Specific Reaction Rate Constants Research Articles

Kinetics of the Reaction of Cotton with Dimethylolethylcarbamate

Crystalline dimethylolethylcarbamate (DMEC) was isolated, characterized, and used to treat cotton fabrics. Physicat and chemical properties of cotton printcloth (80×80) treated with 0.55 M solution of DMEC in the presence of 0.03 M inorganic salt catalysts and cured at 160°C were determined. Kinetics of the cellulose-DMEC reactions in the presence of 0.03 M catalysts in the 45° to 65°C temperature range were investigated. Specific reaction rate constants and activa tion parameters for these reactions were compared with those values reported previously for the reactions of cotton with dimethylolated ureas. 'I'he monomethylol derivative of ethyl carbamate (MMEC) was also isolated in crystalline form and used to treat cotton at 160°C. Specific reaction rate constants for the cotton-MMEC reaction at 65°C were deter mined with each of four catalysts and compared with corresponding rate constants for the cotton-DMEC reactions.

Microheterogeneity of staphylococcal enterotoxin B

Four components have been demonstrated in staphylococcal enterotoxin B by isoelectric focusing in polyacrylamide gels. In a typical preparation their relative concentrations from the most to least cathodic were 6, 56, 31 and 7%. The components were not stable conformers nor were the differences in isoionic points due to bound ligand. A comparison of the measured isoionic points with values calculated for varying numbers of excess basic groups indicated that each component differed from the succeeding one by a single charge. Sequential conversion of the components from the more to the less alkaline forms was obtained by exposure to pH 9.0 at 37 °C. The data gave an excellent fit for two consecutive first-order reacions in whicc the specific reaction rate constants were nearly identical. The reaction was much slower at pH 7.3 and 37 °C and no change at all was observed over a period of 32 days at pH 9.0 and 1 °C. Amide hydrolysis is the mechanism for these conversions, but the rate is too slow to account for the appearance of four components during the comparatively short period of bacterial fermentation. It is suggested, therfore, that only the most cathodic component is synthesized by the organism and that this is converted to the other forms enzymatically.

Kinetics of Acid-Catalyzed Hydrolysis of Dexoxadrol

The kinetics of the hydronium-ion-catalyzed hydrolysis of the ketal group in dexoxadrol hydrochloride [d(+)-2,2-diphenyl-4-(2′ -piperidyl)-1,3-dioxolane hydrochloride], an orally active analgesic agent, were determined as functions of acid concentration, ionic strength (μ), and temperature. Pseudo-first-order kinetics were observed. Specific reaction rate constants increased with increasing μ; log k' /[H*] was linearly related to μ at μ ≤ 0.03. The energy (ΔEa), enthalpy (ΔH‡), and entropy (ΔS‡) of activation were 16.8 kcal./mole, 16.2 kcal./mole, and —18.8 e.u., respectively. The rate of dexoxadrol hydrolysis was about 2% of that reported in the literature for 2,2-diphenyl-1,3-dioxolane, indicating a marked retardation due to the protonated piperidyl moiety. For a 60-min. residence time at pH 2.0 in the stomach, it was estimated that more than 91% of orally ingested dexoxadrol would remain intact.

Shock-tube atom kinetics of nitric oxide decomposition

The rate of formation of ground-state atomic oxygen, O(3P), has been measured behind shock waves in NO−Ar mixtures by atomic resonance absorption spectrophotometry. After experimental calibration of the atomic absorption coefficient, rate measurements were made over a temperature range of 2600°–6300°K, for 0.1%, 1.0%, and 10.0% mixtures of NO in Ar. The specific reaction-rate constants were first calculated, assuming that the dissociation proceeds by a simple bimolecular NO−Ar collision process. On this basis, Arrhenius plots of the data for the mixtures containing the higher concentrations of NO exhibit, at lower temperatures, rate constants which are much greater than the constants corresponding to the lower concentrations. At the higher temperatures, the rate constants converge. A chemical mechanism was then developed and employed to reproduce, by means of a computer calculation, the results obtained experimentally. The experimental data have been explained in terms of six reactions, of which two have been verified as the initial, rate-limiting steps of the dissociation process. These are: NO+NO→N2O+O(3P) and NO+Ar→N+O(3P)+Ar, for which the specific rate-constant expressions k=2.35×1010 exp(−29,000/RT) and k=1.37×1014 exp(−148,400/RT), respectively, have been obtained. The first of these two reactions is dominant at low temperatures and high NO concentrations, while the second predominates at high temperatures and low concentrations.

