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CHEMICAL PROJECTS Research Ideas for Young Chemists JAY A. YOUNG, King's College, Wilker-Barre, Penno. JOHN K. TAYLOR, Nationol Bureau of Standards, Washington, D. C.
Determination of Saponification Equivalents of Phenolic Esters See TOBEY,S. W., el al., J. Chem. Educ., 38, 611 (1961). I n the identification of compounds many different properties can be used such as molecular weight, color, infrared absorption characteristics, behavior in various chemical environments, and others. One identifying feature, often used for esters, is the weight (in grams) of ester per equivalent of base needed to saponify the ester. This ratio is called the "saponification equivalent." Phenolic esters often do not yield reproducible s.qxmifieation equivalents when the procedures described in various reference works are used. The t~uthorshave developed a procedure which does give reliable results with phenolic or any other esters.
Questions: The authors state t h a t they are not sure why the older procedures far the determination of the saponification equivalent of sn ester often fail with phenolic esters, though they do suggest afew possible reasons. Can you establish t h a t one or more of the reasons they suggest are valid, or, can your determine some other explanation? The authors indicate that phenolphthalein cannot be used as an indicator in the hack titration step of their procedure since phenol is itself acidic enough to react appreciably with the base before the phenolphthalein has changed color. Therefore, they recommend the use of another indicator. Phenolphthalein could he used, however, if before the back titration the phenol were tied up chemiertlly in some way so that its acidic character would not he evident. Can you suggest a. practical scheme for accomplishing this result?
When determining the saponification equivalent of phenolic esters which have n nitro substituent on the aromatic nucleus, thymolphthalein should be used as the indicator in the hack titration step because most substituted phenols have pK values less than X 2 . Can you find any phenolic esters with a nitro suhstituent on the aromatic nucleus for which thpophthalein is not required as the indicator in the back titration step? Or, can you find any other aromatic esters, in addition to those mentioned by the authors, which are not nitro derivatives of phenol, for which thymolphth~leinis required as an indicator in the back titration step? Can you succeed where the authors failed, and develop a mixed indicator which would besuitable for both types of phenolic esters, those with phenol derivative moieties with pK values above, and below, 9.2? The saponification equivalents of carhoxylic acid esters of polyhydroxyl aromatic compounds and of esters of p-hydroxybenzoic acid and p-hydroxycinnamic acid cannot be determined by the procedures described. Can you devise s. suitable procedure for one or more of these classes of esters? NOTES: The investigations suggested by the questions here are recommended for the student who has a strong interest in, and comprehensionof,organicchemistry andanalyticalchemistry. The use of tris(hydroxpethyl)aminon~ethaneas a primary standard, though recommended, is not mandatary. See THIS J o m a ~ 36, , 297 (1959). Similarly, apparatus with standard taper joints will facilitate the experimental work but is not essential.
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A Biochemistry Laboratory Experiment See SCREE, I., el al., J . Chern. Bdue., 38,632 (1961). When an electrical discharge is passed through a gas or mixtures of gases, new products m e often formed as a result of the action of the electrical discharge. It has been postulated that prior to the existence of life on the earth, an analogous natural oroeess orodueed the essential cam~onentsfor livine forms. which
for several days through a mixture of ammonia, water vapor, and ordinary burner gas.
Question: Construct an apparatus similar to that described in the article and hll it with a suitable gas or gas mixture. Pass an electrical discharge (a spark coil from a. "Model T" Ford-these are still xvailahle a t reasonable cost-can be used instead of the induction coil recommended) through the gas for a suitable period of time, and identify as many of the products formed as possible. AF count for the formation of these products and test your suggestions by further laboratory work. NOTE: Since explosive mixtures of gas may inadvertently be used initiallv or might be formed during the course of a run, be sure to use safety shields and to wear safety goggles when conducting this investigation.
A Constant Current Source for Student Use See MANN,C. K.,
AND
CHAMPEAUX, V. C., J. Chem. Educ., 38, 519 (1961)
For many modern studies in quantitative analytical chemistry a source of constant current is necessary. Mast of these studies comprise investigations in one of these fields: coulometric titration a t constant current, potentiametric titration a t constant current, ohronopotentiometry, and current scanning potentiometry. Of these the first is probably the simplest for a beginner to study. I n the article, the oonstruotion of an inexpensive transistorized
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constant current source is described. Na specific suggestions are made for its usein an experimentalinvestigation. Construct the constant current source described and use it to help solve a problem posed in another chemical project in this ~t is s u g g e ~ dthat the firstproblem you select involve a titration which you can adapt to 8 constant current conlometric titration.
