Biacetyl, oxidation

Direct oxidation yields biacetyl (2,3-butanedione), a flavorant, or methyl ethyl ketone peroxide, an initiator used in polyester production. Ma.nufa.cture. MEK is predominandy produced by the dehydrogenation of 2-butanol. The reaction mechanism (11—13) and reaction equihbtium (14) have been reported, and the process is in many ways analogous to the production of acetone (qv) from isopropyl alcohol. 

Bravo et al. studied the reaction of various ylides with monooximes of biacetyl and benzil. Dimethylsulfonium methylide and triphenylarsonium methylide gave 2-isoxazolin-5-ol and isoxazoles, with the former being the major product. Triphenylphosphonium methylide and dimethyloxosulfonium methylide gave open-chain products (Scheme 135) (70TL3223, 72G395). The cycloaddition of benzonitrile oxide to enolic compounds produced 5-ethers which could be cleaved or dehydrated (Scheme 136) (70CJC467, 72NKK1452). 

Note that the acetonitrile oxide cyclooligomers (e.g. 13) are not true oxime derivatives. Such derivatives have been prepared from biacetyl, however . Derivatives related to 14, below, were prepared and found not to be good complexing agents. They were, nevertheless, capable of phase transferring either sodium or potassium permanganate into dichloromethane. 

Acetoin consumes 4 equivalents of V(V) to produce some biacetyl via C-H fission however, this cleavage is not accompanied by a hydronium-ion concentration dependence of the rate thereby differing from a secondary alcohol oxidation. The mechanism of breakdown of the complex is depicted as follows... 

Photolytic. Major products reported from the photooxidation of butane with nitrogen oxides under atmospheric conditions were acetaldehyde, formaldehyde, and 2-butanone. Minor products included peroxyacyl nitrates and methyl, ethyl and propyl nitrates, carbon monoxide, and carbon dioxide. Biacetyl, tert-butyl nitrate, ethanol, and acetone were reported as trace products (Altshuller, 1983 Bufalini et al, 1971). The amount of sec-butyl nitrate formed was about twice that of n-butyl nitrate. 2-Butanone was the major photooxidation product with a yield of 37% (Evmorfopoulos and Glavas, 1998). Irradiation of butane in the presence of chlorine yielded carbon monoxide, carbon dioxide, hydroperoxides, peroxyacid, and other carbonyl compounds (Hanst and Gay, 1983). Nitrous acid vapor and butane in a smog chamber were irradiated with UV light. Major oxidation products identified included 2-butanone, acetaldehyde, and butanal. Minor products included peroxyacetyl nitrate, methyl nitrate, and unidentified compounds (Cox et al., 1981). 

Irradiation of ///-xylene isomerizes to p-xylene (Calvert and Pitts, 1966). Glyoxal, methylglyoxal, and biacetyl were produced from the photooxidation of ///-xylene by OH radicals in air at 25 °C (Tuazon et al, 1986a). The photooxidation of ///-xylene in the presence of nitrogen oxides (NO and NO2) yielded small amounts of formaldehyde and a trace of acetaldehyde (Altshuller et al, 1970). ///-Tolualdehyde and nitric acid also were identified as photooxidation products of ///-xylene with nitrogen oxides (Altshuller, 1983). The rate constant for the reaction of ///-xylene and OH radicals at room temperature was 2.36 x 10 " cmVmolecule-sec (Hansen et al., 1975). A rate constant of 1.41 x 10" L/molecule-sec was reported for the reaction of ///-xylene with OH radicals in the gas phase (Darnall et ah, 1976). Similarly, a room temperature rate constant of 2.35 x 10"" cmVmolecule-sec was reported for the vapor-phase reaction of ///-xylene with OH radicals (Atkinson, 1985). At 25 °C, a rate constant of 2.22 x 10"" cm /molecule-sec was reported for the same reaction (Ohta and Ohyama, 1985). Phousongphouang and Arey (2002)... 

Several products were also detected in base-degraded D-fructose solution acetoin (3-hydroxy-2-butanone 62), l-hydroxy-2-butanone, and 4-hydroxy-2-butanone. Three benzoquinones were found in the product mixture after sucrose had been heated at 110° in 5% NaOH these were 2-methylbenzoquinone, 2,3,5-trimethylbenzoquinone, and 2,5-dimethyl-benzoquinone (2,5-dimethyl-2,5-cyclohexadiene-l,4-dione 61). Compound 62 is of considerable interest, as 62 and butanedione (biacetyl 60) are involved in the formation of 61 and 2,5-dimethyl-l,4-benzenediol (63) by a reduction-oxidation pathway. This mechanism, shown in Scheme 10, will be discussed in a following section, as it has been proposed from results obtained from cellulose. 

Bis acylhydrazones or bis aroylhydrazones of a-diketones also give derivatives of 1-aminotriazoles on mild oxidation (Scheme 21).i n The product was originally assigned a dihydrotetrazine structure, and other possibilities were considered,but Curtin and Alexandrou proposed the isoimide structure (8) which was, for the product obtained from biacetyl bis(benzoylhydrazone), confirmed by X-ray crystallography. The mechanism given in Scheme 21 has been put forward for its formation ... 

