R. K. Nanda

Acid hydrolysis of carboxylatopentaamminecobalt(III) complexes Kinetics and mechanism of aquation of malonato, succinato, o-phthalato and o-methoxy benzoato pentaamminecobalt(III) complexes

Abstract The kinetics of aquation of malonato, succinato, o-phthalato and o-methoxybenzoato pentaamminecobalt(III) complexes have been studied in aqueoys acidic media adjusted to 0·3 M ionic strength. At [H+] = 0·005 − 0·3 M and 55 − 70°C, the observed pseudofirst-order rate constants are described by the relationship: kobs = k1 + k2 [H+] where k1 and k2 stand for the rate constants of spontaneous and acid catalysed equation of (NH3)5CoCO2(CH2)nCO2H2+ (n = 1,2), (NH3)5CoCO2C6H4CO2H2+ and (NH3)5CoCO2C6H4OCH32+ species respectively. The rate and the activation parameters for the k1 and k2 paths have been determined. The results indicate that the unbound carboxyl group does not exert a specific catalytic effect on the spontaneous and acid catalysed paths of aquation of the cobalt(III) substrates derived from the dicarboxylic acids. CoO bond fission appears to be rate limiting in both k1 and k2 paths of all complexes. The possibility of CO bond breaking, however, can not be ruled out in the k2 path of the o-phthalato complex.

Kinetics of aquation and base hydrolysis of cis bioxaltoammine bis(ethylenediamine) cobalt(III) ion

Abstract Cis bioxalatoammine bis (ethylenediamine) Co(III) cation has been synthesized and its aquation and base hydrolysis reactions have been investigated in 1·0 M NaCl04 medium. In the range of hydrogen ion concentration 0·02−1·O M and temperature 55–70°C, the rate law for the aquation of (en)2(NH3) CoC204H2+ is given by with k 1 (70°C) = 1·82 (±0·10) x 10 −5 sec −1 ΔH ∗ = 26·9 (±1·6) kcal/mole and ΔS ∗ = -2·4 (±5) e.s.u. : k 2 (70°C) = 3·14 (±0·22) × 10 −5 sec −1 M −1 ΔH ∗ = 24·0 (± 1·7) kcal/mole and ΔS ∗ = −9·7 (±5) e.s.u. : K 1 (70°C) = 3·0(±0·5) × 10 −2 M . The alkaline hydrolysis of (en)2(NH3)CoC204+ was studied at [OH−] with k 2 (30°C) = 2.75(±0·10) × 10 −3 sec −1 M −1 , ΔH ∗ = 30·0(± 1 ·1) kcal/mole and ΔS* = 28·6(±3·6) e.s.u.

Metal ion catalysed acid hydrolysis of acidopentaammine cobalt(III) complexes: Kinetics and mechanism of Al(III), Ga(III) and In(III) catalysed hydrolysis of malonatopentaamminecobalt(III) complex

Abstract Al(III), Ga(III) and In(III) have been found to catalyse the aquation reaction of the malonatopentaamminecobalt(III) complex. The catalytic activities of these metal ions have been ascribed to the formation of the reactive species, (NH3)5CoCO2CH2CO2M4+. At 60°C and 0·3M ionic strength (adjusted with NaClO4), the equilibrium constant (K′2) of the reaction, (NH3)5CoCO2CH2H2+ + M3− ⇌ (NH3)3CoCO2CH2CO2M4− + H4− and the rate constant (k3) of aquation of the binuclear species, (NH3)5CoCO2CH2CO2M4+ + H2O → (NH3)5CoOCH23+ + CH2(CO2)2M4− are found to be 0·334(±0·036), 1·01(±0·07) × 10−5 sec−1 for Al(III); 0·55(±0·02), 1·01(±0·10) × 10−5 sec−1 for Ga(III); and 0·178(±0·086), 0·635(±0·157) × 10−5 sec−1 for In(III) respectively. The species, [(NH3)5CoCO2CH2CO2Ga2OH]6+, has also been found to be involved as the catalytically active labile intermediate in the Ga(III) ion catalysed aquation of the cobalt(III) substrate. The activation parameters for the metal ion catalysed path of aquation of the malonato complex have been determined. CoO bond fission is tentatively suggested to be the rate determining step in the k3 path.

