Laevulic acid

Laevulic acid

Laevulic acid (β-acetylpropionic acid, γ-ketovaleric acid, butan-3-one-1-carboxylic acid), m.p. 34^oC, is the simplest γ-keto-acid. It may be prepared via acetoacetic ester as follows:

It may also be prepared by heating a hexose sugar, particularly laevulose, with concentrated hydrocloric acid: 

C₆H₁₂O₆    -    CH₃COCH₂CH₂CO₂H   +   HCO₂H   +   H₂O

In practice it is customary to use cane-sugar as the starting material:

C₁₂H₂₂O₁₁    -    2CH₃COCH₂CH₂CO₂H   +   2HCO₂H   +   H₂O  (21-22%)

By heating dilute solutions of sucrose under pressure with hydrochloric acid, the yield is increase to 50 per cent.

Leavulic acid behaves as a ketone (forms oxime, etc) and as an acid (forms esters, etc). On the other hand, many of the reactions of laevulic acid indicate that it exists in the lactol form, i.e., hydroxylactone (this is an example of ring-chain tautomerism) e.g.,

When heated for some time, acid is converted into a-and β-angelica lactones (derived from the lactol form):

A general method for preparing y-keto-acids is to treat a ketone with lithium amide and lithium bromoacetate; the ketone undergoes a-carboxymethylation (puterbaugh et al., 1959)

y-keto-acids may also be synthesized by other method. Keto-acid with the oxo group in the d-or a higher position are very conveniently prepared by the action of a dialkylcadmium on the half-ester acid chloride. On the other hand, d-keto-acids may be prepared as follows from cyclohexame-1,3-dione, e.g., 5-oxoheptanoic acid.

The cyclic dione, since it contains an active methylene group, forms the potassium salt which can be alkylated, and product readily undergoes fission, thus behaving like the acyclic B-diketones. The keto-acids may be reduced byteh Wolff-Kishner method to the corresponding saturated acid; in the above example, to heptanoic acid. Alternatively, the alkylated ring may be opened and the carbonyl group reduced in one step by refluxing with hydrazine in alkaline glycol solution.