The reactivity of p-nitrophenyl esters with surfactants in nonaqueous solvents. II. The effects of added water in benzene solutions of dodecylammonium propionate, and the reaction in toluene and cyclohexane

1980 ◽  
Vol 33 (4) ◽  
pp. 771 ◽  
Author(s):  
CJ O'Conner ◽  
RE Ramage
Keyword(s):  
Rate Constant ◽  
Rate Equation ◽  
Surfactant Concentration ◽  
Nonaqueous Solvents ◽  
Base Catalysis ◽  
Head Group ◽  
Bimolecular Rate Constant ◽  
General Base ◽  
Head Groups ◽  
Added Water

The rate of decomposition of p-nitrophenyl acetate, pnpa, in benzene containing up to 0.11 mol dm-3 of solubilized water in the presence of dodecylammonium propionate, dap, has been measured at 298 K. Although the micellar rate constant is decreased due to hydration of the head- groups, the bimolecular rate constant due to general acid-general base catalysis from the head-group components of dap is unchanged. There is no evidence to suggest that the substrate undergoes hydrolysis. Changing the solvent to either toluene or cyclohexane increases the micellar rate constant and changes the second term in the rate equation to one which includes the square of the surfactant concentration.

The reactivity of p-nitrophenyl esters with surfactants in nonaqueous solvents. III. The effect of altering the head-groups of alkylammonium carboxylates dissolved in benzene

1980 ◽  
Vol 33 (4) ◽  
pp. 779 ◽  
Author(s):  
CJ O'Conner ◽  
RE Ramage
Keyword(s):  
Chain Length ◽  
Rate Constant ◽  
Alkyl Chain ◽  
Alkyl Chain Length ◽  
Nonaqueous Solvents ◽  
Bimolecular Rate Constant ◽  
Head Groups

The rate of decomposition of p-nitrophenyl acetate, pnpa, has been measured in benzene solutions of a series of alkylammonium propionates, CH3(CH2),NH3+ -O2CCH2CH3 (where n = 3, 5, 7, 9 or 11), and a series of dodecylammonium carboxylates, CH3(CH2)11NH3+ -O2C(CH2)mCH3 where m = 1, 2, 6 or 7). The micellar rate constant is affected by the alkyl chain length. The bimolecular rate constant is affected by both the chain length and the acidity of the head-groups. The reactivity of longer chain esters with dodecylammonium propionate is markedly less than that of pnpa.

The mechanisms of hydrolysis of alkyl N-alkylthioncarbamate esters at 100 °C

2005 ◽  
Vol 83 (9) ◽  
pp. 1483-1491 ◽  
Author(s):  
Eduardo Humeres ◽  
Maria de Nazaré M. Sanchez ◽  
Conceição ML Lobato ◽  
Nito A Debacher ◽  
Eduardo P. de Souza
Keyword(s):  
Rate Constant ◽  
Order Rate Constant ◽  
Base Catalysis ◽  
Hydrolysis Rate ◽  
Negative Slope ◽  
General Base ◽  
Order Rate ◽  
Basic Hydrolysis ◽  
Rate Profile ◽  
Hydrolysis Of

The hydrolysis of ethyl N-ethylthioncarbamate (ETE) at 100 °C was studied in the range of 7 mol/L HCl to 4 mol/L NaOH. The pH–rate profile showed that the hydrolysis occurred through specific acid catalysis at pH < 2, spontaneous hydrolysis at pH 2–6.5, and specific basic catalysis at pH > 6.5. The Hammett acidity plot and the excess acidity plot against X were linear. The Bunnett–Olsen plot gave a negative slope indicating that the conjugate acid was less hydrated than the neutral substrate. It was concluded that the acid hydrolysis occurred by an A1 mechanism. The neutral species hydrolyzed with general base catalysis shown by the Brønsted plot with β = 0.48 ± 0.04. Water acted as a general base catalyst with (pseudo-)first-order rate constant, kN = 3.06 × 10–7 s–1. At pH > 6.5 the rate constants increased, reaching a plateau at high basicity. The basic hydrolysis rate constant of ethyl N,N-diethylthioncarbamate, which must react by a BAc2 mechanism, increased linearly at 1–3 mol/L NaOH with a second-order rate constant, k2 = 2.3 × 10–4 (mol/L)–1 s–1, which was 10 times slower than that expected for ETE. Experiments of ETE in 0.6 mol/L NaOH with an excess of ethylamine led to the formation of diethyl thiourea, presenting strong evidence that the basic hydrolysis occurred by the E1cb mechanism. In the rate-determining step, the E1cb mechanism involved the elimination of ethoxide ion from the thioncarbamate anion, producing an isothiocyanate intermediate that decomposed rapidly to form ethylamine, ethanol, and COS.Key words: alkylthioncarbamate esters, ethyl N-ethylthioncarbamate, ethyl N,N-diethylthioncarbamate, hydrolysis, mechanism.

