Vinyl Polymerization Initiated by Ceric Ion–Ethyl Cellosolve Redox System in Aqueous Nitric Acid

Abstract

Polymerizations of methyl methacrylate (MMA) and acrylonitrile (AN) were carried out in aqueous nitric acid at 30°C with the redox initiator system ammonium ceric nitrate-ethyl cellosolve (EC). A short induction period was observed as well as the attainment of a limiting conversion for polymerization reactions. The consumption of ceric ion was first order with respect to Ce(IV) concentration in the concentration range (0.2–0.4) × 10^?2 M, and the points at higher and lower concentrations show deviations from a linear fit. The plots of the inverse of pseudo-first-order rate constant for ceric ion consumption, (k ¹)^?1 vs [EC]^?1, gave straight lines for both the monomer systems with nonzero intercepts supporting complex formation between Ce(IV) and EC. The rate of polymerization increases regularly with [Ce(IV)] up to 0.003 M, yielding an order of 0.41, then falls to 0.0055 M and again shows a rise at 0.00645 M for MMA polymerization. For AN polymerization, R _p shows a steep rise with [Ce(IV)] up to 0.001 M, and beyond this concentration R _p shows a regular increase with [Ce(IV)], yielding an order of 0.48. In the presence of constant [NO^? ₃], MMA and AN polymerizations yield orders of 0.36 and 0.58 for [Ce(IV)] variation, respectively. The rates of polymerization increased with an increase in EC and monomer concentrations: only at a higher concentration of EC (0.5 M) was a steep fall in R _p observed for both monomer systems. The orders with respect to EC and monomer for MMA polymerization were 0.19 and 1.6, respectively. The orders with respect to EC and monomer for AN polymerization were 0.2 and 1.5, respectively. A kinetic scheme involving oxidation of EC by Ce(IV) via complex formation, whose decomposition gives rise to a primary radical, initiation, propagation, and termination of the polymeric radicals by biomolecular interaction is proposed. An oxidative termination of primary radicals by Ce(IV) is also included.     

Kinetics and mechanism of urethane formation catalyzed by organotin compounds. I. The reaction of phenyl isocyanate with methanol in dibutyl ether under the action of dibutyltin diacetate

The kinetics of the dibutyltin diacetate (DBTDA) catalyzed reaction of phenyl isocyanate with methanol in dibutyl ether at 25°C were studied by monitoring the rate of change in the absorbance of the reaction mixture at 281.6 nm. The rate equation was The value of k was calculated at 0.96 liter/(mole sec). In addition, it was ascertained that protons behave like extremely strong inhibitors for the catalyzed reaction. On the basis of these data a mechanism for urethane formation is proposed. The subsequent reaction steps are (1) complexation of methanol to DBTDA, (2) dissociation of the complex into a proton and an anion of composition {(n-C₄H₉)₂Sn(OCOCH₃)₂(OCH₃)}^-, (3) insertion of the isocyanate into the tin-alkoxy bond (the rate-determining step), and (4) methanolysis of the urethane precursor formed with simultaneous regeneration of the anion. With this mechanism it is possible to explain the observed kinetics as well as the deviations that occur in the rate expression if strong acids are added to the reaction mixture. The latter effect is caused by a shift in the equilibrium that describes the dissociation of the complex into ions. The retardation of the reaction by weak acids like acetic acid is caused by complexation of DBTDA by the acid.     

Studies in Cyclocopolymerization. XII. Cyclocopolymerization of the Donor:Acceptor Pair 1,4-Diene:Monoolefin Lewis Acid Complex

Acrylonitrile (AN) is known to form a cyclocopolymer with 1,4-dienes such as divinyl ether (DVE) and 3,3-dimethyl-1,4-pentadiene with radical initiators. Since AN has a high tendency toward homopolymerization, the copolymers are not of regular structure. Lewis acids such as ZnCl₂ and Al(Et)₃ were used in this paper to increase the e-values of AN and methacrylonitrile (MAN) through complexation. AN, MAN, and 2- and 4-vinylpyridine were copolymerized with DVE and 1,4-pentadiene with Lewis acids. In all cases the rate of copolymerization was much enhanced and the alter-nating tendency of the cyclocopolymer increased with the amount of added Lewis acids. A 1:2 DVE:AN alternating cyclocopolymer was obtained spontaneously or with AIBN with Al(Et)₃ in hexane. Also 1:2 alternating cyclocopolymer was successfully obtained in acetone by using a large amount of ZnCl₂. The identification of charge-transfer (CT) complex-ation between the DVE and (AN,¹ ₂, ZnCl₂ complex, and between the 1-hexene and (AN)₂ZnCl₂ complex may supoort the par-ticipation of a CT complex formed between all 1,4-dienes studied and the monoolefin-Lewis acid complexes in the     

