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2-methoxyethanol: a remarkably efficient and alternative reaction medium for iodination of reactive aromatics using iodine and iodic acid.

Introduction

Aromatic iodo compounds are valuable and versatile synthetic intermediates in organic chemistry [1]. They react with nucleophiles such as amines or alkoxides to give the corresponding substituted products and can be lithiated to introduce electrophiles via halogen lithium exchange reaction [2]. They are also important and most reactive intermediate for various cross-coupling reactions and especially useful for formation of carbon-carbon and carbon-heteroatom bonds [3].

The moderate reactivity of iodine with aromatic substrates requires the addition of activating agents for its utilization. Generally, aromatic compounds are iodinated using iodine in presence of Lewis acid or an oxidizing agent [4].

Synthesis of iodoaromatics using various reaction medium and iodinating reagent involves [I.sub.2]/petroleum ether [5], KI/[H.sub.2]S[O.sub.4] in [H.sub.2]S[O.sub.4] [6], NaI/Chloramine-T in methanol [7], NaOCl/NaI in aqueous alcohol medium [8], KI/[H.sub.2][O.sub.2] in C[H.sub.3]COOH [9], KCl[O.sub.3]/KI/HCl in aqueous medium [10], and [I.sub.2]/NaB[O.sub.3] x [H.sub.2]O in ionic liquid [11]. The utility of alternative reaction solvents such as water [12], ionic liquid [13], flourous [14], supercritical media [15] and polyethylene glycol [PEG] [16] is rapidly growing. These solvents have attracted the attention of organic chemists due to their solvating ability and aptitude to act as a phase transfer catalyst, negligible vapour pressure, non-hazardous, easy work- up and economical cost. However many of these reported procedures have one or more disadvantages such as use of expensive catalysts, long reaction time, low selectivity, requirements of special apparatus and side reaction.

In continuation of earlier research program on iodination of reactive aromatics using iodine and iodic acid [17], herein we wish to report the use of 2-methoxyethanol as a reaction solvent.

Material and Methods

Melting points were determined in an open capillary tube and are uncorrected. IR spectra were recorded in KBr on a Perkin-Elmer spectrometer. [sup.1]H NMR spectra were recorded on a Gemini 300-MHZ instrument in CD[Cl.sub.3] as solvent and TMS as an internal standard. The mass spectra were recorded on EI-Shimadzu-GC-MS spectrometer. Elemental analyses were performed on a Carlo Erba 106 Perkin-Elmer model 240 analyzer.

General procedures for iodination of hydroxy aromatic aldehydes, hydroxy acetophenones, substituted anilines and phenols in ethanol, acetic acid and 2-methoxyethanol:

Mixture of different aromatic compounds (50 mmol), iodine (20 mmol) dissolved in 5 mL of 2-methoxyethanol and iodic acid (10 mmol) dissolved in water (1 mL) was added with shaking and refluxed for 3-8 minutes (tables 1-4). On cooling reaction mixture, crystalline solid product separated out (reaction monitored on TLC).

Obtained solid product was filtered through Buchner funnel. Physical data is given in Tables 1-4. For synthesis of di-iodo product 40 mmol of iodine and 20 mmol of iodic acid with 50 mmol of substrate was used.

Similar procedure was carried out by using 25 mL of ethanol or 20 mL of acetic acid. Results obtained by these procedures are shown in tables 1-4.

Spectral data of some selected compounds

4-Hydroxy-3,5-diiodo-benzaldehyde: IR ([cm.sup.-1]): 2852 (C-H stretch of CHO), 1660 (C=O), 1558 (C=C stretch). [sup.1]H NMR (CD[Cl.sub.3]): [delta] 7.72 (s, 2H, Ar-H), 8.42 (s, 1H, OH), 10.02 (s, 1H, CHO). [sup.13]C NMR (75 MHz, [DMSOd.sub.6], [delta], ppm):: 91.12 (C of two Ar-I), 131.64 (C of Ar-C), 139.42 (C of two Ar-H), 182.21 (C of Ar-OH), 191.37 (C of CHO). MS m/z: 374 ([M.sup.+]). Anal. calcd. for: [C.sub.7][H.sub.4][O.sub.2][I.sub.2]: C, 22.45; H, 1.06; I, 67.91. Found: C, 22.49; H, 1.09; I, 67.94.

