Terminal alkynes compounds

Alkynes derivatives are utilized as important basic skeletons of function materials such as liquid crystal material (LCD). Terminal alkynes derivatives are very important liquid crystal compounds , because they have certain advantages such as: high thermal stability, low optical anisotropy Δn and small positive or negative value of the dielectric anisotropy ,which are suitable as components of liquid crystalline media , in particular for TFT and STN displays.

 Synthesis of Terminal alkynes compounds


A flame-dried Schlenk flask was charged with a solution of ethynylmagnesium bromide. A solution of anhydrous ZnBr2 in THF was added via cannula at 0 °C. The mixture was stirred for 30 min and added, via cannula, to a solution of 4-bromoiodobenzene and Pd(PPh3)4 in THF. The reaction mixture was stirred at rt for 15 h, diluted with Et2O, washed once with aqueous NH4Cl, once with aqueous NaHCO3, and once with brine, dried over MgSO4, filtered, and concentrated. Chromatography on silica gel gave 4-Bromoethynylbenzene.


To a stirred mixture of olefin and LiBr in acetic acid, NaIO4 (25 mol %) was added portion wise. The reaction was monitored by TLC. After completion of the reaction, it was diluted with water and extracted with CH2Cl2. The organic layers were washed with dilute solution of NaHCO3, Na2SO3, and brine. It was dried over anhydrous Na2SO4 and concentrated under reduced pressure to give crude products, which were purified by column chromatography packed with silica gel using petroleum ether and ethyl acetate (9:1) as eluent to afford the pure products.

A mixture of 1, 2-dibromo-l-phenylethane, n-hexane, and 60% aqueous potassium hydroxide was placed in a three-necked, round-bottomed flask equipped with a mechanical stirrer (standard 4-cm curved Teflon blade). The flask was immersed in an oil bath maintained at 70 deg C, and the mixture stirred for 16 h. The mixture was then cooled to room temperature and filtered, and the resin was washed successively with water, n-hexane, and CH2Cl2. The aqueous portion of the filtrate was extracted with CH2Cl2 and combined with the organic filtrate. After being dried overnight over Na2SO4 the organic layer was then distilled to give 1-ethynylbenzene.


 The application of Terminal alkynes compounds





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