Rate laws acetic acid production

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. 

In the case of 1-phenylpropyne a vinyl cation is suggested as intermediate. The kinetic law is rate = k3 [—C=C—] [HC1]2. The second order dependence on HC1 is explained by assuming that proton transfer to the triple bond results in the anion hydrogen dichloride, HClJ. The product distribution and the stereochemistry, under kinetic control, have been explained by assuming that a cw-oriented intimate ion-pair, 14 is initially formed which, following Scheme 2, may either collapse to cis chloride, undergo anion displacement by acetic acid to form tram acetate or a randomly oriented (solvent separated) ion-pair 15 which gives racemic material. 

The Monsanto process has been thoroughly studied, and the relatively simple catalytic mechanism in Scheme 17.1, consisting of only anionic rhodium species, has been proposed. Virtually any source of rhodium or of iodidemay be introduced as a "precatalyst" to generate [Rh(CO)2lJ and Mel imder catalytic conditions. High-pressure IR spectroscopy has shown that the major rhodium species in the catalytic solutions is [Rh(CO)2l2]"(v Q = 2055 and 1985 cm" ). The overall rate law for the formation of acetic acid contains a linear dependence on rhodium and methyl iodide and no dependence on the concentrations of reactants (CO and methanol) and product (acetic acid). Consistent with the rate law, the turnover-limiting step has been proposed to be the oxidative addition of Mel to [Rh(CO)jIj]". 

Several studies have been made using Pb as an oxidant. The reaction with methanol yields formaldehyde with rupture of a C—H bond as the rate-limiting step. Whereas the product is reportedly stable in the presence of Pb(OAc)4, fact further reaction takes place to yield methyl formate. The mechanism of decarboxylation of 2-hydroxycarboxylic acids, ROH, in anhydrous acetic acid has been investigated using several techniques. The rate law is of the form... 

In 1862, the French chemists Pierre Berthelot and Leon de Saint-Gilles reported on the reaction between ethanol and acetic acid to ethyl acetate and water. They found that the rate of product formation was proportional to the product of the reactant concentrations. In the same years, the Norwegian chemist Waage and the mathematician Guldberg formulated their law of mass action, which, in hindsight, was based on invalid kinetic procedures, although the result was correct. 

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