Showing papers on "Disproportionation published in 1977"

The decomposition of dimethyl peroxide and the rate constant for CH3O + O2 → CH2O + HO2

Abstract: The decomposition of dimethyl peroxide (DMP) was studied in the presence and absence of added NO2 to determine rate constants k1 and k2 in the temperature range of 391–432°K: The results reconcile the studies by Takezaki and Takeuchi, Hanst and Calvert, and Batt and McCulloch, giving log k1(sec−1) = (15.7 ± 0.5) - (37.1 ± 0.9)/2.3 RT and k2 ≈ 5 × 104M−1· sec−1. The disproportionation/recombination ratio k7b/k7a = 0.30 ± 0.05 was also determined: When O2 was added to DMP mixtures containing NO2, relative rate constants k12/k7a were obtained over the temperature range of 396–442°K: A review of literature data produced k7a = 109.8±0.5M−1·sec−1, giving log k12(M−1·sec−1) = (8.5 ± 1.5) - (4.0 ± 2.8)/2.3 RT, where most of the uncertainty is due to the limited temperature range of the experiments.

Elasticity and phase equilibria of spinel disproportionation reactions

Abstract: Summary Ultrasonic data for the velocities of the low- and high-pressure polymorphs of stannate and titanate compounds undergoing the spinel rocksalt + rutile (Mg2SnO4, Co2SnO4) and spinel rocksalt + ilmenite (Mg2TiO4, Co2TiO4) phase transformations have been determined as a function of pressure to 7.5 kbar at room temperature for polycrystalline specimens hot-pressed at pressures up to 60 kbar. The inverse stannate and titanate spinels have significantly lower velocities (elastic moduli) for a given density (molar volume) than the normal A2+2B4+O4 spinels. The observed elasticity moduli for the mixed phase assemblages are in good agreement with theoretical calculations using the Hashin—Shtrikman scheme and the known properties of the individual phases. The velocity (n) - density (ρ) relationships across the spinel disproportionation reactions are critically dependent on the nature and extent of the changes in cation–anion coordination and nearest-neighbour interionic distances which accompany these transformations. For both the stannate and titanate spinels, the coordination of the divalent cation increases on disproportionation. However, in the stannate case the mean interionic distances are unchanged and the n–ρ slopes (linear or logarithmic) are similar to those for the quartz–coesite transition in SiO2 and the olivine–spinel and olivine–beta phase transformations in silicates and germanates. In contrast, the mean interionic distances increase on disproportionation for the inverse titanate and normal silicate, germanate, aluminate and ferrite spinels so that their n–ρ slopes are low and comparable to those observed for the coesiterutile, pyroxene–garnet, pyroxene–ilmenite and ilmenite–perovskite transformations. Experimental studies of the phase boundaries for the disproportionation of the spinels Mg2 SnO4, Co2 SnO4 and Li2 NiF4 into mixtures of their cornponent oxides (fluorides) reveal slopes dP/dT of 40 ° 10, 0 ± 7 and ± bar/K, respectively. These non-negative slopes are consistent with a considerable body of thermodynamic data for spinels. Available thermodynamic data do not support the existence of a distinctly negative slope for the proposed disproportionation of (normal) Mg2, SiO4, spinel. Evidence from X-ray and phase equilibrium studies suggest the possibility that Si4+, Mg2+ and Fe2+ share the octahedral sites in silicate spinels under mantle conditions. The consequences of such cation disorder would be a positive slope accompanied by anomalous elasticity–density behaviour within the transition zone if the 650-km discontinuity were caused by disproportionation of spinel into mixed oxides. The implications for the thermomechanical regime of descending lithospheric plates are also examined.

Oscillations in chemical systems. 19. Mechanisms of chemical oscillators: experimental examples

Abstract: A number of chemical systems that exhibit temporal or spatial periodicities are discussed. The classic acid bromate oxidation of organic compounds catalyzed by cerous or manganous ions is discussed very briefly as the most studied and best understood chemical oscillators. The oscillating systems of the acidic iodate and hydrogen peroxide is discussed briefly, and work involving the addition of manganous ion and malonic acid to the acidic iodate-hydrogen peroxide system for a dramatic enhancement of the oscillations is cited. The oscillatory evolution of gas from the decomposition of formic acid by sulfuric acid reported over 60 years ago and recently reexamined is reviewed. Small additions of formaldehyde, sodium nitrite, or ferrous sulfate are reported to grossly affect the kinetic behavior of this decomposition. Other chemical oscillating systems cited are the autocatalytic disproportionation of aqueous dithionite and the irreversible chemical process resulting from the uv irradiation of 1,5-napthyridine. Oscillatory electrode reactions, periodic precipitation phenomena, and oscillations during gas reactions are discussed. Some oscillations observed in biological systems are mentioned, but not explained. Several characteristics of these known chemical oscillators are summarized. (BLM)

Selective disproportionation of toluene

Abstract: A catalytic process is provided for the selective production of para-xylene by disproportionation of toluene in the presence of a catalyst comprising a crystalline aluminosilicate zeolite having a silica to alumina ratio of at least about 12 and a constraint index within the approximate range of 1 to 12, which catalyst has undergone controlled precoking, i.e. selectivation, by exposing the same to a thermally decomposable organic compound at a temperature in excess of the decomposition temperature of said compound, generally greater than 1000° F., but less than about 1200° F., at a hydrogen to organic compound mole ratio between 0 and 1 to deposit at least about 2 weight percent coke thereon and thereafter contacting toluene with the resulting coke-containing catalyst under disproportionation conditions including a temperature between about 800° F. and 1025° F., and preferably between about 825° F. and 1000° F., at a hydrogen to toluene mole ratio greater than 1 and up to about 10 and recovering a product mixture containing para-xylene in an amount greater than the thermodynamic equilibrium concentration thereof in the total xylenes produced.

