Rupendranath Banerjee

A SELECTIVE KINETIC METHOD FOR THE ESTIMATION OF BENZYL ALCOHOL IN CLOSELY RELATED MIXTURES

Ethylenebis(biguanide)silver(III) ion quantitatively oxidises benzyl alcohol and its derivatives (XC6H4CH2OH; X = H, CH3, Cl or NO2, substituents in ortho or para position). The difference in reaction rates for different alcohols has been utilised in developing a kinetic method for the estimation of benzyl alcohol (2.0–40.0 mmol dm−3) in the presence of a large number of closely related alcohols and hydroxy compounds. The relative standard deviation for ten replicate measurements of 5 mmol dm−3 benzyl alcohol is 1.5%. The method was satisfactorily applied to analyse real samples.

Kinetic and mechanistic studies on the oxidation of hydroxylamine by a tri-bridged manganese(IV,IV) dimer in weakly acidic media

The complex ion, [MnIV2(μ-O)2(μ-MeCO2)(bipy)2(H2O)2]3+ (13+) (bipy = 2,2′-bipyridine) and its aqua derivatives [Mn2IV(μ-O)2(bipy)2(H2O)4]4+ (24+) and [Mn2IV(μ-O)2(μ-MeCO2)(bipy)(H2O)4]3+ (33+) coexists in rapid equilibria in aqueous buffer in the presence of excess of bipy and MeCO2− in the range pH 4.00–5.30. The solutions are reasonably stable up to pH 5.50 and react quantitatively with hydroxylamine to produce manganese(II) and N2O. The reactions follow simple first-order kinetics in the presence of excess hydroxylamine. There is UV–vis spectral evidence for the intermediate MnIII,IV complex, [(bipy)2MnIII(μ-O)2MnIV(bipy)2]3+, in the presence of excess bipy and deficit hydroxylamine which supports that 13+ and its hydrolytic derivatives are reduced by one-electron steps. Increased extent of aquation at the manganese(IV) centre leads to increased kinetic activity in the order: 13+ < 24+ < 33+. The rate of reduction increased with an increase in the concentration of hydroxylamine but decreased with increase in cbipy and cOAc. The mild oxidising character of the complex ion along with major structural changes associated with one-electron oxidation of hydroxylamine disfavours an outer-sphere pathway. The overall first-order rate constants decrease linearly with increased mol% of D2O suggesting proton-coupled electron transfer pathways.

KINETICS AND MECHANISM OF HYDRAZINE OXIDATION BY A TRI-BRIDGED MANGANESE(IV, IV) DIMER IN WEAKLY ACIDIC MEDIA

Abstract The complex ion [ Mn 2 IV (μ-O) 2 (μ-MeCO 2 )(bipy) 2 (H 2 O) 2 ] +3 { 1 { 3+ (bipy = 2,2′-bipyridine) and its aqua derivatives, [Mn2(μ-O)2(bipy)2(H2O)4]+4 {2{4+ and [Mn2(μ-O)2(μ-MeCO2)(bipy)(H2O)4]+3 {3{3+ coexists in rapid equilibria in aqueous buffers (MeCO2− + bipy; pH, 4.5–5.5). The solutions are reasonably stable and react with hydrazine to produce manganese(II) and N2. The reactions follow simple first-order kinetics in the presence of excess hydrazine. The rate determining steps are one-electron reductions of {2{4+ and {3{3+ to (bipy)2]{2{3+ and {3{2+ respectively. The le-reduced products rapidly produce [(bipy)2MnIII(μ-O)2-MnIV(bipy)2]3+ in the presence of excess bipy and deficit hydrazine. Kinetic activity of {1{3+ is insignificant compared to {2{4+ and {3{3+. Rate of reduction increased with increase in the concentration of hydrazine and ethanoate, but it decreased with increase in [bipy]. Increase in rate at higher pH indicates inner-sphere coordination and deprotonation of N2H5+. The mild oxidising character of {2{4+ and {3{3+ along with major structural cha associated with one-electron oxidation of hydrazine disfavours an outer-sphere pathway.