3.5-Diiodo-4-methoxy-benzaldehyde: IR ([cm.sup.-1]): 2845 (C-H stretch of CHO), 1652 (C = O), 1548 (C = C stretch). [sup.1]H NMR (CD[Cl.sub.3]): [delta] 3.27 (s, 3H, OC[H.sub.3]), 7.85 (s, 2H, Ar-H), 9.97 (s, 1H, CHO). [sup.13]C NMR (75 MHz, [DMSOd.sub.6], [delta], ppm): 190.78 (C = O), 137.60, 88.23 (C of Aromatic ring), 60.92 (OC[H.sub.3]). MS m/z: 388 ([M.sup.+]). Anal.calcd. for: [C.sub.8][H.sub.6][O.sub.2][I.sub.2]: C, 24.74; H, 1.54; I, 65.46. Found: C, 24.68; H, 1.51; I, 65.42.

2,4-Dihydroxy-3,5-diiodoacetophenone: IR ([cm.sup.-1]): 3428 (OH), 1660 (C = O), 1555 (C = C stretch). [sup.1]H NMR (CD[Cl.sub.3]): [delta] 2.37 (s, 3H, C[H.sub.3]), 7.90 (s, 1H, Ar-H), 12.62 (s, 1H, OH), 8.92 (s, 1H, OH). [sup.13]C NMR (75 MHz, [DMSOd.sub.6], [delta], ppm): 24.17 (C of methyl group) 76.14 (C of two Ar-I), 141.29 (C of Ar-H), 178.24 (C of two Ar-OH), 197.68 (C of carbonyl group). MS m/z: 404 ([M.sup.+]). Anal.calcd. for: [C.sub.8][H.sub.6][O.sub.3][I.sub.2]: 23.76; H, 1.48; I, 62.87. Found: C, 23.80; H, 1.51; I, 62.93.

1-(1-Hydroxy-4-iodo-naphthalen-2-yl)-ethanone: IR ([cm.sup.-1]): 3438 (OH), 1664 (C = O), 1560 (C = C stretch). [sup.1]H NMR (CD[Cl.sub.3]): [delta] 2.35 (s, 3H, C[H.sub.3]), 6.25-7.91 (m, 5H, Ar-H), 14.12 (s, 1H, OH). [sup.13]C NMR (75 MHz, [DMSOd.sub.6], [delta], ppm): 200.37 (C = O), 164.95, 135.29, 133.20, 130.73, 127.28, 124.62, 122.47, 91.82 (C of Aromatic ring), 26.62 (C[H.sub.3]). MS m/z: 312 ([M.sup.+]). Anal.calcd for: [C.sub.12][H.sub.9][O.sub.2]I: C, 46.15; H, 2.88; I, 40.70. Found: C, 46.10; H, 2.86; I, 40.67.

2.6-diiodo-4-nitroaniline: IR ([cm.sup.-1]): 3348 (NH), 1553 (C = C), 1368 (N[O.sub.2]). [sup.1]H NMR (CD[Cl.sub.3]): [delta] 4.08 (s, 2H, N[H.sub.2]), 7.89 (s, 2H, Ar-H). [sup.13]C NMR (75 MHz, [DMSOd.sub.6], [delta], ppm): 156.20, 145.89, 135.33, 86.90 (C of Aromatic ring). MS m/z: 390 ([M.sup.+]). Anal.calcd. for: [C.sub.6][H.sub.4][N.sub.2][O.sub.2][I.sub.2]: C, 18.46; H, 1.02; I, 65.12. Found: C, 18.52; H, 1.05; I, 65.17.

2,6-diiodo-4-nitrophenol: IR ([cm.sup.-1]): 3442 (OH), 1557 (C = C), 1352 (N[O.sub.2]). [sup.1]H NMR (CD[Cl.sub.3]): [delta] 7.82 (s, 2H, Ar-H). [sup.13]C NMR (75 MHz, [DMSOd.sub.6], [delta], ppm): 161.86, 140.18, 134.70, 90.85. MS m/z: 391 ([M.sup.+]). Anal.calcd. for: [C.sub.6][H.sub.3][O.sub.3][I.sub.2]: C, 18.41; H, 0.76; I, 64.96. Found: C, 18.38; H, 0.75; I, 64.92.

