Showing papers on "Catalysis published in 1971"

Platinum complexes of unsaturated siloxanes and platinum containing organopolysiloxanes

Abstract: PLATINUM COMPLEXES OF UNSATURATED SILOXANES ARE PROVIDED WHICH ARE USEFUL AS HYDROSILATION CATALYSTS. THESE PLATINUM-SILOXANE COMPLEXES MUST CONTAIN LESS THAN ABOUT 0.1 GRAM ATOM OF HALOGEN, PER GRAM ATOM OF PLATINUM, AND PREFERABLY SUBSTANTIALLY FREE OF HALOGEN WHICH INCLUDE PLATINUM-SILOXANE COMPLEXES WHICH ARE SUBSTANTIALLY FREE OF INORGANIC HALOGEN. THESE PLATINUM-SILOXANE COMPLEXES CAN BE MADE BY EFFECTING CONTACT BETWEEN A PLATINUM HALIDE AND AN UNSATURATED SILOXANE, FOR EXAMPLE, 1,3-DIVINYLTETRAMETHYLDISILOXANE, AND REMOVING AVAILABLE INORGANIC HALOGEN FROM THE RESULTING MATERIAL. IN ADDITION, CURABLE ORGANOPOLYSILOXANE COMPOSITIONS ARE PROVIDED COMPRISING AN ORGANOPOLYSILOXANE POLYMER AND AN EFFECTIVE AMOUNT OF SUCH PLATINUM-SILOXANE COMPLEX.

Reduction of stratospheric ozone by nitrogen oxide catalysts from supersonic transport exhaust.

Abstract: Although a great deal of attention has been given to the role of water vapor from supersonic transport (SST) exhaust in the stratosphere, oxides of nitrogen from SST exhaust pose a much greater threat to the ozone shield than does an increase in water. The projected increase in stratospheric oxides of nitrogen could reduce the ozone shield by about a factor of 2, thus permitting the harsh radiation below 300 nanometers to permeate the lower atmosphere.

Ozone production rates in an oxygen-hydrogen-nitrogen oxide atmosphere

Abstract: The distribution of the compounds NO, NO2, NO3, N2O5, and HNO3 has been calculated for different choices of relevant parameters, the values of which are uncertain. An appreciable part of the NO and NO2 is converted to NO3, N2O5, HNO3 and possibly HNO2 is the ozone layer. Reactions of odd oxygen with NO and NO2 may be the dominating reassociation processes for odd-oxygen particles in the region below 45 km which is very important for the global ozone budget. Several processes may lead to the presence of significant amounts of nitrogen oxides, nitrous acid, and nitric acid in the stratosphere. Reported variations during the solar cycle of ozone concentrations above 30 km (Dutsch, 1969) can be explained by corresponding variations in the stratospheric odd nitrogen oxide content. An artificial increase of the mixing ratio of the oxides of nitrogen in the stratosphere by about 1×10−8 may lead to observable changes in the atmospheric ozone level. Chains of reactions involving the constituents OH, H2O2, and HO2 also lead to the catalytic destruction of odd oxygen. The presence of nitric acid with a mixing ratio of about 3×10−9 in the ozone layer (Murcray et al., 1968; Rhine et al., 1969) indicates much larger OH and HO2 concentrations than can be explained solely by the reaction O(1D) + H2O → 2 OH. The reaction N2O5 + H2O → 2HNO3 followed by O + HNO3 → OH + NO3 may also be an important source of OH if the rate constants given by Jaffe and Ford (1967) are adopted. It is difficult to explain the measured nitric acid concentrations between 20 and 30 km with the reaction HO2 + NO + M → HNO3 + M. Laboratory data (Asquith and Tyler, 1969) indicate that the reaction H2O2 + NO2 → HNO3 + OH (Nicolet, 1970α) is unimportant in the atmosphere.

Promising catalyst for auto exhaust.

Abstract: Lanthanum cobalt oxide as potential auto exhaust catalyst from studies of activity in gas phase

The asymmetric synthesis of hydratropic acid and amino-acids by homogeneous catalytic hydrogenation

Abstract: A new optically active diphosphine–rhodium(I) catalytic system has been used in several asymmetric reductions giving optical yields of up to 72%.

