Monocaprylin, chemically known as 1-monooctanoyl-rac-glycerol or glycerol monocaprylate (C₁₁H₂₂O₄, MW 218.29 g/mol), is a medium-chain monoacylglycerol derived from esterification of caprylic acid (octanoic acid, C8:0) with glycerol.

Chemical Structure

Monocaprylin features a glycerol backbone esterified at the sn-1 (primary) position with an eight-carbon saturated fatty acyl chain (-CO(CH₂)₆CH₃), leaving two free hydroxyl groups at sn-2 and sn-3. The IUPAC name is 2,3-dihydroxypropyl octanoate, with formula CH₂(OCOC₇H₁₅)-CH(OH)-CH₂OH. It exists as a racemic mixture or specific enantiomers, exhibiting a colorless to pale yellow viscous liquid or waxy solid form, confirmed by InChI=1S/C11H22O4/c1-2-3-4-5-6-7-11(14)15-9-10(13)8-12/h10,12-13H,2-9H2,1H3.

Physicochemical Properties

The melting point ranges from 39–43 °C, with a boiling point of approximately 296 °C at 101 kPa, density of 1.02–1.04 g/cm³ at 20 °C, and very low vapor pressure (0.001 Pa at 25 °C). A LogP value of ~1.7 indicates moderate lipophilicity. Monocaprylin demonstrates surfactant behavior (HLB ~5–6), forming micelles or lamellar phases in aqueous systems, and exhibits high thermal stability. It is soluble in ethanol and chloroform but shows limited miscibility in water (~1–5%). The pKa is approximately 13.2, attributable to its alcoholic hydroxyl groups.

Synthesis and Stability

Monocaprylin is produced via glycerolysis of tricaprylin or by enzymatic transesterification using lipases (e.g., Candida antarctica) acting on ethyl octanoate and glycerol, typically achieving purities above 90% after distillation. The ester bond shows resistance to mild hydrolysis compared with longer-chain monoacylglycerols, enabling sustained release of caprylic acid in biological media.