CHEMICAL PROCESS TO CONVERT MUCIC ACID TO ADIPIC ACID

Abstract

The present invention provides a method of synthesizing an ester of a saturated carboxylic acid from a saturated polyhydroxycarboxylic acid by performing a deoxydehydration reaction and a hydrogen transfer reaction.

Claims

1. A method for synthesizing an ester of a saturated carboxylic acid, the method comprising: (a) subjecting a polyhydroxycarboxylic acid to a deoxydehydration catalyst to remove hydroxyl groups; and (b) performing a hydrogen transfer reaction to form the ester of a saturated polycarboxylic acid.

2. The method according to claim 1, wherein the hydrogen transfer reaction in operation (b) is performed in the presence of a hydrogen transfer catalyst.

3. The method according to claim 1, wherein operations (a) and (b) are performed in a single reaction vessel.

4. The method according to claim 3, wherein operations (a) and (b) are performed concurrently or consecutively.

5. The method according to claim 4, wherein the polyhydroxycarboxylic acid is contacted with the dehydration catalyst in the presence of the hydrogen transfer catalyst.

6. (canceled)

7. The method according to claim 4, wherein the deoxydehydration catalyst produces at least one intermediate compound, wherein the at least one intermediate compound produced is an ester of an unsaturated polycarboxylic acid after operation (a).

8. (canceled)

9. The method according to claim 7, wherein the ester of an unsaturated polycarboxylic acid is further subjected to operation (b) to produce the ester of a saturated polycarboxylic acid.

10. The method according to claim 1 wherein the ester of an unsaturated polycarboxylic acid comprises esters of muconic acid selected from the group consisting of propyl muconate, dipropyl muconate, butyl muconate, dibutyl muconate, pentyl muconate, dipentyl muconate, octyl muconate, dioctyl muconate and any mixture thereof.

11. (canceled)

12. (canceled)

13. The method according to claim 1, wherein the ester of a saturated polycarboxylic acid is an ester of adipic acid selected from the group consisting of adipic acid monopropyl ester, adipic acid dipropyl ester, adipic acid monobutyl ester, adipic acid dibutyl ester, adipic acid monopentyl ester, adipic acid dipentyl ester, adipic acid monooctyl ester, adipic acid dioctyl ester and any mixture thereof.

14. (canceled)

15. (canceled)

16. The method according to claim 1, wherein the polyhydroxycarboxylic acid is mucic acid.

17. The method according to claim 1, wherein the deoxydehydration catalyst in operation (a) is a rhenium catalyst or a rhenium catalyst with a co-catalyst, wherein the rhenium catalyst is rhenium acid, methyltrioxorhenium or rhenium(III) oxide or rhenium acid and, wherein the co-catalyst is a Brnsted acid or a proton type liquid or solid acid or para-toluene sulfonic acid or sulfuric acid.

18-21. (canceled)

22. The method according to claim 1, wherein the hydrogen transfer catalyst in operation (b) is a metal-on-carbon catalyst containing a metal, wherein the metal is selected from the group consisting of platinum, palladium, ruthenium and any mixture thereof, or the hydrogen transfer catalyst is selected from the group consisting of Ru/C, Pd/C, Pt/C and any mixture thereof.

23. (canceled)

24. (canceled)

25. The method according to claim 17, wherein the hydrogen transfer catalyst comprises up to 5 mol % of the reaction mixture.

26. The method according to claim 4, wherein the method further comprises the use of an alcohol solvent.

27. (canceled)

28. The method according to claim 4, wherein the method is performed at a temperature in the range of 120 C. to 200 C. or for a duration in the range of 24 hours to 36 hours.

29. (canceled)

30. The method according to claim 7, wherein the method further comprises the use of an alcohol solvent in operation (a) and operation (b), wherein the alcohol solvent in operation (a) is selected from the group consisting of propanol, butanol, pentanol, hexanol, heptanol, octanol and any mixture thereof, or is selected from the group of 2-propanol, 1-butanol, 3-pentanol, 3-octanol and any mixture thereof, and wherein the alcohol solvent in operation (b) is 3-pentanol.

