Method for the monodecarboxylation of aromatic carboxylic acid and its salts

Abstract

Method for the monodecarboxylation of aromatic carboxylic acid and its salts The present disclosure relates to a method for the monodecarboxylation of aromatic carboxylic acid and its salts, in particular to a method for selectively preparing benzoic acid by decarboxylating terephthalic acid at a moderate temperature.

Description

[0001] Method for the monodecarboxylation of aromatic carboxylic acid and its salts

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims priority to European patent application EP 24315478.8 filed on October 17, 2024.

[0004] TECHNICAL FIELD

[0005] The present disclosure relates to a method for the monodecarboxylation of aromatic carboxylic acid and its salts, in particular to a method for selectively preparing benzoic acid by decarboxylating terephthalic acid.

[0006] BACKGROUND

[0007] The following discussion of the prior art is provided to place the disclosure in an appropriate technical context and enable the advantages of it to be more fully understood. It should be appreciated, however, that any discussion of the prior art throughout the specification should not be considered as an express or implied admission that such prior art is widely known or forms part of common general knowledge in the field.

[0008] Aromatic carboxylic acid are compounds that have at least one carboxylic group bonded to an aromatic ring. They exhibit both aromatic properties and acidity and are promising feedstock chemicals. For example, benzoic acid, as the simpliest benzene-based carboxylic acid, is widely used in the preservation of food, drugs and in the prevention of bacterial infection.

[0009] CN103467237 discloses a method for preparing aromatic hydrocarbons by catalytic decarboxylation of terephthalic acid residues. The decarboxylation reaction is carried out under the condition of 450°C~550°C, 0~2MPa and a decarboxylation catalyst. The decarboxylation catalyst includes an active component and a carrier. The active component is ZnO, the carrier is AI2O3, and the mass ratio of ZnO to AI2O3 is 0.1 to 5. The target products of this technology are low boiling point compounds such as benzene and toluene. Similarly, Journal of Applied Polymer Science (2011), 120(6), 3687-3694 discloses the decarboxylation of terephthalic acid for the preparation of benzene at a high temperature from 600 to 800°C in the presence of CaO. It has been reported that benzoic acid can be formed by hydrothermal degradation of polyethylene terephthalate (PET) waste by Journal of Analytical and Applied Pyrolysis, Volume 134, September 2018, 621-631 and Processes (2022), 10(1), 24. However, high temperature is still necessary.

[0010] Adv. Synth. Catal. 2007, 349, 2241-2246, J. Org. Chem. 2009, 74, 2620-2623 and Adv. Synth. Catal. 2013, 355, 790-796 disclose copper-catalyzed decarboxylation of aromatic carboxylic acids. The starting materials are all aromatic or heterocyclic aromatic compounds having only one carboxylic acid group.

[0011] US 1939212 relates to the production of monocarboxylic acids and their salts and derivatives by splitting off carboxyl groups from the corresponding poly carboxylic acid compounds in the presence of an oxide of a non-alkali forming metal. Disadvantageous^, high temperature in the range of 325~450°C is needed.

[0012] CA2175535 teaches a process for the preparation of aromatic compounds by decarboxylation of aromatic carboxylic acids in a solvent system comprising water and a water-insoluble amine. Examples 1 to 5 are related to the preparation of fluoro-substituted benzoic acids from fluoro-substituted phthalic acid. The reactions took place in the absence of metal catalysts. The catalyst, copper (I) oxide, was only used in Example 6, which is related to the preparation of fluoro- substituted benzene from fluoro-substituted benzoic acid.

[0013] There is thus a significant need in the art for an improved method for the monodecarboxylation of aromatic carboxylic acid and its salts, in particular to a method for selectively preparing benzoic acid by decarboxylating terephthalic acid at a moderate temperature.

