Inversion dimers dominate the crystal packing in the structure of trimethyl citrate (trimethyl 2-hydroxypropane-1, 2, 3-tricarboxylate)

Abstract

Trimethyl citrate, C9H14O7 (systematic name: trimethyl 2-hydroxypropane-1,2,3-tricarboxylate), 2, was prepared by the esterification of citric acid and methanol in the presence of thionyl chloride at 273 K. The bond lengths and angles in 2 compare closely with those observed in citric acid. The C—C bonds adjacent to the terminal carboxyl groups are significantly shorter than those around the central C atom. The central carboxylate group and the hydroxy group occur in the normal planar arrangement with an r.m.s. deviation of 0.0171 Å from the mean plane involving all six atoms in the central unit. The crystal structure is almost completely dominated by the formation of inversion dimers through an O—H⋯O hydrogen bond, together with an extensive array of weaker C—H⋯O contacts. These generate a three-dimensional network structure with molecules stacked along the c-axis direction.