SOLVOLYSIS OF ALKYL CHLOROSULFATES: PART I. REACTION OF n-PROPYL CHLOROSULFATE WITH NUCLEOPHILES

1965 ◽  
Vol 43 (3) ◽  
pp. 547-555 ◽  
Author(s):  
E. Buncel ◽  
J. P. Millington
Keyword(s):  
Aqueous Dioxane ◽  
Halide Ions ◽  
Leaving Group ◽  
Rate Of Reaction ◽  
Previous Proposal ◽  
Rate Of Hydrolysis ◽  
Hydrolysis Of ◽  
Chlorine Bond ◽  
Bimolecular Mechanism

The effect of various reagents on the rate of hydrolysis of n-propyl chlorosulfate in 10 M aqueous dioxane is reported. Halide ions increase the rate of reaction (I− > Br− > Cl−) but perchlorate is without effect. Hydroxide and pyrrolidine have a strong accelerating effect, but only at higher concentrations. These observations support a bimolecular mechanism: rate-determining displacement by nucleophile on carbon, with OSO2Cl− as the leaving group. The present results are not in accord with a previous proposal that alkyl chlorosulfates react by rate-determining sulfur–chlorine bond fission followed by fast displacement by nucleophile on carbon.

HYDROLYSIS OF A SERIES OF PRIMARY ALKYL CHLOROSULFATES: ENTROPY OF ACTIVATION AS A CRITERION OF FRAGMENTATION IN SOLVOLYTIC REACTIONS

1965 ◽  
Vol 43 (3) ◽  
pp. 556-564 ◽  
Author(s):  
E. Buncel ◽  
J. P. Millington
Keyword(s):  
Transition State ◽  
Multiple Bond ◽  
Aqueous Dioxane ◽  
Methyl Ethyl ◽  
Straight Chain ◽  
Leaving Group ◽  
Entropy Of Activation ◽  
Hydrolysis Of ◽  
Chlorine Bond

The solvolysis of the series of alkyl chlorosulfates, ROSO2Cl, where R = methyl, ethyl, n-propyl, isobutyl, and neopentyl, has been studied in 10 M aqueous dioxane. The relative reactivities fit well a solvolytic mechanism involving displacement by water on carbon, with OSO2Cl as the leaving group. The change in mechanism of solvolysis from bimolecular with the straight-chain chlorosulfates to unimolecular with neopentyl chlorosulfate is shown by the absence of the lyate ion effect and the observation of rearrangement in the latter case.The entropies of activation in chlorosulfate solvolysis appear to be abnormally large. It is proposed that the abnormal ΔS≠ indicates a transition state in which both carbon–oxygen and sulfur–chlorine bond weakening occurs. It is shown that some other solvolytic reactions that are characterized by abnormally high entropies of activation may be interpreted on the basis of multiple bond fission (fragmentation). The mechanism of SNi reactions is considered in this context.

THE CHEMISTRY OF ETHYLENE OXIDE: V. THE REACTION OF ETHYLENE OXIDE WITH HALIDE IONS IN NEUTRAL AND ACID SOLUTION

1952 ◽  
Vol 30 (3) ◽  
pp. 169-176 ◽  
Author(s):  
A. M. Eastham ◽  
G. A. Latremouille
Keyword(s):  
Aqueous Solution ◽  
Ethylene Oxide ◽  
Acid Solution ◽  
Activation Energies ◽  
Hydrogen Halide ◽  
Halide Ions ◽  
Neutral Aqueous Solution ◽  
Rate Of Hydrolysis ◽  
Acid Catalyzed ◽  
Hydrolysis Of

The rates of reaction of halide ions with ethylene oxide in neutral aqueous solution and the rate of hydrolysis of ethylene oxide in acid solution have been measured and the activation energies determined. From these data and from the ratio of glycol to chlorohydrin formed when ethylene oxide reacts with excess aqueous hydrogen halide, the rates of the acid-catalyzed addition of halide ions to ethylene oxide at 25 °C. have been estimated.