Substituent effects on the kinetics of the cerium(IV) oxidation of mandelic acids in sulfate media. Anomalous kinetic behavior of the methoxy derivative

The kinetics of the cerium(IV) oxidation of p-nitro and p-methoxymandelic acids have been investigated in H₂SO₄-MHSO₄ (M⁺ = Li⁺, Na⁺, K⁺) and H₂SO₄-MClO₄ (M⁺ = H⁺, Na⁺) mixtures at a constant total electrolyte concentration of 2.00 mol/dm³. The oxidation of p+nitromandelic acid proceeds through two [H⁺]-independent paths, as was also observed for some substituted mandelic acids studied previously. The kinetic behavior of the p-methoxy derivative differs from that of the other mandelic acids in that (1) the oxidation occurs via two [H⁺]-dependent paths, (2) the reaction rate is anomalously high, (3) the activation enthalpy and entropy of the overall process are markedly lower. It provides strong support to the suggestion that a different mechanism is operative. The substituent effects and the reaction mechanism are discussed.     

Electrokinetic Detection in Reversed Phase High Performance Liquid Chromatography Part II. Quaternary Ammonium Ion-Pairs of Some Volatile Fatty Acids

Abstract

The conditions of electrokinetic detection were elaborated for tetraethylammonium, TEA⁺, ion-pairs of volatile fatty acids(acetic, propionic, isobutyric and valeric) in reversed phase high performane liquid chromatography, HPLC. To eliminate the dependence of the retention volume V _R, on the concentration of acids found in the first part of this work, TEA⁺ was added to the non-buffered mobile phase. In the presence of pairing TEA⁺ ions, V _R appeared to be invariant with the concentration of acids in the sample in a definite concentration range. The detectability of the detector, with a polytetrafluoroethylene, PTFE, capillary as its working unit, was of the order of 10^?10 mole and the reproducibility was 5% (relative standard deviation, R. S. D., for ten consecutive injections). The linear dynamic range extended over two orders of magnitude of the acid concentrations.     

Kinetics and mechanism of formyl- and acetylferrocene oxidation with molecular oxygen in organic solvents

Kinetic laws and the products of autoxidation of formyl- and acetylferrocene in organic solvents in the presence of strong and weak Br?nsted acids were investigated. The special feature of the studied reactions is the extreme dependence of the metal complex oxidation rate on the strong acid concentration. This is explained by protonation of the metal complex at high concentrations of the acids leading to the formation of stable to oxidation ??-ferrocenylcarbenium complexes C₅H₅FeC₅H₄C⁺(OH)R.     

Polymerization of Acrylonitrile Initiated by the System Tetramethyl-2-tetrazene and p-Toluenesulfonic Acid

The polymerization of acrylonitrile (AN) initiated by tetramethyl-2-tetrazene (TMT) and p-toluenesulfonic acid (TSA) in dimethylformamide (DMF) was studied. The polymerization was confirmed to proceed through a radical mechanism. The initial rate of polymerization R was expressed by the equation: R_p = k[TMT]^0.6 [TSA]^0.46 [AN]^1.35. The overall activation energy for the polymerization was estimated as 20.7 kcal/mole. In the absence of monomer, the reaction of TMT with TSA was also studied kinetically by measuring the evolution of nitrogen. From these results and ESR measurement of the TMT/TSA system, a possible initiation mechanism is proposed.     

Metal compounds in free-radical processes. III. Polymerization of acrylonitrile initiated by copper (II) nitrate in presence or absence of triphenylphosphine

The bulk polymerization of acrylonitrile (AN) initiated by copper (II) nitrate, Cu(II), in the absence of light has been studied. The rate of the AN polymerization may be expressed in the Cu(II) concentration range from 5 × 10^?4 to 1 × 10^?1 mole 1.^?1 by the equation, R_p = k₅[Cu(II)]^0.68, where k₅ = K_AN[AN]/(1 + K_AN[AN]). From the spectrophotometric measurements the values of 0.70 l./mole and 0.08 l, mole were obtained for the equilibrium constant at 20 and 60°C, respectively, K_AN = [C]/[AN]-[Cu(II)], corresponding to the formation of the complex C from acrylonitrile and copper (II) nitrate. An addition of triphenylphosphine (C₆H₅)₃P into the polymerization system reduces R_p, and no polymerization takes place at all provided [(C₆H₅)₃P]/[Cu-(II)] ≧ 5. The retardation effect of (C₆H₅)₃P on the polymerization of AN initiated by Cu(II) is attributed to a competitive reaction of Cu(II) with (C₆H₅)₃P in which Cu(II) is reduced and the product of this reduction CuNO₃·2(C₆H₅)₃P is inactive with respect to the polymerization of AN.     

