RKCL3938 CLEAN SYNTHESIS OF ADIPIC ACID BY

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Abstract. In the absence of phase-transfer agents, the ligand effects are studied for the clean synthesis of adipic acid by direct oxidation of cyclohexene catalyzed ...
Jointly published by Akadémiai Kiadó, Budapest and Kluwer Academic Publishers, Dordrecht

React.Kinet.Catal.Lett. Vol. 75, No. 2, 315-321 (2002)

RKCL3938 CLEAN SYNTHESIS OF ADIPIC ACID BY DIRECT OXIDATION OF CYCLOHEXENE IN THE ABSENCE OF PHASE TRANSFER AGENTS Heng Jiang*, Hong Gong, Zhonghua Yang, Xiaotong Zhang and Zhaolin Sun Department of Material Science, Fushun Petroleum Institute, Fushun 113001, China E-mail: [email protected]

Received July 9, 2001 In revised form November 6, 2001 Accepted November 26, 2001

Abstract In the absence of phase-transfer agents, the ligand effects are studied for the clean synthesis of adipic acid by direct oxidation of cyclohexene catalyzed by Na2WO4⋅2H2O with 30% hydrogen peroxide. In most cases, the isolated yield of the target product adipic acid is high if the ligand acidity is strong. Although the acidity of some phenolic ligands, L(+)ascorbic acid and 8-quinolinol is weak, the isolated yield of adipic acid is still high. It is demonstrated that the acid and coordination effect of the ligand play the same important role in the Na2WO4⋅2H2O catalyzed oxidation of cyclohexene to adipic acid with 30% hydrogen peroxide. Kinetic investigations show that the hydrolysis of cyclohexene oxide to 1,2-cyclohexandiol is the critical step and the acidity of reaction system is important. Keywords: Adipic acid, cyclohexene, catalytic oxidation, acidic ligand

INTRODUCTION Adipic acid is an important intermediate utilized in the production of nylon6,6. The usual industrial synthesis of this compound involves nitric acid oxidation [1]. However, N2O emission from nylon-6,6 production accounts for 5 to 8% of the total amount released by man [2]. 0133-1736/2002/US$ 12.00. © Akadémiai Kiadó, Budapest. All rights reserved.

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For the catalytic oxidation of cyclohexene to adipic acid, earlier workers used 35% H2O2 and (N-n-C16H33pyridinum)3(PW12O40) or H2WO4 in tert-butyl alcohol [3] or in other patented procedures either 40% H2O2 and [CH3(nC8H17)3N]3PO4[W(O)(O2)2]4 in 1,2-dichloroethane [4] or 60% H2O2 and H2WO4 [5]. The byproducts were glutaric acid, peroxy acids, and 1,2-cyclohexanediol. With 35% H2O2 and a H2WO4 catalyst, only a trace amount of adipic acid was obtained [6]. Oxidation with aqueous H2O2 as the oxidant is appreciated because water is the sole expected side product [7]. In 1998, R. Noyori et al. described a very efficient cleavage of olefins to carboxylic acids by Na2WO4⋅2H2O/[CH3(nC8H17)3N]HSO4 with 30% hydrogen peroxide at 75-90°C in ca. 8 h [8]. As no organic solvent and halide are involved, this economical method may be of special industrial interest as an example of so-called „green chemistry”. Deng et al. employed peroxytungstate complexes as catalysts for the direct oxidation of cyclohexene with 30% aqueous hydrogen peroxide [9,10]. Considering that the synthesis of [CH3(n-C8H17)3N]HSO4 is complicated and tedious [11], we have reported the method of replacing [CH3(n-C8H17)3N]HSO4 with the simple sulfate and hydrochloride of a higher primary or tertiary amine [12]. Our further research showed that the acidity of ligand plays a very important role for the Na2WO4⋅2H2O catalyzed oxidation of cyclohexene with 30% aqueous hydrogen peroxide, and there is no need of phase-transfer agents. EXPERIMENTAL Materials and reagents Analytical grade 30% aqueous hydrogen peroxide was purchased from Shanghai Yuanda Peroxide, Inc., and used as received. Chemically pure cyclohexene was obtained from Shanghai Chemical Reagent No.1 Factory and was distilled under Nitrogen before use. Analytical grade sodium tungstate dihydrate was purchased from Shenyang No.1 Chemical Reagents Factory. The others reagents are all analytical grade. Catalytic oxidation A 150 mL flask equipped with a magnetic stirring bar and a reflux condenser was charged with 0.825 g (2.5 mmol) of Na2WO4⋅2H2O, 2.5 mmol of ligand, and 44.5 mL (440 mmol) of 30% aqueous H2O2. The mixture was vigorously stirred at room temperature for 15 min and then 10.5 mL (100 mmol) of cyclohexene was added. The biphasic mixture was then heated and refluxed for

