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Epoxidation of cyclooctene with hydroperoxy sultams catalyzed by molybdenum boride
Applied Catalysis A: General 323 (2007) 174–180 www.elsevier.com/locate/apcata
Epoxidation of cyclooctene with hydroperoxy sultams catalyzed by molybdenum boride O. Makota a,*, J. Wolf b, Yu. Trach a, B. Schulze b b
a Lviv Polytechnic National University, S.Bandera Str. 12, U-79013 Lviv, Ukraine Institute of Organic Chemistry, Leipzig University, Johannisallee 29, D-04103 Leipzig, Germany
Received 30 October 2006; received in revised form 8 February 2007; accepted 9 February 2007 Available online 17 February 2007
Abstract The hydroperoxy sultams (HPS) have been investigated in catalytic epoxidation reaction of cyclooctene. We have found that HPS can function as the epoxidation agents in the presence of molybdenum boride MoB as a catalyst. The reaction was sensitive to steric as well as electronic factors. The high epoxides yields were observed in the case of hydroperoxy sultams with chlorine atoms and especially favorable was hydroperoxide structure with a-position of chlorine atom to bond of nitrogen with aromatic ring. # 2007 Elsevier B.V. All rights reserved. Keywords: Catalyst; Epoxidation; Hydroperoxide; Hydroperoxy sultam; Molybdenum boride
1. Introduction The epoxidation reaction of olefins is an important reaction of organic chemistry because epoxides are widely used in an industry and in organic synthesis [1–3]. One of the epoxidation agents which are used in the presence of catalysts in this process are alkyl- and arylhydroperoxides. They allow to carry out the catalytic epoxidation process with sufficient rate but only at temperatures above 80 8C that requires additional expenditure of energy. Hydroperoxy sultams (HPS) are a new class of hydroperoxides [4–8]. They show activity in the oxidation reaction at temperatures 0–40 8C. The rate of oxidation of 1,4-thioxane by HPS was nearly four orders of magnitude faster than that by tert-butyl hydroperoxide (TBHP) under comparable experimental conditions [6]. It makes hydroperoxy sultams potentially possible epoxidation agents. However, the reaction of HPS with various sulfides containing two nucleophilic centres, sulfur atom and double bond, led only to the electrophilic attack at sulfur atom, and no traces of epoxides were detected in the reaction system. Taking into account these facts it is reasonable to investigate the interaction of HPS with substance containing only one * Corresponding author. E-mail address: [email protected] (O. Makota). 0926-860X/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2007.02.013
nucleophilic centre—double bond. It allows to exclude a possible competition of nucleophiles for oxygen atom of –OOH group and to direct the electrophilic attack of hydroperoxide exclusively on multiple bond of unsaturated compound. In this work, the epoxidation ability of hydroperoxy sultams (Table 1) in the epoxidation reaction of cyclooctene in the presence of catalyst—molybdenum boride MoB is investigated. 2. Experimental 2.1. Catalytic epoxidation The epoxidation process of cyclooctene was carried out in an argon atmosphere in a thermostated glass reactor fitted with a reflux condenser and a magnetic stirrer. In a typical run of catalytic measurement, the reactor was loaded with 0.005 g of catalyst, 0.3 ml of cyclooctene and proper amounts of HPS and solvent. It is established that in the absence of catalyst HPS does not decompose and the epoxide is not formed under the reaction conditions. The reaction mixtures were analyzed by using a Hewlett Packard HP 6890 N chromatograph, a capillary column DB-1 (60 m 0.32 mm 0.5 mm) packed with dimethylsiloxane. The column temperature was changed from 50 up to 250 8C with rate of 108 in 1 min. The hydroperoxide concentration was determined by iodometric titration [9].
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Table 1 Hydroperoxy sultams investigated in the epoxidation reaction of cyclooctene catalyzed by MoB Hydroperoxy sultam
HPS-1
HPS-9
HPS-2
HPS-10
HPS-3
HPS-11
HPS-4
HPS-12
HPS-5
HPS-13
HPS-6
HPS-14
HPS-7
HPS-15
HPS-8
HPS-16
2.2. General methods
2.3. General procedure for the preparation of HPS
Melting points were determined on Boetius micromelting-point apparatus and are corrected. IR spectra are expressed in cm 1 and were recorded on Genisis FTIR Unicam Analytical System (ATI Mattson) using KBr pellets. 1 H NMR spectra was recorded on 200-MHz (Varian Gemini200), 300-MHz (Varian Gemini-300) and 400-MHz (Varian Unity-400). The chemical shifts (d) are expressed in ppm relative to tetramethylsilane (TMS) as internal standard. 13C NMR spectra was received on the named spectrometers. Electron impact mass spectra (EI-MS) was recorded on a Quadrupol-MS VG 12-250 at an ionising voltage of 70 eV. Elemental analysis was determined on Heraeus CHNO Rapid Analyzer.
