• M Santappa

      Articles written in Proceedings – Section A

    • Polymerization of vinyl monomers - I. Dye-reducing agent photosensitizing systems

      M Santappa A I Md Sheriff

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      A systematic study of the kinetics of photosensitized polymerization of vinyl monomers with the system Dye (erythrosin or acriflavine)-reducing agent (ascorbic acid), in the presence of oxygen and under buffered conditions (pH 6) in aqueous solution has been made. The determinations of the monomer disappearance, dye disappearance and of chainlengths of the polymers obtained against the different variables like light intensity, concentrations of monomer, dye, ascorbic acid, etc., have been made. A kinetic mechanism proposed for the overall reaction is discussed in the light of the experimental results and certain rate constants have also been evaluated.

    • Polymerization of vinyl monomers - II. Ceric-formaldehyde redox system

      M Santappa V S Ananthanarayanan

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      The kinetics of the polymerization of methyl acrylate initiated by the ceric perchlorate-formaldehyde redox system has been investigated. The rate of monomer disappearance has been found to be proportional to (a) the square of the monomer concentration, (b) the formaldehyde concentration and (c) the reciprocal of ceric ion concentration. The rate of ceric disappearance is found to be proportional to the ceric, monomer and formaldehyde concentrations. The chain-lengths have been found to increase with the monomer concentration and decrease with the ceric ion concentration. A kinetic scheme has been proposed whereby both ceric ions and the radicals produced from oxidation of formaldehyde by ceric ions have been shown to initiate the polmerization, while the termination occurs exclusively by the interaction of the chain radicals with ceric ions. The results obtained in the presence as well as absence of the reducing agent have been compared on the basis of the above kinetic scheme.

    • Vinyl polymerization - III. Polymerization of acrylamide initiated by cobaltic ions in aqueous solution

      M Santappa V Mahadevan K Jijie

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      Polymerization of Acrylamide initiated by cobaltic ions in aqueous solution at 15° C. and 20° C. in HClO4 and H2SO4 media have been studied. Kinetics have been followed by determining the rate of cobaltic ion disappearance as well as monomer disappearance with variations in cobaltic, monomer and hydrogen ion concentrations, temperature, ionic strength, etc. Besides polymer reaction it has been observed that side reactions like water oxidation and monomer oxidation also contribute to rate of cobaltic ion disappearance. Certain anomalous results in H2SO4 medium have been observed. A reaction scheme involving CoOH2+ and Co3+ as initiators in HClO4 and H2SO4 media respectively and mixed termination—mutual and linear—has been suggested. Certain rate parameters involving rate constants for initiation, propagation, termination and the corresponding activation energies have been evaluated.

    • Oxidation studies - I. Oxidation of primary alcohols by peroxydisulfate

      L R Subbaraman M Santappa

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      Results on the oxidation of primary alcohols (methanol, ethanol,n-propanol,n-butanol and isobutanol) by peroxydisulfate in aqueous solution in the temperature range 50°–80°, under uncatalysed, Ag+ catalysed and deaerated conditions are presented. Oxygen was found to have a retarding effect on the rate of peroxydisulfate disappearance,$$ - R_{S_2 O_3 ^ - } $$, and the inhibition period was a maximum in the case of ethanol and isobutanol. Both under uncatalysed and Ag+ catalysed conditions$$ - R_{S_2 O_3 ^ - } $$ varied with [S2O8/=]3/2 for all the alcohols;$$ - R_{S_2 O_3 ^ - } $$ was independent of alcohol concentration for all the alcohols except for methanol and ethanol where a one-half order with respect to [alcohol] was observed. In the Ag+ catalysed oxidation$$ - R_{S_2 O_3 ^ - } $$ varied as [Ag+]1/2 with all the alcohols. The effect of [H+], ionic strength, temperature, initially added product of the reaction on the rate are discussed and the stoichiometries of the reactions determined. In the light of the observed results, reaction mechanisms are postulated with SO4·− as the reactive species formed by thermal decomposition of S2O8= under uncatalysed conditions and by the interaction of Ag+ and S2O8/− under Ag+ catalysed conditions. The existence of Ag++ in catalysed reactions is postulated. The values of rate constants, frequency factors, energies of activation entropies of activation, etc., were evaluated.

    • Vinyl polymerization - IV. Co3+-tert. butylalcohol red-ox system

      K Jijee M Santappa

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      The effect of tert. butyl alcohol on the polymerization of Methylmethacrylate initiated by cobaltic ions in aqueous perchloric acid medium was tried. Rates of cobaltic ion disappearance and rates of polymerization were measured with variables, [M], [A], [Co3+], [H+], etc. at constant ionic strength. From the experimental results it was concluded that at low [A], initiation and termination of polymerization was by Co3+ species. At higher [A], initiation was still by Co3+ species but termination was found to change over to mutual type. At very high [A], Co3+ + tert. butyl alcohol reaction was found to function as a red-ox system for polymerization of monomer. An appropriate kinetic scheme was proposed and the various rate constants under different [A] regions evaluated.

