Organic Syntheses Procedure

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Org. Synth. 2005, 82, 30

DOI: 10.15227/orgsyn.082.0030

PREPARATION OF HEXAKIS(4-BROMOPHENYL)BENZENE (HBB)

[1,1':2',1"-Terphenyl, 4,4"-dibromo-3',4',5',6'-tetrakis(4-bromophenyl)-]

Submitted by Rajendra Rathore¹ and Carrie L. Burns.

Checked by Scott E. Denmark and Shinji Fujimori.

1. Procedure

A 500-mL, three-necked flask, equipped with a mechanical stirrer (fitted with an 11 cm Teflon paddle), a septum and an outlet adapter connected via rubber tubing to a pipette which is immersed in a 10% aqueous sodium hydroxide solution (250 mL) in a 500 mL Erlenmeyer flask is charged with 70 mL of bromine (1.37 mol) (Note 1). The septum is replaced with a 250-mL powder addition funnel charged with 26.7 g (50 mmol) of hexaphenylbenzene (HPB) (Note 2). The flask is placed in a water bath at ambient temperature to control the heat evolved from the reaction. To the slowly stirred bromine, hexaphenylbenzene is added slowly over 1 hour (Note 3). The reaction starts immediately as judged by an evolution of gaseous hydrobromic acid (Note 4). After the addition of hexaphenylbenzene is complete, the dark-orange slurry is stirred for an additional 20 min.(Note 5)

The bromine slurry of resulting product is carefully poured into 500 mL of pre-chilled (approx. −78°C) ethanol in a 1-L Erlenmeyer flask with stirring by a magnetic stir bar (Note 6). To the three-necked flask is added cold (−78°C) ethanol (100 mL × 2) and the remaining precipitate is transferred to the Erlenmeyer flask. The suspension of the product in ethanol is allowed to warm to room temperature over 2 hrs. with stirring, and the suspension is filtered using a Büchner funnel. The pale yellow precipitate is washed with ethanol (50 mL), aqueous sodium bisulfite (5%, 100 mL), and ethanol (2 × 50 mL) successively. After being dried overnight in vacuo (0.5 mmHg) at room temperature to a constant weight, 47.8 g (96% yield) of hexakis(4-bromophenyl)benzene (HBB) is obtained with greater than >95% purity as judged by ¹H NMR spectroscopy.

The precipitated product is sufficiently pure for most purposes; however, it can be further purified by re-precipitation from tetrahydrofuran. Thus, 10 g of HBB was dissolved in refluxing tetrahydrofuran (Note 7) (350 mL) in a beaker. Upon slow evaporation at room temperature, the solution yields a colorless (microcrystalline) precipitate (9.4 g) of hexakis(4-bromophenyl)benzene (HBB). (Note 8) (Note 9).

2. Notes

1. Bromine was obtained from Aldrich Chemical Co. was used as received.

2. Hexaphenylbenzene (HPB) was obtained following the Organic Syntheses procedure (Fieser, L, F. Org. Synth., 1973, 46, 44; CV 5, 604). Commercially available HPB (Aldrich Chemical Co.) can also be used.

3. The reaction is carried out without added solvent and thus for a thorough mixing of reagents an excess of bromine is required for a complete conversion of HPB to HBB. It is critical to maintain the reaction mixture as a slurry for complete conversion.

4. Gaseous HBr was trapped in an aqueous solution of sodium hydroxide.

5. At this point the HBr evolution completely ceases.

6. The slurry should be poured into cold ethanol (−78°C) to prevent an exothermic reaction between excess bromine and ethanol.

7. Tetrahydrofuran (Optima grade) was obtained from Fischer Inc. and was used as received.

8. The spectral data for analytically pure HBB: mp 358-359°C; ¹H NMR pdf (CDCl₃) δ: 6.61 (d, J = 8.5 Hz, 12 H), 7.06 (d, J = 8.6 Hz, 12 H); ¹³C NMR (CDCl₃) δ: 120.3, 130.5, 132.6, 138.4, 139.6. Anal. Calcd for C₄₂H₂₄Br₆: C, 50.04; H, 2.40; Br, 47.56. Found: C, 49.92; H, 2.27.

