Wittig Synthesis of alpha-Ethylstyrene
-Ethylstyrene (2-phenyl-1-butene) was prepared by the Wittig reaction from ethyl phenyl ketone (propiophenone) and methyltriphenylphosphorane according to the following general procedure:
To a solution of diisopropylamine (7.7 g, 76 mmol) in 100 mL of anhydrous tetrahydrofuran cooled at -30°C was added n-butyllithium (51 mL, 1.5 M in hexane, 76 mmol) dropwise under nitrogen. After 15 min, methyltriphenylphosphonium iodide (30.7 g, 76 mmol) was added under stirring.
The cold bath was removed, and the mixture was allowed to react 2 h at room temperature. The ketone (76 mmol) was added dropwise, and the mixture was allowed to react for a period of time ranging from 1 to 10 h depending on the structure of the ketone (follow the reaction on TLC).
After filtration and solvent evaporation, light petroleum was added and most of the crystallized triphenylphosphine oxide was removed by filtration. Chromatography of the resulting solution on silica gel (light petroleum as the eluent) and successive distillation gave
-ethylstyrene more than 99.9% pure by GLC analysis.
-Ethylstyrene (2-phenyl-1-butene): 68%; bp
15 64-64.5°C;
1H NMR 
7.50-7.15 (m, 5 H), 5.28 (m, 1 H), 5.07 (m, 1 H), 2.52 (b q, J = 7.7 Hz, 2 H), 1.10 (t, J = 7.7 Hz, 3 H);
MS m/z 132 (M
+, 67), 117 (100), 103 (9), 91 (33), 77 (16).
Reference: J. Org. Chem., Vol. 56(15), 4772-4778 (1991)
(
https://www.thevespiary.org/rhodium/Rhodium/pdf/alpha-ethylstyrene-0.pdf)
