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Selective synthesis of 3-methoxy-1-propanol from methanol and allyl alcohol with metal oxide catalysts
Catalysis Communications 2 (2001) 191±194
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Selective synthesis of 3-methoxy-1-propanol from methanol and allyl alcohol with metal oxide catalysts Tetsu Yamakawa a,*, Motoaki Takizawa a, Takeshi Ohnishi a, Hiroshi Koyama b, Sumio Shinoda a a
Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan b Daicel Chemical Industries, Ltd., 3-2-5, Kasumigaseki, Chiyoda-ku, Tokyo 100-6077, Japan Received 2 May 2001; received in revised form 18 June 2001
Abstract The addition of methanol to allyl alcohol was investigated with metal oxides and zeolites catalysts in the liquid phase. 3-Methoxy-1-propanol was selectively formed with MgO, ZrO2 and Al2 O3 , while zeolites gave 2-methoxy-1-propanol. This feature suggests that the generation of a methoxide ion on basic sites is an important step. The highest yield, 23.6%, was obtained with MgO treated in a hydrogen ¯ow. Ó 2001 Elsevier Science B.V. All rights reserved. Keywords: 3-Methoxy-1-propanol; Allyl alcohol; Methanol; Metal oxide catalyst; Basicity
1. Introduction 1-Alkoxy-2-propanol is widely used as an industrial solvent for coating materials, printing inks and so on. 3-Methoxy-1-propanol is similar in physical and chemical properties to 1-alkoxy-2propanol, and the investigation of its synthesis has become important. Some methods have been already reported: O-methylation of 1,3-propanediol [1], diazotization of 3-methoxy-1-propyl amine followed by hydrolysis [2], substitution of chlorine in 3-chloro-1-propanol with methoxide ion [3,4], ring opening of 1,4-dioxane [5], hydroboration of allyl methyl ether [6], electrochemical reduction of
* Corresponding address. Tel.: +81-354-52-60-98; fax: +81354-52-6365. E-mail address: [email protected] (T. Yamakawa).
acrolein [7] and catalytic hydrogenation of 3methoxy-1-propanal [8,9]. The addition of methanol across the carbon±carbon double bond in allyl alcohol is one of the candidates for the more convenient method. However, the addition in a Markownikov manner to form 2-methoxy-1-propanol, which reveals the reproduction and developmental toxicity [10], is possible with this reaction. Therefore, the high selectivity is required for this process.
Metal oxides possess the bifunctionality derived from Lewis (Mn and O2 ) and/or Br onsted (±OH) acid±base sites [11,12], and often aord the highly selective transformation of organic compounds [13±19]. Here we applied this unique character of metal oxides to the selective synthesis of 3-methoxy-1-propanol from methanol and allyl alcohol in the liquid phase heterogeneously.
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T. Yamakawa et al. / Catalysis Communications 2 (2001) 191±194
2. Experimental
vanishingly small. Thus, the selectivity for the terminal addition is extremely high (100%). MgO exhibited the highest 3-methoxy-1-propanol selectivity and allyl alcohol conversion. SiO2 showed no activity (entry 4) and an intermediate character was observed for ZrO2 and Al2 O3 . Both the conversion and selectivity were decreased by exposing MgO to a saturated water vapor at room temperature for 20 h (entry 5). The other products were acrolein, 1,1,3-trimethoxypropane, b-methylallyl alcohol and 1-propanol. The sum of their selectivities was less than 100% because of the presence of some unidenti®ed products. Interestingly, the yield of 3-methoxy-1-propanol with MgO catalyst was enhanced in a hydrogen atmosphere. As seen in entry 6 in Table 2, the allyl alcohol conversion was increased more than 2 times with