Oxidation of benzoin

Oxidation of benzoin with concentrated nitric acid or by catalytic amounts of cupric salts in acetic acid solution, which are regenerated continuously by ammonium nitrate, yields the diketone benzil ... 

Oxidation of benzoin, PhCH(OH)COPh (above) yields benzil, PhCOCOPh (133), and this, in common with non-enolisable 1,2-diketones in general, undergoes base-catalysed rearrangement to yield the anion of an a-hydroxy acid, benzilate anion, Ph2C(0H)C02e (134). This is, almost certainly, the first molecular rearrangement to be recognised as such. The rate equation is found to be,... 

Table IV. Catalytic oxidation of benzoin by 1,4-benzoquinone in the presence of 4Fe-, 2Fe-, IFe-complexes...

Mo02(Cys-OMe)2, Mo02(S2CNEt2) and other complexes are reported" to catalyze the air oxidation of benzoin to benzil. The complex MoO2(Cys-0R)2 (R = Me, Et, Pr1 and CH2Ph) catalyzes the 02 oxidation128,184 of PPh3 in DMF by a mechanistically involved process in which excess H20 prevents the catalytic redox cycle.184,185... 

A number of experiments upon the oxidation of benzoin to benzil with nitric acid were made in which the mixture was stirred continuously. An inferior grade of product and smaller yields (seldom over 75 per cent) were obtained. The probable reason for this is to be found in the fact that benzoin is readily soluble in nitric acid while the benzil is not, and the latter there-... 

Benzoins are useful intermediates for the synthesis of other compounds because they can be oxidized to 1,2-diones and reduced in stages to various products, depending upon the reaction conditions. The 1,2-diketone known as benzil, which is obtained by nitric acid oxidation of benzoin, undergoes a base-... 

Benzil. Benzil [134-81-6] (diphenylethanedione) is a yellow solid that crystallizes from alcohol in hexagonal prisms. Benzil can be prepared by the oxidation of benzoin [579-44-2] (2-hydroxy-2-phenylacetophenone) (298,299), which is itself prepared by the self-condensation of benzaldehyde (300). Benzil is commercially produced in Japan and is used as a uv resin curing sensitizer (301). It has also been suggested as a chigger repellant (302). 

Studies of the catalytic or stoichiometric reactions of various 4-Fe-ferredoxin model complexes have been reported using the 3-/2— redox couple with a negative redox potential91 >. Relatively stable are the 2—/I — redox couple for [Fe(Z-cyst-Ile-Ala-OMe)J2 (Z = benzyloxycarbonyl) or [Fe4S4(tipbt)J2 (tripbt = 2,4,6-triiso-propylbenzene-thiolato) in A, A -dimethylformamide. Catalytic oxidation of benzoin by 1,4-benzoquinone in the presence of various cyst-containing peptide complexes or bulky thiolato complexes in DMF has been examined. The postulated mechanism of the catalytic oxidation of benzoin in the presence of [Fe4S2(SR)4]2 is illustrated in Fig. 7. 

The oxidation of benzoin with cerium(IV) in perchloric acid solution is proposed to involve an interaction between Ce4+(aq.) ions and the keto alcohol, resulting in the formation of free radicals. The final product is benzoic acid.66 The rate of oxidation of crotyl alcohol with cerium(IV) is independent of the concentration of Ce(IV). The reaction induced polymerization of acrylonitrile indicating the formation of free radicals. The kinetics and activation parameters for the reaction have been determined.67 For the Ir(III)-catalysed oxidation of methyl ketones68 and cyclic ketones69 with Ce(IV) perchlorate, successive formation of complex between the reductant and Ce(IV) and then with the catalyst has been proposed. Results showed that in acidic solutions, iridium(III) is a more efficient catalyst than osmium and ruthenium compounds. 