Some hydroperoxy sultams were already described and prepared by procedure: HPS-1 [10], HPS-2 [6], HPS-3 [11], HPS-4 [5], HPS-11 [12] and HPS-5, HPS-6, HPS-10, HPS-12, HPS-13 and HPS-14 [13]. HPS-7, HPS-8, HPS-9, HPS-15 and HPS-16 were prepared for the first time (Scheme 1). The synthesis of isothiazolium salts 1 were conveniently performed by intramolecular cyclocondensation of b-thiocyanatovinyl aldehydes and the varied substituted anilines in the presence of perchloric acid in acetic acid. The oxidation of the 4,5-dimethylisothiazolium salts 1a and b with 30% H2O2 in glacial acetic acid at room temperature gave the stable 3-hydroperoxysultim HPS-8 after 24 h and the
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dissolution of salt 1a, a colourless precipitate of HPS-8 was obtained after 24 h and isolated. The crude product was washed with water. Yield 35%; m.p. 132–134 8C; IR (KBr) 1062 (SO) cm 1; 1H NMR (acetone-d6, 300 MHz): d (ppm) 2.05, 2.13 (s, 6H), 5.86 (s, 1H), 7.53–7.83 (m, 3H), 11.21 (s, 1H); 13C NMR (acetone-d6, 50 MHz): d (ppm) 12.2, 14.3, 95.9, 117.4, 124.5, 132.6, 133.4, 134.1, 135.3, 136.6, 137.7; EI-MS (m/z) 330.0 (M H2O)+; anal. calcd. for C11H11Cl2NO3S (308.2): C 42.87, H 3.60, N 4.54, O 10.40; found: C 42.88, H 3.63, N 4.59, O 10.23. 2.6. Synthesis of 2-(2,5-dichlorophenyl)-2,3-dihydro-3hydroperoxy-4,5-dimethylisothiazole 1,1-dioxide (HPS-7) and 2-(3,5-dichlorophenyl)-2,3-dihydro-3-hydroperoxy-4,5dimethylisothiazole 1,1-dioxide (HPS-9) H2O2 (0.7 ml, 30%) was added to a stirred suspension of 1a and b (0.26 mmol) in AcOH (0.7 ml) at room temperature. After dissolution of salts 1a and b a colourless precipitates of HPS-7 and HPS-9 were obtained after 24–96 h and isolated. The crude products were washed with water. 2.6.1. HPS-7 Yield 60%; m.p. 175–178 8C; IR (KBr) 1291 (SO2) 1170 (SO2) cm 1; 1H NMR (acetone-d6, 300 MHz): d (ppm) 2.11, 2.15 (s, 6H), 6.05 (s, 1H), 7.57–7.86 (m, 3H), 10.85 (s, 1H); 13C NMR (acetone-d6, 50 MHz): d (ppm) 7.5, 12.2, 93.3, 122.7, 131.3, 132.6, 133.3, 133.4, 134.2, 134.4, 137.2; EI-MS (m/z) 346.0 (M H2O)+; anal. calcd. for C11H11Cl2NO4S (324.2): C 40.75, H 3.43, N 4.32, O 19.74; found: C 40.43, H 3.15, N 4.23, O 19.55.
3-hydroperoxysultams HPS-7 and HPS-9 after 24–96 h stirring. Furthermore, the oxidation of the 2,4,5-triphenyl (1c and d) substituted isothiazolium salts with H2O2 at room temperature offered the 3-hydroperoxysultams HPS-15 and HPS-16 after 48–192 h, respectively. The mechanism of the oxidation is shown in Scheme 1.
2.6.2. HPS-9 Yield 74%; m.p. 176–177 8C; IR (KBr) 1286 (SO2) 1142 (SO2) cm 1; 1H NMR (acetone-d6, 300 MHz): d (ppm) 2.13, 2.15 (s, 6H), 6.02 (s, 1H), 7.30–7.62 (m, 3H), 10.64 (s, 1H); 13C NMR (acetone-d6, 50 MHz): d (ppm) 7.2, 11.9, 91.4, 118.2, 119.2, 124.0, 124.7, 126.7, 133.2, 136.1, 137.9, 139.2; EI-MS (m/z) 346.0 (M H2O)+; anal. calcd. for C11H11Cl2NO4S (324.2): C 40.75, H 3.43, N 4.32, O 19.74; found: C 40.29, H 3.67, N 4.32, O 19.81.
2.4. Synthesis of 4,5-dimethyl-2-phenyl- (1a and b), 2,4,5triphenyl- (1c) and 5-(4-methoxyphenyl)-2,4-diphenylisothiazolium perchlorates (1d)
2.7. Synthesis of 2,3-dihydro-2-(4-trifluoromethylphenyl)3-hydroperoxy-4,5-diphenyliosthiazole 1,1-dioxide (HPS15)
Compounds 1c and d were already described in Refs. [14,15], respectively. The salts 1a and b were prepared for the first time according to literature procedure [16]. Yields and melting points are 1a: 90%, 178–180 8C and 1b: 96%, 182– 184 8C.
H2O2 (0.7 ml, 30%) was added to a stirred suspension of 1c (0.26 mmol) in AcOH (0.7 ml) at room temperature. After dissolution of salt 1c, a colourless precipitate of HPS-15 was obtained after 72–192 h and isolated. The crude product was washed with water. Yield 81%; m.p. 134–137 8C; IR (KBr) 1290 (SO2) 1126 (SO2) cm 1; 1H NMR (acetone-d6, 300 MHz): d (ppm) 7.20 (s, 1H), 7.42–7.89 (m, 14H), 11.61 (s, 1H); 19F NMR (acetone-d6, 282 MHz): d (ppm) 63.13 (s, 3F); 13C NMR (acetone-d6, 50 MHz): d (ppm) 90.5, 120.9, 128.0, 129.0 (q, J = 212.3 Hz, CF3), 130.0, 130.2, 130.4, 130.7, 130.9, 131.0, 131.2, 131.3,
Scheme 1.
