Termination and transfer of the polymer chain to a maleimide derivative containing the azo group

The copolymerizations of N-(3-dimethylaminophenyl) maleimide (I) and 4-(2-chlorophenyl)azo-3-maleimido-N,N-dimethylaniline (II) with styrene were investigated; the copolymerization parameters of the pairs ($\text{I}\text{+}\text{styrene}$) and ($\text{II}\text{+}\text{styrene}$) and $\text{k}{}_{\mathrm{p}}\text{/k}{}_{\mathrm{t}}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ hr I at 50° were determined; chain transfer to the maleimide ring of I was proved. The homopolymerization of styrene in the presence of 4-(2-chlorophenyl)azo-succinimide-N,N-dimethylaniline (III) was used to determine the ratio of the rate constant for addition of the polystyrene radical to the azo group in III to k_p for styrene.     

The kinetics of photo-initiated oxidation of poly(p-methylstyrene) in solution

The photo-initiated oxidation of poly(p-methylstyrene) has been studied at 25°C in chlorobenzene solution, initiating radicals being produced by the photolysis (λ = 313 nm) of AIBN. The effects of polymer concentration, 313 nm intensity (I₀), AIBN concentration and oxygen pressure have been examined and a rate expression of the form:

$\text{?}\text{d(O}{}_2\text{)}\text{dt}\text{α(O}{}_2\text{)}{}^0\text{(}\text{Polymer}\text{)}{}^{0.6}\text{(}\text{AIBN}\text{)}{}^{0.95}\text{(I}{}_0\text{)}{}^{1.05}$

was obtained. (pO₂ > 300 mbar.)A reaction scheme which accounts for the rate expression is described. The decrease in molecular weight on oxidation is accounted for in terms of hydroperoxide decomposition.The relative reactivities of poly(styrene) and poly(p-methylstyrene) are compared, the latter being more reactive towards oxidation. Reaction at the p-CH₃ group is not ruled out.     

Cyclometallation reactions of N-(benzylidene)benzylamines with palladium compounds

The cyclometallation of p-RC₆H₄CHNCH₂C₆H₂, (R = H, Cl, NO₂) by PdX₂ (X = Cl, AcO) has been studied.In every case the cyclometallation occurs with formation of a five-membered ring containing the methine group. The structure of these compounds [$\text{PdX(}\text{p}\text{-RC}{}_6\text{H}{}_3\text{CHN}$CH₂C₆H₅)]₂, derived from ¹H NMR spectra, are different from those reported previously. Reaction of these compounds with PEt₃ gives the compounds [PdX(p-RC₆H₃CHNCH₂C₆H₅)(PEt₃)₂] but with an excess of PPh₃ only the complexes [$\text{PdX(}\text{p}\text{-RC}{}_6\text{H}{}_3\text{CHN}$CH₂C₆H₅)(PPh₃)] are formed.     

Effects of tris (phenanthroline)-iron(III) complex on the polymerization of styrene

The polymerization of styrene initiated by 2,2′ azobisisobutyronitrile had been studied in N,N-dimethylformamide at 60°, in the presence of Tris(phenanthroline)-iron(III) perchlorate. The complex was prepared in situ by mixing phenanthroline with hexakis (N,N-dimethylformamide) iron(III) perchlorate in the ratio 3:1. The nature of the complex formed was established by Job's method. The equilibrium constant for

$\text{Fe}{}^{\mathrm{3+}}\text{+ 3}\text{Phen}\text{? [}\text{Fe(Phen)}{}_3\text{]}{}^{\mathrm{3+}}$

is 2·3 × 10² 1³ mol^?3. The velocity constant at 60° for the reaction of polystyryl radical with [Fe(Phen)₃]³⁺ is 2·93 × 10⁴ mol^?1 l s^?1.     

The influence of molecular weight on the degradation of poly(N-vinylcarbazole)

The methods of isothermal and dynamic thermogravimetry have been used to study the degradation of poly(_{N-vinylcarbazole}) (PNVC). The multiple heating rate method has been used, as a dynamic method, to obtain kinetic parameters. A linear relationship between the activation energy. E, and $\text{M}{}_{\mathrm{w}}{}^{\mathrm{?1}}$ ($\text{M}{}_{\mathrm{w}}$ being weight average molecular weight) was found. From isothermal experiments, a temperature was found for which E was independent of molecular weight. We could then refer to a degradation characteristic- temperature of the polymer. On the other hand, altering the heating rate leads to changes in the values of E for each molecular weight indicating two kinds of scission: one occurs in the backbone, producing mainly monomer; in the other, both side-group and backbone scissions occur producing different products.     

