Mechanism of decarboxylation of substituted salicylic acids. I. Kinetics in quinoline solution

1968 ◽  
Vol 46 (18) ◽  
pp. 2905-2909 ◽  
Author(s):  
G. E. Dunn ◽  
E. G. Janzen ◽  
W. Rodewald
Keyword(s):  
Carbon Dioxide ◽  
Aromatic Ring ◽  
Rate Constants ◽  
Substituent Effect ◽  
The Other ◽  
Carboxyl Group ◽  
Isokinetic Relationship ◽  
First Order ◽  
Hammett Relationship ◽  
Salicylic Acids

First-order rate constants for the decarboxylation of fourteen 4- and 5-substituted salicylic acids have been determined in quinoline solution in the temperature range 90–230 °C. Substituents have almost no effect on the rate constants, except those with large negative σ-constants: p-amino, p-hydroxy, p-ethoxy. The enthalpies and entropies of activation do not fit the isokinetic relationship, with the same three substituents deviating. It is suggested that the decarboxylation involves a preliminary ionization of the carboxyl group, followed by protonation of the aromatic ring of the anion so formed, and then loss of carbon dioxide. The isokinetic relationship fails because substituents affect all three steps differently, and the Hammett relationship fails because the substituent effect on the ionization is related to σ while that on the other two steps follows σ+. The three substituents which deviate are those for which σ and σ+ differ widely.

The thermal decompositions of carbamates. I. Ethyl N-Methyl-N-phenylcarbamate

1971 ◽  
Vol 24 (12) ◽  
pp. 2541 ◽  
Author(s):  
NJ Daly ◽  
F Ziolkowski
Keyword(s):  
Carbon Dioxide ◽  
Gas Phase ◽  
Rate Constants ◽  
Volume Ratio ◽  
Reaction Vessel ◽  
First Order ◽  
Order Rate

Ethyl N-methyl-N-phenylcarbamate decomposes in the gas phase over the range 329-380� to give N-methylaniline, carbon dioxide, and ethylene. The reaction is quantitative, and is first order in the carbamate. First-order rate constants are described by the equation ������������������� k1 = 1012.44 exp(-45,380/RT) (s-1) and are unaffected by the addition of cyclohexene or by increase in the surface to volume ratio of the reaction vessel. The reaction is considered to be unimolecular and likely to proceed by means of a mechanism of the type represented by the pyrolyses of acetates, xanthates, and carbonates.

THE REACTION OF 2,2-DIPHENYL-1-PICRYLHYDRAZYL WITH SECONDARY AMINES

1958 ◽  
Vol 36 (12) ◽  
pp. 1729-1734 ◽  
Author(s):  
J. E. Hazell ◽  
K. E. Russell
Keyword(s):  
Secondary Amine ◽  
Rate Constants ◽  
Reaction Mechanisms ◽  
Hydrogen Abstraction ◽  
Activation Energies ◽  
Major Product ◽  
The Other ◽  
Secondary Amines ◽  
First Order ◽  
Kinetics Of

The reaction of DPPH (2,2-diphenyl-1-picrylhydrazyl) with N-phenyl-1-naphthylamine, N-phenyl-2-naphthylamine, diphenylamine, and methylaniline has been studied and has been shown to be primarily a hydrogen abstraction process. Two moles DPPH react with 1–1.15 moles secondary amine to give 1.7–1.8 moles 2,2-diphenyl-1-picrylhydrazine and further products.The reaction between DPPH and N-phenyl-1-naphthylamine is first order with respect to each reactant. The reaction of DPPH with the other amines is retarded by the major product 2,2-diphenyl-1-picrylhydrazine and the kinetics of the over-all reaction are complex. However second-order rate constants and activation energies have been obtained using initial rates of reaction. Possible reaction mechanisms are discussed.

