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Thiolation of benzylic bromide; 1,4-phenylenedimethanethiol

SyntheticPage 631
DOI: 10.1039/SP631
Submitted Jul 16, 2013, published Jul 17, 2013
Alan Faulkner (alan.faulkner@warwick.ac.uk), Pratik Gurnani (pratik.gurnani@warwick.ac.uk)
A contribution from Scott group, Warwick University
Reaction Scheme: <IMG src="/images/empty.gif"><IMG src="/images/empty.gif">Thiolation of benzylic bromide<IMG src="/images/empty.gif"><IMG src="/images/empty.gif">

Chemicals Used

α,α′-Dibromo-p-xylene (Fluka)
K2CO3 (M+B)
Thioacetic acid (Aldrich)
Methanol (distilled over calcium hydride)

Procedure

α,α′-Dibromo-p-xylene (2 g, 3.78 mmol) and potassium carbonate (1.3 g, 9.40 mmol) were suspended in methanol (40 mL) under a steady flow of nitrogen. Thioacetic acid (0.65 mL, 9.23 mmol) was added slowly by syringe and the reaction was stirred at room temperature for 30 minutes, at which time a second portion of potassium carbonate (1.3 g, 9.40 mmol) was added. After 1 h the reaction was acidified to pH 6 by addition of 1M HCl, the reaction mixture was then extracted into CHCl3 (2 x 20 mL) and then washed with water (3 x 20 mL). The organic layer was dried over sodium sulfate, filtered and the solvents evaporated under reduced pressure to leave the product, as a white solid which was used without further purification (yield 0.39 g, 66%).

Author's Comments

  • Solution turns cloudy upon addition of potassium carbonate
  • Extraction is easier if methanol is removed prior to the organic workup described above.
  • The product can be dissolved in dichloromethane and filtered through a silica plug to remove any impurities such as grease.
  • Reaction is best done at 25 °C, a hot plate can be used to maintain this temperature.

Data

1H NMR (400 MHz, CDCl3) δ 7.21 (s, 4H, Ar-H), 3.66 (d, J = 7.5 Hz, 4H, Ar-CH2), 1.68 (t, J = 10.1, 5.0 Hz, 2H, SH). 

13C NMR (101 MHz, CDCl3) δ 128.37 (Ph), 77.34 (Ph), 77.02 (Ph), 76.71 (Ph), 28.62 (Ph-CH2).

IR cm-1 : 2926 w, 2545 w, 2357 w, 1912 w, 1511 m, 1417 m, 1257 m, 1209 m, 1107 m, 1022 m, 967 m, 839 s, 764 m, 688 s.

MS (EI/CI) m/z 338.0 (dimer -2H)

Melting point : 37-39 °C

Lead Reference

C. C. Han and R. Balakumar, Tetrahedron Lett., 2006, 47, 8255-8258. http://dx.doi.org/10.1016/j.tetlet.2006.09.093

Supplementary Information

1H NMR (1H NMR.jcamp)
13C NMR (13C NMR.jcamp)

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Keywords: aromatics/arenes, bromide, substitution, thiol