2.5. Synthesis of 2-(2,5-dichlorophenyl)-2,3-dihydro-3hydroperoxy-4,5-dimethylisothiazole 1-oxide (HPS-8) H2O2 (0.7 ml, 30%) was added to a stirred suspension of 1a (0.26 mmol) in AcOH (0.7 ml) at room temperature. After
O. Makota et al. / Applied Catalysis A: General 323 (2007) 174–180
131.5, 131.8, 133.6, 138.4, 140.8, 141.8, 146.4; EI-MS (m/z) 429.0 (M H2O)+ ; anal. calcd. for C22H16F3NO4S (447.4): C 59.05, H 3.60, N 3.13, O 14.30; found: C 58.70, H 3.69, N 3.04, O 14.45. 2.8. Synthesis of 2,3-dihydro-3-hydroperoxy-5-(4methoxyphenyl)-2-(2,4-dinitrophenyl)-4-phenyl-isothiazole 1,1-dioxide (HPS-16) H2O2 (0.7 ml, 30%) was added to a stirred suspension of 1d (0.26 mmol) in AcOH (0.7 ml) at room temperature. After dissolution of salt 1d, a colourless precipitate of HPS-16 was obtained after 48 h and isolated. The crude product was washed with water. Yield 80%; m.p. 120–124 8C; IR (KBr) 15.37 (NO2), 1346 (NO2), 1295 (SO2) 1157 (SO2) cm 1; 1H NMR (acetone-d6, 200 MHz): d (ppm) 3.84 (s, 3H), 6.66 (s, 1H), 6.96–7.03 (m, 4H), 7.35–8.38 (m, 8H); 13C NMR (acetone-d6, 75 MHz): d (ppm) 56.38, 94.87, 116.54, 122.94, 129.71, 130.36, 130.72, 130.85, 131.36, 131.67, 132.36, 132.46, 132.94, 138.67, 143.62, 147.02, 149.93, 162.92; EI-MS (m/z) 481.0 (M H2O)+; anal. calcd. for C22H17N3O9S (499.5): C 52.91, H 3.43, N 8.41, O 28.83; found: C 52.86, H 3.32, N 8.39, O 28.92. 3. Results and discussion The results of the catalytic epoxidation of cyclooctene by some HPS in the presence of MoB at 20 8C in chloroform and at 30 8C in chlorobenzene are summarized in Table 2. The data indicate that investigated hydroperoxides have a different efficiency in the catalytic reaction of epoxide formation. The nature of the substituents in hydroperoxide molecule has significant effect on activity of oxygen atom of hydroperoxide group in electrophilic attack on double bond of cyclooctene. A comparison of HPS-1 and HPS-2 exhibites that in both chlorobenzene and chloroform solvents higher epoxide yield is observed in the presence of chlorine atoms in aromatic ring at nitrogen atom. On the other hand, tert-butyl group in orthoposition to nitrogen atom less favours the epoxide formation. The results of reaction with HPS-3 and HPS-4 which containing the identical substituent in aromatic ring –COOCH3 demonstrate (Table 2) that the hydroperoxide efficiency in the reaction of epoxide formation is also increased in the presence of two methyl groups at double bond of five member cycle. The presence of only –NO2 group (HPS-5) in a paraposition to bond of nitrogen with aromatic ring is not
177
favourably for proceeding of the catalytic epoxidation reaction. However, in the case of HPS with both –NO2 group in a paraposition and chlorine atom in ortho-position (HPS-6) the epoxide yield increased in chlorobenzene from 0 (with HPS-5) to 10% (with HPS-6) and in chloroform from 1.5 to 15% (see Table 2). The obtained results show that increasing of electrophilic character of peroxide oxygen atom due to the induction effect of chlorine atoms in aromatic ring at nitrogen atom leads to the increase in epoxide yield. Higher yield of epoxycyclooctane is observed for the first two HPS (HPS-1 and HPS-2) in chlorobenzene as solvent, whereas for other HPS the best results are obtained in chloroform (Table 2). Since for the majority of HPS used higher yields of epoxide have been obtained in chloroform, further investigations were carried out in this solvent. Additionally, for reason to investigate the effective of HPS consumption on epoxide formation, the hydroperoxide conversion is also determined in the further experiments. The obtained results of the epoxidation process of cyclooctene with HPS catalyzed by MoB at 27 8C in chloroform are given in Figs. 1–4 and Table 3. One can see that the consumed amount of HPS and the formed amount of epoxycyclooctane as well as selectivity of epoxide formation are appreciably defined by HPS structure. The highest hydroperoxide conversions are observed in the cases of HPS-1, HPS-8, HPS-9 and HPS-10, whereas the HPS-11 and HPS-14 show the lowest value of this parameter. It should be noted, HPS-1 is partially transformed to epoxide, as well as HPS-10 is spent mainly unproductively. The data presented in Figs. 3 and 4 indicate that the highest amount of epoxide was formed when HPS-7 was used in the process of cyclooctene epoxidation. In this case, the selectivity of epoxide formation (Table 3) was highest too. HPS-1, HPS-9 and HPS-13 show intermediate selectivity. In the presence of other HPS the selectivity does not exceed 8%.
Table 2 Yield of epoxycyclooctane in the reaction of HPS with cyclooctene catalyzed by MoB Hydroperoxy sultam
HPS-1
HPS-2
HPS-3
HPS-4
HPS-5
HPS-6
Yielda (%) Yieldb (%)
48 21
19 10
6 12.5
5 21.5
0 1.5
10 15
a Reaction conditions: T = 30 8C, chlorobenzene 1 ml, cyclooctene 0.3 ml, 0.01 mol/l HPS, catalyst 0.005 g. b Reaction conditions: T = 20 8C, chloroform 5 ml, cyclooctene 0.3 ml, 0.01 mol/l HPS, catalyst 0.005 g. The reaction time is 40 h.
Fig. 1. HPS concentration as a function of reaction time in the epoxidation reaction: HPS-1 (1), HPS-16 (2), HPS-15 (3), HPS-8 (4), HPS-11 (5). Reaction conditions: T = 27 8C, chloroform 3.5 ml, cyclooctene 0.3 ml, 0.01 mol/l HPS and catalyst 0.005 g.
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Fig. 2. HPS concentration as a function of reaction time in the epoxidation reaction: HPS-10 (6), HPS-9 (7), HPS-7 (8), HPS-12 (9), HPS-13 (10), HPS-14 (11). Reaction conditions: T = 27 8C, chloroform 3.5 ml, cyclooctene 0.3 ml, 0.01 mol/l HPS and catalyst 0.005 g.
Fig. 4. Epoxycyclooctane (EP) concentration as a function of reaction time in the epoxidation reaction: HPS-10 (6), HPS-12 (7), HPS-14 (8), HPS-13 (9), HPS-9 (10), HPS-7 (11). Reaction conditions: T = 27 8C, chloroform 3.5 ml, cyclooctene 0.3 ml, 0.01 mol/l HPS and catalyst 0.005 g.
The comparison of epoxidation process results obtained with HPS-7 and HPS-9 suggests that a-position of chlorine atom to bond of nitrogen with aromatic ring in structure of HPS is favourably disposed for selective transformation of hydroperoxide to epoxide. The corroboration of positive influence of chlorine atoms in a a-position on the epoxidation reaction are values of selectivity obtained by using HPS-12 and HPS-13. As it can be seen from Table 3, the introduction of chlorine atom in a a-position to bond of nitrogen with aromatic ring is resulted in increasing of epoxycyclooctane formation selectivity from 2% with HPS-12 to 19% in the case of HPS-13. On the other hand, in the absence of substituents in aromatic ring only nonproductive HPS consumption is observed. The substituents –CF3, –NO2 and –OCH3 in para-position to bond of nitrogen with aromatic ring slightly
influence on HPS selectivity in the epoxidation process and in their presence the lowest selectivity of epoxide formation is obtained. From Table 3, one can see also that compound HPS-7 is fourfold more efficient compared to HPS-8 regarding epoxide yield (33% versus 8%). This effect might be due to different oxidation state of sulfur atom in both compounds (see Table 1). It is reasonable to assume that some part of non-productive decomposition of hydroperoxide in case of HPS-8 is connected with further oxidation of sulfur atom. The low selectivity of epoxide formation indicates the significant contribution of nonproductive HPS decomposition process in the overall process of hydroperoxide consumption. Therefore, the hydroperoxide decomposition process in the absence of olefine in reaction system is also investigated. The
Fig. 3. Epoxycyclooctane (EP) concentration as a function of reaction time in the epoxidation reaction: HPS-11 (1), HPS-15 (2), HPS-16 (3), HPS-8 (4), HPS1 (5). Reaction conditions: T = 27 8C, chloroform 3.5 ml, cyclooctene 0.3 ml, 0.01 mol/l HPS and catalyst 0.005 g.
