NOTES ON ANALYTICAL PROCEDURES Metallo-Organic Complexes in
Organic Anatysis Some Qualitative Tests for Amines FREDERICK R. DUKE, Princeton University, Princeton, N. J.
S
ALICYLALDEHYDE in ammonia or primary amine solution precipitates nickel, the precipitant being the imine (8). The reaction of 5-nitrosalicylaldehyde is similar to that of salicylaldehyde, except that ammonia solutions produce a precipitate only after a number of hours, the exact time depending upon the ammonia concentration. However, a solution of 5-nitrosalicylaldehyde and nickel ion, when added to a primary amine, produces a immediate precipitation. This is the basis for the qualitative test for primary amines. Secondary amines, when allowed to react with carbon disulfide, produce dialkyldithiocarbamates (1). When the reaction is allowed to proceed in the presence of nickel ion, a precipitate of the carbamate with nickel is formed. Primary amines fail to produce a similar precipitation under the conditions of the test.
PRIMARY AMINES. Reagent. To 15 ml. of triethanolamine are added 0.5 gram of 5-nitrosalicylaldehyde (m.p. 124-5' C.), and about 25 ml. of water, and the aldehyde is brought into solutmn. Then 0.5 gram of nickel chloride hexahydrate dissolved in a few milliliters of water is added, and the total volume is brought to 100 ml. The reagent, now ready for use, is stable for long periods of time. If the triethanolamine contains some ethanolamine, it may be necessary to add another 0.5 gram of the aldehyde and filter off the resulting precipitate. Procedure. To 5 ml. of water are added 1 or 2 drops of the amine to be tested. If necessary a drop or two of concentrated hydrochloric acid may be added to dissolve the amine. When 0.5 to 1 ml. of the amine solution is added to 2 to 3 ml. of the reagent in a test tube, an almost immediate precipitation indicates the presence of a primary amine. The presence of a slight turbidity indicates rimary amine as an impurity only. Aromatic amines genera& require 2 to 3 minutes for the test. Sensitivity. The sensitivity of the test is almost constant on a molar basis from one amine to another. When the concentration of the amine in the test solution is 0.02 M , a test is obtained. Below 0.02 M , the test loses its distinctiveness. SECONDARY AMINES. Reagent. To 0.5 gram of nickel chloride hexahydrate in 100 ml. of water is added enough carbon disulfide so that, after shaking, a globule of the carbon disulfide is left on the bottom of the bottle. The reagent is stable for long periods of time if tightly stoppered. If all the carbon disulfide evaporates, more must be added. Procedure. An aqueous solution of the amine .or its hydrochloride is prepared as under the test for primary amines. To 1 ml. of the reagent in a test tube is added 0.5 to 1 ml. of concentrated ammonium hydroxide, followed by 0.5 to 1 ml. of the amine solution. A precipitate indicates a secondary amine. A slight turbidity is an indication of secondary amine as an impurity. Sensitivity. As in the test for primary amines, this test has about the same sensitivity on a molar basis for all amines. The lower limit is about 0.01 M in the test solution. Each test was applied to the following amines: Primary Methyl Ethyl n-Propyl Isopropyl n-Butyl Isobutyl 6-Butyl Cyclohexyl Aniline Ethanolamine Toluidine Naphthylamine
Secondary Dimethyl Diethyl Di-n- ropy1 Di-n-gut yl n-Methylaniline Diethanolamine Piperidine Morpholine
Tertiary Trimethyl Triethyl Tributyl Dimethylaniline Triethanolamine Pvridine
The tests operated satisfactorily, without exception. I n some cases amines of one class gave slight tests for amines of another, indicating the presence of impurities. INTERFERENCES. Hydroxylamine, hydrazine, and its derivatives where only one nitrogen is substituted, give a positive test for primary amine. Urea and other amides do not give primary amine tests. * No common interference was found for the test for secondary amines. High concentrations of ammonia or tertiary amines invalidate the test for primary amines by rendering the precipitate soluble. High concentrations of secondary amine produce an anomalous precipitate. In general, the tolerances are 75 moles of ammonia, 20 moles of secondary, and 25 moles of tertiary amine t o one of primary amine. The test for secondary amines operates in all concentrations of ammonia, and primary and tertiary amines. Many water-insoluble organic compounds readily dissolve the precipitates, necessitating the removal of such solvents if possible. SUMMARY
Tests for primary and secondary amines which succeed in the presence of relatively high concentrations of amines of other classes and ammonia are described. The former are based upon the reaction of the amine with 5-nitrosalicylaldehyde accompanied by precipitation of the nickel complex with the imine and the latter upon the reaction of the secondary amine with carbon disulfide accompanied by precipitation of the nickel complex with the carbamate. LITERATURE CITED
(1) Hofmann, A. W., Ber., 3,767-8 (1870). (2) Schiff, H., Ann. Chem., 150, 197 (1869).
A
Simple Polarographic Cell
J. B R E N N A N G I S C L A R D Bureau of Industrial Health, Michigan Department of Health, Lansing, Mich.
P
OLAROGRAPHIC cells for small volumes of solution usually call for delicate glass-blowing jobs or platinum wire-to-glass seals which are often unsatisfactory. A satisfactory cell which avoids these difficulties is shown in the diagram. The cell consists of a 5-ml. syringe barrel (of the rubber plunger type) with the rubber stopper held securely in place by a few strands of small copper wire. A 20-gage, 5-cm. (2-inch) stainless steel needle with a piece of wire soldered to its base serves to admit nitrogen and complete the circuit. The unit is mounted on a small clamp (not shown in the diagram). I n operation, the needle is inserted through the stopper but slightly off center to allow a small amount of mercury and the test solution to be more conveniently admitted. I n removing oxygen, nitrogen is first allowed to flow through the needle, the tip of which is then withdrawn beneath the surface of the liquid. After this, the needle is pushed above the surface to prevent re-entry of oxygen from the air while the polarogram is taken. Numerous determinations have shown that repeatedpenetrationaof theneedleinto the stopper do n o t cause it to leak. The cell has proved to be ircult, very convenient for small volumes (1 to Tank nit 2 ml.) and practically unbreakable.
196
