Acetic acid kinetic

Fahey s school has produced a series of very interesting papers dealing with the addition of HCl to various olefins in acetic acid. Kinetic studies including isotope effects and the role of added chloride ions were coupled with detailed product analysis. Styrene and fer-butylethylene ) were found to react with molecidar HCl (or its ion-pair form) in a typical AdE2 fashion ... 

Leyes, C., Othmer, D. (1945). Continuous esterification of butanol and acetic acid, kinetic and distillation considerations. Transactions of the American Institute of Chemical Engineers, 41, 157-196. 

Galstyan, G. A. Galstyan, T. M. Mikulenko, L. I. The Kinetics and Mechanism of the Catalytic Reaction of Ozone with Methylbenzenes in Acetic Acid. Kinetics and Catalysis 9U, 35(2), 231-236. 

All the aliphatic and alicyclic carbamate derivatives (40-48) could be cleaved by adds to yield the free amines. Some of them (45, 46 and 48) are removed by simple treatment with trifluoroacetic acid, while others (43 and 44) require prolonged treatment with hydrogen bromide in acetic acid. Kinetic studies on various alicyclic carbamate derivatives showed a linear correlation between the logarithms of the rate constants of the add fission by means of hydrogen bromide in acetic add, and between the solvolysis of the corresponding ahcyclic tosylates. It was concluded that the cleavage of the ahcyclic carbamates proceeds by solvolysis of the protonated compounds. 

In a carboxylic acid solvent, [Ir(cod)Cl]2 with a Mel promotor effects the isomerization of methyl formate to acetic acid. Kinetic and chemical studies indicate that the reaction proceeds in the carboxylic acid by transesterification to give formic acid which then reacts with iridium (Scheme 9). " ... 

Much of the early work was inconclusive confusion sprang from the production by the reaction of water, which generally reduced the rate, and in some cases by production of nitrous acid which led to autocatalysis in the reactions of activated compounds. The most extensive kinetic studies have used nitromethane,acetic acid, sulpholan,i and carbon tetrachloride as solvents. 

Nitration in acetic acid, in sulpholan and in carbon tetrachloride showed kinetic phenomena similar to those shown in nitromethane this is significant for it denies nitromethane a chemical involvement in the slow step. (Originally the rate of isomerization of nitromethane to its aci-form was believed to be a factor in the reaction. )... 

The anticatalytic effect of nitrous acid in nitration The effect of nitrous acid was first observed for zeroth-order nitrations in nitromethane ( 3.2). The effect was a true negative catalysis the kinetic order was not affected, and nitrous acid was neither consumed nor produced by the nitration. The same was true for nitration in acetic acid. In the zeroth-order nitrations the rate depended on the reciprocal of the square root of the concentration of nitrous acid =... 

The kinetics of nitration of anisole in solutions of nitric acid in acetic acid were complicated, for both autocatalysis and autoretardation could be observed under suitable conditions. However, it was concluded from these results that two mechanisms of nitration were operating, namely the general mechanism involving the nitronium ion and the reaction catalysed by nitrous acid. It was not possible to isolate these mechanisms completely, although by varying the conditions either could be made dominant. 

Chloroanisole and p-nitrophenol, the nitrations of which are susceptible to positive catalysis by nitrous acid, but from which the products are not prone to the oxidation which leads to autocatalysis, were the subjects of a more detailed investigation. With high concentrations of nitric acid and low concentrations of nitrous acid in acetic acid, jp-chloroanisole underwent nitration according to a zeroth-order rate law. The rate was repressed by the addition of a small concentration of nitrous acid according to the usual law rate = AQ(n-a[HN02]atoioh) -The nitration of p-nitrophenol under comparable conditions did not accord to a simple kinetic law, but nitrous acid was shown to anticatalyse the reaction. 

The effect of nitrous acid on the nitration of mesitylene in acetic acid was also investigated. In solutions containing 5-7 mol 1 of nitric acid and < c. 0-014 mol of nitrous acid, the rate was independent of the concentration of the aromatic. As the concentration of nitrous acid was increased, the catalysed reaction intervened, and superimposed a first-order reaction on the zeroth-order one. The catalysed reaction could not be made sufficiently dominant to impose a truly first-order rate. Because the kinetic order was intermediate the importance of the catalysed reaction was gauged by following initial rates, and it was shown that in a solution containing 5-7 mol 1 of nitric acid and 0-5 mol 1 of nitrous acid, the catalysed reaction was initially twice as important as the general nitronium ion mechanism. 

