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Ind. Eng. Chem. Prod. Res. Dev. 1984, 2 3 , 422-425
Complete Control of Product Distribution in the Hydration of Ethylene Oxide with Organoantimony Compounds as Catalyst Haruo Matsuda, Aklra Urabe, and Ryokl Nomura' Department of Applied Chemistty, Faculty of Engineering, Osaka Universlty, Yamada-Oka, Suita, Osaka 565, Japan
Tetraphenyistibonium halldes (PhSbCI and -Br] as catalysts completely control the product distribution in the hydration of ethylene oxide (EO) in the presence of carbon dioxide (CO,) or ethylene carbonate (EC) at 120 OC. With a small excess of water, the stibonium halides gave ethylene glycol (EG) as the predominant product. When the molar ratio of water to EO is 1 or less, a drastic change in the hydration product is seen. In such a reaction these stibonium halides selectively gave diethylene glycol (DEG) directly from EO.
Introduction It is known that glycols, one of the most important chemicals, are manufactured by the hydration of ethylene oxide (Kirk-Othmer, 1966). In the current process, however, some problems still remain to be improved: e.g., to raise both the conversion and selectivity without dilution by excess water which results in uneconomic evaporation loads. Recently, several attempts have been made to solve these problems, and some patent literature claims that certain salts are effective for the purpose. For example, ammonium (Levin and Shapiro, 1970,1973) or phosphonium (Mieno et al., 1979a,b) halides convert ethylene oxide (EO) into ethylene glycol (EG) in high conversion and selectivity, while employing a small excess or even an equivalent amount of water, under pressure of carbon dioxide (CO,). Alkaline salts (Weber et al., 1973; Nippon Shokubai, Co., 1981a; Morris, 1982) and Lewis acids (Nippon Shokubai, Co., 1981b) are also reported to be active in the same manner. These salts are also known to catalyze the synthesis of cyclic carbonates from C02 and oxiranes. I t is suggested that such high conversion and selectivity is attained via the intermediate formation of ethylene carbonate (EC) in situ (Kumazawa, 1977; Lester, 1982). However, up to this time the high selectivity has been limited to the production of monoethylene glycol. In the course of our studies on the utilization of organometallic compounds of main group elements, the remarkably high catalytic activities of the pentavalent organoantimony halides such as tetraphenylstibonium halides for the synthesis of cyclic ethylene carbonates from ethylene oxides and C02 has been reported (Nomura et al., 1979, 1980). Since the activities of these halides for the cycloaddition should be superior to those of the previously reported salts, and in addition, since the pentavalent organoantimony halides also initiate the polymerization of EO (Nomura et al., 1982a), an effort was made to hydrate EO in the presence of the organoantimony compounds under COP,aiming at rapid and selective hydration to EG and the control of the individual hydration step. I t has been found that stibonium halides give EG in high conversion and high selectivity when a small excess of water is used. Further, these salts convert EO into diethylene glycol (DEG) if one equivalent or less of water is employed. This is the first time such a selective synthesis of DEG in the one pot hydration of EO has been reported. It is noteworthy that the same catalysts may be employed for the selective synthesis of either EG or DEG by varing the mole ratio of HzO to EO. Experimental Section Materials. The organoantimony compounds employed as catalyst were derivatized from triphenylstibine by 0196-432118411223-0422$01.50/0