31-33. (canceled)

34. The method according to claim 7, wherein operation (a) is performed at a temperature in the range of 90 C. to 180 C. and operation (b) is performed at a temperature in the range of 120 C. to 200 C., or operation (a) is performed for a duration of 4 hours to 24 hours and operation (b) is performed for a duration of 6 hours to 24 hours.

35. (canceled)

36. An ester of adipic acid synthesized according to a method for synthesizing an ester of a saturated carboxylic acid, the method comprising: (a) subjecting a polyhydroxycarboxylic acid to a deoxydehydration catalyst to remove hydroxyl groups; and (b) performing a hydrogen transfer reaction to form the ester of a saturated polycarboxylic acid.

37. A method for synthesizing an ester of adipic acid, the method comprising the operation of subjecting mucic acid to a deoxydehydration catalyst in the presence of a hydrogen transfer catalyst to form the ester of adipic acid, or the operations of: (a) subjecting mucic acid to a dehydration catalyst to form an ester of muconic acid; and (b) performing a hydrogen transfer reaction on the ester of muconic acid to form the ester of adipic acid.

38. (canceled)

39. A method for synthesizing a saturated carboxylic acid, the method comprising: (a) subjecting a polyhydroxycarboxylic acid to a deoxydehydration catalyst to remove hydroxyl groups; (b) performing a hydrogen transfer reaction to form the ester of a saturated polycarboxylic acid; and (c) hydrolysing the ester to form the saturated carboxylic acid.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0055] The accompanying drawings illustrate a disclosed embodiment and serves to explain the principles of the disclosed embodiment. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.

[0056] FIG. 1 is a reaction scheme showing the conversion of mucic acid to muconic acid and adipic acid.

[0057] FIG. 2A is a graph showing deoxydehydration (DODH) of mucic acid with methyltrioxorhenium (MTO) catalyst.

[0058] FIG. 2B is a graph showing deoxydehydration (DODH) of mucic acid with methyltrioxorhenium (MTO) and TsOH catalyst. Reaction conditions: mucic acid (1.0 mmol), catalyst (5.0 mol %), 3-pentanol (20.0 ml), 120 C.

[0059] FIG. 3 is a reaction schemes showing deoxydehydration (DODH) of mucic acid and mucic acid diester to muconates.

[0060] FIG. 4 is a graph showing the progression of DODH of diethyl mucate to muconates (5+7) with methyltrioxorhenium (MTO) catalyst. Reaction conditions: diethyl mucate (1.0 mmol), catalyst (5.0 mol %), 3-pentanol (20.0 ml), 120 C.

[0061] FIG. 5 is a reaction scheme showing the transfer-hydrogenation of trans, trans-muconic acid to adipic acid and ester.

[0062] FIG. 6 is a scheme showing the conversion of mucic acid to adipic acid ester via deoxydehydration/transfer hydrogenation process in one-pot.

[0063] FIG. 7A is the 1H NMR spectrum of compound 2.

[0064] FIG. 7B is the 1H NMR spectrum of compound 3.

[0065] FIG. 7C is the 1H NMR spectrum of compound 4.

[0066] FIG. 7D is the 1H NMR spectrum of compound 5.

[0067] FIG. 7E is the 1H NMR spectrum of compound 6.

[0068] FIG. 7F is the 1H NMR spectrum of compound 7.

[0069] FIG. 7G is the 1H NMR spectrum of compound 10.

EXAMPLES

[0070] Non-limiting examples of the invention will be further described in greater detail by reference to specific Examples, which should not be construed as in any way limiting the scope of the invention.