small decrease of selectivity compared with entry 1 in Table 1 (argon atmosphere). When MgO was heated at 503 K for 2 h in a hydrogen ¯ow (120 ml/min), the conversion of allyl alcohol was further increased, resulting in the highest yield of 3-methoxy-1-propanol (23.6%). Pre-treatment at 623 K (entry 8) decreased both the conversion and the selectivity to the level of entry 6. Despite allyl alcohol was converted to a lot of unidenti®ed compounds using zeolite catalysts (entries 9 and 10), the addition occurred mainly to form 2methoxy-1-propanol in contrast to MgO catalyst. 2-Methoxy-1-propanol formation with zeolite catalysts will proceed through CH3 ±CH ±CH2 OH intermediate. Highly selective formation of 3methoxy-1-propanol with metal oxides catalysts is noteworthy in view that the addition of methanol
Catalysts were supplied from Wako Pure Chemical Industries (MgO, SBET 111 m2 =g) Daiichi Kigenso Kagaku Kogyo (ZrO2 , SBET 92:5 m2 =g ), Mizusawa Industrial Chemicals Al2 O3 , SBET 189 m2 =g, Fuji Silysia Chemical SiO2 , SBET 719 m2 =g, Tosoh (HY, SBET 570 m2 =g, Si=Al 3) and N.E. Chemcat (Ga-silicate, SBET 358 m2 =g, Si=Ga 40), respectively. All the catalysts were dried in vacuo at 473 K for 2 h just before reactions. A typical reaction procedure is as follows. A catalyst was charged in a stainless-steel autoclave (50 ml) with allyl alcohol (3.3 ml, 48.3 mmol) and methanol (16.7 ml, 412 mmol). Then the autoclave was purged with argon or hydrogen thoroughly, followed by sealing at room temperature and 1 atm with each gas. Reactions were performed at 503 K for 8 h with a constant stirring of 500 rpm. After the reaction, the catalyst was ®ltered o and the ®ltrate was analyzed with GC (PEG-6000 and Porapak-T columns) and GC-MS (DB-FFAP, 30 m). 3. Results and discussion Table 1 shows the allyl alcohol conversion and the selectivity for each product with MgO, ZrO2 , Al2 O3 and SiO2 in an argon atmosphere. 3-Methoxy-1-propanol was obtained as a main product using MgO, ZrO2 and Al2 O3 (entries 1±3) and the formed amount of 2-methoxy-1-propanol was
Table 1 Reactions of allyl alcohol and methanol with metal oxide catalysts in an argon atmosphere Entry 1 2 3 4 5
Catalyst MgO ZrO2 Al2 O3 SiO2 MgOb
Selectivity (%)a
Allyl alcohol conversion (%)
3MP
2MP
AC
1,1,3-MP
MA
PA
10.9 3.9 6.3 0.0 6.3
93.5 45.4 66.0 0.0 77.0
± ± ± 0.0 ±
± 0.4 4.4 0.0 ±
± ± 3.9 0.0 ±
0.9 5.2 ± 0.0 2.1
4.0 43.0 14.8 0.0 10.0
Catalyst 1.0 g; allyl alcohol 48.3 mmol; methanol 412 mmol; reaction temperature 503 K; reaction time 8 h. a 3MP: 3-methoxy-1-propanol; 2MP: 2-methoxyl-1-propanol; AC: acrolein; 1,1,3-MP: 1,1,3-trimethoxypropane; MA: b-methylallyl alcohol; PA: 1-propanol. Dash marks (±) indicates the selectivity is below 0.1%. b Exposed to a saturated water vapor at room temperature for 2 h.
T. Yamakawa et al. / Catalysis Communications 2 (2001) 191±194
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Table 2 Reactions of allyl alcohol and methanol with MgO and zeolite catalysts in a hydrogen atmosphere Selectivity (%)a
Entry
Catalyst
Allyl alcohol conversion (%)
3MP
2MP
AC
1,1,3-MP
MA
PA
6 7 8 9 10
MgO MgOb MgOc HYb Ga-silicateb
23.3 29.3 24.3 69.4 86.1
78.0 80.7 73.5 ± ±
± ± ± 5.2 5.5
± ± ± ± ±
± ± ± ± ±
1.9 1.7 1.8 ± ±
4.7 4.4 7.9 10.8 1.8
Catalyst 1.0 g; allyl alcohol 48.3 mmol; methanol 412 mmol; reaction temperature 503 K; reaction time 8 h.a 3MP: 3-methoxy-1propanol; 2MP: 2-methoxyl-1-propanol; AC: acrolein; 1,1,3-MP: 1,1,3-trimethoxypropane; MA: b-methylallyl alcohol; PA: 1-propanol. Dash marks (±) indicates the selectivity is below 0.1%. b Pre-treated in a hydrogen ¯ow (120 ml/min) at 503 K for 2 h. c Pre-treated in a hydrogen ¯ow (120 ml/min) at 623 K for 2 h.