[0014] SUMMARY

[0015] The present invention provides a method for removing one carboxylate group linked to an aromatic ring of an aromatic compound, comprising reacting the aromatic compound at a temperature ranging from 160°C to 210°C in the presence of a metal catalyst and a nitrogen-containing ligand, wherein the aromatic ring is linked with two carboxylate groups and the aromatic ring is only linked with carboxylate groups. The Applicant surprisingly found that it is possible to prepare monodecarboxylated products selectively by the method according to the present invention. The selectivity is higher than 50%, or even higher than 60%. The invented method is so selective and efficient that it brings advantages, such as no salification to purify benzoic acid and easy catalyst recycling.

[0016] In some preferred embodiments, the conversion of the aromatic compound is higher than 50%, or even higher than 60%.

[0017] Furthermore, the reaction can be carried out under mild conditions.

[0018] Other subjects and characteristics, aspects and advantages of the present invention will emerge even more clearly on reading the detailed description and the examples that follow.

[0019] DEFINITIONS

[0020] Throughout the description, including the claims, the term "comprising one" should be understood as being synonymous with the term "comprising at least one", unless otherwise specified, and "between" should be understood as being inclusive of the limits.

[0021] As used herein, the terminology "(Cn-Cm)" in reference to an organic group, wherein n and m are both integers, indicates that the group may contain from n carbon atoms to m carbon atoms per group.

[0022] As used herein, the term "carboxylate group" refers to "-COO " group.

[0023] The articles "a", "an" and "the" are used to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article.

[0024] The term "and / or" includes the meanings "and", "or" and also all the other possible combinations of the elements connected to this term.

[0025] It is specified that, in the continuation of the description, unless otherwise indicated, the values at the limits are included in the ranges of values which are given.

[0026] Ratios, concentrations, amounts, and other numerical data may be presented herein in a range format. It is to be understood that such a range format is used merely for convenience and brevity and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also all the individual numerical values or sub-ranges encompassed within that range as if each numerical value or sub-range is explicitly recited.

[0027] DETAILS OF THE INVENTION

[0028] In one aspect, the present invention provides a method for removing one carboxylate group linked to an aromatic ring of an aromatic compound, comprising reacting the aromatic compound at a temperature ranging from 160°C to 210°C in the presence of a metal catalyst and a nitrogen-containing ligand, wherein the aromatic ring is linked with two carboxylate groups and the aromatic ring is only linked with carboxylate groups.

[0029] The aromatic compound can notably be a compound having the general formula (I) below: wherein:

[0030] Xi and X2, independently from each other, are a cation.

[0031] The cation can preferably be selected from the group consisting of H+, NHZ, K+, Li+, Na+and Cu+.

[0032] Preferably, Xi and X2 are H+.

[0033] Accordingly, a compound having the general formula (II) below is obtained from the compound having the general formula (I) by the method according to the present invention: wherein:

[0034] Xi is a cation. The cation can preferably be selected from the group consisting of H+, NHZ, K+, Li+, Na+and Cu+.

[0035] Preferably, Xi is H+.

[0036] Preferably, the aromatic compound having the general formula (I) is terephthalic acid.

[0037] Terephthalic acid is an important product obtained for example, by the degradation of polyethylene terephthalate (PET). Thus, the method according to the present invention can reuse PET and is suitable for waste management of PET.

[0038] Preferably, the aromatic compound having the general formula (II) is benzoic acid.

[0039] The method of the present invention can be readily adapted for a batch, a fed- batch or a continuous mode.

[0040] The metal in the metal catalyst can be selected from the group consisting of Fe, Co, Ni, Cu and Zn, preferably from the group consisting of Ni, Cu and Zn and more preferably Cu.

[0041] The metal can be present in elemental, alloy, or compound form, such as metal oxide or metal salt. In a preferred embodiment, the metal is present in metal oxide form.

[0042] Preferably, the catalyst is a copper catalyst selected from the group consisting of elemental copper, copper oxide, copper sulfide, copper salt and any combination thereof. For example, the copper catalyst can be any one of copperbased catalysts as mentioned in Green Chem, 2014, 16, 3089-3097.

[0043] More preferably, the catalyst is selected from the group consisting of copper oxide, copper sulfide, copper acetate and copper carbonate.

[0044] The valence state of copper is not particularly limited, and it can be monovalent or divalent. In a preferred embodiment, the valence state of copper is monovalent.

