Sorbitan esters

Sorbitan esters belong to non-ionic surfactants. The raw material for their production is sorbitol, a six-hydroxy sugar alcohol, obtained by reducing glucose. This reaction changes the aldehyde group to hydroxyl group. Sorbitol during dehydration loses one molecule of water, forming sorbitan, i.e. a mixture of cyclic ethers. It consists of 15% tetrahydropyran and 85% tetrahydrofuran. Further dehydration results in the formation of a bicyclic derivative called sorbide.

The reaction in which the sorbitan esters are obtained is carried out in two stages. The first stage is the dehydration and cyclization of sorbitol, and the second is the esterification of cyclic ethers. Most often, esterification is carried out using fatty acids such as lauric, palmitic, oleic or stearic. Due to the presence of free OH groups, the sorbitan esters may undergo an ethoxylation reaction resulting in obtaining of ethoxylated derivatives called polysorbates.

Physicochemical properties

Sorbitan esters are stable in mixtures with other surfactants. The hydrophilic part in the esters is OH and in their ethoxylated derivatives – the polyoxyethylene chain. Due to the presence of long carbon chains, the esters are lipophilic. They dissolve well in low alcohols and xylene. While their highly ethoxylated derivatives dissolve very well in water, which is the result of increased polarity resulting from the oxide incorporated in the molecule structure.

Applications

Sorbitan esters are non-ionic emulsifiers that stabilize W/O emulsions. In combination with ethoxylated derivatives, they can also act as O/W emulsifiers in formulations. The ethoxylated sorbitan esters (polysorbates) are more hydrophilic and therefore have good solubilizing properties.

Sorbitan esters are surfactants that are one of the mildest for the skin and eyes. In addition to emulsifying properties, they have excellent skin softening properties. For these reasons, they are often used in the cosmetics industry.

Sorbitan esters have a wide range of applications. They are used, among others, as additives in the production of plastics, in the metallurgical industry for metal processing, as well as in the oil and gas mining industry and in the agrochemical industry. They are also used in formulations intended for industrial cleaning and washing, in household and cosmetic chemistry as components of personal care products, detergents, nail polishes and cosmetics. In construction, they play the role of additives for concrete, mortars and sealants. The compounds have also found application in the production of hydraulic oils and fluids as well as lubricants and additives for lubricating oils.