Process for preparing and purifying fatty acids
There is provided a process for purifying a fatty acid, which process comprises reacting a fatty acid with a lithium salt in a first solution and under conditions to allow formation of a precipitate of a lithium salt of the fatty acid; isolating the precipitate; dissolving the precipitate in a second solution followed by separation of the organic and aqueous layers so formed; and evaporating the organic layer to isolate the purified fatty acid. There is also provided a process for increasing the length of a fatty acid, and the use of a lithium salt to purify a fatty acid.
1. A process for purifying a fatty acid which has 1 to 6 centers of unconjugated unsaturation, which process comprises:
(a) reacting a fatty acid with a lithium salt in a first solution and under conditions to allow formation of a precipitate of a lithium salt of the fatty acid;
(b) isolating the precipitate;
(c) dissolving the precipitate in a second solution which is capable of generating two immiscible layers upon dissolution of the precipitate, the two immiscible layers being an organic layer and an aqueous acidic layer;
(d) separating the two immiscible layers formed upon dissolution of the precipitate; and
(e) evaporating the organic layer to isolate the purified fatty acid,
wherein the process does not involve separating fatty acids from one another.
2. A process according to claim 1 wherein the fatty acid is selected from the group consisting of dihomo-gamma-linolenic acid (DGLA), eicosadienoic acid, docosapentaenoic acid (DPA), eicosatetraenoic acid (ETA) and eicosatrienoic acid.
3. A process according to claim 1 wherein the fatty acid is a C 14-24 fatty acid.
4. A process according to claim 1 wherein the lithium salt is lithium hydroxide.
5. A process for preparing a fatty acid which has 1 to 6 centers of unconjugated unsaturation, which process comprises:
(a) decarboxylating a malonic acid derivative of formula R—CH 2 CH(CO 2 H) 2 , wherein R is a fatty acid residue which contains from 1 to 6 centers of unconjugated unsaturation, to form a fatty acid of formula RCH 2 CH 2 CO 2 H;
(b) subjecting the fatty acid thus prepared to a process for purifying a fatty acid as defined in claim 1 .
6. A process for extending the length of a fatty acid which has 1 to 6 centers of unconjugated unsaturation, which process comprises:
(a) reducing a fatty acid of formula R—CO 2 H or a fatty acid ester of formula R—CO 2 R 1 , wherein R is a fatty acid residue which contains from 1 to 6 centers of unconjugated unsaturation and R 1 is a C 1-6 alkyl group, to an alcohol of formula R—CH 2 OH;
(b) sulfonating the alcohol to form a sulfonate of formula R—CH 2 OSO 2 R 2 , wherein R 2 is a C 1-6 alkyl or C 6-10 aryl group;
(c) reacting the sulfonate with a malonate ester derivative and hydrolysing the resulting product to form a malonic acid derivative of formula R—CH 2 CH(CO 2 H) 2 ;
(d) decarboxylating the malonic acid derivative to form a fatty acid of formula R—CH 2 CH 2 CO 2 H; and
(e) subjecting the fatty acid thus prepared to a process for purifying a fatty acid as defined in claim 1 .
7. A process according to claim 6 wherein R is a fatty acid residue comprising from 14 to 22 carbon atoms.
8. A process according to claim 7 wherein R comprises from 18 to 20 carbon atoms.
9. A process according to claim 6 wherein R comprises 2 to 6 unconjugated olefinic groups.
10. A process according to claim 6 wherein R is selected from the group consisting of ω-3 and ω-6 fatty acid residues.
11. A process according to claim 6 wherein R is selected from the group consisting of a C 17 H 29 residue from gamma-linolenic acid, a C 19 H 29 residue from eicosapentaenoic acid, a C 17 H 27 residue from stearidonic acid, a C 17 H 31 residue from linoleic acid and a C 17 H 29 residue from alpha-linolenic acid.
12. A process according to claim 6 wherein the reduction in step (a) is carried out with a solution of lithium aluminium hydride.
13. A process according to claim 6 wherein the malonic acid derivative of formula R—CH 2 CH(CO 2 H) 2 is used directly in the decarboxylation of step (d) without purification and/or without crystallisation.
14. A process according to claim 5 wherein R is a fatty acid residue comprising from 14 to 22 carbon atoms.
15. A process according to claim 14 wherein R comprises from 18 to 20 carbon atoms.
16. A process according to claim 5 wherein R comprises 2 to 6 unconjugated olefinic groups.
17. A process according to claim 5 wherein R is selected from the group consisting of ω-3 and ω-6 fatty acid residues.
18. A process according to claim 5 wherein R is chosen from the group consisting of a C 17 H 29 — residue from gamma-linolenic acid, a C 19 H 29 — residue from eicosapentaenoic acid, a C 17 H 27 — residue from stearidonic acid, a C 17 H 31 — residue from linoleic acid and a C 17 H 29 — residue from alpha-linolenic acid.