[0045] Good results can be obtained when the catalyst is copper oxide, such as copper (II) oxide (CuO), copper (I) oxide (CU2O).

[0046] The molar ratio of the aromatic compound to the catalyst can be from 0.1 to 1000, preferably from 1 to 100. The nitrogen-containing ligand can be selected from the group consisting of aliphatic amines, such as tetramethylethylenediamine, nitrogenous aromatic heterocycles such as 2,2'-bipyridine, 4, 4'-dimethyl-2,2'-bi pyridine, 1,10- phenanthroline, 4,7-diphenyl-l,10-phenanthroline and mixtures thereof, preferably from the group consisting of 2,2'-bipyridine, 4,4'-dimethyl-2,2'- bipyridine, 1,10-phenanthroline, 4,7-diphenyl-l,10-phenanthroline and mixtures thereof, and most preferably from the group consisting of 2,2'-bipyridine, 1,10- phenanthroline, 4, 7-diphenyl- 1,10-phenanthroline and mixtures thereof.

[0047] As used herein, the term "nitrogenous aromatic heterocycle" refers to a compound in which the nitrogen atom occurs as part of an aromatic ring.

[0048] The Applicant found that the selectivity to the mono-decarboxylated product is high by using an aliphatic amine or nitrogenous aromatic heterocycle.

[0049] In some preferred embodiments, high conversion of the aromatic compound can be achieved in the presence of a nitrogenous aromatic heterocycle.

[0050] The molar ratio of the aromatic compound to the nitrogen-containing ligand is from 0.1 to 1000, preferably from 1 to 200, and more preferably from 1 to 100.

[0051] Advantageously, the aromatic compound reacts in the presence of a solvent.

[0052] Non-limiting examples of the solvents inlcude N-alkyl-2 -pyrrolidone with alkyl being C1-C12, dimethylimidazolidinone, N,N'-dimethylpropyleneurea (DMPU), dimethylacetamide, sulfolane, diphenylsulfone, polyethylene glycol (PEG), tributylphosphate, glymes, orthophenanthrolines, succinamides, pyridines, imidazoles, quinoline, nitriles, mesitylene, ionic liquids, diphenylether and mixtures thereof, and preferably from the group consisting of N-alkyl-2- pyrrolidone with alkyl being C1-C12, such as N-methylpyrrolidone (N-methyl-2- pyrrolidone) (NMP), N-octylpyrrolidone (N-octyl-2-pyrrolidone) (NOP) and N- dodecylpyrrolidone, dimethylimidazolidinone, such as l,3-dimethyl-2- imidazolidinone (DMI), sulfolane, quinoline and mixtures thereof.

[0053] The solvent system in the method of the present invention is simple. It is not necessary to prepare a mixed solvent having water and water-insoluble organic solvent.

[0054] In some preferred embodiments, the solvent system is free or substantially free of water. The concentration of the aromatic compound in the solvent is preferably from 0.1 to 5 mol / L, preferably from 0.3 to 2 mol / L.

[0055] Advantageously, the aromatic compound reacts in the presence of an inert atmosphere such as N2, Ar and so on.

[0056] Preferably, the temperature ranges from 175°C to 195°C.

[0057] The reaction time is not particularly limited and generally depends on reaction conditions, such as the reaction mode, temperature and catalyst amount. For example, the aromatic compound reacts for 1 to 12 h in a batch reaction.

[0058] In a further aspect, the present invention relates to a mixture comprising an aromatic compound comprising an aromatic ring, a metal catalyst and a nitrogencontaining ligand, wherein the aromatic ring is linked with two carboxylate groups and the aromatic ring is only linked with carboxylate groups.

[0059] The aromatic compound is preferably a compound having the general formula (I), as defined above and more preferably terephthalic acid.

[0060] In some preferred embodiments, the mixture further comprises a solvent.

[0061] The metal catalyst, the nitrogen-containing ligand and the solvent have the same meanings, as defined above.

[0062] The mixture may further comprise a compound having the general formula (II), as defined above and more preferably benzoic acid.

