SOME OBSERVATIONS ON CYANIC ACID AND CYANATES

1955 ◽  
Vol 33 (2) ◽  
pp. 426-440 ◽  
Author(s):  
M. W. Lister
Keyword(s):  
Activation Energy ◽  
Ionic Strength ◽  
Rate Constant ◽  
Ionization Constant ◽  
Side Reaction ◽  
Cyanic Acid ◽  
First Order ◽  
Second Stage ◽  
Carbonate Concentration ◽  
Considerable Range

Various reactions of cyanic acid and the cyanate ion have been examined. Cyanic acid, in the presence of added hydrochloric or nitric acid, decomposes quantitatively according to the equation: HNCO + H3O+ → CO2 + NH4+. The rate constant for this reaction was measured over a range of temperature and ionic strength, and was found to be 0.86 mole liter−1 min.−1 at unit ionic strength and 1.5 °C. The activation energy is [Formula: see text] The effect of ionic strength on the reaction with hydrochloric acid closely parallels that on the activity coefficients of the acid itself. Without added acid cyanic acid decomposes by a first order reaction: HNCO + 2H2O → NH4HCO3, followed by a rapid second stage: NH4HCO3 + HNCO → NH4NCO + H2CO3. This reaction has a rate constant of 0.011 min.−1 at 0 °C. and an activation energy of 16 kcal. There is also a few per cent of some side reaction. Cyanate ions in alkaline solution decompose thus: OCN− + 2H2O → NH4+ + CO3−−. This reaction was examined over a range of temperature and ionic strength: it is first order with k = 3.0 × 10−3 min.−1at 100 °C. (0.3 ionic strength) and [Formula: see text] activation energy. The rate is somewhat dependent on hydroxide concentration, when this is fairly low. The reaction is catalyzed by carbonate, but not by a number of other anions that were examined. The rate of the catalyzed reaction is proportional to the carbonate concentration, but independent of cyanate, at least over a considerable range. The ionization constant of cyanic acid has been measured by a method that avoids errors from hydrolysis; the value obtained was 2.0 × 10−4. The oxidation of cyanate by hypochlorite and by chlorine was examined more briefly.

The thermal decomposition of cyclobutane-1,2-dione

1985 ◽  
Vol 63 (11) ◽  
pp. 2945-2948 ◽  
Author(s):  
J.-R. Cao ◽  
R. A. Back
Keyword(s):  
Activation Energy ◽  
Thermal Decomposition ◽  
Vapor Pressure ◽  
Gas Phase ◽  
Rate Constant ◽  
Surface Reaction ◽  
Order Rate Constant ◽  
Reaction Vessel ◽  
Arrhenius Parameters ◽  
First Order

The thermal decomposition of cyclobutane-1,2-dione has been studied in the gas phase at temperatures from 120 to 250 °C and pressures from 0.2 to 1.5 Torr. Products were C2H4 + 2CO, apparently formed in a simple unimolecular process. The first-order rate constant was strongly pressure dependent, and values of k∞ were obtained by extrapolation of plots of 1/k vs. 1/p to1/p = 0. Experiments in a packed reaction vessel showed that the reaction was enhanced by surface at the lower temperatures. Arrhenius parameters for k∞, corrected for surface reaction, were log A (s−1) = 15.07(±0.3) and E = 39.3(±2) kcal/mol. This activation energy seems too low for a biradical mechanism, and it is suggested that the decomposition is probably a concerted process. The vapor pressure of solid cyclobutane-1,2-dione was measured at temperatures from 22 to 62 °C and a heat of sublimation of 13.1 kcal/mol was estimated.

Kinetics and mechanism of the hexacyanomanganate(IV)–arsenic(III) redox reaction in acidic medium

1988 ◽  
Vol 66 (11) ◽  
pp. 2855-2859 ◽  
Author(s):  
Guillermo López-Cuetoa ◽  
Carlos Ubide
Keyword(s):  
Sulfuric Acid ◽  
Ionic Strength ◽  
Rate Constant ◽  
Redox Reaction ◽  
Acidic Medium ◽  
Absorption Maximum ◽  
Cyanide Complex ◽  
Acidic Media ◽  
Acid Media ◽  
First Order