Results and Discussion

2-methoxyethanol is non-halogenated, inexpensive and water soluble which facilitate its removal from reaction product. In view of this observation it was thought worthwhile to carry out iodination of reactive aromatics using iodine and iodic acid as iodinating agent in 2-methoxyethanol as an efficient and alternative reaction solvent (Scheme-1).

[FORMULA NOT REPRODUCIBLE IN ASCII]

In order to optimize the reaction conditions in terms of solubility, clean reaction conditions, isolation of product, time required for completion of reaction, yield and purity of product, we carried out the above reaction in ethanol and acetic acid and our results summarized in Table: 1-4. We found that 2-methoxyethanol is remarkably effective reaction solvent consuming shorter reaction time besides increasing yield of product (Table. 1-4). Encouraged by the results, we turned our attention towards variety substituted reactive aromatics. In all cases, the reaction proceeded smoothly in high yields at 120[degrees]C using 2-methoxyethanol as an attractive reaction solvent for iodination reaction.

Conclusion

We reported remarkably efficient reaction medium for modified practical procedure for iodination of aromatics using iodine-iodic acid in 2-methoxyethanol. Present method, offer additional advantages such as comparatively least requirement of amount of solvent, simple reaction conditions, no need of catalyst, economical process with easier setup and workup procedure giving high yields of desired product.

Acknowledgements

The authors gratefully acknowledge UGC-New Delhi for sanctioning major research grant (No. 38-267/2009). The authors are also thankful to principal, Yeshwant Mahavidyalaya, Nanded, for providing laboratory facilities and Director IICT, Hyderabad, for providing necessary instrumental facilities.

References and Notes

[1] Diederich, F. J.; Stang, P. J. Weinheim, Germany: Wiely-VCH, 1998.

[2] Wakefield, B. J. London: Academic press, 1988.

[3] a) Olivera, R.; Sanmartin, R.; Dominguez, E. Tetrahedron Lett. 2000, 41, 4357. [CrossRef] b) Qiang, L.; Juan, N.; Fan, Y.; Rui, Z.; Gang, Z.; Jie, T. Chin. J. Chem. 2004, 22, 419.

[4] Radner, F. J. Org. Chem. 1988, 53, 3548. [CrossRef]

[5] Joseph, R.; Pallan, P.; Sudalai, A.; Ravindranathan T. Tetrahedron Lett. 1995, 36, 609. [CrossRef]

[6] Mattern, D. L. J. Org. Chem. 1983, 48, 4772. [CrossRef]

[7] Hatanaka, Y.; Hashimoto, M.; Kurihara, H.; Nakayama, H.; Kanaoka, Y. J. Org. Chem. 1994, 59, 383. [CrossRef]

[8] Edgar, K. J.; Falling, S. N. J. Org .Chem. 1990, 55, 5287. [CrossRef]

[9] Suresh Kumar R. K.; Narender, N.; Rohitha, C. N.; Kulkarni, S. J. Synth.Commun. 2008, 38, 3894. [CrossRef]

[10] Sathiyapriya, R.; Joel Karunakaran, R. Synth. Commun. 2006, 36, 1915. [CrossRef]

[11] Bhilare, S. V.; Deorukhkar, A. R.; Darvatkar, N. B.; Salunkhe, M. M. Synth. Commun. 2008, 38, 2881. [CrossRef]

[12] a) Chen, J. J.; Spear, S. K.; Huddieston, J. G.; Robin, D. R. Green Chemistry 2005, 7, 64. [CrossRef] b) Zang, Z. H.; Yin, L.; Wang, Y. M.; Liu, J. Y.; Li, Y. Green Chemistry 2004, 6, 563. [CrossRef] c) Kumar, R.; Choudhary, P; Nimesh, S; Chandra, R. Green Chemistry 2006, 8, 356. [CrossRef]

[13] Helderant, D. J.; Jessop, P. G. J. Am. Chem. Soc. 2003, 125, 5600. [CrossRef]

[14] Chandrasekhar, S.; Narsihmulu, Ch.; Sultana, S. S.; Ramakrishna Reddy, N. Org. Lett. 2002, 4, 4399. [CrossRef]