Fig. 5. HPS concentration as a function of reaction time in the decomposition reaction: HPS-10 (1), HPS-7 (2), HPS-1 (3), HPS-15 (4), HPS-9 (5), HPS-14 (6), HPS-13 (7). Reaction conditions: T = 27 8C, chloroform 3.8 ml, 0.01 mol/l HPS and catalyst 0.005 g.
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Table 3 HPS conversion (Conv.) and selectivity (Sel.) of epoxycyclooctane formation (in account on consumpted hydroperoxide) in the epoxidation reaction of cyclooctene with HPS catalyzed by MoB Hydroperoxy sultam
Conv. HPS (%)
Sel. (%)
Hydroperoxy sultam
Conv. HPS (%)
Sel. (%)
HPS-1 HPS-7 HPS-8 HPS-9 HPS-10 HPS-11
93 81 93 90 92 41
22 33 8 23 1 5
HPS-12 HPS-13 HPS-14 HPS-15 HPS-16
75 53 39 76 84
2 19 6 5 5
Reaction conditions: T = 27 8C, chloroform 3.5 ml, cyclooctene 0.3 ml, 0.01 mol/l HPS, catalyst 0.005 g. The reaction time is 4 h.
Table 4 HPS conversion in the decomposition reaction of HPS catalyzed by MoB and amount of HPS additionally consumpted in the presence of cyclooctene (DHPS) Hydroperoxy sultam
HPS-1
HPS-7
HPS-9
HPS-10
HPS-13
HPS-14
HPS-15
Conv. HPS (%) DHPS (%)
65 28
69 12
47 43
76 16
25 28
32 7
56 20
Reaction conditions: T = 27 8C, chloroform 3.8 ml, 0.01 mol/l HPS, catalyst 0.005 g. The reaction time is 4 h.
experimental results given in Fig. 5 demonstrate that the HPS decomposition reaction proceeds actively enough. Hence, the low selectivity of epoxide formation in epoxidation process can be result of proceeding of parallel nonproductive HPS decomposition reaction. As it can be seen from Table 4, the maximal HPS conversion in the catalytic decomposition process is observed in the case of HPS-10 whereas HPS-13 and HPS-14 demonstrate minimum activity in this process. Other HPS show intermediate activity in the decomposition reaction and the conversions were from 47 to 69%. The comparison of results obtained in both decomposition and epoxidation catalytic reactions exhibites that in the presence of olefine the hydroperoxides consumption is increased. The amount of hydroperoxide additionally consumpted in the presence of cyclooctene (DHPS, Table 4) considerably depends on the hydroperoxide structure. In the case of the most effective epoxidation agent HPS-7, the additional hydroperoxide amount is less than amount of hydroperoxide spent on the epoxide formation. This fact indicates the inhibitory effect of olefine on the process of unproductive decomposition of hydroperoxide. This result is consistent with [17] where epoxidation of octene-1 with tertbutyl hydroperoxide in the presence of MoB2 as catalyst was carried out. It is due to the decrease in the number of the catalytic sites of hydroperoxide decomposition (catalyst– hydroperoxide complex) in the presence of olefine and the increase in epoxidation sites (catalyst–olefine complex) which reacts with hydroperoxide and gives epoxide. The change in the direction of hydroperoxide conversion from decomposition to epoxidation with an increase in the olefine concentration is the result of the replacement of the hydroperoxide by the olefine in the catalytic site responsible for hydroperoxide decomposition. In the presence of other HPS, the additional hydroperoxide amount is higher than amount of hydroperoxide which should be spent for epoxide formation. It is probably caused by the
further transformation of epoxide or oxidation of cyclooctene without formation of epoxide. With the purpose to get some information about the influence of reaction temperature on the process, the epoxidation reaction of cyclooctene in the presence of one of the more effective hydroperoxy sultams (HPS-1) was carried out at temperatures between 20 and 30 8C. From linear relationship between ln[HPS] and reaction time the pseudo-first-order reaction rate constants (k) were calculated. The activation energy (Ea) was calculated from the Arrhenius plot (Fig. 6). We have found that the process of epoxide formation during the interaction of cyclooctene with HPS-1 in the presence of MoB has very high activation energy, Ea = 210 kJ/mol. It is not typical for the catalytic epoxidation process of olefins by alkylhydroperoxides. For example, the activation energy of epoxide formation process during the interaction of octene-1 (linear analogue of cyclooctene) with TBHP in
Fig. 6. The ln k as a function of the inverse of reaction temperature. Reaction conditions: chloroform 3.5 ml, cyclooctene 0.3 ml ml, 0.01 mol/l HPS and catalyst 0.005 g.
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the presence of MoB and MoB2 determined by us equals 108 and 64 kJ/mol, respectively. The activation energy of epoxidation reaction of cyclohexene with TBHP catalyzed by Mo(VI) supported on imidazole-containing polymer equals 25 kJ/mol [18] and reaction of oleic acid with same hydroperoxide catalyzed by [Mo(O)2(SAP)(EtOH)] equals 99 kJ/mol [19].
4. Conclusion We have found that hydroperoxy sultams can be used as the epoxidation agents in the catalytic process of cyclooctene epoxidation in the presence of MoB at 27 8C. HPS with chlorine atoms in aromatic ring at nitrogen atom were the most effective in this process. It allows to assume that chlorine atoms increase the electrophilic character of peroxide oxygen atom and evidently also stabilize an intermediate cyclooctene– catalyst–hydroperoxide complex responsible for the epoxide formation. It was shown that the reaction of epoxide formation in the case of HPS-1 proceeds with activation energy 210 kJ/mol. Further investigation will be focused on searching of HPS optimum structure which ensures high selectivity of epoxide formation at low temperatures in the catalytic epoxidation reactions.
