Dismutation

This dismutation or disproportionation reaction is known as the Cannizzaro reaction. 

The analogous dismutation of furfural is described in Section V,8. For crossed Cannizzaro reaction , see discussion following Section IV,199. 

Another mode of preparation includes the dismutation of cumene (qv) in DIPB and benzene in presence of an HZSM-12 catalyst at 200°C (6). The ratio p/m increases with the temperature. Finally, but with purification difficulties, DIPB can be coproduced with cumene (7). 

Olefin Metathesis. The olefin metathesis (dismutation) reaction (30), discovered by Eleuterio (31), converts olefins to lower and higher molecular weight olefins. For example, propylene is converted into ethylene and butene... 

FIO2 has been prepared both by direct fluorination of I2O5 in anhydi ous HF at room temperature and by thermal dismutation of F3IO ... 

Above 110° it dismutates into FIOi and IF5 as mentioned above. 

In boiling ethanol, under nitrogen and in the presence of palladized charcoal, 2-acetyl-l,4-dihydro-3-methylquinoxaline (30) undergoes dismutation to give a mixture of 2-acetyl-3-methylquinoxaline, 2-acetyl-l,2,3,4-tetrahydro-3-methylquinoxaline (33), and 2-l -hydroxy-ethyl-3-methylquinoxaline (34), The latter compound is the product of sodium borohydride or Meerwein-Ponndorf reduction of 2-acetyl-3-methylquinoxaline. 

Instead ef the name metathesis, the term disproportionation is frequently applied to the reaction, and sometimes the term dismutation. For historical reasons the name disproportionation is most commonly used for the heterogeneously catalyzed reaction, while the homogeneously catalyzed reaction is usually designated as metathesis. The name disproportionation is correct in the case of the conversion of acyclic alkenes according to Eq. (1) however, this name is inadequate in most other situations, such as the reaction between two different alkenes, and reactions involving cycloalkenes. Similar objections apply to the name dismutation. The name metathesis is not subject to these limitations and, therefore, is preferred. 

Die Triacycloxy-borane langerkettiger aliphatischer Carbonsauren disproportionieren besonders schnell, wahrend Benzoesaure nur in Benzol/THF (7 1) dismutiert wird. In rei-nem THF entwickelt sie ohne Dismutation nur zwei Mol Wasserstoff, was auf eine Reduktion iiber das Dibenzoyloxy-boran hinweist. 

Figure lb shows the transient absorption spectra of RF (i.e. the difference between the ground singlet and excited triplet states) obtained by laser-flash photolysis using a Nd Yag pulsed laser operating at 355 nm (10 ns pulse width) as excitation source. At short times after the laser pulse, the transient spectrum shows the characteristic absorption of the lowest vibrational triplet state transitions (0 <— 0) and (1 <— 0) at approximately 715 and 660 nm, respectively. In the absence of GA, the initial triplet state decays with a lifetime around 27 ps in deoxygenated solutions by dismutation reaction to form semi oxidized and semi reduced forms with characteristic absorption bands at 360 nm and 500-600 nm and (Melo et al., 1999). However, in the presence of GA, the SRF is efficiently quenched by the gum with a bimolecular rate constant = 1.6x10 M-is-i calculated... 

The above reaction is followed by the spontaneous production (by spontaneous dismutation) of hydrogen peroxide from two molecules of superoxide ... 

Under conditions where the dismutation reaction is slow the exchange between Au(III) and Au(I) has been shown to proceed at a measurable rate at 0 °C in 0.09 M HCl, an exchange half-time of about 2 min was observed. The isotopic method ( Au) and a separation method based on the precipitation of dipyridine -chloroaurate(III) was used to obtain data. An acceleration in the exchange rate was observed as the HCl concentration was increased. ... 

Wolfgang and Dodson suggest that the exchange process in the absence of cyanide is controlled by a rapid dismutation reaction... 

Scheme B) is considered unlikely on the grounds that, at the low concentrations of U(V) involved, the latter would disappear by oxidation with Fe(ni) rather by dismutation. The hydrogen-ion dependence suggests that the rate-controlling step between Fe(irf) and U([V) can be visualised in terms of a series of competitive reactions of hydrolysed species of both reactants viz.

Rikken GB, AGM Croon, CG van Ginkel (1996) Transformation of perchlorate into chloride by a newly isolated bacterium reduction and dismutation. Appl Microbiol Biotechnol 45 420-426. 

Vaz ADN, S Chakraborty, V Massey (1995) Old yellow enzyme aromatization of cyclic enones and the mechanism of a novel dismutation reaction. Biochemistry 34 4246-4256. 

In contrast, dissimilation of acetate may take place by reversal of the pathway used by organisms snch as Clostridium thermoaceticum for the synthesis of acetate from COj. In the degradation of acetate, the pathway involves a dismutation in which the methyl group is successively oxidized via methyl THF to COj while the carbonyl group is oxidized via bound carbon monoxide. Snch THF-mediated reactions are of great importance in the anaerobic degradation of pnrines, which is discussed in Chapter 10, Part 1. 

An unusual reaction was been observed in the reaction of old yellow enzyme with a,(3-unsat-urated ketones. A dismutation took place under aerobic or anaerobic conditions, with the formation from cyclohex-l-keto-2-ene of the corresponding phenol and cyclohexanone, and an analogous reaction from representative cyclodec-3-keto-4-enes—putatively by hydride-ion transfer (Vaz et al. 1995). Reduction of the double bond in a,p-unsaturated ketones has been observed, and the enone reductases from Saccharomyces cerevisiae have been purified and characterized. They are able to carry out reduction of the C=C bonds in aliphatic aldehydes and ketones, and ring double bonds in cyclohexenones (Wanner and Tressel 1998). Reductions of steroid l,4-diene-3-ones can be mediated by the related old yellow enzyme and pentaerythritol tetranitrate reductase, for example, androsta-A -3,17-dione to androsta-A -3,17-dione (Vaz etal. 1995) and prednisone to pregna-A -17a, 20-diol-3,ll,20-trione (Barna et al. 2001) respectively. 

The anaerobe Peptococcus (Micrococcus) aerogenes had a dehydrogenase that carried out specific hydroxylation at the 6-positions of 2- and 8-hydroxypurine, and was therefore distinct from xanthine dehydrogenase from which it could be separated (Woolfolk et al. 1970). It was also able to carry out dismutation of 2-hydroxypurine to xanthine (2,6-dihydroxypurine) and hypoxanthine (6-hydroxypurine). 

The enantiomeric reduction of 2-nitro-l-phenylprop-l-ene has been studied in a range of Gram-positive organisms including strains of Rhodococcus rhodochrous (Sakai et al. 1985). The enantiomeric purity of the product depended on the strain used, the length of cultivation, and the maintenance of a low pH that is consistent with the later results of Meah and Massey (2000). It has been shown that an NADPH-linked reduction of a,p-unsaturated nitro compounds may also be accomplished by old yellow enzyme via the flcf-nitro form (Meah and Massey 2000). This is formally analogous to the reduction and dismutation of cyclic enones by the same enzyme (Vaz et al. 1995), and the reductive fission of nitrate esters by an enzyme homologous to the old yellow enzyme from Saccharomyces cerevisiae (Snape et al. 1997). 

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