Polymerization of ethylene using supported bis-(cyclopentadienyl)chromium(ii)catalysts

Abstract: SUPPORTED BIS - (CYCLOPENTADIENE) CHROMIUM (II) CATALYSTS WHICH ARE FORMED WHEN A BIS-(CYCLOPENTADIENYL) CHROMIUM (II() COMPOUND IS ADSORBED ON AN INORGANIC OXIDE HAING A HIGH SURFACE AREA, HAVE BEEN FOUND TO BE UNUSUALLY EFFECTIVE CATALYSTS FOR THE POLYMERIZATION OF ETHYLENE OVER A WIDE RANGE OF REACTION CONDITIONS. THE ACTIVITY OF THESE CATALYST CAN BE MARKEDLY INCREASED IN THE PRESENCE OF HYDROGEN AND THE RELATIONSHIP OF THE MELT INDEX OF THE POLYMER TO THE HYDROGEN AND ETHYLENE CONCENTRATIONS USED IN THE POLYMERIZATION REACTION HAS BEEN FOUND TO BE GOVERNED BY THE EQUATION WHERE MI REPRESENTS THE MELT INDEX OF THE POLYETHYLENE, A REPRESENTS THE HYDROGEN CONCENTRATION IN MOLE PERCENT B REPRESENTS THE ETHYLENE CONCENTRATION IN MOLE PERCENT AND K AND C REPRESENTS EMPIRICALLY-DETERMINED CONSTANTS.

Inhibition of adenosine 5′-triphosphate–creatine phosphotransferase by substrate–anion complexes. Evidence for the transition-state organization of the catalytic site

Abstract: 1. The substrate combination creatine–MgADP does not significantly protect creatine kinase against inhibition by iodoacetamide in the absence of small anions. 2. Small anions can be divided into three groups according to the way in which they affect creatine kinase: I, acetate reversibly increases enzyme activity in the forward reaction but does not affect the rate of inhibition by iodoacetamide in the presence of creatine plus MgADP; II, planar anions and some halides (HCO3−, HCO2−, NO3−, NO2−, Cl−, Br−, F−) in the presence of creatine plus MgADP protect the enzyme from inhibition by iodoacetamide; III, tetrahedral anions (SO42−, HPO42−, ClO4−, BF4−) and iodide do not affect the rate of inhibition by iodoacetamide in the presence of creatine plus MgADP but may decrease the protection by class II anions under these conditions. Anions of class II and class III also reversibly inhibit enzyme activity. 3. It is concluded that class II anions form a stable and inactive quaternary enzyme–creatine–MgADP–anion complex and this is responsible for the effect attributed by previous workers to the ternary complex lacking anion. Formation of this complex, particularly in the forward reaction, can lead to markedly non-linear enzyme progress curves. Some previous observations are re-appraised in the light of these findings. 4. From the behaviour of chloride and nitrate ions, and the marked lowering of the Ki values for creatine and MgADP they produce, it is inferred that planar or monoatomic anions act in the quaternary complex by simulating the transferable phosphoryl group in the transition state (or another intermediate state) of the reaction. 5. It is suggested that, in the course of the reaction, the tetrahedral phosphate-binding site for the transferable phosphoryl group of the substrate (that also binds class II and class III anions) changes into a trigonal bipyramid site (also occupied by class II anions). This strains the phosphoryl group to adopt the transitional sp3d hybridized state and must contribute significantly to the low activation energy of the reaction. 6. Catalysis is deduced to proceed by an `in line' transfer reaction and from the effects of class II anions it is possible to estimate the approximate dimensions of the anionic site in the transition-state complex. 7. The specific protecting effect of an equilibrium mixture of substrates against inhibition by iodoacetamide provides further evidence for the conformational change suggested above as a step in the catalytic process.

Kinetic study of the dicarboxylate carrier in rat liver mitochondria.

Abstract: The rate of uptake in mitochondria as catalyzed by the dicarboxylate carrier of dicarboxylates and, in the presence of N-ethylmaleimide, of inorganic phosphate, has been analyzed by using the inhibitor stop method 1 By comparing the dependence on substrate concentration of the rate of succinate, malonate and malate uptake, it is found that the Km (malate) = 023 < Km (malonate) = 037 < Km (succinate) = 117 mM The V values, however, are not significantly different for all three dicarboxylates (V∼ 70 μmoles/g protein × min at 9°C) 2 Succinate, malate and malonate are shown to be competitive with each other in the kinetics of uptake 3 The inhibition of the rate of malate uptake by 2–phenylsuccinate is found to be competitive 4 Several “permeant” anionic substrates such as acetate, pyruvate, 3-hydroxybutyrate, glutamate and aspartate have no effect on the rate of dicarboxylate uptake, even when added in large excess 5 The rate of malonate uptake is inhibited by 2-oxoglutarate but unaffected by citrate, while the rates of succinate and malate uptake are decreased by both 2-oxoglutarate and citrate Malate is inhibited more than succinate The inhibition of the rate of malate uptake by citrate and 2-oxoglutarate is shown to be non-competitive This is explained due to a re-exchange of accumulated malate by citrate or 2-oxoglutarate 6 In the presence of N-ethylmaleimide, externally added Pi inhibits the rate of dicarboxylate uptake The Pi inhibition of malate uptake is found to be mixed with a larger share of non-competitive than competitive inhibition 7 The V of the rate of P1 uptake is approximately equal to that of malate uptake in the presence of N-ethylmaleimide The K1 is, however, higher for Pi (Ki=Kp= 195 mM) than for malate 8 It is concluded firstly that the dicarboxylate carrier specifically transports either a dicarboxylate or Pi (but not both together), and secondly that the carrier has two separate binding sites, one specific for Pi and the other specific for the dicarboxylates

