Etude de la nature des especes ioniques intervenant au cours de la polymerisation anionique de la vinyl-4 pyridine

Initiation of anionic polymerization of 4-vinyl-pyridine (4-VP) in tetrahydrofuran solution, using organo-metallic compounds of Na and K, involves the same type of side reactions as the polymerization of 2-vinyl pyridine (2-VP). The living polymers of 2- and 4-VP have similar u.v. spectra. The values of the dissociation constants of ionic species of 2- and 4-VP are similar when the chain [poly(styrene-b vinyl-4 pyridine)] contains one 4-VP unit (K_n ≈ 10^?9). But when the size of 4-VP block increases, the conductivity goes up to the value observed for living polystyrene (K_D ≈ 10^?7). This phenomenon could be due to a solvation of the counter-ion by the poly 4-vinyl pyridine chain, acting as a polydentate complexing agent.     

Cinetique complexe de l'halogenation de cetones en milieu acide—I : Iodation des enols

The kinetics of the iodination of acetone, diethylketone and di-isopropylketone in aqueous media ([H₂SO₄] = 0·1 to 1·0 N; [I₂]_a^o = 10^?7 to 10^?5M) have been studied by couloamperometry under irreversible conditions. At these concentrations the rates of formation of the enol and of its iodination are similar. The general equation, which assumes the steady state approximation for the enol, is applicable, and is used to separate the rate constants of enolisation (k₁) and the apparent enol iodination rate constant (k_II^I₂ = K_Ek₂^I₂). For acetone, the value given by Schwarzenbach for the enol equilibrium constant (K_E = 2·5 x 10^?6) leads to an elementary rate constant for the addition of iodine to the enol (k₂^I₂ = 6·5 x 10⁶ M^?1s^?1). This value is not, however, consistent with k_I2 = 1·5 x 10⁸ M^?1s^?1, the rate constant for the iodination of the corresponding ether 2-ethoxypropene.     

Etude theorique de la reactivite des ions libres intervenant dans la polymerisation anionique de quelques monomeres vinyliques

The reactivities have been calculated for free ions involved in anionic polymerization of vinyl monomers. The copolymerization constants k_AB available in the literature are compared to the stabilization energies involved in the reaction of carbanions with the same monomer. The reactivities of carbanions of living poly (2-vinyl pyridine), poly styrene and poly (substituted styrenes) with respect to 1-1,diphenylethylene have been computed. The rate constants of homopolymerisation have been compared with the variation of π energy between the “monomer” and “carbanion” states of these monomers. The occurrence of side-reactions during the polymerization of vinyl-pyridine has been investigated using quantum chemistry methods.     

Transferts Protoniques de Sels d'Ammonium Substitues—VIII: Sels de Pyridinium 4-Substitues

The deprotonation rate 1/τ of the title compounds, [4 – R – Py H]⁺, where R = NH₂, t-Bu, Me, Cl, Br or CN, is measured using the coalescence of the pyridinic α-protons, in a mixture CF₃COOH/H₂O/HClO₄ of variable acidity Ho, at 38°C. 1/τ is a linear function k/ho of the acidity 1/ho. k is approximately proportional to the water content and independent of the salt concentration, which seems to be evidence for an exchange with an intermediate pyridine hydrate, according to: . After a preliminary ionisation step: k values, like K_A, fit a Hammett relationship (ρ = 5,05), except for R ? NH₂, and are very sensitive to the nature of R (k = 3,44 × 10² for R = NH₂ and k = 3,14 × 10⁸ M^?1 s^?1 for R ? CN), while k_H values (10¹⁰ s^?1) are not.     

