Linear free energy relationships in the kinetic study of oxidation of phenols by quinolinium dichromate

Abstract

The oxidation of ortho-, meta-, and para-substituted phenols by Quinolinium Dichromate (QDC) to the corresponding Quinones in aqueous acetic acid medium is first-order with respect to [QDC] and [phenol]. There is no effect of added Quinoline on rate. The reaction is acid catalyzed. A medium of low dielectric constant favors the oxidation process, and the rate of the oxidation process changes with change in the ionic strength of the medium. Electron releasing groups on the benzene ring enhance the rate of oxidation, while electron withdrawing groups retard, compared to the unsubstituted phenol. A correlation exists between log k 2 and , the Hammett's substituent constant, with a slope of Ϫ 3.79 at 303 K. Analysis of the rate data using I and R values indicate that both inductive and resonance effects of the substituents equally influence the rate of the reaction. The free energy of activation, ⌬G ϶ , is linearly correlated with . A probable mechanism is proposed.

Kinetics and Mechanism of Deamination and Decarboxylation of 2-Aminopentanedioic Acid by Quinolinium Dichromate (QDC) in Aqueous Perchloric Acid Medium

“…The α-hydroxyacids and α-ketoacids are oxidized with QDC, and their reactions are studied kinetically. QDC oxidizes cinnamic and crotonic acids smoothly in N , N -dimethylformamide in the presence of an acid to give aldehydes. − …”

Kinetic Studies on the Oxidation of Some para and meta‐Substituted Cinnamic Acids by Pyridinium Bromochromate in the Presence of Oxalic Acid (A Co‐oxidation Study)

“…The mechanistic path ways and nature of the transition state in the oxidation of single and multiple C-C bonds with chromium(VI) still remains controversial. The oxidation of cinnamic acid by various Cr(VI) reagents such as acid dichromate 3,4,5 , potassium dichromate in presence of picolinic acid 6 and quinolium dichromate 7,8 have been reported.…”

Kinetics and mechanism of quinolinium dichromate mediated oxidation of sugar alcohols in Bronsted acid media

“…During the past several decades, acid dichromate derived from potassium dichromate in general, [1][2][3][4] and Cr(VI) reagents with heterocyclic moeity [5][6][7][8][9][10][11][12][13][14][15][16] in particular, received the attention of chemists all over the world due to their immense importance in synthetic chemistry. Dichromates of heterocyclic bases such as pyridinium dichromate, imidazolium dichromate, nicotinium dichromate, isonicotinium dichromate, and quinolinium dichromate (QDC) were employed as oxidizing agents in organic synthesis.…”

“…Balasubramanian and Pratibha were the first to explore QDC as a synthetic reagent in the oxidation of alcohols. 11 However, over a period of time, QDC was used for the selective oxidation of a wide range of organic compounds [12][13][14][15][16] such as phenols, hydrocarbons, benzaldehydes, ethanolamines, and isoniazid, etc. In our earlier studies, we explored kinetic and mechanistic results of oxidation of ethanolamines by QDC.…”