[0063] The following examples are included to illustrate embodiments of the invention. The disclosure is not limited to such examples.

[0064] EXAMPLES

[0065] Materials

[0066] Terephthalic acid (100-21-0, Thermo Scientific);

[0067] N-methyl-2-pyrrolidone (NMP) (872-50-4, Merck);

[0068] N-octyl-2-pyrrolidone (NOP) (2687-94-7, Merck);

[0069] Sulfolane (126-33-0, Merck); l,3-Dimethyl-2-imidazolidinone (DMI) (80-73-9, Merck);

[0070] Quinoline (91-22-5, Merck);

[0071] Copper (I) oxide (1317-39-1, Merck);

[0072] 4,7-Diphenyl-l,10-phenanthroline (Bphen) (1662-01-07, Merck); 1,10-Phenanthroline (Phen) (66-71-7, Merck);

[0073] 2,2'-Bipyridine (Bipy) (366-18-7, Merck);

[0074] Tetramethylethylenediamine (TMEDA) (110-18-9, Merck).

[0075] Experimental procedure:

[0076] Solvents were degassed by bubbling nitrogen through them for 1 hour prior to use and were dried over activated molecular sieves (4 ) to ensure the removal of any moisture. All reagents were used as received.

[0077] The decarboxylation reaction was carried out in a dry and nitrogen-purged setup for 1 hour prior to the introduction of reactants. Terephthalic acid (1 equiv), the chosen ligand (0.1 equiv), and copper (I) oxide (CU2O, 0.05 equiv) were added to the reaction vessel under a nitrogen atmosphere to prevent oxidation and moisture ingress. The dried and degassed solvent was then introduced to achieve a terephthalic acid concentration of 0.5 M.

[0078] The reaction mixture was heated under magnetic stirring to the desired temperature (between 175°C and 195°C). The progress of the reaction was monitored by HPLC analysis of samples of the reaction mixture to determine the conversion rate of terephthalic acid to benzoic acid and to assess the reaction completion.

[0079] The high-performance liquid chromatography (HPLC) analyses were performed using an Agilent 1260 Infinity II HPLC system. Separation was achieved on a Waters Corporation XSelect HSS T3 column (3.0 mm x 1000 mm, 2.5 pm particle size) maintained at 40°C. The mobile phase consisted of a gradient mixture of solvent A (0.085% phosphoric acid in water) and solvent B (acetonitrile). The gradient program was initiated with 1% B, increased linearly to 80% B over 7.4 min, then returned to the initial conditions over 0.5 min and re-equilibrated for 2.1 min, resulting in a total run time of 10 min. The flow rate was set at 1 mL / min, and the injection volume was 2 pL.

[0080] Detection was carried out using a diode-array detector (DAD) set at a wavelength of 230 nm. Control of the system and data analysis were processed using Agilent OpenLAB software.

[0081] Sample preparation involved dilution in dimethyl sulfoxide to a final concentration of 100 ppm, followed by filtration through a 0.2 pm PTFE filter. Standards for calibration were prepared in the same manner at concentrations ranging from 10 to 100 ppm.

[0082] Examples 1 to 10

[0083] The reactions of Examples 1 to 10 were carried out based on experimental procedure. The experimental results are listed in Table 1. It is shown that the selectivity to benzoic acid is high in the presence of different solvents and ligands.

[0084] The Applicant found that the selectivity to benzoic acid is high by using an aliphatic amine or nitrogenous aromatic heterocycle. In particular, high conversion of terephthalic acid was achieved when different nitrogenous aromatic heterocycles were used.

[0085] Table 1

[0086] Solvent Ligand T(°C) Conv. TA after 6h(%) Yield. BA after 6h(%)

[0087] EXI NMP / quinoline Bphen 180 56 56

[0088] EX2 DMI Bphen 180 82 78

[0089] EX3 NMP Bphen 180 85 79

[0090] EX4 NMP Phen 180 60 60

[0091] EX5 NMP Bipy 180 63 63

[0092] EX6 NMP TMEDA 180 8 8

[0093] EX7 NOP Bipy 180 36 36

[0094] EX8 NOP Bipy 195 98 57

[0095] EX9 NOP TMEDA 180 5 5

[0096] EX10 Sulfolane Bipy 180 76 51

[0097] TA: Terephthalic acid

[0098] BA: Benzoic acid

[0099] Comparative Example

[0100] The reaction of Comparative Example was carried out under the same reaction conditions as Example 7 except that ligand was not used. Benzoic acid was not observed after the reaction.

