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Volumn , Issue 19, 2007, Pages 3058-3062

Guanidinium salt functionalized PEG: An effective and recyclable homogeneous catalyst for the synthesis of cyclic carbonates from CO2 and epoxides under solvent-free conditions

(5) Dou, Xiao Yong a Wang, Jin Quan a Du, Ya a Wang, Er a He, Liang Nian a

a NANKAI UNIVERSITY (China)

Author keywords

Carbon dioxide; Cycloaddition; Epoxide; Functionalized polyethylene glycol; Guanidinium bromide

Indexed keywords

BROMIDE; CARBON DIOXIDE; CARBONIC ACID; EPOXIDE; GUANIDINE; MACROGOL; ORGANIC SOLVENT; SODIUM CHLORIDE;

ARTICLE; CATALYSIS; CHEMICAL REACTION; CHEMICAL STRUCTURE; CYCLOADDITION; RECYCLING; SYNTHESIS;

EID: 37249033099 PISSN: 09365214 EISSN: None Source Type: Journal
DOI: 10.1055/s-2007-992362 Document Type: Article

Times cited : (78)

References (66)

1
- 0043251665
- (a) Anastas, P. T. Green Chem. 2003, 5, G29.
- (2003) Green Chem , vol.5
- Anastas, P.T.¹

2
- 32044461489
- (b) Williamson, T. C.; Kirchhoff, M.; Anastas, P. T. Green Chem. 2000, 2, G85.
- (2000) Green Chem , vol.2
- Williamson, T.C.¹ Kirchhoff, M.² Anastas, P.T.³

3
- 0039000211
- (c) Anastas, P. T.; Lankey, R. L. Green Chem. 2000, 2, 289.
- (2000) Green Chem , vol.2 , pp. 289
- Anastas, P.T.¹ Lankey, R.L.²

4
- 0033440041
- (d) Clark, J. H. Green Chem. 1999, 1, 1.
- (1999) Green Chem , vol.1 , pp. 1
- Clark, J.H.¹

5
- 0030547180
- Darensbourg, D. J.; Holtcamp, M. W. Coord. Chem. Rev. 1996, 153, 155.
- (1996) Coord. Chem. Rev , vol.153 , pp. 155
- Darensbourg, D.J.¹ Holtcamp, M.W.²

6
- 2342477255
- Shaikh, A.-A. G.; Sivaram, S. Chem. Rev. 1996, 96, 951.
- (1996) Chem. Rev , vol.96 , pp. 951
- Shaikh, A.-A.G.¹ Sivaram, S.²

7
- 3042698413
- Yoshida, M.; Ihara, M. Chem. Eur. J. 2004, 10, 2886.
- (2004) Chem. Eur. J , vol.10 , pp. 2886
- Yoshida, M.¹ Ihara, M.²

8
- 0037454053
- Clements, J. H. Ind. Eng. Chem. Res. 2003, 42, 663.
- (2003) Ind. Eng. Chem. Res , vol.42 , pp. 663
- Clements, J.H.¹

9
- 0034644564
- Parrish, J. P.; Salvatore, R. N.; Jung, K. W. Tetrahedron 2000, 56, 8207.
- (2000) Tetrahedron , vol.56 , pp. 8207
- Parrish, J.P.¹ Salvatore, R.N.² Jung, K.W.³

10
- 0001288378
- Peppel, W. J. Ind. Eng. Chem. Res. 1958, 50, 767.
- (1958) Ind. Eng. Chem. Res , vol.50 , pp. 767
- Peppel, W.J.¹

11
- 0027553201
- For examples of the coupling of CO2 and epoxides catalyzed by solid catalysts systems, see: (a) Nishikubo, T, Kameyama, A, Yamashita, J, Tomoi, M, Fukuda, W. J. Polym. Sci, Part A: Polym. Chem. 1993, 31, 939
- 2 and epoxides catalyzed by solid catalysts systems, see: (a) Nishikubo, T.; Kameyama, A.; Yamashita, J.; Tomoi, M.; Fukuda, W. J. Polym. Sci., Part A: Polym. Chem. 1993, 31, 939.

