Oxidation of diols

The observed first-order rate constant for the disappearance of the periodate absorbance in the presence of excess glycol show a hyperbolic dependence on glycol concentration, suggesting the formation of an intermediate present in appreciable concentration, i.e. eqn. (6.4) holds ,where K is the dissociation constant of the complex. 

The parameter K can also, like values in enzyme kinetics, be an agglomeration of rate constants that refers to a steady state, rather than an equilibrium situation. Rapid reaction kinetics, in the case of propane-1,2-diol, established that the intermediate was kinetically competent.The reaction with pinacol, where K is very large and the reaction is cleanly second order over a wide range of pinacol concentration,exhibited general acid and general 

The reaction also proceeds with amines of the form C(OH)-C(NHR) and C(NHRi)-C(NHR2) , where R can be hydrogen, although the reaction takes place through the neutral amine rather than its cation, and therefore requires a higher pH (9-11). The initially formed imines C=NR hydrolyse spontaneously to the carbonyl compounds. The kinetics of the reaction parallel those of diols, with intermediate complexes. 

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Alkah manganate(VI) salts are used as oxidants in synthetic organic reactions (100) and their reactions have been observed to be similar to permanganate, except that manganate(VI) exhibits lower reactivity. Additionally, sohd BaVInO in methylene chloride has been reported to achieve high yields for the oxidation of diols to dialdehydes (101). 

This synthesis has not been attempted, as far as I know. The compound has been made by the random method, oxidation of diol (26) giving 3 per cent of the product. Synthesis ... 

Edegger, K., Stampfer, W., Seisser, B. et al. (2006) Regio- and stereoselective reduction of diketones and oxidation of diols by biocatalytic hydrogen transfer. European Journal of Organic Chemistry, (8), 1904—1909. 

L. Prati and M. Rossi, Gold on carbon as a new catalyst for selective liquid phase oxidation of diols, J. Catal. 176(2), 552-560 (1998). 

Scheme 5 Selective anodic oxidation of diol to a-hydroxyketone...

Scheme 7 Selective anodic oxidation of diols with TEMPO as mediator.

Mechanisms involving glycol bond fission have been proposed for the oxidation of vicinal diols, and hydride transfer for other diols in the oxidation of diols by bromine in acid solution.The kinetics of oxidation of some five-ring heterocyclic aldehydes by acidic bromate have been studied. The reaction of phenothiazin-5-ium 3-amino-7-dimethylamino-2-methyl chloride (toluidine blue) with acidic bromate has been studied. Kinetic studies revealed an initial induction period before the rapid consumption of substrate and this is accounted for by a mechanism in which bromide ion is converted into the active bromate and hyperbromous acid during induction and the substrate is converted into the demethylated sulfoxide. 

Abstract This is one of the most important classes of oxidation effected by Ru complexes, particnlarly by RnO, [RuO ] , [RnO ] and RuCljCPPhj), though in fact most Ru oxidants effect these transformations. The chapter covers oxidation of primary alcohols to aldehydes (section 2.1), and to carboxylic acids (2.2), and of secondary alcohols to ketones (2.3). Oxidation of primary and secondary alcohol functionalities in carbohydrates (sugars) is dealt with in section 2.4, then oxidation of diols and polyols to lactones and acids (2.5). Finally there is a short section on miscellaneous alcohol oxidations in section 2.6. 

The enantioselective CH oxidation of diols was reported by Adam and coworkers . ... 

Yield of 2 steps incl. Swem oxidation of diol)... 

For examples of the preparation of lactones by oxidation of diols, sec Doyle Bagheri J. Org. Chem. 1981, 46, 4806 Ishii Suzuki Ikariya Saburi Yoshikawa J. Org. Chem. 1986, 51, 2822 Jefford Wang J. Chem. Soc., Chem. Commun. 1988, 634 Jones Jakovac Org. Synth. VII, 406. For a list of reagents used to effect this conversion, with references, see Ref. 21. pp. 837-838. 

Oxidation of diols 9-41 Reduction of cyclic anhydrides 9-69 Oxidative-reductive ring closure of dialdehydes... 

See also page 1234, Section 18 for some other selective oxidations of diols. 

In 1976, Ueno and Okawara highlighted the fact that no oxidation of primary saturated alcohols to aldehydes via tin alkoxides had been reported in the literature and published a procedure for the selective oxidation of secondary alcohols.25 Interestingly, rather than performing the oxidation on pre-formed tin alkoxides, these researchers subjected a mixture of the diol and (Bu3Sn)20 in CH2C12 to the action of Br2. Regardless of the fact that no complete formation of tin alkoxides is secured and no HBr quencher is added, this method may provide useful yields of hydroxyketones during the selective oxidation of diols.26... 

Subsequent researchers introduced substantial improvements on the Ueno and Okawara s protocol of selective oxidations via tin alkoxides and broadened considerably the scope of its application.223 24b,c Thus, it was established that good yields in the selective oxidation of diols—and even triols and tetrols can be achieved in two steps i) pre-formation of a tin alkoxide, by reaction with either (Bu3Sn)20 or Bu2SnO with elimination of water by molecular sieves or azeotropic distillation of water ii) treatment of the tin alkoxide with Br2 or NBS in the presence of a HBr quencher. 

The oxidation of diols by quinolinium dichromate (QDC) shows a first-order dependence on QDC and acid.5 The oxidation of phenols to quinones by quinolinium dichromate in aqueous acetic acid is acid catalysed rate-determining formation of a cationic intermediate is indicated by a p value of —3.79 and further analysis shows the rates to be influenced equally by both inductive and resonance effects of the substituents.6... 

From the temperature dependence of the substantial kinetic isotope effect (KIE) observed in the oxidation of diols to hydroxycarbonyl compounds by 2,2/-bipyridinium chlorochromate (BPCC), it is proposed that hydride transfer occurs in a chromate ester intermediate, involving a six-electron Hiickel-type transition state.9 A similar conclusion is drawn for the oxidation of substituted benzyl alcohols by quinolinium chlorochromate.10... 

From the kinetics of oxidation of diols by Fc(CN) in aqueous alkali catalysed by R11CI3, it is concluded that oxidation proceeds not by hydride ion transfer from alcohol to Ru(III) but via hydrogen atom transfer, to generate Ru(II) species and an intermediate radical which is further oxidized by more Ru(III).86 Similar conclusions were made from a related study of die oxidation of propan-l-ol under comparable conditions.87... 

Table 3.4 Oxidation of diols catalyzed by supported Au catalysts.

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