Titration of Aromatic and Aliphatic Amine Picrates in Nonaqueous Solution JOHN R. CLARK and S. M. W A N G M a l t b i e Laboratories, Inc., Newark,
N. J.
C
OSANT, Hall, and Werner (1-4) illustrated in their extensive studies on organic amines too weak to be titrated in aqueous solution that the amines could be successfully titrated in glacial acetic acid with perchloric acid. Sadeau and Branchen (6) first employed the nonaqueous acid-base titration for amine acids successfully. They also employed indicators for their titration. Markunas and Riddick ( 5 ) found most amines could be titrated in acetic acid potentiometrically.
Table I.
Determination of Milliequivalent Weight of Amine Picrates,"
Melting Milliequivalent Weight Sample Point, C. Calculated Found Diinetl.y;aniline picrate 162-163 350 Ethylenediamine dipicrate 232-233 518 Diethanolamine picrate 109-110 332 Aniline picrate 322 165(decomp.) 2-Aminopyridine picrate 2 16-217 324 2,4,6-Collidine Dicrate 155- 156 352 Piperidine picrate 150-152 314 313 a Picrates \yere prepared from commercially available amines by precipitation from alcohol. They were recrystallized from alcohol to obtain a melting point closely corresponding to the accepted value.
These principles were applied to a procedure for the titration of picrates of aromatic or aliphatic amines in glacial acetic acid, using methyl violet as an indicator. Because picrates are in general the most convenient crystalline derivative for the identification of amines in synthetic work, and are easily purified, this method was devised for the determination of the milliequivalent of amines before elemental analysis. REAGENTS
Glacial acetic acid, U.S.P. Methyl violet indicator, 0.2% in chlorobenzene.
Perchloric acid, 0.1S. Mix 8.5 ml. of 72% perchloric acid with 200 ml. of glacial acetic acid and 20 ml. of acetic anhydride. Dilute to 1 liter with glacial acetic acid. Standardize the solution against acid potassium phthalate. PROCEDURE
Dissolve 1to 4 meq. weights of amine picrate in 50 ml. of glacial acetic acid with the aid of gentle heat if necessary. Cool the solution to room temperature and titrate the solution with standardized perchloric acid, using 6 drops of methyl violet indicator, until the disappearance of the purple tinge of the solution. Results arc listed in Table I. SUMMARY
A rapid method was developed for the determination of the milliequivalent weight of amine picrates by direct titration with perchloric acid in glacial acetic acid. By using methyl violet indicator, a reasonably sharp end point was obtained. The yellow coloration of the picrates did not interfere with the end point. This method was found useful for the titration of primary, secondary, and tertiary amines, whether aromatic or aliphatic. LITERATURE CITED (1)
Conant, J. B., and Werner, T. H., J . Am. Chem. Soc., 52, 4 4 3 6 (1930).
Hall, N. F., Zbid., p. 5115. Hall, N. F., and Conant, J. B., Ibid., 49, 3047 (1927). (4) Hall, N. F., and Werner, T. H., Ibid., 50, 2367 (1928). (5) hfarkunas, P. C., and Riddick, J. A., ANAL. CHEM.,23, 3 3 7
(2) (3)
(1951). (6)
Nadeau, G . F., and Branchen, L. B., J. Am. Chem. Soc., 57, 1 3 6 3 (1935).
RECEIVED for review October
16, 1953.
Accepted March 18. 1954.
Colorimetric Determination of Niobium by Molybdenum Blue Method GEORGE NORWITZ and MAURICE CODELL Pitman-Dunn Laboratories, Frankford Arsenal, PhiIade/phia, Pa.
T
HIS laboratory was called upon to develop a method for the
determination of niobium in titanium alloys. I n investigating the problem an attempt was made to determine the niobium by a molybdenum blue method either directly or after a tannin separation of the niobium from the bulk of the titanium. These attempts were unsuccessful owing t o the interference of titanium with the color. However, because of the great current interest in niobium and the lack of good colorimetric methods for niobium, the authors decided to investigate the molybdenum blue color obtained with niobium. The use of the molybdenum blue color for niobium was proposed in 1947 by Davydov, Vaisberg, and Burkser ( I ) , who applied the method to the determination of niobium in steels. Since that time no other paper has appeared on the method. In the procedure proposed by these investigators the sample of steel is dissolved in a mixture of sulfuric, nitric, and hydrofluoric acids,
and the solution is diluted to 50 ml. An aliquot of this solution is diluted so that the normality is approximately 0.5N. Disodium hydrogen phosphate and ammonium molybdate are added and the yellow phosphomolybdate and niobiophosphomolybdste colors are allowed to develop. .4n excess of sulfuric acid is then added to destroy the phosphomolybdate color and the solution is treated with stannous chloride. The molybdenum blue color due to the niobiophosphomolybdate complex is then measured with a colorimeter. At first, attempts to duplicate the results of this procedure were not successful. However, a thorough investigation finally clarified the many factors affecting the method and resulted in the development of an improved procedure. APPARATUS AND R E.AG EYTS
Beckman spectrophotometer, Model B, with four 1-em. matched cells.
1230