occurred apparently in an anti-Markownikov fashion; this is believed to be the ®rst example for the addition of alcohol to allyl alcohol. Plausible mechanism is illustrated in Scheme 1. At ®rst, a proton is abstracted from the hydroxyl group of methanol and a methoxide ion is generated (path (i)). The methoxide ion and proton are adsorbed on acidic and basic sites on the catalyst surface, respectively. In path (ii), dehydrogenation of allyl alcohol and/or hydrogen transfer from allyl alco-
hol form acrolein (a), which was detected in all entries. 1-Propanol formation suggests that a hydrogen acceptor for the latter reaction is allyl alcohol itself. Subsequently, acrolein was added to the adsorbed methoxide ion to 3-methoxy-1propanal anion (path (iii)), followed by pick up of the proton to form 3-methoxy-1-propanal (b). Although 3-methoxy-1-propanal was not found in any entries, 1,1,3-trimethoxypropane (c), which is acetalization product of 3-methoxy-1-propanal
Scheme 1. Plausible mechanism of 3-methoxy-1-propanol formation.
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with methanol, was observed. Particularly, its formation was remarkable with Al2 O3 . Addition of alcohols including methanol across carbon± carbon double bond in acrolein is known to proceed in a Michael addition-like manner to form 3-alkoxy-1-propanal [8,9,20]. This addition requires acid±base or base catalysts; the formers are acetic acid and potassium acetate [8] or a partially K -exchanged weakly acidic cation exchange resin [20] and the latter is NaOH aqueous solution [9]. At the last step, hydrogenation of 3-methoxy-1propanal yields 3-methoxy-1-propanol (path (iv)). This step may be accelerated by hydrogen atmosphere and/or treatment (Table 2). A similar anionic mechanism was proposed in cyanoethylation of alcohol to 3-alkoxypropanenitrile [21]. However, the present reaction mechanism includes dehydrogenation of allyl alcohol and hydrogenation of formyl group in 3-methoxy-1-propanal. The catalytic activities of metal oxides used here for these reactions are considered not to be so high [8,9,22]. Therefore, the other reaction path may be possible. As for b-methylallyl alcohol observed with MgO and ZrO2 catalysts, the mechanism of formation is not clear now. It was reported that the a-position of saturated primary alcohols was methylated by methanol with MgO catalyst [23]. The similar reaction may occur here to form bmethylallyl alcohol from allyl alcohol and methanol. It seems reasonable to consider that the highest activity of MgO is due to the ability for a proton and a methoxide ion generation from methanol [21]. In the present study, the pre-treatment temperature was 473, 503 and 623 K. MgO surface may be covered with OH groups for MgO pretreated at 473 and 503 K. These OH groups are the candidates of the active sites. The basic strength of OH groups is considered to be lower than that of the O2 ion, which is generated by pre-treatment at the higher temperature, ca. 600 K [22]. However, the acidity of methanol may be high enough to be dissociated by weak basic sites of these OH groups. The pre-treatment at 623 K (entry 8 in
Table 2) may generate partially dehydrated basic sites. Such stronger basic sites seem unfavorable for the present reaction because of strong adsorption of reactants and/or products (entry 7 vs. 8 in Table 2). Thus, moderate basic sites may be eective for the present reaction. Detailed mechanistic consideration including the eect of hydrogen is now in progress.