[15] Jiang, R.; Kuang, Y. Q.; Sun, X. L.; Zhang, S. Tetrahedron Asymmetry, 2004, 15, 743. [CrossRef]

[16] Namboodiri, V. V.; Varma, R. S. Green Chemistry 2001, 3, 146. [CrossRef]

[17] a) Shinde, A. T.; Zangade, S. B.; Chavan, S. B.; Vibhute, A. Y.; Nalwar, Y. S.; Vibhute, Y. B. Synth. Commun. 2010, 40, 3506. [CrossRef] b) Patil, B. R.; Bhusare, S. R.; Pawar, R. P.; Vibhute, Y. B. Tetrahedron Lett. 2005, 46, 7179. [CrossRef] c) Patil, B. R.; Bhusare, S. R.; Pawar, R. P.; Vibhute, Y. B. Arkivoc 2006, i, 104. d) Zangade, S.; Mokle, S.; Shinde, A.; Vibhute, Y. Eur. J. Chem. 2012, 3, 314. [CrossRef]

[18] Khansole, S. V.; Mokle, S. S.; Sayyed, M. A.; Vibhute, Y. B. J. Chin. Chem. Soc. 2008, 55, 871.

[19] Aldrich Chemical Company. Handbook of Fine Chemicals; Aldrich Chemical Company: Bangalore, India, 2007-2008.

[20] Maciej, S.; Lech, S.; Katarzyna, W. Molecules 2004, 9, 617. [CrossRef]

[21] Gallo, R. D. C.; Gebara, K. S.; Muzzi, R. M.; Raminelli, C. J. Braz. Chem. Soc. 2010, 21, 770. [CrossRef]

[22] Agnieszka, Z.; Lech, S. Molecules 2005, 10, 1307. [CrossRef] Arvind M. Patil, Sainath B. Zangade, Yeshwant B. Vibhute*, and Sarala N. Kalyankar Laboratory of Organic Synthesis, Department of studies in Chemistry, Yeshwant Mahavidyalaya, Nanded-431602 (M.S) India.

* Corresponding author. E-mail: drybv@rediffmail.com

Received: 02 May 2012; revised: 04 December 2012; accepted: 29 December 2012. Available online: 31 December 2012.
Table 1. Physical data of iodo hydroxy benzaldehydes

Entry    Substrate       Product          M.P.       Effect of
No.                                   ([degrees]C)   solvent on
                                         Found       iodination
                                       (Reported)    of hydroxy
                                                     aldehydes

                                                     Ethanol

                                                     Time    Yield
                                                     (min)    (%)

1       [FORMULA NOT   [FORMULA NOT    110 (110)      05      82
        REPRODUCIBLE   REPRODUCIBLE       [19]
         IN ASCII]      IN ASCII]
2       [FORMULA NOT   [FORMULA NOT    194 (195)      07      80
        REPRODUCIBLE   REPRODUCIBLE       [18]
         IN ASCII]      IN ASCII]
3       [FORMULA NOT   [FORMULA NOT    184 (185)      09      85
        REPRODUCIBLE   REPRODUCIBLE       [18]
         IN ASCII]      IN ASCII]
4       [FORMULA NOT   [FORMULA NOT    185 (185)      05      80
        REPRODUCIBLE   REPRODUCIBLE       [19]
         IN ASCII]      IN ASCII]
5       [FORMULA NOT   [FORMULA NOT    105 (107)      08      80
        REPRODUCIBLE   REPRODUCIBLE       [19]
         IN ASCII]      IN ASCII]
6       [FORMULA NOT   [FORMULA NOT    70 (69-72)     10      80
        REPRODUCIBLE   REPRODUCIBLE       [19]
         IN ASCII]      IN ASCII]

Entry    Substrate     Effect of solvent on
No.                    iodination of hydroxy aldehydes

                       Acetic acid     2-Methoxyethanol

                       Time    Yield   Time    Yield
                       (min)    (%)    (min)    (%)

1       [FORMULA NOT    18      58      03      96
        REPRODUCIBLE
         IN ASCII]
2       [FORMULA NOT    20      62      05      88
        REPRODUCIBLE
         IN ASCII]
3       [FORMULA NOT    22      50      05      90
        REPRODUCIBLE
         IN ASCII]
4       [FORMULA NOT    17      63      04      86
        REPRODUCIBLE
         IN ASCII]
5       [FORMULA NOT    21      55      05      92
        REPRODUCIBLE
         IN ASCII]
6       [FORMULA NOT    23      68      05      85
        REPRODUCIBLE
         IN ASCII]

