Kinetic evidence for the copper peroxide intermediate with two copper ions in proximity

Self Cite

The Ni(II) ion catalyzed thermal decomposition of peroxomonosulfate (PMS) was studied in the pH range 3.42-5.89. The rate is first order in [PMS] and Ni(II) ion concentrations. At pH greater than or equal to 5.23, the reaction becomes zero order in [PMS] and this changeover in the order of the reaction occurs at a higher concentration of nickel ions. The first-order kinetics in PMS can be explained as a rate-limiting step and is the transformation of nickel peroxomonosulfate into nickel peroxide. This peroxide intermediate reacts rapidly with another PMS to give oxygen and Ni(II). The formation of nickel peroxide is associated with a small negative or nearly zero entropy of activation. The zero-order kinetics in [PMS] can be explained by the fact that the hydrolysis of aquated nickel(II) ions into hydroxocompounds is the rate-limiting step. The turnover number is 2 at pH 3.42 and increases with pH.

Section: Resultsmentioning

confidence: 71%

“…(1). Results from this laboratory 24 suggest that Cu(II)‐ and Ni(II)‐catalyzed decomposition of PMS in alkaline medium proceeds through a peroxide intermediate. In the case of Ni(II), dark brown/black nickel peroxide is slowly precipitated and the reaction becomes heterogeneous.…”

Section: Introductionmentioning

confidence: 89%

Nickel peroxide: A more probable intermediate in the Ni(II)‐catalyzed decomposition of peroxomonosulfate

Thendral¹,

Shailaja²,

Ramachandran³

2007

Self Cite

“…The results, from this laboratory, on the self‐decomposition of Cu(II)‐PMS in aqueous alkaline medium 28 and Ni(II)‐PMS in the pH range of approximately 3.4–5.9 29, suggest that the metal ion‐catalyzed reaction proceeds through a molecular mechanism with a metal peroxide intermediate. Thus, under favorable conditions, molecular intermediates instead of radicals may be possible for the PMS activation by transition metal ions.…”

Section: Introductionmentioning

confidence: 88%

The role of Ni(II) in the oxidation of glycylglycine dipeptide by peroxomonosulfatex

Thendral

Shailaja

Ramachandran

2008

Self Cite

The kinetics of oxidation of the dipeptide glycylglycine by peroxomonosulfate (PMS) was studied in the pH range of 3.42-5.89. The rate is first order in [PMS], glycylglycine concentration, and inverse first order in [H + ]. The kinetic data suggest that SO 2− 5 reacts, with glycylglycine, faster than H SO − 5 by five orders of magnitude. The observed kinetics can be explained as due to the formation of an intermediate by the nucleophilic interaction of peroxide with the terminal protonated amine of glycylglycine, which then decomposes in the rate-limiting step to the product aldehyde. The thermodynamic parameters are evaluated. The reaction is catalyzed by Ni(II) ions only when pH ≤ 4.63, and above this pH the rate is zero order with respect to [Ni(II)]. Perusal of the enhanced rate constant values suggests that the Ni-peroxide intermediate also reacts with glycylglycine. The Ni-dipeptide complex is not oxidized by PMS, and this complex in fact inhibits the formation of Ni-peroxide intermediate.

“…7. Studies from this laboratory on the metal ions catalyzed decomposition of PMS suggest that the catalysis by Cu(II) (in alkaline medium) 26 and Ni(II) (in acidic pH) 19 proceeds through molecular process that involves, NiSO

_{−}^{5}

, nickelperoxomonosulfate intermediate. The nickel peroxomonosulfate intermediate slowly transforms into a nickel peroxide intermediate that reacts rapidly with another molecule of PMS to give oxygen.…”

Section: Resultsmentioning

confidence: 99%

Studies on the oxygen atom transfer reactions of peroxomonosulfate: Catalytic effect of hemiacetal

Shailaja

Ramachandran

2009

Self Cite

The reaction of peroxomonosulfate (PMS) with glycolic acid (GLYCA), an alpha hydroxy acid, in the presence of Ni(II) ions and formaldehyde was studied in the pH range 4.05-5.89 and at 31 • C and 38 • C. When formaldehyde and Ni(II) ions concentrations are ∼5.0 × 10 −4 M to 10.0 × 10 −4 M, the reaction is second order in PMS concentration. The rate is catalyzed by formaldehyde, and the observed rate equationThe number of PMS decomposed for each mole of formaldehyde (turnover number) is 5-10, and the major reaction product is oxygen gas. The first step of the reaction mechanism is the formation of hemiacetal by the interaction of HCHO with the hydroxyl group of nickel glycolate. The peroxomonosulfate intermediate of the Ni-hemiacetal reacts with another molecule of PMS in the rate-limiting step to give the product. This reaction is similar to the thermal decomposition of PMS catalyzed by Ni(II) ions.