Reuben L. Baumgarten, Charles M. Dougherty, and Ohannes Nercessian Herbert H. Lehman College Bronx. New York 10468
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The Sodium Nitmprusside Reagent A classification test for aliphatic and aryl amines
T h e conventional classification tests used i n t h e detection and identification of m i n e s , such as the Hinsberg test and the nitrous acid test, sometimes give confusing results and may be difficult t o interoret. For example, t h e comoound D - ( N methylamino)-benziic acid can be mistaken for a amine on t h e basis of t h e Hinsberg test. Another difficulty with t h e Hinsberg test is t h a t t h e i o d i u m salts of t h e be". zenesulfonamides of some primary amines (e.g. t-butylamine and n-heptylamine) and of some high molecular weight amines such as cyclohexylaminel are only slightly soluble or insoluble in t h e stronelv alkaline reaeent solution. Oils a r e often obtained i n s t e i o f solid benzenesulfonamides, particularlv if t h e amine used is n o t oure. Nevertheless. t h e test is used extensively in the identification of amines, perhaps, because when run successfully, a solid derivative of the amine results. T h e nitrous acid test must be r u n a t a temperature close t o O°C t o prevent oremature decomposition of t h e nitrous acid. ~ h e i e s ct a n b e inconsistent, giving inconclusive results with some amines, particularly if other functional groups are also present. Many other assays have been used t o t r y to differentiate among various types of m i n e s . Two of these, the Rimini and Simon tests, seem to have drifted into o b s c ~ r i t ydespite ,~ their utility i n distinguishing primary a n d secondary aliphatic amines. These tests have been known since 1898,",4and have roved oarticularlv useful i n classifvine beta-hv. - orimarv . h r o x y G i n e s whici give anomalous results i n the &ow aAd t e s t . U n advantage of these tests is t h a t a positive reaction is indicated by t h e appearance of a n intense color when t h e amine is treated with the sodium n i r o ~ r u s s i d ereaeent. W e wish to present a modification we have developid which permits t h e extension of these tests t o aryl amines.
Results and Discussion The conventional Rimini and Simon tests using sodium nitroprusside reagent can be used to distinguish between primary and secondary aliphatic mines. Primary aliphatic mines produce a deep red color in the Rimini test. and a nale yellow to reddish brown solution or orecinitate . . in the &on t&t (which is considered a neeative result). In most cases the deeo color annears . . in several seconds. hut romeamines take up to2 min;opruducean intensly colored &tion ur precipitate. The secondary aliphatic amines produce a deep red or wine-red color in the Rimini test and a deep blue color in the Simon lest. The time fur the appearance 01 there culum again \.a& hum several seconds tu 2 min depending on the amine bring tested. The 'Fanta, P. E., and Wang, C. S., J. CHEM. EDUC., 41, 280 (1964). $The Rimini and Simon tests are discussed in Cheronis, N. D., and Entrikin, J. B., "Identification of Organic Compounds," Interscience Publishers, John Wiley & Sons, Inc., New York, 1963,pp. 131and 133; howpver, two of the most currently used texts in the field, Shriner, R. L., Fuson, R. C., and Curtin,D. Y.,"TheSystematic Identification of Organic Compounds," Fifth Edition, John Wiley & Sans, Inc., New York, 1967. and Pasto, D., and Johnson, C. R., "Organic Structure Determination," Prentice-Hall, Ine. Englewood Cliffs, New Jersey, 1969, do not discuss them. "Simon, L., Comptes Rendus, 125,534 (1897). 'Rimini. . E... Chemisches Zentralblatt.. 11.132 . (1898). SHaumgarten. R. L.. unpublished results. ',Inwrested parties ma" ohtain cumplete tables listing the data for the rumpwnds tested by writing tu the authors.
Modified Sodium Nitroprurride Reagent Compound
Rimini
Simon
Primnry A romatic A mines
aniline o-ethyisnllinc O-toluidine m-toiuldine p-chloroaniiine p-iodoaniline p-fluoroaniline 2.4-dimethylantline 2.6-dimethylaniline 2.4.6-trimethylaniline o-nitroaniline
red redarange red-brown red-brown redarange red rea-orange red-orange orange-brown red-orange orange
i-amino'na~nths~ene 2amino nmthaiene red-orange Secondarv Aromatic A m h e s red-brown ale red
N-~henyibenzylamine~ aiphenylamineC
red-brown
. .. ...
red-orange red-brown wine-red red-brown deep red red-brown red-brown deep red red-oranoe red-orange red-brown red-range
red-brown purple purple
.~ u. r
~le
..