9. Crystallization can be performed in refrigerator (−15°C) over 3 days to provide larger size crystals.

Handling and Disposal of Hazardous Chemicals

The procedures in this article are intended for use only by persons with prior training in experimental organic chemistry. All hazardous materials should be handled using the standard procedures for work with chemicals described in references such as "Prudent Practices in the Laboratory" (The National Academies Press, Washington, D.C., 2011 www.nap.edu). All chemical waste should be disposed of in accordance with local regulations. For general guidelines for the management of chemical waste, see Chapter 8 of Prudent Practices.

These procedures must be conducted at one's own risk. Organic Syntheses, Inc., its Editors, and its Board of Directors do not warrant or guarantee the safety of individuals using these procedures and hereby disclaim any liability for any injuries or damages claimed to have resulted from or related in any way to the procedures herein.

3. Discussion

The hexaphenylbenzene core is being extensively investigated as a platform for the preparation of nanometer-size macromolecules and supramolecular assemblies owing to their importance as materials that can be used as molecular devices such as sensors, switches, ferromagnets, and other electronic and optoelectronic devices.²^,³^,⁴^,⁵ As we recently demonstrated, the elaboration of the hexaphenylbenzene core can be readily achieved using HBB for the preparation of a hexacation-radical salt⁶ for use as a (multi)electron-transfer catalyst in a variety of organic and organometallic transformations.⁷ The hexaphenylbenzene core is also being utilized for the preparation of well-defined graphite-like structures by Müllen and others and the progress in the area has been reviewed in two recent Chemical Review articles.⁸^,⁹

There is one reported procedure for the preparation of HBB, which utilizes the Diels-Alder approach using tetrakis(4-bromophenyl)cyclopentadienone and bis(4-bromophenyl)acetylene (also known as 4,4'-dibromotolan) as the starting materials.¹⁰ Both of these starting materials are prepared via multi-step syntheses. We have also discovered that trimerization of 4,4'-dibromotolan using bis(acetonitrile)palladium dichloride affords HBB in fair yield.¹¹

A similar bromination procedure (as described above for the preparation of HBB) can be employed for the preparation of tetrakis(4-bromophenyl)methane using tetraphenylmethane and bromine.⁶

The method described here for the preparation of HBB is essentially a detailed description of our recently published procedure⁶ using hexaphenylbenzene and neat bromine. It is believed that the ready availability of HBB from hexaphenylbenzene will facilitate the synthesis of a variety of materials, which were otherwise not readily accessible.¹²

References and Notes

Department of Chemistry, Marquette University, P.O. Box 1881, Milwaukee, WI, 53201-1881.
Lambert, C.; Noll, G. Angew. Chem. Int. Ed. Engl. 1998, 37, 2107.
Praefcke, K.; Khone, B.; Singer, D. Angew. Chem. Intl. Ed. Engl. 1990, 29, 177.
Laschewsky, A. Angew. Chem. Intl. Ed. Engl. 1989, 28, 1574.
Kobayashi, K.; Shiraska, T.; Horn, E.; Furukawa, N. Tetrahedron Lett. 2000, 41, 89 and references therein.
Rathore, R.; Burns, C.L.; Deselnicu, M. I. Org. Lett. 2001, 3, 2887.
Connelly, N.G.; Geiger, W.E. Chem. Rev. 1996, 96, 877 and references therein.
Watson, M.D.; Fechtenkotter, A.; Mullen, K. Chem. Rev. 2001, 101, 1267 (review) and references therein.
Berresheim, A.J.; Muller, M.; Mullen, K. Chem. Rev. 1999, 99, 1747 (review) and references therein.
Broser, W.; Siegle, P.; Curreck, H. Chem. Ber. 1968, 101, 69–83.
Rathore, R. (unpublished results).
Rathore, R., Burns, C. L., Guzei, I. A. J. Org. Chem. 2004, 69. 1524–1530.

Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

Hexaphenylbenzene:
1,1':2',1"-Terphenyl, 3',4',5',6'-tetraphenyl-; (992-04-1)

hexakis(4-Bromophenyl)benzene:
1,1':2',1"-Terphenyl, 4,4"-dibromo-3',4',5',6'-tetrakis(4-bromophenyl)-; (19057-50-2)

Sodium bisulfite:
Sulfurous acid, monosodium salt; (7631-90-5)

Bromine; (7726-95-6)

Notes

References/EndNotes

Article Compounds

Authors