Table 2. Physical data of iodo hydroxy acetophenones

Entry    Substrate       Product          M.P.       Effect of
No.                                   ([degrees]C)   solvent on
                                         Found       iodination of
                                       (Reported)    hydroxy
                                                     acetophenones

                                                     Ethanol

                                                     Time    Yield
                                                     (min)    (%)

1       [FORMULA NOT   [FORMULA NOT    164 (162)      05      80
        REPRODUCIBLE   REPRODUCIBLE       [19]
         IN ASCII]      IN ASCII]
2       [FORMULA NOT   [FORMULA NOT    132 (132)      08      85
        REPRODUCIBLE   REPRODUCIBLE       [18]
         IN ASCII]      IN ASCII]
3       [FORMULA NOT   [FORMULA NOT     89 (90)       05      84
        REPRODUCIBLE   REPRODUCIBLE       [19]
         IN ASCII]      IN ASCII]
4       [FORMULA NOT   [FORMULA NOT    177 (178)      09      85
        REPRODUCIBLE   REPRODUCIBLE       [18]
         IN ASCII]      IN ASCII]
5       [FORMULA NOT   [FORMULA NOT     90 (90)       05      82
        REPRODUCIBLE   REPRODUCIBLE       [19]
         IN ASCII]      IN ASCII]
6       [FORMULA NOT   [FORMULA NOT     78 (76)       06      85
        REPRODUCIBLE   REPRODUCIBLE       [19]
         IN ASCII]      IN ASCII]
7       [FORMULA NOT   [FORMULA NOT    156 (155)      07      82
        REPRODUCIBLE   REPRODUCIBLE       [19]
         IN ASCII]      IN ASCII]
8       [FORMULA NOT   [FORMULA NOT    156 (156)      05      79
        REPRODUCIBLE   REPRODUCIBLE       [19]
         IN ASCII]      IN ASCII]

Entry    Substrate     Effect of solvent on iodination
No.                    of hydroxy acetophenones

                       Acetic acid     2-Methoxyethanol

                       Time    Yield   Time    Yield
                       (min)    (%)    (min)    (%)

1       [FORMULA NOT    18      58      05      87
        REPRODUCIBLE
         IN ASCII]
2       [FORMULA NOT    22      64      06      92
        REPRODUCIBLE
         IN ASCII]
3       [FORMULA NOT    17      60      04      95
        REPRODUCIBLE
         IN ASCII]
4       [FORMULA NOT    24      62      05      90
        REPRODUCIBLE
         IN ASCII]
5       [FORMULA NOT    18      50      03      85
        REPRODUCIBLE
         IN ASCII]
6       [FORMULA NOT    25      70      05      88
        REPRODUCIBLE
         IN ASCII]
7       [FORMULA NOT    19      62      04      90
        REPRODUCIBLE
         IN ASCII]
8       [FORMULA NOT    16      55      05      96
        REPRODUCIBLE
         IN ASCII]

Table 3. Physical data of iodo anilines

Entry    Substrate       Product          M.P.        Effect of
No.                                   ([degrees]C)    solvent on
                                          Found       iodination
                                       (Reported)     of anilines

                                                      Ethanol

                                                      Time    Yield
                                                      (min)    (%)

1       [FORMULA NOT   [FORMULA NOT    62 (62-63)      10      80
        REPRODUCIBLE   REPRODUCIBLE       [20]
         IN ASCII]      IN ASCII]
2       [FORMULA NOT   [FORMULA NOT     120 (122)      05      75
        REPRODUCIBLE   REPRODUCIBLE       [20]
         IN ASCII]      IN ASCII]
3       [FORMULA NOT   [FORMULA NOT     115 (116)      06      80
        REPRODUCIBLE   REPRODUCIBLE       [19]
         IN ASCII]      IN ASCII]
4       [FORMULA NOT   [FORMULA NOT   252 (251-253)    09      75
        REPRODUCIBLE   REPRODUCIBLE       [19]
         IN ASCII]      IN ASCII]
5       [FORMULA NOT   [FORMULA NOT    40 (39-41)      07      75
        REPRODUCIBLE   REPRODUCIBLE       [19]
         IN ASCII]      IN ASCII]
6       [FORMULA NOT   [FORMULA NOT      85 (80)       05      80
        REPRODUCIBLE   REPRODUCIBLE       [19]
         IN ASCII]      IN ASCII]
7       [FORMULA NOT   [FORMULA NOT     255 (258)      10      70
        REPRODUCIBLE   REPRODUCIBLE       [19]
         IN ASCII]      IN ASCII]
8       [FORMULA NOT   [FORMULA NOT   222 (220-225)    06      60
        REPRODUCIBLE   REPRODUCIBLE       [19]
         IN ASCII]      IN ASCII]

