Esterification of fluorinated aromatic carboxylic acids with methanol by using UiO-66-NH2 as a heterogeneous catalyst and process optimization by the Taguchi method

Abstract

Fluorobenzoic acids (FBAs) are used as chemical tracers in enhanced oil recovery and reduction in their limit of detection is a crucial issue. GC-MS is a versatile tool to detect and quantify FBAs at very low limits of concentration, but they require esterification prior to analysis by GC-MS. The present article presents a study of the catalytic methyl esterification of fluorinated aromatic carboxylic acids (FBAs) using methanol as methyl source and UiO-66-NH₂ as a heterogeneous catalyst. The reaction time was reduced to 10 hours which is a 58% reduction in time over the traditional BF₃·MeOH complex as derivatizing agent. The yield of the esterification reaction was evaluated with respect to the BF₃–MeOH complex and determined by GC-EI-MS. The catalytic procedure was optimized by the Taguchi model with a 99.99% fit. Good catalytic performance was observed for 23 different isomers of fluorinated aromatic acids showing a relative conversion yield of up to 169.86%, which reduced the detection limit of FBAs up to 2.60 ng mL⁻¹.