VOLUME 33, NO. 8, AUGUST, 1996
SLEUTHING IN THE CHEMISTRY LABORATORY: AN IMPROMPTU PROJECT LEROY D. JOHNSON Lincoln University, Lincoln Unive!.sity, Pennsylvania
CHEMICALS closed up in cabinets for long periods and subject to the varying seasonal changes of temperature and humidity though seemingly protected by plastic caps may escape slowly and be absorbed by wood or other surrounding materials. These vapors may even interact and cause some interesting phenomena. The localized growth of crystalline, stalactite-like structures suspended from the bottom of a reagent shelf beneath which a thionyl chloride bottle had previously stood was responsible for this investigation. Students in the general organic laboratory were given some of the crystals as "unknowns." Reports from these students indicated the presence of carbon, hydrogen, nitrogen, chlorine, a melting point above 200°C., solubility in water and alcohol but only slight solubility in benzene. These observations suggested a polar compound. An attempt to detect the chemical or chemicals causing this seldom observed phenomenon was made by isolating the various chemicals lower in the cabinet than where the thionyl chloride bottle had previously stood. Among the chemicals on these shelves protected by seemingly tight-fitting plastic caps were the following: resorcinol, sodium potassium tartrate, succinic anhy-
dride, sulfanilic acid, toluene, thiourea, o-tolidine, otoluidine, trichloroethylene, petroleum ether, xylene, tartaric acid, phenylhydrazine hydrochloride, picric acid, and pentamethylene bromide. One by one each of these was placed alone in the cabinet to see if the crystals reappeared. After careful observation for several days as the chemicals were replaced it was discovered that ortho-toluidine was the culprit responsible for the beautiful crystals. The wooden shelf absorbed hydrogen chloride fumes which had been formed from the hydrolysis of thionyl chloride by atmospheric moisture. These then formed a salt with ortho-toluidine vapors. SOCla
(air) + Hg0
o-CHsCnH4NHz
-
-r
+ HCI
SOnT
+ 2HCl T
[a-CHaC6H4NHalfCL-
This project in detective work in the chemistry laboratory was unexpectedly valuable in that (1) it provided experiences and experiments for introducing prospective chemistry majors to problem-solving in qualitative organic analysis, (2) it gave pertinent information about storage and inspection of chemicals, and (3) it served as an introduction to the use of chemical reference literature.
