Heterocyclic Compounds from Milk A simple experiment showing the relationship between the hexoses and five-membered heterocyclic compounds is available using a natural material, milk. Lactose ("milk-sugar"), comprising some 4 4 % of cows milk, on treatment with hot dilute nitric aeid, hydrolyses to equal amounts of galactose and glucose which in turn are oxidized t o mueie and saccharic acids, respectively. Mucic acid (C6H100s)precipitates in the presence of saccharic acid due to its much greater insolubility, being a source for the compounds furan, pyrrole, and thiophen which can be identified on a small scale by characteristic qualitative tests.
Mucic Acid Milk (100 ml) is diluted with water (50 ml) and 2-3 ml of dilute acetic acid added with stirring t o precipitate the eaesin and fats. The latter are filtered off using a fluted paper and IO-12 ml of about 5 M nitric scid added to the filtrate which is evaporated to low bulk an a water-bath. On ewling, the precipitated mueic scid is collected and washed using a Buchner funnel. This can be used directly or purified by dissolution in a little dilute alkali and reprecipitated by addition of a little dilute mineral acid, yielding a white powder (m.p. 206-214 decamp.') or can be identified under the microscope by addition of a drop of 5%potassium hydroxide t o s trace of the acid on a glass slide whence characteristic prisms of potassium mueate are observed.
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CsHl0O8 2Ca0 GH.0 2CaC03 + 3H20 Furan A little mu& acid is mixed with some calcium oxide and heated in a small test tube or crucible. A pine-wood splint moistened with eonc. HC1 turns green2 indicating the evolution of furan. (Furfural gives the same test, hut gives a characteristic red color with a mixture of aniline and hydrochloric acid,3 unlike furan
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CsHs08(NH1)2 ClHsN + NH3 2C02 4Hz0 ~yrrole A little mucic acid in a test tube is treated with a few drops of cone. ammonia solution till reaction ceases giving ammonium mueate. On heating this salt, a pine-woad splint moistened with cone. HCI is turned a deep red color when placed in the vapor indicating the evolution of pyrmle."
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Thiophen C6HloOs B a s d C 4 H & BaO 2CO2 3Hz0 A little mucic aeid is mixed with some barium sulfide in a small test tube and heated whence thiophen is evolved. A drop of cone. H2SOa containing a crystal of isatin on a glass rod placed in the vapor turns blue (the "iudophenin reaction"): this being characteristic for thiophen.
' Dean, J. A., Editor, "Lange's Handbookof Chemistry",
11th Ed., McGraw-Hill, New York, 1973, p. 7-286. Cheronis, N. B., Entrikin, J. B., "Identification of Organic Compounds," Wiley-Interscience, New York, 1963, p. 392. Finar I. L., "Organic Chemistry (Vol. I),.' 3rd Ed., Longmans-Green, London, 1959, p. 714. Reference (31, p. 717. "Reference (31, p. 715.
S. A. Institute of Technology P. 0. Box 1. lngle Farm, Australia, 5098
256 / Journal of Chemical Education
M. Lampard