The reactivity of p-nitrophenyl esters with surfactants in apolar solvents. VI. Structural effects on the reaction of p-nitrophenyl acetate with alkanediamine bis(dodecanoate) salts

1983 ◽  
Vol 36 (5) ◽  
pp. 907 ◽  
Author(s):  
CJ O'Conner ◽  
TD Lomax
Keyword(s):  
Chain Length ◽  
Rate Constant ◽  
Structural Effects ◽  
Detergent Concentration ◽  
Bimolecular Rate Constant ◽  
Head Groups

The rate of decomposition of p-nitrophenyl acetate has been measured in benzene solutions of a series of alkane-α,ω-diamine bis(dodecanoate) salts. Me(CH2)10CO2-+NH3(CH2)NH3N+ -O2C(CH2)10ME(n=2-7,9,10,12) The micellar rate constant is affected by the diamine chain length, and the bimolecular rate constant is affected both by the chain length (and whether the number of carbon atoms is even or odd) and by the acidity of the diammonium head groups. The Br�nsted plot is linear but the slope in creases with increasing detergent concentration.

The reactivity of p-nitrophenyl esters with surfactants in apolar solvents. VII. Substituent effects on the reactivity of 4'-nitrophenyl 4-substituted benzoates in benzene solutions of dodecylammonium propionate and butane-1,4-diamine bis(dodecanoate)

1983 ◽  
Vol 36 (5) ◽  
pp. 917 ◽  
Author(s):  
CJ O'Conner ◽  
TD Lomax
Keyword(s):  
Substituent Effects ◽  
Base Catalysis ◽  
Head Group ◽  
Rate Data ◽  
Linear Free Energy Relationships ◽  
Carbonyl Carbon ◽  
General Base ◽  
Linear Free Energy ◽  
General Acid ◽  
Energy Relationships

The rate of decomposition of a series of 4'-nitrophenyl 4-substituted benzoates has been measured at 341 K in benzene solutions of dodecylammonium propionate and butane-1,4-diamine bis-(dodecanoate). The bimolecular rate constant due to general acid-general base catalysis from the head-group components of the surfactants is dependent on the nature of the substituents, and the rate data have been correlated by Hammett σ and σ+, Tsuno-Yukawa, and Taft dual substituent parameter linear free energy relationships. The reactivity of the esters has also been compared with the 13C n.m.r. chemical shift of their carbonyl carbon atoms. The results are consistent with a mechanism involving a general-acid-catalysed aminolysis of the unprotonated ester.

scholarly journals Reactions of l-ergothioneine and some other aminothiones with 2,2′- and 4,4′-dipyridyl disulphides and of l-ergothioneine with iodoacetamide. 2-Mercaptoimidazoles, 2- and 4-thiopyridones, thiourea and thioacetamide as highly reactive neutral sulphur nucleophiles

1974 ◽  
Vol 139 (1) ◽  
pp. 221-235 ◽  
Author(s):  
Jan Carlsson ◽  
Marek P. J. Kierstan ◽  
Keith Brocklehurst
Keyword(s):  
Transition State ◽  
Isotope Effect ◽  
Rate Constant ◽  
Order Rate Constant ◽  
Base Catalysis ◽  
The Other ◽  
Deuterium Isotope Effect ◽  
General Base ◽  
Nucleophilic Reactivity ◽  
Ph Range

