The present invention relates to a novel process for the preparation of FDCA of formula- (1 ) whose chemical name is 2,5-furandicarboxylic acid (also known as dehydromucic acid or pyromucic acid). 2,5-Furandicarboxylic acid is found to be one of the top 12 bio- based products identified by the US Department of energy for green chemistry industry.

(FDCA)

> ( 1 )

There is a growing interest in the use of renewable resources as abundantly available feed stocks for the chemical industry mainly due to the progressive reduction of natural resources. 2,5-Furandicarboxylic acid (FDCA) is found to be one of the most versatile building blocks for chemical and polymer applications since FDCA can be obtained from green sources like widely available carbohydrates and cellulosic materials.

2,5-Furandicarboxylic acid (FDCA) is a replacement for terephthalic acid made on large scale from petroleum-based para-xylene for the manufacture of various polyesters, such as polyethylene terephthalate (PET) and polybutylene terethalate(PBT). In this context, 2,5-furandicarboxylic acid (FDCA) received significant attention as a desirable substitute for terephthalic acid for the manufacture of various polymeric materials like polyethylene furanoate (PEF) a furan counterpart of PET and it showed comparable functional properties and thermal stability. Therefore, there is an urgent need in the chemical industry for an efficient process to produce furan based carboxylic acids, their derivatives and compositions. 2,5-Furandicarboxylic acid (FDCA) is invented way back in 1876 and today the product has been attracting tremendous commercial significance. There are more than 100 research publications and over 40 patents filed on this compound. However, there is still an unmet need to develop a commercially viable process for its production. On the laboratory scale it is often prepared from 5-Hydroxymethyl furfural (HMF), which in turn is obtained from carbohydrate-containing sources such as glucose and fructose.

The present invention is related to the process for making 2,5-furandicarboxylic acid (FDCA) of formula (1 ), starting from 5-Hydroxymethyl furfural (HMF) obtained from non-fossil bio-sources.

BACKGROUND OF INVENTION:

2,5-Furandicarboxylic acid (FDCA) is first reported by Fittig and Heinzelmann in 1876 by dehydration of mucic acid using fuming hydrobromic acid under pressure {Chem. Ber., 1876, vol 9, 1 198) for two days at 100° C (Scheme- 1 ).

2 I

Scheme- 1

Several modifications in the above reactions conditions, like using concentrated HCl {Chemische Berichte, 1879, vol 12, 1085), a mixture of concentrated HCl and HBr {Journal fuer Praktische Chemie, 1882, 25, 51), aq. sulfuric acid at 135° C {Chemische Berichte, 34; (1901 , vol 34, 3447), benzenesulfonic acid {Revue Roumaine de Chimie,

2000, vol 45, pages 883 - 886), toluene-4-sulfonic acid {Polish Journal of Chemistry,

2001 , vol 75(12), pages 1943-1946), with HCl at 150° C {Chemische Berichte, 1891, vol 24, 3623) and with a mixture HCl and HBr at 150° C {Chemische Berichte, 1891 , vol 24, 2140) etc are reported. A comprehensive review {American Chemical Journal, 1901 , vol 25, pages 439-484) on dehydromucic acid is also published.

In another approach 5-Hydroxymethyl furfural (HMF) is oxygenated under varying conditions to get 2,5-furandicarboxylic acid (FDCA).

