GC—MS analysis of carboxylic acids in petroleum after esterification with fluoroalcohols

Abstract

AbstractThe GC–MS characteristics of carboxylic acid esters prepared from fluorine‐containing alcohols were compared to those of methyl esters. The GC retention of 2,2,2‐trifluoroethyl (TFE) esters was less than, and 2,2,3,3,4,4,4‐heptafluoro‐1‐butyl (HFB) esters was approximately equivalent to that of methyl esters. Mass spectra of TFE and HFB aliphatic esters show significantly more intense molecular and key fragment ions than those of methyl esters. Also, owing to their significantly higher molecular weights, TFE or HFB ester molecular ions and most fragment ions of interest occur at significantly higher m/z values than most potential interfering ions.Data for about 70 individual TFE and HFB esters are reported. Application of the methodology to a petroleum‐derived carboxylic acid concentrate resulted in identification of straight chain, isoprenoid, methyl‐substituted straight chain (2‐, 3‐, 5‐,10‐, 12‐positions along chain), and dimethyl‐substituted straight chain acids containing from 11 to 22 carbons. Benzoic acid and homologs with up to 3‐carbons in alkyl substitutents were minor components in the sample.The procedure provided for forming TFE and HFB esters from free acids requires less time and effort than a previously reported method, while retaining its capability for achieving essentially quantitative conversion. Free hydroxyl groups in alcohols and phenols are converted to trifluoroacetate esters concurrently with formation of TFE/HFB carboxylic acid esters. The reaction products, including compounds with two functional groups (diacids, salicylic acid, etc.), chromatograph well on conventional nonpolar GC stationary phases.