SOME IMPROVED PROCEDURES for the ELEMENTARY ORGANIC LABORATORY KEITH M. SEYMOUR* Reed College, Portland, Oregon
A pewration of oxalic acid is described which is be- solutions, he 6nds that the first reagent produces a comlieved to be a useful addition to the aliphatic acid p e w r a - plex mixture very diicult to purify and that the second reagent involves the use of unwieldly volumes (1). twns suitable for elementary organic students. One widely used acid preparation is that of oxalic The aduantuges of using ethylene dichloride, or other halogenated solvents, to replace ethyl ether are discussed. acid from sugar. From the technical viewpoint this is Several applications are described, one of which is a time- an excellent experiment, but i t is m c u l t to see how the student, who usually has no idea of the constitution sauing method of purifying acetamide. of sugar a t the time oxalic acid is studied, can obtain much of educational value from this experiment. The oxidation of ethylene glycol to oxalic acid with PART I. THE PREPARATION OF OXALIC ACID hot nitric acid has been known (2) for many years. One H E common preparations of aliphatic acids are laboratory manual (3)uses it as a test-tube preparation, generally unsatisfactory in the hands of the begin- but no larger scale use of this experiment for elementary ning student. He is told by lecturer and textbook organic students has been noted, despite the fact that that primary alcohols can be oxidized to acids but if the reaction is mentioned in most textbooks. Since he attempts this reaction with the standard organic this test-tube reaction gave good results i t was tested oxidizing reagents, dichromate and permanganate with larger quantities. Due to the volatility of the . glycol a t the temperature attained during the reaction -i t was found necessary to use a flask with a reflux conPresent address: Carleton College, Northfield, Minnesota.
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denser. The following preparation was developed which has been satisfactory in the hands of the students. DIRECTIONS
Twelve and four-tenths grams (0.2 mole) (Note 1) of ethylene glycol are placed in a 500-cc. (Note 2) ringneck flask and about 200 g. (excess) of 6 N nitric acid are added (Note 3). The flask is equipped with a reflux condenser and either placed in the hood or connected to a system for absorbing the nitrogen oxides. The set-up used by Adams and Johnson (4) in their preparation of n-butyl bromide is very satisfactory. The flask is cautiously heated with a small flame. When the solution becomes yellow the flame is removed. If brown fumes are not immediately evolved replace the flame for a moment. The heating should not be continued after the reaction starts. Usually the reaction becomes quite vigorous and it is necessary to cool the flask with a basin of cold water. When the reaction has subsided (ten to fifteen minutes) the small flame is replaced and the mixture gently boiled for thirty to forty minutes (Note 4). The solution is then removed to an evaporating dish, concentrated in the hood (Note 5) to about 25 cc. and allowed to cool. The crystals which form are filtered off with suction. If the filtrate is concentrated a small additional crop of crystals may be obtained. The product is recrystallized once from the least possible hot water. Fourteen to sixteen grams (fifty-five to sixty-seven per cent.) (Note 6) of hydrated oxalic acid are obtained, M.P. 99-100°.
As one method of eliminating these hazards in the elementary organic laboratory the substitution of ethylene dichloride for ether has been investigated. This material was chosen since i t was cheaper than other halogenated solvents with suitable boiling points. However, there are many others covering a wide range of boiling points which are not expensive. Whitmore (6) has recommended dichlorethylene as a substitute for ether. The chief disadvantage in the use of this solvent is the health hazard. Ethylene dichloride, (7) in common with many organic solvents, particularly halogen derivatives, is toxic when breathed in quantity. For this reason, while there is no tire hazard connected with the evaporation of ethylene dichloride from an open beaker over a free flame, such procedure should not be permitted. If ordinary precaution is taken to prevent excessive evaporation of the vapors into the laboratory no difficulty should arise. Ethylene dichloride, like most halogenated solvents, is sufficiently dense that even when extracting a rather concentrated aqueous solution it forms the lower layer in the separatory funnel. This is a v e ~ ydecided advantage when performing repeated extractions. A.
THE PREPARATION OF ANILINE AND 0-TOLUIDINE (WITH ETHEL ~ b PETERSEN) .
