PHOTO-INITIATED REACTIONS OF THIOLS AND OLEFINS: II. THE ADDITION OF METHANETHIOL TO UNCONJUGATED OLEFINS

1964 ◽  
Vol 42 (10) ◽  
pp. 2250-2255 ◽  
Author(s):  
D. M. Graham ◽  
R. L. Mieville ◽  
R. H. Pallen ◽  
C. Sivertz
Keyword(s):  
Activation Energy ◽  
Thermal Decomposition ◽  
Rate Constant ◽  
Rate Constants ◽  
Kinetic Studies ◽  
Addition Product ◽  
Isomerization Reaction ◽  
Ethylene Propylene ◽  
Intermittent Illumination ◽  
Competing Reactions

Kinetic studies have been made of the addition of methanethiol to ethylene, propylene, and butene-2. The results obtained are consistent with the mechanism postulated for the isomerization reaction (1). The overall activation energy was found to be negative and could be explained in terms of two competing reactions of the adduct radical: thermal decomposition leading to [Formula: see text] and olefin and dehydrogenation of thiol yielding addition product. Only the ratio of the rate constants for these two reactions could be determined. The method of intermittent illumination was used to evaluate the termination rate constant for the combination of two [Formula: see text] radicals which was found to be (2.5 ± 0.7) × 1010 l mole−1 s−1.

PHOTO-INITIATED REACTIONS OF THIOLS AND OLEFINS: I. THE THIYL RADICAL CATALYZED ISOMERIZATION OF BUTENE-2 AND 1,2-ETHYLENE-d2

1964 ◽  
Vol 42 (10) ◽  
pp. 2239-2249 ◽  
Author(s):  
D. M. Graham ◽  
R. L. Mieville ◽  
C. Sivertz
Keyword(s):  
Activation Energy ◽  
Thermal Decomposition ◽  
Kinetic Study ◽  
Rate Constants ◽  
Reaction Rate ◽  
Kinetic Studies ◽  
Thiyl Radical ◽  
First Order ◽  
Thiyl Radicals ◽  
Simple Mechanism

Kinetic studies have been made of the isomerization of butene-2 and 1,2-ethylene-d2 catalyzed by thiyl radicals produced from the photolysis of methanethiol. The rate of isomerization was found to be first order with respect to both the olefin and [Formula: see text] concentrations. The lack of influence of pressure on the reaction rate, at pressures above about 4 mm, leads to a simple mechanism in which isomerization is considered to occur as a result of thermal decomposition of the collisionally stabilized adduct radical produced in the reaction [Formula: see text]. The rate constants for this attack step were found to be 2 × 107 and 4.8 × 106 l mole−1 s−1 for butene-2 and ethylene-d2, respectively. In both cases the activation energy for isomerization was found to be close to zero. From a kinetic study of the isomerization of cis-butene-2 in the presence of butadiene-1,3, which acts as a retarder, the attack constant for butadiene at 25 °C was found to be 4.5 × 108 l mole−1 s−1.

Kinetic Studies on Antibody–Hapten Reactions. II. Reactions with Antibodies and their Polypeptide Chains

1973 ◽  
Vol 51 (10) ◽  
pp. 1355-1364 ◽  
Author(s):  
K. A. Kelly ◽  
A. H. Sehon ◽  
A. Froese
Keyword(s):  
Thin Layer ◽  
Rate Constant ◽  
Rate Constants ◽  
Kinetic Studies ◽  
Light Chains ◽  
Gel Chromatography ◽  
Equilibrium Studies ◽  
Polypeptide Chains

Kinetic and equilibrium studies were performed on the reactions of the hapten ε-dinitrophenyl-lysine with specific intact antibodies, reduced, alkylated, and polyalanylated antibodies, and reduced, alkylated, and polyalanylated γ-chains. No reaction was detected between the hapten and light chains. The γ-chains were found to have 0.5 combining sites per chain, and thin layer gel chromatography revealed that they existed as monomers. The rate constant of association for the reaction of γ-chains with hapten was found to be almost 1000 times lower than that for the corresponding reaction with the parent antibody. Differences in the rate constants of dissociation were much less pronounced. These results suggested that the combining site in the separated γ-chain had undergone a change in conformation.