general methods, and triphenylstibine was prepared by the Grignard procedure. They were checked by elemental analyses. Ethylene oxide (EO) and propylene oxide were distilled over calcium hydride before use. Ion-exchanged water was further purified by distillation before use. Cyclic carbonates were synthesized by reacting the corresponding oxides with C02 in the presence of Ph4SbBr as catalyst, as described previously (Nomura et al., 1980). They were then fractionally distilled under reduced pressure. EC was further purified by recrystallization from ether. Other reagents and solvents were used as received. Reaction. General autoclave reactions were carried out in a 50-mL stainless steel reactor (Taiatsu Garasu Kogyo Co., Ltd., Tokyo, TVS-1 type made of SUS 304) while stirring with a small magnetic bar. The typical procedure employed is as follows. Desired amounts of EO, water, catalysts, and additives were charged into the autoclave, and then CO, was introduced. The reactor was heated in a temperature-regulated oil bath for the prescribed reaction time. After heating, the reactor was cooled and decompressed. Analysis. Analysis of the product was carried out by the GLC method. The yields of products were determined with both a Shimadzu GC-4BP equipped with a flame ionization detector (FID) connected to a Apiezon L grease coated 30 m X 0.25 mm Golay column, and with a GC-3B equipped with a thermal conductivity detector (TCD) linked to a 2 m X 3 mm glass column packed with Silicone SE-30 on Uniport KS. N2was used as the carrier gas. The results obtained were rechecked by means of a GC-3B with TCD joined to a 2 m X 3 mm stainless steel column packed with PEG 20M on celite 545. In these analyses He was used as the carrier gas. Results and Discussion Hydration of EO Catalyzed by Organoantimony Compounds. The hydration of EO using two moles of water per mole of EO and a 2-h reaction time gave about a 1:l mixture of EG and DEG in the absence of any catalyst at 120 "C. The DEG/EG product ratio was cut in half when the hydration was carried out in the presence of 1mol '70of tetraphenylstibonium bromide (Ph4SbBr) with respect to EO; however, the conversion of EO was still low. The reaction was carried out under elevated COz pressure to improve the conversion and selectivity further. As expected in the reactions carried out under COz pressure, it was found that almost quantitative conversion was achieved and that DEG or higher glycols were not detected. Significant amounts of ethylene carbonate (EC) were recovered, however. In such reactions carried out at CO, pressures of 50 kg/cm2, EC was the predominant product (79% yield). It is surprising that carbonate for0 1984 American Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 23, No. 3, 1984 423
Table I. Hydration of Ethylene Oxide in the Presence of Ornanoantimony Compounds at 120 O C for 2 ha distribn, % total conv Sb compds COZ,kg/cm2 of EO, % EG DEG EC ratio, DEG/EG 0 55 51 49 0 0.96 5 51 51 49 0 0.96 Ph4SbC1 5 87 40 58 2 1.45 Ph4SbBr 0 53 68 32 0 0.47 5 98 78 0 22 0 50 90 12 0 88 0 5 87 72 0 28 0 26 32 42 1.23 Ph3SbBrz 5 81 (p-C1C6H4)3SbBrz 5 67 0 54 49 33 28 39 0.85 @-CH3C6H4)3SbBrz 5 87 Me3SbCl2 5 74 78 22 0 0.28 MeBSbBrz 5 89 74 0 26 0 Me3SbIz 5 98 71 0 29 0 Ph3Sb 5 31 100 0 0 0 PhzSbC1 5 41 68 0 32 0 "HZO/EO = 100/50 (mmol), Sb compounds 0.5 mmol. *50 mmol of propylene oxide was used; the products were propylene glycol and propylene carbonate. Table 11. Control of the Hydration Products by Tetraphenylstibonium Halides at 120 O c a distribn, % ratio, EG DEG EC DEG/EG 40 58 2 1.45 1 81 7 90 3 12.9 0.5 86 0 93 7 1 EC 20% 99 46 50 0 1.09 Br 2 5 98 78 0 22 0 1 5 78 63 19 18 0.31 0.5 5 100 0 89 11 2 EC 20% 96 100 0 0 0 2 5 EC 20% 95 77 0 22 0 1.5 EC 20% 65 51 49 0 0.96 1 EC 20% 48 0 100 0 0 2 EC 10% 69 100 0 0 0 2 EC 40% 42 100 0 0 0 2= 5 PC 20% 71 76 0 24 0 "EO 50 mmol, Ph4SbX 0.5 mmol. bMol % to EO. 'Propylene oxide 50 mmol wa8 used; the products were propylene glycol and propylene carbonate (PC). Ph4SbX, X = c1
HzO/EO 2
COz, kg/cm2 5 5 5
additives*