Pulse Radiolysis Studies in Lanthanide Aqueous Solutions. II. Formation, Spectrum, and Some Chemical Properties of Praseodymium(IV) in Aqueous Solution

Pulse radiolysis of Pr(III) gives a transient absorption spectrum with a maximum at 290. This is due to the formation of Pr(IV) through the reaction of OH radicals and Pr(III). The rate of the reaction has been determined by four different methods and the rate constant was found to be 1–4 × 106M−1 sec−1. The variation of the optical density of Pr(IV) ions with pH lead to the conclusion that the form of Pr(IV) is Pr(OH)3+ and Pr4+ in neutral and acid solutions, respectively. The equilibrium constant of hydrolysis, Pr4+ + H2O ⇄ Pr(OH)3++ H+, was found to be 7 × 10−4. The spectrum obtained is assigned to the Laporte-allowed transition between 4f and 5d. The specific reaction rate constants of Pr(IV) with water, HSO4−, NO2−, H2O2, and Br− have been determined, as well as those of Pr(III) with eaq− and H atoms.

The Degradation Kinetics of an Ester of Silvex and the Persistence of Silvex in Water and Sediment

The degradation kinetics of propylene glycol butyl ether (hereafter referred to as PGBE) ester of 2-(2,4,5-trichlorophenoxy) propionic acid (silvex) and the persistence of silvex in water and sediment were studied under impounded conditions. PGBE ester of silvex was applied to the surface of three ponds at the rate of 9 kg/ha/A. Water and sediment samples were collected at 4, 12, 24, and 48 hr after treatment and were extracted for PGBE ester of silvex immediately after collection. The concentrations of PGBE ester of silvex and silvex present in the water and sediment samples were determined by gas chromatography. Physico-chemical and mineralogical characteristics of the sediment samples collected prior to treatment were determined. The hydrolysis of PGBE ester of silvex to silvex obeyed first order reaction kinetics, the specific reaction rate constants for the three ponds being 0.09 hr−1, 0.10 hr−1, and 0.14 hr−1. Fifty percent hydrolysis of PGBE ester of silvex occurred in 5 to 8 hr, 90% hydrolysis occurred in 16 to 24 hr, and 99% hydrolysis occurred in 33 to 49 hr. The concentration of silvex in water initially increased, but decreased to zero by the end of 3 weeks. Adsorption of both the PGBE ester of silvex and silvex appeared to occur on the sediment; essentially complete disappearance of both occurred by the fifth week following treatment. Under laboratory conditions, silvex adsorption by the sediments conformed to the Freundlich adsorption equation.

Nitrogen Isotope Effects in the Reduction of Nitrate, Nitrite, and Hydroxylamine to Ammonia. II. The MgO and CuSO4 Systems

Nitrogen kinetic isotope effects were used to study reaction mechanisms associated with reductions of NO3−, NO2−, and NH2OH in hot alkaline solutions that contained Fe(II). In the CuSO4 system the specific reaction rate constants varied in the order kNO2− > kNO3− > kNH2OH, rather than the order kNO2− > kNH2OH > kNO3− found previously in the Ag2SO4 system. When MgO was used, the order of the specific reaction rate constants was the same as that observed with Ag2SO4, but different mechanisms operated in the reduction of NO3− and NO2−, although not in the reduction of NH2OH. Reactions consistent with the observed isotope effects and the known chemistry of nitrogen were postulated for the most probable reaction paths in the various systems.

