DMF distillation
A method of obtaining purified DMF from a mixture comprising DMF and hydrogen chloride (HCl) involving distillation is provided.
1. A method of producing purified dimethylformamide from a feed mixture comprising dimethylformamide and hydrogen chloride, comprising:
distilling the feed mixture to afford a more volatile fraction and a less volatile fraction, wherein the more volatile fraction is lower in hydrogen chloride, measured as chloride, than the less volatile fraction, and
collecting the more volatile fraction to afford a collected more volatile fraction, at least a portion of which affords a purified dimethylformamide product that is lower in hydrogen chloride, measured as chloride, than the feed mixture;
wherein the hydrogen chloride content of the feed mixture, measured as chloride, is from 0.1% to 10% (w/w) and the hydrogen chloride content of the purified dimethylformamide, measured as chloride, is from 0 to 1000 ppm.
2. The method according to claim 1 wherein the hydrogen chloride content, measured as chloride (w/w), of the purified dimethylformamide is less than 50% of the hydrogen chloride content, measured as chloride (w/w), of the feed mixture.
3. The method according to claim 1 wherein the hydrogen chloride content, measured as chloride (w/w), of the purified dimethylformamide is less than 25% of the hydrogen chloride content, measured as chloride (w/w), of the feed mixture.
4. The method according to claim 1 wherein the hydrogen chloride content, measured as chloride (w/w), of the purified dimethylformamide is less than 10% of the hydrogen chloride content, measured as chloride (w/w), of the feed mixture.
5. The method according to claim 1 , wherein the distillation of the feed mixture is carried out in a distillation column.
6. The method according to claim 5 , wherein the distillation column comprises an upper rectifying section and a lower stripping section.
7. The method according to claim 6 , wherein the feed mixture is introduced to the distillation column between the rectifying and stripping sections thereof.
8. The method according to claim 5 , wherein another portion of the collected more volatile fraction is returned to the distillation column as a reflux stream.
9. The method according to claim 8 , wherein the reflux stream is introduced to the distillation column at a point above the point at which the feed mixture is introduced to the distillation column.
10. The method according to claim 8 , wherein the reflux stream is introduced to the distillation column at the top of the rectifying section.
11. The method according to claim 8 , wherein the ratio of the amount of the collected more volatile fraction returned as a reflux stream to the amount of the collected more volatile fraction taken forward as purified dimethylformamide product is from 0.1:1 to 4:1 (w/w).
12. The method according to claim 11 , wherein the ratio of the amount of the collected more volatile fraction returned as a reflux stream to the amount of the collected more volatile fraction taken forward as purified dimethylformamide product is from 0.2:1 to 1.5:1 (w/w).
13. The method according to claim 1 , wherein the feed mixture is an overhead vapor derived from a distillation of a reaction mixture, wherein the reaction mixture is derived from a a chlorination reaction of a sucrose-6-acylate to afford a sucralose-6-acylate and the reaction mixture comprises dimethylformamide, hydrogen chloride, sucralose-6-acylate, and reactants; or the reaction mixture comprises dimethylformamide, hydrogen chloride, sucralose-6-acylate, and other reaction products; or the reaction mixture comprises dimethylformamide, hydrogen chloride, reactants, sucralose-6-acylate, and other reaction products.
14. The method according to claim 13 , wherein the feed mixture is distilled from the reaction mixture to further afford a reaction mixture bottoms stream.
15. The method according to claim 13 , wherein the reaction mixture is non-aqueous.
16. The method according to claim 13 , wherein the reaction mixture is unquenched.
17. The method according to claim 14 , wherein the less volatile fraction is collected and mixed with the reaction mixture bottoms stream thereby producing a collected mixture, and
the collected mixture is added to a vessel and a base is simultaneously added to the vessel to quench the reaction mixture in the collected mixture and to neutralize the hydrogen chloride.
18. The method according to claim 1 , wherein the less volatile fraction is collected and treated with a base to form a chloride salt of the base, and the chloride salt of the base is removed.
19. The method according to claim 5 , wherein the pressure in the distillation column is from 1 mbar to 1014 mbar.
20. The method according to claim 19 , wherein the pressure in the distillation column is from 1 mbar to 100 mbar.
21. The method according to claim 5 , wherein the temperature in the distillation column is from 0° C. to 150° C.
22. The method according to claim 21 , wherein the temperature in the distillation column is from 10° C. to 85° C.
23. The method according to claim 13 , wherein the reaction mixture is distilled to afford the feed mixture under a pressure of from 1 mbar to 300 mbar.
24. The method according to claim 13 , wherein the reaction mixture is distilled to afford the feed mixture at a temperature of from 40° C. to 150° C.
25. The method according to claim 13 , wherein the chlorination reaction further comprises the step of converting at least one portion of said sucralose-6-acylate to sucralose.
26. The method according to claim 25 , wherein the sucralose is isolated from the reaction mixture.