mation predominates to a much greater extent in the reaction of propylene oxide and water under 50 kg/cm2 of C02pressure (99% conversion of PO and 97% selectivity). These phenomena indicated that it may be necessary to limit the initial pressure of COz. We thus adopted 5 kg/cm2 as a convenient initial pressure of C02 in the following runs. In contrast with the use of stibonium bromide, the use of tetraphenylstibonium chloride (Ph4SbC1)increased the ratio of DEG to EG in the hydrolysate to 1.45 and it therefore seems to be a favorable catalyst to enhance production of DEG rather than that of EG. In addition, the production of ethylene carbonate is reduced. Other organoantimony compounds were also examined as catalysts and the results obtained with these compounds are summarized in Table I. It is very interesting to compare the efficiency of the organoantimony catalysts for this hydration with their catalytic activities for the polymerization of EO or for the cycloaddition of oxiranes with COP It was reported that Hammett's p values in the polymerization of EO was positive for triarylantimony dibromide (Nomura et al., 1982a), in other wurds, that the polymerization rates resulting from use of these compounds changed in the following order: @-C1C6H4)3-> Ph3- > (p-CH3C6H4)3SbBr2. In the hydration, the increasing production of DEG relative to EG agreed with the above order for the polymerization. Recently, it has been reported that the halogen moieties of the pentavalent organoantimony halides should affect the rate of the cycloaddition of oxiranes with COz. The iodides are most effective for the cycloaddition, and passing into the chlorides,
conv, % 87
the activity was decreased. In the case of the trimethyl derivatives, it is clear that the yield of EG relative to DEG increases with the order, C1< Br < I (Nomura et al., 1982a) and that the formation of EC increases in the same order. Subsequently, trivalent antimony compounds were found to result in low conversion. It appeared that use of Ph4SbC1as catalyst would be suitable for the synthesis of DEG rather than EG. Thus, we attempted to synthesize DEG selectively by the hydration of EO in a one pot reaction. As shown in Table 11, use of molar equivalents of EO and H20 resulted in production of DEG in 90% selectivity and use of a stoichiometric mixture of EO and H20 (i.e., two moles EO per mole of H20) gave DEG in 97% selectivity and no EG. Further decrease of H20/E0 feed ratio brought about the considerable formation of triethylene glycol or higher glycols. Similar attempts were also made to utilize Ph4SbBr as catalyst for the selective synthesis of both EG and DEG, respectively. This goal of high selectivity was attained when EO was hydrated by a stoichiometric amount 0.5 mol of water, but more carbonation occurred in this case than when Ph4SbC1was used. As a result of this study it can be said that stibonium halides are most effective as the hydration catalyst with respect to both conversion of EO and selectivity of product. Low selectivity resulted from use of pentavalent compounds such as triphenyl or trimethyl halides, and low conversion resulted from use of trivalent compounds such as triphenylstibine. Mode of Hydration. The initial stages of the hydrations are shown in Figures 2, lA, lB, and 1C: uncatalyzed
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0
0
I
n
2 3 Reaction time, h
IC
Q
L
0
1 2 Reactiontime, h
Reaction time, h
Figure 1. Increase of the yields of the products in the hydration of EO(H,O/EO = 2) or propylene oxide (H,O/PO = 2) catalyzed by PhlSbBr at 120 OC: (A) the hydration of EO under C02 pressure (5 kg/cm2); (B) in the presence of EC (20 mol 3'% to EO); (C) the hydration of PO EG; (0) EC; ( 0 ) propylene glycol; (e) propylene carbonate. under C02 pressure (5 kg/cm2); (0)
Scheme I 1
EO
EG
EG
DEG 5
Reaction time, h
Figure 2. Uncatalyzed hydration of EO (H20/E0 = 1) under 5 kg/cm2 C02 pressure a t 120 OC: (0) EG; ( 0 )DEG.