Example 1

Materials

[0071] All starting materials are commercially available and were used as received, unless otherwise indicated. Mucic acid (98%), 3-pentanol (98%), TsOH (98%), 2-propanol (99.9%) were purchased from Merck; trans,trans-muconic acid (98%), 3-octanol (99%) and 5%Pt/C were purchased from Aldrich. Methyltrioxorhenium (MTO) (98%), Re.sub.2O.sub.7(99.99%) and Re.sub.2(CO).sub.10 were purchased from Strem Chemical, USA; 1-butanol (99.5%) were purchased from BDH Laboratory Supplies, England. Other regents involved were from Sigma or Merck. .sup.1H and .sup.13C NMR spectra were obtained using a Brucker AV-400 (400 MHz) spectrometer. Chemical shifts are reported in ppm with reference to tetramethylsilane with the solvent resonance as the internal standard.

Example 2

General Procedure for the Synthesis of Diethylmucate 6

[0072] A mixture of mucic acid (5.0 g), H.sub.2SO.sub.4 (1 ml), and ethanol (150.0 ml) was refluxed (80 C.) for 24 h under stirring. The reaction mixture was cooled to room temperature, and then stored at 3 C. for 1 day. The white precipitate was filtered out, washed with small amount of cold ethanol, and then vacuum dried at 50 C. overnight. The mother liquid was evaporated to dryness to give a brown solid. The solid obtained from the mother liquid was recrystallized in 10 ml ethanol and recovered by the procedure as described above. The total amount of the diethylmucate was 5.1 g (90.0% yield).

Example 3

General Procedure for the Deoxydehydration (DODH) of Mucic Acid

[0073] A mixture of mucic acid (1 mmol, 210 mg), methyltrioxorhenium (MTO) (0.05 mmol, 12 mg), TsOH (0.05 mmol, 12 mg), and 3-pentanol (20.0 ml) was refluxed (120 C.) in a 50 ml flask under flowing air or N.sub.2. The mixture was initially a white suspension and then changed to a brown and transparent solution after 4 h. After 12 h, the reaction mixture was evaporated to dryness. The solid was recrystallized to get products. For kinetic study, 1 ml of reaction mixture was taken at certain time interval and dried for NMR analysis; known amount of mesitylene was added as an internal standard.

Example 4

General Procedure for the Deoxydehydration/Transfer-Hydrogenation of Mucic Acid to Adipic Acid Ester (One-Step)

[0074] A mixture of mucic acid (210 mg, 1 mmol), 5.0% Pt/C (10.0 mg), methyltrioxorhenium (MTO) (0.05 mmol, 12 mg), TsOH (0.05 mmol, 12 mg), and 3-pentanol (20.0 ml) was charged into a pressure flask. The reaction mixture was stirred at 200 C. for 36 hours (75% yield).

Example 5

General Procedure for the Deoxydehydration/Transfer-Hydrogenation of Mucic Acid to Adipic Acid Ester (Two-Step, One-Pot)

[0075] A mixture of mucic acid (210 mg, 1 mmol), methyltrioxorhenium (MTO) (0.05 mmol, 12 mg), TsOH (0.05 mmol, 12 mg), and 3-pentanol (20.0 ml) was charged into a pressure flask. The reaction mixture was stirred at 120 C. under flowing air for 12 hours. Then, 5.0% Pt/C (10.0 mg) was added into the flask. The flask was sealed and the reaction mixture was stirred at 200 C. for another 12 hours. The reaction mixture was then cooled down to room temperature. The catalyst was separated by filtration, the solvent was removed by evaporation, and adipic acid ester was obtained as a white liquid.

