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.

Keywords

• crystal structure
• trimethyl citrate
• hydrogen bonds
• inversion dimers
• ring motifs