Polyhydroxy compounds, oxidative

A study518 of the mechanism of oxidation of alcohols by the reagent suggested that a reversible, oriented adsorption of the alcohol onto the surface of the oxidant occurs, with the oxygen atom of the alcohol forming a coordinate bond to a silver ion, followed by a concerted, irreversible, homolytic shift of electrons to generate silver atoms, carbon dioxide, water, and the carbonyl compound. The reactivity of a polyhydroxy compound may not, it appears, be deduced from the relative reactivity of its component functions, as the geometry of the adsorbed state, itself affected by solvent polarity, exerts an important influence on the selectivity observed.519... 

Lead tetraacetate is a selective oxidizing agent causing oxidative cleavage of polyhydroxy compounds. It cleaves compounds that have hydroxyl groups on adjacent carbon atoms, breaking the carbon-carbon bonds to form carbonyl compounds, such as aldehydes, ketones or acids. The reaction is carried out in organic solvents. A typical example is as follows ... 

Selectivity can be an overriding commodity in cases where reactivity is dictated by logic and accepted concepts. Such is the case with stannylene acetals of diols and trialkyl-stannyl ethers of alcohols. Enhanced nucleophilicity of oxygen attached to tin and well-documented stereoelectrorric effects associated with methine carbon atoms of trialkyhin ethers lead to remarkably selective reactions of (7-substitution and oxidation in polyhydroxy compounds. 

Polyhydroxy compounds are oxidized by such metal ions as vanadium(V), chromium(VI), cerium(IV), iridium(IV), and gold(III), among others. These oxidations were found to be catalyzed by acids.171 173 Vanadium(V) and chromium(VI) are closely related in their chemical properties, but the reduction of V(V) is difficult compared with that of Cr(VI) because of its lower redox potential [V(V)-V(IV) = 1.00 V Cr(VI)-Cr(III) = 1.20 V], However, the redox potential increases at lower pH values, facilitating the oxidation of sugars. 

Methyl iodide + silver oxide CH3I + Ag20 (in dimethylformamide) Used to convert polyhydroxy compounds to the methyl ethers... 

The reaction is most important for the preparation of carbinols from certain aromatic and heterocyclic aldehydes and for the preparation of several aliphatic polyhydroxy compounds. In the normal Cannizzaro reaction the theoretical yield of alcohol is only 50% because half of the aldehyde is converted to the acid. A mixture of an aldehyde with excess formaldehyde, however, results in a dismutation in which most of the higher aldehyde is reduced formaldehyde is oxidized to sodium formate, viz., ... 

Polyhydroxy compounds can be considered to be oxidized stepwise, the first step giving an a-hydroxy carbonyl compound, which is oxidized to a carboxylic acid. If each carbon atom has a hydroxyl group, the final products are formic acid and formaldehyde ... 

Sodium iodate, NalOj, is used rarely its applications are limited to the oxidation of aromatic polyhydroxy compounds to quinones [753, 754]. 

The heating could be effected at temperatures as high as 300° C, which would be favorable with regard to reaction velocity, but it is preferred to apply relatively moderate temperatures, i.e. temperatures between 110° and 180° C, because aromatic polyhydroxy compounds are readily oxidized in alkaline media at temperatures above 180° C. Preferably the temperature is between 130° and 160° C. 

The reactions are carried out in dilute solutions (about 2 to 7% of oxidant). Concentrations of over 10% of oxidant cause a retardation of reaction velocity, and the yields are diminished. The proportion of catalyst required is relatively large 10 to 50% of the quantity of substrate to be oxidized. Water serves as the best solvent for the reaction thus, the method is especially suitable for water-soluble polyhydroxy compounds. If the reaction product is water-soluble, substances insoluble in water can be oxidized in suspension for example, a carboxylic acid may be soluble as its salt. Liquid substances that are only slightly soluble in water cannot be suitably oxidized, as they form gums which inactivate the catalyst. 

This chapter focuses on the metal-catalyzed amination of alcohols and related compounds such as aminoalcohols, phenols and di- and polyhydroxy compounds. Details of the synthesis of amines with acidic catalysts, including zeolites, mixed oxides and metal phosphates, can be found elsewhere [3,5-7]. 

ANTIMONY(III) OXIDE (1309-64-4) (1309-64-4) OjSbj Ignites and bums in heated air above 420°F/215°C. Violent reaction with strong oxidizers bromine trifluoride. Reacts with chlorinated mbber, alcohols/glycols, organic and a-hydroxy acids (fruit acids), o-dihydric phenols polyethylene glycol and other polyhydroxy compounds. 

Many examples exist wherein a silyl enol ether is deprotected and oxidised in a one-pot procedure using Swem conditions. Godfroid and co-workers report the selective oxidation of primary TMS or TES protected 1,2-diols, 1,3-triols, and polyhydroxy compounds to the corresponding silyloxy aldehydes even when using excess Swem reagents.36... 

---