K. Thomas Finley
Kodak Company Rochester, New York 14650 and James Wilson, Jr. Rochester Institute of Technology Rochester, New York 14608
An Analytical Approach to a
Eostmon
I
Short Organic Laboratory
Everyone who has a serious interest in the teaching of organic chemistry for nonmajors must, have asked themselves, "What is it these students should learn from this course?" The most satisfactory answer is that they should he given the opportunity to master the intellectual framework upon which a physical science is built. The most important thing organic chemistry has to offer someone who does not intend t,o become an organic chemist is its demands in ways of thinking. If anything is to be gained from a hrief exposure to organic chemistry it must be the ability and confidence to take facts to the laboratory for some purpose. If this is accomplished, it then seems likely that, the student will also bring useful knowledge and understanding back from the laboratory to his reading and lectures. Since early in this century the ideal laboratory for accomplishing the objective we have suggested has been in use: the qualitative organic analysis laboratory so common for senior level courses can be adapted to the needs of the nonmajor. There is a compelling reason for using this method for the hrief organic course. We are not really interested in teaching reactions, syntheses, techniques, etc. for themselves, hut rather for the method of observing and reasoning they represent. The student who is told to prepare N-phenylacetamide by reacting aniline with acetyl chloride, learns the techniques and hopefully something about the physical and chemical properties of amines, acid chlorides, and anlides. On the other hand the student who has discovered that his compound is an amine through its
666 / Journal of Chemical Education
solubility characteristics and classification tests and now knows that he must prepare a suit.able solid derivative, such as an amide, in order to complete its identification has learned all of this plus the met,hods of good scientific observation and thought. Laboratory Organization
The basic plan for our laboratory is a simplified qualitative organic analysis scheme based on Shriner, I k o n , and Curtin's hook. The major modification we have made is that of limiting the number of classes of functional groups and the scope of possible unknowns within those classes. The flexibility of this approach is a t least as great as the traditional synthetic laboratory while the reduced scale of operation and time required for each significant step in the identification often makes it possible to examine more types of compounds and reactions than in the conventional lahoratory. We have found that the typical student can easily complete the identification of three simple unknowns (of a purity in the order of Eastman Practical grade or better) in a course which meets for one three-hour laboratory per week for ten weeks. During the second ten weeks, these same students will be able to separate and identify three components of a mixture, providing care is taken to issue mixtures which do not react, form azeotropes, etc. The variety of degrees of purity found in commercially available chemicals is a definite advantage from the point of view of teaching the student that measuring and drawing conclusions from physical constants is a task which requires both skill and
thoughtfulness. This factor requires that different amounts of unknowns he issued, but in general we have obtained good results with about 15 ml of liquid and 3 g of solid. For the mixture these amounts are increased somewhat and at least 30 g of total mixture has produced satisfactory results. Advantages of the Qualitative Laboratory
The advantages we see in this approach are illustrated by examining a typical set of unknowns and noting the specific areas of organic chemistry to which the student is exposed. Simnle Unknowns N-methylaniline p-nitrophenol 3,4-dimethoxybensaldehyde
Alizlure o-ehl~robenaoicacid 1-botyl alcohol 5-hexen-2-one
The variety of types of organic compounds represented here is obvious and needs no further discussion; it seems unlikely that any more functional group classes could be handled with the synthetic approach. The real question, however, is how thoroughly can they be treated? The matter of determining physical constants is not, apparently different from that which would be involved in synthetic experiments. The advantage is in the fact that the studelit sees a very practical reason for doing the laboratory work. The same thing is true for determining the presence of atoms (or ions) other than carbon, hydrogen, and oxygen as well as the solubility classification procedure. These very useful techniques of the organic chemist are seldom included in the typical synthetic laboratory. The application of classification tests for the determination of the functional group present represents an opportunit,y to carry out a number of the classic reactions of organic chemistry. The particular compounds in our example require: the Hinsberg, the Tollens', the iodoform, and the Baeyer reactions among others. Quantitative techniques learned in other courses are put to use in the neutralization equivalent determination. Even more important is the requirement that the student himself decides which test must be applied in order to provide the necessary information. Later he must make deductions on the basis of these data being careful to consider all of the possibilities and not be misled by amhigious observations.
The fact that our laboratory is an analytical one ill no way removes or diminishes the importance of synthetic organic chemistry. The preparation of a solid derivative is simply a practical application of the synthesis of new organic molecules. The often heard complaint of the undergraduate that he must go into the laboratory and make compounds in which he is unable t o see any point, makes this application a most desirable one. The randomly selected sample of unknowns TX-e are discussing introduce amides, esters, 2,4-dinitrophenylhydranones, and possibly other new classes of compounds. They also involve acylation, condensation, displacement, and esterification reactions. The techniques of vacuum filtration, hot filtration, recrystallization, and mixed melting points among others are involved. As useful and as interesting as this lahoratory is, there can he difficulties. The liberal use of lecture demonstrations is required and the laboratory instructor has to be working with the students especially during the first use of any new technique and the separation of the mixture. Another requirement is the careful coordination of lecture with lahoratory. For example, the fact that the preparation of derivatives is really a synthesis. It, is quite possible for students to think only of the identification of their unknown and miss this very important idea. An even more subtle point is found in cases like the iodoform oxidation or the bisulfite addition. Here the treatment in lecture and laboratory might reasonably he quitedifferent. Most of these considerations are the basic requirements of any well taught college laboratory science course. The fact that they are especially important in the format suggested in this paper only serves to illustrate the great opportunity the met,hod offers. It has the additional advantage of allowing great flexability. For example, if the library is good, students can search for information about their unknowns or new derivatives, classification tests, etc. I n laboratories which have such instruments as an infrared spectrophotometer or a gas chromatograph, a whole new area of interesting possibilities is available. A good case can be made for this approach being as much fun and as interesting for the faculty as for the students.
Volume 44, Number 7 I , November 1967
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