1. The reactions of 2,2′- and 4,4′-dipyridyl disulphide (2-Py–S–S–2-Py and 4-Py–S–S–4-Py) with l-ergothioneine (2-mercapto-l-histidine betaine), 2-mercaptoimidazole, 1-methyl-2-mercaptoimidazole, thiourea, thioacetamide, 2-thiopyridone (Py–2-SH) and 4-thiopyridone (Py–4-SH) were investigated spectrophotometrically in the pH range approx. 1–9. 2. These reactions involve two sequential reversible thiol–disulphide interchanges. 3. The reaction of l-ergothioneine with 2-Py–S–S–2-Py and/or with the l-ergothioneine–Py–2-SH mixed disulphide, both of which provide Py–2-SH, is characterized by at least three reactive protonic states. This provides definitive evidence that neutral l-ergothioneine is a reactive nucleophile, particularly towards the highly electrophilic protonated disulphides. 4. A similar situation appears to obtain in the reactions of l-ergothioneine and Py–2-SH with 4-Py–S–S–4-Py and in the reactions of the other 2-mercaptoimidazoles, thiourea and Py–4-SH with 2-Py–S–S–2-Py. The nucleophilic reactivity of Py–4-SH suggests that general base catalysis provided by the disulphide in a cyclic or quasi-cyclic transition state is not necessary to generate nucleophilic reactivity in the other amino-thiones whose geometry could permit such catalysis. 5. The existence of a positive deuterium isotope effect in the l-ergothioneine–2-Py–S–S–2-Py system at pH6–7 provides no evidence for general base catalysis but is in accord with a mechanism involving specific acid catalysis and post-transition-state proton transfer. 6. The pH-dependences of the overall equilibrium positions of the various thiol–disulphide interchanges are described. 7. Reaction of thioacetamide with a stoicheiometric quantity of 2-Py–S–S–2-Py at pH1 provides 2 molecules of Py–2-SH per molecule of thioacetamide and elemental sulphur; these findings can be accounted for by thiol–disulphide interchange to provide a thioacetamide–Py–2-SH mixed disulphide followed by fragmentation to provide CH3CN, S and Py–2-SH. 8. Provision of high reactivity in the neutral forms of the members of this series of sulphur nucleophiles by electron donation by the amino group is compared with the well known α effect that provides enhanced nucleophilicity in compounds containing an electronegative atom adjacent to the nucleophilic atom. 9. The decrease in the u.v. absorption of l-ergothioneine at 257nm consequent on transformation of its aminothione moiety into an S-alkyl-2-mercaptoimidazole moiety provides a convenient method of following the alkylation of l-ergothioneine by iodoacetamide. 10. The pH dependence of the extinction coefficient of l-ergothioneine at 257nm is described by ε257={8×103/(1+Ka/[H+]} +6×103m−1·cm−1 in which pKa=10.8. 11. In the pH range 3–11 the reaction is characterized by two reactive protonic states (X and XH). 12. The X state, reaction of the ionized 2-mercaptoimidazole moiety of the l-ergothioneine dianion with neutral iodoacetamide, is characterized by the second-order rate constant 4.0m−1·s−1 (25.0°C, I=0.05). The XH state, characterized by the second-order rate constant 0.03m−1·s−1, is interpreted as reaction of the thione form of the neutral 2-mercaptoimidazole moiety of the l-ergothioneine monoanion with neutral iodoacetamide. 13. The XH state of the alkylation reaction does not exhibit a deuterium isotope effect.

Kinetics of cyclization of S-ethoxycarbonylmethylisothiouronium chloride to 2-imino-4-thiazolidone

1979 ◽  
Vol 44 (3) ◽  
pp. 912-917 ◽  
Author(s):  
Vladimír Macháček ◽  
Said A. El-bahai ◽  
Vojeslav Štěrba
Keyword(s):  
Hydrochloric Acid ◽  
Dilute Hydrochloric Acid ◽  
Base Catalysis ◽  
General Base ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Kinetics Of Formation ◽  
Acid Catalyzed ◽  
Rate Limiting ◽  
Kinetics Of

Kinetics of formation of 2-imino-4-thiazolidone from S-ethoxycarbonylmethylisothiouronium chloride has been studied in aqueous buffers and dilute hydrochloric acid. The reaction is subject to general base catalysis, the β value being 0.65. Its rate limiting step consists in acid-catalyzed splitting off of ethoxide ion from dipolar tetrahedral intermediate. At pH < 2 formation of this intermediate becomes rate-limiting; rate constant of its formation is 2 . 104 s-1.

