Ind. Eng. Chem. Res. 2007, 46, 1039-1044
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Synthesis of 2-Adamantane Derivatives from 1-Adamantanol on Solid Acid Catalysts Shanmugam P. Elangovan,† Katsuki Inoue,† Tatsuya Okubo,† Akio Kojima,‡ and Masaru Ogura*,§ Department of Chemical System Engineering, The UniVersity of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan, Materials and Chemicals Research Laboratory, Idemitsu Kosan Company Ltd., Chiba, Tokyo, Japan, and Institute of Industrial Science, The UniVersity of Tokyo, 4-6-1 Komaba, Meguro, Tokyo 153-8505, Japan
Catalytic transformation of 1-adamantanol (1-AdOH) has been carried out by selecting microporous materials, viz., aluminosilicate molecular sieves (zeolite-Y, USY, beta, and mordenite), aluminophosphate-based molecular sieves (SAPO-8, SAPO-5, and CoAPO-5) whose pore size is close to the kinetic diameter of the reactant and product molecules, and montmorrillonite clay, K10. In the presence of chloroacetic acid solvent, 1-AdOH forms 1-adamantyl acetate (1-AdOAc) and equilibrium is established between 1-AdOH and formed 1-AdOAc. This results in the reduction of polymerization of 1-AdOH to some extent. The 1,2-hydride shift of 1-adamantyl cation leads to the formation of 2-adamantyl cation, resulting in the products of 2-adamantane derivatives (2-derivatives), viz., 2-adamantanol (2-AdOH), 2-adamantanone (2-AdO), and 2-adamantyl acetate (2-AdOAc). Adamantane (AdH) is formed in the product ascribed to the hydride shift of 1-adamantyl and 1-hydroxyadamantane. 2-AdO is produced via disproportionation of formed 2-AdOH over solid acid catalysts. Acidity plays an important role in producing 2-derivatives selectively. Influence of the pore size of solid acid catalysts on the transformation of 1-AdOH reveals that a pore size close to the kinetic diameter of the reactant is preferable for the effective transformation of 1-AdOH. An improved experimental strategy by the addition of AdH along with the reactant restricts the formation of AdH and some of the polymerized products from 1-AdOH and, in turn, increases the selective formation of 2-derivatives. The formation of products through a different route has been completely explained with the assistance of a detailed reaction mechanism. Introduction Adamantane (AdH) derivatives have attracted special attention in the fields of optical and functional materials because they are characterized by a low energy of molecular strain and excellent heat resistance.1 Oxidation of AdH yields 1-adamantanol (1-AdOH), 2-adamantanol (2-AdOH), and 2-adamantanone (2-AdO) with a maximum amount of 1-AdOH.2-7 In recent years, among adamantane derivatives 2-AdOH and 2-AdO (2derivatives) have been spotlighted as important intermediates for a variety of pharmaceuticals and functional materials. Geluk and Schlatmann8,9 reported that 2-derivatives are obtained at a yield of 72% by maintaining 1-AdOH under heating at 30 °C for 12 h in concentrated sulfuric acid. Although this method enhances the yield of 2-derivatives, the problem remaining unsolved is that a large amount of concentrated sulfuric acid is used, thereby complicating the step of separation and refining after the reaction and, at the same time, necessitating the use of expensive and corrosion-resistant equipment and materials. Hence, the present study focuses on the transformation of 1-AdOH to obtain 2-derivatives on solid acid catalysts (zeolites, viz., H-Y (pore diameter, dp ∼ 0.74 nm), H-USY (dp ∼ 0.74 nm), H-*BEA ((dp ∼ 0.67 nm), and H-mordenite (dp ∼ 0.65 nm); aluminophosphates, viz., SAPO-8 (dp ∼ 0.8 nm), SAPO-5 (dp ∼ 0.73 nm), and CoAPO-5 (dp ∼ 0.73 nm); and montmorrillonite clay) to arrive at a comprehensive conclusion on the * To whom correspondence should be addressed. E-mail: oguram@ iis.u-tokyo.ac.jp. † Department of Chemical System Engineering, The University of Tokyo. ‡ Idemitsu Kosan Co. Ltd. § Institute of Industrial Science, The University of Tokyo.