Aqueous polymerization of methyl methacrylate initiated by the redox system Ce(IV)–isopropyl alcohol. Kinetics and molecular weight

Polymerization of methyl methacrylate was carried out in aqueous nitric acid in the temperature range 26–40°C, with the redox initiator system ceric ammonium nitrate–isopropyl alcohol. A short induction period was observed, as well as the attainment of a limiting conversion, and the total ceric ion consumption with reaction time. The reaction orders were 1/2 and 3/2 with respect to the IPA and monomer concentration, respectively, within the range (3–5) × 10^?3M of Ce(IV). But at lower Ce(IV) concentration (≤ 1 × 10^?3M), the order with respect to monomer and Ce(IV) changed to 1 and 1/2, respectively. The rate of ceric ion disappearance was first order with respect to Ce(IV) concentration and (R_Ce)^?1 was proportional to [IPA]^?1. Both the rate of polymerization and the rate of ceric ion consumption increase with rise in temperature. The average-molecular weight can be controlled by variations in IPA, Ce(IV), and monomer concentrations, and in temperature. A kinetic scheme involving oxidation of IPA by Ce(IV) via complex formation, whose decomposition gives rise to a primary radical, initiation, propagation, and termination of the polymeric radicals by bimolecular interaction is proposed. An oxidative termination of primary radicals by Ce(IV) is also included.     

Polymerization of Acrylonitrile-Metal Haiide Complexes in the Frozen State. III. Relationship between Rate of Radiation-Induced Polymerization and Complex Concentration

Radiation-induced polymerization of acrylonitrile (AN) in the ZnCl₂-AN-H₂O ternary system was carried out at temperatures ranging from 30 to ?78°C, and correlation between the polymerization rate and the concentration of complexed AN with zinc atom was clarified. The selected systems were in the supercooled liquid state at ?78^CC with the molar composition ratio of ZnC12:AN:H₂O of 1:1:3. The polymerization is free-radical in character. The 0.5-power dependence of the polymerization rate on the dose rate at 30°C indicates bimolecular termination, while the 0.9-power dependence at ?78°C shows predominant unimolecular termination because of the high viscosity of the systems at Just above the glass transition temperature. The negative temperature dependence of the polymerization rate is indicative of the tendency of the complex concentration to increase with lower temperatures. The polymerization rate, therefore, is proportional to the 2 and 1.5 powers of the complex concentration at ?78 and 30°C, respectively. These results indicate participation of the complexed monomer both in generation of the initiating radical species on irradiation and in the propagation step. A kinetic scheme has been proposed on the basis of the results.     

Kinetic Studies on the Copolymerization of Acrylonitrile and Itaconic Acid in Dimethylsulfoxide

The free radical copolymerization of acrylonitrile (AN) with itaconic acid (IA) in dimethylsulfoxide (DMSO) initiated by azobisisobutyronitrile (AIBN) has been found to be chemically controlled even at high conversion. In order to explain this specific finding by Walling's kinetic model, a detailed study on the monomer reactivity ratios (MMRs), decomposition kinetics of AIBN and homopolymerization kinetics of AN was carried out in DMSO from 50 to 80°C. The results suggest that the reactivity ratio of IA is less than unity and always larger than that of AN. Thus, the reaction has an ideal copolymerization behavior when the temperature is increased. It is also found that decomposition of AIBN in DMSO is strictly first order and the decomposition rate constants (k _d) determined by nitrogen evolution technique are acceptable. k_p /k ^0.5 _t ratios of AN were estimated from the off-line conversion data under various monomer and initiator concentration. Additionally, the temperature dependences on MRRs, k _d and k_p /k ^0.5 _t were believed to follow the Arrhenius's law very well.     