    • Oxidation studies - II. Oxidation of water and tertiary alcohols by cobaltic ions

      K Jijee M Santappa

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      Studies on oxidation of water by cobaltic ions in perchloric, nitric and sulfuric acid media in the temperature range 20–30° C. at constant ionic strength of 2·2 M were carried out. An overall order of 3/2 for cobaltic ion concentration was observed in perchloric, nitric acid media and at low [Co3+]<4×10−3 M in sulfuric acid medium. At high [Co3+] in sulfuric acid medium an order 2 was observed. In all the three acid media an inverse dependence of the rates on [H+] was noticed. From the experimental results, an acid-independent reaction path was inferred in perchloric and nitric acid media. The effect of ionic strength, HSO4 and initially added cobaltous ions as well as temperature was studied. Suitable reaction schemes were suggested to explain the experimental results and activation energy values for some of the rate parameters were evaluated. Kinetic studies on oxidation of tertiary amyl and tertiary butyl alcohols in sulfuric acid medium and that of the former in perchloric acid medium were carried out. The reaction rates were found to vary linearly with [Co3+] and [Alcohol]. From the effect of acidity and of [HSO4] in H2SO4 medium on the reaction rates it was concluded that in HClO4 medium CoOH2+ species were the active entities while in H2SO4 medium Co3+ as well as CoOH2+ species were the active entities. The influence of ionic strength, temperature, etc., on the raction rates were studied and activation energy values for some rate constants were evaluated.

    • Oxidation studies—III - Oxidation of ketone by ceric ions in perchloric acid

      M Rangaswamy M Santappa

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      The oxidation of aliphatic unsymmetrical ketones-n-propyl methyl ketone and isobutyl methyl ketone and cyclic ketone-cyclohexanone by ceric perchlorate in perchloric acid (≈0·5–2·0 M) was studied in the temperature range 10°–30° C. The kinetics of the reactions were followed by measuring rate of Ce4+ disappearance effecting variations in [Ce4+], [Ketone], [HClO4], ionic strengthμ, temperature, etc., and the reactions were found to be 2nd order—first order each with respect to [Ce4+] and [ketone]. No evidence for complex formation between Ce4+ and ketone was obtained from kinetics or by an independent absorptiometric method. Ce4+ (aq) and enol of the ketones were the active species for oxidation. Correlations between rates of enolisation of ketones and oxidation of the latter by Ce4+ were observed. The rate constants and their thermodynamic data were calculated and discussed. A mechanism based on the concept of oxidation as a process of successive hydroxylation of organic molecules is proposed.

    • Vinyl polymerization - V. Synthesis of graft polymers from brominated poly (styrene)

      S Prabhakara Rao M Santappa

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      Vinyl monomer [methyl methacrylate (MMA), or ethyl methacrylate (EMA) or methyl acrylate (MA)] was polymerized in benzene solution with benzoyl peroxide as catalyst and in the presence of varying amounts of bromopoly (styrene) (Br PS). Branching occurred by chain transfer reaction of the growing polymer radicals with bromine atoms of the bromopoly (styrene) backbone, followed by initiation of polymerization by the Br PS radicals thus obtained. The chain transfer constants of the branching reaction and the degree of grafting were determined and by suitable correlation of the two,kp/(kt)1/2 for the grafting reactions were evaluated. The graft polymers were isolated by fractional precipitation, and were characterized by IR spectra and molecular weight determination by osmotic pressure measurements. The high values of chain transfer constant, molecular weight of the graft polymers much in excess of the backbone Br PS, the order of magnitudes or second virial coefficients, etc., proved the formation of graft polymers.

    • Oxidation studies - IV. Kinetics of oxidation of HCHO and some alcohols by ceric salts in HNO3 medium

      M Santappa B Sethuram

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      The results on the kinetics of oxidation of HCHO and some alcohols,viz.,n-propanol, allyl alcohol, cyclohexanol and benzyl alcohol by ceric nitrate in nitric acid medium in the temperature range of 10–35° C. are presented. The active form of Ce4+ during the oxidation of the above organic substrates was assumed to be the neutral Ce(NO3)4. The mechanism of oxidation and thermodynamic parameters for the above compounds are also given.

    • Vinyl polymerization - VI. Dilute solution properties of 1:1 Poly (styrene-co-ethylmethacrylate)

      K Karunakaran M Santappa

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      1:1 Poly (styrene-co-ethylmethacrylate) (PSEM) was prepared by bulk polymerization and fractionated using methylethyl ketone/petroleum ether system. IR and NMR analyses of the copolymer substantiated the composition kinetically expected. As the composition heterogeneity of the compolymer was narrow, the characterization of the copolymer was effected in a single solvent by light scattering as well as viscosity measurements at 35° C. The molecular weight dependence of [η], the limiting viscosity number;$$\left( {\bar r^2 } \right)w^{_2^1 } $$, therms end to end distance and A2 the second virial coefficient were established. The solvent ethylacetate was found to be thermodynamically more ideal for PSEM, than for polyethylmethacrylate. In an attempt to evaluate K, the Flory’s constant, application of various methods appeared to give almost similar values. In order to explain the low value ofΦ, the Flory’s universal parameter, rough estimates of$$\left( {\bar r_0 ^2 } \right)^{_2^1 } $$, the unperturbedrms end to end distance;b, the statistical chain element;q, the persistence length and$${{\bar r_0 ^2 } \mathord{\left/ {\vphantom {{\bar r_0 ^2 } {l\bar r_{\max .} }}} \right. \kern-\nulldelimiterspace} {l\bar r_{\max .} }}$$, the semiflexibility parameter were also made.