Physicochemical Study of the Cotton Cellulose— Dimethylolpropyleneurea Reaction1

Physical and chemical properties of cotton print cloth treated with 0.55 M solutions of 1,3-bis(hydroxymethyl)-2(1H)-tetrahydropyrimidinone (dimethylolpropyleneurea or DMPU) in the presence of 0.03 and 0.1 M inorganic salt catalysts have been determined. The kinetics of the reaction in the presence of 0.03 M catalysts have been investigated. Specific reaction-rate constants at 45, 55, and 65°C in the presence of ZnCl2, Zn(NO 3)2, MgCl2, and Mg(NO3)2 have been calculated by following the changes in nitrogen and formaldehyde contents. Changes in crease recovery properties of finished fabrics with changes in nitrogen and formaldehyde contents were also followed. Enthalpies, entropies, and free energies of activation at 45°C for the reaction have been calculated. Specific reaction-rate constants and activation parameters were compared with those values reported previously for the reactions of cotton with derivatives of ethyleneurea. Infrared spectral data of fabrics finished with DMPU were analyzed.

Kinetics of the Reactions of Ethyleneurea Derivatives with Cotton Cellulose

The kineties of the reactions of cotton print cloth treated with 0.55 M solutions of 4.5-dihydroxy-1,3-bis(hydroxymethyl)-2-imidazolidinone (dimethyloldihydroxyethylene urea) in the presence of 0.03 M inorganic salt catalysts have been investigated. The present two-stage delayed-cure process for chemically modifying the performance of cellulosic fabrics depends on the significant differences in reactivities of cellu lose with methylol functional groups and with the hydroxyl groups of the urea derivatives. Specific reaction rate constants at 45, 55, 65, 75, and 85°C in the presence of ZnCl2, Zn(NO3)2, MgCl 2, and Mg(NO3)2 have been calculated by following the changes in nitrogen and formaldehyde contents and the changes in crease recovery properties of finished fabrics. These rates have been compared with those determined when cotton retets with an etherifying agent having ring hydroxyls only, as in the cellulose-dihydroxy ethyleneurea reactions, and with those determined when the etherifying agent has methylol hydroxyls only, as in the cellulose-dimethylolethyleneurea reactions. Enthalpies, entropies, and free energies of activation have been compared.

Effects of metal chelation on intraligand bonds—I kinetics of metal-catalysed decarboxylation of histidine

The kinetics of the metal ion-catalysed thermal decarboxylation of histidine have been studied in glycol-type solutions. The decarboxylation reaction was found to be first order with respect to histidine concentration. First order rate constants range from 0·39 × 10 −6 to 8·15 × 10 −6 sec −1 for the series of reactions using histidine with the following metal ions, arranged in decreasing order of effectiveness: Cu(II), Cr(III), Ni(II), Co(II), Al(III), Cd(II), Zn(II), Pd(II). Specific reaction rate constants have been studied as functions of temperature between 90° and 150°C for Cu(II) catalysed histidine decarboxylations in three solvent systems. The Arrhenius equations for kinetic behaviour for these systems are as follows: ethylene glycol, k = 2·089 exp (−10,180/ RT), ethylene glycol water (10:1 by volume), k = 20·09 exp (−11,740/ RT) and diethylene glycol, k = 1·142 exp (−10,300/ RT). It appears that a competitive oxidation reaction is occurring since the first order decarboxylation reaction is deactivated before the theoretical amount of CO 2 is evolved.

Hydrogenation of linolenate. XII. Effect of solvents on selectivity.

AbstractSelectivity of heterogeneous catalysts for hydrogenation of linolenate over linoleate is increased by the presence of certain polar solvents. A ratio of specific reaction rate constants for linolenate to linoleate of 4 was obtained with a 5% palladium‐on‐alumina catalyst when dimethyl formamide (DMF) was used as the solvent. This high selectivity of DMF was independent of temperature and catalyst concentration. Other solvents that improved selectivity include furfural, acetonitrile, tetramethyl urea and trimethyl phosphate.

