Catalytic oxidation of uronic acids to aldaric acids
Disclosed is the oxidation of uronic acids, such as galacturonic acid, to the corresponding aldaric acids (characterized by the formula HOOC—(CHOH)n-COOH, with n being an integer of from 1 to 5) such as galactaric acids. The starting material comprising the uronic acid is subjected to oxygen under the influence of a supported gold catalyst and in the presence of a base. The oxidation occurs in good selectivity and yield, under unexpectedly mild conditions. A source of galacturonic acids is pectin, such as that derived from sugar beet pulp.
1. A process for the preparation of an aldaric acid by the oxidation of the corresponding uronic acid, wherein a starting material comprising the uronic acid is subjected to oxygen under the influence of a supported gold catalyst and in the presence of a base.
2. A process according to claim 1 , wherein the oxygen is in the form of air.
3. A process according to claim 1 , wherein the oxygen is in the form of an oxygen-containing gas-stream comprising at least 40% oxygen, preferably at least 60% oxygen.
4. A process according to claim 3 , wherein the oxygen-containing gas stream is oxygen-enriched air.
5. A process according to claim 1 , wherein the uronic acid is selected from the group consisting of galacturonic acid, glucuronic acid, mannuronic acid, guluronic acid, and mixtures thereof.
6. A process according to claim 1 , wherein the starting material further comprises at least one aldose.
7. A process according to claim 5 , wherein the starting material comprises a pectin hydrolyzate, preferably sourced from sugar beet pulp.
8. A process according to claim 1 , wherein the oxidation is carried out at a temperature in the range of from 0° C. to 50° C., preferably from 15° C. to 35° C.
9. A process according to claim 1 , followed by the purification of the aldaric acid.
10. A process according to claim 1 , wherein the aldaric acid is selected from the group consisting of galactaric acid, xylaric acid, glucaric acid, mannaric acid, gularic acid and iduronic acid.