    • Oxidation studies—V - Oxidation of light and heavy water by peroxydisulphate

      S Padma M Santappa

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      Oxidation of light and heavy water by peroxy disulphate was studied at 60–70° C. The acid independent and acid dependent rate constants and respective ΔE values were computed. An attempt is made to explain the kinetic isotopic effect observed. A probable mechanism is proposed.

    • Vinyl polymerisation - VII. Polymerisation of acrylamide photoinitiated by anthraquinone sulphonates

      M Santappa Q Anwaruddin

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      A systematic study of the kinetics of photo-chemical polymerisation of acrylamide using the system anthraquinone sulphonate-NaCl-HClO4 under deaerated condition in aqueous solution has been done. The determinations of the monomer disappearance (bromometry), the sensitiser disappearance (spectrophotometry) and chainlengths of polymers with respect to light intensity, concentration of monomer, light absorption fraction (ke) of sensitiser, etc., have been carried out. An overall kinetic mechanism is given in the light of experimental results.

    • Oxidation studies-VI - Oxidation of some mono- and Di-basic acids by peroxy disulphate

      S Padma M Santappa

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      Uncatalysed oxidation of malonic, maleic, succinic, malic, mandelic and lactic acids by peroxydisulphate have been studied at 60°–80°C. Rates of oxidation and E values are reported. Probable mechanisms are proposed.

    • Oxidation studies-VII - Oxidation of hydrazine sulphate and hydroxylamine by cobalt (III)

      K Jijee M Santappa

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      Kinetics of oxidation of hydrazine sulphate and hydroxylamine by Co3+ in nitric and sulphuric acid media at 10–15° C. were studied. In H2SO4 medium, kinetic evidence was obtained for complex formation between Co3+-Substrate for both substrates whereas no such evidence was found in HNO3 medium. The effects of [H+], μ [HSO4], [SO4=], [Co2+] and temperature on the reaction rates were studied. An inverse dependence of the rates on [H+] was noticed in both media with both substrates but decreasing effect of [HSO4] was observed only with NH2OH in H2SO4 medium. Conclusions were drawn as to the nature of the active species: In H2SO4 medium for hydrazine sulphate, Co3+ (aq.) was concluded to be the active species; similarly for NH2OH, CoOH2+ was the active species. In HNO3 medium for both substrates CoOH2+ was the active oxidant. Nitrogen and Ammonia were found to be the products of oxidation with both substrates in both media. Stoichiometries were established and suitable mechanisms were proposed. The rate laws were formulated and the various equilibria and rate constants were evaluated.

    • Vinyl polymerization - VIII. Photopolymerization of vinyl monomers by azidopentamminecobalt (III) chloride

      M Santappa L V Natarajan

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      A systematic study of the kinetics of photopolymerization of vinyl monomers initiated by the complex azidopentamminecobalt (III) chloride in aqueous solution has been made. The determinations of monomer disappearance, complex disappearance, chainlengths of polymers, obtained against the different variables like light intensity, concentrations of monomer, light absorption fraction, etc., have been made. A kinetic mechanism proposed for the overall reaction is discussed in the light of the experimental results and certain rate constants have also been evaluated.

    • Vinyl Polymerization - IX. Polymerization of acrylonitrile by V5+ + Pinacol redox system

      S Saccubai M Santappa

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    • Oxidation studies - VIII. Oxidation of some carboxylic acids by peroxydisulphate catalysed by metal ions

      S Padma M Santappa

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    • Vinyl Polymerisation - X. The ternary system: Polymer Fraction 1/Fraction 2/Solvent

      Padma Vasudevan M Santappa

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      The ternary system Poly (methyl methacrylate) Fraction 1/Fraction 2/n-butyl bromide has been studied. A viscometric method is proposed for the estimation of the individual polymer concentration in the two conjugate phases in equilibrium.

    • Vinyl polymerization - XI. Binary systems of poly (methyl methacrylate)/and poly (ethyl methacrylate)/solvdnt by phase separation

      S Padma Vasudevan M Santappa

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      The thermodynamic interaction parameters of the systems, poly (ethyl methacrylate) /n-butanol and poly (methyl methacrylate) /n-butyl bromide and poly (methyl methacrylate)/isoamyl acetate were determined by methods involving phase separation and compared critically with values obtained by other methods. The validity of some of the well-known theoretical equations in the region of phase separation is considered.

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