Acetoacetic Acid

Acetoacetic acid, CH₃.CO.CH₂.COOH, a colorless strongly acidic liquid, mixes with water, alcohol, and ether in all proportions. When heated, it easily decomposes into carbon dioxide and acetone. For qualitative detection of A. acid, the Gerhardt reaction is used. To 10-15 cubic centimeters of urine, a solution of ferric chloride is added drop by drop until a precipitate still forms, then it is filtered and a few more drops of ferric chloride are added to the filtrate. In the presence of A. acid, a brown-red color appears. At room temperature, the color gradually fades over the course of a day, but when boiled, it quickly disappears due to the destruction of A. acid, which can serve to distinguish A. acid from salicylic acid, phenol, and hydrocyanic acid, which also give a red coloration with ferric chloride. Quantitative determination of A. acid is based on the fact that the preformed acetone is distilled off in a vacuum, the residue in the flask is acidified, the liquid is boiled, the acetone formed during the decomposition of A. acid is distilled off, and its quantity is determined iodometrically in the distillate. A. acid is formed in the body from β-oxobutyric acid. In diabetes, when acidosis develops, acetoacetic acid, along with other acetone bodies, acetone and β-oxobutyric acid, can be found in urine, where its amount can reach 24 grams per day; its presence indicates greater severity of the case than the presence of acetone alone.