QUALITATIVE ORGANIC ANALYSIS IN THE TRAINING OF THE ORGANIC CHEMIST* The student of organic chemistry must undergo a rather abrupt transition in his training as he progresses from the almost purely descriptive lectures and precise laboratory procedures of his beginning organic chemistry courses to research. The latter involves considerable mental initiative in intelligently planning the mode of attack on a problem and ingenuity in adapting procedures given in the literature, which are often inadequately described, to the synthesis of the compound desired. One of the best means of bridging this gap and developing research ability is the course in qualitative organic analysis. The purpose of the present discussion is to outline briefly the essential features of this course and to point out its value in the development of the organic chemist. Content of the Course Since the primary objective is to develop originality in the student, the course is based on laboratory work which the student must plan for himself. His first experiments are designed to review and emphasize certain reactions important from a laboratory standpoint. Although any of the qualitative organic analysis schemes may be used the present discussion will be based on the procedure developed by Kamm.' The following outline shows the topics studied and gives a brief discussion of each. I. Solubility Study.-The student determines the solubility of known compounds in water, ether, dilute hydrochloric acid, dilute sodium hydroxide and cold concentrated sulfuric acid. The compounds used in these tests are so chosen that several examples of all the common homologous series are studied. As a result of this study, the student correlates structure and solubility and learns to classify organic compounds into seven groups. 11. Class Reactions or Homologous Tests.-The second subject studied is the action of certain common laboratory reagents on known compounds. Here the student is taught to associate the results of these tests with the functional groups. He learns not only the scope of these tests but also their limitations. Some of the common reagents whose behavior is studied are: 1. Bromine in Carbon Tetrachloride 2. Bromine Water 3. Dilute Potassium Permanganate Solution
4. Fuming Sulfuric Acid 5. Metallic Sodium 6. Acetyl Chloride 7. Benzoyl Chloride (Schotten-Bauman)
'Presented before the Colloquium on the Teaching of Organic Chemistry at the Third Symposium on Organic Chemistry, Princeton, N. J., December, 1929. 0. Kamm, "Qualitative Organic Analysis." J. Wiley and Sons, New York, 1923. 1593
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8. Sodium Amalgam 9. Alcoholic Silver Nitrate 10. Benzene Sulfonyl Chloride (Hinsberg) 11. Nitrous Acid 12. Phenyl Hydrazine
13. 14. 15. 16.
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Fehling's Solution Tollen's Reagent Sodium Bisulfite Ferric Chloride
The student also learns to run DuClaux constants, neutral equivalents, and saponification equivalents a t this time. 111. Identification of Individual Unknown Compounds.-The third step in the student's training consists in the identification of five pure unknowns. The following outline shows the general procednre for identification. 1. Determination of physical constants. 2. Qualitative analysis for the elements, N, S, P, Cl, Br, I, and metals. 3. Solubility determination. 4. Homologous tests. 5. Consultation of the literature and preparation of a list of possihlc compounds whose properties agree with the above data. 6. Final identification by preparation of a unique derivative; i. e., conversion of the unknown into another compound by an accepted reaction which proceeds in a known way and determination of the physical constants of this derivative. 7. Presentation of a written report on the unknown which lists and tabulates the above data and indicates the proof offered that the unknown is actually the compound reported.
IV. Study of Mixtnres.-The last subject on which the student works is the separation of the constituents of mixtures. After isolation of each constituent in a pure state, it is identified by the above procednre. Three types of mixtures are studied: 1. Mixtures whose components are water soluble. 2. Mixtures whose components are water insoluble. 3. Mixtures which are intermediate between Types 1 and 2.
The foregoing outline represents the major portion of the course. A series of conferences which parallel the above laboratory work are used to discuss the theoretical aspects of solubility and class reactions. The factors governing the choice of derivatives and a general discussion of the mode of attack on mixtures are also taken up during these conferences. The last part of the course is devoted to the solution of problems. These problems present laboratory data on unknown compounds and the student deduces the structure from the experimental behavior. It is here that the student learns to coordinate data and to reason clearly and logically. Value of the Course to the Student As the student proceeds through the course his viewpoint of organic chemistry changes. He correlates his information and begins to connect the observed behavior of compounds with their structures. He sees a
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relationship between structure and solubility, and structure and chemical behavior. In his elementary organic chemistry, compounds were studied by homologous series. Here the student studies the behavior of different homologous series with a few reagents. He sums up his knowledge of organic chemistry and arranges it in an orderly fashion in his mind. In the second place qualitative organic analysis is not a "cook-book course. The procedure and method of attack are provided in a very general way hut the student is compelled to use his own knowledge in choosing class reactions and deducing information therefrom. He must actually think and plan the laboratory work on his individual unknowns. The course also provides the best possible introduction to chemical literature and the practical use of the library. In order to prepare the list of possible compounds the student must not only consult the handbooks of Mulliken, Kamm and Clarke, but also Beilstein, Richter, Stelzner, and for recent work, Chemical Abstracts. By this use of common reference records of previous work in organic chemistry the student is brought to recognize not only the value hut also the limitations of the chemical literature. In his search for suitable derivatives he h d s great gaps in our knowledge and so becomes aware of the necessity for research. The preparation of the written reports on the unknowns is of great value to the student. Here he tabulates his data and really sees that his tests have proved the structure of his compound. This written report also places the emphasis on the proof of the identification and not merely on the identification itself. This is a point that is emphasized over and over again in the conferences; i. e., it is the proof that is worth everything. It is this factor which makes identification by the "smell and guess" method impossible. No credit is given for an identification without proof. This removes any tendency to cheat. Assigning each student different unknowns gives h i a feeling of individual responsibility and pride in his identifications. The net result is the development in the student of a proper scientific attitude of mind toward investigating the unknown. The general esprit de corps of the students in this course surpasses that in any of the other courses. Finally, as the result of his work in this course the lahoratory technic of students is very greatly improved. The amount of the unknown supplied to the student is limited in quantity. He learns to work with small quantities and hence becomes of necessity more careful, neat, and precise in his manipulation. From the viewpoint of both student and teacher the course is a most enjoyable one. The students enjoy the chemical detective work necessary to run down and prove "beyond a reasonable doubt" the identity of an unknown compound. The teaching of the course is a pleasure since it is a fruitful source of new ideas for research. New reagents, new re-
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actions, new procedures, and new derivatives are continually suggested, while improvements in the old methods are made each time the course is taught. The deadly monotony of constant repetition is entirely missing. Men Responsible for Development of Course Any discussion of qualitative organic analysis would he incomplete without mentioning the men who have been primarily responsible for its development. Professor S. P. Mulliken was the Ijioneer in the field and his monumental volumes of "Identification of Pure Organic Compounds," the first volume of which appeared in 1905, marks the beginning of this line of work. H. T. Clarke's "Handbook of Organic Analysis" (first edition, 1911) offered an abbreviated identification of the more common organic compounds. The tables in this handbook, which has been revised and brought up to date (1926), are excellent. At the University of Illinois this course was instituted by Dr. C. G. Derick in 1908 and elaborated and developed by Dr. Oliver Kamm (191115). Dr. Kamm's great contribution to systematic identification was the classification of compounds into seven groups by means of their solubilities. Smce then new derivatives and procedures have been contributed with the result that the course now represents the experience of many men. Staudinger, at Zurich, also gives a course in qualitative organic analysis which is based on volatility and solubility. ' His scheme was published in 1925. Regardless of the specific procedure adopted, there is no doubt that qualitative organic analysis occupies an important place in the training of the organic chemist and assists in preparing him for research.
