbonyl group is reduced by an alkoxide group, which is oxidized. Note that each aluminum triisopropoxide molecule is capable of reducing three ketone molecules. 

Lanthanide isopropoxides, usually written Ln(OPr )3, but more likely to be oxo-centred clusters Ln50(0Pr )i3, are used, not just as starting materials for the synthesis of catalysts such as the naphthoxides but also as catalysts in their own right. They have been used in the Meerwein-Ponndorf-Verley reaction, where carbonyl compounds are reduced to alcohols, recent studies having shown that the reaction takes place exclusively by a carbon-to-carbon hydrogen transfer. 

The reduction of a carbonyl compound containing an additional functional group is a common practice. If the other group is easily reduced, best results are frequently obtained by the Meerwein-Ponndorf-Verley reaction (method 80). The following paragraphs, however, describe certain useful selective reductions. 

The Meerwein-Ponndorf-Verley reaction involves reduction of a ketone by treat-ment with an excess of aluminum triisopropoxide. The mechanism of the process is closely related to the Cannizzaro reaction in that a hydride ion acts as a leaving group. Propose a mechanism. 

Method II, The Meerwein-Ponndorf-Verley reaction A solution of 3 g of acetylferrocene in 300 mL of isopropyl alcohol was passed through a tube of diameter 25 mm and length 700 mm filled with activated AI2O3 for 3 h at a pressure of 900 to 1300 Pa and 200-210 °C. From the condensate 2.3 g of vinylferrocene was isolated and chromatographed via a column with AI2O3, hexane was used as the eluent. After evaporation of the solvent, 1.95 g of the metallomonomer was obtained (70% of the yield). 

Organic hydride sources, such as the Cannizzaro reaction, and the Meerwein Ponndorf-Verley reaction... 

The process of reducing carbonyl compounds (aldehydes or ketones) to alcohols is therefore known as the Meerwein-Ponndorf-Verley reaction. Although alkoxides of a number of metal(loid)s such as sodium, magnesium, titanium, zirconium, iron, boron, aluminium, tin, and antimony have been used for these reactions, those of aluminium are by far preferred, since they tend to give the minimum degree of side reactions. The use of aluminium isopropoxide over other alkoxides was also preferred by Young et al as well as by Adkins and Cox. ... 

The potentialities of the Meerwein-Ponndorf-Verley reaction as an alternative method for preparation of metal alkoxides have also been studied (Eqs 2.341-... 

The main feature of the Meerwein-Ponndorf-Verley reaction pathway involves the coordination of both reactants to the Lewis-acid metal eentre and hydride transfer from the alcohol to the earbonyl group. Aluminium or titanium alkoxides are usually effective homogeneous catalysts. With tin-Beta catalyst, cyclohexanone reduction with 2-butanol led selectively to cyclohexanol at 100 °C. Ketone conversion was >95%, whereas silicon-Beta, Sn02/Si02 and SnCl4 -5H20 were inaetive under the same experimental conditions. Therefore, the activity is likely due to tetrahedral tin in the zeolite framework, and not to extra-framework tin or to leached tin. ... 

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