Kinetic studies on the mechanism of the nitraminopyridine rearrangement

1982 ◽  
Vol 35 (10) ◽  
pp. 2035 ◽  
Author(s):  
LW Deady ◽  
OL Korytsky
Keyword(s):  
Sulfuric Acid ◽  
Rate Constants ◽  
Kinetic Studies ◽  
Current Evidence ◽  
Rate Data ◽  
Rate Determining Step

Rate data are reported for the rearrangement, in 92% sulfuric acid at 30�, of a series of 4-X-2-nitra-minopyridines (X = H, Me, Br, CI, MeO, CO2H) and of 4-methyl-2-nitramino(3-D)pyridine. Values of pKa for second protonation of the corresponding pyridin-2-amines were also measured and rate constants for nitration of the monoprotonated pyridinamines were thereby calculated. The results suggest that the rate-determining step occurs prior to formation of the appropriate 3-and 5-nitro σ complexes. The nature of this step is not clear, however, and a key role for the nitramine itself is not proven by the current evidence.

Substituent Effects on the Hydrolysis of p-Substituted Benzonitriles in Sulfuric Acid Solutions at (25.0± 0.1) °C

2008 ◽  
Vol 63 (9) ◽  
pp. 603-608 ◽  
Author(s):  
Khamis A. Abbas
Keyword(s):  
Sulfuric Acid ◽  
Rate Constants ◽  
Inductive Effect ◽  
Substituent Effects ◽  
Acid Solutions ◽  
Rate Determining Step ◽  
Inductive Effects ◽  
High Concentrations ◽  
Sulfuric Acid Solutions ◽  
Hydrolysis Of

The rate constants of the hydrolysis of p-substituted benzonitriles with sulfuric acid solutions (18.2 M to 10 M) have been determined spectrophotometrically at (25.1±0.1) °C. It was found that the catalytic activity of sulfuric acid was strongly inhibited by water. The logarithms of the observed rate constants were correlated with different substituent inductive (localized) and resonance (delocalized) constants. The results of the correlation studies indicated that the rate-determining step of the hydrolysis of benzonitriles in 18.2 M sulfuric acid was the addition of a nucleophile, and the hydrolysis was clearly enhanced by the electron-withdrawing inductive effect, while the rate-determining step of the hydrolysis of p-substituted benzonitriles in 10.0 M sulfuric acid was most probably the protonation of benzonitriles, and the rate constants increased by both electron-donating resonance and inductive effects. A mixture of the two mechanisms most probably occurred in 15.3 to 17.0 M sulfuric acid. HSO4 − rather thanwater most probably acted as nucleophile in the hydrolysis of benzonitriles especially at high concentrations of sulfuric acid solutions.

KINETIC STUDIES OF PROTON TRANSFER FROM PHENOLS TO TRINITROBENZYL ANION

1966 ◽  
Vol 44 (2) ◽  
pp. 119-124 ◽  
Author(s):  
J. A. Blake ◽  
M. J. B. Evans ◽  
K. E. Russell
Keyword(s):  
Proton Transfer ◽  
Rate Constants ◽  
Dissociation Constants ◽  
Kinetic Studies ◽  
Sodium Cation ◽  
Rate Determining Step ◽  
Rate Of Reaction ◽  
Hammett Relationship ◽  
Measurable Concentration ◽  
Acetic Acids

The rates of reaction of various phenols with the 2,4,6-trinitrobenzyl anion in the solvent ethanol have been determined by a spectrophotometric method. The rate constants at −40 °C are related to the dissociation constants of the phenols in water at 25 °C and the value of α in the Brönsted relation is 0.84 ± 0.07; α drops to 0.44 ± 0.05 if the results for the substituted acetic acids (1) are included. The rate constants for the phenols are also correlated by the Hammett relationship, the ρ value at −40 °C being 1.82 ± 0.2. The activation energies range from 9.4 to 10.9 kcal/mole.The rate of reaction of trinitrobenzyl anion with 3-methylphenol at −30 °C is reduced by a factor of 12 if the phenol is deuterated at the OH group and the solvent is deuteroethanol. The large isotope effect confirms that the rate-determining step involves proton transfer from the OH group of the phenol. Substitution of lithium or potassium cations for the sodium cation does not affect the rate constant at −10 °C.In the reaction with 3-methylphenol, a measurable concentration of trinitrobenzyl anion remains at equilibrium and the equilibrium constant for the reaction is 1.3 ± 0.2 at 25 °C. The heat and entropy changes are approximately −6.5 kcal/mole and −21 e.u./mole respectively.