Kinetic studies of the reactions of pentacyanoferrate(III) complexes with L‐ascorbic acid

The reduction of Fe(CN)₅L^2? (L = pyridine, isonicotinamide, 4,4′‐bipyridine) complexes by ascorbic acid has been subjected to a detailed kinetic study in the range of pH 1–7.5. The rate law of the reaction is interpreted as a rate determining reaction between Fe(III) complexes and the ascorbic acid in the form of H₂A(k₀), HA^?(k₁), and A^2? (k₂), depending on the pH of the solution, followed by a rapid scavenge of the ascorbic acid radicals by Fe(III) complex. With given Ka₁ and Ka₂, the rate constants are k₀ = 1.8, 7.0, and 4.4 M^?1 s^?1; k₁ = 2.4 × 10³, 5.8 × 10³, and 5.3 × 10³ M^?1 s^?1; k₂ = 6.5 × 10⁸, 8.8 × 10⁸, and 7.9 × 10⁸ M^?1 s^?1 for L = py, isn, and bpy, respectively, at μ = 0.10 M HClO₄/LiClO₄, T = 25°C. The kinetic results are compatible with the Marcus prediction. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 126–133, 2005     

Cinetique complexe de l'halogenation de cetones en milieu acide—II : Controle par la diffusion des vitesses d'halogenation des enols-consequences

The kinetics of the bromination and chlorination of acetone, diethylketone and di-isopropylketone (bromination only) have been studied at [X₂]_a^o ≈ 10^?7 to 10^?5 M; the apparent rate constants k_II^X₂ = K_Ek₂^X₂ (where K_E is the keto-enol equilibrium constant) for iodination, bromination and chlorination are approximately equal. This result is attributed to diffusion-controlled kinetics. The order of magnitude of such a limiting rate constant, 10⁹ M^?1s^?1 calculated from Smoluchowski's equation, leads to new values for K_E in solution (1·5 x 10^?8 for acetone) much smaller than those in the literature. The rate constants derived for enol ketonisation are then in good agreement with those from proton addition to the corresponding enol ethers.     

Polymerization of Cyclosiloxanes. I. Kinetic Studies on Living Polymer—Octamethylcyclotetrasiloxane Systems

The kinetics of the anionic polymerization of octamethylcyclotetrasiloxane (D₄) initiated by α-methylstyrene living polymer in tetrahydrofuran was studied. The following kinetic scheme was postulated: Initiation: Propagation: where S^- and M represent the initiator and D₄, respectively. At a living end concentration of 0.0377 mole/l. and a monomer concentration of 1.5 mole/l. in tetrahydrofuran at 25°C. the following kinetic data were obtained: k₁ = 2.3 × 10^?4 l./mole-sec., k₂ < 2.3 × 10^?5 sec.^?1, k₃ = 2.75 × 10^?2l./mole-sec. k₄ ≈ 1.17 × 10^?2 sec.^?1, K₁ > 10 l./mole and K₂ ≈ 2.35 l./mole. The rate constants k₁ and k₃ were found to be dependent on the concentration of anions. This is attributed to the dissociation of ion pairs to free ions at lower concentration. Under the experimental conditions studied the majority of the anions were present in the form of ion pairs. The reactivity of the free ions is about 100 times greater than that of ion pairs. There is no temperature effect on K₂, indicating zero ΔH and positive ΔS in the propagation reaction.     

新型三脚架苯甲醛苯腙醋酸根选择性比色化学传感器

本文合成了一个新的基于三脚架苯甲醛苯腙的能够选择地检测醋酸根离子的比色化学传感器1。用紫外可见吸收光谱证实了受体1在二甲基亚砜溶液中对醋酸根离子高选择的键合能力超越了其它阴离子。和其他所研究的阴离子相比,其在二甲基亚砜中紫外可见吸收光谱对具有高选择性醋酸根离子的存在显示了应答,当存在（2´10^-5mol·dm^-3）醋酸根离子时其溶液的颜色也由黄色变化到蓝色。当用其他不同的客体阴离子（F^-, Cl^-, Br^-, I^-, H₂PO₄ ^–和 OH^-）处理受体1时,仅出现了很小的紫外可见吸收光谱变化。受体1对醋酸根的结合常数 K_ass为1.69´ 10⁴。     

The kinetics of ClO formation in the flash photolysis of chlorine–oxygen mixtures

The production of ClOO and ClO radicals following the flash photolysis of chlorine + oxygen mixtures has been studied. For the mechanism the following kinetic parameters were measured: k₃K = 1.3 × 10¹⁰ l²/mol²·sec; k₂/k₃ = 17; and k₃/?(ClOO; 250 nm) = 9.7 × 10⁵ cm/sec. Then k₃ = 5.9 × 10⁹ l/mol·sec, k₂ = 1.0 × 10¹¹ l/mol·sec, and ?(ClOO; 250 nm) = 6.1 × 10³ l/mol·cm. From limits established for the equilibrium constant K, ΔH°_f (ClOO) = 94 ± 2 kJ/mol.     