effect of various parameters, viz., acidity, acidic strength, and pore diameter. Based on the preliminary results, H-USY (nSi/nAl ) 15) has been chosen to study the effective formation of 2-derivatives by an improved experimental strategy which allows not only an increased yield of desired products to some extent but also an alternative to the use of highly concentrated sulfuric acid, which leads to an environmentally benign method for the preparation of 2-derivatives. Experimental Procedures H-Y (nSi/nAl ) 2.8), H-*BEA (nSi/nAl ) 20, 240), and H-MOR (nSi/nAl ) 5.1) were obtained from Tosoh Corporation, and H-USY (nSi/nAl ) 15) was supplied by Catalysts & Chemicals Co. Ltd. SAPO-5 and CoAPO-5 were synthesized according to the procedure reported in the literature.10 In a typical synthesis, pseudoboehmite (75 wt % Al2O3) was dispersed in half the total amount of water required for the synthesis. Then, orthophosphoric acid diluted with the remaining amount of water was added dropwise. After stirring for 30 min, a Si or Co source was added, followed by the addition of triethylamine and aging for a further 2 h. The resulting gel was transferred to an autoclave and kept in an oven at 200 °C under static conditions for about 36 h. The resulting crystalline product was washed with water and dried overnight at 100 °C. SAPO-8 was synthesized by hydrolyzing pseudoboehmite with water followed by the addition of orthophosphoric acid diluted with water. Subsequently, the mixture was stirred for 25 min. Then the template dipropylamine was added, and the mixture was aged for 10 min. Thereafter, tetraethylorthosilicate dissolved in hexanol was added to this mixture, and the resulting gel was
10.1021/ie060783i CCC: $37.00 © 2007 American Chemical Society Published on Web 01/12/2007
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Figure 2. Temperature-programmed desorption of ammonia. Table 1. Textural Properties of Zeolites and Silicoaluminophosphate Molecular Sieves
Figure 1. XRD pattern of aluminophosphate-based molecular sieves.
charged into an autoclave, heated to 140 °C with a heating rate of 5 °C/min, and maintained at the same temperature for 105 min. Then the solids were washed several times with water and dried at 100 °C for about 24 h, where phase transformation of MCM-9 to SAPO-8 took place.11 Al-MCM-41 (nSi/nAl ) 50) and Al-SBA-15 (nSi/nAl ) 30) were also used for comparison along with microporous materials. All the materials synthesized in this study were calcined in a stream of dry air at 540 °C for about 6 h. The synthesized and calcined materials were characterized by X-ray diffraction (XRD; Bruker-AX, MO3X-HF system with Cu KR radiation), and the acidity of the materials was determined by temperature-programmed desorption (TPD) of ammonia. Catalytic transformation of 1-AdOH was carried out in a liquid phase where a round-bottomed flask was filled with 6.5 mmol of 1-AdOH, 1 g of the catalyst, and 0.106 mol of chloroacetic acid as a solvent. Prior to the reaction 1 g of catalyst was degassed overnight at 300 °C. The reaction was carried out at 150 °C typically for 4 h. After the reaction, the product mixture was extracted with 20 g each of toluene and acetone. Then the products were analyzed and identified by a gas chromatograph coupled with a mass spectrometer (Shimadzu GC-5050P with a capillary polysilane column).