Acknowledgment The work was partly supported by the Deutscher Akademischer Austauschdienst (DAAD).
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Epoxidation of cyclooctene with hydroperoxy sultams catalyzed by molybdenum boride O. Makota a,*, J. Wolf b, Yu. Trach a, B. Schulze b b
a Lviv Polytechnic National University, S.Bandera Str. 12, U-79013 Lviv, Ukraine Institute of Organic Chemistry, Leipzig University, Johannisallee 29, D-04103 Leipzig, Germany
Received 30 October 2006; received in revised form 8 February 2007; accepted 9 February 2007 Available online 17 February 2007
Abstract The hydroperoxy sultams (HPS) have been investigated in catalytic epoxidation reaction of cyclooctene. We have found that HPS can function as the epoxidation agents in the presence of molybdenum boride MoB as a catalyst. The reaction was sensitive to steric as well as electronic factors. The high epoxides yields were observed in the case of hydroperoxy sultams with chlorine atoms and especially favorable was hydroperoxide structure with a-position of chlorine atom to bond of nitrogen with aromatic ring. # 2007 Elsevier B.V. All rights reserved. Keywords: Catalyst; Epoxidation; Hydroperoxide; Hydroperoxy sultam; Molybdenum boride
1. Introduction The epoxidation reaction of olefins is an important reaction of organic chemistry because epoxides are widely used in an industry and in organic synthesis [1–3]. One of the epoxidation agents which are used in the presence of catalysts in this process are alkyl- and arylhydroperoxides. They allow to carry out the catalytic epoxidation process with sufficient rate but only at temperatures above 80 8C that requires additional expenditure of energy. Hydroperoxy sultams (HPS) are a new class of hydroperoxides [4–8]. They show activity in the oxidation reaction at temperatures 0–40 8C. The rate of oxidation of 1,4-thioxane by HPS was nearly four orders of magnitude faster than that by tert-butyl hydroperoxide (TBHP) under comparable experimental conditions [6]. It makes hydroperoxy sultams potentially possible epoxidation agents. However, the reaction of HPS with various sulfides containing two nucleophilic centres, sulfur atom and double bond, led only to the electrophilic attack at sulfur atom, and no traces of epoxides were detected in the reaction system. Taking into account these facts it is reasonable to investigate the interaction of HPS with substance containing only one * Corresponding author. E-mail address: [email protected] (O. Makota). 0926-860X/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2007.02.013
nucleophilic centre—double bond. It allows to exclude a possible competition of nucleophiles for oxygen atom of –OOH group and to direct the electrophilic attack of hydroperoxide exclusively on multiple bond of unsaturated compound. In this work, the epoxidation ability of hydroperoxy sultams (Table 1) in the epoxidation reaction of cyclooctene in the presence of catalyst—molybdenum boride MoB is investigated. 2. Experimental 2.1. Catalytic epoxidation The epoxidation process of cyclooctene was carried out in an argon atmosphere in a thermostated glass reactor fitted with a reflux condenser and a magnetic stirrer. In a typical run of catalytic measurement, the reactor was loaded with 0.005 g of catalyst, 0.3 ml of cyclooctene and proper amounts of HPS and solvent. It is established that in the absence of catalyst HPS does not decompose and the epoxide is not formed under the reaction conditions. The reaction mixtures were analyzed by using a Hewlett Packard HP 6890 N chromatograph, a capillary column DB-1 (60 m 0.32 mm 0.5 mm) packed with dimethylsiloxane. The column temperature was changed from 50 up to 250 8C with rate of 108 in 1 min. The hydroperoxide concentration was determined by iodometric titration [9].
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Table 1 Hydroperoxy sultams investigated in the epoxidation reaction of cyclooctene catalyzed by MoB Hydroperoxy sultam
HPS-1
HPS-9
HPS-2
HPS-10
HPS-3
HPS-11
HPS-4
HPS-12
HPS-5
HPS-13
HPS-6
HPS-14
HPS-7
HPS-15
HPS-8
HPS-16
2.2. General methods
2.3. General procedure for the preparation of HPS
Melting points were determined on Boetius micromelting-point apparatus and are corrected. IR spectra are expressed in cm 1 and were recorded on Genisis FTIR Unicam Analytical System (ATI Mattson) using KBr pellets. 1 H NMR spectra was recorded on 200-MHz (Varian Gemini200), 300-MHz (Varian Gemini-300) and 400-MHz (Varian Unity-400). The chemical shifts (d) are expressed in ppm relative to tetramethylsilane (TMS) as internal standard. 13C NMR spectra was received on the named spectrometers. Electron impact mass spectra (EI-MS) was recorded on a Quadrupol-MS VG 12-250 at an ionising voltage of 70 eV. Elemental analysis was determined on Heraeus CHNO Rapid Analyzer.
