Process for oxidation of fatty alkenols to alkenal pheromone products
The present invention relates, in part, to an improved process for oxidation of alcohols containing oxidatively sensitive functional groups, using inexpensive reagents under mild reaction conditions to provide high yields of carbonyl products such as aldehydes or ketones. In certain embodiments, an aldehyde product is obtained by contacting an oxidatively sensitive alcohol, such as an alkenol, with an oxidant and a TEMPO catalyst under conditions sufficient to convert the alkenol to the aldehyde.
1. A method for preparing a compound according to Formula
the method comprising:
forming a reaction mixture comprising sodium hypochlorite (NaOCl), a TEMPO catalyst, and an alcohol according to Formula II
and
maintaining the reaction mixture under conditions sufficient to form the compound according to Formula I;
wherein:
R 1 is selected from the group consisting of H, C 1-18 alkyl, C 2-18 alkenyl, and C 2-18 alkynyl;
R 2 is H; and
x is an integer from 0 to 17.
2. The method of claim 1 , wherein R 1 C 1-18 alkyl or C 2-18 alkenyl.
3. The method of claim 1 , wherein the reaction mixture comprises 1.0 to 1.5 molar equivalents of NaOCl with respect to the alcohol according to Formula II.
4. The method of claim 1 , wherein the TEMPO catalyst is selected from the group consisting of 4-hydroxy-(2,2,6,6-tetramethylpiperidin-1-yl)oxyl; 4-acetamindo-(2,2,6,6-tetramethylpiperidin-1-yl)oxyl; 4-amino-(2,2,6,6-tetramethylpiperidin-1-yl)oxyl; 4-cyano-(2,2,6,6-tetramethylpiperidin-1-yl)oxyl; 4-carboxy-(2,2,6,6-tetramethyl-piperidin-1-yl)oxyl; 4-(2-bromoacetamido)-(2,2,6,6-tetramethylpiperidin-1-yl)oxyl; 4-(2-idodoacetamido)-(2,2,6,6-tetramethylpiperidin-1-yl)oxyl; 4-methoxy-(2,2,6,6-tetramethyl-piperidin-1-yl)oxyl; 4-oxo-(2,2,6,6-tetramethylpiperidin-1-yl)oxyl; 4-maleimido-(2,2,6,6-tetramethylpiperidin-1-yl)oxyl; (2,2,6,6-tetramethylpiperidin-1-yl)oxyl methacrylate; and combinations thereof.
5. The method of claim 4 , wherein the TEMPO catalyst is 4-hydroxy-(2,2,6,6-tetramethylpiperidin-1-yl)oxyl.
6. The method of claim 1 , wherein the reaction mixture comprises no more than 0.1 molar equivalents of the TEMPO catalyst with respect to the alcohol according to Formula II.
7. The method of claim 6 , wherein the reaction mixture comprises no more than 0.05 molar equivalents of the TEMPO catalyst with respect to the alcohol according to Formula II.
8. The method of claim 1 , wherein the reaction mixture is maintained under the conditions sufficient to form the compound according to Formula I for a period of time ranging from about 1 minute to about 30 minutes.
9. The method of claim 8 , wherein the period of time ranges from about 5 minutes to about 10 minutes.
10. The method of claim 1 , further comprising stirring the reaction mixture at a stir rate ranging from about 1,000 RPM to about 10,000 RPM.
11. The method of claim 1 , wherein the reaction mixture further comprises one or more components selected from the group consisting of a phase transfer catalyst, a buffer, and a solvent.
12. The method of claim 11 , wherein the solvent comprises an organic phase and an aqueous phase.
13. The method of claim 11 , wherein the phase transfer catalyst is selected from the group consisting of tetrabutylammonium chloride (n-Bu 4 NCl), tetrabutylammonium bromide (n-Bu 4 NBr), tetrabutylammonium sulfate (n-Bu 4 NHSO 4 ), tricaprylylmethylammonium chloride, and combinations thereof.
14. The method of claim 13 , wherein the reaction mixture comprises from about 0.01 to about 0.1 molar equivalents of the phase transfer catalyst with respect to the alcohol according to Formula II.
15. The method of claim 11 , wherein the buffer is selected from the group consisting of NaHCO 3 , Na 2 HPO 4 , Na 2 HPO 4 , sodium acetate, KHCO 3 , K 2 HPO 4 K 2 HPO 4 , potassium acetate, and combinations thereof.
16. The method of claim 15 , wherein the pH of the reaction mixture ranges from about 8.0 to about 9.0.
17. The method of claim 1 , wherein the reaction mixture is maintained at a temperature ranging from about 18° C. to about 25° C.