First-order nitrations. The kinetics of nitrations in solutions of acetyl nitrate in acetic anhydride were first investigated by Wibaut. He obtained evidence for a second-order rate law, but this was subsequently disproved. A more detailed study was made using benzene, toluene, chloro- and bromo-benzene. The rate of nitration of benzene was found to be of the first order in the concentration of aromatic and third order in the concentration of acetyl nitrate the latter conclusion disagrees with later work (see below). Nitration in solutions containing similar concentrations of acetyl nitrate in acetic acid was too slow to measure, but was accelerated slightly by the addition of more acetic anhydride. Similar solutions in carbon tetrachloride nitrated benzene too quickly, and the concentration of acetyl nitrate had to be reduced from 0-7 to o-i mol 1 to permit the observation of a rate similar to that which the more concentrated solution yields in acetic anhydride. 

In the nitration and acetoxylation of o-xylene the addition of acetic acid increased the rate in proportion to its concentration, the presence of 3-0 mol 1" accelerating the rate by a factor of 30. In the presence of a substantial concentration (2-2 mol 1 ) of acetic acid the rate of reaction obeyed the following kinetic expression... 

Similarly, acetic acid catalysed the zeroth-order nitration of mesitylene without affecting the kinetic form... 

The kinetics of the nitration of benzene, toluene and mesitylene in mixtures prepared from nitric acid and acetic anhydride have been studied by Hartshorn and Thompson. Under zeroth order conditions, the dependence of the rate of nitration of mesitylene on the stoichiometric concentrations of nitric acid, acetic acid and lithium nitrate were found to be as described in section 5.3.5. When the conditions were such that the rate depended upon the first power of the concentration of the aromatic substrate, the first order rate constant was found to vary with the stoichiometric concentration of nitric acid as shown on the graph below. An approximately third order dependence on this quantity was found with mesitylene and toluene, but with benzene, increasing the stoichiometric concentration of nitric acid caused a change to an approximately second order dependence. Relative reactivities, however, were found to be insensitive... 

It has not been found possible to reconcile all these observations with a simple kinetic scheme. A major difficulty is that whilst the stoichiometric concentrations of nitric acid and of acetic acid can be varied independently, the actual concentrations of these species cannot, because of the existence of the equilibrium ... 

Mixtures of trioctylamine and 2-ethylhexanol have been employed to extract 1—9% by volume acetic acid from its aqueous solutions. Reverse osmosis for acid separation has been patented and solvent membranes for concentrating acetic acid have been described (58,59). Decalin and trioctylphosphine were selected as solvents (60). Liquid—Uquid interfacial kinetics is an especially significant factor in such extractions (61). 

Noncatalytic ring chlorination of toluene in a variety of solvents has been reported. Isomer distributions vary from approximately 60% ortho in hydroxyhc solvents, eg, acetic acid, to 60% para in solvents, eg, nitromethane, acetonittile, and ethylene dichloride (49,50). Reaction rates are relatively slow and these systems are particularly appropriate for kinetic studies. 

Kinetic Considerations. Extensive kinetic and mechanistic studies have been made on the esterification of carboxyHc acids since Berthelot and Saint-GiHes first studied the esterification of acetic acid (18). Although ester hydrolysis is catalyzed by both hydrogen and hydroxide ions (19,20), a base-catalyzed esterification is not known. A number of mechanisms for acid- and base-catalyzed esterification have been proposed (4). One possible mechanism for the bimolecular acid-catalyzed ester hydrolysis and esterification is shown in equation 2 (6). 

With these kinetic data and a knowledge of the reactor configuration, the development of a computer simulation model of the esterification reaction is iavaluable for optimising esterification reaction operation (25—28). However, all esterification reactions do not necessarily permit straightforward mathematical treatment. In a study of the esterification of 2,3-butanediol and acetic acid usiag sulfuric acid catalyst, it was found that the reaction occurs through two pairs of consecutive reversible reactions of approximately equal speeds. These reactions do not conform to any simple first-, second-, or third-order equation, even ia the early stages (29). 

In a study of the kinetics of the reaction of 1-butanol with acetic acid at 0—120°C, an empirical equation was developed that permits estimation of the value of the rate constant with a deviation of 15.3% from the molar ratio of reactants, catalyst concentration, and temperature (30). This study was conducted usiag sulfuric acid as catalyst with a mole ratio of 1-butanol to acetic acid of 3 19.6, and a catalyst concentration of 0—0.14 wt %. 