Bis-porphyrin derivatives. Part 1. Reaction of meso-hydroxymethylporphyrinatometal derivatives with acids

Abstract: Treatment of the nickel(II) or copper(II) derivative of octaethyl-meso-hydroxymethylporphyrin with sulphuric acid in dimethyl-formamide or -acetamide gives mainly the meso,meso′-ethylenebis(porphyrinatometal) derivative by reactions involving electron transfer from the metal, In the absence of metal, only disproportionation reactions occur. Vilsmeier formylation of the nickel dimer yields mono- and di-substitution products.

Photoreduction of 1,10-phenanthroline

Abstract: The effects of solvent polarity on the photophysical properties of 1,10-phenanthroline indicate the close proximity of (n, π*) and (π, π*) excited singlet states, whilst the lowest triplet state is (π, π*) in all solvents. In hydrocarbon solvent, the first excited singlet state is of (n, π*) character but in water a (π, π*) is situated ∼ 700 cm–1 below this state. Even in water, the (n, π*) state is capable of abstracting a hydrogen atom from the solvent forming an intermediate semidiaza radical. The radical can be detected by flash photolysis and e.s.r. techniques and, in organic solvents, it decays with second order kinetics due to a disproportionation reaction. The major product of reaction is dihydrophenanthroline which, in hydrocarbon solvents, is formed with a quantum efficiency of ∼ 25 %. In aqueous solvent, the yield and rate of decay of the semidiaza radical are pH dependent, and the pK for protonation of the radical is 7.3. Thus, irradiation in water at pH 5 results in formation of the stable diprotonated radical cation.

Radiation chemistry of aqueous cyanide ion

Abstract: Dilute KCN solutions, irradiated with ..gamma.. rays in the presence of N/sub 2/O, give radicals CONH/sub 2/ which react quantitatively by disproportionation to yield equal amounts of cyanate and formamide. In the absence of N/sub 2/O, the radicals CONH/sub 2/ and H/sub 2/CN are formed and interact to yield a more complicated spectrum of products.

Catalyst for disproportionation of toluene

Abstract: Disproportionation of toluene to produce benzene and xylenes rich in the para isomer is accomplished by subjecting toluene to disproportionation conditions in the presence of a catalyst comprising a crystalline aluminosilicate zeolite, said zeolite having a silica to alumina ratio of at least about 12 and a constraint index, as hereinafter defined, within the approximate range of 1 to 12, said catalyst having been modified by initial treatment with an ammonium phosphate followed by treatment with a magnesium compound to yield a composite containing a minor proportion of an oxide of phosphorus and a minor proportion of an oxide of magnesium.

Synthetic studies with carbonates. Part 6. Syntheses of 2-hydroxyethyl derivatives by reactions of ethylene carbonate with carboxylic acids or heterocycles in the presence of tetraethylammonium halides or under autocatalytic conditions

Abstract: Reactions of ethylene carbonate (1a) with a variety of carboxylic acids catalysed by tetraethylammonium halides gave the corresponding 2-hydroxyethyl esters along with the diesters arising from disproportionation of the former products induced by the quaternary ammonium halides. Formation of the disproportionation products could be minimized by use of a short reaction time. The autocatalytic reactions of (1a) with strongly acidic carboxylic acids at elevated temperature gave ethylene glycol diesters selectively. Reaction mechanisms are discussed. Reactions of cyclic carbonates such as (1a) and propylene carbonate(1b) with acid anhydrides or active acyl compounds such as p-nitrophenyl acetate in the presence of tetraethylammonium iodide gave alkylene glycol diesters or 2-acyloxyalkyl aryl ethers in high yields. An attempt to extend this reaction to cyclohexane-1,2-diyl carbonate was unsuccessful, but a reaction with 1,2-epoxycyclohexane succeeded; this enabled us to examine the stereochemistry of the reaction. Finally, N-2-hydroxyethylation of a series of heterocyclic compounds having acidic imino hydrogen atoms was performed, both with tetraethylammonium iodide as catalyst and without a catalyst.

Disproportionation Equilibrium in Iron-Bearing Systems at Pressures above 100 Kbar with Applications to Chemistry of the Earth’s Mantle

Abstract: Chemical disproportionation of ferrous iron-bearing phases to an equilibrium mixture of ferric iron-bearing phases plus metallic iron is stabilized at high pressures. The effect is observed in olivine, and is the basis of a model of the earth’s mantle and core that is evolved from a primitive earth. The model is consistent with an equilibrium process of formation of the earth, and satisfies known physical properties of materials that are suitable for the mantle.

Metal Phosphinylides and Phosphinothioylides. VII. The Structure of [Ph2PX]M (X=O, S) in Solution and Their Disproportionation

Abstract: The species [Ph2PO]M in THF were found to exist as Ph2P–O–M by 31P-NMR, and [Ph2PS]MgCl as Ph2P–S–MgCl by Raman spectrum. The species [Ph2PS]M undergo easy disproportionation by heating.

Halide ion-induced disproportionation of cobalt carbonyls; formation of [Co(CO)4]– and subsequent cyclic ketone synthesis

Abstract: Free or complexed halide ions catalyse the disproportionation of [Co2(CO)8] and [Co4(CO)12] to give [Co(CO)4]–(I) in ethers or, using [K(crown)]2[CoX4](crown = dicyclohexyl-18-crown-6), in benzene; (I) reacts with o-xylylene dihalides (IIa,b), 2,3-bis(bromomethyl)naphthalene (III), or sebacoyl chloride to give indan-2-one (IV), 1H-benz[f]inden-2-(3H)-one (V), or [(OC)4CoCO[CH2]8COCo(CO)4], benzene being the preferred solvent for the latter two reactions.