Scheme-2

Catalytic oxidation processes like Ru(OH)x/hydrotalcite (HT) catalyst/1-40 bar 0 ₂ pressure/38h/ 140° C/water (Catal. Lett., 201 1 , vol 141 , pages 1752-1760); gold nano particle catalyst-HT-1.92 wt%/ 94.8° C/water/0 ₂ {Green Chem., 2,1 1, vol 13, pages 824- 827); 5% Pt/C/aq. NaHC0 ₃ /0 ₂ 5bar/100° C (WO201217052); 5-13% supported platinum catalyst/aq. NaOH/0 ₂ bubbling/24 ⁰ C/4.5h (US3326944); cobalt acetate tetrahydrate/manganese acetate tetrahydrate/HBr/aq. acetic acid/ 30 bar-0 ₂ pressure/180 ⁰ C/30 min. (WO201333081); 5% Pt/C/30% aq. NaOH/pH 7.0-7.5/70° CI 0 ₂ bubbling (US4977283); cobalt acetate tetrahydrate /manganese acetate tetrahydrate/ sodium bromide/150 ⁰ C/30 bar/4A° molecular sieves (US201 192720); zirconiun tetraacetate/anhydrous cobalt acetate/manganese acetate/sodium bromide/acetic acid/3h/50-125° C/70 bar air (Adv. Synth and Catal. 2001, vol 343, pages 102-1 1 1); cobalt acetate/cerium acetate/ sodium bromide/1.5h/l 00° C/27.5 bar 0 ₂ (WO2010132740); cobalt acetate/manganese acetate/sodium bromide/180° C/20 bar air (WO201 143661 ); Ru(OH)x/Mg ₆ Al ₂ C0 ₃ (OH) ₁₆ . 4H ₂ 0/ionic liquid/24h/ 10-30 bar oxygen/100- 140 ⁰ C {Catal. Lett., 2012, vol 142, pages 1089-1097); Ru(OH) _x /water/ 1 -40 bar 0 ₂ pressure/140 ⁰ C (Top. Catal, 201 1 , vol 54, pages 1318-1324); Au on Ti0 ₂ / aq. NaOH/20 bar 0 ₂ (Catal. Today, 201 1 , vol 160, pages 55-60); Au-Ce0 ₂ catalyst/water/NaOH/1000 rpm/10 bar air/65° C (Chemsuschem, 2009, vol 2, pages 1 138- 1 144); cobalt acetylacetonate encapsulated in Si0 ₂ /water (Catal. Commun., 2003, vol 4, pages 83-86); cobalt acetate/manganese acetate tetrahydrate/sodium bromide/HBr/acetic acid/peracetic acid/2h/132° C/10 bar oxygen (US2012302770) are known in the literature. Chemical oxidation processes like aq. NaOH/KMn0 ₄ (WO20070232815); Cu ₂ Cl ₂ /acetonitrile/ tert. butylhydrogenperoxide (Appl. Catal. A: Gen, 2013, vol 456, pages 44-50); aq. NaOH/silver oxide/ water/nitric acid/ultra sound {Pol. J. Chem., 1994, vol 68, pages 693-698) have also been reported.

In other similar approaches, 2,5-furandicarboxylic acid is prepared by oxidation of 2,5- diformyl furan with potassium permanganate in aq. NaOH (US2007/232815) or with silver oxide {Bull. Soc. Chim. Fr., 1987, vol 5, pages 855-860); oxidation of 5-formyl- furancarboxylic acid with hydrogen peroxide in aq. sodium hydroxide {Justus Liebigs Annalen der Chem. , 1953, vol 580, 169); oxidation of 5-chloromethylfurfural with nitric acid {Green Chem., 201 1 , vol 13, pages 1 1 14-1 1 17); oxidation of methyl-5- chloromethylfuroate with nitric acid (J Prakt. Chem., 1988, vol 330, pages 825-829) and oxidation of 5-formylfurancarboxylic acid with silver oxide {Chem. Ber., 1894, vol 27, 1570) and the like are also reported in the literature.

However, these chemical oxidation methods are beset with disadvantages like uncontrollable exothermicity, long reaction times and generation of large quantity of effluents containing metal salts posing environmental hazards. Some of the reactions when tried in our laboratory did not result in the expected yield and purity.

Thus, in spite of having the choice of a variety of methods for preparation of 2,5- furandicarboxylic acid (FDCA), there is still a need to develop commercially viable process suitable for large scale manufacturing. The following common disadvantages are associated with the existing processes.

Usage of highly expensive catalysts like platinum oxide, platinum on carbon or gold nano catalysts etc., in the catalytic oxidation reactions.

Oxidation under high pressures (70 bar) and temperatures (180° C) requiring special equipment and safety infrastructure.

Uncontrollable exothermic nature associated with some of the reactions. 4 Very poor catalyst recovery and recyclability.

5 Formation of side products in most of the processes.

6 Non-scalable purification methods like chromatographic separations.

7 Non-commercial viability of the methods because of low conversions.

Hence there is an urgent need for a safe, economically viable high yielding manufacturing process to meet the industry requirements.

SUMMARY OF INVENTION:

Keeping in view of the difficulties associated with the above processes for the preparation of 2,5-furandicarboxylic (FDCA) acid on commercial scale, we aimed to develop a simple, economically viable high yielding process for the preparation of 2,5- furandicarboxylic acid of formula (1). Accordingly, the main objective of the present invention is to provide an improved process for the preparation of 2,5-furandicarboxylic acid (FDCA) of formula- (1), which is simple, economical and commercially applicable.