Oxidation of unsaturated fatty acids by ozone and nitrogen dioxide. A common mechanism of action

Abstract: Trace quantities of ozone and nitrogen dioxide, 1.5 ppm, catalyzed the rapid oxidation of unsaturated fatty acids. Nitrogen dioxide-catalyzed oxidations were dependent upon the NO2 concentration in the atmosphere. Both thin films and aqueous emulsions of fatty acids are oxidized by NO2 through a mechanism akin to the spontaneous autoxidation in air. Phenolic antioxidants, including vitamin E, retarded the oxidation. Ozone catalyzed a more rapid and complete oxidation than NO2 by a direct attack upon the double bonds of the fatty acid. Phenolic antioxidants are protective only in aqueous emulsions where the oxidation proceeds by peroxidation as well. Oxidation of essential tissue polyunsaturated fatty acids by O3 and NO2 is a likely common mechanism of toxicity.

Synthetic lubricants by oligomerization and hydrogenation

Abstract: OLIGOMERS OF NORMAL -C6-16 ALPHA-OLEFINS AS LUBRICANTS CAN BE MADE BY REACTING C6-16 NORMAL-ALPHA-OLEFINS OR MIXTURES THEREOF AT A TEMPERATURE OF FROM ABOUT 10-60* C. USING AN ALCOHOL-PROMOTED BORON TRIFLUORIDE CATALYST IN WHICH BORON TRIFLUORIDE IS USED IN MOLAR EXCESS OF THE ALCOHOL. PREFERABLY, ADDITIONAL BORON TRIFLUORIDE IS INJECTED INTO THE REACTION LIQUID PHASE DURING THE COURSE OF THE OLIGOMERIZATION. STABILITY OF THE RESULTANT PRODUCT IS IMPROVED BY CATALYTIC HYDROGENATION. THE PRODUCTS HAVE A LOW POUR POINT AND HIGH VISCOSITY INDEX.

Mechanism of the Electrocrystallization of Nickel and Cobalt in Acidic Solution

Abstract: This mechanism is studied by means of the analysis of the polarization characteristic and of the cathodic impedance. The results, obtained from an acidic solution of the Watts type, strongly support the hypothesis that the cathodic reaction occurs in several steps probably involving an adion . In the case of nickel, the results can be accounted for by a mechanism implying two successive transfer reactions in which acts as an intermediate compound and not as a catalyst. The presence in the electrolyte of either sodium benzenesulfonate or 2‐butyne 1,4‐diol (two inhibitors commonly used for the electrocrystallization of nickel) specifically modifies the kinetic parameters of transfer reactions and diminishes the capacity of the electrochemical double‐layer. This capacity is defined thanks to a least‐squares analysis of the cathodic impedance.

Hydrolysis of the borohydride ion catalysed by metal–boron alloys

Abstract: The hydrolysis of the borohydride ion according to the equation (i) is catalysed by nickel–boron and cobalt–boron, BH4–+ 3H2O → H2BO3–+ 4H2(i) alloys. The metal-catalysed hydrolysis has been studied at 22·0 °C by measurement of the hydrogen gas evolved. Analysis of the gas evolved when the reaction is carried out in deuterium oxide shows that approximately half the hydrogen evolved originates from the borohydride and half from the solvent. The deuterium content of the gas increases with reaction time. In mixtures of H2O and D2O, preferential hydrogen evolution occurs and isotope separation factors of 8·5 (for a nickel–boron catalyst) and 9·2 (for a cobalt–boron catalyst) have been derived.

Methods of Asymmetric Synthesis—Enantioselective Catalytic Hydrogenation

Abstract: It is proposed that asymmetric syntheses be divided into enantioselective and diastereoselective syntheses. The enantioselective hydrogenations discussed in the present progress report were catalyzed by Raney nickel that had previously been treated with solutions of optically active compounds. Relationships exist between the enantioselectivity of the catalyst and the structure of the chiral compound used to modify it.