Kinetics and mechanism of the interaction of hexaaquochromium(III) with octacyanomolybdate(IV) ions

The kinetics of the interaction of hexaaquochromium(III) ion with potassium octacyanomolybdate(IV) have been studied using conductance and spectrophotometric data. The mechanism of the reaction is discussed and the effect of H⁺ ion and the ionic strength on the rate of the reaction determined. The reaction is found to be pseudo-first order with respect to potassium octacyanomolybdate(IV) and inverse first order with [H₃O⁺]. The rate of the reaction increases with increase in ionic strength and temperature. Activation parameters have been calculated using the Arrhenius equation and have the values ΔE^* = 1.3 × 10² kJ mol^?1, ΔH^* = 129 kJ mol^?1, ΔS^* = ?315 e.u., ΔF^* = 2.3 × 10² kJ and A = 1.5 × 10^?3. The mechanism proposed is based on ion-pair formation and the rate equation obtained is given by: k_obs=$\text{[}{}_{\mathrm{kK}}{}_{\mathrm{<mtext>E</mtext>}}\text{[H}{}_3\text{O}{}^{\mathrm{+}}\text{]+}\text{k′K′k}{}_{\mathrm{E}}\text{k}{}_{\mathrm{h}}\text{][Mo(CN)}{}_8{}^{\mathrm{4?}}\text{]}\text{[H}{}_3\text{O}{}^{\mathrm{+}}\text{]+}\text{k}{}_{\mathrm{<mtext>h</mtext>}}\text{+[}\text{K}{}_{\mathrm{<mtext>E</mtext>}}\text{[H}{}_3\text{O}{}^{\mathrm{+}}\text{]+}\text{K′}{}_{\mathrm{E}}\text{k}{}_{\mathrm{h}}\text{][Mo(CN)}{}_8{}^{\mathrm{4?}}\text{]}$     

N-lines and chromium-pairs in the luminescence spectra of the spinels ZnAl2O4:Cr3+ and MgAl2O4:Cr3+

It is shown that the N-lines in the luminescence spectra of the two spinels ZnAl₂O₄:Cr³⁺ and MgAl₂O₄:Cr³⁺ exhibit quite similar dependencies on chromium concentration, excitation frequency, and thermal treatment of the samples. While most of these lines are structure dependent, the line N₄ at $\text{ν}{}_{\mathrm{R}}\text{?}\text{ν}\text{≈ 400}\text{cm}{}^{\mathrm{?1}}$ and two very weak lines are in both cases due to chromium-pairs. The exchange Hamiltonian H_ex = JS₁ · S₂ + j(S₁ · S₂)² used for the ground-state splitting is fitted by the parameters J = 40.9 cm^?1, j = 1.5 cm^?1 and J = 45.6 cm^?1, j = 2.0 cm^?1 for ZnAl-spinel and MgAl-spinel, respectively. The differences between the spectra of low-doped and high-doped samples are in both cases caused by the existence of a phonon sideband of the N₄-line, which is in many respects similar to the well-known phonon side band of the R-line.     

Kaempferol (3,5,7,4′-tetrahydroxyflavone) as a chromogenic reagent for tin(IV)

Kaempferol forms a yellow colored chelate with tin(IV) in 0.1 to 0.01 N HCl medium. Based on this reaction a sensitive spectrophotometric method for determination of micro amounts of tin(IV) has been developed. The sensitivity of the color reaction 0.0029 μg of $\text{Sn/cm}{}^2\text{}\text{log}\text{I}{}_0\text{I}\text{= 0.001}$, at 430 nm in 0.1 N HCl medium and Beer's law is obeyed up to 3.6 ppm of tin. Several complexing anions do not interfere and they have been used for masking some of the cations which interfere in the determination.     

Chiral 1,4-benzodiazepines—-XI: Kinetics of degenerate nucleophilic exchange of C(3)-hydroxy group

The rate for degenerate nucleophilic exchange (k_e) of the C(3)-OH group in the racemic compound 1 was determined in DMSO/H₂¹⁸O using mass spectrometry. Epimerization rates for diastereomers 15 and 16 were determined by polarimetry (k_ep) and NMR spectroscopy (k_r-c—for $\text{r}$ing-$\text{c}$hain tautomery). The ratio $\text{k}{}_{\mathrm{e}}\text{k}{}_{\mathrm{ep}}$ ~ 3.5 35° is close to that obtained for degenerate nucleophilic exchange of the C(3)-OMe group in the compound 1a ($\text{k}{}_{\mathrm{e}}\text{k}{}_{\mathrm{\alpha }}$ ~4, Refs. [3,4]). These data confirm the C(3)-OH substituted 1,4-benzodiazepin-2-ones lose the configurational identity of the C(3) chiral centre by both direct nucleophilic substitution of the OH group, and ring-chain tautomery processes.The synthesis of the diastereomeric compounds 15 and 16, and their chromatographic separation is described.     