Another objective of the present invention is to provide an improved process for the preparation of 2,5-furandicarboxylic acid (FDCA) of formula- (1 ), which involves readily and cheaply available raw materials.

During our elaborate research in developing a process for the preparation of 2,5- furandicarboxylic acid (FDCA) of formula (1), we observed that 5- Hydroxymethylfurfural (HMF) commercially obtained from a bio-source could be a suitable starting material. Accordingly, the basic raw material selected for the synthesis of 2,5-furandicarboxylic acid (FDCA) of formula (1) is 5-Hydroxymethyl furfural (HMF) of formula (3). The process is as outlined in Scheme (3).

Scheme 3

where R= hydrogen, C 1 -C6 alkyl, aryl

The key intermediate 5-Acyloxymethylfurancarboxylic acid of formula (5) is prepared starting from 5-Hydroxymethylfurfural (HMF), through acylation followed by oxidation of 5-acyloxymethylfurfural of formula (4).

Accordingly, the invention provides a novel process for the preparation of 2,5- furandicarboxylic acid (FDCA) of formula (1 )

I

which comprises,

(i) reacting 5-Hydroxymethylfurfural (HMF) of formula (3)

3

with an acylating agent to get 5-acyloxymethylfurfural of formula (4)

R

o // \\ , o

o'

4

where R= hydrogen, C 1 -C6 alkyl, aryl

ii) oxidation of the resulting intermediate of formula (4) with an oxidizing agent to get 5- acyloxymethylfurancarboxylic acid of formula (5)

where R= hydrogen, C1 -C6 alkyl, aryl

iii) further oxidation of the resulting compound of formula (5) employing the same (or) different oxidant to get 2,5-furandicarboxylic acid (FDCA) of formula (1 ).

DETAILED DESCRIPTION OF INVENTION

In a preferred embodiment of the present invention,

In the first step, 5-hydroxymethyl furfural (HMF) of formula (3) is reacted with an acylating agent like acetic acid, acetyl chloride or acetic anhydride or acetic-formic anhydride or formic acid or formyl chloride or propionic acid or propionyl chloride or propionic anhydride or butyric acid or butyryl chloride or butyric anhydride or benzoic acid or benzoyl chloride or Boc anhydride or benzyloxy carbonyl chloride or any acylating agent preferably acetic anhydride to get 5-acyloxymethylfurfural of formula(4). The reaction may be done without organic solvent or with a solvent selected from ethyl acetate, toluene, diisopropyl ether, chloroform, dichloromethane, tetrahydrofuran, dioxane, dimethylformamide and dimethyl acetamide. The catalytic base used in the reaction is selected from inorganic base (sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate) or from organic base (trimethyl amine, triethyl amine, Ν,Ν-dimethylaminopyridine, N-methylmorpholine, Ν,Ν-diisopropylethyl amine) preferably N,N-dimethylaminopyridine (DMAP). The reaction can be done at 0-100° C preferably at 5-50° C and most preferably at 20-25° C. After completion of reaction, the compound, 5-acyloxymethylfurfural is extracted with organic solvent selected from ester solvent like ethyl acetate, ether solvent like diisopropyl ether, aromatic hydrocarbon solvent like toluene, chlorinated solvents like chloroform, dichloromethane preferably ethyl acetate or toluene and most preferably ethyl acetate. The product solution is washed with aq. base preferably selected from aq. NaHC0 ₃ or aq. NaOH or aq. Na ₂ C0 ₃ or aq.

2CO3. After extraction and separation, the excess solvent is recovered by distillation under diminished pressure to get 5-acyloxymethylfurfural of formula (4) in 90% yield having more than 98% HPLC purity.