Kinetics and mechanism of oxidation of hypophosphite ion by diaquobis(pentane-2,4-dionato)manganese(III) in aqueous perchlorate media

SummaryIn aqueous perchlorate media (pH 4.0–5.5) two moles of [Mn(pd)2(H2O)2]+ (Hpd=pentane-2,4-dione) are consumed per mole of H2PO2− oxidised to H2PO3−. The experimental rate law is:

Oxidation of NO2− by [Mn2IV (μ-O)2(μ-OAc) (H2O)2(bipy)2]3+ ion: a probable example of a two-electron transfer reaction

\frac{{d(ln[Mn^{III} ]}}{{dt}} = \frac{{2kK_1^H K_c [H_2 PO_2^ - ]_0 [H^ + ]}}{{[Hpd]_0 + K_1^{\rm H} [H^ + ]}}

Thermodynamic and Kinetic Studies on the Iron(III)-Hydroxamate Interaction in Acid Media

where K1H (=1.44×105) and Kc are the equilibrium constants for the reactions: [Mn(pd)3]+H++2H2O⇋[Mn(pd)2(H2O)2]++Hpd and [Mn(pd)2(H2O)2]++H2PO2−⇋[Mn(pd)2(H2O)(H2PO2)]+H2O respectively, while kKc (=4.3×10−4 mol−1 dm3 s−1 at 40° C, I=1.0 mol dm−3) is the second-order rate constant for the reduction of [Mn(pd)2(H2O)2]+ by H2PO2−. The thermodynamic reducing strength of H2PO2− is greater than that of S2O32− but the rate of reduction of MnIII-pd complexes by H2PO2− is slower than that by S2O32−. It appears that the rate-determining step involves the tautomerization (‘normal’→active) of H2PO2− bound to [Mn-(pd)2(H2O)2]+ which under the experimental conditions is the only kinetically active oxidant.

Catalase-like activity of the polyoxovanadate anion [MnIVV13O38]7−: a mechanistic study

Abstract In the pH range 1.91–5.24, an aqueous solution of the complex [Mn3IV(μ-O)4(bipy)4(H2O)2]4+ (1) oxidises ascorbic acid quantitatively to dehydroascorbic acid and is itself reduced to MnII. In the presence of excess ascorbic acid, the reaction follows first-order kinetics. The first-order rate constant k0 measured in the presence of excess ascorbic acid increases linearly with increasing concentration of the reductant but decreases as more and more 2,2′-bipyridine is added. k0 also increases with [H+] but tends to saturate at higher [H+]. The proposed rate-determining step involves simultaneous transfer of one electron and one proton from the ascorbate ion to [Mn3IV(μ-O)4(bipy)3(H2O)4]4+, an aquated form of 1. Subsequent rapid reactions via a dinuclear {Mn2O2}3+ intermediate lead to the final products.

Kinetics of oxidation of phenylhydrazine by a μ-oxo diiron(III,III) complex in acidic aqueous media

Abstract The title complex 1 coexists in equilibrium with [Mn 2 IV (μ-O) 2 (H 2 O) 4 (bipy) 2 ] 4+ ( 2 ) and [Mn 2 IV (μ-O) 2 (μ-OAc)(H 2 O) 4 (bipy)] 3+ ( 3 ) in mixed (OAc − + bipy) aqueous buffer. The complexes are quantitatively reduced to Mn 11 by NO 2 − , which is itself oxidised to NO 3 − . There is no kinetic and UV-vis spectral evidence for any intermediate Mn III,IV complex, and the reactions appear to be two-electron transfer processes. The rate of reduction increases with increasing extent of hydrolysis in the sequence 1 2 3 . A plausible interpretation has been presented.