Oxidation of benzoin to benzil with Fe(III), in the presence of 2,2/-bipyridine or ferrozine is of first order in Fe(III) and benzoin. An inverse second-order dependence was observed with respect to hydrogen ions. For oxidation of substituted benzoins the reaction constant is p 1.2, indicating an electron-rich transition state and an inner sphere mechanism has been proposed.66 The order with respect to iodide, in the reaction of iodide ions with a diiron(III)-l,10-phenanthroline complex, is 2. The hydrolytic derivatives of the complex are not kinetically active. Both inner and outer sphere pathways are operative.67... 

Benzoin.—Benzile, by reduction in dilute alcoholic sodium hydroxide and in alcoholic sulphuric acid, according to James,2 can inversely be converted into benzoin. Oxidation of benzoin in alkaline and sulphuric-acid solution gives a poor yield of benzoic acid. In alcoholic hydrochloric acid, especially at a high current density, benzile is formed. 

Nitroaromatics can act as catalysts of some oxidation reactions, such as the oxidation of benzoin [110] and poiynitroaromatics in the oxidation of hindered phenols [111]. Russell and co-workers [112a,b] rationalized it in terms of ndical ion reactions where the radical ion Ar NO activates oxygen (27) ... 

A detailed Organic Synthesis procedure is available for the conversion of benzil into benzilic acid. It is advantageous to isolate the acid as its potassium salt, for this enables the removal of the more soluble potassium benzoate, which results from a competitive cleavage reaction. Benzilic acid is then obtained in 77-79% yield by acidifying an aqueous solution of potassium benzilate. Since benzil is usually obtained by the oxidation of benzoin, both this conversion and rearrangement can be performed in tandem by using alkaline sodium bromate. Thus, benzilic acid is obtained in 84-90% yield from benzaldehyde via benzoin. 

Oxidation of benzoins.5 Benzoins are oxidized to aldehydes and acids in good yield by treatment with 2 mole eq. of CAN in aqueous acetonitrile at 60° for 10 min. 

Dehn found sodium bromate (or iodate) a superior reagent for eifecting a few specific oxidations. One is for oxidation of benzoin to benzil under conditions such... 

The equation representing the oxidation of benzoin to benzil has been given under the preceding preparation. The analogues of benzoin also give, on oxidation, compounds of the benzil series. Thus from anisoin and cuminoin, anisil and cuminil respectively are obtained ... 

Oxidation of Benzoin to Benzil by MnOz as a Typical Procedure for the Oxidation of Biaryl Acyloins. A mixture of benzoin 3 a (0.212 g, 1 mmol) and Mn02 (0.174 g, 2 mmol) was prepared and magnetically agitated in an oil bath at 90 °C for 4 h. The progress of the reaction was monitored by TLC. The reaction mixture was applied on a silica gel pad (3 g) and washed with Et20 (20 mL) to afford pure benzil 4 a quantitatively (mp 94 °C). The same reaction with BaMn04 proceeded to completion after 2 h using 1.5 mmol of the oxidant. 

Copper(II) sulfate supported on alumina has been sucessfully used to catalyse the oxidation of benzoins under microwave.58 Microwave radiation can drastically reduce the reaction time and enable milder conditions to be used in a wide range of reactions catalysed by solids. Full industrial exploitation is, however, yet to be realised. 

The a-diketones, e.g. (37), made by oxidation of benzoin or acyloin products, can be converted into acetylenes either by removing both oxygens with P(OR)j or via the 6is-hydrazone (38) and oxidation with Hg(ll). This method is useful for acetylenes such as (39) which cannot be made by displacement on alkyl halides by acetylide ion (Chapter 16). In this case, the starting material (37) is made from benzoin (Chapter 23) by nitric add oxidation. 

Oxidation of benzoins to benzils. Benzoins can be converted to benzils by oxidation with cupric sulfate in HMPT with air (or O2) ebullition yields are 60-95%. This method was used for preparation of 4,4 -divinylbenzil from 4,4 -divinylbenzoin (73% yield). 

Oxidation of benzoins to benzils Benzoins (1) are oxidized to benzils(2) in high yield by catalytic amounts of this lanthanide nitrate and 1 eq. of HCl in aqueous glyme. Benzil can also be obtained from desoxybenzoin and diphenyl-acetylene under these conditions. This oxidation has recently been reported with... 

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