Picosecond radical kinetics. Rate constants for ring openings of 2-aryl-substituted cyclopropylcarbinyl radicals

1999 ◽  
Vol 77 (5-6) ◽  
pp. 1123-1135 ◽  
Author(s):  
Martin Newcomb ◽  
Seung-Yong Choi ◽  
Patrick H Toy
Keyword(s):  
Aromatic Ring ◽  
Rate Constants ◽  
The Other ◽  
Radical Reactions ◽  
Methyl Radicals ◽  
Kinetic Methods ◽  
Mechanistic Probe ◽  
Radical Rearrangements ◽  
Kinetics Of

The kinetics of ring openings of a series of eight (trans-2-arylcyclopropyl)methyl radicals (1) were studied by indirect kinetic methods using Barton's PTOC esters as radical precursors and reaction with PhSeH as the competition reaction. The substituents were CF3, F, Me, and OMe located on both the para and meta positions of the aromatic ring. Syntheses of the radical precursors and the products of the radical reactions are described. Kinetics were determined between -43 and 25°C in four cases (CF3 and OMe substituents) and at 0 and 25°C in the other four cases. The rate constants at 25°C ranged from 1.0 × 1011 s-1 (p-CH3) to 4.1 × 1011 s-1 (p-CF3). The relatively large acceleration of the p-CF3 group, ca. 2.5 times as fast as the parent system with Ar = Ph, correlates well with Adam's ΔD substituent parameters but not with other radical substituent parameters. These calibrated radical rearrangements provide a new set of ultrafast reactions that can be applied in mechanistic probe studies.Key words: cyclopropylcarbinyl radical, kinetics, PTOC esters, benzeneselenol.

scholarly journals Quantitative analysis of proton-linked transport system. β-Galactoside exit in Escherichia coli

1980 ◽  
Vol 188 (2) ◽  
pp. 467-473 ◽  
Author(s):  
I R Booth ◽  
W A Hamilton
Keyword(s):  
Escherichia Coli ◽  
Quantitative Analysis ◽  
Transport System ◽  
Rate Constants ◽  
The Other ◽  
First Order ◽  
First Order Kinetics ◽  
Solute Accumulation ◽  
External Ph

The exit of lactose and thiomethyl-beta-D-galactoside from Escherichia coli ML308-225 has been studied to determine the role of carrier-dependent (zero-trans efflux) and carrier-independent (leak) processes. On the basis of its sensitivity to p-chloromercuribenzene sulphonate the exit of lactose was found to be almost wholly mediated by the carrier. Consistent with this conclusion was the finding that the rate of exit of this sugar was dependent on the external pH, being considerably slower at acid pH. On the other hand exit of thiomethyl-beta-D-galactoside was found to be composed of both carrier-dependent and carrier-independent processes. Both processes exhibited first-order kinetics with the rate constants for zero-trans efflux and leak being 0.137 min-1 and 0.079 min-1, respectively. The relevance of these findings for out earlier proposal for the methods of attenuation of solute accumulation is discussed [Booth, Mitchell & Hamilton (1979) Biochem. J. 182, 687–696].

scholarly journals Reaction Kinetics of Carbon Dioxide in Aqueous Diethanolamine Solutions Using the Stopped-Flow Technique

2012 ◽  
Vol 19 (1) ◽  
pp. 55-66 ◽  
Author(s):  
Marta Siemieniec ◽  
Hanna Kierzkowska-Pawlak ◽  
Andrzej Chacuk
Keyword(s):  
Carbon Dioxide ◽  
Reaction Kinetics ◽  
Rate Constants ◽  
Reaction Rate ◽  
Reaction Rate Constant ◽  
Stopped Flow ◽  
First Order ◽  
Pseudo First Order ◽  
Kinetics Of ◽  
Good Agreement