Zinc chloride-doped natural phosphate was shown to have catalytic behavior in the 1,3-dipolar cycloadditions of nucleoside acetylenes with azides to form triazolonucleosides <99SC1057>. A soluble polymer-supported 1,3-dipolar cycloaddition of carbohydrate-derived 1,2,3-triazoles has been reported <99H(51)1807>. 2-Styrylchromones and sodium azide were employed in the synthesis of 4(5)-aryl-5(4)-(2-chromonyl)-1,2,3-triazoles <99H(51)481>. Lead(IV) acetate oxidation of mixed bis-aroyl hydrazones of biacetyl led to l-(a-aroyloxyarylideneamino)-3,5-dimethyl-l,2,3-triazoles <99H(51)599>. Reaction of 1-amino-3-methylbenzimidazolium chloride with lead(fV) acetate afforded l-methyl-l/f-benzotriazole <99BML961>. Hydrogenation reactions of some [l,2,3]triazolo[l,5-a]pyridines, [l,2,3]triazolo[l,5-a]quinolines, and [l,2,3]triazolo[l,5-a]isoquinolines were studied <99T12881>. 

In modern medicinal chemistry, the creation of diversity on a structural framework is important. In principle, diversity at positions 2, 4, 6, 7, and 8 of pteridines can be achieved using such solid-phase chemistry. This prototype solid-phase synthesis involved nitrosation of the resin-bound pyrimidine, reduction of nitroso group with sodium dithionite, and subsequent cyclization with biacetyl to afford pteridines 114 and 115. Cleavage from the resin by nucleophilic substitution of the oxidized sulfur linker using w-chloroperbenzoic acid or DMDO led to the pteridine products 116 and 117 (Scheme 23). 

Faust, B. C., K. Powell, C. J. Rao, and C. Anastasio, Aqueous-Phase Photolysis of Biacetyl (an a-Dicarbonyl Compound) A Sink for Biacetyl and a Source of Acetic Acid, Peroxyacetic Acid, Hydrogen Peroxide, and the Highly Oxidizing Acetylperoxyl Radical in Aqueous Aerosols, Fogs, and Clouds, Atmos. Environ., 31, 497-510 (1997). 

The first step in the constmction of the terminal side chain in the first glitazones comprises a reaction of benzaldehyde (106-1) with the mono-oxime (106-2) from biacetyl to afford the benzoxazole Al-oxide (106-3). Reaction of that intermediate with phosphoms oxychloride leads the chlorination of the adjacent methyl group in a version of the Plonovski reaction to afford the choromethyl derivative (106-4). This is then used to alkylate the carbanion from the substimted acetoacetate... 

The acetyl radicals produced in this reaction must be oxidized by cobalt (III) to acetic acid and/or anhydride in a fast step since only traces of other possible by-products (biacetyl and acetone) were found. 

Figure 9-24. The oxidation of the nickel(ii) complex formed from the template condensation of biacetyl bishydrazone with formaldehyde gives a neutral, conjugated complex, in which the ligand is doubly deprotonated.

In some cases a whole series of dehydrogenation reactions may proceed sequentially to yield aromatic or highly conjugated products. An example of this is seen in the aerial oxidation of the nickel(n) complex of the macrocycle formed by the template condensation of biacetyl bishydrazone with formaldehyde. The product of the oxidation is the fully aromatic dianionic macrocyclic complex (Fig. 9-24). 

As a further possibility the ac electrolysis may lead to other products than those of the photolysis. In this case an excited state mechanism is, of course, excluded. Although there is a certain similarity between the electronic structure of an excited state and the reduced or oxidized form of a molecule, they are not identical. Consequently, it is not surprising when photolysis and electrolysis do not yield the same product. Another reason for such an observation may be the different lifetimes. An excited state can be extremely short-lived. Non-reactive deactivation could then compete successfully with a photoreaction. The compound is not light-sensitive. On the contrary, the reduced and oxidized intermediates generated by ac electrolysis should have comparably long life times which may permit a reaction. The ac electrolysis of Ni(II)(BABA)(MNT) (BABA = biacetyl-bis(anil) and MNT - = disulfidomaleonitrile) is an example of this reaction type (63). 

Results of Photochemical Oxidation of Biacetyl by Molecular Oxygen at 3130 A. (Blacet and Taylor )1 ... 

In view of the difficulty observed by all workers on the photooxidation of biacetyl in obtaining reproducible results, it is difficult to write a satisfactory mechanism. The products are much the same whether 3130 or 4358 A. radiation is used and can be summarized as oxidation products of acetyl radicals or carbon monoxide plus the oxidation products of methyl radicals. 

Porter108 has made a careful study of the photooxidation at 3650 A. at both room temperature and at 160°C. At room temperature the quantum yield of products were very small (e.g., fao = 0.03) and the product ratios were rather different from those given when 2700 A. radiation was used. It seems that, in contrast to biacetyl photooxidation, the main role of oxygen was in deactivating ketene molecules but there was some direct reaction with the electronically excited ketene molecules. At 160°C. there was a chain oxidation similar to that when 2700 A. radiation was used, but the ethylene forming step appeared to be different. 

A study of [Rh(phen)3]3+ confirmed that emission comes from a (n-n ) state.819 No emission was observed in fluid solution, but a long-lived excited state occurs in DMF at room temperature, as 290 nm irradiation of [Rh(phen)3]3+ causes the characteristic 780 nm phosphorescence of [Cr(CN)6]3 (equation 146). The Sterm-Volmer constant of 3.0 x 103 M I implies a lower limit for the excited state lifetime of ca. 0.30 ms. Sensitization of biacetyl, and the oxidation of diphenylamine (in acetonitrile) and of 1,3,5-trimethoxybenzene are also observed for [Rh(phen)3]i+, implying that the 3(7t-7t ) state of [Rh(phen)3]3+ is a powerful oxidant. A potential of 2.00 V is calculated for the [Rh(phcn),]3+/[Rh(phen),]3 + couple,819 making the excited state of [Rh(bipy)3]3+ a better oxidant than the Ru , Cr111 or Os11 analogs. 

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