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.

The acid-catalyzed decomposition of nitramide

1996 ◽  
Vol 74 (10) ◽  
pp. 1779-1783 ◽  
Author(s):  
Robin A. Cox
Keyword(s):  
Rate Constants ◽  
Activation Parameters ◽  
Cyclic Process ◽  
Dilute Acid ◽  
Acid Media ◽  
Dilute Acid Solution ◽  
Acid Catalyzed ◽  
Reaction With Water ◽  
Hydrochloric And Sulfuric Acids ◽  
Good Agreement

Much attention has been paid to the base-catalyzed decomposition of nitramide, but despite this it was not certain that a corresponding acid-catalyzed reaction even existed before the work described in this paper. The excess acidity method has been applied to nitramide decomposition rate constants obtained in aqueous perchloric acid media, and to a lesser extent in aqueous hydrochloric and sulfuric acids. This analysis shows that the decomposition in dilute acid solution is actually a base-catalyzed reaction, with water acting as the base (perhaps in a cyclic process involving two water molecules), with rate constants in good agreement with previous estimates. However, in more concentrated acid media a true acid-catalyzed reaction can be dissected out. Activation parameters are given for both mechanisms, and it is shown that the acid-catalyzed process is similar to the acid-catalyzed decomposition of alkylnitramines. In sulfuric acid the reaction is slightly faster than it is in the other acids, due to the presence of a base-catalyzed process involving sulfate. Key words: nitramide, excess acidity, acid-catalyzed, base-catalyzed, kinetics.

Lactams in sulfuric acid. The mechanism of amide hydrolysis in weak to moderately strong aqueous mineral acid media

1998 ◽  
Vol 76 (6) ◽  
pp. 649-656 ◽  
Author(s):  
Robin A Cox
Keyword(s):  
Sulfuric Acid ◽  
Water Molecule ◽  
Kinetic Method ◽  
Activation Parameters ◽  
Mineral Acid ◽  
Medium Effect ◽  
Acid Media ◽  
Unknown Mechanism ◽  
Reaction Rate Constants ◽  
The One

Reaction rate constants obtained in moderately concentrated sulfuric acid for the hydrolysis of simple lactams of ring sizes five, six, seven, and eight as a function of acidity and temperature have been analyzed using the excess acidity kinetic method. The basicity constants for these substrates have been recalculated; the 13C NMR spectra used to obtain these values are very sensitive to medium effects. It was found that the basicities of the lactams at 0.003-0.1 M lactam concentration were over half a pK unit more basic than they were at 0.5 M lactam, presumably because of the medium effect. Apart from this, the rate constant results obtained at different times by different groups using different techniques for monitoring the kinetics are in adequate agreement. The excess acidity analysis showed that the kinetics could be fitted according to the "three-water-molecule followed by one-water-molecule" mechanistic scenario previously found, or could just as well be fitted by a "one-water-molecule followed by unknown mechanism" scenario, with the mechanistic change taking place at 50 wt.% sulfuric acid for all the substrates. Other evidence makes the latter seem the more likely possibility of the two, and activation parameters based upon the "one-water-molecule" process were determined. Sufficient data points to enable the unknown mechanism to be established were not present; possible mechanisms applicable in media more concentrated than 50 wt.% sulfuric acid are discussed. Previously obtained values of the parameter r, the number of water molecules involved with the substrate in A2 processes, are now questionable.Key words: amides, lactams, excess acidity, hydrolysis, mechanism.

Kinetics and mechanism of aminolysis of (Z)-4-arylidene-2-phenyl-5(4H)oxazolones

1992 ◽  
Vol 70 (10) ◽  
pp. 2515-2519 ◽  
Author(s):  
Sharifa S. Alkaabi ◽  
Ahmad S. Shawali
Keyword(s):  
Rate Constants ◽  
Activation Parameters ◽  
Order Conditions ◽  
Kinetics And Mechanism ◽  
Hammett Equation ◽  
Third Order ◽  
First Order ◽  
Different Temperatures ◽  
Pseudo First Order ◽  
Kinetics Of

The kinetics of the reactions of a series of (Z)-4-arylidene-2-phenyl-5(4H)oxazolones 1 with n-butylamine and piperidine were studied spectrophotometrically in dioxane, ethanol, and cyclohexane under pseudo-first-order conditions and at different temperatures. The relation k1(obs) = k2[amine] + k3[amine]2 was found applicable for all reactions studied in either dioxane or ethanol. However, in cyclohexane the n-butylaminolysis of 1 followed only third-order kinetics k1(obs) = k3[n-BuNH2]2. The kinetics of the reaction of 1 with n-butylamine in the presence of catalytic amounts of triethylamine in dioxane followed the equation: k1(obs)k2 = [n-BuNH2] + k3[n-BuNH2]2[Formula: see text] [Et3N]. The rate constants k2 and k3 correlated well with the Hammett equation and the corresponding activation parameters were determined. The results were interpreted in terms of a mechanism involving solvent- and amine-catalyzed processes.