Reaction Kinetics of Carbon Dioxide in Aqueous Diethanolamine Solutions Using the Stopped-Flow Technique The pseudo-first-order rate constants (kOV) for the reactions between CO2 and diethanolamine have been studied using the stopped-flow technique in an aqueous solution at 293, 298, 303 and 313 K. The amine concentrations ranged from 167 to 500 mol·m-3. The overall reaction rate constant was found to increase with amine concentration and temperature. Both the zwitterion and termolecular mechanisms were applied to correlate the experimentally obtained rate constants. The values of SSE quality index showed a good agreement between the experimental data and the corresponding fit by the use of both mechanisms.

scholarly journals The interaction of microorganisms and the herbicides chlorthiamid and dichlobenil

1981 ◽  
Vol 53 (6) ◽  
pp. 341-390 ◽  
Author(s):  
Helvi Heinonen-Tanski
Keyword(s):  
Carbon Dioxide ◽  
Aromatic Ring ◽  
The Other ◽  
Arthrobacter Strain

The herbicides chlorthiamid and dichlobenil inhibited the growth of some actinomycetes in starch-casein medium. The effect of these herbicides on the other bacteria tested was insignificant. Chlorthiamid and dichlobenil arc slowly degradable herbicides. Bacteria such as Arthrobacter, unidentified coryneforms and Bacillus could degrade the herbicides by cometabolism. 2,6-Dichlorobenzamide, 2,6-dichlorobenzoic acid, carbon dioxide, chloride, a catechol compound and many unidentified compounds were found as metabolites. Arthrobacter strains capable for dechlorination could also cleave the aromatic ring, both processes occurring in aerated cultures. More than half of the chloride was liberated in three weeks at 28°C by the most active Arthrobacter strain.

Kinetics and mechanism of the decarboxylation of pyrimidine-2-carboxylic acid in aqueous solution

1977 ◽  
Vol 55 (13) ◽  
pp. 2478-2481 ◽  
Author(s):  
Gerald E. Dunn ◽  
Edward A. Lawler ◽  
A. Brian Yamashita
Keyword(s):  
Carbon Dioxide ◽  
Aqueous Solution ◽  
Carboxylic Acid ◽  
Rate Constants ◽  
Kinetics And Mechanism ◽  
First Order ◽  
Order Rate ◽  
Pseudo First Order ◽  
Positively Charged

Pseudo-first-order rate constants for the decarboxylation of pyrimidine-2-carboxylic acid have been determined at 65 °C in aqueous solution over the acidity range pH = 2 to H0 = −9.5. Rate constants increase rapidly from pH = 2 to H0 = −3, then remain constant. This behaviour can be accounted for by a Hammick-type mechanism in which monoprotonated pyrimidine-2-carboxylic acid loses carbon dioxide to form an ylide (stabilized by the adjacent positively charged nitrogens) which rapidly converts to pyrimidine.

Vulcanization of Elastomers. 12. Perbunan with Thiuram Monosulfide and Sulfur. I

1959 ◽  
Vol 32 (1) ◽  
pp. 128-138 ◽  
Author(s):  
Walter Scheele ◽  
Horst-Eckart Toussaint
Keyword(s):  
Activation Energy ◽  
Natural Rubber ◽  
Temperature Dependence ◽  
Induction Period ◽  
Rate Constants ◽  
The Other ◽  
Tetramethylthiuram Disulfide ◽  
First Order ◽  
The One ◽  
Limiting Value

Abstract The vulcanization of Perbunan 2818 by tetramethylthiuram monsulfide plus sulfur (1 mole monosulfide per gram-atom S) was thoroughly studied. The following results were shown: The limiting value for dithiocarbamate formation is 66 mole per cent of the initial thiuram monosulfide, indicating a two-thirds transformation. The limiting value is practically independent of temperature. The formation of dithiocarbamate can be described as a reaction of the first order. The formation of dithiocarbamate is characterized by an induction period which grows longer with lowering of the temperature, and at 100° C it amounts to about 100 minutes. The rate constants for dithiocarbamate formation were calculated, and it was shown that they were practically the same as those for the vulcanization of Perbunan with tetramethylthiuram disulfide. The activation energies as derived from the temperature dependence of the rate constants for dithiocarbamate formation in the vulcanization of Perbunan by thiuram monosulfide plus sulfur on the one hand and with thiuram disulfide on the other, are only very slightly different and are practically the same as the activation energy for dithiocarbamate formation during the vulcanization of natural rubber with thiuram monosulfide plus sulfur. The results were thoroughly discussed in light of the present conceptions of the course of thiuram vulcanizations.

