Isolation of Benzylideneacetophenone from a Crude Reaction Mixture

Benzylideneacetophenone forms the central core for a variety of important biological compounds, known collectively as chalcones. Many of these compounds have significant medicinal value as they demonstrate antibacterial, antifungal, antitumor, and anti-inflammatory properties. They are synthesized by an aldol condensation between a benzaldehyde and an acetophenone in the presence of NaOH as catalyst. In this application note, benzylideneacetophenone is isolated from a crude reaction mixture using flash chromatographic technique, including consideration for scale-up.

Figure 1: TLC of crude mixture.

TLC of the Crude Reaction Mixture

TLC on silica gel Si60_F254, developed in n-hexane/ethyl acetate 19:1, detection UV 254nm.

Sepacore Configuration

Cartridge 12 × 150 mm, prepacked with silica gel 60, 40–63 µm

2 Pump modules C-605

Fraction collector C-660

Control-Unit C-620 with SepacoreControl software

UV Photometer C-635

Figure 2: Separation 1.

Separation Conditions

Eluent: see below

Flow rate: 10 mL/min

100 mg crude mixture, dissolved in n-hexane and some drops of toluene (solubility of the sample in pure n-hexane too low)

Loading: approx. 0.4 mL

1. Test runs

Separation 1

Eluent: n-hexane with 2% ethyl acetate, isocratic

Figure 3: Separation 2.

Separation 2

Eluent: n-hexane with 1%, 2% and 3% ethyl acetate, step gradient. Each step was initiated after a component was completely eluted (at the end of a peak).

TLC Check

TLC on silica gel Si60_F254, developed in n-hexane/ethyl acetate 19:1, detection: UV 254 nm

1 = Benzaldehyde

2 = Benzylideneacetophenone

3= Benzophenone

Figure 4: TLC check of Separation 2.

Recovery

Fraction 7: 65 mg

2. Scale-up

Calculation of the scale-up factor

Cartridge 12 × 150 mm: cross sectional area = 1.13 cm²

Cartridge 40 × 150 mm: cross sectional area = 12.56 cm²

Scale-up-factor = 12.56 cm² / 1.13 cm² = 11.1 ≈ 10

Figure 5: Scale-up separation.

Separation conditions

Eluent: n-hexane with 1%, 2% and 3% ethyl acetate, step gradient

Sample: 1 g crude mixture, dissolved in n-hexane/toluene 7:3 (solubility of the sample in n-hexane too low, toluene is eluted as front peak)

Injection volume: 2 mL

Figure 6: TLC check of scale-up.

TLC-Check

TLC on silica gel Si60_F254, developed in n-hexane/ethyl acetate 19:1, detection: UV 254 nm

Recovery

Fraction 13–16: 512 mg crystalline product, mp 57 °C

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