Benzhydrol Benzophenone

Oxidation. - The reagent is convenient for oxidation of aldehydes to carboxylic acids in pyridine solution in high yield (85-99%). Other reported oxidations are benzyl alcoholbenzoic acid (98%,) benzhydrol benzophenone (97% ) cM-stilbene benzoic acid (98% ). The advantage of this reagent over KMn04 is that water, which decomposes KMn04 slowly, is avoided. 

Mn02 crystals (99%) ultrasonically activated under neutral conditions in H2O for 12 h, mixed with cinnamyl alcohol in acetonitrile, and stirred at 50 for 30 min cin-namaldehyde. Y 97%. Similarly, benzhydrol- benzophenone. Y 100%. Unactivated MnO, was not effective. F.e. and conditions s. T. Kimura et al., Chem. Letters 1988, 1387-8. 

In the following preparation to illustrate the Meen.vein-Pormdorf-Verley reduc tion, a solution of benzophenone in isopropanol is rapidly reduced in the presence of aluminium isopropoxide to benzhydrol (CaHs)2CO (C Hj)jCH OH. It is clear that the aluminium isopropoxide must take some essential part in this reaction, for benzophenone when dissolved even in cold isopropanol with a trace of acetic acid is reduced to tetraphenylethyleneglycol (p. 150). 

In verdiinnter Natronlauge wird Benzophenon praktisch. quantitativ zu Benzhydrol re-duziert (vgl. S. 654, 608) . 

Category 5. Hydrogen Atom Abstraction. When benzophenone is irradiated in isopropyl alcohol, the initially formed Si state crosses to the Ti state, which abstracts hydrogen from the solvent to give the radical 7. Radical 7 then abstracts another hydrogen to give benzhydrol (8) or dimerizes to benzpinacol (9) ... 

Decomposition Pyrolysis occurs at 170°C after prolonged periods yielding CO, COz, benzophenone, and benzhydrol appreciable hydrolysis in acidic or basic solutions occurs yielding 3-quinuclidinol and benzilic acid BZ is oxidized by hypochlorite at a pH of 1-13. 

Bell and Linschitz(8) subjected the benzophenone-benzhydrol system to a flash spectroscopic study and found two transient species, a long-lived one that is believed to be the benzhydrol radical and a shorter-lived one believed to be the benzophenone triplet. Kinetic analysis of the system revealed the rate data shown in Table 3.2. 

Thus for the photoreduction of benzophenone in the presence of benzhydrol (RH = < 2CHOH, C—H x 78 kcal/mole) the overall reaction is exothermic by 26 kcal/mole. For the photoreduction of acetophenone the value calculated in this way is —31 kcal/mole, while for fluorenone the abstraction is still exothermic by 10 kcal/mole. Clearly, the energetics of the abstraction reaction is not the reason why benzophenone and acetophenone photoreduce but fluorenone does not, since the values for the overall reaction would indicate that all three compounds should react. However, this conclusion is not necessarily valid if large activation energies are involved. ... 

Benzophenone has also been found to be photoreduced in the presence of amines as hydrogen donors, although less efficiently than in the presence of benzhydrol or isopropyl alcohol. The photoreduction of ketones in aromatic amines is thought not to go by the same mechanism as the photoreduction in alcohols, for the following reasons ... 

A number of different mechanisms have been proposed to account for the fact that this product is not observed. Recently, however, a report appeared that described the formation of the mixed pinacol from the photoreduction of benzophenone with isopropyl alcohol and the photoreduction of acetone with benzhydrol. The data from this study are presented in Table 3.10.(73)... 

We saw earlier that when benzophenone is photoreduced in the presence of optically active 2-butanol, the alcohol recovered from the reaction loses no optical activity/541 This was presented as evidence that there could be no appreciable reversibility of the initial hydrogen abstraction since this should lead to racemization of the unreacted alcohol. However, if one uses relabeled benzhydrol and examines the initially produced benzpinacol for the presence of the label, one finds that the product pinacol contains no 14C. This would indicate that there must be some type of rapid transfer of the hydrogen radical from the ketyl radical produced upon abstraction from benzhydrol,... 