sample
SBET, m2/g
micropore vol, cm3/g
acid sites, mmol/g
H-USY(15) H-BEA(20) H-MOR(5.1) SAPO-5 SAPO-8 CoAPO-5
650 630 555 235 225 230
0.24 0.20 0.20 0.11 0.14 0.09
0.37 0.40 1.55 0.25 0.16
Results and Discussion Characterization. Powder X-ray patterns of both the samples synthesized and those obtained from the industry exhibited a high purity of the desired phase. XRD patterns of the samples CoAPO-5, SAPO-5, and SAPO-8 are presented in Figure 1. Ammonia TPD profiles for zeolite and aluminophosphate samples are presented in Figure 2. All samples showed a sharp maximum at ca. 200 °C corresponding to the weakly adsorbed ammonia and the samples H-*BEA(20), H-USY(15), and H-MOR(5.1) exhibited a high-temperature peak, showing the presence of relatively stronger acid sites.12 Textural properties along with the number of acid sites for zeolites and SAPOs are given in Table 1. Effect of Acidity. The products from 1-AdOH, anticipated on the solid acid catalysts, are given in Scheme 1. Figure 3 presents the conversion of 1-AdOH and product yields in mole percent represented by the following: 1-derivatives, which include 1-AdOAc (where Ac ) chloroacetic acid) and 1-chloroadamantane (1-AdCl); 2-derivatives, which mainly include 2-AdO, 2-AdOH, and 2-AdOAc. Apart from 1- and 2-derivatives, AdH was also formed in a considerable amount. Other products, namely, polymerized products and traces of adamantanediol and adamantanecarboxylic acid were also formed. It is clear from the results presented in Figure 3 that the desired
Ind. Eng. Chem. Res., Vol. 46, No. 4, 2007 1041 Scheme 1. Formation of Products from 1-AdOH Transformation
2-derivatives formed in a considerable amount over H-USY(15) followed by H-beta(20). The other catalysts used in this study conferred 1-derivatives with the complete absence of the 2-derivatives. The product distribution as a function of different parameters, viz., acidic sites, acidic strength, and pore size of the catalysts, provides a preface on the reaction mechanism of the transformation of 1-AdOH. Figure 4 exhibits the yield of 1- and 2-derivatives as a function of acidic sites (Figure 4, top) and acidic strength (Figure 4, bottom). The temperature maximum (Tmax) from TPD of ammonia was taken as a measure of acidic strength. A method to determine the acidic strength from the peak maximum temperature was previously proposed and can be applied for the TPD of ammonia over zeolites with 10-5-10-2 g‚min‚cm-3 of the weight of sample to flow rate of carrier ratio (W/F).13,14 In our measurement of the TPD of ammonia, the W/F was ∼10-3 g‚min‚cm-3. When both
Figure 3. Yield of products from the catalytic transformation of 1-AdOH. Reaction conditions: catalyst, 1 g; 1-adamantanol, 6.5 mmol; chloroacetic acid (as a solvent), 0.106 mol; temperature, 150 °C; reaction time, 4 h. *2-Derivatives consist of 2-AdO and 2-AdOAc, while 1-derivatives include 1-AdOAc and 1-AdCl. **Blank reaction was carried out without the presence of solid acid catalyst and similar conditions were maintained as for other reactions. ***Other products include adamantanediol, acetyladamantanol, and polymerized products.
the number of acid sites and acidic strength are increased, the yield of 2-derivatives increases and attains a maximum of ca. 10 mol % and then declines. The yield of 1-derivatives
Figure 4. Yield of 1- and 2-derivatives as a function of acidic sites (top) and acidic strength (bottom).
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Figure 5. Dependence of pore size on yield of 1- and 2-derivatives.
and other products, on the other hand, decreases with an increasing number of acidic sites and acidic strength. On further increase in these parameters the yield of the 1-derivatives increases with the simultaneous decrease of 2-derivatives (cf. Figure 3). Influence of Pore Size. Figure 5 presents the yield of 1- and 2-derivatives as a function of pore size. The pore size of catalysts is close to the kinetic diameter of the reactant (ca. 0.7 nm) with balanced acidic sites and acidic strength providing a maximum yield of 2-derivatives. When the pore size is increased to greater than 1 nm, the formation of 2-derivatives decreases tremendously although the same number of acidic sites is present in the catalyst. This indicates that confined shape selectivity also plays a vital role in obtaining the desired products. It is briefly concluded that acidic sites, acidic strength, and pore size have an influence on the transformation of 1-AdOH toward the formation of 2-derivatives. The overall results provide insight into this reaction that, when the acidic sites and acidic strength are low, the reaction is slowed down after the equilibration of 1-AdOH with 1-AdOAc. On the other hand, an increase in these parameters increases the other products, namely, polymerized products; i.e., higher acidic strength may cause ring opening of 1-AdOH15 to undergo polymerization. The initial results on the transformation of 1-AdOH on microporous materials and some