Mechanism of hydration and isomerisation of 4-ethylidene-2,6-di-tert-butyl-2,5-cyclohexadien-1-one. Kinetics, acid-base catalysis and solvent deuterium isotope effects

1979 ◽  
Vol 44 (1) ◽  
pp. 110-122 ◽  
Author(s):  
Jiří Velek ◽  
Bohumír Koutek ◽  
Milan Souček
Keyword(s):  
Aqueous Medium ◽  
Rate Equation ◽  
Kinetic Data ◽  
Isotope Effects ◽  
Base Catalysis ◽  
Quinone Methide ◽  
Reaction Products ◽  
Acid Base ◽  
Deuterium Isotope Effects ◽  
Hydroxybenzyl Alcohol

Competitive hydration and isomerisation of the quinone methide I at 25 °C in an aqueous medium in the region of pH 2.4-13.0 was studied spectrophotometrically. The only reaction products in the studied range of pH are 4-hydroxybenzyl alcohol (II) and 4-hydroxystyrene (III). The form of the overall rate equation corresponds to a general acid-base catalysis. The mechanism of both reactions for three markedly separated pH regions is discussed on the basis of kinetic data and solvent deuterium effect.

Evidence for general base catalysis by protic solvents in a kinetic study of alcoholyses and hydrolyses of 1-(phenoxycarbonyl)pyridinium ions under both solvolytic and non-solvolytic conditions

2009 ◽  
Vol 74 (1) ◽  
pp. 43-55 ◽  
Author(s):  
Dennis N. Kevill ◽  
Byoung-Chun Park ◽  
Jin Burm Kyong
Keyword(s):  
Second Order ◽  
Base Catalysis ◽  
Substitution Reactions ◽  
Third Order ◽  
Methoxy Derivative ◽  
First Order ◽  
General Base ◽  
Protic Solvents ◽  
Kinetics Of ◽  
Pyridinium Ions

The kinetics of nucleophilic substitution reactions of 1-(phenoxycarbonyl)pyridinium ions, prepared with the essentially non-nucleophilic/non-basic fluoroborate as the counterion, have been studied using up to 1.60 M methanol in acetonitrile as solvent and under solvolytic conditions in 2,2,2-trifluoroethan-1-ol (TFE) and its mixtures with water. Under the non- solvolytic conditions, the parent and three pyridine-ring-substituted derivatives were studied. Both second-order (first-order in methanol) and third-order (second-order in methanol) kinetic contributions were observed. In the solvolysis studies, since solvent ionizing power values were almost constant over the range of aqueous TFE studied, a Grunwald–Winstein equation treatment of the specific rates of solvolysis for the parent and the 4-methoxy derivative could be carried out in terms of variations in solvent nucleophilicity, and an appreciable sensitivity to changes in solvent nucleophilicity was found.

scholarly journals Exchange Speed of Four-Component Nanorotors Correlates with Hammett Substituent Constants

Chemistry ◽  
2021 ◽  
Vol 3 (1) ◽  
pp. 116-125
Author(s):  
Yi-Fan Li ◽  
Amit Ghosh ◽  
Pronay Kumar Biswas ◽  
Suchismita Saha ◽  
Michael Schmittel
Keyword(s):  
Linear Correlation ◽  
Bond Cleavage ◽  
Head Group ◽  
Ligand Interaction ◽  
Exchange Frequency ◽  
Rate Determining Step ◽  
Head Groups ◽  
Substituent Constants ◽  
First Time ◽  
Determining Factor

Three distinct four-component supramolecular nanorotors were prepared, using, for the first time, bipyridine instead of phenanthroline stations in the stator. Following our established self-sorting protocol to multicomponent nanodevices, the nanorotors were self-assembled by mixing the stator, rotators with various pyridine head groups, copper(I) ions and 1,4-diazabicyclo[2.2.2]octane (DABCO). Whereas the exchange of a phenanthroline vs. a bipyridine station did not entail significant changes in the rotational exchange frequency, the para-substituents at the pyridine head group of the rotator had drastic consequences on the speed: 4-OMe (k298 = 35 kHz), 4-H (k298 = 77 kHz) and 4-NO2 (k298 = 843 kHz). The exchange frequency (log k) showed an excellent linear correlation with both the Hammett substituent constants and log K of the copper(I)–ligand interaction, proving that rotator–copper(I) bond cleavage is the key determining factor in the rate-determining step.

Sign in / Sign up

Export Citation Format

Share Document