12
- 22544442751
- (b) Du, Y.; Cai, F.; Kong, D. L.; He, L. N. Green Chem. 2005, 7, 518.
- (2005) Green Chem , vol.7 , pp. 518
- Du, Y.¹ Cai, F.² Kong, D.L.³ He, L.N.⁴

13
- 0035746802
- (c) Tu, M.; Davis, R. J. J. Catal. 2001, 199, 85.
- (2001) J. Catal , vol.199 , pp. 85
- Tu, M.¹ Davis, R.J.²

14
- 0037173397
- (d) Yasuda, H.; He, L. N.; Sakadura, T. J. Catal. 2002, 209, 547.
- (2002) J. Catal , vol.209 , pp. 547
- Yasuda, H.¹ He, L.N.² Sakadura, T.³

15
- 0042809564
- (e) Yasuda, H.; He, L. N.; Sakadura, T. Stud. Surf. Sci. Catal. 2003, 145, 259.
- (2003) Stud. Surf. Sci. Catal , vol.145 , pp. 259
- Yasuda, H.¹ He, L.N.² Sakadura, T.³

16
- 0242607608
- (f) Aresta, M.; Dibenedetto, A.; Gianfrate, L.; Pastore, C. Appl. Catal. A: Gen. 2003, 255, 5.
- (2003) Appl. Catal. A: Gen , vol.255 , pp. 5
- Aresta, M.¹ Dibenedetto, A.² Gianfrate, L.³ Pastore, C.⁴

17
- 9744267180
- (g) Aresta, M.; Dibenedetto, A.; Gianfrate, L.; Pastore, C. J. Mol. Catal. A: Chem. 2003, 204, 245.
- (2003) J. Mol. Catal. A: Chem , vol.204 , pp. 245
- Aresta, M.¹ Dibenedetto, A.² Gianfrate, L.³ Pastore, C.⁴

18
- 37249048573
- (h) Yano, T.; Matsui, H.; Koike, T.; Isighuro, H.; Fujihara, H.; Yoshihara, M.; Maeshima, T. Chem. Commun. 1997, 1229.
- (1997) Chem. Commun , pp. 1229
- Yano, T.¹ Matsui, H.² Koike, T.³ Isighuro, H.⁴ Fujihara, H.⁵ Yoshihara, M.⁶ Maeshima, T.⁷

19
- 0035812997
- (i) Bhanage, B. M.; Fujita, S.; Ikushima, Y.; Arai, M. Appl. Catal. A: Gen. 2001, 219, 259.
- (2001) Appl. Catal. A: Gen , vol.219 , pp. 259
- Bhanage, B.M.¹ Fujita, S.² Ikushima, Y.³ Arai, M.⁴

20
- 0033549092
- (j) Yamaguchi, K.; Ebitani, K.; Yoshida, T.; Yoshida, H.; Kaneda, K. J. Am. Chem. Soc. 1999, 121, 4526.
- (1999) J. Am. Chem. Soc , vol.121 , pp. 4526
- Yamaguchi, K.¹ Ebitani, K.² Yoshida, T.³ Yoshida, H.⁴ Kaneda, K.⁵

21
- 11944265330
- (k) Xiao, L. F.; Li, F. W.; Xia, C. G. Appl. Catal. A: Gen. 2005, 279, 125.
- (2005) Appl. Catal. A: Gen , vol.279 , pp. 125
- Xiao, L.F.¹ Li, F.W.² Xia, C.G.³

22
- 9744267180
- (l) Aresta, M.; Dibenedetto, A.; Gianfrate, L.; Pastore, C. J. Mol. Catal. A: Chem. 2003, 204, 245.
- (2003) J. Mol. Catal. A: Chem , vol.204 , pp. 245
- Aresta, M.¹ Dibenedetto, A.² Gianfrate, L.³ Pastore, C.⁴

23
- 0036159906
- (m) Kim, H. S.; Kim, J. J.; Kwon, H. N.; Chung, M. J.; Lee, B. G.; Jang, H. G. J. Catal. 2002, 205, 226.
- (2002) J. Catal , vol.205 , pp. 226
- Kim, H.S.¹ Kim, J.J.² Kwon, H.N.³ Chung, M.J.⁴ Lee, B.G.⁵ Jang, H.G.⁶

