General Description
4′-Pentyl-4-biphenylcarbonitrile (5CB) is a nematic liquid crystal. 5CB undergoes phase transition from crystalline to nematic then to isotropic state at 18
oC and 35
oC respectively. It may be produced by modifying biphenyl.2
Synthesis
General procedure for the synthesis of 4'-n-pentyl-4-cyanobiphenyl from p-bromopentyl biphenyl: To a dry flask containing magnesium shavings (0.29 g, 12 mmol) was added a solution of 1-bromo-4-methylbenzene (1.37 g, 8.0 mmol) in tetrahydrofuran (THF, 8 mL) at room temperature. After stirring the reaction mixture for 2 h, N,N-dimethylformamide (DMF, 1.3 mL, 12 mmol) was slowly added. The reaction mixture was cooled to 0°C and stirring was continued for 2 hours. Subsequently, ammonia solution (7 mL, 28-30%) and iodine (I2, 4.06 g, 16 mmol) were added to the reaction system. After stirring the reaction mixture for 2 h at room temperature, it was poured into saturated aqueous sodium sulfite (Na2SO3) solution and extracted with chloroform (CHCl3, 3 x 30 mL). The organic layers were combined, dried with anhydrous sodium sulfite (Na2SO4) and filtered. After the solvent was removed by distillation under reduced pressure, the residue was purified by silica gel short column chromatography (eluent: hexane/ethyl acetate = 9:1, v/v) to afford pure 4-methylbenzonitrile (0.77 g) in 82% yield.
References
[1] Tetrahedron, 2013, vol. 69, # 5, p. 1462 - 1469