References [1] F. Dobert, B.-M. Konig, P. Wagner, A. Klausener, Eur. Pat. Appl., EP 949235, 1999. [2] S. Kadono, M. Nakatani, K. Tamai, Jpn. Kokai Tokkyo Koho, JP 10316605, 1998. [3] S. Hitomi, Jpn. Kokai Tokkyo Koho, JP 08113546, 1996. [4] W.H. Richardson, C.M. Golino, R.H. Wachs, M.B. Yelvington, J. Org. Chem. 36 (1971) 943. [5] T.G. Bonner, D. Lewis, K. Rutter, J. Chem. Soc., Perkin Trans. I (1981) 1807. [6] H.C. Brown, J.C. Chen, J. Org. Chem. 46 (1981) 3978. [7] Continental Oil Co. US 3526581, 1970. [8] H. Kawasaki, T. Jintoku, PCT Int. Appl., WO 9850339, 1998. [9] T. Kawahara, H. Suzuki, Jpn. Kokai Tokkyo Koho, JP 07025821, 1995. [10] ECETOC Technical Report No. 64, Brussels, 1995, pp. 221±229. [11] G. Sz oll osi, M. Bart ok, J. Mol. Struct. 482±483 (1999) 13. [12] G. Sz oll osi, M. Bart ok, Catal. Lett. 59 (1999) 179. [13] W. Ueda, T. Ohshida, T. Kuwabara, Y. Morikawa, Catal. Lett. 12 (1992) 97. [14] Y. Ono, T. Baba, Catal. Today 38 (1997) 321. [15] S. Sato, K. Koizumi, F. Nozaki, J. Catal. 178 (1998) 264. [16] K. Parida, H.K. Mishra, J. Mol. Catal. A: Chemical 139 (1999) 73. [17] G. Sz oll osi, M. Bart ok, J. Mol. Catal. A: Chemical 148 (1999) 265. [18] T. Baba, H. Kizuka, H. Handa, Y. Ono, Appl. Catal. A: General 194±195 (2000) 203. [19] S. Shinoda, S. Shima, T. Yamakawa, Synlett (2000) 809. [20] H. Kawasaki, T. Yoshitome, Jpn. Kokai Tokkyo Koho, JP 2000072708, 2000. [21] H. Kabashima, H. Hattori, Catal. Today 44 (1998) 277. [22] H. Hattori, Chem. Rev. 95 (1995) 537. [23] W. Ueda, H. Ohowa, K. Iwasaki, T. Kuwabara, T. Oshida, Y. Morikawa, Acid±Base Catalysis II, Kodansha±Elsevier, Tokyo, Amsterdam, 1994, pp. 35±46.
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Selective synthesis of 3-methoxy-1-propanol from methanol and allyl alcohol with metal oxide catalysts Tetsu Yamakawa a,*, Motoaki Takizawa a, Takeshi Ohnishi a, Hiroshi Koyama b, Sumio Shinoda a a
Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan b Daicel Chemical Industries, Ltd., 3-2-5, Kasumigaseki, Chiyoda-ku, Tokyo 100-6077, Japan Received 2 May 2001; received in revised form 18 June 2001
Abstract The addition of methanol to allyl alcohol was investigated with metal oxides and zeolites catalysts in the liquid phase. 3-Methoxy-1-propanol was selectively formed with MgO, ZrO2 and Al2 O3 , while zeolites gave 2-methoxy-1-propanol. This feature suggests that the generation of a methoxide ion on basic sites is an important step. The highest yield, 23.6%, was obtained with MgO treated in a hydrogen ¯ow. Ó 2001 Elsevier Science B.V. All rights reserved. Keywords: 3-Methoxy-1-propanol; Allyl alcohol; Methanol; Metal oxide catalyst; Basicity
1. Introduction 1-Alkoxy-2-propanol is widely used as an industrial solvent for coating materials, printing inks and so on. 3-Methoxy-1-propanol is similar in physical and chemical properties to 1-alkoxy-2propanol, and the investigation of its synthesis has become important. Some methods have been already reported: O-methylation of 1,3-propanediol [1], diazotization of 3-methoxy-1-propyl amine followed by hydrolysis [2], substitution of chlorine in 3-chloro-1-propanol with methoxide ion [3,4], ring opening of 1,4-dioxane [5], hydroboration of allyl methyl ether [6], electrochemical reduction of
* Corresponding address. Tel.: +81-354-52-60-98; fax: +81354-52-6365. E-mail address: [email protected] (T. Yamakawa).
acrolein [7] and catalytic hydrogenation of 3methoxy-1-propanal [8,9]. The addition of methanol across the carbon±carbon double bond in allyl alcohol is one of the candidates for the more convenient method. However, the addition in a Markownikov manner to form 2-methoxy-1-propanol, which reveals the reproduction and developmental toxicity [10], is possible with this reaction. Therefore, the high selectivity is required for this process.