The reaction between hexacyanomanganate(IV) and arsenic(III), in acidic media, proceeds with a stoichiometry Δ[Mn(IV)]/Δ[As(III)] = 1. The reaction in sulfuric acid media has been followed spectrophotometrically at 387 nm, where the Mn(IV) cyanide complex has an absorption maximum, and shows a first-order dependence on the hexacyanomanganate(IV) concentration, viz., −d[Mn(IV)]/dt = k[Mn(IV)], the value of k being dependent on the acidity and the arsenic(III) concentration. At As(III), 0.1 M; H+, 0.16 M; ionic strength, 2.0; and T, 30 °C, the value of the rate constant was found to be k = (1.04 ± 0.06) × 10−5 s−1. The proposed mechanism, through three parallel pathways, explains satisfactorily the experimental results observed.

scholarly journals The combination of carbon monoxide–haem with apoperoxidase

1969 ◽  
Vol 114 (4) ◽  
pp. 719-724 ◽  
Author(s):  
Charles Phelps ◽  
Eraldo Antonini
Keyword(s):  
Activation Energy ◽  
Carbon Monoxide ◽  
Rate Constant ◽  
Binding Sites ◽  
Order Process ◽  
First Order ◽  
Effects Of Ph ◽  
Kinetics Of

1. Static titrations reveal an exact stoicheiometry between various haem derivatives and apoperoxidase prepared from one isoenzyme of the horseradish enzyme. 2. Carbon monoxide–protohaem reacts rapidly with apoperoxidase and the kinetics can be accounted for by a mechanism already applied to the reaction of carbon monoxide–haem derivatives with apomyoglobin and apohaemoglobin. 3. According to this mechanism a complex is formed first whose combination and dissociation velocity constants are 5×108m−1sec.−1 and 103sec.−1 at pH9·1 and 20°. The complex is converted into carbon monoxide–haemoprotein in a first-order process with a rate constant of 235sec.−1 for peroxidase and 364sec.−1 for myoglobin at pH9·1 and 20°. 4. The effects of pH and temperature were examined. The activation energy for the process of complex-isomerization is about 13kcal./mole. 5. The similarity in the kinetics of the reactions of carbon monoxide–haem with apoperoxidase and with apomyoglobin suggests structural similarities at the haem-binding sites of the two proteins.

Pseudo-Homogenous Kinetics Model for the Synthesis of Dimethyl Carbonate from Urea and Methanol with Heterogeneous Catalyst

2011 ◽  
Vol 233-235 ◽  
pp. 481-486
Author(s):  
Wen Bo Zhao ◽  
Ning Zhao ◽  
Fu Kui Xiao ◽  
Wei Wei
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Dimethyl Carbonate ◽  
Side Reaction ◽  
Order Reaction ◽  
Zero Order ◽  
Kinetics Model ◽  
First Order ◽  
Zero Order Reaction ◽  
Kinetics Of

The synthesis of dimethyl carbonate (DMC) from urea and methanol includes two main reactions: one amino of urea is substituted by methoxy to produce the intermediate methyl carbamate (MC) which further converts to DMC via reaction with methanol again. In a stainless steel autoclave, the kinetics of these reactions was separately investigated without catalyst and with Zn-containing catalyst. Without catalyst, for the first reaction, the reaction kinetics can be described as first order with respect to the concentrations of methanol and methyl carbamate (MC), respectively. For the second reaction, the results exhibit characteristics of zero-order reaction. Over Zn-containing catalyst, the first reaction is neglected in the kinetics model since its rate is much faster than second reaction. After the optimization of reaction condition, the macro-kinetic parameters of the second reaction are obtained by fitting the experimental data to a pseudo-homogenous model, in which a side reaction of DMC synthesis is incorporated since it decreases the yield of DMC drastically at high temperature. The activation energy of the reaction from MC to DMC is 104 KJ/mol while that of the side reaction of DMC is 135 KJ/mol.