Substituent effects of rate constants for thermal [4π + 2π] cycloreversion of spiro-fused β-lactam oxadiazolines

1993 ◽  
Vol 71 (6) ◽  
pp. 907-911 ◽  
Author(s):  
Michel Zoghbi ◽  
John Warkentin
Keyword(s):  
Thermal Decomposition ◽  
Rate Constant ◽  
Rate Constants ◽  
Transition States ◽  
Substituent Effects ◽  
Ground States ◽  
Phenyl Substituent ◽  
First Order ◽  
Average Value ◽  
Carbonyl Ylide

Twelve Δ3-1,3,4-oxadiazolines in which C-2 is also C-4 of a β-lactam moiety (spiro-fused β-lactam oxadiazoline system) were thermolyzed as solutions in benzene. Substituents in the β-lactam portion affect the rate constant for thermal decomposition of the oxadiazolines to N2, acetone, and a β-lactam-4-ylidene. The total spread of first-order rate constants at 100 °C was 47-fold and the average value was 6.7 × 10−4 s−1. A phenyl substituent at N-1 or at C-3 was found to be rate enhancing, relative to methyl. At C-3, H and Cl were also rate enhancing, relative to methyl. The data are interpreted in terms of the differential effects of substituents on the stabilities of the ground states, and on the stabilities of corresponding transition states for concerted, suprafacial, [4π + 2π] cycloreversion. The first products, presumably formed irreversibly, are N2 and a carbonyl ylide. The latter subsequently fragments to form acetone (quantitative) and a β-lactam-4-ylidene.

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.

Synthetic and kinetic studies of the reversible addition of a bridging NSN fragment to the electron-rich heterocycles (R2PN)(SN)2 (R = Me, Ph, F)

1984 ◽  
Vol 62 (4) ◽  
pp. 712-715 ◽  
Author(s):  
Neil Burford ◽  
Tristram Chivers ◽  
Richard T. Oakley ◽  
Tom Oswald
Keyword(s):  
Activation Energy ◽  
Thermal Decomposition ◽  
Nmr Spectroscopy ◽  
Kinetic Studies ◽  
Reductive Elimination ◽  
Membered Ring ◽  
High Yield ◽  
Kinetic Measurements ◽  
Bicyclic Compounds ◽  
Reversible Addition

The oxidative addition of Cl2 (using SO2Cl2) to the six-membered ring (R2PN)(SN)2 (R = Me, Ph) produces the mixed phosphazene–thiazyl heterocycles, (R2PN)(NSCl)2, which react with Me3SiNSNSiMe3 to give the bicyclic compounds R2PS3N5. The latter undergo thermal decomposition, at ca. 100 °C in toluene, via reductive elimination of an NSN unit to regenerate (R2PN)(SN)2 in high yield. Kinetic measurements of this process, using 31P nmr spectroscopy, yield an activation energy of 102.4 ± 6.0 kJ mol−1 for the release of the NSN fragment from Me2PS3N5. The thermolysis route has been used to prepare the thermally unstable (F2PN)(SN)2, characterized as a 1:1 adduct with norbornadiene.

THE STERIC FACTOR IN THE HYDROLYSIS OF β-1,4′-OLIGOGLUCOSIDES BY MYROTHECIUM CELLULASE

1956 ◽  
Vol 34 (1) ◽  
pp. 102-115 ◽  
Author(s):  
D. R. Whitaker
Keyword(s):  
Activation Energy ◽  
Rate Constant ◽  
Rate Constants ◽  
Activation Energies ◽  
Enzymic Activity ◽  
Degree Of Polymerization ◽  
Steric Factor ◽  
Collision Theory ◽  
Hydrolysis Of