Example 6

Larger Scale synthesis of Adipic Acid Esters from Mucic Acid

[0076] A mixture of mucic acid (25.0 mmol, 5.25 g), MTO (1.25 mmol, 300 mg), TsOH (1.25 mmol, 215 mg), and 3-pentanol (250.0 mL) was charged into a pressure flask. The reaction mixture was stirred at 120 C. for 12 h. A water separator was used to remove the produced water. After that, 1.56 g of 5.0% Pt/C was added into the flask. The flask was sealed and the reaction mixture was stirred at 160 C. for another 12 h. The reaction mixture was then cooled down to room temperature. The catalysts were separated by filtration through Celite-545, the solvent was removed by evaporation, and the obtained adipic acid esters were purified by flash column chromatography (CHCl.sub.3/MeOH 10:1) to give colorless liquid (6.84 g, 98% yield, dipentyl ester/ monopentyl ester 93:7).

Example 7

Hydrolysis of Adipic Acid Dipentyl Ester

[0077] Hydrolysis of adipic acid dipentyl ester: The separated adipic acid dipentyl ester (286.0 mg, 1 mmol) was refluxed for 12 h in an EtOH/H.sub.2O solution of sodium hydroxide (0.133 molL.sup.1, 15.0 mL; EtOH/H.sub.2O 1:2). After that, the reaction mixture was evaporated to dryness, and the obtained solid was dissolved in 10.0 mL deionized water. The pH value of the aqueous solution was adjusted to about 3.0 with 1M HCl. The solution was again evaporated to dryness, and the obtained solid was stirred in 10.0 mL methanol for 3 min. The mixture was then filtered through Celite-545, and the filtrate was evaporated to afford adipic acid as a white solid. The product was vacuum dried at 60 C. overnight, and adipic acid was obtained at 94% yield (136.8 mg).

Example 8

Initial Trial

[0078] As shown in FIG. 1, Mucic acid 1 is a C.sub.6 sugar acid that can be produced from galactose in large scale by the established method. The mucic acid was firstly tested under typical deoxydehydration (DODH) reaction condition with methyltrioxorhenium (MTO) catalyst. In the initial trial, mucic acid was heated in 3-octanol at 180 C. for 2 hours. The reaction went very slow and the selectivity was low. The majority of mucic acid remained as insoluble solid throughout the reaction.

[0079] With 3-pentanol as the solvent, at 120 C., the reaction was still slow in the initial stage, probably due to low solubility of mucic acid, but with excellent selectivity. Kinetic study showed that mucic acid gradually converted to the conjugated double bond products in boiling 3-pentanol (120 C.) with 5 mol % MTO (FIG. 2A). It was found that the products were in the forms of monoester 4 and diester 5. The yield of monoester 4 was continuously increased and reached the maximum at 24 h, and then decreased. Meanwhile, the yield of diester 5 kept increasing even after 24 hours. It was clear that mucic acid was first converted to monoester 4 and then further converted to diester 5 (FIG. 3).

[0080] The full conversion to 4 and 5 was observed after 24 hours. Although the reaction temperature of this system is lower, the reaction rate is also slow as compared to other deoxydehydration (DODH) reactions of polyols. This could be due to the low solubility of mucic acid and/or the interference of carboxylic acid groups. In fact, higher temperature led to lower selectivity, while the reaction was sluggish at lower temperature (90 C.).

[0081] To understand more about this reaction, diethylmucate 6 (FIG. 3) was prepared according to reported method as the starting material for the deoxydehydration (DODH) reaction. Under the same reaction conditions, full conversion of diethylmucate 6 to muconate 5 (30%) and 7 (70%) were achieved at 20 hours (FIG. 4). The ester exchange reaction occurred and 65.0% of the ethyl groups were substituted by 3-pentanol. Despite the fact that diethylmucate has much better solubility than the free mucic acid in hot alcohols, the reaction of diethylmucate proceeded only slightly faster than that of mucic acid. This result may indicate that mucic acid was first subject to esterification before it underwent deoxydehydration (DODH) reaction. The reaction was generally conducted under air or N.sub.2 flow (Entry 3, Table 1). In contrast, slower reaction was observed under the sealed system (Entry 4, Table 1) and much faster reaction was achieved when a water separator was employed (Entry 5, Table 1).