Kinetics of the zinc fluoborate- and hydrogen ion-catalyzed hydrolyses of butadiene diepoxides

Optimum conditions for the etherification of cotton cellulose rather than hydrolysis or solvolysis of the diepoxide had been found to occur with zinc fluoborate catalysis when the diepoxide/catalyst molar ratio was 10–20, and water/diepoxide ratio was less than 100. Data in the literature on specific reaction rates of hydrolysis of butadiene diepoxide at approximately 1M in the presence of zinc fluoborate 0.05M were not available, nor were there such data for the H+ catalyzed-hydrolysis of the diepoxide at a pH = 3.25, which was the pH of the zinc fluoborate–butadiene diepoxide solution. Therefore, kinetics of the hydrolysis of the racemic mixture of the d,l-isomers (BDO) and of the meso-isomer of butadiene diepoxide (called BDE) catalyzed by dilute zinc fluoborate and by dilute HCl at 25–90°C. have been investigated. Rates of hydrolysis of both BDO and BDE were measured by following the change in oxirane oxygen content with time at 25, 40, 60, 75, and 90°C. Analysis of the experimental data at each temperature by the modified Swain method confirmed the assumption of consecutive first order reaction kinetics for the opening of the first and second oxirane rings for both Zn(BF4)2- and H+-catalyzed reactions. The relative rates (k2z/k1z) for the overall reaction with Zn(BF4)2 catalysis exceeded unity at each temperature, while the relative rates (k2H/k1H) with H+ ion catalysis was always less than unity. Thus, with Zn(BF4)2 catalysis, the second oxirane oxygen ring opened more rapidly than the first; but with H+ catalysis, the reverse was true. Correction of specific reaction rate constants of the Zn(BF4)2-catalyzed hydrolysis for the H+- control rates produced the same net result observed in the overall reaction; i.e., the corrected k2′/k1′ was much greater than unity. The zinc fluoboratecatalyzed hydrolysis was much faster than the H+-catalyzed hydrolysis of both rings. Enthalpies, entropies, and free energies of activation for both oxirane rings were calculated. Large negative entropies of activation indicated and SU2 mechanism for both ring openings.

Analog computers and kinetics of hydrogenation

AbstractInvestigations of the kinetics of consecutive reactions frequently require complicated calculations to determine specific reaction rate constants from experimental data. Analog computers permit a convenient empirical adjustment of rate constants in kinetic equations to match experimental results. Once an electronic network analogous to the chemical reaction system is set up, specific reaction rates can be determined by adjusting potentiometers, which are the analogs of the rate constants, until an acceptable fit of calculated and experimental data is reached. Applicability of a small analog computer to the kinetics of hydrogenation is presented.

Co‐oxidation of the Sulfur‐Containing Amino Acids in an Autoxidizing Lipid System

SUMMARYMOxidation of the sulfur amino acids by autoxidizing lipids was studied in a model system consisting of an amino acid dispersed in cold‐pressed, molecularly distilled menhaden oil (20–80% w/w). Under all conditions investigated, cysteine was oxidized completely to cystine. Preliminary results suggest that at 110°C the oxidation follows first‐order kinetics for at least the first 8 hr. A specific reaction rate constant of 0.25 per hour was calculated. When fatty acids were added to the system, cystine was oxidized to its thiosulfinate ester. When the fatty acid‐cystine ratio was 1:2, oxidation of cystine was a maximum. No oxidation of cystine occurred unless either a fatty acid, volatile organic acid, or ethanol was added. Under the conditions investigated, methionine was not oxidized to either its sulfoxide or its sulfone.

Chemical kinetics and thermodynamic consistency

The requirements of thermodynamic consistency provide a very satisfactory way of obtaining the functional form of specific reaction rate constants.

