Liebermann-Burchard Reaction with Compounds Containing Five-Membered Monoheterocyclic Rings

Sterols, 1 terpenes, 2 carotene, 3 vitamin A 4 and 5-membered monoheterocyclic ring compounds 5 have the characteristic in common that they react with the Carr-Price reagent, antimony trichloride in chloroform solution, and with the Shear reagent, aniline-hydrochloric acid. 6 Reasoning on the probability of the existence of some common factor in the chemistry of sterols, terpenes, carotene and vitamin A, we determined to find out whether the Liebermann-Bur-chard reagent, used qualitatively in the detection of cholesterol and quantitatively in its estimation, was also given by the other compounds in the group we have mentioned.

We accordingly studied the Liebermann-Burchard test with respect to certain 5-membered monoheterocyclic compounds. Unless otherwise stated, we adopted the procedure of dissolving 1 to 2 drops of a given liquid compound to be tested or 10 to 20 mg. of a solid compound in 2 cc. of chloroform, adding 10 drops of acetic anhydride and 1 to 3 drops of concentrated sulphuric acid. The color reaction undergoes many variations depending upon the concentration in chloroform of the compound tested and the quantity of concentrated sulphuric acid added.

Pyrrol at first gave a yellow turbidity, which gradually turned to very deep orange. On standing a deep blood-orange precipitate separated out, leaving a colorless liquid above. On the addition of sulphuric acid alone slightly heavy droplets separate at the bottom. On standing these droplets solidified and developed an orange tinge, which gradually darkened. Thiophene on the addition of 5 drops to 2 cc. of chloroform gave yellow oily droplets at the bottom of the tube. On standing over night the droplets disappeared and the liquid contents of the tube turned green. The reaction was very slow. The green color, however, once formed became deeper and lasted more than 2 weeks. Black granules finally precipitated out in the colored mixture. With sulphuric acid alone yellow droplets formed at the bottom. These gradually turned deep reddish brown, and at the end of a week the colorless liquid assumed a very slight green tinge.