M. Santappa

Polymerization of acrylonitrile initiated by Ce4+/thiourea system

Abstract Kinetics of polymerization of acrylonitrile initiated by the Ce4+-thiourea redox system have been investigated at 10°. The rate of monomer disappearance is proportional to (a) (monomer concentration)2, (b) thiourea concentration and, (c) (ceric ion concentration)−1. The rate of ceric disappearance is proportional to the ceric and thiourea concentrations, but independent of monomer concentration. A kinetic scheme has been proposed involving production of initiating radicals from oxidation of thiourea by ceric ions and termination exclusively by the interaction of the chain radicals with ceric ions. The scheme is consistent with experimental findings. The results obtained either in the presence or the absence of the reducing agent have been compared and interpreted in terms of the proposed kinetic scheme.

Grafting of methyl methacrylate onto cellulose nitrate initiated by benzoyl peroxide

It has been observed that grafting of vinyl monomers onto cellulose nitrate in solution takes place using benzoyl peroxode. The graft copolymer was isolated from the unreacted backbone and homopolymer by selective solvent extraction. The effect of variables, such as the initiator concentration, the monomer concentration and the reaction time on the percent grafting and the grafting efficiency, were discussed. A probable mechanism for grafting of vinyl monomers to cellulose nitrate in solution has been proposed.

Ternary complexes: Equilibrium studies of mixed-ligand complexes of uranyl ion with dicarboxylic acids in aqueous solution

Abstract The stability constants of the ternary uranyl ion complexes involving dicarboxylic acids were determined by pH metric titrations at a temperature of 31 ± 0·1°C and an ionic strength, μ = 0·1 M (NaClO4). The stability values clearly show the discriminating qualities of uranyl ion-dibasic acid 1:1 complex toward the secondary ligand to be coordinated. The values of log K2YX are inversely related to the product of the acid dissociation constants of the secondary ligands. The overall stability is found to be dependent on the binary stabilities. Ring size of the chelates formed by the secondary ligands is found to influence the formation of ternary complexes.

Stability constants in aqueous solution of complexes of uranyl ion with mixed dibasic acids—II

Abstract Systems of uranyl ion-succinic-adipic; uranyl ion-succinic-thiomalic and uranyl ion-succinic-itaconic acids were studied by pH titration method at μ = 0·1 (NaClO 4 ) and T = 31°C. The formation of 1:1:1 complexes was inferred from the titration curves and their stability constants are reported.

Binary and ternary complexes of chromium(III) involving iminodiacetic acid, L(+)-aspartic acid, L(+)-glutamic acid, or L(+)-cysteine as ligands

Stability constants for binary complexes of the type MAH, MA, MA2H2, MA2H,MA2, or M2A3 in the CrIII–iminodiacetic acid (H2ida), –L(+)-aspartic acid (asp), –L(+)-glutamic acid (glu), and –L(+)-cysteine (cys) systems and for ternary complexes MABH2, MABH, or MAB in the CrIII–H2ida(A)–asp or –glu(B) and CrIII–cys(A)–asp or –glu(B) systems have been determined for the first time at 50 ± 0.1 °C and l= 0.1 mol dm–3(Na[ClO4]) by potentiometry using a computer iteration technique. The acid dissociation constants of these ligands have also been obtained under identical conditions. The pH dependence of the electronic spectra of the equilibrated solutions provides information on the nature and type of complexes formed. The results suggest that H2ida and asp act as tridentate ligands in the binary complexes MA and MA2, as well as in the ternary complex MAB. However, it appears that glu is tridentate in the MA complex, but bidentate in MA2 and MAB. The potentially tridentate ligand cys has been established to behave as a bidentate ligand towards CrIII. The probable site of protonation in the binary complexes MAH, MA2H, and MA2H2 is discussed on the basis of the dissociation constant of the ligand and the stability-constant data for the complexes. Preferential formation and enhanced stability were observed for the ternary relative to the binary complexes. This has revealed factors such as ring size, ligand–ligand interactions, and steric effects which influence the stabilization of chromium(III) mixed-ligand complexes.

Equilibrium studies of mixed-ligand complexes of uranyl ion with mono- and dicarboxylic acids in aqueous solution

Abstract Equilibrium studies on mixed-ligand complexes of uranyl ion with carboxylic acids, malonic, diglycollic, maleic, crotonic, glycollic, thioglycollic and mercaptopropionic, as ligands were carried out by the pH titration method at 31 ± 0·1°C and ionic strength μ = 0·1 mol dm −3 (NaClO 4 ). Different equilibrium constants, characteristic of mixed-ligand complexes were calculated. In most of the systems studied, ternary complexes were found to be more stable than the corresponding binary complexes. The stabilities of ternary complexes appear to depend on the size of the chelate ring; the difference in stabilities of 1:1 and 1:2 binary complexes; the nature of the donor atom and the charge neutralization if any. In general, the stability is attributed to the unsymmetrical nature of the ternary complex.

Spectrophotometric investigation of complexes involving Cu++ and some carboxylic acids

Abstract Complexometric studies on Cu(ClO 4 ) 2 -carboxylic acid (formic, acetic, propionic, α- and β-hydroxy propionic, chloro and phenyl acetic acids, triammonium aurin tricarboxylate etc.) systems were carried out by spectrophotometric methods at 30°C ± 0·1°C and μ = 0· 1 and stability constants for various complexes were evaluated.

Acid decomposition reactions of diperoxo(amine)chromium(IV) complexes

Etude des reactions de decomposition de Cr(O 2 ) 2 en (H 2 O) et Cr(O 2 ) 2 (dien). Les produits et leurs proportions varient en fonction de [H + ]

Polymerization of methyl methacrylate in the presence of molecular oxygen - a kinetic study

Abstract Methyl methacrylate was polymerized in aqueous medium initiated by a copper(II)-ascorbic acidoxygen system at 40°C and a kinetic study of the reaction is presented. The rate of polymerization, Rp showed an increase, constancy and then a decrease with increase in the [Cu2+]. The order with respect to [Cu2+] was 0.5 in the rate increase region. The order in monomer concentration changed gradually from 1.0 to 2.0 with increase in [Cu2+]. Rp became independent of ascorbic acid (AA) concentration and oxygen concentration at high concentrations. These results indicate that termination by mutual interaction of chain radicals predominates at low [Cu2+] while termination was exclusively by metal ions at high [Cu2+]. Rp was also observed to increase with temperature and ionic strength and to K p K t 1 2 value was calculated and compared with literature values. Chain lengths were determined by viscometry for the polymers obtained under various experimental conditions.

Photochemical Oxidation of Aliphatic Aldehydes by Uranyl Ions

The photochemical oxidation of formaldehyde and acetaldehyde by Uranyl percholate in aqueous perchloric acid was studied three monochromatic wavelength, 365 mμ, 405 mμ and 436 mμ. The rate of Uranous ion formation was directly proportional to light intensity and light absorption fraction by the active species. Plots of reciprocal rates versus reciprocal aldehyde concentrations were linear with intercepts on the ordinates indicating complex formation between Uranyl ions and the aldehydes. Hydrogen ions had marked effect on the rates. The results are consistent with the hypothesis that there is complex formation between Uranyl ions and aldehyde and the excitation of the complex (active species) is the primary photochemical process and the excited complex docomposes by an electron transfer process yielding U4+ and substrate radical in a secondary dark reaction. Quantum yield for U4+ production increased with decreasing wavelength of light.