4-Methylbenzophenone → 4-(Bromomethyl)benzophenone

Participants

Reaction Steps

4-Methylbenzophenone, 750 g (3.82 moles), was added to a 5 liter Morton flask equipped with an overhead stirrer and dissolved in 2850 ml of benzene. The solution was then heated to reflux, followed by the dropwise addition of 610 g (3.82 moles) of bromine in 330 ml of benzene. The addition rate was approximately 1.5 ml/min and the flask was illuminated with a 90 watt (90 joule/sec) halogen spotlight to initiate the reaction. A timer was used with the lamp to provide a 10% duty cycle (on 5 seconds, off 40 seconds), followed in one hour by a 20% duty cycle (on 10 seconds, off 40 seconds). At the end of the addition, the product was analyzed by gas chromatography and was found to contain 71% of the desired Compound VI, 8% of the dibromo product, and 20% unreacted 4-methylbenzophenone. After cooling, the reaction mixture was washed with 10 g of sodium bisulfite in 100 ml of water, followed by washing with 3×200 ml of water. The product was dried over sodium sulfate and recrystallized twice from 1:3 toluene:hexane. After drying under vacuum, 635 g of Compound VI were isolated, providing a yield of 60% and having a melting point of 112-114° C. Analysis on an NMR spectrometer was consistent with the desired product: 1H NMR (CDCl3) aromatic protons 7.20-7.80 (m, 9H) and benzylic protons 4.48 (s, 2H). The final compound was stored for use in the preparation of a photoactivatable chain transfer agent as described in Example 7.

Provenance & Evidence