The reactivity of aromatic and aliphatic esters in on-line thermochemolysis in the presence of methylation reagents was studied using model compounds. Guaiacyl and 2-nonyl palmitates were synthesised, representing aromatic and aliphatic ester bonds, respectively. These model compounds were analysed by on-line thermochemolysis using tetramethylammonium acetate (TMAAc) and tetramethylammonium hydroxide (TMAH) in order to differentiate free acids from esterified acids. The released palmitic acid with TMAH for both model compounds was close to the theoretical palmitic acid content in the model compounds, even if part of the aliphatic ester had not reacted with TMAH. The free palmitic acid content by TMAAc was one third of the theoretical value for aromatic ester and only a few percentages for aliphatic ester. The result indicated that the less basic reagent is able to hydrolyse the aromatic ester linkage to some extent, whereas the aliphatic ester remains intact. Thus, differentiation of free acids by TMAAc from the esterified acids cannot be reliably performed from matrices containing aromatic esters. It was found that transesterification due to the use of methanol as a solvent with TMAAc is an insignificant reaction in on-line thermochemolysis.
- Ester bond
- free acids
- tetramethylammonium acetate
- tetramethylammonium hydroxide