Some hydroperoxy sultams were already described and prepared by procedure: HPS-1 [10], HPS-2 [6], HPS-3 [11], HPS-4 [5], HPS-11 [12] and HPS-5, HPS-6, HPS-10, HPS-12, HPS-13 and HPS-14 [13]. HPS-7, HPS-8, HPS-9, HPS-15 and HPS-16 were prepared for the first time (Scheme 1). The synthesis of isothiazolium salts 1 were conveniently performed by intramolecular cyclocondensation of b-thiocyanatovinyl aldehydes and the varied substituted anilines in the presence of perchloric acid in acetic acid. The oxidation of the 4,5-dimethylisothiazolium salts 1a and b with 30% H2O2 in glacial acetic acid at room temperature gave the stable 3-hydroperoxysultim HPS-8 after 24 h and the
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dissolution of salt 1a, a colourless precipitate of HPS-8 was obtained after 24 h and isolated. The crude product was washed with water. Yield 35%; m.p. 132–134 8C; IR (KBr) 1062 (SO) cm 1; 1H NMR (acetone-d6, 300 MHz): d (ppm) 2.05, 2.13 (s, 6H), 5.86 (s, 1H), 7.53–7.83 (m, 3H), 11.21 (s, 1H); 13C NMR (acetone-d6, 50 MHz): d (ppm) 12.2, 14.3, 95.9, 117.4, 124.5, 132.6, 133.4, 134.1, 135.3, 136.6, 137.7; EI-MS (m/z) 330.0 (M H2O)+; anal. calcd. for C11H11Cl2NO3S (308.2): C 42.87, H 3.60, N 4.54, O 10.40; found: C 42.88, H 3.63, N 4.59, O 10.23. 2.6. Synthesis of 2-(2,5-dichlorophenyl)-2,3-dihydro-3hydroperoxy-4,5-dimethylisothiazole 1,1-dioxide (HPS-7) and 2-(3,5-dichlorophenyl)-2,3-dihydro-3-hydroperoxy-4,5dimethylisothiazole 1,1-dioxide (HPS-9) H2O2 (0.7 ml, 30%) was added to a stirred suspension of 1a and b (0.26 mmol) in AcOH (0.7 ml) at room temperature. After dissolution of salts 1a and b a colourless precipitates of HPS-7 and HPS-9 were obtained after 24–96 h and isolated. The crude products were washed with water. 2.6.1. HPS-7 Yield 60%; m.p. 175–178 8C; IR (KBr) 1291 (SO2) 1170 (SO2) cm 1; 1H NMR (acetone-d6, 300 MHz): d (ppm) 2.11, 2.15 (s, 6H), 6.05 (s, 1H), 7.57–7.86 (m, 3H), 10.85 (s, 1H); 13C NMR (acetone-d6, 50 MHz): d (ppm) 7.5, 12.2, 93.3, 122.7, 131.3, 132.6, 133.3, 133.4, 134.2, 134.4, 137.2; EI-MS (m/z) 346.0 (M H2O)+; anal. calcd. for C11H11Cl2NO4S (324.2): C 40.75, H 3.43, N 4.32, O 19.74; found: C 40.43, H 3.15, N 4.23, O 19.55.
3-hydroperoxysultams HPS-7 and HPS-9 after 24–96 h stirring. Furthermore, the oxidation of the 2,4,5-triphenyl (1c and d) substituted isothiazolium salts with H2O2 at room temperature offered the 3-hydroperoxysultams HPS-15 and HPS-16 after 48–192 h, respectively. The mechanism of the oxidation is shown in Scheme 1.
2.6.2. HPS-9 Yield 74%; m.p. 176–177 8C; IR (KBr) 1286 (SO2) 1142 (SO2) cm 1; 1H NMR (acetone-d6, 300 MHz): d (ppm) 2.13, 2.15 (s, 6H), 6.02 (s, 1H), 7.30–7.62 (m, 3H), 10.64 (s, 1H); 13C NMR (acetone-d6, 50 MHz): d (ppm) 7.2, 11.9, 91.4, 118.2, 119.2, 124.0, 124.7, 126.7, 133.2, 136.1, 137.9, 139.2; EI-MS (m/z) 346.0 (M H2O)+; anal. calcd. for C11H11Cl2NO4S (324.2): C 40.75, H 3.43, N 4.32, O 19.74; found: C 40.29, H 3.67, N 4.32, O 19.81.
2.4. Synthesis of 4,5-dimethyl-2-phenyl- (1a and b), 2,4,5triphenyl- (1c) and 5-(4-methoxyphenyl)-2,4-diphenylisothiazolium perchlorates (1d)
2.7. Synthesis of 2,3-dihydro-2-(4-trifluoromethylphenyl)3-hydroperoxy-4,5-diphenyliosthiazole 1,1-dioxide (HPS15)
Compounds 1c and d were already described in Refs. [14,15], respectively. The salts 1a and b were prepared for the first time according to literature procedure [16]. Yields and melting points are 1a: 90%, 178–180 8C and 1b: 96%, 182– 184 8C.
H2O2 (0.7 ml, 30%) was added to a stirred suspension of 1c (0.26 mmol) in AcOH (0.7 ml) at room temperature. After dissolution of salt 1c, a colourless precipitate of HPS-15 was obtained after 72–192 h and isolated. The crude product was washed with water. Yield 81%; m.p. 134–137 8C; IR (KBr) 1290 (SO2) 1126 (SO2) cm 1; 1H NMR (acetone-d6, 300 MHz): d (ppm) 7.20 (s, 1H), 7.42–7.89 (m, 14H), 11.61 (s, 1H); 19F NMR (acetone-d6, 282 MHz): d (ppm) 63.13 (s, 3F); 13C NMR (acetone-d6, 50 MHz): d (ppm) 90.5, 120.9, 128.0, 129.0 (q, J = 212.3 Hz, CF3), 130.0, 130.2, 130.4, 130.7, 130.9, 131.0, 131.2, 131.3,
Scheme 1.
2.5. Synthesis of 2-(2,5-dichlorophenyl)-2,3-dihydro-3hydroperoxy-4,5-dimethylisothiazole 1-oxide (HPS-8) H2O2 (0.7 ml, 30%) was added to a stirred suspension of 1a (0.26 mmol) in AcOH (0.7 ml) at room temperature. After
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131.5, 131.8, 133.6, 138.4, 140.8, 141.8, 146.4; EI-MS (m/z) 429.0 (M H2O)+ ; anal. calcd. for C22H16F3NO4S (447.4): C 59.05, H 3.60, N 3.13, O 14.30; found: C 58.70, H 3.69, N 3.04, O 14.45. 2.8. Synthesis of 2,3-dihydro-3-hydroperoxy-5-(4methoxyphenyl)-2-(2,4-dinitrophenyl)-4-phenyl-isothiazole 1,1-dioxide (HPS-16) H2O2 (0.7 ml, 30%) was added to a stirred suspension of 1d (0.26 mmol) in AcOH (0.7 ml) at room temperature. After dissolution of salt 1d, a colourless precipitate of HPS-16 was obtained after 48 h and isolated. The crude product was washed with water. Yield 80%; m.p. 120–124 8C; IR (KBr) 15.37 (NO2), 1346 (NO2), 1295 (SO2) 1157 (SO2) cm 1; 1H NMR (acetone-d6, 200 MHz): d (ppm) 3.84 (s, 3H), 6.66 (s, 1H), 6.96–7.03 (m, 4H), 7.35–8.38 (m, 8H); 13C NMR (acetone-d6, 75 MHz): d (ppm) 56.38, 94.87, 116.54, 122.94, 129.71, 130.36, 130.72, 130.85, 131.36, 131.67, 132.36, 132.46, 132.94, 138.67, 143.62, 147.02, 149.93, 162.92; EI-MS (m/z) 481.0 (M H2O)+; anal. calcd. for C22H17N3O9S (499.5): C 52.91, H 3.43, N 8.41, O 28.83; found: C 52.86, H 3.32, N 8.39, O 28.92. 3. Results and discussion The results of the catalytic epoxidation of cyclooctene by some HPS in the presence of MoB at 20 8C in chloroform and at 30 8C in chlorobenzene are summarized in Table 2. The data indicate that investigated hydroperoxides have a different efficiency in the catalytic reaction of epoxide formation. The nature of the substituents in hydroperoxide molecule has significant effect on activity of oxygen atom of hydroperoxide group in electrophilic attack on double bond of cyclooctene. A comparison of HPS-1 and HPS-2 exhibites that in both chlorobenzene and chloroform solvents higher epoxide yield is observed in the presence of chlorine atoms in aromatic ring at nitrogen atom. On the other hand, tert-butyl group in orthoposition to nitrogen atom less favours the epoxide formation. The results of reaction with HPS-3 and HPS-4 which containing the identical substituent in aromatic ring –COOCH3 demonstrate (Table 2) that the hydroperoxide efficiency in the reaction of epoxide formation is also increased in the presence of two methyl groups at double bond of five member cycle. The presence of only –NO2 group (HPS-5) in a paraposition to bond of nitrogen with aromatic ring is not
