Acylation of unprotected lactose with 1,18-octadec-9-enedioyl chloride for the synthesis of monocatenary and bolaform agro-based surfactants

Agro-based surfactants have one of two hydrophilic or hydrophobic parts of vegetable origin. They can be produced from renewable and readily available resources. Carbohydrate fatty acid esters are non-toxic, non-ionic, and biodegradable agro-based surfactants with applications in the pharmaceutical, cosmetic, and food industries. In this work, the chemical synthesis of agro-based surfactants through lactose acylation with 1,18-octadec-9-enedioyl chloride (Acyl-Cl) was investigated at room temperature. The acylation reaction proved to be regioselective to the primary hydroxyl group of the glucose-moiety in the lactose molecule and was promoted by an excess of lactose to produce higher substituted derivatives. Acyl-Cl conversion was ∼98 % after 1 h of reaction. The production of monocatenary agro-based surfactant, mono-lactose 1,18-octadec-9-enoate, was favoured with a molar ratio lactose/Acyl-Cl of 1 achieving a yield of 48 % after 20 min. Moreover, production of bolaform agro-based surfactant, di-lactose 1,18-octadec-9-enedioate, was favoured with a molar ratio of 3 lactose/Acyl-Cl with a yield of 33 % after 1 h of reaction. A one-pot synthesis of agro-based bolaform surfactant was successfully achieved for the first time in the open literature.

Monocatenary and bolaform agro-based surfactants were isolated by preparative liquid chromatography with high purity according to their chemical structure identification by liquid chromatography coupled to mass spectrometry and ¹H nuclear magnetic resonance. Their critical micellar concentration (12–9 μM) determined by fluorescence spectroscopy with pyrene used as a probe, and hydrophilic:lipophilic balance values (10.7–14.2) indicated that monocatenary and bolaform agro-based surfactants can act as oils in water emulsion.