“Normal” and “cine” substitution in the thioalkoxy-dehalogenation of halogenobenzofurazans—III: Investigation on the solvent effect

The reaction of 4-chloro- and 4-chloro-7-deuteriobenzofurazan with MeS^-, isopropyl-S^-, and t-Butyl-S^- in different alcohols as solvents has been investigated. In going from methanol through isopropanol to t-butanol, a progressive decrease of the contribution of the cine-substitution as compared with the normal substitution pathway has been found. By proceeding in the same order, a decrease of the ratio and $\text{k}\text{MeS}{}^{\mathrm{?}}\text{k}{}_{\mathrm{<mtext>t</mtext>}}$-ButylS^? has also been observed.     

Diffusion of point defects participating in solid-phase chemical reactions (trap diffusion): Demonstration for the Ti3+ → Ti4+ transition in corundum

A problem of trap diffusion, that is diffusion of point defects in crystals participating in a solid-phase chemical reaction with motionless impurity ions, is solved. Time dependences of the reaction-front displacement, X_f, and its steepness, $\text{(}\text{?C}\text{?X}\text{)}{}_{\mathrm{f}}$ are determined analytically for N₀ ? C₀ and numerically for all relations of N₀ and C₀$\text{x}{}_{\mathrm{f}}{}^2\text{=2}\text{N}{}_0\text{C}{}_0\text{Dt; (}\text{ac}\text{ax}\text{)}{}_{\mathrm{f}}\text{=0.3C}{}_0{}^{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{(}\text{g}\text{D}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2></mtext>}}$where C₀ and N₀ are the initial concentration of impurity and the eqilibrium defect concentration, respectively, D is a diffusion coefficient, and g is a chemical reaction constant. Dependence of X_f vs C₀ and t is confirmed for oxygen annealing of corundum crystals doped with titanium which, reacting with the point defects, changes its valency. The data are obtained for dependence of displacement X_f upon partial oxygen pressure and thermotreatment temperature as well as upon the sign of the constant electric field applied to the sample. From these data we conclude that the reaction of titanium impurity, changing from the three-valent to the tetravalent state at the activation energy of 80 ± 8.5 kcal/mole is due to anisotropic diffusion of charged aluminum vacancy and holes in the valence band. The diffusion coefficient for that process at 1500°C is estimated to be larger than 10^?5 cm²/sec. Using the trap-diffusion features, the concentration of optical centers of the 0.315-μm absorption band in ruby is also estimated.     

Unusual effects of anisotropic bonding in Cu(II) and Ni(II) oxides with K2NiF4 structure

Geometric constraints present in A₂BO₄ compounds with the tetragonal-T structure of K₂NiF₄ impose a strong pressure on the BO_IIB bonds and a stretching of the AO_IA bonds in the basal planes if the tolerance factor is $\text{t ?}\text{R}{}_{\mathrm{<mtext>AO</mtext>}}\text{√2 R}{}_{\mathrm{<mtext>BO</mtext>}}\text{< 1}$, where R_AO and R_BO are the sums of the AO and BO ionic radii. The tetragonal-T phase of La₂NiO₄ becomes monoclinic for Pr₂NiO₄, orthorhombic for La₂CuO₄, and tetragonal-T′ for Pr₂CuO₄. The atomic displacements in these distorted phases are discussed and rationalized in terms of the chemistry of the various compounds. The strong pressure on the BO_IIB bonds produces itinerant bands and a relative stabilization of localized d_z² orbitals. Magnetic susceptibility and transport data reveal an intersection of the Fermi energy with the d²_z² levels for half the copper ions in La₂CuO₄; this intersection is responsible for an intrinsic localized moment associated with a configuration fluctuation; below 200 K the localized moment smoothly vanishes with decreasing temperature as the d²_z² level becomes filled. In La₂NiO₄, the localized moments for half-filled d_z² orbitals induce strong correlations among the electrons above $\text{T}{}_{\mathrm{<mtext>d</mtext>}}\text{? 200}\text{K}$; at lower temperatures the electrons appear to contribute nothing to the magnetic susceptibility, which obeys a Curie-Weiss law giving a μ_eff corresponding to $\text{S =}\text{1}\text{2}$, but shows no magnetic order to lowest temperatures. These surprising results are verified by comparison with the mixed systems La₂Ni_1?xCu_xO₄ and La_2?2xSr_2xNi_1?xTi_xO₄. The onset of a charge-density wave below 200 K is proposed for both La₂CuO₄ and La₂NiO₄, but the atomic displacements would be short-range cooperative in mixed systems. The semiconductor-metallic transitions observed in several systems are found in many cases to obey the relation $\text{E}{}_{\mathrm{<mtext>a</mtext>}}\text{? kT}{}_{\mathrm{<mtext>min</mtext>}}$, where $\text{? = ?}{}_0\text{exp}\text{(}\text{?E}{}_{\mathrm{<mtext>a</mtext>}}\text{kT}\text{)}$ and T_min is the temperature of minimum resistivity ?. This relation is interpreted in terms of a diffusive charge-carrier mobility with $\text{E}{}_{\mathrm{<mtext>a</mtext>}}\text{? ΔH}{}_{\mathrm{<mtext>m</mtext>}}\text{? kT}$ at T = T_min.     

