Reaction scheme:
Reagents:
Reagents:
- 4′-Methylpropiophenone (cas 5337-93-9) 1000 g;
- Hydrobromic acid 48% aq. 1300 g;
- Hydrogen peroxide (H2O2) 35% 750 g;
- Sodium bicarbonate (NaHCO3);
- Distilled water;
- Three necked round bottom flask 5 L;
- Retort stand and clamp for securing apparatus;
- Reflux condenser;
- Funnel;
- Drip funnel 1 L;
- Top stirrer;
- Sieve filter (kitchen grade is ok);
- Water bath;
- Heating plate;
- Syringe or Pasteur pipette;
- pH indicator papers;
- Beakers (600 mL x2, 2 L, 1 L, 100 mL x2);
- Vacuum source;
- Laboratory scale (0.1-1000 g is suitable);
- Measuring cylinders 1000 mL and 100 mL;
- Glass rod and spatula;
- Laboratory grade thermometer;
- Buchner flask and funnel;
- Filter paper;
Bromination reaction is easily scaled under these conditions. Basic rule: hydrogen peroxide is added slowly in order to avoid the reaction mixture splashing. It is better to use a top stirrer because a magnetic stirrer doesn't cope with the sediment. Blades of stirrer must be covered with ftoroplast (Teflon) in order to avoid reactions with hydrobromic (HBr) acid.
Synthesis:1. 4'-Methylpropiophenone 1000 g is added into a flask.
2. Hydrobromic (HBr) acid 1300 g 48% is poured into the flask and stirred for 5 min.
3. Hydrogen peroxide 750 g 35% is added into a drip funnel 1 l.
4. Hydrogen peroxide is added dropwise to the stirred reaction mixture.
5. Bromine is released during hydrogen peroxide addition to the mixture, dissolved in solution and reacted.
6. Hydrogen peroxide must be added at an appropriate rate so that the reaction mixture becomes colorless.
7. Reaction mixture temperature have to be kept less than 65 °C. An external cooling is applied in case of overheating. If reaction temperature is higher, hydrogen peroxide addition is stopped.
8. The second part of discoloration reaction can be conducted for longer time. Hydrogen peroxide is added according with reaction temperature.
9. Reaction mixture is left for a 12 h with a constant stirring at room temperature as soon as all hydrogen peroxide is added.
10. After 12 h precipitate is formed.
11. Sodium bicarbonate aq solution is added to the reaction mixture to reach neutral pH 6-7, stir it well. The mixture with 2-bromo-4'-methylpropiophenone is filtered through a Buchner funnel. Product is washed with small amount of distilled water.
12. Crude 2-bromo-4'-methylpropiophenone (cas 1451-82-7) is used for further reactions. Theoretical yield up to 1530 g. Practice yield is almost quantitative (video yield 94%).
2. Hydrobromic (HBr) acid 1300 g 48% is poured into the flask and stirred for 5 min.
3. Hydrogen peroxide 750 g 35% is added into a drip funnel 1 l.
4. Hydrogen peroxide is added dropwise to the stirred reaction mixture.
5. Bromine is released during hydrogen peroxide addition to the mixture, dissolved in solution and reacted.
6. Hydrogen peroxide must be added at an appropriate rate so that the reaction mixture becomes colorless.
7. Reaction mixture temperature have to be kept less than 65 °C. An external cooling is applied in case of overheating. If reaction temperature is higher, hydrogen peroxide addition is stopped.
8. The second part of discoloration reaction can be conducted for longer time. Hydrogen peroxide is added according with reaction temperature.
9. Reaction mixture is left for a 12 h with a constant stirring at room temperature as soon as all hydrogen peroxide is added.
10. After 12 h precipitate is formed.
11. Sodium bicarbonate aq solution is added to the reaction mixture to reach neutral pH 6-7, stir it well. The mixture with 2-bromo-4'-methylpropiophenone is filtered through a Buchner funnel. Product is washed with small amount of distilled water.
12. Crude 2-bromo-4'-methylpropiophenone (cas 1451-82-7) is used for further reactions. Theoretical yield up to 1530 g. Practice yield is almost quantitative (video yield 94%).
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