Kinetics of formation and dissociation of the ternary complex ion (pentane-2,4-dionato)(nitrilotriacetato)chromate(III) in aqueous media

Synthesis of solid [Cr(nta)(H₂O)₂] 1, kinetics and equilibrium of ots reaction with pentane-2,4-dione (Hpd) to form [Cr(nta)(pd)]⁻ 2 (H₃nta is nitrilotriacetic acid), aquation of 2 into 1, and some related reactions have been described. Parallel proton-independent and inverse proton-dependent paths lead from 1 to 2. The [H⁺]⁻¹ path arises from metal assisted deprotonation of HE, the enol form of Hpd. Aquation of 2 into 1 involves [Cr(Hnta)(pd)(H₂O]⁺ 2H (Hnta is tridentate nta) in addition to 2. The nta comples 1 is considerably more labile and a weaker acid than [Cr(H₂O)₆]³⁺.     

Kinetics of oxidation of hydrazine by a dioxo-bridged dimanganese(III,IV) complex ion

In aqueous acidic media containing an excess of Hbipy⁺–bipy buffer in the pH 3.5–4.5 range, the complex ion [(bipy)₂Mn^III(-O)₂Mn^IV(bipy)₂]³⁺ (1) coexists in rapid equilibrium with its diaqua derivative [Mn^III,IV ₂ (-O)₂(bipy)₃(H₂O)₂]³⁺ (1a) (bipy = 2,2-bipyridine). An excess of N₂H₅ ⁺ quantitatively reduces the mixture to Mn^II, itself being oxidised to N₂. The first order rate constant, k _o decreases with increasing C _bipy (C _bipy = [Hbipy⁺] + [bipy]) but increases with increasing [N₂H₅ ⁺] and [H⁺]. The observed kinetic dependence can be explained in terms of a reaction between (1a) and N₂H₅ ⁺. Replacement of solvent H₂O with D₂O decreases k _o substantially and the effect suggests simultaneous transfer of an electron and a proton in the rate-determining step. The relevance of this observation to the delayed oxidation of H₂O in the hydrazine-treated photosystem II is discussed.     

Kinetics and mechanism of the oxidation of oxalic acid and bioxalate ion by [ethylene bis (biguanide)] silver (III) cation in aqueous perchlorate media

In acidic aqueous media the complex [Ag^IIILL⁻)³⁺[L = ethylenebis (bi-guanide)] reacts quantitatively with oxalic acid and bioxalate ion to produce CO₂, Ag⁺ and L. Kinetic evidence indicates preequilibrium adduct formation, but the reactions appear to be outer-sphere with these adducts (I₁ and I₂) acting as kinetic dead ends.No Ag⁺ catalysis could be detected.     

In alkaline media,Fremy’s salt oxidizes alkanols by a hydrogen atom transfer mechanism

In aqueous alkali, Fremy’s salt (potassium nitrosodisulfonate dimer), homolyses nearly exclusively to the monomer radical anion, nitrosodisulfonate (NDS). In this media, NDS almost quantitatively oxidizes benzyl alcohol (PhCH₂OH) to benzaldehyde (PhCHO), itself being reduced to hydroxylamine disulfonate (HNDS). The reaction is very nearly first-order in [NDS], [alkanol] and in [OH⁻]. However, with progressive addition of HNDS, decay kinetics of NDS gradually deviates from first-order. Ultimately, with sufficient excess of HNDS, the reaction becomes second-order in [NDS]. The consumption ratio, (ΔPhCH₂OH]/Δ[NDS]), is ∼2. PhCD₂OH manifests a large primary kinetic isotope effect (k_H/k_D = 11.6). Substituted benzyl alcohols (RBzCH₂OH) with R-groups withdrawing electron density from the O–H bond accelerated the reaction; those with R-groups donating electron density to the O–H bond retarded the reaction. The conversion of 2-propanol to 2-propanone is much slower compared to that of benzyl alcohol to benzaldehyde. An alpha-H atom transfer mechanism seems logical.