24
- 16244410453
- (n) Shi, F.; Zhang, Q.; He, Y.; Deng, Y. J. Am. Chem. Soc. 2005, 127, 4182.
- (2005) J. Am. Chem. Soc , vol.127 , pp. 4182
- Shi, F.¹ Zhang, Q.² He, Y.³ Deng, Y.⁴

25
- 20344394685
- (o) Srivastava, R.; Srinivas, D.; Ratnasamy, P. J. Catal. 2005, 233, 1.
- (2005) J. Catal , vol.233 , pp. 1
- Srivastava, R.¹ Srinivas, D.² Ratnasamy, P.³

26
- 25444475496
- (p) Xie, H. B.; Duan, H. F.; Li, S. H.; Zhang, S. B. New J. Chem. 2005, 29, 1199.
- (2005) New J. Chem , vol.29 , pp. 1199
- Xie, H.B.¹ Duan, H.F.² Li, S.H.³ Zhang, S.B.⁴

27
- 0037474637
- (q) Barbarini, A.; Maggii, R.; Mazzacani, A.; Mori, G.; Sartori, G.; Sartorio, R. Tetrahedron Lett. 2003, 44, 2931.
- (2003) Tetrahedron Lett , vol.44 , pp. 2931
- Barbarini, A.¹ Maggii, R.² Mazzacani, A.³ Mori, G.⁴ Sartori, G.⁵ Sartorio, R.⁶

28
- 33645792625
- (r) Wang, J. Q.; Kong, D. L.; Chen, J. Y.; Cai, F.; He, L. N. J. Mol. Catal. A: Chem. 2006, 249, 143.
- (2006) J. Mol. Catal. A: Chem , vol.249 , pp. 143
- Wang, J.Q.¹ Kong, D.L.² Chen, J.Y.³ Cai, F.⁴ He, L.N.⁵

29
- 33645474279
- (s) Takahashi, T.; Watahiki, T.; Kitazume, S.; Yasuda, H.; Sakakura, T. Chem. Commun. 2006, 1664.
- (2006) Chem. Commun , pp. 1664
- Takahashi, T.¹ Watahiki, T.² Kitazume, S.³ Yasuda, H.⁴ Sakakura, T.⁵

30
- 33845957553
- (t) Wang, J. Q.; Yue, X. D.; Cai, F.; He, L. N. Catal. Commun. 2007, 8, 167.
- (2007) Catal. Commun , vol.8 , pp. 167
- Wang, J.Q.¹ Yue, X.D.² Cai, F.³ He, L.N.⁴

31
- 34248173385
- (u) Zhao, Y.; Tian, J. S.; Qi, X. H.; Han, Z. N.; Zhang, Y. Y.; He, L. N. J. Mol. Catal. A: Chem. 2007, 271, 284.
- (2007) J. Mol. Catal. A: Chem , vol.271 , pp. 284
- Zhao, Y.¹ Tian, J.S.² Qi, X.H.³ Han, Z.N.⁴ Zhang, Y.Y.⁵ He, L.N.⁶

32
- 22144432663
- (v) Srivastava, R.; Srinivas, D.; Ratnasamy, P. Appl. Catal. A: Gen. 2005, 289, 128.
- (2005) Appl. Catal. A: Gen , vol.289 , pp. 128
- Srivastava, R.¹ Srinivas, D.² Ratnasamy, P.³

33
- 33846931302
- (w) Zhu, A. L.; Jiang, T.; Han, B. X.; Zhang, J. C.; Xie, Y.; Ma, X. M. Green Chem. 2007, 9, 169.
- (2007) Green Chem , vol.9 , pp. 169
- Zhu, A.L.¹ Jiang, T.² Han, B.X.³ Zhang, J.C.⁴ Xie, Y.⁵ Ma, X.M.⁶

34
- 0038413985
- For recent reports concerning the properties and applications of PEGs, see: a
- For recent reports concerning the properties and applications of PEGs, see: (a) Heldebrant, D. J.; Jessop, P. G. J. Am. Chem. Soc. 2003, 125, 5600.
- (2003) J. Am. Chem. Soc , vol.125 , pp. 5600
- Heldebrant, D.J.¹ Jessop, P.G.²

35
- 0000951649
- (b) Annunziata, R.; Benaglia, M.; Cinquini, M.; Cozzi, F.; Tocco, G. Org. Lett. 2000, 2, 1737.
- (2000) Org. Lett , vol.2 , pp. 1737
- Annunziata, R.¹ Benaglia, M.² Cinquini, M.³ Cozzi, F.⁴ Tocco, G.⁵