ChemInform Abstract: Hydroxylamine Production via Hydrogenation of Nitric Oxide in Aqueous Sulfuric Acid Catalyzed by Carbon-Supported Platinum.

ChemInform ◽  
1987 ◽  
Vol 18 (51) ◽  
Author(s):  
S. POLIZZI ◽  
A. BENEDETTI ◽  
G. FAGHERAZZI ◽  
C. GOATIN ◽  
R. STROZZI ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Sulfuric Acid ◽  
Aqueous Sulfuric Acid ◽  
Supported Platinum ◽  
Acid Catalyzed

Kinetics and Mechanism of Acid Catalyzed Decomposition of 1-Phenyl-3,3-dialkyltriazenes

1994 ◽  
Vol 59 (2) ◽  
pp. 401-411 ◽  
Author(s):  
Miroslav Ludwig ◽  
Pavla Valášková ◽  
Oldřich Pytela
Keyword(s):  
Rate Constants ◽  
Steric Effect ◽  
Aqueous Ethanol ◽  
Pivalic Acid ◽  
Decomposition Kinetics ◽  
Methyl Ethyl ◽  
Rate Determining Step ◽  
Alkyl Groups ◽  
Acid Catalyzed ◽  
Catalytic Rate

Five model 1-phenyl-3,3-dialkyltriazenes (methyl, ethyl, 2-propyl, butyl, cyclohexyl) have been synthesized and their acid-catalyzed decomposition kinetics have been investigated spectrophotometrically in aqueous ethanol (40 vol.%) with pivalic acid as the catalyst. The results show that the rate-determining step is catalyzed by the proton. The decrease in the observed rate constant at higher concentrations of pivalic acid is explained by the formation of an unreactive complex of the nondissociated acid and respective triazene. The steric effect of alkyl groups on the catalytic rate constants is discussed.

The hydrolyses of some sterically crowded benzoate esters in sulfuric acid. The excess acidity method at different temperatures

1979 ◽  
Vol 57 (22) ◽  
pp. 2960-2966 ◽  
Author(s):  
Robin A. Cox ◽  
Malcolm F. Goldman ◽  
Keith Yates
Keyword(s):  
Sulfuric Acid ◽  
Activation Enthalpy ◽  
Sulfuric Acid Concentration ◽  
Hydrolysis Rate ◽  
Water Molecules ◽  
Steric Strain ◽  
Methyl Substitution ◽  
Different Temperatures ◽  
Acid Catalyzed ◽  
Aqueous Standard

The excess acidity method has been used to analyze the observed acid-catalyzed hydrolysis rate constants for methyl benzoate, methyl para-toluate, methyl ortho-toluate, and methyl 2,6-dimethylbenzoate, over a wide sulfuric acid concentration range, at several different temperatures. Enthalpies and entropies of activation in the aqueous standard state are reported, with slope parameters m≠ also given are the [Formula: see text] and m* values found for the protonation of these compounds. The mechanistic changeover from AAc-2 to AAc-1 hydrolysis occurs at lower acidity with increasing methyl substitution, mainly due to the decrease in activation enthalpy in the transition state for the AAc-1 process, caused by release of steric strain and increased mesomeric interaction. The AAc-2 hydrolysis involves two water molecules, and is energetically favourable and entropically unfavourable. The AAc-1 reaction is difficult energetically, but this is offset by the large positive activation entropies found.

THE WALLACH REARRANGEMENT: PART II. KINETICS AND MECHANISM OF THE ACID-CATALYZED REARRANGEMENT OF AZOXYBENZENE

1965 ◽  
Vol 43 (4) ◽  
pp. 862-875 ◽  
Author(s):  
E. Buncel ◽  
B. T. Lawton
Keyword(s):  
Sulfuric Acid ◽  
Proton Transfer ◽  
Acid Concentration ◽  
Entire Range ◽  
Kinetics And Mechanism ◽  
The Other ◽  
Rate Data ◽  
Spectrophotometric Methods ◽  
Aqueous Sulfuric Acid ◽  
Acid Catalyzed

The rate of rearrangement of azoxybenzene to p-hydroxyazobenzene has been measured in 75.3–96.4% sulfuric acid at 25° and in 65.0–90.4% sulfuric acid at 75.5° by spectrophotometric methods. The pKa of azoxybenzene in aqueous sulfuric acid has also been determined. It is found that although azoxybesssnzene is almost completely protonated over the entire range of acid concentration studied, the rate increases by more than 1 000-fold. A two-proton process is therefore indicated and mechanisms are proposed involving a dication (II) as the key intermediate. The rate data do not allow differentiation between two proposed mechanisms, one involving two equilibrium protonations, and the other a single equilibrium protonation followed by rate-determining proton transfer. Past mechanisms of the Wallach rearrangement are discussed.