A comparison of the rate constants and activation energies for the hydrolysis of cellobiose, cellotriose, cellotetraose, and cellopentaose by Myrothecium cellulase showed that while the rate constant was increased by a factor of about 450 as the degree of polymerization (D.P.) of the substrate was increased from two to five, the activation energy remained at about 12,000 cal. The results are interpreted, in terms of classical collision theory, as indicating that the increase in rate constant with D.P. is determined by an increase in the steric factor with D.P. Addition of a β-linked sorbityl group to an oligoglucoside increased the rate constant; the increase was less than that from addition of an anhydroglucose unit and, relative to the latter, diminished as the D.P. of the chain undergoing addition was increased. Exposing the enzyme to conditions favoring thermal or surface denaturation caused varying losses in enzymic activity towards the four oligoglucosides; wherever the loss in activity towards one oligoglucoside differed substantially from the loss in activity towards any other oligoglucoside, the greater loss was shown towards the substrate of lower D.P. The results are discussed.

Catalytic influence of certain foreign gases on the thermal decomposition of di-tertiary butyl peroxide

1959 ◽  
Vol 249 (1257) ◽  
pp. 173-179 ◽  
Keyword(s):  
Activation Energy ◽  
Thermal Decomposition ◽  
Carbon Tetrachloride ◽  
Rate Constant ◽  
Tertiary Butyl ◽  
Extended Theory ◽  
Uncatalyzed Reaction ◽  
Butyl Peroxide ◽  
Limiting Value ◽  
Induced Reaction

Silicon tetrafluoride accelerates the decomposition of di-tertiary butyl peroxide, the rate constant k n,x for a given pressure, n , of the peroxide rising with the fluoride pressure, x , to a limiting value k n ,∞ . This value is different for different values of n . The activation energy of the induced reaction is 27 ± 1 kcal compared with 37 kcal for the uncatalyzed reaction. The products are little different from those of the normal decomposition except that the ratio of methane to ethane is slightly increased. The order of effectiveness of fluorides is SiF 4 > SF 6 > CF 4 , the inverse order of the ease with which they should release fluorine atoms. Carbon tetrachloride causes acceleration comparable with that caused by the silicon fluoride with a much more drastic shift in the product ratios. The mechanism of these actions is discussed in relation to the extended theory of unimolecular reactions.

Vulcanization of Elastomers XV. The Vulcanization of Natural and Synthetic Rubber with Sulfur in Presence of Organic Bases (I)

1958 ◽  
Vol 31 (2) ◽  
pp. 286-300 ◽  
Author(s):  
Walter Schelle ◽  
Martin Cherubim
Keyword(s):  
Activation Energy ◽  
Fractional Order ◽  
Rate Constant ◽  
Kinetic Studies ◽  
Secondary Amines ◽  
Primary Amines ◽  
Sulfur Concentration ◽  
Organic Bases ◽  
Fractional Orders ◽  
Basic Strength

Abstract The results obtained from preliminary kinetic studies of the vulcanization of natural rubber (NR) with sulfur in the presence of organic bases may be summarized as follows. 1) The change of concentration of sulfur with time during reaction with NR for an initial sulfur concentration of 2.5 g per 100 g of mixture follows a fractional reaction order, n, of 0.6 at all temperatures. This result and the findings of other authors suggest that the reaction of sulfur with rubber is autocatalytic. From the temperature dependence of the rate constant the activation energy is found to be 35.3 kcal. 2) In the presence of zinc oxide and with a similar initial sulfur concentration, the reaction is first order and the activation energy, namely 35.6 kcal, is practically the same. 3) In the presence of diphenylguanidine (DPG) during cure sulfur decrease is a reaction of fractional order, n=0.75, and the activation energy is 29.8 kcal. 4) For a given initial concentration of sulfur and at constant temperature the rate of sulfur decrease during vulcanization increases with rising DPG content and reaches a limiting value; i.e., the rate constant depends on DPG concentration. Also, for various base (DPG is basic) concentrations sulfur decrease is of various fractional orders, n=0.5…0.7, etc. 5) The influence of base on the rate of sulfur decrease is interpreted broadly as a case of intermediate-catalysis (Zwischenstoff-Katalyse). 6) Vulcanization with sulfur is unaffected by tertiary amines and secondary amines have only a slight effect. 7) Primary amines, depending on basic strength, are strong accelerators of the rate of sulfur decrease. 8) In the presence of organic bases (aromatic amines) other than DPG, sulfur decrease is of fractional order where n varies between 0.5 and 0.7.