36
- 11144296402
- (c) Reetz, M. T.; Wiesenhöfer, W. Chem. Commun. 2004, 2750.
- (2004) Chem. Commun , pp. 2750
- Reetz, M.T.¹ Wiesenhöfer, W.²

37
- 14644420299
- and references cited therein
- (d) Chen, J.; Spear, S. K.; Huddleston, J. G.; Rogers, R. D. Green Chem. 2005, 7, 64; and references cited therein,
- (2005) Green Chem , vol.7 , pp. 64
- Chen, J.¹ Spear, S.K.² Huddleston, J.G.³ Rogers, R.D.⁴

38
- 0038639869
- (e) Chandrasekhar, S.; Narsihmulu, C.; Sultana, S. S.; Reddy, N. R. Chem. Commun. 2003, 1716.
- (2003) Chem. Commun , pp. 1716
- Chandrasekhar, S.¹ Narsihmulu, C.² Sultana, S.S.³ Reddy, N.R.⁴

39
- 17644424685
- (f) Solinas, M.; Jiang, J.; Stelzer, O.; Leitner, W. Angew. Chem. Int. Ed. 2005, 44, 2291.
- (2005) Angew. Chem. Int. Ed , vol.44 , pp. 2291
- Solinas, M.¹ Jiang, J.² Stelzer, O.³ Leitner, W.⁴

40
- 14844321851
- (g) Hou, Z.; Theyssen, N.; Brinkmann, A.; Leitner, W. Angew. Chem. Int. Ed. 2005, 44, 1346.
- (2005) Angew. Chem. Int. Ed , vol.44 , pp. 1346
- Hou, Z.¹ Theyssen, N.² Brinkmann, A.³ Leitner, W.⁴

41
- 2942717056
- (h) Cernovska, K.; Kemter, M.; Gallmeier, H.-C.; Rzepecki, P.; Schrader, T.; König, B. Org. Biomol. Chem. 2004, 2, 1603.
- (2004) Org. Biomol. Chem , vol.2 , pp. 1603
- Cernovska, K.¹ Kemter, M.² Gallmeier, H.-C.³ Rzepecki, P.⁴ Schrader, T.⁵ König, B.⁶

42
- 20544448265
- (i) Attanasi, O. A.; Crescentini, L. D.; Favi, G.; Filippone, P.; Lillini, S.; Mantellini, F.; Santeusanio, S. Org. Lett. 2005, 7, 2469.
- (2005) Org. Lett , vol.7 , pp. 2469
- Attanasi, O.A.¹ Crescentini, L.D.² Favi, G.³ Filippone, P.⁴ Lillini, S.⁵ Mantellini, F.⁶ Santeusanio, S.⁷

43
- 0034696878
- (j) Jessop, P.; Wyne, D. C.; DeHaai, S.; Nakawatase, D. Chem. Commun. 2000, 693.
- (2000) Chem. Commun , pp. 693
- Jessop, P.¹ Wyne, D.C.² DeHaai, S.³ Nakawatase, D.⁴

44
- 30944459438
- (k) Du, Y.; Wang, J. Q.; Chen, J. Y.; Cai, F.; Tian, J. S.; Kong, D. L.; He, L. N. Tetrahedron Lett. 2006, 47, 1271.
- (2006) Tetrahedron Lett , vol.47 , pp. 1271
- Du, Y.¹ Wang, J.Q.² Chen, J.Y.³ Cai, F.⁴ Tian, J.S.⁵ Kong, D.L.⁶ He, L.N.⁷

45
- 0000135009
- For the properties and applications of ionic liquids, see: a
- For the properties and applications of ionic liquids, see: (a) Holbrey, J. D.; Seddon, K. R. Clean Prod. Process. 1999, 1, 223.
- (1999) Clean Prod. Process , vol.1 , pp. 223
- Holbrey, J.D.¹ Seddon, K.R.²

46
- 0347417134
- (b) Welton, T. Chem. Rev. 1999, 99, 2071.
- (1999) Chem. Rev , vol.99 , pp. 2071
- Welton, T.¹

47
- 0035923960
- (c) Gordon, C. M. Appl. Catal. A: Gen. 2001, 222, 101.
- (2001) Appl. Catal. A: Gen , vol.222 , pp. 101
- Gordon, C.M.¹

48
- 0000034575
- Wasserscheid, P.; Keim, W. Angew. Chem. In. Ed. 2000, 39, 3772.
- (d) Wasserscheid, P.; Keim, W. Angew. Chem. In. Ed. 2000, 39, 3772.