Preparation and properties of PdPSe single crystals

Single crystals of PdPSe were shown to be n-type semiconductors. Weak Pauli paramagnetic behavior was observed, which is consistent with the presence of delocalized electrons. Electrical measurements showed a room-temperature resistivity ? = 70 ohm-cm, activation energy of resistivity E_a = 0.32 eV, and Hall mobility μ = 34 cm² V^?1 sec^?1. Photoelectronic measurements in aqueous solutions of $\text{I}{}^{\mathrm{?}}\text{I}{}^{\mathrm{?}}{}_3$ indicate that PdPSe has high quantum efficiencies below 800 nm. The indirect optical band gap is 1.28(2) eV.     

Mutual solubility of n-butanol + water under high pressures

The mutual solubilities of {xCH₃CH₂CH₂CH₂OH+(1-x)H₂O} have been determined over the temperature range 302.95 to 397.75 K at pressures up to 2450 atm. An increase in temperature and pressure results in a contraction of the immiscibility region. The results obtained for the critical solution properties are: T_o(U.C.S.T.) = 397.85 K and x_o = 0.110 at 1 atm; $\text{(}\text{dT}{}_{\mathrm{o}}\text{d}\text{p}\text{) = ?(12.0±0.5)×10}{}^{\mathrm{?3}}\text{K atm}{}^{\mathrm{?1}}$ at p < 400 atm and $\text{(}\text{dT}{}_{\mathrm{o}}\text{d}\text{p}\text{) = ?(7.0±0.7)×10}{}^{\mathrm{?3}}\text{K atm}{}^{\mathrm{?1}}$ at 800 atm < p < 2500 atm; $\text{(}\text{dx}{}_{\mathrm{o}}\text{d}\text{T}\text{) = ?(4.0±0.5)×10}{}^{\mathrm{?4}}\text{K}{}^{\mathrm{?1}}$.     

Vinyl polymerization initiated by the (dimethylaniline-n-oxide)/(phenacyl bromide) system

Binary systems consisting of dimethylaniline-N-oxide (DMOA) and some α-halo-carbonyl compounds, such as phenacyl halide and α-halo-acetic acid ester, were found to induce radical polymerization of vinyl monomers. Bromo-derivatives showed higher initiating activities than chloroderivatives. The polymerization of methyl methacrylate (MMA) with DMAO and phenacyl bromide (PBr) was investigated kinetically. The polymerization rate (R_p) was expressed as follows; $\text{R}{}_{\mathrm{<mtext>p</mtext>}}\text{=}\text{k[DMAO]}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{[}\text{PBr}\text{]}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{[}\text{MMA}\text{]}$.The overall activation energy of the polymerization was calculated to be 42.7 kJ mol^?1. No noticeable chain-transfer from the polymer radical to DMAO or PBr was observed. The benzoyl radical was trapped by 2-nitroso-2-methylpropane, a spin trapping reagent, in the reaction of DMAO and PBr. The u.v. spectrum of poly (MMA) obtained suggests that the polymer contains end-groups similar to acetophenone and DMA. From the results, an initiation mechanism for the polymerization has been proposed and discussed.     