THE REDUCTION OF NITROBENZENE BY HYDROSULPHIDE ION IN AQUEOUS MEDIA

1962 ◽  
Vol 40 (12) ◽  
pp. 2317-2328 ◽  
Author(s):  
O. J. Cope ◽  
R. K. Brown
Keyword(s):  
Reaction Time ◽  
Rate Constants ◽  
Aqueous Media ◽  
The Other ◽  
First Order ◽  
Order Dependence ◽  
Other Hand ◽  
Nitrobenzene Reduction ◽  
Autocatalytic Effect

The reduction of nitrobenzene by sodium hydrosulphide and sodium hydrodisulphide in aqueous media at 50° has been examined. Goldschmidt's report of first-order dependence upon both nitrobenzene and hydrosulphide is corroborated. The action of hydrosulphide on nitrobenzene produces phenylhydroxylamine, which is reduced by hydrosulphide much more slowly than is nitrobenzene. As reaction progresses, nitrobenzene reduction produces yellow hydrodisulphide, which is responsible for the observed autocatalytic effect. Hydrodisulphide reduces phenylhydroxylamine more rapidly than it does the original nitrobenzene, and hence as reaction time is extended, phenylhydroxylamine disappears more rapidly than does nitrobenzene, yielding only aniline and some unreacted nitrobenzene towards the end of the reaction. Hydrosulphide reduction of phenylhydroxylamine to aniline produces thiosulphate but apparently no hydrodisulphide. Hydrodisulphide reduction of the phenylhydroxylamine leads only to conversion of the yellow hydrodisulphide to a colorless species, apparently thiosulphate. On the other hand hydrosulphide or hydrodisulphide reduction of nitrobenzene is accompanied by thiosulphate formation and some increase in hydrodisulphide. A comparison of the rate constants shows that under the conditions of the reaction, hydrodisulphide ion reduces nitrobenzene about seven times more rapidly than does hydrosulphide ion while phenylhydroxylamine is reduced two to three times more rapidly by hydrodisulphide than is nitrobenzene.

Desorption rate of volatile compounds in polishing ponds

2011 ◽  
Vol 63 (6) ◽  
pp. 1177-1182
Author(s):  
Eudes M. Alves ◽  
Paula F. C. Cavalcanti ◽  
Adrianus van Haandel
Keyword(s):  
Carbon Dioxide ◽  
Experimental Investigation ◽  
Volatile Compounds ◽  
Rate Constants ◽  
Driving Force ◽  
Co2 Removal ◽  
Desorption Rate ◽  
Order Process ◽  
First Order ◽  
Co2 Desorption

Increase of pH in polishing ponds can be predicted quantitatively from variations in alkalinity and acidity. These variables are affected by processes that develop simultaneously in ponds: (1) CO2 desorption, (2) biological CO2 removal by photosynthesis and (3) NH3 desorption. An experimental investigation was carried out to determine the desorption rate of carbon dioxide and ammonium. It is shown that CO2 and NH3 desorption can be described by Fick’s law, which describes desorption of a gaseous compounds from water as a first order process with respect to the degree of oversaturation, which is the driving force of the process. An experimental investigation was carried out to determine the desorption rate constants. The value of the constant proved to be inversely proportional to the depth of the pond (H) and its value for H=1 m and at 26°C was established as KCO2=0.34/H d−1 for carbon dioxide and KNH3=0.33/H d−1 for ammonium.

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