49
- 0035824303
- (e) Sheldon, R. Chem. Commun. 2001, 2399.
- (2001) Chem. Commun , pp. 2399
- Sheldon, R.¹

50
- 0034583251
- (f) Earle, M. J.; Seddon, K. R. Pure Appl. Chem. 2000, 72, 1391.
- (2000) Pure Appl. Chem , vol.72 , pp. 1391
- Earle, M.J.¹ Seddon, K.R.²

51
- 0036809725
- (g) Dupont, J.; de Souza, R. F.; Suarez, P. A. Z. Chem. Rev. 2002, 102, 3667.
- (2002) Chem. Rev , vol.102 , pp. 3667
- Dupont, J.¹ de Souza, R.F.² Suarez, P.A.Z.³

52
- 0037092828
- (h) Zhao, D. B.; Wu, M.; Kou, Y.; Min, E. Z. Catal. Today 2002, 74, 157.
- (2002) Catal. Today , vol.74 , pp. 157
- Zhao, D.B.¹ Wu, M.² Kou, Y.³ Min, E.Z.⁴

53
- 0037173845
- (i) Anthony, J. L.; Maginn, E. J.; Brennecke, J. F. J. Phys. Chem. B. 2002, 106, 7315.
- (2002) J. Phys. Chem. B , vol.106 , pp. 7315
- Anthony, J.L.¹ Maginn, E.J.² Brennecke, J.F.³

54
- 33646799466
- (j) Zhang, S. J.; Chen, Y. H.; Li, F. W.; Lu, X. M.; Dai, W. B.; Mori, R. Catal. Today 2006, 115, 61.
- (2006) Catal. Today , vol.115 , pp. 61
- Zhang, S.J.¹ Chen, Y.H.² Li, F.W.³ Lu, X.M.⁴ Dai, W.B.⁵ Mori, R.⁶

55
- 33646023707
- (k) Xie, H. B.; Li, S. H.; Zhang, S. B. J. Mol. Catal. A: Chem. 2006, 250, 30.
- (2006) J. Mol. Catal. A: Chem , vol.250 , pp. 30
- Xie, H.B.¹ Li, S.H.² Zhang, S.B.³

56
- 28444432285
- (l) Li, H.; Wu, J.; Brunel, S.; Monnet, C.; Baudry, R.; Perchee, P. L. Ind. Eng. Chem. Res. 2005, 44, 8641.
- (2005) Ind. Eng. Chem. Res , vol.44 , pp. 8641
- Li, H.¹ Wu, J.² Brunel, S.³ Monnet, C.⁴ Baudry, R.⁵ Perchee, P.L.⁶

57
- 0037078276
- (m) Violleau, F.; Thiehaud-Roux, S.; Borredon, E.; Gars, L. P. Tetrahedron 2002, 58, 8607.
- (2002) Tetrahedron , vol.58 , pp. 8607
- Violleau, F.¹ Thiehaud-Roux, S.² Borredon, E.³ Gars, L.P.⁴

58
- 37249032608
- (n) Xie, H. B.; Zhang, S. B.; Duan, H. F. Tetrahedron Lett. 2004, 45, 1271.
- (2004) Tetrahedron Lett , vol.45 , pp. 1271
- Xie, H.B.¹ Zhang, S.B.² Duan, H.F.³

59
- 8844246514
- (o) Duan, H. F.; Li, S. H.; Li, Y. J.; Xie, H. B.; Zhang, S. B.; Wang, Z. M. Chem. Res. Chin. Univ. 2004, 20, 568.
- (2004) Chem. Res. Chin. Univ , vol.20 , pp. 568
- Duan, H.F.¹ Li, S.H.² Li, Y.J.³ Xie, H.B.⁴ Zhang, S.B.⁵ Wang, Z.M.⁶