In preparing aniline by Degering's (8) procedure, the substitution of three 20-cc. portions of ethylene chloride for the ether led to yields averaging sixty per cent. To obtain satisfactory reduction of o-nitrotoluene i t was found necessary to modify Degering's procedure for NOTES aniline by doubling the quantities of reactants, using 1. Half of this quantity may be used. Students 16 cc. of hydrochloric acid and lengthening the heating using 0.1 mole averaged about forty to fifty per cent., time to three and one-half hours. Ordinary stirrers were but with 0.2 mole there were fewer small yields. found ineffective, but a satisfactory one was made by 2. Due to the vigor with which the reaction some- tacking to the end of a piece of quarter-inch doweling times starts i t is safer to use a large flask. two crossed one-half-inch by three-inch strips cut from 3. Concentrated acid may be used, but 6 N acid a tin can. These blades were twisted around the rod gave better yields in a long series of experiments. to permit the stirrer to pass through the neck of the Smaller quantities of acid gave incomplete reactions. flask, and were then bent out again bymanipulation with 4. If the heating is stopped too soon, the reaction is a rod. The iron strips required occasional replacement, incomplete, leaving glycol which is difficult to remove as they were attacked during the reduction, but this was from the oxalic acid without considerable loss of prod- to some degree an advantage, as it ensured the liberauct. tion of hydrogen in all parts of the mixture. Using the 5. If there is insufficienthood space the flask may be above procedure and substituting ethylene dichloride for connected to a downward condenser and the major por- ether, two reductions of o-nitrotoluene gave a product tion of the liquid removed by distillation. This evapo- collected in the range 198-203". largely 199-ZOO0, in ration may be hastened by the use of reduced pressure average yields of eighty-three per cent. if water pumps are available. Not quite as large B. THE PREPARATION OF ACETAMIDE yields were obtained by this method. (WITH ETHEL M. PETERSEN AND AILAH WILLIS) 6. Yields as high as eighty per cent. were obtained by the better students. This preparation does not involve the substitution of a solvent but is an improvement of a standard experiPART 11. ETHYLENE DICHLORIDE AS A SOLVENT TO ment. The common preparation of acetamide by amREPLACE ETHERS monolysis of ethyl acetate as described by Fieser (9) was The fire hazard involved in the use of diethyl ether followed,with the exception that a ten-inch fractionating is universally recognized, and the danger of explosion column was used, to the point where the temperature when ethers are evaporated has been discussed (5) ex- of the distilling mixture had reached 170'. At this point tensively recently. the residue in the flask was cooled to about 70' and ex-
tracted with 20 cc. of hot ethylene dichloride. The mixture was filtered hot, cooled to room temperature, and the crystals, which formed quickly, were filtered with suction. The product was recrystallized with 15-20 cc. of hot solvent. Yields of nineteen to twenty-one grams (sixty-five to seventy-one per cent.) were ohtained of a white, odorless product melting 80-81'. Without the column smaller yields were obtained due to the difficultyof removing the last of the acetic acid by crystallization. With the extraction method the yield is slightly greater than obtained by the usual method and the product is of a t least equal purity. The chief advantages are, however, its greater speed and the elimination of the annoying solidification of acetamide in the air condenser. Crystallization of acetamide from ethylene dichloride requires about fifteen minutes, is more convenient, gives a better recovery than the alcohol-ether method of Wagner (lo), and yields a comparable product.
While there are certain reactions in which the substitution cannot he made, chieffy those. involving the reaction of a halide, many other experiments where halogenated solvents could be suhstituted for ethers will undoubtedly occur to the reader. One of. the more complete recent references (1) on organic preparations contains more than one hundred reactions in which ethyl ether was used. In more than half of these i t appears that a halogenated solvent could be substituted with no loss in efficiency and in some cases, e. g., the extraction of the halogenated product in the Sandmeyer reaction, the use of a solvent such as ethylene dichtoride should he more satisfactory. D. SUMMARY OF ADVANTAGES OF ETEYLENE DICHLORmE
Where it can be used, ethylene dichloride has these advantages:
1. It is cheaper than ethers. 2. For some materials it is a more efficient extracting C. OTEER USES AND SUGGESTIONS agent than ether. Ethylene dichloride has been suhstituted successfully 3. It forms the lower layer with aqueous solutions in this laboratory for ether as the extracting agent in thus simplifying many extractions. the preparation of benzyl alcohol by the Cannizzaro 4. It can be easily and safely recovered where dereaction, in the preparation of phenetole from diethyl sired. sulfate and phenol and in the preparation of p-cresol by 5. It is less soluble in water than ethers. 6. It greatly minimizes fire hazards. the diazo-reaction on p-toluidine. BIBLIOGRAPHY
HICKINBOTTOM, W. J., "Reactions of organic compounds,"
Longmans. Green and Co., New York City, 1936. W u ~ r z A.. . Ann. chim. 4hvs.. (3). 55. 417 (1859). WILU.~S,' R. J. AND k: BREWSTER,' "A'laboratory manual of organic chemistry," D. Van Nostrand Company. Inc.. New York City. 1928. ADAMS,R. AND J. R. JOHNSON. "Elementary laboratory exoeriments in ormnic chemistrv. The Macmillan company, New ~ o c kCity, 1931.
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(5) DEGERING, E. F., J. CKEM.EDUC.,13, 494 (1936). E C., , "Organic chemistry," D. Van Nostraud (6) W R ~ O RF. Co.. Inc., New York City, 1937. (7) ST. GEORGE, A. V., Am. I. Ckn. Path.. 7, 69 (1937). (8)DEGERING, E. F., J. CHEM.EDUC.,13, 377 (1936). (9) FIESER, L. F., "Experiments in organic chemistry," D. C. Heath and Co.. New York City. 1935. (10) WAGNER, E. C., J. CHEM.EDUC., 7, 1135 (1930).