mesoporous materials provide an outlook that balanced acidic sites and acidic strength with a pore size close to the kinetic diameter of the reactants and products are prerequisite for the transformation of 1-AdOH to 2-derivatives to a considerable amount. Role of Adamantane. The formation of AdH from 1-adamantyl cation is inevitable under such conditions (cf. Figure 3) via a hydride shift to form 1-hydroxyadamantyl cation, thereby not only reducing the formation of 2-adamantyl cation but also increasing the formation of undesired polymerized products. To suppress the formation of adamantane from 1-AdOH, AdH was added to the reaction mixture and the reaction was allowed to proceed under identical reaction conditions on H-USY(15) with the catalyst amount of 40 mg. The amounts of 1-AdOH and chloroacetic acid were taken correspondingly to maintain a similar concentration. It is clear from Figure 6 that on increasing the amount of AdH addition in the reaction mixture the yield of 2-derivatives is found to increase, and it attains a maximum of ca. 35 mol % when the mole ratio of AdH to 1-AdOH is 2. It is interesting to note that the “other products” decrease simultaneously from 40 to 20 mol %. 1-Derivatives decreased considerably from 10 to 2 mol % (Figure 6, left). This indicates that the addition of adamantane in the reaction mixture allows the 1,2-hydride shift to proceed to 2-AdOH rather than the formation of AdH from 1-adamantyl cation. The influence of the addition of adamantane in the reaction mixture on the distribution of 2-derivatives is presented in Figure 6 (right). It is clear from the figure that increasing AdH in the reactant mixture increases 2-AdO. AdH addition might enhance the 1,2hydride shift of 1-AdOH to form 2-AdOH. However, the presence of 2-AdOH could not be detected in a considerable quantity in the product mixture. The 2-AdOH formed might undergo disproportionation to form 2-AdO. To clarify this observation further, 2-AdOH was subjected to the catalytic reaction under identical conditions. The results presented in Table 2 reveal that the conversion of 2-AdOH is 99.3 mol % and ca. 90 mol % of 2-AdOH yields an equimolar quantity of AdH and 2-AdO/2-AdOAc. This supports the results presented in Figure 6 (right) for the low amount of 2-AdOH in the mixture of 2-derivatives, where 2-AdOH can be disproportionated into AdH and 2-AdO in accordance with a hydride transfer reaction of known type.16 In this case, 2-AdOH acts as a hydride donor, splitting off its R-hydrogen. The adamantyl cation, either
Figure 6. Effect of adamantane addition on the yield of 1- and 2-derivatives and polymerized products (left) and influence of addition of adamantane on the distribution of 2-derivatives (right).
Ind. Eng. Chem. Res., Vol. 46, No. 4, 2007 1043 Table 2. Conversion of 2-AdOH and Product Yields on H-USY(15) product yield, mol % conversion of 2-AdOH, mol %
1-AdOH
1-AdOAc
AdH
1-AdCl
2-AdOAc
2-AdO
other products
99.3
0.5
1.8
45.5
0.4
8.8
36.6
7.9
Table 3. Comparison of Product Yields on H-USY(15) under Static and Rotating Conditions product yield, mol %
static conditions
rotating conditions
1-AdOHa 1-AdOAc 1-AdCl AdH 2-AdO 2-AdOAc 2-AdOH other products
98.0 4.0 3.7 29 8.2 5.4 0.8 46.0
99.0 1.6 4.0 25.0 20.0 2.7 0.0 46.0
a
Conversion of 1-AdOH (mol %).
secondary or tertiary, will be the hydride acceptor. Also, the formation of 1-AdOH from 2-AdOH did not occur under this condition. Under identical conditions AdH was also subjected to reaction on H-USY(15). The result shows that AdH undergoes only a little conversion, ca. 11.6 mol %, out of which 11.3 mol % is the “other products”, 0.2 mol % is 1-AdOAc, and 0.1 mol % is 1-AdCl, with the complete absence of 2-derivatives. This result indicates that hydroxylation of AdH rather needs different experimental conditions to obtain the hydroxylated product. The absence of hydroxylated products from AdH clearly indicates that, during the catalytic transformation of 1-AdOH, the formed AdH might not undergo hydroxylation to form 1-AdOH, 2-AdOH, or 2-AdO under this condition. It is confirmed from this result that all of the 2-derivatives are formed from the catalytic transformation of 1-AdOH. Under these conditions, AdH starts solidifying on the sides of reaction vessel. This causes reduction of AdH concentration in the reaction mixture, allowing further formation of AdH from 1-adamantyl cation. Hence, the yield of 2-derivatives is minimized to a larger extent. To overcome this problem, the reaction was also carried out in a 60 mL autoclave under identical conditions, where the autoclave was maintained at 150 °C under rotating conditions. The results presented in Table 3 indicate that after 4 h of reaction, the yield of 2-AdO was found to be much higher (ca. 20 mol %) than the yield under
Figure 7. Mechanism of the solid-acid-catalyzed 1-AdOH transformation.