Homogeneous Hydrogenation of Unsaturated Carboxylic Acids Using Chlororhodate(I) Complexes and Rhodium(I) Diethylsulfide Complexes

1975 ◽  
Vol 53 (6) ◽  
pp. 797-804 ◽  
Author(s):  
Brian R. James ◽  
Flora T. T. Ng
Keyword(s):  
Carboxylic Acids ◽  
Rate Constants ◽  
Maleic Acid ◽  
Activation Parameters ◽  
Kinetic Studies ◽  
Homogeneous Hydrogenation ◽  
Chloride Solutions ◽  
Rate Determining Step ◽  
Square Planar ◽  
Unsaturated Carboxylic Acids

N,N-Dimethylacetamide solutions of the cyclooctene complex [Rh(C8H14)2Cl]2, in the presence of excess chloride or diethylsulfide, are effective for the homogeneous hydrogénation of unsaturated carboxylic acids at ca. 80 °C and 1 atm H2. Kinetic studies on the hydrogenation of maleic acid are consistent with a rate determining step involving oxidative addition of H2 to square planar rhodium(I) olefin species. Rate constants and activation parameters agree with those determined previously from similar studies using corresponding rhodium(III) complexes and give confirmation that rhodium(I) catalysts are involved in the rhodium(III) systems. Discussion of the systems is limited by the somewhat uncertain nature of the catalysts; however, chlororhodate(I) species are involved in the chloride solutions, and bis(diethylsulfide) complexes appear likely in the sulfide systems.

Hydrolysis mechanisms for acylhydrazines in aqueous sulfuric acid, determined using the excess acidity method

1984 ◽  
Vol 62 (8) ◽  
pp. 1613-1617 ◽  
Author(s):  
Robin A. Cox ◽  
Keith Yates
Keyword(s):  
Sulfuric Acid ◽  
Water Molecule ◽  
Proton Transfer ◽  
Medium Composition ◽  
Hydrolysis Rate ◽  
Bond Rupture ◽  
Rate Data ◽  
Dilute Acid ◽  
Aqueous Sulfuric Acid ◽  
Rate Determining Step

The excess acidity method has been applied to hydrolysis rate data for some acyl- and benzoylhydrazines, obtained as a function of medium composition in aqueous sulfuric acid mixtures. Two hydrolysis mechanisms are indicated, both involving a second proton transfer to monoprotonated substrate. In the first mechanism this transfer is to oxygen, which is the rate-determining step in dilute acid, followed by attack of a water molecule in an A-2 hydrolysis, which is rate determining in more concentrated acid. Bisulfate ion becomes the nucleophile at high acidity. The second mechanism, found at higher acid concentrations, involves rate-determining nitrogen protonation, probably concerted with C—N bond rupture, to give an acylium ion, for those substrates capable of forming one.

scholarly journals Understanding the reaction mechanism of the regioselective piperidinolysis of aryl 1-(2,4-dinitronaphthyl) ethers in DMSO: Kinetic and DFT studies

2021 ◽  
Vol 46 ◽  
pp. 146867832110274
Author(s):  
Yasmen M Moghazy ◽  
Nagwa MM Hamada ◽  
Magda F Fathalla ◽  
Yasser R Elmarassi ◽  
Ezzat A Hamed ◽  
...  
Keyword(s):  
Carbon Atom ◽  
Density Functional ◽  
Function Analysis ◽  
Density Functional Theory Method ◽  
Activation Parameters ◽  
Kinetic Studies ◽  
Nucleophilic Attack ◽  
Common Mechanism ◽  
Slow Step ◽  
Rate Determining Step

Reactions of aryl 1-(2,4-dinitronaphthyl) ethers with piperidine in dimethyl sulfoxide at 25oC resulted in substitution of the aryloxy group at the ipso carbon atom. The reaction was measured spectrophotochemically and the kinetic studies suggested that the titled reaction is accurately third order. The mechanism is began by fast nucleophilic attack of piperidine on C1 to form zwitterion intermediate (I) followed by deprotonation of zwitterion intermediate (I) to the Meisenheimer ion (II) in a slow step, that is, SB catalysis. The regular variation of activation parameters suggested that the reaction proceeded through a common mechanism. The Hammett equation using reaction constant σo values and Brønsted coefficient value showed that the reaction is poorly dependent on aryloxy substituent and the reaction was significantly associative and Meisenheimer intermediate-like. The mechanism of piperidinolysis has been theoretically investigated using density functional theory method using B3LYP/6-311G(d,p) computational level. The combination between experimental and computational studies predicts what mechanism is followed either through uncatalyzed or catalyzed reaction pathways, that is, SB and SB-GA. The global parameters of the reactants, the proposed activated complexes, and the local Fukui function analysis explained that C1 carbon atom is the most electrophilic center of ether. Also, kinetics and theoretical calculation of activation energies indicated that the mechanism of the piperidinolysis passed through a two-step mechanism and the proton transfer process was the rate determining step.