Entry    Substrate     Effect of solvent on
No.                    iodination of anilines

                       Acetic acid     2-Methoxyethanol

                       Time    Yield   Time    Yield
                       (min)    (%)    (min)    (%)

1       [FORMULA NOT    25      62      05      88
        REPRODUCIBLE
         IN ASCII]
2       [FORMULA NOT    17      54      03      84
        REPRODUCIBLE
         IN ASCII]
3       [FORMULA NOT    19      60      07      82
        REPRODUCIBLE
         IN ASCII]
4       [FORMULA NOT    23      50      08      90
        REPRODUCIBLE
         IN ASCII]
5       [FORMULA NOT    21      58      05      94
        REPRODUCIBLE
         IN ASCII]
6       [FORMULA NOT    17      60      08      86
        REPRODUCIBLE
         IN ASCII]
7       [FORMULA NOT    28      48      06      82
        REPRODUCIBLE
         IN ASCII]
8       [FORMULA NOT    25      42      08      85
        REPRODUCIBLE
         IN ASCII]

Table 4. Physical data of iodo phenols

Entry    Substrate       Product          M.P.        Effect of
No.                                   ([degrees]C)    solvent on
                                          Found       iodination
                                       (Reported)     of Phenols

                                                      Ethanol

                                                      Time    Yield
                                                      (min)    (%)

1       [FORMULA NOT   [FORMULA NOT     105 (107)      10      82
        REPRODUCIBLE   REPRODUCIBLE       [21]
         IN ASCII]      IN ASCII]
2       [FORMULA NOT   [FORMULA NOT   108 (108-110)    06      80
        REPRODUCIBLE   REPRODUCIBLE       [19]
         IN ASCII]      IN ASCII]
3       [FORMULA NOT   [FORMULA NOT      95 (93)       12      85
        REPRODUCIBLE   REPRODUCIBLE       [22]
         IN ASCII]      IN ASCII]
4       [FORMULA NOT   [FORMULA NOT     150 (152)      13      80
        REPRODUCIBLE   REPRODUCIBLE       [19]
         IN ASCII]      IN ASCII]
5       [FORMULA NOT   [FORMULA NOT     185 (190)      09      80
        REPRODUCIBLE   REPRODUCIBLE       [19]
         IN ASCII]      IN ASCII]
6       [FORMULA NOT   [FORMULA NOT     220 (220)      12      80
        REPRODUCIBLE   REPRODUCIBLE       [19]
         IN ASCII]      IN ASCII]

Entry    Substrate     Effect of solvent on
No.                    iodination of Phenols

                       Acetic acid     2-Methoxyethanol

                       Time    Yield   Time    Yield
                       (min)    (%)    (min)    (%)

1       [FORMULA NOT    27      52      08      88
        REPRODUCIBLE
         IN ASCII]
2       [FORMULA NOT    22      60      05      92
        REPRODUCIBLE
         IN ASCII]
3       [FORMULA NOT    30      66      04      90
        REPRODUCIBLE
         IN ASCII]
4       [FORMULA NOT    28      52      07      82
        REPRODUCIBLE
         IN ASCII]
5       [FORMULA NOT    25      60      05      85
        REPRODUCIBLE
         IN ASCII]
6       [FORMULA NOT    27      52      08      86
        REPRODUCIBLE
         IN ASCII]
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Author:Patil, Arvind M.; Zangade, Sainath B.; Vibhute, Yeshwant B.; Kalyankar, Sarala N.
Publication:Orbital: The Electronic Journal of Chemistry
Date:Oct 1, 2012
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