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A NEW DERIVATIVE FOR THE IDENTIFICATION OF PRIMARY AROMATIC AMINES GERALD R. LAPPIN University of Arizona, Tucson, Arizona
Warm engaged in synthetic work involving the ethyl aminomethylenemalonates (II), the products of the reaction of ethyl ethoxymethylenemalonate (I) with primary aromatic amines, the author was impressed by
the ease with which these crystalline compounds were prepared and purified. They seemed to offer the possibility of being useful as derivatives for the identification of primary aromatic and heterocyclic amines, particularly for use on the semimicro and micro scale where isolation and purification of the more common benzoates and acetates present difficulties for the inexperienced student. Accordingly a procedure was developed and tried experimentally with five groups of students in qualitative organic analysis. In each case where the new derivative was applicable the student reported greater ease in preparation and purification as compared to other more common derivatives prepared. The chief advantages of the method were found to be: 1. Derivative could be prepared and purified in a shorter time than was usually possible with other derivatives. 2. No solvent was required, making it easier to isolate small quantities of the derivative. 3. No reaction or interference occurred with secondary or tertiary amines or with aliphatic primary amines under the conditions employed. 4. The derivative (11) can be readily cyclized to a second derivative (111) which has a readily hydrolyzable ester grouping, allowing for saponification-equivalent determination. The major disadvantages of the method were: 1. The reagent (EMME) is not commercially available a t the present time. However, it can readily be prepared and keeps well. 2. Alkoxy and aryloxyanilines give oils. 3. Meltiig point differences between some similar .compounds are not sufficientlygreat.
Preparation of EMME Derivative (11). Approximately equal weights of the amine and ethyl ethoxymethylenemalonate (I) were mixed in a small test tube and heated on the steam bath for fifteen to thirty minutes (nitroanilines require a temperature of about 130") and cooled to room temperature. If necessary, crystallization was induced by scratching. The solid was removed and pressed between filter papers. It was then recrystallized from the minimum amount of hot ethanol, using charcoal if decolorization was required. One recrystallization ordinarily gave a sharp-melting derivative. The table lists the melting points of the derivatives of a number of amiues. Cyclization of II to III. For best results a t least 0.5 g. of I1 should be available. To 2 ml. of boiling diphenyl ether was added 0.5 g. of 11, boiling being continued for five to ten minutes. After cooling, the solution was diluted with 10 ml. of petroleum ether and the solid product was collected by suction filtration. Recrystallization from ethanol, pyridine, or a mixture of these gave a sharp melting compound. The table lists the melting points of a number of these derivatives. Melting Points of Derivatives
MARCH, 1951 LITERATURE CITED (1) LAPPIN, G. R., J. Am. Chem. Soc., 70, 3348 (1946).
(2) LAPPIN, G . R., unpublished resultn.
127 (3) PRICE,E. W., AND J. B. ROBERTS, J. Am. Chem. Soc., 68, 1204 (1946). (4) RIEGEL, B., R. H. BAKER, et. al., ibid., 68,1264 (1946). (5) TARBELL, D. S., ibid., 68,1277 (1946).
