NOVEMBER, 1938 A SIMPLE EXPERIMENT IN COAL TAR DISTILLATION C. W. BENNETT Western Illinois Stete Teacher's College, Macomb, Illinois
THE author has found that experiments which show commercial processes are, in general, very inter-
esting to beginning students. Many elementary lahoratory manuals contain an experiment on the de-
structive distillation of wood. The students enjoy i t because it deals with common materials and the pyroligneous acid collected reminds them of patent meat curers. An experiment on the fractional distillation of crude petroleum is often found in organic manuals. Work with coal tar, however, is rarely taken up in any elementary course. The use of coal tar products is so extensive and the nature of the products as compared to the parent coal tar is so astounding that it would seem to be a worth-while addition to an elementary laboratory course. The author, after consulting various commercial analytical texts, has prepared the following
directions based on a section in Allen's "Commercial Organic Analysis."' These have been successfully used by about ten different classes. The tar used here was obtained from the local gas plant, but any coal tar may be used. Place 150 ml. of the tar in a liter round-bottom Pyrex flask fitted with a two-bulb distilling tube and an aircooled condenser. Cork stoppers are preferable to rubber stoppers. A tin can just a little larger than the flask should be used to promote even heating. Remove the top of the can, and cut a small hole in the middle of the bottom to fit over the neck of the flask. Turn the can upside down over the flask. Provide three coutainers for the products which will consist of: (1) (a) Ammoniacal liquor from which ammonia and pyridine (CsHsN) are obtained commercially and (b) light oil from which by fractional dis-
' DAVIS, W. A. AND S. S. SADTLER, "Allen's commercial organic analysis," Vol. 111, pp. 20-9, 4th ed., P. Blakiston's Son and Co., Philadelphia, Pa.
tillation benzene (CsHB), toluene, (CsHsCH8), the xylenes, (CeHa(CH&), naphthalene, (CloHI) from which mothballs are made. (2) Creosote oil which consists of carbolic acid or phenol (C6HaOH),the cresols (C6H4(CHa)OH)used in lysol, naphthalene (CIIHZ),and some small amounts of other compounds including those of sulfur. mostly anthra(3) Anthracene oil ~hich~contains cene (ClaHlo), phenanthrene (C,rH,o), and carbazole (CIZH~N). (4) Pitch which remains on the flask and consists of coke and unidentifiable'tarry materials. It is unnecessary to use a thermometer, as the character of the distillate is sufficient to indicate the point a t which the receiver should be changed. When all is ready place a small burner under the flask over a wire gauze and heat very slowly a t first. Caution is necessary since the water in the tar causes steam distillation, and superheating may cause frothing. The first fraction which is received will consist of a mixture of oil and an aqueous solution, the latter being on the bottom. (1) Ammoniacal l&or and light oils.-During this distillation the vapors should be tested for ammonia by the use of moistened red litmus and by the odor. When this fraction of the distillation is complete, distillation will cease for a while and a peculiar noise called the "rattles" will be heard. Change the receiver a t this point. (2) Creosote oil.-Apply more heat gradually until distillation recommenc& A d collect this fraction until another break in the process is noted. Provide a third container. (3) Anthracene oil.-Heat more strongly. The distillate will become crystalline in the condenser and receiver. The solid material is mostly anthracene. Continue heating until no more liquid distills. If extreme care is not exercised here the liter flask may melt or crack during this process. (4) Pitch.-The residue in the flask is pitch. Separate the oil from the ammoniacal liquor, note the volume of each and record. Likewise record the volume of the other fractions and any other pertinent observations. Place each of the fractions in the separate larger containers for the whole class. Repeated fractionation of these combined portions may be carried out if time permits. The writer has found, however, that the anthracene oil fraction gives the best results, since crystalline anthracene is obtained and may be identified.
