Reaction rates acetoxylations

The addition of sulphuric acid increased the rate of nitration of benzene, and under the influence of this additive the rate became proportional to the first powers of the concentrations of aromatic, acetyl nitrate and sulphuric acid. Sulphuric acid markedly catalysed the zeroth-order nitration and acetoxylation of o-xylene without affecting the kinetic form of the reaction. ... 

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... 

The constancy of the acetoxylation nitration ratio and zeroth reaction order in aromatic suggested that both reactions were brought about by a common species (protonated acetyl nitrate) the formation of which was rate-determining according to equilibria (30) and (31), with the latter being a slow step. Since the total rate of acetoxylation plus nitration is given by... 

Another mechanistically useful nucleophile is acetate ion and related carboxylates. Acetate ion is difficult to oxidize (Eberson, 1963) and reacts with radical cations in a bond-forming reaction (Eberson and Nyberg, 1976). The oxidation product, the acetoxyl radical, has properties which make trapping it very unlikely in that its decarboxylation rate constant is 1.3 X 109 s 1 (Hillborn... 

The anodic oxidation of 4-methoxyphcnols in acetic acid effectively stabilises the phenoxonium ion, in an equlibrium with the acetoxylation product. Tbis allows an intermolecular [5 + 2] bx-cycloaddition processes with some alkenes [110], The cycloaddition process has been used very successfully in the synthesis of a number of natural products [III]. The rate of cycloaddition is sensitive to substituents on the alkene bond and in imfavourable cases other reactions of the phenoxonium ion predominate. 

The effects of added species. The rate of nitration of benzene, according to a rate law kinetically of the first order in the concentration of aromatic, was reduced by sodium nitrate, a concentration of io 3 mol l-1 of the latter retarding nitration by a factor of about 4.llc>28 Lithium nitrate anticatalysed the nitration and acetoxylation of o-xylene in solutions of acetyl nitrate in acetic anhydride. The presence of 6 x io-4 mol 1 1 of nitrate reduced the rate by a factor of 4, and modified the kinetic form of the nitration from a zeroth-order dependence on the concentration of aromatic towards a first-order dependence. However, the ratio of acetoxylation to nitration remained constant.146 Small concentrations of sodium nitrate similarly depressed the rate of nitration of anisole and again modified the reaction away from zeroth to first-order dependence on the concentration of the aromatic.116... 

Acetoxylation of poly(vinyl chloride) can be carried out under homogeneous conditions. Crown ethers, like 18-crown-6, solubilize potassium acetate in mixtures of benzene, tetrahydrofuran, and methyl alcohol to generate unsolvated, strongly nucleophilic naked acetate anions. These react readily with the polymer under mild conditions. Substitutions of the chlorine atoms on the polymeric backbones by anionic species take place by a Sn2 mechanism. The reactions can also proceed by a Sivl mechanism. That, however, requires formations of cationic centers on the backbones in the rate-determining step and substitutions are in competition with elimination reactions. It is conceivable that anionic species may (depending upon basicity) also facilitate... 

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