THE THERMAL DECOMPOSITION OF METHYL HYDROPEROXIDE

1965 ◽  
Vol 43 (8) ◽  
pp. 2236-2242 ◽  
Author(s):  
Alexander D. Kirk
Keyword(s):  
Activation Energy ◽  
Thermal Decomposition ◽  
Gas Phase ◽  
Rate Constants ◽  
Dimethyl Phthalate ◽  
Kcal Mole ◽  
First Order ◽  
Methyl Hydroperoxide ◽  
Expected Values ◽  
Homogeneous Decomposition

The thermal decomposition of methyl hydroperoxide has been studied in solution and in the gas phase. The decomposition was found to be partly heterogeneous in solution in dimethyl phthalate and no reliable rate constants were obtained. Use of the toluene carrier method for the gas phase work enabled measurement of the rate constant for the homogeneous decomposition. The first order rate constants obtained range from 0.19 s−1 at 292 °C to 1.5 s−1 at 378 °C, leading to log A, 11± 2, and activation energy, 32 ± 5 kcal/mole. These results are compared with the expected values of log A, 13–14, and activation energy, 42 kcal/mole. The significance of these findings is discussed.

THE REACTION OF CYCLOPENTANE VAPOR WITH Hg 6(3P1) ATOMS AT ELEVATED TEMPERATURES: THE RECOMBINATION, DISPROPORTIONATION, AND DECOMPOSITION OF CYCLOPENTYL RADICALS

1964 ◽  
Vol 42 (2) ◽  
pp. 357-370 ◽  
Author(s):  
Harry E. Gunning ◽  
Richard L. Stock
Keyword(s):  
Activation Energy ◽  
Thermal Decomposition ◽  
Elevated Temperatures ◽  
Arrhenius Plot ◽  
New Products ◽  
Reaction Vessel ◽  
Rate Data ◽  
Kcal Mole ◽  
Low Light ◽  
Ethylene Propylene

The static reaction of Hg 6(3P1) atoms with cyclopentane vapor (c-C5H10) has been studied with temperatures from 26 to 376°, at constant c-C5H10 concentration and at low light intensities.From 26 to 250°, the only important products are hydrogen, cyclopentene, and bicyclopentyl. Above 250° new products appearing are ethylene, biallyl, and allyl cyclopentane, together with smaller yields of propylene, ethane, propane, and methane. To 250°, the reaction can be explained in terms of a 5-step paraffinic sequence, involving initial C—H scission to form H atoms and cyclopentyl (c-C5H9) radicals. The Arrhenius plot of a function equal to kdisp/kcomb for c-C5H9 radicals showed that Edisp−Ecomb = 0. Above 250° c-C5H9 radicals decompose into C2H4 and C3H5 radicals. The activation energy for this process was determined from a number of product functions to be 36.9 ± 1.2 kcal/mole. Evidence was also found for scission of c-C5H9 into cyclopentene and H atoms, above ca. 300°.A brief examination was also made of the thermal decomposition of c-C5H10 up to 457° in a quartz reaction vessel. The substrate is unstable above 350° forming ethylene, propylene, cyclopentene, cyclopentadiene, and hydrogen. The rate data can be satisfactorily explained by two intramolecular decompositions of the substrate into (a) ethylene and propylene and (b) cyclopentene and hydrogen with the cyclopentene further dehydrogenating to cyclopentadiene. From the data Ea = 49.6 ± 2.0 kcal/mole and Eb = 44.0 ± 2.0 kcal/mole.

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