The solvolysis of 2, 35-3-(4-methoxyphenyl)but-2-yl/>-toluensulfonate in acetic acid can be followed by several kinetic measurements (a) rate of decrease of observed rotation (k ) rate of release of the leaving group (k,) and, when 0-labeled sulfonate is used, the rate of equilibration of the sulfonate oxygens (k ). At 25°C, the rate constants are... 

The behavior of compounds A and B on solvolysis in acetic acid containing acetate ion has been studied. The solvolysis of A is about 13 times faster than that of B. Kinetic studies in the case of A show that A is racemized competitively with solvolysis. A single product is formed from A, but B gives a mixture. Explain these results. 

Alkynes react with mercuric acetate in acetic acid to give addition products. In the case of 3-hexyne, the product has -stereochemistry, but the Z-isomer is isolated from diphenylacetylene. The kinetics of the addition reaction are first-order in both alkyne and... 

Molecular chlorine is believed to be the active electrophile in uncatalyzed chlorination of aromatic compounds. Simple second-order kinetics are observed in acetic acid. The reaction is much slower in nonpolar solvents such as dichloromethane and carbon tetrachloride. Chlorination in nonpolar solvents is catalyzed by added acid. The catalysis by acids is probably the result of assistance by proton transfer during the cleavage of the Cl-Cl bond. ... 

Molecular bromine is believed to be the reactive brominating agent in uncatalyzed brominations. The brominations of benzene and toluene are first-order in both bromine and the aromatic substrate in trifluoroacetic acid solution, but the rate expressions become more complicated when these reactions take place in the presence of water. " The bromination of benzene in aqueous acetic acid exhibits a first-order dependence on bromine concentration when bromide ion is present. The observed rate is dependent on bromide ion concentration, decreasing with increasing bromide ion concentration. The detailed kinetics are consistent with a rate-determining formation of the n-complex when bromide ion concentration is low, but with a shift to reversible formation of the n-complex... 

In Eq. (6-35), A/Z is the molar heat of ionization of the buffer acid at the conditions (temperature, solvent composition) of the kinetic studies. It happens that for many commonly used acidic buffers this quantity is small. Hamed and Owen give A//2 = —0.09 kcal/mol for acetic acid at 25°C, for example. The very important buffer of dihydrogen phosphate-monohydrogen phosphate is controlled by pK2 of phosphoric acid at 25°C its heat of ionization is —0.82 kcal/mol. 

By analogy with the kinetic protonation of steroidal zl -enolate anions with weak acids such as acetic acid, which proceeds at the C-4 atom, since the maximum negative charge resides at this position (54,55), the kinetic protonation of the -dienamines with weak acids also occurs at this... 

Kinetic studies of pyrolysis of azides, giving oxadiazole A-oxides in near-quantitative yields, showed that the 5-azido-6-nitroquinoline pyrolyzed in acetic acid 27.6 times faster than did 5-azidoquinolines, because of the -M effect of the group adjacent to the azide group (85AJC1045). 

When diazomethane is slowly added to excess lactam, the anions formed can interact with unreacted lactam by means of hydrogen bonds to form ion pairs similar to those formed by acetic acid-tri-ethylamine mixtures in nonpolar solvents. The methyldiazonium ion is then involved in an ion association wdth the mono-anion of a dimeric lactam which is naturally less reactive than a free lactam anion. The velocity of the Sn2 reaction, Eq. (7), is thus decreased. However, the decomposition velocity of the methyldiazonium ion, Eq. (6a), is constant and, hence, the S l character of the reaction is increased which favors 0-methylation. It is possible that this effect is also involved in kinetic dependence investigations have shown that with higher saccharin concentrations more 0-methylsaccharin is formed. 

Thorium oxide on activated carbon was prepared by absorption of thorium nitrate from its solution in anhydrous acetone on the activated carbon Supersorbon. The excess solution was decanted, the catalyst was dried at 80 °C, and the adsorbed thorium oxide was decomposed by excess 5% ammonium hydroxide solution. After repeated washing and decanta-nation with distilled water and acetone, the catalyst was dried at 180°C. It was then stabilized by heating to 360°C for 5 hr in a stream of nitrogen. The content of thorium oxide was 2.9% (wt.). The BET surface area was 870 m2/g. Prior to kinetic measurements, the catalyst was modified by passing over acetic acid vapors (100 g acid/1 g catalyst). 

Parallel ketonization of acetic acid and propionic acid was one of the transformations of this type studied in our Laboratory. Ryba6ek and Setinek (94) investigated the kinetics of these reactions in the gaseous phase at 316°C using thorium oxide on activated carbon (p. 27) as the catalyst. This model system allowed the study of each reaction separately as well as of the simultaneous conversion of both acids. 

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