THE REACTION BETWEEN CYANATE AND HYPOCHLORITE

1956 ◽  
Vol 34 (4) ◽  
pp. 489-501 ◽  
Author(s):  
M. W. Lister
Keyword(s):  
Activation Energy ◽  
Ionic Strength ◽  
Rate Constant ◽  
Hypochlorous Acid ◽  
Effect Of Temperature ◽  
Slow Step ◽  
True Activation Energy ◽  
Rate Of Reaction ◽  
Different Temperatures ◽  
Kinetics Of

The reaction between sodium hypochlorite and potassium cyanate in the presence of sodium hydroxide has been examined. The main products are chloride, and carbonate ions and nitrogen; but, especially if much hypochlorite is present, some nitrate is formed as well. The rate of reaction is proportional to the cyanate and hypochlorite concentrations, but inversely proportional to the hydroxide concentration: the rate constant is 5.45 × 10−4 min.−1 at 65 °C, at an ionic strength of 2.2. The rate constant increases somewhat as the ionic strength rises from 1.7 to 3.5. The effect of temperature makes the apparent activation energy 25 kcal./gm-molecule. The kinetics of the reaction suggest that the slow step is really a reaction of hypochlorous acid and cyanate ions, and possible intermediate products of this reaction are suggested. Allowing for the different extent of hydrolysis of hypochlorite at different temperatures, the true activation energy is found to be 15 kcal./gm-mol., which is consistent with the observed rate of reaction.

Correlation analysis of reactivity in the addition of substituted benzylamines to β-nitrostyrene

1996 ◽  
Vol 74 (4) ◽  
pp. 625-629 ◽  
Author(s):  
Neeta Jalani ◽  
Seema Kothari ◽  
Kalyan K. Banerji
Keyword(s):  
Activation Energy ◽  
Correlation Analysis ◽  
Rate Constant ◽  
Steric Hindrance ◽  
Nucleophilic Addition ◽  
Regression Coefficients ◽  
Nucleophilic Attack ◽  
Arrhenius Activation Energy ◽  
First Order ◽  
Kinetics Of

The kinetics of addition of a number of ortho-, meta-, and para-substituted benzylamines to β-nitrostyrene (NS) in acetonitrile have been studied. The reaction is first order with respect to NS. The order with respect to the amine is higher than one. It has been shown that the reaction follows two mechanistic pathways, uncatalyzed and catalyzed by the amine. The Arrhenius activation energy for the catalyzed path is negative, indicating the presence of a pre-equilibrium (k1, k−1) leading to the formation of a zwitterion. The values of the rate constant, k1, for the nucleophilic attack have been determined for 28 benzylamines. The rate constant k1 was subjected to correlation analysis using Charton's LDR and LDRS equations. The polar regression coefficients are negative, indicating the formation of a cationic species in the transition state. The reaction is subject to steric hindrance by ortho substituents. Key words: nucleophilic addition, benzylamines, correlation analysis, kinetics, alkene.

scholarly journals Kinetic and Thermodynamic Study of Oxidative Decolourisation of a Typical Food Dye (Tartrazine) in an Aqueous Environment

2020 ◽  
Vol 24 (6) ◽  
pp. 1021-1026
Author(s):  
F.O. Okeola ◽  
E.O. Odebunmi ◽  
M.A. Amoloye ◽  
H.F. Babamale ◽  
S. Thema ◽  
...  
Keyword(s):  
Activation Energy ◽  
Ionic Strength ◽  
Rate Constant ◽  
Metal Ion ◽  
Reaction Medium ◽  
Order Rate Constant ◽  
Aqueous Environment ◽  
Food Dye ◽  
Typical Food ◽  
Homogenous Catalyst

The study was carried out to describe the kinetics and thermodynamics of hydrogen peroxide oxidation of a typical food dye (Tartrazine). The effect of different operational factors were investigated spectrophotometricallyat wavelength460 nm under pseudo first order reaction.These included concentration of the oxidant and the dye, the pH, ionic strength and temperature of the reacting medium and the presence of transition metal ion as homogenous catalyst. A complete and smooth decolourisation was observed. The results showed that the rate of oxidation of dye increased with increasing in concentration of substrate and oxidant. Increasing in temperature, ionic strength and pH of the basic reaction medium also raised the reaction rate. The rate of oxidation also increased with increasing in the concentration of Fe (III) ion. Pseudo second order rate constant (k2) obtained was 1.95 x 10-3 M-1s-1 and 3.8 x10-3M-1s-1 in the absence and presence of Fe (III) ion respectively. The Arrhenius activation energy for the oxidation in the absence and presence of Fe (III) ion were 47.23 kJmol-1 and 42kJmol-1 respectively. Other thermodynamic parameters showed entropy of activation (ΔS#), free energy of activation (ΔG#) and Enthalpy of activation of the reaction (ΔH#) in the presence of Fe (III) as -34.7  JK-1mol-1, 48.4 kJmol-1 and 40.30 kJmol-1 respectively. The results in the absence of Fe (III) ion were -24.6 JK-1mol-1, 51.2 kJmol-1 and 44.0 kJmol-1respectively. The relative lower activation energy (Ea),fairly higher negative value of (ΔS#) and higher (ΔG#) , with higher rate constant in the presence of Fe(III) ion showed Fe(III) ion enhancement of rate of decolourisation. Keywords: Tartrazine Food dye, Kinetics, Thermodynamics, Hydrogen Peroxidede colourisation,