177
favourably for proceeding of the catalytic epoxidation reaction. However, in the case of HPS with both –NO2 group in a paraposition and chlorine atom in ortho-position (HPS-6) the epoxide yield increased in chlorobenzene from 0 (with HPS-5) to 10% (with HPS-6) and in chloroform from 1.5 to 15% (see Table 2). The obtained results show that increasing of electrophilic character of peroxide oxygen atom due to the induction effect of chlorine atoms in aromatic ring at nitrogen atom leads to the increase in epoxide yield. Higher yield of epoxycyclooctane is observed for the first two HPS (HPS-1 and HPS-2) in chlorobenzene as solvent, whereas for other HPS the best results are obtained in chloroform (Table 2). Since for the majority of HPS used higher yields of epoxide have been obtained in chloroform, further investigations were carried out in this solvent. Additionally, for reason to investigate the effective of HPS consumption on epoxide formation, the hydroperoxide conversion is also determined in the further experiments. The obtained results of the epoxidation process of cyclooctene with HPS catalyzed by MoB at 27 8C in chloroform are given in Figs. 1–4 and Table 3. One can see that the consumed amount of HPS and the formed amount of epoxycyclooctane as well as selectivity of epoxide formation are appreciably defined by HPS structure. The highest hydroperoxide conversions are observed in the cases of HPS-1, HPS-8, HPS-9 and HPS-10, whereas the HPS-11 and HPS-14 show the lowest value of this parameter. It should be noted, HPS-1 is partially transformed to epoxide, as well as HPS-10 is spent mainly unproductively. The data presented in Figs. 3 and 4 indicate that the highest amount of epoxide was formed when HPS-7 was used in the process of cyclooctene epoxidation. In this case, the selectivity of epoxide formation (Table 3) was highest too. HPS-1, HPS-9 and HPS-13 show intermediate selectivity. In the presence of other HPS the selectivity does not exceed 8%.
Table 2 Yield of epoxycyclooctane in the reaction of HPS with cyclooctene catalyzed by MoB Hydroperoxy sultam
HPS-1
HPS-2
HPS-3
HPS-4
HPS-5
HPS-6
Yielda (%) Yieldb (%)
48 21
19 10
6 12.5
5 21.5
0 1.5
10 15
a Reaction conditions: T = 30 8C, chlorobenzene 1 ml, cyclooctene 0.3 ml, 0.01 mol/l HPS, catalyst 0.005 g. b Reaction conditions: T = 20 8C, chloroform 5 ml, cyclooctene 0.3 ml, 0.01 mol/l HPS, catalyst 0.005 g. The reaction time is 40 h.
Fig. 1. HPS concentration as a function of reaction time in the epoxidation reaction: HPS-1 (1), HPS-16 (2), HPS-15 (3), HPS-8 (4), HPS-11 (5). Reaction conditions: T = 27 8C, chloroform 3.5 ml, cyclooctene 0.3 ml, 0.01 mol/l HPS and catalyst 0.005 g.
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Fig. 2. HPS concentration as a function of reaction time in the epoxidation reaction: HPS-10 (6), HPS-9 (7), HPS-7 (8), HPS-12 (9), HPS-13 (10), HPS-14 (11). Reaction conditions: T = 27 8C, chloroform 3.5 ml, cyclooctene 0.3 ml, 0.01 mol/l HPS and catalyst 0.005 g.
Fig. 4. Epoxycyclooctane (EP) concentration as a function of reaction time in the epoxidation reaction: HPS-10 (6), HPS-12 (7), HPS-14 (8), HPS-13 (9), HPS-9 (10), HPS-7 (11). Reaction conditions: T = 27 8C, chloroform 3.5 ml, cyclooctene 0.3 ml, 0.01 mol/l HPS and catalyst 0.005 g.
The comparison of epoxidation process results obtained with HPS-7 and HPS-9 suggests that a-position of chlorine atom to bond of nitrogen with aromatic ring in structure of HPS is favourably disposed for selective transformation of hydroperoxide to epoxide. The corroboration of positive influence of chlorine atoms in a a-position on the epoxidation reaction are values of selectivity obtained by using HPS-12 and HPS-13. As it can be seen from Table 3, the introduction of chlorine atom in a a-position to bond of nitrogen with aromatic ring is resulted in increasing of epoxycyclooctane formation selectivity from 2% with HPS-12 to 19% in the case of HPS-13. On the other hand, in the absence of substituents in aromatic ring only nonproductive HPS consumption is observed. The substituents –CF3, –NO2 and –OCH3 in para-position to bond of nitrogen with aromatic ring slightly
influence on HPS selectivity in the epoxidation process and in their presence the lowest selectivity of epoxide formation is obtained. From Table 3, one can see also that compound HPS-7 is fourfold more efficient compared to HPS-8 regarding epoxide yield (33% versus 8%). This effect might be due to different oxidation state of sulfur atom in both compounds (see Table 1). It is reasonable to assume that some part of non-productive decomposition of hydroperoxide in case of HPS-8 is connected with further oxidation of sulfur atom. The low selectivity of epoxide formation indicates the significant contribution of nonproductive HPS decomposition process in the overall process of hydroperoxide consumption. Therefore, the hydroperoxide decomposition process in the absence of olefine in reaction system is also investigated. The
Fig. 3. Epoxycyclooctane (EP) concentration as a function of reaction time in the epoxidation reaction: HPS-11 (1), HPS-15 (2), HPS-16 (3), HPS-8 (4), HPS1 (5). Reaction conditions: T = 27 8C, chloroform 3.5 ml, cyclooctene 0.3 ml, 0.01 mol/l HPS and catalyst 0.005 g.