TABLE-US-00001 TABLE 1 Catalysts screening for the conversion of mucic acid to muconates..sup.a Time Conv. Yield Entry Catalyst (mol %) (h) (%) (%)b 1 CH3ReO3 (5) 12 97.8 71.1 2 CH3ReO3 (5) 24 100.0 98.6 3 CH3ReO3 (5) 24c 100.0 96.6 4 CH3ReO3 (5) 28d 100.0 87.0 5 CH3ReO3 (5) 8e 100.0 99.1 6 CH3ReO3 (5), TsOH 12 100.0 99.5 (5) 7 CH3ReO3 (5), H2SO4 12 100.0 99.3 (5) 8 CH3ReO3 (2.5), TsOH 12 100.0 99.7 (5) 9 CH3ReO3 (1.25), TsOH 12 100.0 95.1 (2.5) 10 CH3ReO3 (0.5), TsOH 12 57.3 47.6 (2.5) 11 CH3ReO3 (0.5), TsOH 24 100.0 99.3 (2.5) 12 Re2(CO)10 (5) 12 0 0 13 Re2O7 (5) 4 100.0 87.3 14 Re2O7 (5) 8 100.0 95.4 15 Re2O7 (5), TsOH (5) 4 100.0 82.4 16 Re2O7 (5), TsOH (5) 8 100.0 99.8 .sup.aReaction conditions: mucic acid (1.0 mmol), 3-pentanol (20.0 ml), 120 C., flowing N.sub.2. bNMR yield of 4 + 5. cFlowing air. dClosed reaction system. eWater separator was employed.

Example 9

Investigating the Effect of Brnsted Acids

[0082] In an attempt to accelerate the reaction, Brnsted acids were added as a co-catalyst to promote the esterification step to enhance the solubility of the starting material. As shown in FIG. 2B, the addition of para-toluene-sulfonic acid (TsOH) remarkably shortened the reaction time to reach the full conversion, while the products distribution and the trends of products formation remained the same. Sulfuric acid also showed the similar promoting effect (Entry 7, Table 1), In fact, the acid additives for the deoxydehydration (DODH) reaction would assist olefin extrusion by protonation of the rhenium diolate intermediate, while the extrusion of olefin from oxorhenium complex is the key step in deoxydehydration (DODH) reaction. With the aid of acid co-catalyst, the methyltrioxorhenium catalyst (MTO) loading can be reduced to as low as 0.5 mol % (Entries 8-11, Table 1).

Example 10

Investigating the Effect of Different Re Catalysts

[0083] Various Re catalysts were tested for the reaction. Re.sub.2(CO).sub.10 is efficient for the deoxydehydration (DODH) of a variety of vicinal diols. However, Re.sub.2(CO).sub.10 is inactive for the deoxydehydration (DODH) of mucic acid (Entry 12, Table 1), probably due to the poor tolerance of Re.sub.2(CO).sub.10 to the carboxylic acid group. In contrast, high reaction rate was observed for the Re.sub.2O.sub.7 catalyzed deoxydehydration (DODH) reaction of mucic acid in 3-pentanol (Entries 13-14, Table 1). The reaction with Re.sub.2O.sub.7 catalyst is even faster than that catalyzed by methyltrioxorhenium (MTO) in combination with TsOH. Re.sub.2O.sub.7 is hydroscopic and can react easily with even the moisture to form HReO.sub.4.sup.19, which may promote the esterification and olefin extrusion steps in the deoxydehydration (DODH) catalytic cycle. Addition of TsOH to the Re.sub.2O.sub.7 reaction system didn't further improve the reaction efficiency (Entries 15-16, Table 1).

