Microwave-assisted preparation of naphthenic acid esters

Abstract

The synthesis of esters of natural petroleum acids of the naphthenic type assisted with microwave irradiation under the conditions of acid catalysis was carried out with various alcohols: methanol, ethanol, n-butanol and tert-butyl alcohol. Microwave dielectric heating of the reaction mixture in an unmodified microwave oven with activation of the naphthenic acids with sulfuric and p-toluenesulfonic acid afforded the esters of the naphthenic acids. Depending on the catalyst and the steric and nucleophilic properties of the alcohols, the yield of naphthenic esters ranged from 31.25% to 88.90%. As a consequence of microwave dielectric heating, the esterification time was reduced from 6-10 h to 5 min. .

Acid‐catalyzed esterification of naphthenic acids

“…The reason is that sulfuric acid releases H 1 at concentrations twice that of PTSA. Furthermore, other studies showed that the naphthenic acid methyl ester (NAME) yield obtained by PTSA was lower than that obtained using sulfuric acid [12,13]. Furthermore, other studies showed that the naphthenic acid methyl ester (NAME) yield obtained by PTSA was lower than that obtained using sulfuric acid [12,13].…”

“…In the acid-catalyzed esterification reaction, the amount of catalyst should be determined by considering the number of acidic protons that each catalyst bears [22]. Furthermore, other studies showed that the naphthenic acid methyl ester (NAME) yield obtained by PTSA was lower than that obtained using sulfuric acid [12,13]. In summary, comparing Figures 4 through 6 shows that the esterification of NAs is highly dependent on the amount of catalyst and the number of acidic protons released by the catalyst.…”

“…The acid-catalyzed esterification of NAs assisted with microwave irradiation has been studied with various alcohols and two different catalysts [12]. This study showed that the microwave procedure accelerated reactions and the ester yields obtained with sulfuric acid were higher than those using p-toluenesulfonic acid (PTSA) [12]. Veliev et al studied the acid-catalyzed esterification of NAs with acetylenic alcohols at different temperatures in the range of 80-1108C.…”