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Tertrarv Aromotic Amines
N,N-aimethylaniline greend N.N-aiethyianiiina greend 3-dimethv~amino~heno~~w a y weend
greend greend red-brown
a C ~ i o rhere war not as intense a r in Other tests. b U ~ o nstanding a Dale green precipitate formed. Ccom~ounawar insoluble in nitroorusride reaaent. dsoi~tionwar initially rea-orange but cnangedrapiaiy to green with formation o f a green Drecipitate. eDi6~01vedin 95% ethanol. tests appear to be inconclusive for tertiary aliphatic amines. All the aryl and aromatic heterocyclic amines tested with the conventional Rimini and Simon nitroorusside reaeent .. ,.e w e neeative tests. No dlstrnct color uas produced: occasionally a rather inrmrlusive yellow to yellow-green,o r olive udur appeared alter a few m i n ~ t e s . ~ We have developed a variation of these tests which permits their extension to classify aryl amines. We postulated the reason the aryl amines did not produce intense colors in the conventional Rimini and Simon tests could be attributed to one or more of the following: 1) aryl amines are, in general, less basic than aliphatic mines, 2) the rate of color formation bv the arvl amines could be much slower than bv the aliphatic amines, 3) thesolubilities of the aryl nminrr in the R~mini and Simon test reagents ere generally less than those ofthe aliphatic amines. Different solvent systems were tried to attempt to overcome these difficulties. Of the many solvent systems investigated to date, the best one appears to be a 0.13 Msolution of sodium nitmprusside in 80% dimethylsulfaxide-20%water, using zinc chloride as a Lewis Acid catalyst. The table contains emarimental results for some of the comoounds tested using the n i t r o p k i d e reagent i n B W , DMSO-20%h w r in the presence of the zinc chloride camlyst. Upon examination ol the data it ran be seen clearly that the use of the zinc chloride catalyst increases the reaction rate and makes the colors more intense so that the reaction can now he extended to primary, secondary, and tertiary aryl amines. The primary aryl amines tested give orange-red to redbrown solutions or precipitates aver a period of a few seconds up to 5 min depending on the m i n e tested. Even relatively weak bases such as the nitromilines. that mav . escane . detection bvother ~.~chemical and soluldity tests, giw positive term under rhcre conditions. In the case of secondary aryl amines, the n h r s seem tc, get darker on standing. slowly changing from red to purple. Tertiary aryl amines, such as ~~~
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Volume 54, Number 3, March 1977 1 189
N,N-dimethylanilime, give colors that change from orange-red to green over a period of 5 min. Sulfanilic acid, which exists as a zwitterion, and diphenylamine and triphenylamine (which behave as neutral campounds, insoluble in 5% hydrochloric acid) give negative tests. This modification of the Rimini and Simon tests permits the rapid detection of aryl amines. A basic compound which gives a negative test using the conventional Rimini and Simon tests, hut s w i t i v e test usins ~n the nitroorusside reseent in 80% DMSO-20% water with a zinc chloride catalyst con he rlnssified as an aryl amine. The rolora pro. durrd by the tertiary aryl amines ere not as distinctive as the oranre-red, red, red-brown. or purple solutions andlor precipitates formed by primary and secondary aryl amines. We are currently investigating this in hopes of distinguishing even more clearly among primary, secondary, and tertiary aryl amines. Most aromatic heteroeyelie amines give negative tests with the modified nitroorusside reaeent:. however. indale and 2-methvlindole give deep. mtenae red-purple and orange-red colors, respectivrly.l'he o r a n p r e d colur.These compound I -methyl-2-pyridonealsogivesan compounds are very weak bases, nnd at present wc have nocxplnnation to rationalize these results. We are presently studying the reactions of other, more complex amines with the nitroprusside reagent. We are also investigating the effect of different Lewis Acid catalysts and different solvent systems on the rate and intensity of color formation. The replacement of DMSO by same less hazardous solvent is the first goal of our efforts. ~
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Experimental The Rimini Test T o 1 ml of sodium nitroprusside reagent (0.13 M in 50% aqueous methanol), add 1ml of water, 0.2 ml of acetone, and then about 30 mg of an amine. Primary and secondary aliphatic amines pmduce a deep red color. The Simon Test To 1 ml of sodium nitroprusside reagent (0.13 M in 50% aqueous methanol), add 1ml of water, 0.2 ml of acetaldehyde solution (10%).
I 9 0 I Journal of Chemical Education
and then about 30 mg of an amine. Primary aliphatic amines p r d u c e red, yellow, or red-brown colors; secondary aliphatic mines, produce a deep blue color.
Preparation of Modified Nitroprusside Reagent Compuunds which are suspected of heing sryl aminer (negative ) he r e a d s with the conventional Rimini and Simon I P R ~ should tested with the modified sodium nitroprusrde reagent described below. The sodium nitroprusside reagent is prepared (0.13 M )in 80%dimethylsulfaxide-20%water instead of aqueous methanol as asolvent. The reagent should he stored in a refrigerator t o prevent decomposition, using small amounts in a dropping bottle as needed. Caution: Precautions should he taken in the handling of the nitroprusside reagent in DMSO. Contact with the skin and breathing DMSO vapors should be avoided. Modified Rimini Test To 1 ml of 0.13 M sodium nitroorusside in 80% dimethvlsulfoxide-21% watrr,add ( i n t h ~order,: s 1 mlsaturated aqueuusincchloride.0.2 mlolacetone,nnd thanahout ROmg oftheamine. Ruth primary and secondary awl m i n e s produce a red or red-brown solution andlor precipitate; tertiary aryl amines give a green solution andlor precipitate. ~
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Modified Simon Test T o 1 ml of 0.13 M sodium nitroprusside in 8Wb dimethylsulfoxide-20% water, add (in thisorder): 1mlsaturated aqueous zinc chloride, 0.2 ml of acetaldehyde (10%), and then a b u t 30 mg of the amine. Primary aryl amines give a red-orange or brown solution andlor precipitate, secondary aryl amines, a purple solution andlor precipitate, and tertiary aryl amines, a green solution andlor precipitate. Acknowledgment W e would like to t h a n k Professor M. Lazarus for helpful discussions during the course of t h i s work.