Anionic polymerization of 4-methyl-2-oxetanone (β-butyrolactone)

Polymerization of 4-methyl-2-oxetanone ( 1 ) initiated with potassium acetate-dibenzo-18-crown-6 complex ( 2 ) in THF as solvent, was studied. Transfer reactions, leading to both crotonate anions and carboxylic acid formation, have been observed. Two kinetic effects of these reactions, hampering the living polymerization, have been established. The first results from reinitiation with the crotonate anions and thereby lowers the polymer molecular weight. The second is the decrease in the overall polymerization rate due to complexation of the growing carboxylate anions with carboxylic acid moieties. Kinetic scheme of polymerization involves propagation accompanied by transfer followed by slow reinitiation. This scheme, including complexation of the active species has been solved numerically. The apparent rate and equilibrium constants (k_p, k_tr, k_ri, and K_ass and respectively) have been determined. Although these kinetic parameters depend strongly on the polymerization conditions, but the ratio of the rate constants k_p : k_t : k_ri is fairly constant and equal to 10⁻⁴ : 10⁻⁶ : 10⁻⁶, respectively (at 20°C). Conditions of the controlled anionic synthesis of the amorphous poly(4-methyl-2-oxetanone) with $\bar M_n$ as high as 1.7 × 10⁴ and ${{ \le \bar M_n } \mathord{\left/ {\vphantom {{ \le \bar M_n } {\bar M_n }}} \right. \kern-\nulldelimiterspace} {\bar M_n }} \le 1.20$ have also been elaborated.     

Reaction de metathese des olefines induite photochimiquement en presence d'un complexe de metal de transition. IV.- etude cinetique de l'interconversion catalysee cis-trans du butene-2.

The cis-trans interconversion of olefins in the system W(CO)₆ + CCl₄ + 2-butene is studied, both with initial irradiation of a solution of W(CO)₆ in CCl₄ (photoinduction), and with continuous irradiation of the system, for cis- and trans-butene concentrations between 0.09 and 6.0 M. Analysis of the results of the photoinduction experiments (rate of conversion and kinetic law as a function of the initial concentration of the olefin) allowed us to propose a simple kinetic scheme comprising a cis-trans interconversion of 2-butene and olefin-catalyzed destruction of the catalytic entity (k₂ = (0.62 ± 0.06)x10^?4 M s^?1). In the continuous irradiation experiments the final distribution of the olefin was independent of the initial butene concentration (cis-2-butene/trans-2-butene 3.0) and the reaction kinetics are of first-order (k_obs = (3±1) x10^?4 s^?1. Comparison of the two experiments suggests continuous photochemical regeneration of the catalytically active entity. The first-order reaction kinetics are in agreement with a carbene-metal carbonyl structure of the intermediate     

Aspects of the radiation-induced polymerization of 2-vinyl anthraquinone

2-Vinyl anthraquinone has been polymerized, via radiation-induced initiation, in dimethyl-sulphoxide and in dichloromethane. Solvent to monomer ratios of 1 : 0.030 to 1 : 0.0167 mol have been examined for dose rates in the range 0.035 to 0.129 Gy s^?1 and exposure times in the range 1.44 × 10⁴ to 4.32 × 10⁶ s. Rates of polymerization were found to lie in the range from 2.4 × 10^?8 to 1.92 × 10^?6 mol L^?1 s^?1. Values for the chain transfer constant to dimethyl-sulphoxide and to dichloromethane have been calculated. In addition, values of the kinetic ratio k/k_t, for the polymerization of 2-vinyl anthraquinone have been estimated. The dependence of R_p on the monomer concentration and on the radiation intensity have been shown to be in broad agreement with a simplified steady-state kinetic scheme. A value of G(radical) for 2-vinyl anthraquinone was obtained via electron spin resonance studies, and shown to be 0.24. This G(radical) value and those obtained indirectly from kinetic data are discussed in relation to the molar mass values obtained from the poly(2-vinyl anthraquinone) products.     