Example 11

Investigating the Effect of Solvent

[0084] Though it can be operated at a higher temperature by using 3-octanol as the solvent, slower reaction was observed, As to the solvent of this reaction, 3-octanol is less active even though it can be operated at a higher temperature, probably due to the less polarity of 3-octanol (Table 2). 2-propanol is almost inactive, as the reaction was carried at lower temperature due to its low boiling point. The viability of using bio-derivable 1-butanol for this reaction has also been explored. It turned out that the reaction efficiency is similar to that of 3-pentanol, almost quantitative conversion of mucic acid to muconate was achieved in 12 hours with Re.sub.2O.sub.7 as catalyst (Entry 3, Table 2). In 1-butanol system, only dibutyl-muconate 8 (FIG. 2) was observed, probably due to the less steric effect of primary alcohol.

TABLE-US-00002 TABLE 2 Deoxydehydration (DODH) reaction of mucic acid in different alcohol solvents. T t Entry Solvent ( C.) (h) Conv. [%] Yield [%] 1 3-octanol 180 20.0 100.0 67.0 2 3-pentanol 120 12.0 97.8 71.1 24.0 100.0 98.6 3 1-butanol 120 24.0 78.9 68.7 12.0.sup.b 100.0 99.7.sup.c 4 2-propanol 90 24.0 9.6 .sup.a Reaction conditions: mucic acid (1.0 mmol), methyltrioxorhenium (MTO) (0.05 mmol, 5.0 mol %), 3-pentanol (20.0 ml). Yield and conversion were determined by .sup.1H NMR with internal standard. .sup.bRe.sub.2O.sub.7 (0.05 mmol, 5.0 mol %) was used as catalyst, n-butyl muconate 8 was produced.

Example 12

Hydrogen Transfer Reaction

[0085] As the high yield of muconates from mucic acid was achieved, subsequently, hydrogen transfer reaction was demonstrated for the conversion of muconic acid or muconate to adipic acid or ester (FIG. 5) Firstly, muconic acid 2 could be quantitatively converted to adipic acid 3 or monoester 9 in 3-pentanol at 200 C. in 12 to 24 hours. Similar results were achieved when different catalysts (Ru/C, Pd/C or Pt/C) were used. Encouraged by this result, crude muconates that obtained from deoxydehydration (DODH) reaction were directly used as feedstock for the hydrogen transfer reaction. Remarkably, the muconates obtained from mucic acid via deoxydehydration (DODH) reaction were fully converted to adipic acid esters 9 and 10 (Table 3). The reaction is highly selective and no other by-product was observed.

TABLE-US-00003 TABLE 3 Catalyst screening for transfer hydrogenation reaction..sup.a [00001] [00002] Entry Catal. t (h) Conv. (%) Yield (%).sup.b 1 5%Ru/C 24 100.0 99.5 2 12 100.0 86.3 3 6 82.7 81.7 4 5%Pd/C 24 60.4 38.5 5 12 54.4 29.0 6 6 45.9 23.4 7 5%Pt/C 24 100.0 99.5 8 12 100.0 99.3 9 6 78.2 76.3 .sup.aReaction conditions: 1. mucic acid (1 mmol); 3-pentanol (20.0 ml); 2. catalyst (5 mol %). .sup.bNMR yield of 9 and 10.

Example 13

One Pot Reaction

[0086] Since both deoxydehydration (DODH) and hydrogen transfer reaction could be conducted in 3-pentanol, the one-pot reaction for the conversion of mucic acid to adipic acid or ester was tested (FIG. 6). In a closed reaction system with methyltrioxorhenium (MTO) and Pt/C catalysts, mucic acid was converted to adipic acid ester in 75% yield at 200 C. in 48 hours. The moderate efficiency is due to the low reaction rate for the deoxydehydration (DODH) step in the closed system, as mentioned above. As the reaction was carried in the manner, first conducted at 120 C. under air flow for 12 hours and then sealed the system to elevate the temperature to 200 C. for further reaction for another 12 hours, the one-pot reaction efficiency was dramatically increased and 99% of adipic acid ester was achieved directly from mucic acid in 24 hours. As mucic acid can be obtained from renewable galactose in large scale by the already established procedure, the method developed here provided a highly efficient synthetic protocol for the production of renewable adipic acid.

