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Benzilic Acid

Benzilic acid is used in the preparation of quite a few pharmaceuticals, and is chiefly known as the acid used in the esterfication to make BZ - the incapacitating hallucinogen. The reaction to produce this is called the benzillic acid rearrangement, which is a classic organic chemistry reaction. It is produced by heating a solution of benzil, ethanol, and potassium hydroxide to produce the potassium salt. This is then acidified to obtain the acid.

(C6H5CO)2 + KOH --heat--> (C6H5)2COHCOOK

(C6H5)2COHCOOK + HCl ----> (C6H5)2COHCOOH + KCl

Benzil 500ml flask
96% Ethanol Reflux condenser
Potassium hydroxide Water bath equipment
31.45% Hydrochloric acid 250ml beaker
  600ml beaker
  Filtration equipment (vacuum recommended)


Into a 500ml flask, add 24g of benzil. To this, add 75ml ethanol. Attach a reflux condenser to this and begin heating it on a water bath. As it is warming up, prepare a solution of potassium hydroxide in water by dissolving 28g of potassium hydroxide in 60ml of distilled water. Now moving back to the benzil, swirl the flask to dissolve the benzil completely. Keep in mind, it should not be boiling yet, just warm. Now, add 60ml of the potassium hydroxide solution previously prepared to this. Once it is added and thoroughly swirled in, reflux the mixture for 30min. It should change colors from a dark blue to a brown color. After the time is up, turn the heating off and lift the flask out of the water bath. Once it has stopped boiling and has dropped down in temperature, transfer the contents to a 250ml beaker. Let this beaker cool to room temperature, then place it in an ice bath. The contents will form a solid mass of crystals.

Filter out the crystals. It may be wise to use vacuum filtration at this point. Add successive portions of ice cold ethanol to the contents of the filter. This will remove most of the color of the crystals. Once it has sufficiently drained, add the contents of the filter to a 600ml beaker. Add 250ml of distilled water and heat it until the crystals dissolve. If anything doesn't dissolve, filter it out at this point. Now prepare a solution using 15ml of hydrochloric acid and 105ml of distilled water. Add this to the solution above. Place the beaker in a salt ice bath and keep it there for an hour. After an hour, there should be a decent amount of crystals at the bottom. Filter these out and rinse with distilled water. Theoretical yield is 26g.