Micellar effects on aromatic esters hydrolysis

Abstract

Highlights Cationic surfactants catalyze the alkaline hydrolysis of aromatic esters.  Variation of counter-ions association degree to micelles explains experimental data.  Adsorption equilibrium constants of esters do not depend on micelle counter-ion. AbstractThe alkaline hydrolysis of two aromatic esters, 2-naphthyl acetate (2NA) and phenyl acetate (PhA) has been tackled in this work. The reaction has been followed in water and in the presence of cationic surfactants with different chain lengths: dodecyltrimethylammonium bromide (DTABr), tetradecyltrimethylammonium bromide (TTABr), and hexadecyltrimethylammonium bromide (CTABr) and the corresponding hydroxides (DTAOH, TTAOH and CTAOH) at 25 °C. The pseudo-first order rate constants increase with surfactant concentration in the presence of surfactants with reactive counter-ions, while a maximum is reached for bromide surfactants with a constant concentration of hydroxyl ion. Both, the association equilibrium constants of 2NA and PhA with micelles and the rate constant in this medium were determined. The degree of counter-ion association to micelles was considered as a variable parameter, using the adsorption equilibrium of bromide and hydroxide ions to the micelle. Graphical abstract Keywords Hydrolysis; Ion-exchange equilibrium; Micelles; Mass action model; Pseudo-phase model Corresponding author. Tel.: +34 981 167000x2068; fax: +34 981 167065.

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

“…This type of rate profile, i.e. the appearance of a rate maximum, for the hydrolysis reactions of various organic compounds in the presence of cationic surfactants, is well documented . 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 (Scheme ).…”

“…Enzymatic and enzyme‐analogous systems including micelles have a practical significance for the hydrolytic detoxifications of organic compounds and even for treatment of waste water . Micelles can cause an acceleration or inhibition of a given chemical reaction rate relative to the equivalent reaction in an aqueous medium, depending upon the type of surfactants used for micelle formation .…”

“…Reactivity maxima have been frequently found for substrates of a certain chain length in reactions in micellar aggregates, which leads to the conclusion that there must be an optimal reaction site for the reactions. The proximity of the reaction partners (hydroxide ions and the carbonyl group of the ester in the case of alkaline ester hydrolysis) in the Stern layer determines the higher rate of reaction relative to that in aqueous media .…”

Hydrolysis of phenyl trifluoroacetate in mixed surfactant systems

“…Base‐catalyzed ester hydrolysis have been widely used as model reactions to evaluate MME on chemical reactions because of its well‐known, relatively simple mechanism . Besides, its study is very important as they are key reactions in biological systems.…”

“…Base-catalyzed ester hydrolysis have been widely used as model reactions to evaluate MME on chemical reactions because of its wellknown, relatively simple mechanism. [27,28] Besides, its study is very important as they are key reactions in biological systems. Several years ago, we studied the hydrolysis reaction of phenyl trifluoroacetate esters, [29] and the transition state of these reactions can be schematically represented by 2, [30] where B is any base, including water.…”