Kinetics of the hydrolysis of acyl chlorides in pure water

1967 ◽  
Vol 45 (14) ◽  
pp. 1619-1629 ◽  
Author(s):  
A. Queen
Keyword(s):  
Pure Water ◽  
Activation Parameters ◽  
Acyl Chlorides ◽  
Reversible Addition ◽  
Electron Donation ◽  
Kinetics Of ◽  
Hydrolysis Of ◽  
Chlorine Bond ◽  
Oxygen Bond ◽  
Bimolecular Mechanism

The activation parameters ΔH≠, ΔS≠, and ΔCP≠ for the hydrolyses of a series of alkyl chloroformates and dimethylcarbamyl chloride in water have been determined. The results indicate that, with increasing electron donation to the chlorocarbonyl group, the mechanism changes from bimolecular to unimolecular (SN1) displacement at this position. For isopropyl chloroformate, some concurrent alkyl–oxygen bond fission is also indicated. The bimolecular mechanism involves reversible addition of water to the carbonyl group followed by ionization of the carbon–chlorine bond.

scholarly journals The mechanism of the solvolysis of p-methoxybenzyl chloride in aqueous acetone containing pyridine or thiourea. Evidence for concurrent substitution by unimolecular and bimolecular processes

1979 ◽  
Vol 57 (19) ◽  
pp. 2646-2651 ◽  
Author(s):  
Alan Queen
Keyword(s):  
Aqueous Acetone ◽  
Rate Of Reaction ◽  
Rate Of Hydrolysis ◽  
Hydrolysis Of

The overall rate of reaction of p-methoxybenzyl chloride with 70% aqueous acetone is increased by the addition of pyridine but the rate of hydrolysis is decreased. Comparison of these data with those for benzhydryl chloride under the same conditions shows that the rate of hydrolysis of p-methoxybenzyl chloride is less than the rate of ionisation. These results are discussed in terms of concurrent operation of the SN1 mechanism and a bimolecular process. Similar results are obtained when thiourea is used instead of pyridine.

Solvolysis of Sulphonyl Halides. IV. The Hydrolysis of Some Substituted Aliphatic Sulphonyl Chlorides and of Ethanesulphonyl Bromide in Aqueous Dioxan

1962 ◽  
Vol 15 (4) ◽  
pp. 684 ◽  
Author(s):  
R Foon ◽  
AN Hambly
Keyword(s):  
Maximum Rate ◽  
Pure Water ◽  
Aqueous Media ◽  
Sulphur Atom ◽  
Enthalpy Of Activation ◽  
Rate Of Hydrolysis ◽  
Hydrolysis Of ◽  
Chlorine Bond ◽  
Transition Complexes ◽  
Continuous Range

The effects of substitution in the alkyl group of an alkanesulphonyl chloride, on the rate of hydrolysis, vary with the solvent composition. The relative rates can be explained in terms of the theory of Grunwald and Winstein that there is a continuous range of transition complexes, with " bond making " between the water molecule and the sulphur atom controlling the rate in the less aqueous media, while the stretching and charging of the sulphur to chlorine bond controls the rate in solvents of higher water content. The inhibition of the simple SN2 reaction, which gives rise to a maximum rate constant as the composition of the solvent approaches pure water, resembles that noted with methane- and ethanesulphonyl chlorides.�The hydrolysis of ethanesulphonyl bromide, at 25 �C, proceeds at three to eight times the rate for the corresponding sulphonyl chloride in solvents varying in composition from 0.99 to 0.2 mole fraction of water with dioxan. Over most of the solvent range both the entropy and enthalpy of activation are favourable to a higher rate of solvolysis for the sulphonyl bromide.