Fig. 5. HPS concentration as a function of reaction time in the decomposition reaction: HPS-10 (1), HPS-7 (2), HPS-1 (3), HPS-15 (4), HPS-9 (5), HPS-14 (6), HPS-13 (7). Reaction conditions: T = 27 8C, chloroform 3.8 ml, 0.01 mol/l HPS and catalyst 0.005 g.
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Table 3 HPS conversion (Conv.) and selectivity (Sel.) of epoxycyclooctane formation (in account on consumpted hydroperoxide) in the epoxidation reaction of cyclooctene with HPS catalyzed by MoB Hydroperoxy sultam
Conv. HPS (%)
Sel. (%)
Hydroperoxy sultam
Conv. HPS (%)
Sel. (%)
HPS-1 HPS-7 HPS-8 HPS-9 HPS-10 HPS-11
93 81 93 90 92 41
22 33 8 23 1 5
HPS-12 HPS-13 HPS-14 HPS-15 HPS-16
75 53 39 76 84
2 19 6 5 5
Reaction conditions: T = 27 8C, chloroform 3.5 ml, cyclooctene 0.3 ml, 0.01 mol/l HPS, catalyst 0.005 g. The reaction time is 4 h.
Table 4 HPS conversion in the decomposition reaction of HPS catalyzed by MoB and amount of HPS additionally consumpted in the presence of cyclooctene (DHPS) Hydroperoxy sultam
HPS-1
HPS-7
HPS-9
HPS-10
HPS-13
HPS-14
HPS-15
Conv. HPS (%) DHPS (%)
65 28
69 12
47 43
76 16
25 28
32 7
56 20
Reaction conditions: T = 27 8C, chloroform 3.8 ml, 0.01 mol/l HPS, catalyst 0.005 g. The reaction time is 4 h.
experimental results given in Fig. 5 demonstrate that the HPS decomposition reaction proceeds actively enough. Hence, the low selectivity of epoxide formation in epoxidation process can be result of proceeding of parallel nonproductive HPS decomposition reaction. As it can be seen from Table 4, the maximal HPS conversion in the catalytic decomposition process is observed in the case of HPS-10 whereas HPS-13 and HPS-14 demonstrate minimum activity in this process. Other HPS show intermediate activity in the decomposition reaction and the conversions were from 47 to 69%. The comparison of results obtained in both decomposition and epoxidation catalytic reactions exhibites that in the presence of olefine the hydroperoxides consumption is increased. The amount of hydroperoxide additionally consumpted in the presence of cyclooctene (DHPS, Table 4) considerably depends on the hydroperoxide structure. In the case of the most effective epoxidation agent HPS-7, the additional hydroperoxide amount is less than amount of hydroperoxide spent on the epoxide formation. This fact indicates the inhibitory effect of olefine on the process of unproductive decomposition of hydroperoxide. This result is consistent with [17] where epoxidation of octene-1 with tertbutyl hydroperoxide in the presence of MoB2 as catalyst was carried out. It is due to the decrease in the number of the catalytic sites of hydroperoxide decomposition (catalyst– hydroperoxide complex) in the presence of olefine and the increase in epoxidation sites (catalyst–olefine complex) which reacts with hydroperoxide and gives epoxide. The change in the direction of hydroperoxide conversion from decomposition to epoxidation with an increase in the olefine concentration is the result of the replacement of the hydroperoxide by the olefine in the catalytic site responsible for hydroperoxide decomposition. In the presence of other HPS, the additional hydroperoxide amount is higher than amount of hydroperoxide which should be spent for epoxide formation. It is probably caused by the
further transformation of epoxide or oxidation of cyclooctene without formation of epoxide. With the purpose to get some information about the influence of reaction temperature on the process, the epoxidation reaction of cyclooctene in the presence of one of the more effective hydroperoxy sultams (HPS-1) was carried out at temperatures between 20 and 30 8C. From linear relationship between ln[HPS] and reaction time the pseudo-first-order reaction rate constants (k) were calculated. The activation energy (Ea) was calculated from the Arrhenius plot (Fig. 6). We have found that the process of epoxide formation during the interaction of cyclooctene with HPS-1 in the presence of MoB has very high activation energy, Ea = 210 kJ/mol. It is not typical for the catalytic epoxidation process of olefins by alkylhydroperoxides. For example, the activation energy of epoxide formation process during the interaction of octene-1 (linear analogue of cyclooctene) with TBHP in
Fig. 6. The ln k as a function of the inverse of reaction temperature. Reaction conditions: chloroform 3.5 ml, cyclooctene 0.3 ml ml, 0.01 mol/l HPS and catalyst 0.005 g.
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the presence of MoB and MoB2 determined by us equals 108 and 64 kJ/mol, respectively. The activation energy of epoxidation reaction of cyclohexene with TBHP catalyzed by Mo(VI) supported on imidazole-containing polymer equals 25 kJ/mol [18] and reaction of oleic acid with same hydroperoxide catalyzed by [Mo(O)2(SAP)(EtOH)] equals 99 kJ/mol [19].
4. Conclusion We have found that hydroperoxy sultams can be used as the epoxidation agents in the catalytic process of cyclooctene epoxidation in the presence of MoB at 27 8C. HPS with chlorine atoms in aromatic ring at nitrogen atom were the most effective in this process. It allows to assume that chlorine atoms increase the electrophilic character of peroxide oxygen atom and evidently also stabilize an intermediate cyclooctene– catalyst–hydroperoxide complex responsible for the epoxide formation. It was shown that the reaction of epoxide formation in the case of HPS-1 proceeds with activation energy 210 kJ/mol. Further investigation will be focused on searching of HPS optimum structure which ensures high selectivity of epoxide formation at low temperatures in the catalytic epoxidation reactions.
Acknowledgment The work was partly supported by the Deutscher Akademischer Austauschdienst (DAAD).
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