Effets de micelles cationiques sur l'hydrolyse alcaline d'acetanilides a groupe acyle active par des substituants electro-attracteurs

Micellar effects of CTAB upon the alkaline hydrolysis of CF₃-CO-N(CH₃)C₆H₅, CHCl₂-CO-N(CH₃)C₆H₄X and CH₂Cl-CO-N(CH₃)C₆H₄X, (X=p-OCH₃H,p-Cl) are reported. Variations of k_obs, and of kinetic order of the reaction with respect to HO^? ion, are interpreted as an acceleration of HO^?-catalyzed steps, and a decrease of catalysis by water for decomposition of tetrahedral intermediates; these two effects oppose each other in HO^? and H₂O catalyzed steps. Differences between micellar and DMSO effects suggest a very small local concentration of HO^? ions in micelles.     

Study and Application of Polarographic Catalytic Wave of Chlordiazepoxide in the Presence of Persulfate

ＩｎｔｒｏｄｕｃｔｉｏｎＣｈｌｏｒｄｉａｚｅｐｏｘｉｄｅ (7 ｃｈｌｏｒｏ 2 ｍｅｔｈｙｌａｍｉｎｏ 5 ｐｈｅｎｙｌ 3Ｈ 1,4 ｂｅｎｚｏｄｉａｚｅｐｉｎｅ 4 ｏｘｉｄｅ)ｓｈｏｗｉｎｇｐｏｗｅｒｆｕｌａｎ ｔｉａｎｘｉｅｔｙｅｆｆｅｃｔｈａｓｂｅｅｎｗｉｄｅｌｙｕｓｅｄａｓａｐｓｙｃｈｏｔｈｅｒａｐｅｕ ｔｉｃｄｒｕｇ .Ｃｏｎｓｅｑｕｅｎｔｌｙ ,ｔｈｅｎｅｅｄａｒｏｓｅｆｏｒｓｅｎｓｉｔｉｖｅａｎｄｒａｐｉｄｄｅｔｅｒｍｉｎａｔｉｏｎｏｆｃｈｌｏｒｄｉａｚｅｐｏｘｉｄｅｉｎｂｌｏｏｄ ,ｕｒｉｎｅａｎ…     

Etude de la solvolyse des tosylates d'aryl-2 propyle dans le dimethylformamide

Aryl-2 propyltosylate solvolysis occurs in DMF as in a protic medium, via two competing mechanisms: solvent nucleophilic substitution (rate constant k_s) unimolecular solvolysis with aryl participation (k_Δ). Nucleophilic solvent participation is more important in DMF than in a protic solvent; this is due to the lack of electrophilic assistance of DMF compared to a hydroalcoholic solvent (k_Δ^DMF < k_Δ^{EtOH aq.}), DMF and aqueous carbon nucleophilicities being nearly the same (k_s^DMF ? k_s^{EtOH aq.}). Charge distribution in transition states are of the same type in both solvents.     

Structure cristalline d'un dihydrogeno-sulphato-iodate de potassium

The iodato-sulfate K₄H₂(S₂I₂O₁₄) is monoclinic, $\text{P2}{}_1\text{n}$ with a unit cell: a = 13.84(1) Å, b = 7.173(5) Å, c = 7.443(5) Å, β = 93.16(1)°, and Z = 2. The crystal structure of this salt has been solved using 1956 independent reflections, with a final R value of 0.03. The main feature of this salt is the existence of a finite new heteropolyanion: (I₂S₂O₁₄)^?6.     