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8 h with stirring at 1000 rpm. The homogeneous solution was allowed to stand at 5ºC for 12 h, and the resulting white precipitate was separated by filtration and washed with 10 mL of cold water. The product was dried at room temperature with a melting point of 151.0ºC to 152.0ºC. Adipic acid and byproducts were determined on GC-MS (MAT90, Finnigan Company). In most cases, the purity of adipic acid is more than 99.0% and there is no need to recrystallize it with water. RESULTS AND DISCUSSION As Hill pointed out [13], the ideal homogeneous oxidation catalyst should be selective, oxidatively and hydrolytically stable, oxidant green (O2 or H2O2) and solvent green (H2O or CO2). Since the quaternary ammonium salt is toxic [14], our goal is to achieve real green oxidation of cyclohexene to adipic acid catalyzed by Na2WO4⋅2H2O in the absence of quaternary ammonium salt. In the absence of quaternary ammonium salt as phase transfer agents, we investigated the effects of various ligands on the Na2WO4⋅2H2O catalyzed oxidation of cyclohexene to adipic acid with aqueous 30% hydrogen peroxide. The results are shown in Table 1. The pKa of ligands in Table 1 is the first dissociation constant in aqueous solution at 25°C [15, 16]. It can be seen from Table 1 that basic ligands (entries 40 - 44) and neutral ligands (entries 45 - 46) are not effective for the Na2WO4⋅2H2O catalyzed oxidation of cyclohexene. In most cases, the isolated yield of adipic acid (based on cyclohexene) is fairly high when the pKa of the acidic ligand is in the range of 1 - 3. For example, the isolated yield of adipic acid increases in the sequence acetic acid (entry 10), formic acid (entry 9) and bromoacetic acid (entry 11). For aliphatic diacid (entries 12-15), the isolated yield of adipic acid decreases with increasing carbon chain length because the acidity decreases in that order. Although the target product in the present catalytic system is adipic acid, it can also be used as ligand. The same empirical rule can be observed from the aromatic carboxylic acid ligands (entries 12-15). Strong acidic ligands such as sulfosalicylic acid (entry 1) give excellent isolated yield of adipic acid. The isolated yield of adipic acid is more than 75% when a relatively strong inorganic acid such as phosphoric acid (entry 34) and phosphorous acid (entry 35) is employed as ligand. From these experimental facts, we believe that an acid effect of the ligand exists in the present catalytic system. Some exceptional circumstances appear in Table 1. Although the acidities of phenols (entries 16-21), L(+)ascorbic (entry 3) acid and 8-quinolinol (entry 4) are very weak, the isolated yield of adipic acid is still very high. It can be inferred that ligand effects may exist for this reaction apart from the acidic effect of ligands. Generally speaking, ligands can change the electronic and

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geometrical environment of the central metal atom. These changes affect the coordination of reactant to the metal ion [17]. Phenols such as hydroquinone can be used as free radical inhibitors or antioxidants. They usually decrease the rate of free radical autoxidation. From the experimental results for entries 16-21, we believe that the reaction mechanism may involve coordination catalysis. Table 1 Ligand effect in Na2WO4-catalyzed oxidation of cyclohexene with 30% hydrogen peroxide for the synthesis of adipic acid No.

