Studies on kinetics and preparation of C₃₆ dimer acid esters

Abstract

C3e Dimer acids were esterified with various short-chain alcohols, namely 2-propanol, n-butanol, n-hexanol, noctanol, 2-octanol and 2-ethyl-l-hexanol by using sulfuric acid as catalyst and benzene as an azeotropic solvent. Various reaction parameters were standardized. In case of isopropyl esters, acid-to-alcohol mole ratio of 1:5 and sulfuric acid concentration of 2% based on the weight of dimer acids were found to be optimum. In case of straightchain primary alcohols, namely n-butanol, n-hexanol and n-octanol, 1:2.5 mole ratio of acid to alcohol and 1% by weight of sulfuric acid were found satisfactory. Esterification reaction rates were determined from the fall in acid value of the product. The reaction followed pseudo first order kinetics. The reaction rates increased with the increase in chainlength of straight-chain primary alcohols from n-butanol to n-octanol. The rate of reaction decreased from n-octanol to 2-ethyl-l-hexanol to 2-octanol due to the branching of the chain in 2-ethyl-l-hexanol and secondary nature of the --OH group in 2-octanol.

Synthesis of Dimerate Esters by Solvent-Free Method

“…Increasing the mole ratio of 1-octanol with respect to C 36 dimer acid is unfavourable as this may reduce the reaction rate gradually as reported by Kale et al (1991) as the mole ratio of C 36 dimer acid to 2-propanol changed from 1:5 to 1:10 and further increment of alcohol used may cause excess dilution of the reaction mixture. All the reactions (having different molar ratios of C 36 dimer acid to octanol) were then prolonged to 40 hr and the acid values were tabulated ( Table 2).…”

“…Mandake et al (2013) showed the acceleration of reaction rate in the presence of 10% w/w of Amberlyst 15 ® which afforded 54% conversion in 3 hr in contrast to only 14% conversion for non-catalytic esterification of acetic acid and methanol (1:3 molar ratio) within the same period of time. Conventionally, the esterification reaction is carried out in the presence of homogeneous inorganic catalyst such as sulphuric (Kale et al, 1991;Zeki et al, 2010), sulphonic and hydrochloric acid. To date, this trend has shifted towards the use of heterogeneous catalysts due to their several advantages over homogeneous catalysts.…”

“…Several studies on acid-catalysed preparation of C 36 dimerate with various short-chain alcohols (Burg and Kleiman, 1991;Kale et al, 1991) and their applications have been reported in several publications and patents (Henry and Tierney, 1962;Tierney, 1960) which showed the importance of the dimerates as versatile products such as lubricants, lubricant additives, surface-active agents and corrosion and rust inhibitors. Kale et al (1991) had previously described preparation of C 36 dimer ester in the presence of 1% (w/w) of sulphuric acid (H 2 SO 4 ) in benzene as an azeotropic solvent. However, no studies of the spontaneous esterification of C 36 dimer acid have been reported.…”