Cleaning Up of α-Methylstyrene by Flash Chromatography

A. Talamona, BÜCHI Labortechnik AG

The isolation of α-Methylstyrene from the crude reaction mixture seems easy. However the reaction mixture contains some dimethyl sulfoxide and the oily wetting agent from the sodiumhydride. Both of them are not UV-active and therefore invisible in the TLC.

TLC of the crude reaction mixture

TLC on silica gel Si60_F254, developed in n-hexane/ethyl acetate 90:10, detection UV 254 nm.

Figure 1: Chromatogram of α-Methylstyrene crude reaction mixture.

TLC of the the separated fractions

TLC on silica gel 60_F254, developed in n-hexane-ethyl acetate 9:1, detection UV 254 nm.

Figure 2: TLC of crude reaction mixture and pooled fractions 14–18.

Recovery

Fraction 11–12: 0.4 g colorless oily liquid.

Figure 3: TLC of crude reaction mixture and pooled fractions 11–12.

Sepacore configuration

Cartridge 40 × 150 mm, prepacked with silica gel 60, 40–63 µm

2 Pump Modules C-605

Fraction Collector C-660

Control-Unit C-620 with Sepacore Control software

UV Photometer C-635

Separation conditions

Eluent: n-hexane with 0%, 2%, and 15% ethyl acetate, step gradient

Flow rate: 100 mL/min

Sample: 3 g crude mixture, dissolved in toluene

Injection volume: 4.5 mL (although the mixture is liquid, the sample is not fully miscible with n-hexane and must be dissolved in toluene and injected directly onto the cartridge).

Fractions

2–10: mainly toluene and wetting agent

11–12: α-Methylstyrene

14–18: Acetophenone (reactant)

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