The temperature dependence of the rates of neutral hydrolysis of a series of alkyl trifluoroacetates (CF3COOR; R = methyl, ethyl, s-propyl, t-butyl) has been determined in both light and heavy water. From these studies the thermodynamic parameters (AH*, AS*) which characterize the activation process have been calculated. Sufficient rate data have been obtained in the case of the ethyl ester to calculate the heat capacity of activation (AC,*) for the hydrolysis of this compound in light water. Both the entropies and enthalpies of activation as well as the solvent isotope effects are consistent with the proposal that the primary and secondary esters react by an acyl-oxygen B,,2 mechanism, in contrast to the tertiary ester, which appears to react either by a carbonium ion (SN1) process or by a route which combines both the B,,2 and SN1 paths.
Treatment of N-methyl-N-nitro-9-aminoanthracene with sulphuric acid (ca. 7 ~) yielded I O-nitroanthrone (90%) together with nitrous acid (5%). The reaction which involved intramolecular shift of the nitro-group, was first order in substrate its rate was linearly correlated with the ho function ; but, unexpectedly, the reaction had a solvent isotope effect (kD1o/kHoo) of less than unity.It is proposed that rate-limiting protonation of the aromatic ring and either direct migration of the nitro-group or migration via the intermediacy of a tightly-bound ion or radical pair occurred.The present status of the ' radical-pair ' and ' cartwheel mechanisms for the nitroamine rearrangement is discussed. * D. V. Banthorpe in ' Chemistry of the Amino Group,' ed.
The rates of neutral hydrolysis of a series of 4-substituted benzyl trifluoroacetates 4-X-C,H,CH,OCOCF,, X = NO,, C1, H, CH,, and OCH, have been studied in water and deuterium oxide, both solvents containing 0.012 mol fraction of acetone. The alteration of the rates with the nature of the 4-substituent and the kinetic solvent isotope effect (k(H,O)/k(D,O)) are consistent with the proposal that the esters with X = NO,, CI, H, and CH, all react by an acyl-oxygen BA,2 mechanism. On the other hand, the same mechanistic criteria indicate that the 4-methoxybenzyl ester reacts by both the BA,2 and the S,1 alkyl-oxygen fission paths in equal amounts.
Can. J. Chem. 59,839 (1981). The rates of rearrangement of N-bromo-4-chloroacetanilide to 2-bromo-4-chloroacetanilide catalyzed by trifluoroacetic acid and trifluoroacetic acid-d have been measured as a function of acid concentration in chlorobenzene at T = 323 K. Similar experiments have been carried out with N-bromoacetanilide and N-bromo-4-chloro-2,6-dideuterioacetanilide. A comprehensive analysis of the observed rates for each substrate as a function of acid concentration reveals that the rearrangements involve at least three mechanistic steps when trifluoroacetic acid is the catalyst. In contrast, the rate of rearrangement of N-bromoacetanilide catalyzed by trichloroacetic acid at T = 288 K appears to follow a limiting form of the same rate law. Earlier observations are assessed in the light of the proposed mechanism, and it is concluded that both present and past work can be satisfactorily rationalized in terms of an intramolecular migration of bromine.
The rate of solvolysis of ethyl trifluoroacetate has been investigated in a series of H,O/D,O mixtures at 9.97 "C. The secondary isotope effects related to the hydrolysis of the isotopic pairs, methyllmethyl-d,, ethyllethyl-d,, i-propylli-propyl-8-4 and I-butyllt-butyl-d, trifluoroacetates have been established as well as the temperature dependence for the hydrolysis of t-butyl trifluoroacetate. The significance of all these measurements with respect to the mechanism of these reactions is discussed.La vitesse de la solvolyse du trifluoroacktate d'bthyle a ktt Ctudike dans divers melanges H,0/D20 a 9.97 "C.Les effets isotopiques secondaires concernant les paires isotopiques des trifluoroacktates de mtthylelmtthyl-d,, d'kthyle/ethyl-d,, d'i-propyleli-propyl-P-d, et de t-butylelt-butyl-4, ont Bti: Ctablis ainsi que I'influence de la tempbrature sur I'hydrolyse du trifluoroacetate de t-butyle. La signification de toutes ces mesures, quant au mecanisme de ces rkactions, est discutke.
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