Electrostatic, Polar, and steric factors in the Acid Hydrolysis of the Dipeptides

1957 ◽  
Vol 10 (3) ◽  
pp. 256 ◽  
Author(s):  
RJL Martin
Keyword(s):  
Carbon Atom ◽  
Water Molecule ◽  
Peptide Bond ◽  
Bimolecular Reaction ◽  
Carbonyl Carbon Atom ◽  
Rate Of Reaction ◽  
Steric Factors ◽  
Rate Of Hydrolysis ◽  
Reaction With Water ◽  
Hydrolysis Of

Published kinetic data concerning the rates of hydrolysis of dipeptides are discussed and interpreted in terms of the expected electrostatic, polar, and steric influences of the constituent groups. The evidence is consistent with a reaction mechanism in which a proton is first added reversibly to the peptide nitrogen, and the amide cation so formed reacts at the carbonyl carbon atom with a water molecule in a rate-controlling bi molecular substitution. Substitution at the glycyl carbon atom of the parent substance glycylglycine will alter the steric hindrance to substitution by the water molecule. On the other hand, the polar effect of these substituents will be small and will have little influence on the rate of reaction. Substituents at the glycine carbon atom introduce polar factors only with little evidence of steric effects. This absence of a steric effect applies both to the formation of the amide cation and to the substitution by the water. Electron repelling groups decrease the rate of hydrolysis and must be considered to have a greater effect on decreasing the electron accession to the peptide nitrogen necessary for the rupture of the bend than on increasing the concentration of the amide cation. Electron attracting substituents act in the reverse manner. There is some evidence for a small amount of steric compression between groups on either side of the peptide bond for the bimolecular reaction with water.

Substituent Effects on the Micelle-Catalysed and Uncatalysed Basic Hydrolysis of a Series of Substituted N-Methyl-p-toluanilides

1979 ◽  
Vol 32 (8) ◽  
pp. 1717 ◽  
Author(s):  
TJ Broxton ◽  
NW Duddy
Keyword(s):  
Substituent Effects ◽  
Cationic Micelles ◽  
Mechanism Of Reaction ◽  
Rate Of Reaction ◽  
Hammett Correlation ◽  
Rate Of Hydrolysis ◽  
Linear Plot ◽  
Basic Hydrolysis ◽  
Hydrolysis Of ◽  
Reaction In Water

The rate of hydrolysis of a series of substituted N-methyl-p-toluanilides has been measured in water and in the presence of cationic micelles [cetyltrimethylammonium bromide (ctab)]. A Hammett correlation of the rates of hydrolysis gave a curved Hammett plot for the reaction in water (k2,W) but a linear plot for the rate of reaction at optimal concentrations of ctab (k2,max) and for derived rate constants within the micelle (k2,m) These results are discussed in terms of the mechanism of reaction, and for two compounds a micelle-induced change of mechanism is indicated.

The Effects of Amines on the Esterase Activities of Thrombin and Thrombokinase and on Several Clotting Tests

1974 ◽  
Vol 31 (02) ◽  
pp. 309-318
Author(s):  
Phyllis S Roberts ◽  
Raphael M Ottenbrite ◽  
Patricia B Fleming ◽  
James Wigand
Keyword(s):  
Choline Chloride ◽  
Polymerization Process ◽  
Ammonium Bromide ◽  
Bovine Thrombin ◽  
One Stage ◽  
Human Proteins ◽  
Rate Of Hydrolysis ◽  
The One ◽  
Hydrolysis Of Esters ◽  
Hydrolysis Of