scholarly journals Theoretical insight on the treatment of β-hexachlorocyclohexane waste through alkaline dehydrochlorination

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Alicia Bescós ◽  
Clara I. Herrerías ◽  
Zoel Hormigón ◽  
José Antonio Mayoral ◽  
Luis Salvatella
Keyword(s):  
Density Functional ◽  
Kinetic Studies ◽  
Alkaline Treatment ◽  
Functional Study ◽  
Reaction Intermediates ◽  
Preferential Formation ◽  
Reaction Intermediate ◽  
Rate Determining Step ◽  
Dehydrochlorination Reaction ◽  
Theoretical Results

AbstractThe occurrence of 4.8–7.2 million tons of hexachlorocyclohexane (HCH) isomers stocked in dumpsites around the world constitutes a huge environmental and economical challenge because of their toxicity and persistence. Alkaline treatment of an HCH mixture in a dehydrochlorination reaction is hampered by the low reactivity of the β-HCH isomer (HCl elimination unavoidably occurring through syn H–C–C–Cl arrangements). More intriguingly, the preferential formation of 1,2,4-trichlorobenzene in the β-HCH dehydrochlorination reaction (despite the larger thermodynamical stability of the 1,3,5-isomer) has remained unexplained up to now, though several kinetic studies had been reported. In this paper, we firstly show a detailed Density Functional study on all paths for the hydroxide anion-induced elimination of β-HCH through a three-stage reaction mechanism (involving two types of reaction intermediates). We have now demonstrated that the first reaction intermediate can follow several alternative paths, the preferred route involving abstraction of the most acidic allylic hydrogen which leads to a second reaction intermediate yielding only 1,2,4-trichlorobenzene as the final reaction product. Our theoretical results allow explaining the available experimental data on the β-HCH dehydrochlorination reaction (rate-determining step, regioselectivity, instability of some reaction intermediates).

POWER RATE LAW BASED CHEMICAL KINETICS AND THERMODYNAMIC MODELING OF AFRICAN PEAR SEED OIL CONSECUTIVE IRREVERSIBLE BASE METHANOLYSIS FOR BIODIESEL PRODUCTION

2021 ◽  
Vol 36 (1) ◽  
pp. 53-66
Author(s):  
C. Esonye ◽  
O. D Onukwuli ◽  
S. O. Momoh
Keyword(s):  
Rate Constants ◽  
Seed Oil ◽  
Scale Up ◽  
Cetane Number ◽  
Calorific Value ◽  
Biodiesel Production ◽  
Rate Determining Step ◽  
Increase With Increase ◽  
African Pear ◽  
Kinetics And Thermodynamic

Currently the major challenge of biodiesel application as a replacement to petrodiesel is its industrial production sustainability.Consequently, the successful scale-up of laboratory results in transesterification requires so much information obtained through chemical kinetics.This paper presents the kinetics and thermodynamic study of alkali-homogeneous irreversible methanolysis of seed oil derived from African pear. The transesterification process was carried out from 0-100 minutes at temperature range of 55-65°C. The reaction mixture compositions were ascertained using gas chromatography- flame ionization detector (GC-FID) technique. Rate constants of the triglyceride (Tg), diglycerides (Dg) and monoglycerides(Mg) hydrolysis were in the range of 0.0140- 0.07810 wt%/min and increased with increase in temperature. The rate of reaction was found to increase with increase in temperature. Activation energies were found to be 6.14, 20.01 and 28.5kcal/mol at 55, 60 and 65oC respectively. Tg hydrolysis to Dg was observed asthe rate determining step while the reaction agreed with second order principles. A biodiesel yield of 93.02% was obtained with cloud point of 10°C , flash point of 125°C , pour point of 4°C , calorific value of 34.4MJ/kg, and cetane number of 54.90 which satisfy EN14214 and ASTM D 6751 standards. Results presented in this report would serve as idealized conditions for industrial scale up of biodiesel production from African pear seed oil. Keywords:Kinetics; methanolysis; rate constants; activation energy; African pear seed oil; biodiesel

Effect of Medium on Reactivity for Alkaline Hydrolysis of p-Nitrophenyl Acetate and S-p-Nitrophenyl Thioacetate in DMSO-H2O Mixtures of Varying Compositions: Ground State and Transition State Contributions

