Structure-reactivity correlations for reactions of substituted phenolate anions with acetate and formate esters

Abstract

The reactions of substituted phenolate anions with m-nitrophenyl, p-nitrophenyl, and 3,4-dinitrophenyl formates follow nonlinear Bransted-type correlations that might be taken as evidence for a change in the rate-limiting step of a reaction that proceeds through a tetrahedral addition intermediate. However, the correlation actually represents two different Bronsted lines that are defined by meta-and para-substituted phenolate anions and by meta-and para-substituted o-chlorophenolate anions. A concerted mechanism for both acetyl-and formyl-transfer reactions is supported by the absence of a detectable change in the Bronsted slope at ApK = 0 for the attacking and leaving phenolate anions within each class of Bronsted correlations. Regular increases in the dependence of log k on the pAa of the nucleophile with increasing pAa of the leaving group correspond to a positive interaction coefficient pxy = d/3lg/d(pA"uc) = d/3nuc/5(pAlg). The observation of two different Bronsted lines for the reactions of substituted phenolate anions with phenyl acetates is attributed to a steric effect that decreases the rate of reaction of substituted o-chlorophenolate anions by 25-50%. The reactions of metaand para-substituted phenolate and o-chlorophenolate anions with substituted phenyl acetate esters follow values of /3nlic = 0.53-0.66 and -j5lg = 0.50-0.63. The reactions of meta-and para-substituted phenolate anions with formate esters are ~103 times faster and follow smaller values of j6nuc = 0.43-0.64 and -/3|g = 0.31-0.48. However, the reactions of meta-and para-substituted o-chlorophenolate anions with the same formate esters follow larger values of /3nuc = 0.63-0.90 and -/3,g = 0.46-0.90. The large values of /3nuc and -/Slg for the reactions of substituted o-chlorophenolate anions with formate esters may arise from destabilization by the o-chloro group of a stacking interaction that is present in the transition state for reactions of formate esters, but not acetate esters.

Kinetics and Mechanism of the Aminolysis of Aryl N-Cyclohexyl Thiocarbamates in Acetonitrile

“…Especially, the ΔH ≠ values are somewhat lower and the ΔS ≠ values are higher negative values than other aminolysis systems. 13 The expulsion of ArO − anion in the rate determining step (an endoergic process) is assisted by the hydrogen-bonding with an amino hydrogen of the benzylammonium ion within the intermediate, T…”

On the mechanism of the reaction between aryl acetates and hydroxylamine

“…Investigating the reaction of p-nitrophenylacetate and phenolate ions, Buncel 35 described the process as a multi-step reaction and proposed the rate-limiting step to be the intermediate formation, regardless of whether the leaving group departure is synchronized with the nucleophilic attack or not. On the other hand, Williams 6a and Jencks 7 , studying the same reaction have proposed a concerted mechanism based on a constant β NU value even for ∆pKa= 0 when phenolate acts as both the nucleophile and the leaving group. This suggestion is supported by Hengge following his kinetic isotope effect studies of reactions between p-nitrophenylacetate and several oxyanions, such as, the hydroxyl anion, phenolates, hexafluormethylisopropoxide and aliphatic oxyanions.…”

“…[1][2][3][4][5][6][7][8][9] Besides describing the structural relationships which lead to the reactivity of carboxylic acid derivatives, the search for nucleophiles able to cleave selectively peptide and ester bonds is still a challenge in many areas of chemistry and biochemistry. [10][11][12] The development of such stable and highly reactive nucleophiles has a wide range of applications in chemical detoxification, e.g., where quantitative phosphate bond cleavage is the target.…”

Reactions of 4-Nitrophenyl 2-Thiophenecarboxylates with R2NH/R2NH2+in 20 mol % DMSO (aq). Effects of 5-Thienyl Substituent and Base Strength

“…[4][5][6][7][8][9][10][11][12][13] The first is the concerted mechanism. The acyl-group transfer reactions of aryl phenyl carbonates with phenoxides and 4-nitrophenyl acetate with phenoxides have been concluded to be of this type.…”

“…The acyl-group transfer reactions of aryl phenyl carbonates with phenoxides and 4-nitrophenyl acetate with phenoxides have been concluded to be of this type. [7][8][9] The aminolysis can also proceed via a zwitterionic tetrahedral intermediate. [14][15][16][17] In contrast, much less is known about the corresponding acyl transfer reactions involving heterocyclic aromatic compounds.…”