Regioselective synthesis of mono-alkyl citric acid esters

DETAILED DESCRIPTION What is claimed is: 1.
A method for the preparation of pure 1-mono esters of citric acid characterized by the formula: ##STR3## where (CH.
sub.
2).
sub.
n is an alkyl group of 7 to 19 carbon atoms, which method involves the steps of: (a) reacting citric acid with paraformaldehyde to form anhydromethylene citric acid; (b) reacting the anhydromethylene citric acid with acetic anhydride to form the corresponding anhydride; (c) reacting the corresponding anhydride with an alcohol of the formula HO(CH.
sub.
2).
sub.
n CH.
sub.
3 where n is as defined above to form the corresponding 1-mono substituted derivative; and (d) refluxing the 1-mono substituted derivative with 1 equivalent of base in aqueous dioxane to provide the desired 1-mono ester of citric acid as characterized by the above formula.
2.
The method of claim 1 wherein n is 7, 9, 11, 13, 15 or 17.
3.
The method of claim 1 wherein n is 15.




Description:
BACKGROUND OF THE INVENTION The esterification of citric acid with varying molar ratios of long chain fatty alcohols can yield the mono-, di-, or tri- ester depending upon the molar ratio of the reactants.
For example, EPO Published Application 0 199 131 reveals that citric acid may be esterified with one, two or three mole equivalent of ethoxylated long chain alcohols to yield products which consist mainly of mono-, di-, or tri- esters.
The reaction of one mole of citric acid with about 2 moles of a long chain fatty alcohol yields mixtures of mono-, di-, and tri- ester compounds (U.
S.
Pat.
No.
2,518,678).
It is difficult to isolate the desired pure mono- or di- esters from these mixtures because of their similar solubility characteristics.
It is generally agreed that the predominant mono-ester product produced from the esterification of citric acid is the unsymmetrical 1-mono ester, while the predominant di-ester obtained is the 1,3 symmetrical product.
Procedures have not been reported which reveal how to obtain the kinetically unfavored 2- mono substituted esters