G e o r g e W. Latimer, Jr. University of Utoh Salt Lake City, Utah
Piperazine as the Diacetate An o r g a n i c gravimetric experiment
Although there is increasing interest in incorporating :L new and wider range of instrumental techniques into elementary quantitative analysis, equal emphasis should be placed on illustrating how the basic concepts taught in classical analytical experiments extend beyond the range of the narrow scope of the one or two experiments at hand and into areas of work in which their appearance is less than obvious. Many classical volumetric titrations, e.g., iodometry, can be used successfully by students in the introductory course to determine organic compounds;' but without similar exposure to an organic gravimetric experiment a student may be left with the impression that gravimetric analysis, the phenomena associated with gravimetry, and the techniques for handling precipitates are applicable only to inorganic systems. I n 1960, Bond published a procedure for the precipitation as piperazine diacetate,2 which has been found readily adaptable to the undergraduate laboratory with quite acceptable results. Procedure: Weigh out a. sample containing about 0.3 g of piperasine into a 150-ml beaker. Dissolve the sample in 25 ml of acetone. Add 1 ml of glacial acetic acid while stirring canstantly with s. glms st,irring rod. Cover the beaker, permit the soht,ion to stand five minutes, and filter the solution through a tared (llO°C) crucible and suck completely dry. Transfer the precipitate remaining in the beaker to the crucible by using five 5-ml portions of acetone. (If the precipitate adheres tenaciously to the sides of the beaker, wet the policeman with a drop of water. All scrubbing should he done below the surface of the acetone.) After the final washing, apply suction for a t least ten minutes. Ilesiecate the precipitate overnight in a vacuum desiccator containing concentrated sulfuric acid.
The average value (94.5y0, standard deviation of 1.9y0) obtained by a typical class of 209 students is very close to that found for many commercial materials, and the standard deviation (s) is about 2.5 times that of an experienced analyst (3). Since this determination represents not only the students' first gravimetric expenment, but also their first quantitative experiment, the results appear quite satisfactory.
' SCHENK, G. H., J. CFIEM.EDUC., 39, 33 (1962). %BOND, G. R., Anal. Chem., 32, 1332 (1960).
148 / lournol of Chemical Education
A thorough discussion of the method including its limitations is given in the original work by Bond. The above procedure differs from that of Bond in two respects: (1) No attempt is made to evacuate the desiccator to a given pressure. A "good" vacuum is quite satisfactory. (2) The drying period has been extended from 20 minutes to overnight. These modifications were made in a systematic investigation of this method for use on substituted piperazines and, in our hands, appeared to offer more consistent result^.^ This determination along with two 'Lclassical" experiments-a soluble sulfate and a gravimetric ironcomposed the gravimetric portion of one quarter's work. The table summarizes, in brief, the differences in the determinations. Since impurities in the piperazine may appear as brown oils-easily visible, but fortunately soluble in the wash acetone-the concepts of occlusion and adsorption as well as the techniques of efficient washing can be effectively demonstrated. A relatively large amount of piperazine must be taken for precipitation to minimize the effect on solubility losses on the precipitate. Since many of the students come directly fromorganic chemistry, the experiment appears to provide a natural transition into the analytical laboratory work. "FURMAN, D. L.,AND LATIMER, G. W.,
unpublished work.
Piperazine Diocetate Compared With Two Inorganic Grovmietric Experiments -
Piperazine dmeetate Type precipitate Fibrous Solubility (g/100 0.03 in 947, ml 1 acetone Type contamina- Occh~sion of tion oils
Barium sulfate
Ferric oxide
Crystalline
Gelatinous Surface ad5orption
Wash liquid
Acetone
Adsorption and occlumn Hot water
Drying techntqoe
Vacuum desiccation
Ignition800T
NH4N03NHDH Ignition1000T