Metal oxides possess the bifunctionality derived from Lewis (Mn and O2 ) and/or Br onsted (±OH) acid±base sites [11,12], and often aord the highly selective transformation of organic compounds [13±19]. Here we applied this unique character of metal oxides to the selective synthesis of 3-methoxy-1-propanol from methanol and allyl alcohol in the liquid phase heterogeneously.
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T. Yamakawa et al. / Catalysis Communications 2 (2001) 191±194
2. Experimental
vanishingly small. Thus, the selectivity for the terminal addition is extremely high (100%). MgO exhibited the highest 3-methoxy-1-propanol selectivity and allyl alcohol conversion. SiO2 showed no activity (entry 4) and an intermediate character was observed for ZrO2 and Al2 O3 . Both the conversion and selectivity were decreased by exposing MgO to a saturated water vapor at room temperature for 20 h (entry 5). The other products were acrolein, 1,1,3-trimethoxypropane, b-methylallyl alcohol and 1-propanol. The sum of their selectivities was less than 100% because of the presence of some unidenti®ed products. Interestingly, the yield of 3-methoxy-1-propanol with MgO catalyst was enhanced in a hydrogen atmosphere. As seen in entry 6 in Table 2, the allyl alcohol conversion was increased more than 2 times with small decrease of selectivity compared with entry 1 in Table 1 (argon atmosphere). When MgO was heated at 503 K for 2 h in a hydrogen ¯ow (120 ml/min), the conversion of allyl alcohol was further increased, resulting in the highest yield of 3-methoxy-1-propanol (23.6%). Pre-treatment at 623 K (entry 8) decreased both the conversion and the selectivity to the level of entry 6. Despite allyl alcohol was converted to a lot of unidenti®ed compounds using zeolite catalysts (entries 9 and 10), the addition occurred mainly to form 2methoxy-1-propanol in contrast to MgO catalyst. 2-Methoxy-1-propanol formation with zeolite catalysts will proceed through CH3 ±CH ±CH2 OH intermediate. Highly selective formation of 3methoxy-1-propanol with metal oxides catalysts is noteworthy in view that the addition of methanol
Catalysts were supplied from Wako Pure Chemical Industries (MgO, SBET 111 m2 =g) Daiichi Kigenso Kagaku Kogyo (ZrO2 , SBET 92:5 m2 =g ), Mizusawa Industrial Chemicals Al2 O3 , SBET 189 m2 =g, Fuji Silysia Chemical SiO2 , SBET 719 m2 =g, Tosoh (HY, SBET 570 m2 =g, Si=Al 3) and N.E. Chemcat (Ga-silicate, SBET 358 m2 =g, Si=Ga 40), respectively. All the catalysts were dried in vacuo at 473 K for 2 h just before reactions. A typical reaction procedure is as follows. A catalyst was charged in a stainless-steel autoclave (50 ml) with allyl alcohol (3.3 ml, 48.3 mmol) and methanol (16.7 ml, 412 mmol). Then the autoclave was purged with argon or hydrogen thoroughly, followed by sealing at room temperature and 1 atm with each gas. Reactions were performed at 503 K for 8 h with a constant stirring of 500 rpm. After the reaction, the catalyst was ®ltered o and the ®ltrate was analyzed with GC (PEG-6000 and Porapak-T columns) and GC-MS (DB-FFAP, 30 m). 3. Results and discussion Table 1 shows the allyl alcohol conversion and the selectivity for each product with MgO, ZrO2 , Al2 O3 and SiO2 in an argon atmosphere. 3-Methoxy-1-propanol was obtained as a main product using MgO, ZrO2 and Al2 O3 (entries 1±3) and the formed amount of 2-methoxy-1-propanol was
Table 1 Reactions of allyl alcohol and methanol with metal oxide catalysts in an argon atmosphere Entry 1 2 3 4 5
Catalyst MgO ZrO2 Al2 O3 SiO2 MgOb
Selectivity (%)a
Allyl alcohol conversion (%)
3MP
2MP
AC
1,1,3-MP
MA
PA
10.9 3.9 6.3 0.0 6.3
93.5 45.4 66.0 0.0 77.0
± ± ± 0.0 ±
± 0.4 4.4 0.0 ±
± ± 3.9 0.0 ±
0.9 5.2 ± 0.0 2.1
4.0 43.0 14.8 0.0 10.0
Catalyst 1.0 g; allyl alcohol 48.3 mmol; methanol 412 mmol; reaction temperature 503 K; reaction time 8 h. a 3MP: 3-methoxy-1-propanol; 2MP: 2-methoxyl-1-propanol; AC: acrolein; 1,1,3-MP: 1,1,3-trimethoxypropane; MA: b-methylallyl alcohol; PA: 1-propanol. Dash marks (±) indicates the selectivity is below 0.1%. b Exposed to a saturated water vapor at room temperature for 2 h.