Transformations of the chameleon ligand 1,10‐phenanthroline‐5,6‐dione/diol: cis‐dichlorido(1,10‐phenanthroline‐5,6‐dione‐κ2N,N′)‐trans‐dipyridinecobalt(II) pyridine disolvate prepared from the diol

The title compound, [CoCl₂(C₅H₅N)₂(C₁₂H₆N₂O₂)]·2C₅H₅N, is a neutral Co^II complex with two chloride anions coordinated in a cis fashion, two pyridine ligands in trans positions and a chelating 1,10‐phenanthroline‐5,6‐dione ligand that completes the octahedral coordination geometry. Two pyridine solvent molecules reside in channels (about 7 × 4 Å wide; the closest atom–atom distance within the channel is 10 Å). The three‐dimensional structure supporting these channels is held together by C—H...Cl [3.466 (8)–3.670 (9) Å] and C—H...O [3.014 (9)–3.285 (8) Å] hydrogen bonds, and can be viewed as a CsCl or bcu (body‐centred cubic) net.     

Utilisation d'un “blanc interferences” dans la determination des nitrates par potentiometrie selective

(Use of an interference blank in the determination of nitrate by ion-selective potentiometry.) During selective potentiometry of nitrate in meat product additives, a new interference originating from polyphosphate ions was encountered. The selectivity coefficients measured were 5 × 10^?2 for tripolyphosphate, 10^?2 for chloride, 8 × 10^?4 for pentapolyphosphate and 6 × 10^?4 for pyrophosphate. An “interference blank” techniques is proposed; nitrate is destroyed in the medium to be studied, so that calibration is possible in the presence of interfering substances regardless of their identity or concentration. The method is successfully applied to monitoring of meat product additives.     

Reactivite de lithiens derives d'ethers de la cyanhydrine du benzaldehyde vis-a-vis d'α-enones cycliques

Conjugate addition of reagent 1A to 2-cyclohexenone 3 can be realized in THF-HMPT, so that one-pot conjugate addition—CH₃I enolate trapping, leading to trans 2-methyl 3-benzoylcyclohexanone 17 can be easily performed. From isophorone 4 and Δ¹⁽⁹⁾-2-octalone 5, 1, 4-addition under kinetic control is observed in THF. In the presence of HMPA, the reaction is under thermodynamic control. At low temperatures enolate 19a is in equilibrium with 1A and 4; from 4 at 0° or 5 at ?65° or at 0°, the equilibrium lies on the side of starting materials. No reaction between 1A and 6 takes place in any solvent.The reaction of 1B and isophorone 4 in THF leads to 1, 2-addition under kinetic control and to 1, 4-addition under thermodynamic control. In THF-HMPT, retro-Michael addition is observed. However, 1, 2-addition takes place in THF to 6.The different results are interpreted in terms of interplay of ion-pairing, steric decompression and steric hindrance to 1, 4-addition as well as the possibility of participation of the Li cation for 1, 2-addition.     

Kinetic Studies on the Reaction of Sodium Hexacyanoferrate（ll） Complex with Peroxydisulfate Anion

The oxidation of Na₄Fe(CN)₆ complex by S₂O anion was found to follow an outer‐sphere electron transfer mechanism. We firstly carried out the reaction at pH=1. The specific rate constants of the reaction, k_ox, are (8.1±0.07)×10^?2 and (4.3±0.1)×10^?2 mol^?1·L·s^?1 at μ=1.0 mol·L^?1 NaClO₄, T=298 K for pH=1 (0.1 mol·L^?1 HCl0₄) and 8, respectively. The activation parameters, obtained by measuring the rate constants of oxidation 283–303 K, were ΔH^≠=(69.0±5.6) kJ·mol^?1, ΔS^≠=(?0.34±0.041)×10² J·mol^?1·K^?1 at pH=l and ΔH^≠=(41.3±5.5) kJ·mol^?1, ΔS^≠=(?1.27±0.33)×10² J·mol^?1·K^?1 at pH=8, respectively. The cyclic voltammetry of Fe(CN) shows that the oxidation is a one‐electron reversible redox process with E_1/2 values of 0.55 and 0.46 V vs. normal hydrogen electrode at μ=1.0 mol·L^?1 LiClO₄, for pH=1 and pH=8 (Tris). respectively. The kinetic results were discussed on the basis of Marcus theory.