Oxidation of Alcohol by Lipopathic Cr(VI):  A Mechanistic Study

Abstract

The oxidation kinetics of various aliphatic primary and secondary alcohols having varied hydrocarbon chain length were studied using cetyltrimethylammonium dichromate (CTADC) in dichloromethane (DCM) in the presence of acetic acid and in the presence of a cationic surfactant. The rate of the reaction is highly sensitive to the change in [CTADC], [alcohol], [acid], [surfactant], polarity of the solvents, and reaction temperature. A Michaelis-Menten type kinetics was observed with respect to substrate. The chemical nature of the intermediate and the reaction mechanism were proposed on the basis of (i) observed rate constant dependencies on the reactants, that is, fractional order with respect to alcohol and acid and a negative order with respect to oxidant, (ii) high negative entropy change, (iii) inverse solvent kinetic isotope effect, k(H2O)/k(D2O) = 0.76, (iv) low primary kinetic isotope effect, kH/kD = 2.81, and (v) the k(obs) dependencies on solvent polarity parameters. The observed experimental data suggested the self-aggregation of CTADC giving rise to a reverse micellar system akin to an enzymatic environment, and the proposed mechanism involves the following: (i) formation of a complex between alcohol and the protonated dichromate in a rapid equilibrium, equilibrium constant K = 5.13 (+/-0.07) dm(3) mol(-1), and (ii) rate determining decomposition (k(2) = (7.6 +/- 0.7) x 10(-3) s(-1)) of the ester intermediate to the corresponding carbonyl compound. The effect of [surfactant] on the rate constant and the correlation of solvent parameters with the rate constants support the contribution of hydrophobic environment to the reaction mechanism.

Deoximation by cetyltrimethylammonium dichromate: A kinetic study

“…7). Earlier, a similar type of observation was reported during the oxidation of alcohol, and the result was attributed to the reversed micellization of CTAB in organic solvents [24,25]. CTAB is known to form reversed micelle with an inner hydrophilic core.…”

Distinct Reactivity Differences of Metal Oxo and Its Corresponding Hydroxo Moieties in Oxidations: Implications from a Manganese(IV) Complex Having Dihydroxide Ligand

“…Accordingly, the anthraquinone formed by the Mn IV ÀOH at pH 1.5 is most probably the product of sequential oxidation of anthracene by electron transfer, whereas anthracene is not 3+ is essential for electron transfer as has previously been demonstrated for the oxygenation of triphenylphosphine. [14,15] Such an inverse KIE value also suggests that the formation of minor amounts of anthraquinone from 9,10-dihydroanthracene at pH 4.0 could be attributed to electron transfer by the Mn IV À OH, present in trace amounts as [Mn =O functional groups were definitively distinguished through the tests with 2,2'-azino-di-(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS), a relatively facile electrontransfer reagent. [16] At pH 4.0 and 13.4, ABTS is in the same protonation state (pK a = 2.2) with identical electrochemical properties, [16c] and the UV/Vis spectra of ABTS are also identical in the pH range 3-13.4 (see Figure S11).…”

Chemical Degradation of a Mixture of tri-n-Octylamine and 1-Tridecanol in the Presence of Chromium(VI) in Acidic Sulfate Media

“…Likewise, n-dodecane tridecanoate can be formed by the reaction between 1-tridecanol and 1-tridecanal in the presence of Cr(V) or Cr(VI) as depicted in Scheme 2 [21][22][23][24]:…”