Claims

C L A I M S1. A method for removing one carboxylate group linked to an aromatic ring of an aromatic compound, comprising reacting the aromatic compound at a temperature ranging from 160°C to 210°C in the presence of a metal catalyst and a nitrogen-containing ligand, wherein the aromatic ring is linked with two carboxylate groups and the aromatic ring is only linked with carboxylate groups.

2. The method according to claim 1, wherein the aromatic compound has the general formula (I) below:wherein:Xi andX2, independently from each other, are a cation.

3. The method according to claim 2, wherein the aromatic compound having the general formula (I) is terephthalic acid.

4. The method according to claim 2, wherein a compound has the general formula (II) below is obtained from the compound having the general formula (I):wherein:Xi is a cation.

5. The method according to claim 4, wherein the compound has the general formula (II) is benzoic acid.

6. The method according to any one of the preceding claims, wherein the aromatic compound reacts in the presence of a copper catalyst.

7. The method according to any one of the preceding claims, wherein the molar ratio of the aromatic compound to the catalyst is from 0.1 to 1000, preferably from 1 to 100.

8. The method according to any one of the preceding claims, wherein the nitrogen-containing ligand is selected from the group consisting of aliphatic amines, such as tetramethylethylenediamine, nitrogenous aromatic heterocycles such as 2,2'-bipyridine, 4,4'-dimethyl-2,2'-bipyridine, 1,10-phenanthroline, 4,7- diphenyl-l,10-phenanthroline and mixtures thereof, preferably from the group consisting of 2, 2'-bi pyridine, 4,4'-dimethyl-2,2'-bipyridine, 1,10- phenanthroline, 4,7-diphenyl-l,10-phenanthroline and mixtures thereof, and most preferably from the group consisting of 2,2'-bipyridine, 1,10- phenanthroline, 4, 7-diphenyl- 1,10-phenanthroline and mixtures thereof.

9. The method according to any one of the preceding claims, wherein the nitrogen-containing ligand is a nitrogenous aromatic heterocycle.

10. The method according to any one of the preceding claims, wherein the molar ratio of the aromatic compound to the nitrogen-containing ligand is from 0.1 to 1000, preferably from 1 to 200, and more preferably 1 to 100.

11. The method according to any one of the preceding claims, wherein the aromatic compound reacts in the presence of a solvent.

12. The method according to any one of the preceding claims, wherein the solvent is selected from the group consisting of N-alkyl-2-pyrrolidone withalkyl being C1-C12, dimethylimidazolidinone, N,N'-dimethylpropyleneurea (DMPU), dimethylacetamide, sulfolane, diphenylsulfone, polyethylene glycol (PEG), tributylphosphate, glymes, orthophenanthrolines, succinamides, pyridines, imidazoles, quinoline, nitriles, mesitylene, ionic liquids, diphenylether and mixtures thereof, and preferably from the group consisting of N-alkyl-2-pyrrolidone with alkyl being C1-C12, such as N-methylpyrrolidone (NMP), N-octylpyrrolidone (NOP) and N-dodecylpyrrolidone, dimethylimidazolidinone, such as l,3-dimethyl-2-imidazolidinone (DMI), sulfolane, quinoline and mixtures thereof.

13. The method according to any one of the preceding claims, wherein the method is suitable for waste management of polyethylene terephthalate.

14. A mixture comprising an aromatic compound comprising an aromatic ring, a metal catalyst and a nitrogen-containing ligand, wherein the aromatic ring is linked with two carboxylate groups and the aromatic ring is only linked with carboxylate groups.

15. The mixture according to claim 14, wherein the nitrogen-containing ligand is a nitrogenous aromatic heterocycle.

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