T. Yamakawa et al. / Catalysis Communications 2 (2001) 191±194
193
Table 2 Reactions of allyl alcohol and methanol with MgO and zeolite catalysts in a hydrogen atmosphere Selectivity (%)a
Entry
Catalyst
Allyl alcohol conversion (%)
3MP
2MP
AC
1,1,3-MP
MA
PA
6 7 8 9 10
MgO MgOb MgOc HYb Ga-silicateb
23.3 29.3 24.3 69.4 86.1
78.0 80.7 73.5 ± ±
± ± ± 5.2 5.5
± ± ± ± ±
± ± ± ± ±
1.9 1.7 1.8 ± ±
4.7 4.4 7.9 10.8 1.8
Catalyst 1.0 g; allyl alcohol 48.3 mmol; methanol 412 mmol; reaction temperature 503 K; reaction time 8 h.a 3MP: 3-methoxy-1propanol; 2MP: 2-methoxyl-1-propanol; AC: acrolein; 1,1,3-MP: 1,1,3-trimethoxypropane; MA: b-methylallyl alcohol; PA: 1-propanol. Dash marks (±) indicates the selectivity is below 0.1%. b Pre-treated in a hydrogen ¯ow (120 ml/min) at 503 K for 2 h. c Pre-treated in a hydrogen ¯ow (120 ml/min) at 623 K for 2 h.
occurred apparently in an anti-Markownikov fashion; this is believed to be the ®rst example for the addition of alcohol to allyl alcohol. Plausible mechanism is illustrated in Scheme 1. At ®rst, a proton is abstracted from the hydroxyl group of methanol and a methoxide ion is generated (path (i)). The methoxide ion and proton are adsorbed on acidic and basic sites on the catalyst surface, respectively. In path (ii), dehydrogenation of allyl alcohol and/or hydrogen transfer from allyl alco-
hol form acrolein (a), which was detected in all entries. 1-Propanol formation suggests that a hydrogen acceptor for the latter reaction is allyl alcohol itself. Subsequently, acrolein was added to the adsorbed methoxide ion to 3-methoxy-1propanal anion (path (iii)), followed by pick up of the proton to form 3-methoxy-1-propanal (b). Although 3-methoxy-1-propanal was not found in any entries, 1,1,3-trimethoxypropane (c), which is acetalization product of 3-methoxy-1-propanal
Scheme 1. Plausible mechanism of 3-methoxy-1-propanol formation.
