Reduction of benzaldehyde

In general, an ethyl(monoalkoxy)zinc is formed with amino alcohols6. Therefore, in the presence of an equimolar amount of chiral amino alcohol, a slow reduction of benzaldehyde to benzyl alcohol is observed rather than alkylation1. Alkylation only occurs with a ratio of diethylzinc to amino alcohol greater than equimolar. Consequently, a two-zinc species is postulated to be the actual catalyst1, n. 

Cr(II) reduction of benzaldehyde in aqueous acidic ethanol also yields largely hydrobenzoin although other products were characterised, e.g. hydrobenzoin monoethyl ether, and a 1 1 stoichiometry is preserved. The rate law in ethanol acidified both with HCIO4 and HCl is complex for example, in HCl-ethanor°°,... 

These reaction conditions also permit the chemoselective quantitative reduction of benzaldehyde to benzyl alcohol without any concomitant reduction of either acetophenone or 3,3-dimethylbutan-2-one present in the same reaction mixture.83 Additionally, this useful method permits the reduction of aldehyde functions in polyfunctional compounds without affecting amide, anhydride, eth-ylenic, bromo, chloro, or nitro groups.79,80,319... 

Homogeneous Catalytic Reduction of Benzaldehyde with Carbon Monoxide and Water... 

We chose to investigate the C0/H20/K0H and Rh6(C0)i6 catalyzed reduction of benzaldehyde and substituted benzaldehydes because ... 

Because of the complexity of the rhodium-catalyzed reduction of benzaldehyde to benzyl alcohol with CO and H20, it is not possible to fully elucidate the mechanism of catalytic reduction given the extent of the kinetic studies performed to date. However, the results do allow us to draw several important conclusions about the reaction mechanism for benzaldehyde hydrogenation and several related reactions. 

Much emphasis has been placed on the selectivity of quaternary ammonium borohydrides in their reduction of aldehydes and ketones [18-20]. Predictably, steric factors are important, as are mesomeric electronic effects in the case of 4-substituted benzaldehydes. However, comparison of the relative merits of the use of tetraethyl-ammonium, or tetra-n-butylammonium borohydride in dichloromethane, and of sodium borohydride in isopropanol, has shown that, in the competitive reduction of benzaldehyde and acetophenone, each system preferentially reduces the aldehyde and that the ratio of benzyl alcohol to 1-phenylethanol is invariably ca. 4 1 [18-20], Thus, the only advantage in the use of the ammonium salts would appear to facilitate the use of non-hydroxylic solvents. In all reductions, the use of the more lipophilic tetra-n-butylammonium salt is to be preferred and the only advantage in using the tetraethylammonium salt is its ready removal from the reaction mixture by dissolution in water. 

Reduction of benzaldehyde and p-alkylbenzaldehydes to the corresponding hydrocarbons was carried out by lithium in liquid ammonia and tetrahydro-furan in the presence of tert-h xiy alcohol or ammonium chloride (yields 90-94%) [775]. 

The carbon-nitrogen double bond in imines is reduced at less negative potentials than the corresponding carbonyl function. Also imine radical-anions are more basic than carbonyl radical-anions. Imines with at least one phenyl substituent on the carbon-nitrogen double bond are sufficiently stable for examination in aprotic solvents and reversible one-electron reduction of benzaldehyde anil [179] or benzophenone anil [ISO] can be demonstrated with rigorous exclusion of moisture. 

The highly enantioselective production of ( + )-(S )-benzenemethan-a-configurational determination of 8 rests on an asymmetric Meerwein-Ponndorf reduction (with isobornyloxymagnesium bromide). On mechanistic grounds the reduction of benzaldehyde-rf was assumed to produce preferentially the 7 -isomer225. 

This scheme was found to be applicable to the reduction of benzaldehyde in aqueous ethanol. The final product is 1,2-diphenylglycol [152]. 

The enzyme-product complexes of the yeast enzyme dissociate rapidly so that the chemical steps are rate-determining.31 This permits the measurement of kinetic isotope effects on the chemical steps of this reaction from the steady state kinetics. It is found that the oxidation of deuterated alcohols RCD2OH and the reduction of benzaldehydes by deuterated NADH (i.e., NADD) are significantly slower than the reactions with the normal isotope (kn/kD = 3 to 5).21,31 This shows that hydride (or deuteride) transfer occurs in the rate-determining step of the reaction. The rate constants of the hydride transfer steps for the horse liver enzyme have been measured from pre-steady state kinetics and found to give the same isotope effects.32,33 Kinetic and kinetic isotope effect data are reviewed in reference 34 and the effects of quantum mechanical tunneling in reference 35. 

Intramolecular protonation on the more hindered face of a steroid from a neighbouring hydroxyl group best explains a reversal of diastereoselectivity in the Birch reduction of styrene double bonds.266 The kinetics and product distribution of lithium metal reduction of benzaldehyde to benzyl alcohol in THF have been studied electron transfer from Li to PhCHO occurs in a slow step, but absorption of the PhCHO onto the metal surface is also crucial in determining the overall kinetics. The proposed mechanism successfully accounts for the formation of minor products, benzoin and... 

Attention has turned recently to the mechanistic details underlying these processes. Probably the most significant development in this area in recent years is the discovery that the ketyl radical produced by electrochemical reduction of benzaldehyde in buffered neutral ethanol is harder to reduce than benzaldehyde itself46. All previous discussions had assumed that the ketyl radical would be reduced as quickly as it is formed, but fast scan cyclic voltammetry demonstrated the existence of a short-lived intermediate, apparently the ketyl radical. Computer simulation of the voltammograms showed that the radical dimerizes at a rate ca 106 1VD1 s 1. 

Alkyl Benzoates. Reduction of benzaldehyde with four-fold excess of LiAlH4 may be dangerous.4... 

Dismutations of the same type, but involving two unlike aldehyde molecules, will be classed as crossed Cannizzaro reactions. The reduction of benzaldehyde to benzyl alcohol by means of formaldehyde and alkali is an example. 

Reduction of Benzaldehyde with 0.5 Equivalent of Aluminum Isopropoxide. Use of the Hahn Condenser.201... 

Reduction of Benzaldehyde with 0.5 Equivalent of Aluminum Iso-propoxide. Use of the Hahn Condenser. In a 1-1. round-bottomed flask are placed 21 g. (0.2 mole) of benzaldehyde, 7 g. (0.034 mole) of distilled aluminum isopropoxida (or 34 cc. of a 1 M solution in isopropyl... 

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