Reduction benzophenones

The oxygen atom in these molecules can in many cases be dispensed with as well substitution of sulfur for nitrogen affords a molecule whose salient biologic properties are those of a sedative and tranquilizer. Friedel-Crafts acylation of the n-butyl ether of thiophenol with benzoyl chloride gives the corresponding benzophenone. Reduction of the ketone (15) followed by... 

Electrochemical or Li-benzophenone reduction of Fe(Pc) and Co(Pc) gives [M Pc] and [M (Pc)]2. 198,199 These monovalent metal complexes react with alkyl halides to give organometallic compounds which transfer the alkyl group to alkenes in the presence of Pd11 salts (Scheme 61). [Co PCTS]5- and [Co PCTS]6- reductively bind one and two molecules of oxygen respectively in DMF,198 The second 02 addition is reversible (Scheme 62). 

Decacarbonyldimanganese(O), Mn2(CO)io, a golden-yellow solid, (mp 154 C) was first obtained by reaction of Mnl2 with Mg, Cu, and Culj at room temperature in diethyl ether under CO at 200 atm P. Yields are low ( 1%). The most frequently used reducing agents for carbonylation of Mn(II) salts are (1) Na metal or Na in the presence of benzophenone or (2) aluminum alkyls. The sodium-benzophenone reduction occurs at superatmospheric CO pressures (2Ci0-700 atm)... 

Using transition state analog [136] benzophenone reduction by ruthenium half-sandwich complex... 

Fig. 45. (a) Transmission spectrum of benzophenone. (b) SNIFTIRS difference spectrum of benzophenone reduction to the ketyl anion radical. 

In addition to measuring the activity of the imprinted polymer, Polburn et al. also examined the selectivity of the catalytic site. Use of the diphenylphosphinate ligand creates cavities that resemble the transition state for the reduction of benzo-phenone. It should follow that the MIP should be most effective towards benzo-phenone reduction. A series of competition reductions with equimolar amounts of benzophenone and a cosubstrate was conducted using polymers P-1 and P-2 as catalysts (Table 1). It is interesting to note that both the imprinted catalyst and nonim-printed catalyst show a preference towards benzophenone reduction. The MIP P-1 shows approximately 1.3-2.0 fold enhancement of selectivity. As indicated by entries 4-6, the aromatic ketones were not as easily differentiated by the MIP P-I, however, P-1 showed a preference forbenzophenone over other aromatic ketones demonstrating the ability to differentiate structurally similar substrates. 

The air-sensitive compound was isolated without any coordinating ligands in addition to the alkyne, but an associated structure is supposed. It reacts with aldehydes LCHO and ketones LjCO followed by hydrolysis with formation of alcohols (PhC=C)LCHOH or (PhC=C)L2COH, but, with benzophenone, reduction to benzopinacol is also found (Deacon and Tuong, 1981). 

Benzophenone reductions using commercially available CRED enzymes. 

The condensation of aldehydes and ketones with succinic esters in the presence of sodium ethoxide is known as the Stobbe condensation. The reaction with sodium ethoxide is comparatively slow and a httlo reduction of the ketonic compound to the carbinol usually occurs a shorter reaction time and a better yield is generally obtained with the more powerful condensing agent potassium ieri.-butoxide or with sodium hydride. Thus benzophenone condenses with diethyl succinate in the presence of potassium [Pg.919]

To the wa-propyl alcohol filtrate is added another i5o-g. portion of benzophenone and the solution is exposed to sunlight as in the first reduction. The benzopinacol which separates is filtered and dried. The yield in the second and subsequent runs is 142-143 g. (94-95 per cent of the calculated amount). This procedure can be repeated with the same filtrate until six or seven portions (900-1050 g.) of benzophenone have been reduced. 

Benzopinacol has been prepared by the action of phenylmag-nesium bromide on benzil 1 or methyl benzilate. Usually it has been obtained by reduction of benzophenone, the reducing agents being zinc and sulfuric acid or acetic acid, aluminum amalgam, and magnesium and magnesium iodide. The present... 