reactions; reactions catalyzed by Ph4SbBr-C02;reactions catalyzed by Ph,SbBpEC; and Ph4SbB~EC-CO2 systems. When Ph4SbBr was absent it was found that the yields of EG and DEG increased slowly. In contrast, when Ph,SbBr and C02 were present, the mode of the reaction was quite different. The yields of EC rapidly increased to ca. 20%, which meant that nearly all C02 in the reactor had been converted into EC. During the fast increase in EC, no EG was detected. After about 10 min, EG suddenly began to form and the yield of EG increased very rapidly. Even after 4 h of reaction time, the composition of the reaction mixture does not change (Figure 1A). Such alternation of the reaction mode was also observed in the initial stage of the reaction catalyzed by stibonium chloride and may indicate that the selective formation of EG was due to the formation of EC in situ. Recently, hydration of EO catalyzed by salts such as ammonium or phosphonium halides under C02 pressure has been reported to give EG selectively. In these reactions, EC has been considered to be an intermediate. In addition, hydrolysis of EC catalyzed by the same salts also have been reported to give EG as a sole product (Taylor and Wolf, 1979; Showa Denko, Co., 1981a). One could consider that the hydration catalyzed by the stibonium compounds may proceed via EC as an intermediate. However, the hydrolysis of EC in the presence of Ph,SbBr was slow in the absence of COz pressure (only 63% of EC was consumed at 120 OC after 3 h). Further, no hydrolyzed product was detected in the case of autoclave reactions. These results may indicate that the reaction path may be a complicated one and may not proceed mainly via free EC. Addition of EC. It has been found that the formation of cyclic carbonate precedes the hydration and that it may accelerate only the formation of EG, thereby affecting the selectivity of the final reaction. Thus, a reaction was carried out in which EC was added initially in place of COz
pressure. Recently, similar studies have been made employing the salt catalysts (Showa Denko, Co., l980,1981b), but the effect of such EC addition was not investigated in detail. The results of the reactions in which EC was added initially are presented in Table 11. The amounts of EC initially added corresponded to the amounts of EC which were formed in reactions conducted under COz pressure while using Ph4SbBr as a catalyst (namely 20 mol % with respect to EO feed). As shown in Table 11, initial addition of EC yielded glycols in the same distribution as in the reactions carried out under COz pressure, with an exception of EC formation. Replacement of COz pressure with EC did not increase the total conversion of EO into glycols beyond 100%. This indicates that the initially added EC can be recovered unreacted and that the recovered amounts of EC did not change through the reaction. No induction was observed for EG formation in hydrations under EC added conditions as shown in Figure 1B. The hydration catalyzed by the Ph,SbBr-EC system under C 0 2 was also carried out, and a residual amount of EC corresponding to the amount initially present only influenced the hydration rate. A similar effect was detected when propylene carbonate was initially present in the propylene oxide hydration experiment; however, diethyl carbonate apparently did not affect the distribution of the hydration products. Some other carbonyl compounds such as acetone, DMF, and butyl acetate were also examined as additives and it was found that these carbonyls had no effect. Hydration of PO was also carried out and propylene glycol (PG) was obtained selectively when Ph,SbBr and COz pressure was employed along with two equivalents of water. In the initial stage of the reaction, similar relations between the formation of PG and propylene carbonate were observed (Figure IC). Reaction Path. Since the hydration of EO essentially has consecutive and competitive kinetics (Dabis et al., 1952; Corrigan et al., 1968), high conversion of EO must cause a significant degree of formation of higher glycols, thereby lowering the selectivity to the idividual glycols. In the spontaneous hydration, such consecutive and competitive paths (1and 2 in Scheme I) result in a mixture of EG and
Ind. Eng. Chem. Prod. Res. Dev., Vol. 23, No. 3, 1984
Scheme 11. Plausible Reaction Path
Sb
EOCO2 adduct
% E ;[;]
-EC -
pseudo.cyclic complex
EG co/
425
steadily. The complex should react with EO rather than with H20 for the selective formation of DEG. This happens when the initial amount of water is limited. Registry No. Ph3SbBrz, 20265-30-9; (p-C1C6H4)3SbBrz, 91002-41-4; (p-CH3C&&3bBr2, 91002-42-5; Me3SbC12,91108-42-8; Me3SbBr2,91002-43-6; Me3Sb12,91002-44-7;PhSbCl, 16894-68-1; Ph4SbBr, 16894-69-2;Ph,Sb, 603-36-1; Ph,SbCl, 2629-47-2; EG, 107-21-1; DEG, 111-46-6; EC, 96-49-1; ethylene oxide, 75-21-8; propylene oxide, 75-56-9; propylene glycol, 57-55-6; propylene carbonate, 108-32-7.