60
- 0000951649
- Annunziata, R.; Benaglia, M.; Cinquini, M.; Cozzi, F.; Tocco, G. Org. Lett. 2000, 2, 1737.
- (2000) Org. Lett , vol.2 , pp. 1737
- Annunziata, R.¹ Benaglia, M.² Cinquini, M.³ Cozzi, F.⁴ Tocco, G.⁵

61
- 84922428804
- (a) Pruszynski, P. Can. J. Chem. 1987, 65, 626.
- (1987) Can. J. Chem , vol.65 , pp. 626
- Pruszynski, P.¹

62
- 33845270855
- (b) Duan, H. F.; Zhang, S. B.; Lin, Y. J.; Qiu, Z. M.; Wang, Z. M. Chem. J. Chin. Univ. 2003, 24, 2024.
- (2003) Chem. J. Chin. Univ , vol.24 , pp. 2024
- Duan, H.F.¹ Zhang, S.B.² Lin, Y.J.³ Qiu, Z.M.⁴ Wang, Z.M.⁵

63
- 37249002980
- The pentaalkylguanidine 3 was synthesized from 1,3-dimethylimidazolidin-2-one(1, POCl3 and BuNH2 by the methods reported in the literature;12b colorless liquid; yield: 71, lit.12b 85, 1H NMR (300 MHz, CDCl 3, δ, 0.91 (t, J, 14.4 Hz, 3 H, Me, 1.33-141 (m, 2 H, CH2, 148-1.58 (m, 2 H, CH2, 2.79 (s, 6 H, Me, 3.14 (s, 4 H, NCH2, 3.34 s, 2 H, CH2
- 2).

64
- 37249055686
- Procedure for the Synthesis of PEG-Supported Guanidinium Bromide 4: To a solution of polyethylene glycol bromide (12 g, 0.002 mol) in toluene (150 mL, pentaalkylguanidine 3 (3.38 g, 0.02 mol) was added, and the resulting solution was stirred at 65°C for 72 h. After the reaction was completed, the solvent was removed under reduced pressure, and then anhyd Et2O (40 mL) was added. The product was precipitated and isolated by filtration, then washed by anhyd Et2O and dried to obtain the product 4 (94, white powder; mp 53-55°C. IR: 1638 (C=N) cm-1. 1H NMR (400 MHz, CDCl3, δ, 0.89 (t, J, 14.7 Hz, 6 H, 2 x Me, 1.29-1.36 (m, 4 H, 2 x CH2, 1.62-1.72 (m, 4 H, 2 x CH 2, 3.11 (s, 6 H, 2 x Me, 3.60 (m, 4 H, OCH2CH 2O, 13C NMR 75 MHz, CDCl3, δ, 13.08, 19.13, 31.69, 34.85, 43.08, 49.02, 69.90, 158.72
- 3): δ = 13.08, 19.13, 31.69, 34.85, 43.08, 49.02, 69.90, 158.72.

65
- 37249066396
- Representative Procedure for the Cycloaddition Reaction of Epoxide with CO2: In a 25-mL inner stainless-steel autoclave equipped with a magnetic stirrer, isopropyl glycidyl ether (15.8 mmol) and PEG-supported hexaalkylguanidinium bromide (0.5 mol, were added, and CO 2 (liquid, 3.0 MPa) was charged into the reactor at r.t. The initial pressure was generally adjusted to 4 MPa at 110°C. The reactor was heated at that temperature for 4 h. After cooling, the products were separated by adding Et2O and analyzed by a gas Chromatograph (Shimadzu GC-2014) equipped with a capillary column (RTX-5, 30 m x 0.25 μm) using a flame ionization detector and the side-products were detected by GC-MS. All of the products were further identified using GC-MS by comparing the retention times and fragmentation patterns with authentic samples. The structures of the isolated products were also characterized by 1H NMR and 13C NMR spectros
- 3): δ = 66.17, 68.84, 74.11, 114.57, 121.92, 129.63, 154.65, 157.71.

66
- 37249059068
- 4 and concentrated in vacuo to give the product cyclic carbonate. We conducted further reaction by the addition of successive portions of the epoxide to the recovered catalyst under identical reaction conditions.
- 4 and concentrated in vacuo to give the product cyclic carbonate. We conducted further reaction by the addition of successive portions of the epoxide to the recovered catalyst under identical reaction conditions.

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