Kinetics and mechanism of decarboxylation of aspartic acid with ninhydrin

The kinetic study of the decarboxylation of aspartic acid has been carried out at various [ninhydrin], [H⁺] and at different temperature ranging from 60–95°C. The reaction follows an irreversible first-order reaction path under pseudo first-order kinetic conditions. The variation of pseudo first-order rate constant (k_obs) with ninhydrin concentration was found to be in agreement with equation 1/k_obs = B₁ + B₂/[Ninhydrin]. One mol of carbondioxide evolved from decarboxylation of α-COOH and second mol of carbondioxide comes from the decarboxylation of β-keto acid which is an intermediate and formed during the course of ninhydrin and aspartic acid reaction. On the basis of the observed data, a possible mechanism has been proposed.     

Formation and Structural Characterization of Metal Complexes derived from Thiosalicylic Acid

The formation and structural aspects of some metal complexes of thiosalicylic acid (TSA) were studied. The μ‐bridging tetra‐coordinated Ru complex, [Ru(C₆H₄(CO₂)(μ‐S)(H₂O)]₂ ( 1 ) was formed by hydrothermal reaction of TSA with RuCl₃. The complexes [M(dtdb)(phen)(H₂O)]_n ( 2 – 4 ) (M = Zn^II, Co^II, Ni^II, dtdb = 2,2′‐dithiodibenzoate anion, phen = 1,10‐phenanthroline) were obtained by the slow diffusion technique and the in situ S–S bond formation was confirmed by elemental, spectral and X‐ray analysis. Reaction of TSA with CuCl₂ and 2,2′‐bipyridine (bipy) under the slow diffusion technique yielded the dimer [Cu(tdb)(bipy)] ( 5 ) (tdb = thiodibenzoic acid), where the in situ generation of 2,2′‐thiodibenzoic acid was observed.     

Vinyl polymerization. Part 268. Polymerization of acrylonitrile initiated by the system of tetramethyl tetrazene and bromoacetic acid

The polymerization of acrylonitrile (AN) initiated by the system of tetramethyl tetrazene (TMT) and bromoacetic acid (BA) in dimethylformamide (DMF) was studied. The TMT–BA system could initiate the polymerization of AN more easily than TMT alone. The polymerization was confirmed to proceed through a radical mechanism. The initial rate of polymerization R_p was expressed by the equation: R_p = [TMT]^0.62-[BA]^0.5[AN]^1.5. The overall activation energy for the polymerization was estimated as 9.4 kcal/mole. In the absence of monomer, the reaction of TMT with BA in DMF was also studied kinetically by measuring the evolution of nitrogen gas. The reaction was first-order in TMT and first-order in BA; the rate data at 49°C were k₂ = 9.1 × 10^?2l./mole-sec., ΔH? = 17.0 kcal/mole, and ΔS? = ? 6.6 eu. In addition, the treatment of TMT with BA in benzene led to the formation of tetramethylhydrazine radical cation, which was identified by its ESR spectrum. On the other hand, the relatively strong interaction between TMT and DMF was observed by absorption spectrophotometry.     

Kinetics and mechanism of ligand substitution in binuclear nickel(II) and cobalt(II) complexes

The kinetics and mechanism of the removal of M²⁺ from bis-(heptane-2,4,6-trionato)M(II) [M = Ni, Co] by ethylenediminetetraacetic acid (EDTA), nitrilotriacetic acid (NAT), 1,2-cyclohexanediamine-N, N, N′, N′-tetraacetic acid (C_yDTA), and ethylenebis(oxyethylenenitrilo)tetraacetic acid (EGTA) have been investigated using stopped-flow spectrophotometry in methanol-water at 25°C and ionic strength 0.1 mol dm^?3 KNO₃. The reactions were investigated at a number of different pHs. An associative mechanism is proposed to account for the kinetic data. Although all the ligands have similar functional groups, their reactivity towards the parent complex is quite different. The pH dependence of the rate constants has been used to determine the relative reactivities of the various ligand species present. In the case of nitrilotriacetic acid, a nonlinear dependence on ligand concentration is observed, thus confirming the mechanism proposed. © 1995 John Wiley & Sons, Inc.     

