Bronsted acid catalyzed oxidation of certain sugar alcohols (polyols) has been studied by quinolinium dichromate (QDC) using aqueous sulfuric, perchloric, and hydrochloric acids at different temperatures. At constant acidity, reaction kinetics revealed the second-order kinetics with a first order in [Alcohol] and [QDC]. Zucker-Hammett, Bunnett, and Bunnett-Olsen criteria were used to analyze acid-dependent rate accelerations. Bunnett-Olsen plots of (log k + H ) versus (H + log [H + ]), and (log k) versus (H + log [H + ]) afforded slope values ( and * , respectively) > 0.47, suggesting that a water molecule acts as a prton transfer agent in the slow step of the mechanism in the oxidation of alcohols by QDC in the presence of aqueous sulfuric, perchloric, and hydrochloric acids. K E Y W O R D S acidity functions, Bronsted acid catalysis, Bunnett-Olsen, Bunnett, oxidation of certain sugar alcohols, quinolinium dichromate, Zucker-Hammett Int J Chem Kinet. 2020;52:167-177.

Potassium hydrogen sulfate (KHSO 4) mediated oxidation of certain alcohols (Polyols) has been studied by quinolinium bound Cr(VI) reagents like quinolinium dichromate (QDC) and quinolinium chlorochromate (QCC) at different temperatures. Reaction kinetics revealed second order kinetics with a first order in [Alcohol] and [Cr(VI) reagent] at constant bisulfate concentration. Ten fold variation of added [KHSO 4 ] enhanced the observed rateconstant (k′) by ten fold, showing first order dependence on [KHSO 4 ]. Most plausible mechanisms for QDC oxidation and QCC oxidation of polyols are proposed on the basis of observed kinetic features.

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Quinolinium dichromate (QDC) and quinolinium chlorochromate (QCC) were studied as efficient reagents for electrophilic aromatic nitration using sodium nitrite and thiocyanation by using ammonium thiocyanate under conventional, ultrasonic and solvent-free microwave assisted conditions. The microwave-assisted protocols exhibited remarkable rate acceleration and offered selective thiocyanation of the aromatic and heteroaromatic compounds with good yields. Addition of anionic (SDS) micelle to the reaction medium afforded considerable rate enhancements, while cationic (CTAB) and nonionic (Tx-100) micelles did not affect the rate noticeably. These protocols have were extended to regioselective thiocyanation of various aromatic compounds. Results were are completely similar to the nitration protocols. However, the reactions revealed comparatively shorter reaction times, and better yields in nitration reactions than in thiocyanation protocols. Catalytic effect of the SDS was attributed to the electrostatic stabilization of the cationic electrophile (NO2 + in nitration, and SCN + in thiocyanation). KEYWORDS

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