static conditions (ca. 8 mol %) and the yield of 2-derivatives was about 26 mol % compared to 14 mol % under static conditions. Proposed Mechanism for the Transformation of 1-AdOH. Based on the results, a mechanism is proposed, and the detailed reaction mechanism is presented in Figure 7. 1-AdOH is stabilized with chloroacetic acid and forms 1-AdOAc, establishing equilibrium with 1-AdOH. Thereafter, 1-AdOH adsorbs over the acid sites to form 1-adamantyl cation and this might undergo a 1,2-hydride shift to form 2-adamantyl cation, which on further hydroxylation results in the formation of 2-AdOH. The rate of 1,2-hydride shift has been proved to be strongly influenced by the acidity of catalysts.7 2-Adamantyl cation might also undergo acetylation in the presence of chloroacetic acid to form 2-AdOAc. AdH may be formed from 1-adamantyl cation and 1-AdOH/1-AdOAc by a hydride shift and the hydroxyadamantyl cation undergo ring opening under acidic conditions, resulting in the formation of polymerized products. It is worth noting from the reaction on H-USY(15) presented in Figure 8 as a function of time that the amount of 1-AdOAc observed at 30 min of reaction decreases, as the reaction proceeds, with the simultaneous increase of both adamantane and polymerized product (Figure 8, top). 1-Adamantyl cation might react with Cl- to form 1-chloroadamantane, while the solid acid is not sufficient to form 2-adamantyl cation through a 1,2-hydride shift. 2-AdOH/2-AdOAc is formed from a 1,2-hydride shift of 1-adamantyl cation and adamantane, which is easily transformed to 2-AdO on the acidic sites (bimolecular transformation followed by dehydration) to form equimolar quantities of 2-AdO and AdH. The results presented in Figure 8 (bottom) indicate that 2-AdOAc forms in a higher amount during the initial reaction and decreases with the simultaneous increase of 2-AdO. Conclusion A viable route to produce most useful derivatives of adamantane is identified; viz., 1-AdOH isomerizes into 2-AdOH by a 1,2-hydride shift and is followed by an intermolecular
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unwanted AdH from 1-AdOH and the reaction shifts toward the 1,2 hydride shift of 1-adamantyl cation to 2-adamantyl cation, which in turn leads to the formation of 2-derivatives in a higher yield. An improved experimental condition to selectively obtain 2-derivatives over H-USY(15) catalyst is achieved to some extent. It should be mentioned that the formation of a considerable amount of polymerized product is a great handicap in the production of 2-derivatives from 1-AdOH on solid acid catalysts. There is an existing challenge for further reduction in the formation of polymerized product to obtain 2-derivatives selectively on solid acid catalysts. Acknowledgment Part of this work was financially supported by the program of CRNavi: the joint research activity of the Department of Chemical System Engineering, the University of Tokyo, and several companies. S.P.E., T.O., and M.O. express their appreciation to Idemitsu Kosan Co. Ltd. for additional support of this program. Literature Cited
Figure 8. Conversion of 1-AdOH and the product distribution on H-USY(15) as a function of time.
hydride shift of 2-AdOH to 2-AdO. The overall acidic sites and acidic strength play an important role in the product distribution; viz., low acidity and low acidic strength of the catalysts fail to activate the 1,2-hydride shift of 1-adamantyl cation to yield 2-derivatives, instead producing a lot of 1-derivatives such as 1-AdOAc and 1-AdCl. Strong solid acid catalysts, on the other hand, result in a ring opening of 1-AdOH to yield polymerized products. Since the formation of 2-AdOH is greatly influenced by the acidity of the catalysts, it is clear that the formation of 2-AdO must also be dependent on the acidity. Confined shape selectivity, i.e., pore size close to the kinetic diameters of adamantane derivatives, is prerequisite for this reaction to occur toward the favorable products. Conversely, a very large pore size, e.g., above 1 nm, results in the catalyst behaving almost like a solvent. A modified reaction procedure according to the need for solid acid catalysts, as an alternative to a well-known homogeneous sulfuric acid catalyst, is proposed. Solid acid catalysts serve as better materials for the above reactions, leading to the formation of 2-derivatives in higher yield. The addition of AdH in the reaction mixture decreases the formation of
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ReceiVed for reView June 20, 2006 ReVised manuscript receiVed October 31, 2006 Accepted November 18, 2006 IE060783I