Summary1. Choline chloride, 0.1 M (in 0.25 M Tris. HCl buffer, pH 7.4 or 8.0, 37°), doubles the rate of hydrolysis of TAME by bovine thrombokinase but has no effect on the hydrolysis of this ester by either human or bovine thrombin. Only when 1.0 M or more choline chloride is present is the hydrolysis of BAME by thrombokinase or thrombin weakly inhibited. Evidence is presented that shows that these effects are due to the quaternary amine group.2. Tetramethyl ammonium bromide or chloride has about the same effects on the hydrolysis of esters by these enzymes as does choline chloride but tetra-ethyl, -n.propyl and -n.butyl ammonium bromides (0.1 M) are stronger accelerators of the thrombokinase-TAME reaction and they also accelerate, but to a lesser degree, the thrombin-TAME reaction. In addition, they inhibit the hydrolysis of BAME by both enzymes. Their effects on these reactions, however, do not follow any regular order. The tetraethyl compound is the strongest accelerator of the thrombokinase-TAME reaction but the tetra-ethyl and -butyl compounds are the strongest accelerators of the thrombin-TAME reaction. The ethyl and propyl compounds are the best (although weak) inhibitors of the thrombokinase-BAME and the propyl compound of the thrombin-BAME reactions.3. Tetra-methyl, -ethyl, -n.propyl and -n.butyl ammonium bromides (0.01 M) inhibit the clotting of fibrinogen by thrombin (bovine and human proteins) at pH 7.4, imidazole or pH 6.1, phosphate buffers and they also inhibit, but to a lesser degree, a modified one-stage prothrombin test. In all cases the inhibition increases regularly as the size of the alkyl group increases from methyl to butyl. Only the ethyl com pound (0.025 M but not 0.01 M), however, significantly inhibits the polymerization of bovine fibrin monomers. It was concluded that inhibition of the fibrinogen-thrombin and the one-stage tests by the quaternary amines is not due to any effect of the com pounds on the polymerization process but probably due to inhibition of thrombin’s action on fibrinogen by the quaternary amines.

The effect of polymeric and model imidazolium halides on the rate of hydrolysis of 4-acetoxy-3-nitrobenzoic acid

1985 ◽  
Vol 50 (4) ◽  
pp. 845-853 ◽  
Author(s):  
Miloslav Šorm ◽  
Miloslav Procházka ◽  
Jaroslav Kálal
Keyword(s):  
Catalyst Concentration ◽  
Low Molecular Weight ◽  
Imidazolium Chloride ◽  
First Order ◽  
Nitrobenzoic Acid ◽  
Rate Of Hydrolysis ◽  
Acid Catalyzed ◽  
Hydrolysis Of ◽  
Ethanol In Water ◽  
Direct Attack

The course of hydrolysis of an ester, 4-acetoxy-3-nitrobenzoic acid catalyzed with poly(1-methyl-3-allylimidazolium bromide) (IIa), poly[l-methyl-3-(2-propinyl)imidazolium chloride] (IIb) and poly[l-methyl-3-(2-methacryloyloxyethyl)imidazolium bromide] (IIc) in a 28.5% aqueous ethanol was investigated as a function of pH and compared with low-molecular weight models, viz., l-methyl-3-alkylimidazolium bromides (the alkyl group being methyl, propyl, and hexyl, resp). Polymers IIb, IIc possessed a higher activity at pH above 9, while the models were more active at a lower pH with a maximum at pH 7.67. The catalytic activity at the higher pH is attributed to an attack by the OH- group, while at the lower pH it is assigned to a direct attack of water on the substrate. The rate of hydrolysis of 4-acetoxy-3-nitrobenzoic acid is proportional to the catalyst concentration [IIc] and proceeds as a first-order reaction. The hydrolysis depends on the composition of the solvent and was highest at 28.5% (vol.) of ethanol in water. The hydrolysis of a neutral ester, 4-nitrophenyl acetate, was not accelerated by IIc.

Kinetics of hydrolysis of peroxodisulphate ions in acidic medium to peroxomonosulphuric acid

1981 ◽  
Vol 46 (5) ◽  
pp. 1229-1236 ◽  
Author(s):  
Jan Balej ◽  
Milada Thumová
Keyword(s):  
Ionic Strength ◽  
Rate Constants ◽  
Acidic Medium ◽  
Measured Data ◽  
Molar Ratios ◽  
Starting Solution ◽  
Kinetics Of Hydrolysis ◽  
Rate Of Hydrolysis ◽  
Kinetics Of ◽  
Hydrolysis Of

The rate of hydrolysis of S2O82- ions in acidic medium to peroxomonosulphuric acid was measured at 20 and 30 °C. The composition of the starting solution corresponded to the anolyte flowing out from an electrolyser for production of this acid or its ammonium salt at various degrees of conversion and starting molar ratios of sulphuric acid to ammonium sulphate. The measured data served to calculate the rate constants at both temperatures on the basis of the earlier proposed mechanism of the hydrolysis, and their dependence on the ionic strength was studied.

Sign in / Sign up

Export Citation Format

Share Document