Example 12

Compound Characterization

[0087]

TABLE-US-00004 Compound NMR characterization NMR spectrum [00003] 1H NMR (400 MHz, DMSO- 6d), = 7.33-7.25 (m, 2H); = 6.36-6.27 (m, 2H). FIG. 7A 2 [00004] .sup.1H NMR (400 MHz, DMSO- 6d), = 2.20 (s, 4H); = 1.48 (s, 4H). FIG. 7B 3 [00005] .sup.1H NMR (400 MHz, DMSO- 6d) , = 7.41-7.27 (m, 2H); = 6.49-6.29 (m, 2H); = 4.78-4.72 (m, 1H); = 1.63-1.46 (m, 4H); = 0.84, 0.83, FIG. 7C 4 0.81 (t, J = 7.4 Hz, 6H, CH.sub.3). [00006] .sup.1H NMR (400 MHz, DMSO- 6d), = 7.35 (q, 2H); = 6.45 (q, 2H); = 4.78-4.72 (m, 2H) ; = 1.63-1.46 (m, 8H); = 0.84, 0.83, 0.81 (t, J = 7.4 Hz, 12H, CH.sub.3). FIG. 7D 5 [00007] .sup.1H NMR (400 MHz, DMSO- 6d) , = 4.85 (d, J = 8.0 Hz, 2H, CHOH); 4.79 (m, 2H, OH); 4.28 (d, J = 8.0 Hz, 2H, CHOH); 4.11 (m, 4H, FIG. 7E 6 CH.sub.2); 3.78 (m, 2H, OH); 1.20 (t, J = 8.0 Hz, 6H, CH.sub.3). [00008] .sup.1H NMR (400 MHz, DMSO- 6d), = 7.37 (m, 2H); 6.45 (m, 2H); 4.75 (m, 1H, CH); 4.16 (m, 2H, CH.sub.2); 1.55 (m, 4H, CH.sub.2); 1.22 (t, J = FIG. 7F 7 7.2 Hz, 3H, CH.sub.3); 0.83 (t, J = 7.4 Hz, 6H, CH.sub.3). [00009] .sup.1H NMR (400 MHz, DMSO- 6d), = 7.37 (m, 2H); 6.45 (m, 2H); 4.11 (t, J = 6.4 Hz, 4H); 1.58 (m, 4H, CH.sub.2); 1.34 (m, 4H, CH.sub.2); 0.89 (t, J = FIG. 7G 8 8.0 Hz, 6H, CH.sub.3).

Example 14

Summary

[0088] In conclusion, the highly efficient synthetic protocol for the conversion of mucic acid to muconic acid, and then adipic acid through oxorhenium complex catalyzed deoxydehydration (DODH) Pt/C catalyzed hydrogen transfer sequence was demonstrated. Almost quantitative yields were achieved from mucic acid to muconic acid and The result presented here not only demonstrated a high efficient, simple and green protocol for the production of renewable adipic acid from sugar acid. It indicates the huge potential of formation of various industrial chemicals from various sugar acids.

Applications

[0089] The disclosed method is useful in synthesizing an ester of a saturated carboxylic acid from a polyhdroxycarboxylic acid.

[0090] The disclosed method may be used to convert mucic acid to adipic acid, which is used commonly as a monomer precursor for the production a variety of polymers including nylon and polyurethane. Adipic acid may also be used in medicine, such as in controlled-release formulation matrix tablets to obtain pH-independent release of both weakly basic and weakly acidic drugs. In addition, small but significant amounts of adipic acid may be used in food as a flavorant or gelling aid. The disclosed method may therefore be useful in the industrial-scale production of adipic acid for the above applications.

[0091] The disclosed method may simplify the synthetic process of saturated carboxylic acids such as adipic acids from polyhdroxycarboxylic acids such as mucic acid, as the reaction conditions are milder and more time- and cost-efficient compared to conventional methods.

[0092] It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.