Structure and Temperature Effects on the Reaction Rate of Aryloxiranes with 3,5-Dinitrobenzoic Acid in Acetonitrile

Abstract

The effects of temperature and structure of aryloxiranes on the rate of their reaction with 3,5-dinitrobenzoic acid in acetonitrile are additive, and the process is entropy-controlled.Reactions accompanied by opening of oxirane ring have long attracted researchers' attention due to their diversity, specificity of their mechanisms under catalytic and noncatalytic conditions, and wide application in organic synthesis (in particular, in the preparation of polymeric epoxy compounds [1][2][3][4][5][6]. An important problem in the chemistry of oxiranes is to reveal quantitative relations holding in opening of the oxirane ring upon variation of internal (structure of the reactants and catalysts) and external factors (reaction medium, temperature).We previously [6,7] made an attempt to simulate the reactivity of the system epoxy substrate-acid reagent by mathematical modeling with the aid of cross correlation analysis of the results of multifactor kinetic experiments. While studying the joint effect of the structure of arenesulfonic acids (YC 6 H 4 SO 3 H) and temperature on the kinetics of oxirane ring opening in 4-nitrophenyloxirane in dioxane, we showed that quantitative estimation of the reactivity in terms of a polylinear regression model (which includes statistically significant cross correlation coefficient ρ YT = -5.8 ± 0.4 [6]) requires that nonadditive effects of factors being varied be taken into consideration. Nonadditive effect of structural factors was found in reactions of X-substituted phenyloxiranes with Y-substituted benzoic acids in acetonitrile at 343 K (ρ XY = -1.1 ± 0.2 [7]).The goal of the present work was to examine joint effect of temperature and structure of aryloxiranes on the rate of their reactions with 3,5-dinitrobenzoic acid (HA) in acetonitrile. The products of these reactions are primary alcohols, 1-aryl-2-hydroxyethyl 3,5-dinitrocarboxylates (Scheme 1) [7]. The kinetic relations holding in the process were studied using more than tenfold excess of the oxirane substrate (S) with respect to 3,5-dinitrobenzoic acid [S] 0 >> [HA] 0 , 0.08-0.17 M, according to the procedure described in [7]. The procedure is based on acid-base titration of the unreacted acid reagent with an aqueous solution of sodium hydroxide. Under the given conditions, the reaction was of first order with respect to the substrate and of second order with respect to HA, in keeping with the following kinetic equation:In all cases, the apparent pseudosecond rate constants k 2 (l mol -1 s -1 ) remained unchanged during the process until an acid reagent conversion of 70-80% (the error in the determination of k 2 did not exceed 7%). The third-order rate constants (k 3 = k 2 /[S] 0 ; Table 1) increased as the temperature rose, as well as the electron-acceptor power of the X substituent decreased. The latter relation is consistent with the negative sign of ρ + . The ρ + (r) values calculated for particular reaction series at 323, 333, and 343 K are, respectively, -3.0 ± 0.2 (0.999), -2.9 ± 0.1 (0.998), and -3.1 ± 0.2 (0.993). The ...

Nucleophilic Aliphatic Substitution

“…26 Since the reaction is first order in the oxirane and second order in the acid, it has been suggested that pre-equilibrium association with HA is followed by attack of a second HA at the benzyl carbon. The much slower rate found when a more electron-withdrawing substituent is on the aryl ring was due to a large decrease in S = (i.e.…”