In the second step, the 5-acyloxymethylfurfural of formula (4) is oxidized to get 5- acyloxymethylfurancarboxylic acid of the formula (5). The oxidizing agent is selected from nitric acid, bromine water, sodium hypochlorite, sodium chlorite, sodium bromite, potassium chlorite, potassium bromite, hydrogen peroxide, potassium permanganate or a combination of sodium chlorite-hydrogen peroxide or potassium chlorite-hydrogen peroxide preferably sodium chlorite-hydrogen peroxide combination. The percentage of hydrogen peroxide used in the reaction is selected from 6-60% preferably 35-50% and most preferably 50%. The reaction solvent is selected from acetonitrile, tetrahydrofuran, ethyl acetate, chloroform preferably acetonitrile or ethyl acetate and most preferably ethyl acetate. The reaction can be carried out at 0-100° C preferably at 5-50° C and most preferably at 15-20° C. After completion of the reaction, 5 -acyloxymethylfurancarboxylic acid of formula (5) is extracted with organic solvent selected from an ester solvent like ethyl acetate, ether solvent like diisopropyl ether, aromatic hydrocarbon solvent like toluene, chlorinated solvents like chloroform, dichloromethane preferably ethyl acetate or toluene. After extraction and separation, the excess solvent is recovered by distillation under diminished pressure to get 5-acyloxymethylfurancarboxylic acid of formula (5) in 91 % yield having more than 98% HPLC purity.

In the third step, 5-acyloxymethylfurancarboxylic acid of formula (5) is oxidized to 2,5- furandicarboxylic acid (FDCA) of formula (1 ). The oxidizing agent is selected from nitric acid, dilute bromine water, sodium hypochlorite, sodium chlorite, sodium bromite, potassium chlorite, potassium bromite, hydrogen peroxide, potassium permanganate, sodium permanganate or a combination of sodium chlorite-hydfogen peroxide or potassium chlorite-hydrogen peroxide or sodium bromite-hydrogen peroxide or potassium bromite-hydrogen peroxide preferably nitric acid or hydrogen peroxide. The percentage of nitric acid used in the reaction is selected from 10-70% preferably 25-65% and most preferably 55%. The reaction is conducted with or without water as solvent. The reaction can be carried out at 0-100° C preferably at 25-95° C and most preferably at 55-60° C. After completion of the reaction, 2,5-furandicarboxylic acid (FDCA) of formula (1) is filtered by suction as off- white solid having more than 98% HPLC purity. The product may be further purified by simple acid-base treatment.

The entire scheme (scheme-3) may be carried out sequentially by isolating product of each step. Alternatively it can also be condensed into a single pot procedure wherein the 2,5-furandicarboxylic acid of formula (1 ) (72% overall yield) is isolated at the end of the sequence. The details of the invention as examples are given below which are provided to illustrate the invention only and therefore should not be construed to limit the scope of the present invention.

Example-1:

Preparation of 2,5-furandicarboxylic acid (FDCA):

(i) Preparation of 5-acetyIoxymethylfurfural (4): [R=CH3]

Into a 250 mL four necked round bottomed flask equipped with a mechanical stirrer, a reflux condenser and a thermometer socket are charged 5-hydroxymethylfurfural (25 g; 0.198 mol), ethyl acetate (125 mL) and DMAP (2.42 g; 0.019). To the cooled solution, acetic anhydride (24.3 g; 0.238 mol) was added. After addition, the reaction mixture was stirred for 1 -2 hours. The reaction mixture was then washed with water and the resulting layers were separated. The organic layer was distilled off under diminished pressure to get 5-acetoxymethylfurfural (30.0 g; 90% by theory) as yellow oil.

HPLC: > 98% ii) Preparation of 5-acetyloxymethylfurancarboxylic acid (5): [R=CH3]

Into a 500 mL four necked round bottomed flask equipped with a mechanical stirrer, gas bubbler, thermometer socket are charged 5-acetyloxymethylfurfural (30 g) as obtained above and 300 mL acetonitrile. To the stirred solution, an aq. solution of sodium chlorite (24.2 g; 0.267 mol) and 50% hydrogen peroxide (25 mL; 0.367 mol) were added. After addition, the reaction mixture was stirred for 2-3 hours. The product was extracted with ethyl acetate. Excess solvent was recovered by distillation under reduced pressure to get 5-acetyloxymethylfurancarboxylic acid (29.9 g; 91 % by theory) as off-white solid. HPLC purity: > 98%

(iii) Preparation of 2,5-furandicarboxylic acid (1): [R=CH3]

Into a 250 mL four necked round bottomed flask equipped with reflux condenser, thermometer socket are charged 5-acetoxymethylfurancarboxylic acid (25 g; 0.135 mol) and 25 mL water. To this stirred mixture, 70% nitric acid (125 mL, 1.38 mol) was added at 20-30° C. The temperature of the reaction mixture was raised to 40-50° C and maintained for 10- 12 hours. After reaction, the reaction mixture was cooled to 25-35° C and filtered. The product cake was washed with water and dried.

