Chromium(VI) Based Oxidants; IV.1Zinc Chlorochromate Nonahydrate as an Efficient and Mild Oxidizing Agent

Kinetics and Mechanism of the Oxidation of Some Secondary Alcohols by Benzimidazolium Dichromate

Benzimidazolium dichromate (BIDC), in dimethylsulfoxide, oxidizes secondary alcohols to the corresponding ketones. The reaction is first order with respect to BIDC. The order with respect to alcohol is more than one but less than two. Michaelis - Menten type kinetics were observed with respect to alcohol. The formation constants of the alcohol-BIDC complexes and the rates of their decomposition were determined at different temperatures.

The oxidation of deuterated 2-propanol indicated the presence of a substantial primary kinetic isotope effect. The reaction exhibited a second order dependence on hydrogen-ion concentration. The reaction was studied in nineteen organic solvents. The solvent effect was analyzed using multiparametric equations. It was found that the cation-solvating power of the solvent played the major role. The rates of oxidation exhibited an excellent correlation with polar and steric substituent constants. A suitable mechanism has been proposed.

Kinetics and Mechanism of the Oxidation of Dl-Methionine by Benzimidazolium Dichromate

The oxidation of DL-methionine (MT) by benzimidazolium dichromate (BIDC), in dimethyl sulfoxide, leads to the formation of the corresponding sulfoxide. The reaction is first order with respect to BIDC. Michaelis - Menten type kinetics were observed with respect to MT. The reaction is catalysed by hydrogen ions and the dependence is of the form kobs = k‘[H+]. The rate of oxidation of MT was determined in 19 organic solvents. An analysis of the solvent effect by solvatochromic equations indicated that though both the anion- and cation-solvating powers of the solvent contribute to the observed solvent effect, the role of cation-solvation is much the major. A suitable mechanism has been proposed.

Kinetics and Correlation Analysis of Reactivity in the Oxidation of Aromatic Aldehydes by Butyltriphenylphosphonium Dichromate

The oxidation of a number of para-, meta- and ortho-substituted benzaldehydes by butyltriphenylphosphonium dichromate (BTPPD), in dimethyl sulphoxide, leads to the formation of the corresponding benzoic acid. The reaction is first-order with respect to BTPPD. Michaelis-Menten type kinetics were observed with respect to the aldehyde. The formation constants of the aldehyde-BTPPD complexes and the rates of their decomposition were determined at different temperatures. The reactions are catalysed by hydrogen ions and the dependence is of the second order. The oxidation of [2H] benzaldehyde (PhCDO) exhibited the presence of a substantial kinetic isotope effect. The rates of oxidation of meta- and para-substituted benzaldehydes were correlated in terms of Charton's triparametric LDR equation, whereas the oxidation of ortho-substituted benzaldehydes were correlated with tetraparametric LDRS equation. The oxidation of para- and ortho-substituted benzaldehydes are more susceptible to the delocalization effect than is the oxidation of meta-substituted compounds, which display a greater dependence on the field effect. The positive value of η suggests the presence of an electron-deficient reaction centre in the rate-determining step. The reaction is subjected to steric hindrance by the ortho-substituents. The rates of oxidation of benzaldehyde were determined in nineteen organic solvents. An analysis of the solvent effect by multiparametric equations indicated the greater importance of the cation-solvating power of the solvents. Suitable mechanisms have been discussed.

A Facile Asymmetric Route to (−)-Aphanorphine

8O-methylaphanorphine was synthesized from 4-methoxyphenylacetaldehyde in 36% overall yield and in nine steps, featuring the formation of ring B via a Friedel-Crafts alkylative cyclization with the concomitant stereospecific introduction of the benzylic quaternary carbon center. The current work constitutes an efficient enantioselective formal synthesis of 3-benzazepine marine alkaloid (-)-aphanorphine.

An Investigation of the Reactions of Substituted Homoallylic Alcohols with Various Oxidation Reagents

Substituted homoallylic alcohols have been synthesised both by [2,3]-Wittig rearrangement of unsymmetrical bis-allylic ethers and reaction of alkenyl chloromethyl oxiranes with Mg/THF. These substrates were then oxidized using four different oxidants. When the substituted homoallylic alcohols were oxidized with pyridinium chlorochromate or zinc chlorochromate nonahydrate the corresponding carbonyl compounds were produced. The same substrates formed the corresponding allylic oxidation products together with epoxidation products when oxidized with t-BuOOH. When and t-BuOOH and catalytic amounts of OsO₄ were used the allylic oxidation reaction was prevented and the only products formed were those in which the substituted double bond was epoxidized.

Efficient, Solvent-Free Oxidation of Organic Compounds with Potassium Dichromate in the Presence of Lewis Acids

The synthetic utility of potassium dichromate in the presence of Lewis acids under solid phase conditions is described. This reagent efficiently oxidizes alcohols, acyloins, oximes and semicarbazones to their corresponding carbonyl compounds, while trimethylsilyl and tetrahydropyranyl ethers, ethylene acetals and ketals undergo oxidative deprotection to produce carbonyl compounds efficiently.