2021 ◽  
Author(s):  
Ik-Hwan Um ◽  
Seungjae Kim
Keyword(s):  
Transition State ◽  
Alkaline Hydrolysis ◽  
Ground State ◽  
Rate Constants ◽  
Kinetic Data ◽  
Reaction Medium ◽  
Stepwise Mechanism ◽  
Rate Determining Step ◽  
Leaving Group ◽  
Hydrolysis Of

Second-order rate constants (kN) for reactions of p-nitrophenyl acetate (1) and S-p-nitrophenyl thioacetate (2) with OH‒ have been measured spectrophotometrically in DMSO-H2O mixtures of varying compositions at 25.0 ± 0.1 oC. The kN value increases from 11.6 to 32,800 M‒1s‒1 for the reactions of 1 and from 5.90 to 190,000 M‒1s‒1 for those of 2 as the reaction medium changes from H2O to 80 mol % DMSO, indicating that the effect of medium on reactivity is more remarkable for the reactions of 2 than for those of 1. Although 2 possesses a better leaving group than 1, the former is less reactive than the latter by a factor of 2 in H2O. This implies that expulsion of the leaving group is not advanced in the rate-determining transition state (TS), i.e., the reactions of 1 and 2 with OH‒ proceed through a stepwise mechanism, in which expulsion of the leaving group from the addition intermediate occurs after the rate-determining step (RDS). Addition of DMSO to H2O would destabilize OH‒ through electronic repulsion between the anion and the negative-dipole end in DMSO. However, destabilization of OH‒ in the ground state (GS) is not solely responsible for the remarkably enhanced reactivity upon addition of DMSO to the medium. The effect of medium on reactivity has been dissected into the GS and TS contributions through combination of the kinetic data with the transfer enthalpies (ΔΔHtr) from H2O to DMSO-H2O mixtures for OH‒ ion.

The decomposition of aliphatic N-nitro amines in aqueous sulfuric acid. Bisulfate as a nucleophile

1996 ◽  
Vol 74 (10) ◽  
pp. 1774-1778 ◽  
Author(s):  
Robin A. Cox
Keyword(s):  
Sulfuric Acid ◽  
Water Molecule ◽  
Rate Constants ◽  
Activation Parameters ◽  
Standard State ◽  
Aqueous Sulfuric Acid ◽  
Alkyl Groups ◽  
Different Temperatures ◽  
State Rate ◽  
Acid Catalyzed

In aqueous sulfuric acid, aliphatic N-nitro amines decompose to N2O and alcohols. An excess acidity analysis of the observed rate constants for the reaction shows that free carbocations are not formed. The reaction is an acid-catalyzed SN2 displacement from the protonated aci-nitro tautomer, the nucleophile being a water molecule at acidities below 82–85% H2SO4, and a bisulfate ion at higher acidities. Bisulfate is the poorer nucleophile by a factor of about 1000. Twelve compounds were studied, of which results obtained for nine at several different temperatures enabled calculation of activation parameters for both nucleophiles. The reaction appears to be mainly enthalpy controlled. The intercept standard-state rate constants are well correlated by the σ* values for the alkyl groups; the slopes are negative, with a more negative value for the slower bisulfate reaction. Interestingly the m≠m* slopes also correlate with σ*, although the scatter is bad. Key words: N-nitro amines, excess acidity, bisulfate, nucleophiles, acid-catalyzed, kinetics.

Electrophilic additions to allenes. VI. The role of steric versus electronic effects in the reactions of arenesulphenyl halides with allenes

1980 ◽  
Vol 58 (24) ◽  
pp. 2737-2744 ◽  
Author(s):  
Dennis G. Garrattz ◽  
Pierre L. Beaulieu
Keyword(s):  
Positive Charge ◽  
Steric Effects ◽  
Rate Data ◽  
Electronic Effects ◽  
Rate Determining Step ◽  
Minimal Importance ◽  
Electrophilic Additions

The role of steric and electronic effects during the rate and product determining steps for the addition of arenesulphenyl chlorides to 1,3-disubstituted allenes has been briefly examined. Both effects appear to be generally of minimal importance during the rate determining step. The available rate data indicate the presence of little, if any, build up of positive charge on sulphur. These results are interpreted in terms of an SN2 attack on bivalent sulphur leading to an alkylidenethiiranium ion intermediate. Steric effects are of greater importance in the product determining step, particularly when the sulphenyl chlorides possess two bulky ortho substituents, as in the case of 2,4,6-triisopropylbenzenesulphenyl chloride.

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