A similar result has been obtained by Schenck et al.isey When perdeutero-benzophenone is photoreduced with benzhydrol, only perdeuterated benzpinacol is isolated,... 

Table 3.10. Ratio of Mixed to Normal Pinacol in the Photoreduction of Benzophenone with Isopropyl Alcohol and Acetone with Benzhydrol...

During the hydrogenation of benzophenone to benzhydrol, the undesired side-product, diphenylmethane, is obtained by hydrogenolysis of the C-O bond (Scheme 4.25). 

An interesting example of hydrogenation with hydrogen in the absence of transition metal catalyst is reduction of benzophenone to benzhydrol with hydrogen in /er/-butyl alcohol containing potassium /er/-butoxide at 150-210° and 96-135 atm. Although the yields range from 47 to 98% the method is not practical because of its drastic conditions, and because of a cornucopia of more suitable reductions. 

F. Bellamy, D. Horton, J. Millet, F. Picart, S. Samreth, and J. B. Chazan, Glycosylated derivatives of benzophenone, benzhydrol and benzhydril as potential venous antithrombotic agents,./. Med. Chem., 36 (1993) 898-903. 

Oxidation of diphenylmethane in basic solutions involves a process where rate is limited by and equal to the rate of ionization of diphenylmethane. The diphenylmethide ion is trapped by oxygen more readily than it is protonated in dimethyl sulfoxide-text-butyl alcohol (4 to 1) solutions. Fluorene oxidizes by a process involving rapid and reversible ionization in text-butyl alcohol solutions. However, in the presence of m-trifluoromethylnitrobenzene, which readily accepts one electron from the carbanion, the rate of oxygen absorption can approach the rate of ionization. 9-Fluorenol oxidizes in basic solution by a process that appears to involve dianion or carbanion formation. Benzhydrol under similar conditions oxidizes to benzophenone by a process not involving carbanion or dianion formation. 

If the oxidation of diphenylmethane in DMSO (80% )-tert-butyl alcohol (20% ) is interrupted after the absorption of one mole of oxygen per mole of diphenylmethane, one obtains an 86% yield of benzhydrol, 10% yield of unreacted diphenylmethane, and a few percent of the benzophenone-DMSO adduct. The over-all course of the reaction fol-... 

Oxidation of Benzhydrol in Basic Solution. Reaction of benzhydrol with oxygen in basic solution results in the formation of benzophenone, or in DMSO solutions the benzophenone—DMSO adduct. Table VIII summarizes data on the oxidation of benzhydrol in three solvents and in the presence of various concentrations of potassium ferf-butoxide. The rates are the maximum oxidation rates, often observed after an inductive period (Figure 3). 

The stoichiometry of the oxidation appears to require the formation of potassium superoxide as one of the oxidation products, particularly at long reaction periods and high base concentrations. An oxidation of 3.00 mmoles of benzhydrol (0.12M) in the presence of 9.9 mmoles of potassium terf-butoxide (0.37M) in DMSO (80% )-ter -butyl alcohol (20%) absorbed 4.95 mmoles of oxygen in 27.7 minutes at 25°C. and yielded 2.2 mmoles of the benzophenone-DMSO adduct and 0.8 mmole of benzophenone. A precipitate formed (0.307 gram) which analyzed (23) as 103% (4.25 mmoles) potassium superoxide (K02). 

To ascertain the possibility of the intervention of benzophenone ketyl, (C6H5)2CO ", in the oxidation of benzhydrol, the oxidation of... 

One of the limitations of the photocycloaddition reaction is that the unsaturated system may itself act as a quencher. Conjugated dienes fall within this category since they quench the n,ir triplet of some carbonyl compounds. For the photoreduction of benzophenone in benzhydrol, the ratio, kqlka, for m-piperylene is 750 (Table II), which indicates that this diene is indeed an efficient quencher for the reaction. 

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