Ligand [CAS RN]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33

Sulfosalicylic acid [97-05-2] Salicylic acid [69-72-7] L(+)ascorbic acid [50-81-7] 8-quinolinol [148-24-3] picolinic acid [55-22-1] Nicotinic acid [59-67-6] Lactic acid [50-21-5] Tartaric acid [87-69-4] Formic acid [64-18-6] Acetic acid [64-19-7] Bromoacetic acid [79-08-3] Oxalic acid [144-62-7] Malonic acid [141-82-2] Succinic acid [110-15-6] Adipic acid [124-04-9] Phenol [108-95-2] Pyrocatechol [120-80-9] Resorcinol [108-46-3] Hydroquinone [123-31-9] 2-Aminophenol [95-55-6] 2,4-Dinitrophenol [51-28-5] Benzoic Acid [65-85-0] Phthalic acid [88-99-3] Anthranilic acid [118-92-3] Acetyl acetone [123-54-6] (S)-(+)-Arginine [74-79-3] L-Alanine [56-41-7] p-Toluenesulfonic acid [104-15-4] EDTA(2Na) [6381-92-6] Hydroxylamine hydrochloride [5470-11-1] Hydrazine dihydrochloride [5341-61-7] Hydrazine sulfate [10034-93-2] m-Phenylene diamine hydrochloride

pKa

Isolated yield of adipic acid (%)

2.98 4.17 5.10 3.88 3.22 3.77 4.75 2.90 1.23 2.85 4.21 4.43 9.95 9.45 9.44 10.00 4.09 4.21 2.95 2.05 9.00 -

88.0 81.5 75.3 75.9 53.0 53.3 8.0 46.4 57.9 13.9 65.2 80.4 72.9 18.4 23.7 77.4 77.7 74.1 63.8 62.1 71.8 54.5 77.2 77.8 20.7 16.8 10.9 61.2 51.9 63.8 64.1 82.4 60.9

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Table 1 contd. 34 35 36 37 38 39 40 41 42 43 44 45 46

Phosphoric acid [14265-44-2] Phosphorous acid [10294-56-1] Metaphosphoric acid [37267-86-0] NaH2PO4.2H2O [7558-80-7] Na2HPO4.12H2O [7558-79-4] Boric acid [11113-50-1] Ethylidenediamine [107-15-3] o-Phenylenediamine [95-54-5] 2,2'-Bipyridine [366-18-7] 1,10-Phenanthroline [66-71-7] Quinoline [91-22-5] n-C16H33(CH3)3N⋅Br [57-09-0] (n-C4H9)4N⋅Br [1643-19-2]

2.12 2.15 9.24 -

76.8 75.6 59.8 12.4 ~0 10.5 ~0 ~0 ~0 ~0 ~0 ~0 ~0

According to the proposal of Noyori et al. [8], the reaction pathway involves olefin epoxidation, vicinal diol oxidations, Baeyer-Villiger oxidation, and hydrolysis (Fig. 1). Usually, epoxide is found to be hydrolyzed favorably under acidic conditions [18]. Therefore, the role of the above acidic ligands is to accelerate cyclohexene epoxidation and cyclohexene oxide hydrolysis. The isolated yield of adipic acid increases significantly when the amounts of acetic acid and adipic acid as ligand are increased. These results demonstrate that the hydrolysis of cyclohexene oxide to 1,2-cyclohexandiol is the controlling step of the whole reaction and the acidic conditions in the reaction system is necessary. In the absence of acidic ligand, the isolated yield of adipic acid is about 30% when H2WO4 alone is employed as catalyst. However, the isolated adipic acid must be recrystallized because H2WO4 is insoluble in water. O