scholarly journals Pyrolysis of phenylmercaptoacetic acid

1968 ◽  
Vol 46 (2) ◽  
pp. 191-197 ◽  
Author(s):  
A. T. C. H. Tan ◽  
A. H. Sehon
Keyword(s):  
Carbon Dioxide ◽  
Activation Energy ◽  
Carbon Monoxide ◽  
Acetic Acid ◽  
Rate Constant ◽  
Order Reaction ◽  
First Order Reaction ◽  
Kcal Mole ◽  
Dissociation Process ◽  
First Order

The pyrolysis of phenylmercaptoacetic acid was investigated by the toluene-carrier technique over the temperature range 760–835 °K. The main products of the decomposition were phenyl mercaptan, carbon dioxide, acetic acid, phenyl methyl sulfide, carbon monoxide, and dibenzyl.The overall decomposition was a first-order reaction with respect to phenylmercaptoacetic acid and could be represented by the two parallel steps:[Formula: see text]Reaction [1] was shown to be a homogeneous first-order dissociation process, and its rate constant was represented by the expression[Formula: see text]The activation energy of this reaction, i.e. 58 kcal/mole, was identified with D(C6H5S—CH2COOH).

OXYGEN EVOLUTION FROM SODIUM HYPOCHLORITE SOLUTIONS

1962 ◽  
Vol 40 (4) ◽  
pp. 729-733 ◽  
Author(s):  
M. W. Lister ◽  
R. C. Petterson
Keyword(s):  
Activation Energy ◽  
Ionic Strength ◽  
Oxygen Evolution ◽  
Rate Constant ◽  
Sodium Hypochlorite ◽  
Chloride Ions ◽  
Effect Of Temperature

The rates of oxygen evolution from carefully purified solutions of sodium hypochlorite have been measured. Methods of purification are described, and it is found that substantially the same rate is observed regardless of the method of purification. The rate of oxygen evolution is proportional to the square of the concentration of hypochlorite ions. The effect of temperature and ionic strength are examined. The rate constant is 7.5 × 10−6 (g-mol/I.)−1(min)−1 at 60 °C and an ionic strength of 3.5; the activation energy is 26.6 kcal/g-mol. These results are compared with the corresponding quantities for the reaction of hypochlorite ions to form chlorite and chloride ions, and some tentative explanations are offered.

THE OXIDATION OF MERCAPTANS BY POTASSIUM PERSULPHATE IN HOMOGENEOUS SOLUTION

1948 ◽  
Vol 26b (7) ◽  
pp. 527-540 ◽  
Author(s):  
C. A. Winkler ◽  
R. L. Eager
Keyword(s):  
Activation Energy ◽  
Acetic Acid ◽  
Rate Constant ◽  
Salt Effect ◽  
Homogeneous Solution ◽  
Ion Concentration ◽  
Potassium Persulphate ◽  
First Order ◽  
Homogeneous Oxidation ◽  
Wide Range

In the homogeneous oxidation of mercaptans by potassium persulphate in concentrated acetic acid, the rate of disappearance of potassium persulphate during an experiment is first order with respect to the measured persulphate concentration. The rate constant is independent of the kind of mercaptan used, and is independent of mercaptan concentration over a wide range of mercaptan concentrations. The rate constant falls off, however, at low mercaptan concentrations, this falling-off being less pronounced if the rate is reduced by the addition of salts. The mercaptan concentration at which the rate constant, calculated from persulphate disappearance, becomes independent of mercaptan concentration increases as the temperature is increased. A salt effect prevails, the rate constant being decreased with increased potassium ion concentration. The equivalent conductance of solutions of potassium persulphate in the solvent used shows a behavior on dilution which indicates that potassium persulphate is incompletely ionized in the solvent. A mechanism is proposed for the reaction, in which it is assumed that dissociation of persulphate ions into sulphate free radicals is rate-controlling, with an activation energy of the order 26,000 cal. per mole.

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