Preparation of erythorbic acid and ascorbis acid 6-fatty acid esters

DETAILED DESCRIPTION OF THE INVENTION The process of the present invention results in esterification of erythorbic and ascorbic acids specifically at the C-6 primary alcohol.
Such monoesterification is accomplished in high yield, as disclosed hereinafter, when using only stoichiometric quantities of reactants, mild reaction conditions and short reaction times.
While both of the optical isomers of either erythorbic acid or ascorbic acid may be used in the practice of this invention, the natural isomer, namely D-erythorbic acid or L-ascorbic acid, is commonly employed.
Fatty acids are those carboxylic acids derived from or contained in animal or vegetable fat or oil.
They are generally composed of a chain, either straight or branched, of alkyl groups terminating in a carboxyl radical.
The acid may be saturated or unsaturated and either solid, semisolid or liquid in form.
Fatty acids suitable for the practice of this invention are those saturated acids containing from about 12 to 18 carbon atoms, including lauric, myristic, palmitic and stearic.
With saturated acids having less than about 12 carbon atoms, the monoester product tends to be too water soluble for practical recovery, while with such acids having more than about 18 carbon atoms, the starting acid is inclined to require an inordinate amount of solvent for suitable reaction and the monoester product may be too oil insoluble for suitable use.
Unsaturated fatty acids do not appear to lend themselves to this reaction system.
Preferred are lauric acid and palmitic acid.
Liquid anhydrous hydrogen fluoride serves as both the reaction solvent and catalyst.
In order to ensure the essential solution of the fatty acid in the solvent under the reaction conditions employed, at least about 10 moles of hydrogen fluoride per mole of fatty acid is used.
Additional solvent results in improved product yield, and about 25 to 50 moles of hydrogen fluoride per mole of fatty acid is therefore preferred.
At the especially preferred solvent level of about 50 moles of hydrogen fluoride per mole of fatty acid, the reaction yield is nearly quantitative, and while a greater amount of the solvent may be used without detriment, little economic advantage exists for such usage