OH

H 2O 2 O

H 2O

H 2O 2 OH

O H 2O 2

O H 2O 2

O OH

OH

H 2O

O

CO O H CO O H

O

Fig. 1. Proposed reaction pathway for the synthesis of adipic acid by oxidation of cyclohexene with 30% hydrogen peroxide (Noyori et al. [8])

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In order to elucidate the reaction mechanism in Fig. 1, the Na2WO4⋅2H2O/C2H2O4⋅2H2O catalyzed oxidation of cyclohexene was monitored by GC. The kinetic curves are shown in Fig. 2. The cyclohexene oxide produced in the initial stage is rapidly hydrolyzed to 1,2-cyclohexandiol, while 1,2-cyclohexandiol is converted to other intermediates. The yield of adipic acid increases rapidly after 3 h.

Distribution, mol%

100 80 60 Cyclohexene Cyclohexene oxide 1,2-Cyclohexandiol Adipic acid

40 20 0 0

1

2

3

4

5

6

7

8

9

Time, h

Fig. 2. Kinetic curves for the oxidation of cyclohexene catalyzed by Na2WO4⋅2H2O/C2H2O4⋅2H2O with 30% hydrogen peroxide

Since unproductive decomposition of H2O2 is negligible under such Wcatalyzed conditions, the oxidation requires only 4.4-fold amounts of H2O2 per cyclohexene to obtain a satisfactory yield. Rapid stirring is necessary to facilitate the biphasic reaction. The catalyst in the filtrate can be reused after it is concentrated on a rotary evaporator. For example, Na2WO4/H3PO4 can be reused at least four times (70% isolated yield). In the first run, the main byproducts in the filtrate are glutaric acid (2.0%) and 1,2-cyclohexandiol

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(0.6%). After several times of reuse, the isolated adipic acid must be recrystallized because glutaric acid is cumulated in the reaction system. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.

D.D. Davis, D.R. Kemp, in: Kirk-Othmer Encyclopedia of Chemical Technology, 4th ed., Vol. 1, pp. 466-493, (Eds J. I. Kroschwitz, M. Howe-Grant) Wiley, New York 1991. C. Bolm, O. Beckmann, O.A.G. Dabard: Angew. Chem., 907 (1999). T. Oguchi, T. Ura, Y. Ishii, M. Ogawa: Chem. Lett., 857 (1989). C. Venturello, M. Ricci: European Patent, 122, 804 (1984). T. Fujitani, M. Nakazawa: Japanese Patent, 63-93746 (1988). Y. Ishii, K. Yamawaki, T. Ura, H. Yamada, T. Yoshida, M. Ogawa: J. Org. Chem., 53, 3587 (1988). G. Strukul (Ed.): Catalytic Oxidation with Hydrogen Peroxide as Oxidant. Kluwer, Dordrecht 1992. K. Sato, M. Aoki, R. Noyori: Science, 281, 1646 (1998). Y.Q. Deng, Z.F. Ma, K. Wang, J. Chen: Green Chem., 1, 275 (1999). Y.Q. Deng, Z.F. Ma, J. Chen, K. Wang: Chinese Patent, 1,250,769 (2000). K. Sato, M. Aoki, M.Ogawa, T. Hashimoto, R. Noyori: J. Org. Chem., 61, 8310 (1996). H. Gong, H. Jiang, Z. B. Lu: Chem. J. Chinese Universities, 21, 1121 (2000). C.L. Hill: Nature, 401, 436 (1999). S.M. Reed, J.E. Hutchison: J. Chem. Edu., 77, 1627 (2000). R.C. Weast: CRC Handbook of Chemistry and Physics, 58th edition, D150, D151. CRC PRESS Inc, Cleveland, 1977-1978. Y.J. Yin: Chemistry Handbook of College, p. 299-310. Shandong Science and Technology Press, Jinan 1985. Y. Wu: Chemistry of Catalysis, p. 214. Science Press, Beijing 1990. R.A. Sheldon, J.K. Kochi: Metal-Catalyzed Oxidation of Organic Compounds. Academics Press, New York 1981.

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