scholarly journals Kinetics and Thermodynamics of the Adsorption of Lead (II) on a Activated Carbon from Coconut Shells

2013 ◽  
Vol 15 (4) ◽  
pp. 283 ◽  
Author(s):  
L. Largitte ◽  
P. Lodewyckx
Keyword(s):  
Activated Carbon ◽  
Standard Enthalpy ◽  
Rate Constants ◽  
Equilibrium Constants ◽  
Activation Parameters ◽  
Effect Of Temperature ◽  
Standard Entropy ◽  
Exponential Factor ◽  
Different Temperatures ◽  
Coconut Shells

The effect of temperature on the adsorption of lead by an activated carbon from coconut shells is investigated. The pseudo second order equation is applied to the kinetic data obtained at different temperatures in order to determine the adsorption rate constants at these temperatures. Then, the Arrhenius equation is applied to the rate constants to determine the activation energy of the sorption reaction and the pre-exponential factor. By applying the Eyring equation to the rate constants, the standard thermodynamic activation parameters of the sorption reaction can also be calculated. In addition, the isotherms of lead adsorption on the activated carbon from coconut shells, at different temperatures, are determined and fitted by the Langmuir equation. The Van’t Hoff equation is applied to the Langmuir equilibrium constants in order to determine the standard enthalpy of the sorption reaction. The other standard thermodynamic parameters<br />(Gibbs standard enthalpy and standard entropy) are deduced. The isosteric standard sorption enthalpy is also determined by using both the classical approach and an adapted Clausius Clapeyron equation. The results are identical. The value obtained is higher, but more correct than that of Langmuir. On the basis of these<br />thermokinetic parameters, the activated carbon from Coconut shells can be considered as a very efficient carbon for the sorption of lead and its sorption efficiency (rate and quantity) increase with the temperature.

ortho-Effect on the acid-catalyzed hydration of 2-substituted α-methylstyrenes

2009 ◽  
Vol 74 (1) ◽  
pp. 85-99 ◽  
Author(s):  
Ondřej Prusek ◽  
Filip Bureš ◽  
Oldřich Pytela
Keyword(s):  
Sulfuric Acid ◽  
Benzene Ring ◽  
Rate Constants ◽  
Reaction Centre ◽  
Acidity Function ◽  
Isopropyl Group ◽  
Kinetic Acidity ◽  
Reaction Constant ◽  
Acid Catalyzed ◽  
Catalytic Rate

α-Methylstyrene and nine ortho-substituted analogs have been synthesized and the kinetics of their acid-catalyzed hydration in aqueous solutions of sulfuric acid at 25 °C have been investigated. The kinetic acidity function HS has been constructed from the dependence of the observed rate constants kobs on the sulfuric acid concentration. The catalytic rate constants of the acid-catalyzed hydration kortho have been calculated as well. The identical shape of the kinetic acidity functions for ortho- and para-derivatives confirms what the consistent mechanism A-SE2 of the acid-catalyzed hydration has already proved for the corresponding para-derivatives. The A-SE2 mechanism involves a rate-determining proton transfer of the hydrated proton to the substrate. From the dependence of the catalytic rate constants of the ortho-derivatives on the catalytic rate constants of the para-derivatives, it is seen that the logarithm of the catalytic rate constant for hydrogen as a substituent is markedly out of the range of the other substituents and, simultaneously, that the ortho-derivatives react significantly slower than the corresponding para-derivatives. In correlation with the substitent constants σp+, a reaction constant of ρ+ = –1.45 have been found. The constant is, in absolute value, considerably smaller than that for para-derivatives (ρ+ = –3.07). In parallel, the steric effects are enforced more significantly for the monoatomic substituents (slope of the Charton’s constants 3.92) than for substituents including more atoms (slope of the Charton’s constants 2.09). A small value of the reaction constant ρ+ has been elucidated due to the lower conjugation between the reaction centre and the benzene ring as a consequence of the geometric twist of the reaction centre out of the main aromatic plane accompanied by fading mesomeric interaction between the reaction centre and the substituents attached to the benzene ring. The isopropyl group in the carbocation is twisted less out of the aromatic plane for the monoatomic substituents and, therefore, also a small difference in the bulk of substituents has considerable steric influence on the conjugation between the carbocation and the benzene ring bearing substituents. On the contrary, the isopropyl group in the carbocations with polyatomic substituents is twisted to such a degree that changes in the bulk of substituents affect the resonant stabilization negligibly. Similar conclusions were also deduced from the correlations of the substitution constants σI and σR+.

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