Role of N,N-dimethyl-para-toluidine and saccharin in the radical polymerization of methyl methacrylate initiated by a redox system. I. Cumene hydroperoxide/copper saccharinate

Kinetics of methyl methacrylate polymerization initiated by a redox system [cumene hydroperoxide (CHP)/copper saccharinate] were studied in bulk at 20°C in the presence of accelerators such as N,N-dimethyl-p-toluidine (DMPT) and o-benzoic sulphimide (saccharin). Assuming a steady-state concentration of propagating radicals, the polymerization rate depends on the square root of the initiation rate and the kinetic orders with respect to each compound in the initiation step may be deduced. Initiation is first-order in CHP, copper saccharinate, and saccharin and second-order in DMPT. A reaction scheme consistent with these orders is proposed. The main features are the following: (1) CHP reduces rapidly Cu(II) to Cu(I); (2) a small fraction of Cu(I) is complexed with DMPT; (3) the complexed ions (Cu⁺, DMPT₂) are strong reductants with respect to CHP whereas uncomplexed Cu⁺ are almost inactive; (4) the decomposition of CHP is strongly catalyzed by saccharin (protonated CHP is 13000 times more reactive than free CHP). Thus both accelerators are necessary to get high polymerization rates. © 1994 John Wiley & Sons, Inc.     

Kinetics and mechanism of Os(VIII)-catalyzed hexacyanoferrate(III) oxidation of α amino acids in alkaline medium

The kinetics of the Os(VIII)-catalyzed oxidation of glycine, alanine, valine, phenylalanine, isoleucine, lycine, and glutamic acid by alkaline hexacyanoferrate(III) reveal that these reactions are zero order in hexacyanoferrate(III) and first order in Os(VIII). The order in amino acid as well as in alkali is 1 at [amino acid] ?2.5 × 10^?2M and [OH^?] ?1.3 × 10^?M, but less than unity at higher concentrations of amino acids or alkali. The active oxidizing species under the experimental conditions is OsO₄(H₂O) (OH)^?. The ferricyanide is merely used up to regenerate the Os(VIII) species from Os(VI) formed during the reaction. The structural influence of amino acids on the reactivity has been discussed. The amino acids during oxidation are shown to be degraded through intermediate keto acids. The kinetic data are accommodated by considering the interaction between the conjugate base of the amino acids and the active oxidizing species of Os(VIII) to form a transient complex in the primary rate-determining step. The catalytic effect of hexacyanoferrate(II) has been rationalized.     

On the Beckmann rearrangement of ketoximes: A kinetic study in trifluoromethanesulfonic acid

The formation and the destruction of an intermediate involved in the Beckmann rearrangement of 2,4,6‐trimethylacetophenone oxime have been studied in concentrated trifluoromethanesulfonic acid by kinetic and spectroscopic measurements. Observed (k_obs) and thermodynamic rate constants (k^o) have been estimated and the values compared with the ones obtained in perchloric, sulfuric, and methanesulfonic acids. In the range 80–100 wt% of sulfuric acid, combined analysis of k_obs and k^o rates shows a specific catalysis due to [H₂SO₄] species. In trifluoromethanesulfonic acid, lower rate constants, compared to the values in sulfuric acid, have been observed which differ at 99 wt% by a factor of 10³ ca. The catalytic effect of different strong acids, the structure of the intermediate inferred from Raman and NMR spectra, and the role of the ion‐pairs involved in the reaction are discussed. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 417–426, 2004     

Kinetics and mechanism of the oxidation of formic and oxalic acids by quinolinium fluorochromate

Kinetics and mechanism of oxidation of formic and oxalic acids by quinolinium fluorochromate (QFC) have been studied in dimethylsulphoxide. The main product of oxidation is carbon dioxide. The reaction is first-order with respect to QFC. Michaelis-Menten type of kinetics were observed with respect to the reductants. The reaction is acid-catalysed and the acid dependence has the form: k_obs =a +b[H⁺]. The oxidation of α-deuterioformic acid exhibits a substantial primary kinetic isotope effect (k_H/k_D = 6.01 at 303 K). The reaction has been studied in nineteen different organic solvents and the solvent effect has been analysed using Taft’s and Swain’s multiparametric equations. The temperature dependence of the kinetic isotope effect indicates the presence of a symmetrical cyclic transition state in the rate-determining step. Suitable mechanisms have been proposed.     

Kinetics and mechanism of oxidation of 1,4-butanediol by chromium(VI) in acid perchlorate medium

Summary The kinetics of oxidation of 1,4-butanediol by chromium(VI) was studied in acid perchlorate medium and the oxidation product of the diol was identified as 4-hydroxybutanal. The kinetic rate law observed accounted for the complex dependence of the hydrogen ion k=(k₂K₁[H+]+k₃K₁K₂[H+]²)/(1+K₁[H]+) where k is the observed second-order rate constant.