The benzopinacol obtained by photochemical reduction of benzophenone (p. 8) may be used directly without purification. 

Diphenylmethane has been prepared with aluminum chloride as a catalyst from methylene chloride and benzene, from chloroform and benzene as a by-product in the preparation of triphenylmethane, and from benzyl chloride and benzene. It has been prepared by the reduction of benzophenone with hydriodic acid and phosphorus, or with sodium and alcohol. It has also been made by heating a solution of benzyl chloride in benzene with zinc dust, or with zinc chloride. The above method is only a slight modification of the original method of Hirst and Cohen. ... 

Two classes of charged radicals derived from ketones have been well studied. Ketyls are radical anions formed by one-electron reduction of carbonyl compounds. The formation of the benzophenone radical anion by reduction with sodium metal is an example. This radical anion is deep blue in color and is veiy reactive toward both oxygen and protons. Many detailed studies on the structure and spectral properties of this and related radical anions have been carried out. A common chemical reaction of the ketyl radicals is coupling to form a diamagnetic dianion. This occurs reversibly for simple aromatic ketyls. The dimerization is promoted by protonation of one or both of the ketyls because the electrostatic repulsion is then removed. The coupling process leads to reductive dimerization of carbonyl compounds, a reaction that will be discussed in detail in Section 5.5.3 of Part B. 

In 2-propanoI, the quantum yield for photolytic conversion of benzophenone to the coupled reduction product is 2.0. The reason is that the radical remaining after abstraction of a hydrogen atom from 2-propanol transfers a hydrogen atom to ground-state benzophenone in a nonphotochemical reaction. Because of this process, two molecules of benzophenone are reduced for each one that is photoexcited ... 

The efficiency of reduction of benzophenone derivatives is greatly diminished when an ortho alkyl substituent is present because a new photoreaction, intramolecular hydrogen-atom abstraction, then becomes the dominant process. The abstraction takes place from the benzylic position on the adjacent alkyl chain, giving an unstable enol that can revert to the original benzophenone without photoreduction. This process is known as photoenolization Photoenolization can be detected, even though no net transformation of the reactant occurs, by photolysis in deuterated hydroxylic solvents. The proton of the enolic hydroxyl is rapidly exchanged with solvent, so deuterium is introduced at the benzylic position. Deuterium is also introduced if the enol is protonated at the benzylic carbon by solvent ... 

The reduction is general for a variety of substituted benzophenones Such substituents as CH3 OH, OCH3, F, Br. N(CH3)2, NO2. COOH, COOCH3, NHCOC Hreaction conditions and do not alter the course of the reduction Diarylmethanols are reduced to diarylmethanes under the same conditions and probably are the intermediates in the reduction of ketones [26] Triethylsilane also can be used as a reducing agent in trifluoroacetic acid medium [27J This reagent is used for the reduction of benzoic acid and some other carboxylic acids under mild condiUons (equation 14) Some acids (phthalic, sue cinic, and 4-nitrobenzoic) are not reduced under these conditions [27]... 

An analogous sequence leads to the anthelmintic agent, etibendazole (50). Reaction of the benzophenone 47, which can be obtained by acylation of o-nitroaniline with g-fluorobenzoyl chloride, with ethylene glycol leads to acetal 48. Sequential reduction of the nitro group and cyclization of the resulting diamine (49) with N,N-dicarbomethoxy-S-methylthiourea gives the benzimidazole etibendazole (50) fl6]. 

Unless the benzophenone is heated with the alcoholic alkali until a brown color is produced it is impossible to get a reduction. Several runs were made in which the alkali was dissolved in the hot alcohol, the benzophenone put in and the zinc dust added immediately in portions. No reduction took place. 

Fig. 13. Dependence of half-wave potentials for the reduction of substituted benzenes on the total polar substituent constant, ax- Examples shown benzophenones [pH 0], benzophenone-oximes [pH 0], thiobenzophenones [pH 0], nitrobenzenes [pH 2-0], azo derivatives [pH 2-6]. (Taken from Zuman, 1969.)...

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