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T. Yamakawa et al. / Catalysis Communications 2 (2001) 191±194
with methanol, was observed. Particularly, its formation was remarkable with Al2 O3 . Addition of alcohols including methanol across carbon± carbon double bond in acrolein is known to proceed in a Michael addition-like manner to form 3-alkoxy-1-propanal [8,9,20]. This addition requires acid±base or base catalysts; the formers are acetic acid and potassium acetate [8] or a partially K -exchanged weakly acidic cation exchange resin [20] and the latter is NaOH aqueous solution [9]. At the last step, hydrogenation of 3-methoxy-1propanal yields 3-methoxy-1-propanol (path (iv)). This step may be accelerated by hydrogen atmosphere and/or treatment (Table 2). A similar anionic mechanism was proposed in cyanoethylation of alcohol to 3-alkoxypropanenitrile [21]. However, the present reaction mechanism includes dehydrogenation of allyl alcohol and hydrogenation of formyl group in 3-methoxy-1-propanal. The catalytic activities of metal oxides used here for these reactions are considered not to be so high [8,9,22]. Therefore, the other reaction path may be possible. As for b-methylallyl alcohol observed with MgO and ZrO2 catalysts, the mechanism of formation is not clear now. It was reported that the a-position of saturated primary alcohols was methylated by methanol with MgO catalyst [23]. The similar reaction may occur here to form bmethylallyl alcohol from allyl alcohol and methanol. It seems reasonable to consider that the highest activity of MgO is due to the ability for a proton and a methoxide ion generation from methanol [21]. In the present study, the pre-treatment temperature was 473, 503 and 623 K. MgO surface may be covered with OH groups for MgO pretreated at 473 and 503 K. These OH groups are the candidates of the active sites. The basic strength of OH groups is considered to be lower than that of the O2 ion, which is generated by pre-treatment at the higher temperature, ca. 600 K [22]. However, the acidity of methanol may be high enough to be dissociated by weak basic sites of these OH groups. The pre-treatment at 623 K (entry 8 in
Table 2) may generate partially dehydrated basic sites. Such stronger basic sites seem unfavorable for the present reaction because of strong adsorption of reactants and/or products (entry 7 vs. 8 in Table 2). Thus, moderate basic sites may be eective for the present reaction. Detailed mechanistic consideration including the eect of hydrogen is now in progress.
References [1] F. Dobert, B.-M. Konig, P. Wagner, A. Klausener, Eur. Pat. Appl., EP 949235, 1999. [2] S. Kadono, M. Nakatani, K. Tamai, Jpn. Kokai Tokkyo Koho, JP 10316605, 1998. [3] S. Hitomi, Jpn. Kokai Tokkyo Koho, JP 08113546, 1996. [4] W.H. Richardson, C.M. Golino, R.H. Wachs, M.B. Yelvington, J. Org. Chem. 36 (1971) 943. [5] T.G. Bonner, D. Lewis, K. Rutter, J. Chem. Soc., Perkin Trans. I (1981) 1807. [6] H.C. Brown, J.C. Chen, J. Org. Chem. 46 (1981) 3978. [7] Continental Oil Co. US 3526581, 1970. [8] H. Kawasaki, T. Jintoku, PCT Int. Appl., WO 9850339, 1998. [9] T. Kawahara, H. Suzuki, Jpn. Kokai Tokkyo Koho, JP 07025821, 1995. [10] ECETOC Technical Report No. 64, Brussels, 1995, pp. 221±229. [11] G. Sz oll osi, M. Bart ok, J. Mol. Struct. 482±483 (1999) 13. [12] G. Sz oll osi, M. Bart ok, Catal. Lett. 59 (1999) 179. [13] W. Ueda, T. Ohshida, T. Kuwabara, Y. Morikawa, Catal. Lett. 12 (1992) 97. [14] Y. Ono, T. Baba, Catal. Today 38 (1997) 321. [15] S. Sato, K. Koizumi, F. Nozaki, J. Catal. 178 (1998) 264. [16] K. Parida, H.K. Mishra, J. Mol. Catal. A: Chemical 139 (1999) 73. [17] G. Sz oll osi, M. Bart ok, J. Mol. Catal. A: Chemical 148 (1999) 265. [18] T. Baba, H. Kizuka, H. Handa, Y. Ono, Appl. Catal. A: General 194±195 (2000) 203. [19] S. Shinoda, S. Shima, T. Yamakawa, Synlett (2000) 809. [20] H. Kawasaki, T. Yoshitome, Jpn. Kokai Tokkyo Koho, JP 2000072708, 2000. [21] H. Kabashima, H. Hattori, Catal. Today 44 (1998) 277. [22] H. Hattori, Chem. Rev. 95 (1995) 537. [23] W. Ueda, H. Ohowa, K. Iwasaki, T. Kuwabara, T. Oshida, Y. Morikawa, Acid±Base Catalysis II, Kodansha±Elsevier, Tokyo, Amsterdam, 1994, pp. 35±46.