Product weight: 15 g (70.7% by theory).

HPLC purity: > 98%.

Example-2:

Preparation of 2,5-furandicarboxylic acid (FDCA) (One pot procedure):

Into a 250 mL four necked round bottomed flask equipped with a mechanical stirrer, a reflux condenser and a thermometer socket are charged 5-hydroxymethylfurfural (25 g; 0.198 mol) and acetic anhydride (24.3 g; 0.238 mol). The reaction mixture was then stirred for 1 -2 hours. After completion of the reaction to the resulting crude yellow oil an aq. solution of sodium chlorite (44.7 g; 0.495 mol) and 35% hydrogen peroxide (39 mL; 0.396 mol) were added. The reaction mixture was then stirred for 2-3 hours. After completion of reaction, excess hydrogen peroxide was quenched with sodium meta bisulfite. To the reaction mixture, 70% nitric acid ( 155 mL, 1.72 mol) was added and the reaction mixture was maintained for 10-12 hours at 60-65° C. After completion of reaction, the reaction mixture was cooled to 25-35° C and filtered. The product cake was washed with water and dried.

Product weight: 22.3 g (72% by theory).

HPLC purity: > 98%.

Example-3:

Preparation of 2,5-furandicarboxylic acid (FDCA) (One pot procedure):

Into a 250 mL four necked round bottomed flask equipped with a mechanical stirrer, a reflux condenser and a thermometer socket are charged 5-hydroxymethylfurfural (25 g; 0.198 mol) and acetic anhydride (24.3 g; 0.238 mol). The reaction mixture was then stirred for 1 -2 hours. After completion of the reaction to the resulting crude yellow oil was washed with water and separated an aq. solution of sodium chlorite (44.7 g; 0.495 mol) and 35% hydrogen peroxide (39 mL; 0.396 mol) were added. The reaction mixture was then stirred for 2-3 hours. After completion of reaction, excess hydrogen peroxide was quenched with sodium meta bisulfite. To the reaction mixture, 10% aq. Sodium hydroxide (500 mL) and potassium permanganate (54.0 g, 0.341 mol) were added and the reaction mixture was maintained for 4-5 hours at 20-25° C. After completion of the reaction, the mixture was filtered and the filtrate was adjusted to acidic pH to get the product. The product cake was washed with water and dried.

Product weight: 22 g (71 % by theory).

HPLC purity: > 98%. Example-4:

Preparation of 2,5-furandicarboxylic acid (FDCA) (One pot synthesis):

Into a 250 mL four necked round bottomed flask equipped with a mechanical stirrer, a reflux condenser and a thermometer socket are charged 5-hydroxymethylfurfural (25 g; 0.198 mol) and acetic anhydride (24.3 g; 0.238 mol). The reaction mixture was then stirred for 1 -2 hours. After completion of the reaction to the resulting crude yellow oil 10% aq. Sodium hydroxide (500 mL) and potassium permanganate (54.0 g, 0.341 mol) were added and the reaction mixture was maintained for 4-5 hours at 20-25° C. After completion of the reaction, the mixture was filtered and the filtrate was adjusted to acidic pH to get the product. The product cake was washed with water and dried.

Product weight: 21.5 g (69.5% by theory).

HPLC purity: > 98%.

Advantages of the present process:

( 1 ) Present process does not require expensive reagents or catalysts.

(2) Present process uses commercially available raw materials like acetic anhydride, nitric acid and hydrogen peroxide etc.

(3) Present process does not require any chromatographic purification.

(4) No exothermic nature observed in the oxidation reaction

(5) 2,5-furandicarboxylic acid obtained by this process is of high pure (>98% by HPLC)

(6) No pressure is required for oxidation reaction

(7) No special equipment or special safety infrastructure is required for operation.

(8) This process exemplifies a novel process of making 2,5-furandicarboxylic acid of formula- 1.

(9) The reaction sequence can be condensed to a one-pot procedure.

(10) The procedure can be easily scaled up to multi-kilogram level.

(1 1 ) The effluents generated are free of transition metal salts and are easily treatable.

( 12) The present process successfully reduces the formation of impurities.