Analytical Studies of Dipicrylamine. I. pH‐Metric Study of Dipicrylaminate

AbstractDipicrylaminate can be determined by pH‐metric titration with strong mineral acids in aqueous solution. The end point is sharp if the concentration of dipicrylaminate exceeds 10−3M. The reaction consists of the replacement of metal ion by hydrogen ion.The solubility product, Ksp, and the dissociation constant, Ka of dipicrylamine were evaluated from the titration data. pH‐metric kinetic study of the recombination of dipicrylaminate ion with hydrogen ion was also carried out, from which the specific reaction rate constant was evaluted.

THE THERMAL DECOMPOSITION OF ANHYDROUS URANYL NITRATE AND URANYL NITRATE DIHYDRATE1

The thermal decomposition of anhydrous uranyl nitrate followed first- order kinetics in vacuo at temperatures from 250 to 450 deg . Amorphous uranium trioxide was the only nonvolatile product of decomposition. No intermediate compounds were observed. The thermal decomposition of uranyl nitrate dihydrate occurred as two independent reactions following first-order kinetics: dehydration to form anhydrous uranyl nitrate and denitration to form uranium trioxide. The decomposition was studied both in vacuo and at atmospheric pressure under nitrogen, at temperatures from 250 to 400 deg . Intermediate and final decomposition products were identified. The specific reaction-rate constants were measured for the dehydration and denitration reactions. From these data, the heats and entropies of activation were calculated. (auth)

A study of the recombination of atomic oxygen by means of the flash spectra of the Schumann-Runge system

The recombination of atomic oxygen has been studied at temperatures not exceeding several hundred degrees above room temperature. The process has been followed by obtaining flash absorption spectra in the vacuum ultra-violet of the entire Schumann-Runge system of molecular oxygen as a function of time. A third-order specific reaction rate constant of 1·2 × 10 15 (cm 3) 2mole 2-sec. has been obtained, for the reaction O + O + M, and vibrationally excited oxygen has been observed in only the first level of the ground state.

THE KINETICS OF THE OXALATE CATALYSIS OF THE IRON(II)—IRON(III) ELECTRON-EXCHANGE REACTION IN AQUEOUS SOLUTION1

The kinetics of the electron-exchange reaction between the two oxidation states of iron is first order in both iron(II) and iron(III) and oxalate- catalyzed in aqueous perehloric-oxalic acid media of 0.55 ionic strength. The specific reaction rate constants for the reaction path involving ferrous ion and FeC/sub 2/O/sup +//sub 4/ are 700, 1100, and 2140 sec/sup -1/ f/sup -1/ at O.lO, and 20 deg C respectively, corresponding to an activation energy of 9.2 kcal mole/ sup -1/ and an entropy of activation of -14.l kcal/mole/sup -1/ deg/sup -1/. The specific reaction rate constants for the path involving ferrous ion and f/sup -1/ .The exchange is also catalyzed by silver foil and by acetate, succinate, and phenolate anions. (auth)

A Kinetic Analysis of Phosphate Absorption by Excised Roots of Millet, Barley, and Alfalfa

AbstractA kinetic analysis was made of P absorption at steady state by excised roots of millet, barley, and alfalfa. Short‐time absorption studies indicated that the rate of P absorption is greater for millet than barley and greater for barley than alfalfa. The specific reaction rate constants for the metabolic turnover of the two carriers of P are of the same order of magnitude for the three plant species. They are approximately 1 × 10‐2 moles of P per mole of combined carrier per second. The apparent dissociation constant for carrier “a” is approximately 9 × 10‐4 for all three plant species, but the value for carrier “b” varies from 3 × 10‐6 for millet and alfalfa to 8 × 10‐6 for barley. The major difference between species is in concentration of carrier. These values are 2 × 10‐7, 3 × 10‐8, and 1 × 10‐8 moles per g. of millet, barley, and alfalfa roots, respectively.