Transformations of meso-lactide

Patent metadata

Field	Value
Publication number	US-2018244841-A1
Application number	US-201615756670-A
Country	US
Kind code	A1
Filing date	Sep 2, 2016
Priority date	Sep 2, 2015
Publication date	Aug 30, 2018
Grant date	—

Abstract

B/N Lewis pairs have been discovered to catalyze rapid epimerization of meso-lactide (LA) or LA diastereomers quantitatively into rac-LA. The obtained rac-LA can be kinetically polymerized into poly(L-lactide) and optically resolved D-LA, with a high stereoselectivity factor kL/kD of 53 and an ee value of 91% at 50.6% monomer conversion, by a bifunctional chiral catalyst. The epimerization and enantioselective polymerization can be coupled into a one-pot process for transforming meso-LA directly into poly(L-lactide) and D-LA.

First claim

What is claimed is:

1 . A method to epimerize meso-lactide into racemic lactide comprising contacting meso-lactide and a Lewis acid/base pair for a period of time sufficient to epimerize meso-lactide to racemic lactide, wherein at least about 0.001 mol % of the Lewis acid/base pair is present with respect to the initial molar amount of meso-lactide.

2 . The method of claim 1 wherein the Lewis acid/base pair is a boron/nitrogen Lewis acid/base pair.

3 . The method of claim 1 wherein the Lewis acid of the Lewis acid/base pair is B(C 6 F 5 ) 3 .

4 . The method of claim 1 wherein the Lewis base of the Lewis acid/base pair is 1,4-diazabicyclo [2.2.2]octane (DABCO) or triethylamine.

5 . The method of claim 1 wherein at least about 80% of the meso-lactide is epimerized into racemic lactide.

6 . The method of claim 1 wherein the contacting is carried out in the presence of solvent, such as toluene, wherein meso-lactide is soluble in the solvent at 25° C. and racemic lactide is not soluble in the solvent at 25° C.

7 . The method of claim 6 wherein the initial concentration of the meso-lactide in the solvent is at least about 0.2 M.

8 . The method of claim 6 wherein the initial concentration of the meso-lactide in the solvent is about 1 M to about 3 M.

9 . The method of claim 6 wherein the method is carried out at about 0° C. to about 100° C.

10 . The method of claim 1 wherein the contacting is carried out in the absence of solvent.

11 . The method of claim 10 wherein the meso-lactide is heated to at least about 54° C. but not more than about 116° C.

12 . The method of claim 1 wherein the concentration of the Lewis acid/base pair is about 10 ppm to about 5 mol % with respect to the meso-lactide.

13 . The method of claim 1 further comprising isolating substantially pure racemic lactide after meso-lactide has been epimerized into racemic lactide, wherein the isolating comprises one or more of filtering, washing, and chromatographing the racemic lactide.

14 . The method of claim 1 further comprising kinetic resolution of the racemic lactide by contacting the racemic lactide with a compound of Formula I:

wherein X is —NH—C(═O)—R, wherein R is —CH 3 , —CF 3 , 2-propenyl, or optionally substituted aryl;
under suitable conditions to initiate ring-opening polymerization of L -lactide to provide a mixture of isotactic poly( L -lactide) and D -lactide.

15 . The method of claim 14 wherein the compound of Formula I is compound 4:

16 . The method of claim 14 further comprising separating the isotactic poly( L -lactide) and D -lactide.

17 . The method of claim 1 wherein the meso-lactide prior to epimerization is in a composition that comprises one or more impurities selected from racemic lactide, lactic acid, lactic acid salts, and oligomers of lactide.

18 . The method of claim 17 wherein the composition that comprises one or more impurities is treated, prior to epimerization, by a method comprising contacting the composition with about 1 mol % to about 10 mol % of AlCl 3 prior to contacting the meso-lactide with the Lewis acid/base pair.

19 . The method of claim 18 wherein the composition, after having been contacted with the AlCl 3 , is purified prior to epimerization.

20 . A compound of Formula I:

wherein X is —NH—C(═O)—R, wherein R is —CH 3 , —CF 3 , 2-propenyl, or optionally substituted aryl.

Assignees

• Univ Colorado State Res Found

Inventors

• Chen Eugene Y
• Zhu jian-bo

Classifications

• C07D515/08

  Bridged systems · CPC title

• C08G63/823 Primary

  for the preparation of polylactones or polylactides · CPC title

• C07D405/04

  directly linked by a ring-member-to-ring-member bond · CPC title

• C08G63/08

  Lactones or lactides · CPC title

• C08L2207/10

  Peculiar tacticity · CPC title