Acetate ester ions, decomposition

Studies on the acetate of A -hydroxy-AAF indicated that esterification of the hydroxamic acid could be the requisite transformation of an aromatic amine to an ultimate carcinogen. Bioassays indicated that A -acetoxy-AAF resembled direct-acting carcinogens in producing subcutaneous tumors at the site of injection. Unlike /V-hydroxy-AAF, this acetate ester reacted in vitro with various cellular macromolecules (339, 410). The metabolic activation of AAF and decomposition of A -acetoxy-AAF to an electrophile are illustrated in Fig. 1. The possibility that -hydroxy-AAF was esterified in vivo to sulfate or phosphate esters has been examined. Evidence that sulfate esters may be involved in the formation of the ultimate carcinogen of AAF has been supported by several in vivo bioassays. Coadministration of acetanilide, which depletes the intracellular level of sulfate, reduced the carcinogenicity of AAF (487). Coadministration of sulfate ion with AAF enhanced its activity as a liver carcinogen (97). 

Front-side exchange (path (e)) partakes of the character of an add-base reaction in the nitrosoamide decomposition (section a (2) (e)), and in view of the basicity of the incipient hydroxide ion, one would expect extensive exchange of the counter ion in the nitrous add deamination (equation 146, path (e)). In fact, acetate esters are the chief products from deaminations in acetic add (ref. of Table 12), and the alcohol component of the reaction has only rarely been reported (Table 12). In acetic acid runs, the adds present in the medium (HX, equation 146) are HO2CCH3, HONO and HONO2 (the latter from the disproportionation of nitrous add). Acetate esters have invariably been reported as products in deamination and in a few instances nitrite and nitrate estershave been isolated. 

The reactions obeyed pseudo-first-order kinetics consistent with a rapid reversible protonation of the substrate, S, at the ester carbonyl followed by a rate-determining decomposition to acetic acid and nitrenium ion according to Scheme 19. In accordance with equation 13, the pseudo-first-order rate constant, k, was shown to be proportional to acid concentration and inversely proportional to the activity of the water/acetonitrile solvent . 

The most numerous cases of homogeneous catalysis are by certain ions or metal coordination compounds in aqueous solution and in biochemistry, where enzymes function catalytically. Many ionic effects are known. The hydronium ion H3O and the hydroxyl ion OH catalyze hydrolyses such as those of esters ferrous ion catalyzes the decomposition of hydrogen peroxide decomposition of nitramide is catalyzed by acetate ion. Other instances are inversion of sucrose by HCl, halogenation of acetone by H and OH , hydration of isobutene by acids, hydrolysis of esters by acids, and others. 

The consistancy of the observed /4-factors, the magnitude of the activation entropies, the a correlations in the substituent effects at the a- and /8-carbon positions, the collective influence of all three substitutable centers on the reaction rates, the importance of charge stabilization in the transition state, and the primary deuterium isotope effects on the alkyl acetic acid ester decomposition, all favor the concerted polar 6-center transition state shown below (IV). However, an alternative possibility involving intimate ion-pair formation has been proposed by Scheer et al.. ... 

The next step in the reaction scheme—decomposition of the a-bonded alkylpalladium (XIV or XV)—has caused some controversy. To account for the results of several deuterium-labelling studies (15, 36, 54), a. palladium-assisted hydride transfer reaction (Reaction 4) has been proposed (36, 54). A number of inconsistencies in the studies using 2-deuteropro-pylene as substrate (54) have been discussed (i). In addition, the formation of a free carbonium ion such as VII [as proposed by Moiseev (36)], while accounting well for the formation of ethylidene diacetate, is much less satisfactory in accounting for the production of the unsaturated esters in an acetate-acetic acid medium. A simple elimination of -hydrogen (Reactions 13a and b) could also account for the products formed. While not necessary for the reaction, chloride assistance for proton removal is a possibility and has been postulated previously for a similar reaction (i, 37). 

LaMar direct fluorination (see p. 2) of ethyl acetate in a four-zone cryogenic reactor (lowest temperature —100 °C) provides the trifluoroacetates CF3 C02 C2F6 and CF3-C02-CHF-CF3 in 5 and 20% yield, respectively, after isolation by g-l.c. " apparently fluoride ion readily initiates decomposition of these esters according to F" + CFa COs-CFX CFsCFa COF -I- CFs-CFX-Q- -> F -I-CFa CXO (X = H or J). 

The /-butane chemical ionization spectra of benzyl acetate and t-amyl acetate have been investigated at a number of temperatures, and the rate constants for the decomposition of the protonated esters to benzyl and r-amyl ions, respectively, have been obtained at the several temperatures from (41) to (42). It is found that the rate constants obey the Arrhenius relationship, and this is illustrated in Fig. 5. Activation energies and frequency factors obtained from the Arrhenius plots are given in Table XIV. 

In solvent systems containing low concentrations of water in acetic acid, dioxane, or sulfolane, the alcohol product (capture by water) occurs with retention, whereas the ester product (capture by acetic acid solvent) is a mixture of retained and inverted product. These results can be rationalized in terms of a hydrated ion pair formed by decomposition of the diazotized intermediate ... 

In Scheme 1, the reactive species of Cr(VI) and paracetamol readily form chromate ester as the first step in the reduction of Cr(VI) [14]. Chromate ester undergoes oxidative decomposition in the next step (rate determining), leading to the formation of an intermediate and Cr(IV) [15]. The proposed mechanism is further supported by analysis of the products. Ammonia has been detected as ammonium ions in aqueous solution. Benzoquinone and acetic acid were also detected by the spot tests [16]. 

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