Influences of Micelle Formation and Added Salts on the Hydrolysis Reaction Rate of p‐Nitrophenyl Benzoate in Aqueous Buffered Media

Abstract

The hydrolysis reaction rate of p-nitrophenyl benzoate (p-NPB) has been examined in aqueous buffer media of pH 9.18, containing surfactants, cetyltrimethylammonium bromide (CTAB) and chloride (CTAC), or sodium dodecyl sulfate (SDS) at 35°C. Although the rate constant [log (k/s −1 )] of p-NPB hydrolysis has once decreased slightly below the critical micelle concentration (CMC) value for CTAB and CTAC, it has begun to increase drastically with micellar formation. With increasing concentrations larger than the CMC value, the log (k/s −1 ) value has reached the optimal value, i.e., a 140-and 200-fold rate acceleration for CTAB and CTAC, respectively, compared to that without a surfactant. Whereas the anionic surfactant, SDS, has caused only a gradual rate deceleration in the whole concentration range (up to 0.03 mol dm −3 ). Increases in pH of the buffer have resulted in increases of the hydrolysis rate. In the CTAB micellar solution, the remarkably enhanced rate has been retarded significantly by the addition of only 0.10 mol dm −3 bromide salts. The effects of rate retardation caused by the added salts follows in the order of NaBr > Me 4 NBr > Et 4 NBr > Pr 4 NBr > n-Bu 4 NBr. In the absence of surfactant, however, the addition of the bromide salts has accelerated the hydrolysis rate, except for the metallic salt of NaBr, with the order of Me 4 NBr < Et 4 NBr < Pr 4 NBr < n-Bu 4 NBr. In the CTAC micellar solution, similar rate retardation effects have been observed in the presence of chloride salts (NaCl, Et 4 NCl, and n-Bu 4 NCl). The effects of added salts have

Reactivity differences of O‐aryl O‐(4‐nitrophenyl) thionocarbonates versus their homolog carbonates: Micellar catalysis in hydrolysis reactions

“…The pseudo‐first‐order rate constant increases in the presence of a small amount of surfactant above the critical micelle concentration (cmc) until it reaches a maximum; after this point, an increase in surfactant concentration diminishes the observed rate constant (see Figures ). This behavior is explained considering the micelle formation, the amount of substrate in the micelles, the competition between OH − , borate and the increasing amount of Br − , and the dilution of the substrate in the micelles …”

“…This behavior is explained considering the micelle formation, the amount of substrate in the micelles, the Table S3 in the Supporting Information) and the curves were calculated with Equations 2 to 7 and values of Table 2. competition between OH − , borate and the increasing amount of Br − , and the dilution of the substrate in the micelles. [12] These studies have suggested strongly that in micellar media, most reactions take place on the surface of micelle at or near the highly charged double layer, commonly called the Stern layer.…”

“…Recent studies by Hojo et al have reported that the hydrolysis reactions of p ‐nitrophenyl benzoate in the presence of cationic surfactants, such as CTAB or CTAC, lead to an increment in the rate constant values of 140‐fold and 200‐fold for CTAB and CTAC, respectively. Whereas, the anionic surfactant, sodium dodecyl sulfate, has caused only a gradual rate deceleration by the same reaction …”

“…Whereas, the anionic surfactant, sodium dodecyl sulfate, has caused only a gradual rate deceleration by the same reaction. [12] Thus, taking into account the catalytic effect that cationic micelles would have on reactions of hydrolysis of carbonyl compounds, it is interesting to assess the micellar effect on such reactions in a series of thionocarbonates and their homolog carbonates. To this end, in the present work, a kinetic study of the hydrolysis reaction toward 4-cyanophenyl, phenyl and 4methylphenyl 4-nitrophenyl thionocarbonates (1, 2, and 3, respectively; Scheme 1), and 4-cyanophenyl and phenyl 4-nitrophenyl carbonate (4 and 5, respectively; Scheme 1) in the presence of increasing concentrations of CTAB was carried out.…”

“…In this line, studies conducted by Al‐Lohedan et al (2017) have demonstrated that the alkaline hydrolysis of carboxylate (1‐naphthylbutyrate) and carbonate esters (2‐(methylsulfonyl)‐ethyl‐4‐nitrophenylcarbonate) is enhanced in the presence of cationic micelles of cetyltrimethylammonium (CTA) bromide and CTA sulfate and inhibited by anionic micelles of sodium dodecyl sulfate . Recent studies by Hojo et al have reported that the hydrolysis reactions of p ‐nitrophenyl benzoate in the presence of cationic surfactants, such as CTAB or CTAC, lead to an increment in the rate constant values of 140‐fold and 200‐fold for CTAB and CTAC, respectively. Whereas, the anionic surfactant, sodium dodecyl sulfate, has caused only a gradual rate deceleration by the same reaction …”