Kinetics of the polymerization of potassium p-styrenesulphonate in various media

The free radical polymerization of potassium p-styrenesulphonate has been investigated at 70° for solutions in dimethyl sulphoxide (DMSO)-water mixtures (1:3 and 3:1) and in DMSO using 2,2′-azobisisobutyronitrile as initiator. The kinetic orders with respect to monomer and initiator increase but the rate of polymerization, the value of $\text{k}{}_{\mathrm{p}}\text{/k}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}{}_{\mathrm{t}}$ and the average molecular weight of the resulting polymer decrease with increasing DMSO concentration in the DMSO-water mixture. These effects have been attributed to changing of parameters of the electrostatic interactions in the system “macroradical-counterions-anions of monomer” with change of composition of the medium.     

Nd3+, Eu3+, and Gd3+ ions as local probes in the NaxSr3−2xLnx(PO4)2 and KCaLn(PO4)2 rare earth phosphates

Use of Nd³⁺, Eu³⁺, and Gd³⁺ as local structural probes allows the determination of the rare earth positions in the Na_xSr_3?2xLn_x(PO₄)₂ (Ln = La to Tb) and KCaLn(PO₄)₂ phases (Ln = rare earth). Moreover, a common feature of both series is a particularly high splitting of the excitation ${}^6\text{P}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ and ${}^6\text{P}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ levels of the Gd³⁺ ions.     

Studies on the kinetics of the ligand-substitution reaction of the Zinc(II)-4-(4′-methyl-2-́thiazolylazo)-2-methylresorcinol with 1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid

Spectrophotometric studies have been carried out on the kinetics of the ligand-substitution reaction of the Zinc(II)-4-(4′-methyl-2′-thiazolylazo)-2-methylresorcinol complex with 1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid, in the pH range 8.4–9.4 at μ = 0.25 and 25 °C. The reaction rate constant was established to be $\text{?}\text{(d[}\text{ZnR}{}_2\text{]}\text{dt)}\text{= K[}\text{ZnR}{}_2\text{][H}{}^{\mathrm{+}}\text{][Y′]/[HR}{}^{\mathrm{?}}\text{], and}\text{K = 6.88 × 10}{}^4\text{liter · mol}{}^{\mathrm{?1}}\text{· sec}{}^{\mathrm{?1}}$ was obtained.     

Tracer diffusion coefficient of oxide ions in LaCoO3 single crystal

The tracer diffusion coefficient, $\text{D1}{}_{\mathrm{<mtext>O</mtext>}}$, of oxide ions in LaCoO₃ single crystal was determined over the temperature range of 700–1000°C by a gas-solid isotopic exchange technique using ¹⁸O tracer. For the determination, two methods, the gas phase analysis and the depth profile measurement, were employed. Under an oxygen pressure of 34 Torr, the temperature dependence of $\text{D1}{}_{\mathrm{<mtext>O</mtext>}}$ in LaCoO₃ was expressed by

$\text{D1}{}_{\mathrm{<mtext>O</mtext>}}\text{(}\text{cm}{}^2\text{·}\text{sec}{}^{\mathrm{?1}}\text{) = 3.63 × 10}{}^4\text{exp}\text{?}\text{(74 ± 5)}\text{kcal}\text{·}\text{mole}{}^{\mathrm{?1}}\text{RT}$

$\text{D1}{}_{\mathrm{<mtext>O</mtext>}}$ at 950°C was found to be proportional to P^?0.35_O2. The diffusion of oxide ions occurs through a vacancy mechanism. The activation energy for the migration of oxide ion vacancies was estimated as 18 kcal · mole^?1.     

NMR study of hydrogen molybdenum bronzes: H1.71MoO3 and H0.36MoO3

Proton NMR relaxation times (T₂T₁, and T_1?) and absorption spectra are reported for the compounds H_1.71MoO₃ (red monoclinic) and H_0.36MoO₃ (blue orthorhombic) in the temperature range 77 K < T < 450 K. Rigid lattice dipolar spectra show that both compounds contain proton pairs, as OH₂ groups coordinated to Mo atoms in H_1.71MoO₃ and as pairs of OH groups in H_0.36MoO₃. The room temperature lineshape for H_1.71MoO₃ shows that the average chemical shielding tensor has a total anisotropy of 20.1 ppm. The relaxation measurements confirm that hydrogen diffusion occurs and give E_A = 22 kJ mole^?1 and $\text{τ}{}^0{}_{\mathrm{<mtext>C</mtext>}}\text{? 10}{}^{\mathrm{?13}}\text{sec}$ for H_1.71MoO₃ and E_A = 11 kJ mole^?1 and $\text{τ}{}^0{}_{\mathrm{<mtext>C</mtext>}}\text{? 3 × 10}{}^{\mathrm{?8}}\text{sec}$ for H_0.36MoO₃.