kco2 DEG
Literature Cited
DEG as shown in Figure 2. When PhlSbBr and C02 are employed the hydration may follow the route shown by paths 3 and 4, in which EC is formally generated as an intermediate. It is known that the hydrolysis of EC gives only EG. Thus, such a route may result in the high selectivity to EG. Some results, however, did not indicate the intermediate formation of free EC. For example, under autoclave conditions, EC was not hydrolyzed in the presence of the catalysts. Even in prolonged hydration experiments, EC could be recovered. These observations indicate that free EC may not be the principal intermediate. Recently, we proposed a cyclic intermediate between the antimony compounds and the oxirane-C02 adduct for the cycloaddition of C02to oxiranes (Scheme 11) (Nomura et al., 1982b). A similar complex, the structure of which is not yet clear, may also have an important role in the hydration. If COz in excess of that complexed with the catalyst remains in the reactor, the complex may give EC. When COPis consumed, the complex becomes easily hydrolyzed to give EG. To avoid this, COzmust be circulated
Corrlgan, T. E.; Lesseis, G. A.; Dean, M. J. Ind. Eng. Chem. 1988, 6 0 , 62. Davis, P. C.; Von Waaden, C. E.; Kurata, F. Chem. Eng. Prog., Symp. Ser. 1952, 48, 4. Kirk-0th" "Encyclopedia of Chemical Technology"; Wlley-Intersclence: New York, 1966; Vol. 10, p 638. Kumazawa, T. Yuki &sei Kagaku Kyokai Shi 1977, 35, 590. Lester, D. J. Brit. UK Patent Appl. 2098985, 1982. Levin, S. 2.; Shaplro, A. L. Brit.Patent 1177677, 1970. Levln, S. 2.; Shapiro, A. L. Ger. Offen 1793247, 1973. Mieno, M.; Kasal, H.; Nakanlshi, J.; Mori, H. Japan Kokai 79 19 905, 1979a. Mieno, M.; Mori, H.; Nakanishi, J. US. Patent 4 160 116, 1979b. Morris, K. P. Brit. UK Patent Appl. 2086894, 1982. Nlppon Shokubai, Co. Japan Kokai 81 71 026, 71 028 and 71 029, 198la. Nlppon Shokubai, Co. Japan Koakl 81ptc73035 and 73036, 1981b. Nomura, R.; Hlsada, H.; Nlnagawa A.; Matsuda, H. Mekromol. Chem. 1982a, 183, 1073. Nomura, R.; Klmura, M.; Teshlma, S.; Ninagawa, A.; Matsuda, H. Bull. Chem. SOC.Jpn. 1982b, 55,3200. Nomura, R.; Nlnagawa, A,; Matsuda, H. Chem. Letf. 1979, 1261. Nomura, R.; Nlnagawa, A.; Matsuda, H. J. Org. Chem. 1980, 45, 3735. Showa Denko, Co.Japan Kokai 81 139432, 140941 and 140942, 1961a. Showa Denko, Co. Japan Kokai 81 8335 and 8336, 1981b. Showa Denko, Co. Japan Kokai 80 145 623, 1980. Taylor, G. A.; Wolf, P. F. Ger. Offen 2855233, 1979. Weber, J.; Bruns, L.; Schnuchel, G. Ger. Offen 2 141 470, 1973.
Received for reuiew January 11, 1984 Accepted April 16, 1984