Interaction of oxalato pentaammine cobalt(III) with some Bi- and trivalent metal ions: Stability constants of (NH3)5CoC2O4M(n + 1)+ species

Abstract The association of Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Al3, Ga3+, In 3+ and Fe3+ with (NH3)5CoC2O4+ has been studied spectrophotometrically. The acid dissociation constant of (NH3)5CoC2O4H2+ and the stability constants of the binuclear complexes, (NH3)5CoC2O4M(n+1)+, are reported at 28°C and 0·3M ionic strength. The order of stabilities of the binuclear complexes is given by Mn2+ Zn2+ and Al3+

Kinetics and mechanism of acid and base hydrolysis of cis-chloro and bromo-(cyclohexylamine)bis-(ethylenediamine) cobalt(III) complexes

Abstract The kinetics of acid and base hydrolysis of chloro- and bromo-(cyclohexylamine)bis-(ethylenediamine) cobalt(III) complexes have been studied. The rate constants for acid hydrolysis of the chloro and bromo complexes are found to be 3·45 × 10−5 sec−1 and 15·3 × 10−5 sec−1, respectively, at 45°C. These are found to be independent of hydrogen ion concentration below pH 3·0 and ionic strength in the range 0·01–0·1 M. The activation parameters, EA and ΔS‡ , for the acid hydrolysis reaction of the chloro and bromo complexes are 20·0, 22·8 kcal/mole and −18.4, −·2 eu, respectively. The second order rate constants for base hydrolysis of the chloro and bromo complexes at 0°C and 0·1 M are found to be 2·5 and 8·9 M−1sec−1, respectively.

The effect of ion-pairing on the kinetics of the acid hydrolysis of chloropentaamine cobalt(III) ion—I. Effect of sulphate on the aquation of chloropentaamine cobalt(III) ion

Abstract The rate of solvolytic aquation of chloropentaammine cobalt(III) ion has been measured in aqueous medium in the presence of sulphate anion at 40°, 45°, 50° and 55°C. The rate accelerating effect of sulphate has been ascribed to more labile ion-pairs and the association constants and rate constants of the ion-pair have been calculated. The product analysis has been carried out to investigate the participation of the ion-pairing anion and the activation parameters of the aquation reaction of the ion-pair and different paths of reaction and enthalpy, entropy and free energy changes of the association equilibrium have been computed and discussed.

KINETICS AND MECHANISM OF ANATION OF β-cis-(DIAQUO)-(TRIEN)COBALT(III) BY OXALATE

Abstract The anation of β-cis-[Co(trien)(OH2)2]3+ ion by oxalic acid, bioxalate anion and oxalate dianion has been studied at 30–45°C and I = 1.0 M (KNO3). The common anation rate constant, k 0, of {β-cis-[Co(trien)(OH2)2]3+, H2C2O4} and {β-cis-[Co(trien)(OH2)2]3+, HC2O4 −} ion-pairs is found to be 6.7 × 10−5 sec−1 at 40°C. The observed anation rate constant levels off to a limiting value (7.0 (·0.8) X 10−3, sec−1) at 40°C, pH = 4.00 (·0.05) and [C2O4 2-] ± 0.15 M, which is characteristic of the anation rate constant (k 1) of the oxalate dianion ion-pair. Activation enthalpy and entropy for the k 0 and k 1, paths are 24.5 K.cal mole−1, 0.8 cal. deg−1 mole−1 and 28.9 K.cal mole−1, 24.0 cal. deg−1 mole−1, respectively. The temperature independent ion-pair equilibrium constant for H2C2O4 ion-pair was found to be 6.8 (·1.2) M−1. The anation of {β-cis-[Co(trien)(OH2)2]3+-X} ion pairs (X = H2C2O4, HC2O4 − or C2C4 2-) is believed to involve an ‘Id’ mechanism.

Kinetics and mechanism of elimination of chloride from cis-chlorobis-(ethylenediamine)(glycinato-N)cobalt(III) ion: a study of copper(II)-ion catalysis

The rate of elimination of chloride from the cis-chlorobis(ethylenediamine)(glycinato-N-)cobalt(III) ion has been studied under varying conditions of pH and copper(II) concentration in a medium of constant ionic strength of 0·3M. Copper(II) has been found to catalyse the reaction via formation of the binuclear species [(en)2CoCl-(NH2CH2CO2)Cu]3+. The product of the reaction in the presence and absence of CuII has been identified as the cis-bis(ethylenediarnine)(glycinato-ON)cobalt(III) chelate. At 50 °C the rate constant, activation enthalpy, and entropy for loss of chloride ion from [(en)2CoCl(NH2CH2CO2)]+, [(en)2CoCl(NH2CH2CO2H)]2+, and [(en)-CoCl(NH2CH2CO2)Cu]3+ species are: (2·65 ± 0·03)× 10–5 s–1, 90·4 ± 1·7 kJ mol–1, –54·1 ± 5·4 J K–1 mol–1; (1·27 ± 0·01)× 10–5 s–1, 92·5 ± 1·3 kJ mol–1, –53·1 ± 3·3 J K–1 mol–1; and (2·74 ± 0·10)× 10–4 s–1, 88·3 ± 2·9 kJ mol–1, –41·0 ± 9·2 J K–1 mol–1, respectively. Co–Cl Bond breaking is tentatively suggested to be rate limiting for the loss of chloride ion from all the three species mentioned above.