The kinetics of oxidation ofortho-substituted phenyl methyl sulphides by peroxoanions, Cr(VI) and picolinic acid catalysed Cr(VI) have been investigated. Regression analyses of the rate data by using Taft and Charton equations to separate steric effect from electronic effects have been carried out. In peroxoanion oxidations, the localized electronic effect plays a major role. In the uncatalysed and picolinic acid catalysed Cr(VI) oxidations, both localized and delocalized effects are significant. Steric effect plays a minor role in all the oxidations

Detailed kinetic investigations of the oxidation of methyl phenyl sulphoxide and diphenyl sulphoxide by peroxomonosulphate in aqueous acetic acid medium reveal that the reactions are first-order, both in the sulphoxide and in the oxidant. Studies with substituted phenyl methyl sulphoxides and 4,4′-disubstituted diphenyl sulphoxides show that electron-releasing groups accelerate the rate of oxidation and electron-withdrawing groups retard it. A fair correlation between log k₂ and Hammett substituent constants has been observed in the two series. The mechanism proposed involves the rate-determining nucleophilic attack of the sulphoxide sulphur at the outer terminal peroxo oxygen atom of HSO₅⁻.

The kinetics of oxidation of ortho-substituted phenylmercaptoacetic acids by bromamine T and metaperiodate ion and also thepk_a values of these acids have been studied. Regression analyses of the rate and equilibrium data indicate that the ortho-substituent effect can be explained by the electrical effects alone, and that in these acids when the reaction site is in close proximity to the ortho-substituent or not, the steric effect is insignificant. The rates of oxidation and the ionization constants of these acids are largely controlled by the inductive effect.

The oxidation of 4,4′-disubstituted diphenyl sulphoxides by potassium permanganate on Hammett type correlations give a small positive ρ value (0.34). This is in contrast to the oxidation of aryl methyl sulphides (ρ = −1.36) by the permanganate ion. On the basis of rate data a mechanism of nucleophilic attack of MnO₄⁻ on the substrate has been proposed.

The quenching rate constants,k_q, for the excited state electron transfer reactions oftris(2,2′-bipyridine)chromium(III) ion with several aryl methyl sulphides (ArSMe) obtained by the luminescence quenching technique, are accelerated by electron releasing groups and retarded by electron withdrawing groups present in the aryl moiety of ArSMe. The plot ofRT Ink_q vs.E_1/2 values of different sulphides is linear, indicating the electron transfer nature of the reaction. Studies with alkyl phenyl sulphides demonstrate the importance of the steric effect in these photoredox reactions.

The kinetics of oxidation of N-acetylphenothiazine (NAPT) by Cr(VI) in 80% acetic acid-20% water (v/v) mixture is first-order each in [NAPT] and [Cr(VI)]. The reaction is catalysed by added acid with a third-order dependence in [HCIO₄], Increase in polarity of the solvent medium decreases the rate. The oxidation is insensitive to variations in ionic strength as well as added acrylamide. Oxidations of phenothiazine (PT) and N-methylphenothiazine (NMPT) under similar conditions are found to be very fast. However kinetic investigations with NMPT in an acetic acid-sodium acetate buffer show first-order dependence each in [NMPT] and [Cr(VI)] and a fractional-order dependence in [H⁺] in the pH range 1.80-3.09. Increase in polarity of the medium increases the rate. In both the cases, the corresponding sulphoxides are identified as oxidation products. Based on the kinetic results, mechanisms for oxidations are proposed.

Montmorillonite-and cellulose-adsorbed 3,6-diaminoacridine are prepared. The adsorption isotherm studies show that while 3,6-diaminoacridine molecules are adsorbed in the interlayer spaces of the montmorillonite clay, the dye molecules are adsorbed on the surface of cellulose. Quenching studies reveal that the Al³⁺ ions of the aluminosilicate layers of the clay also quench the excited state emission of the adsorbed 3,6-diaminoacridine.

The rate of electron transfer (ET) in a variety of chemical and biological processes is influenced by factors like the free energy change (†G), the donor-acceptor electronic coupling and the medium. The effect of donor-acceptor electronic coupling on the rate of photoinduced intermolecular electron transfer is considered by taking Ru(II) and Cr(III) metal complexes in the excited state as electron acceptors and organic compounds as electron donors. The electronic coupling between the donor and acceptors depends strongly on donor-acceptor distance. The electron transfer distance is varied by introducing alkyl groups of different sizes either on the bipyridine ligand of the metal complex or on the quencher. The semiclassical theory of electron transfer expresses k_ET as the product of a nuclear and an electronic transmission coefficient (K_n andK_el respectively) and an effective nuclear-vibration frequency (v_n),k_ET =v_nK_el, K_n. The electron transfer reaction becomes nonadiabatic if the donor-acceptor distance is long. The change of electron transfer mechanism from adiabatic to nonadiabatic due to the introduction of bulky groups is explained in terms of semiclassical theory and from the temperature-dependence study of photoinduced electron transfer reactions of metal complexes.

Photoamination of 4-nitroveratrole in cyclodextrins with the nucleophiles ammonia, methylamine and hexylamine provides a new route to regioselectivity. This method gives a displaced product para to the nitro group as the predominant product, in contrast to the solution reaction wherein the meta-displaced product predominates. This is due to the change in the mechanistic shift fromS_N2Ar*, wherein the nitro group is meta-directing, to a mechanism involving electron transfer from the nucleophile to the excited aromatic substrate(S_N (ET)Ar*) to give the para-displaced product