Two Tests for Detecting Nitriles and Amides SWIATOSLAW TROFIMENKO' and JOHN W. SEASE Department o f Chemistry, Wesleyan Universify, Middletown, Conn. ,Two tests are described for the identification of amides and nitriles. The first involves pyrolysis of the test substance with soda lime, any ammonia or amine which is formed being detected b y volatilization into methanolic copper sulfate solution. The second depends upon the formation of organomercury compounds by those amides which have a hydrogen atom attached to the amide nitrogen. Designed for the qualitative organic laboratory, the tests make possible a ready differentiation among nitriles, N-unsubstituted amides, N-monosubstituted amides, and N,N-disubstituted amides. HEX nitrogen is knon-n to be present in a qualitative organic unknown, basic functional groups can be detected by solubility behavior d h dilute hydrochloric acid (10) or more reliably by color changes wit'h acidindicator mistures ( 5 ) . Of the neutral nitrogen-containing functions the nitro, nitroso, azosy, azo, alkyl nitrite, and alkyl nitrate groups can lie reduced with ferrous hydroxide or n-ith zinc and ammonium chloride (10). Sitriles and amides can be detected, but not differentiated, by the hyclrosamic acid test, if no ester, acid anhydride, acid chloride, or trichloromethyl grouping is present (1, 10, 1%'). The two tests for amides and nitriles described are designed to supplcrnent the hydrosamic acid test. confirming its results !Then it can be used, and furnishing an alternatiT-e, more generally applicable procedure n-hen it' cannot' be used. I n most cases the proposed tests can not only differentiate betn-een nitriles and amides but also indicate whether a n amide is 1%'-unsubstituted, S-monosubstituted, or N-disubstituted and whethcr an aromatic substituent or only aliphatic substituents are present. SODA
LIME-METHANOLIC TEST
COPPER
SULFATE
This test is a modification of the soda linie pyrolysis test described by Cheronis and Entrikin ( S ) , n h o decomposed amides and nitriles by heating lvith soda lime. It differs from their pro1 Present address, Department of Chemistry, Xorthwestern University, Evanston, Ill.
1432
ANALYTICAL CHEMISTRY
cedure in that a dilute methanolic solution of copper sulfate is used as reagent to detect any ammonia or amine formed in the pyrolysis. Ammonia, in the amounts Iiberated, gives a characteristic behavior that is distinctly different from that of aliphatic or aromatic amines, so that nitriles and unsubstituted amides maj' be distinguished from S-substituted amides. The niethanolic copper sulfate reagent is particularly useful because it possesses an adequate, but not escessive, sensitivity and is a t the same time highly specific. Overly sensitive reagents, such as Kessler's reagent, are unreliable because they often give positive tests n i t h the traces of animonia which are liberated under the drastic conditions of the soda lime pyrolj-sis by most compounds containing nitrogen and hydrogen (6). Other tests, such as the sodium nitropriissiate-resorcinol test (2) or the thymolhypobromite test ( 7 ) , cannot distinguish between ammonia and some of the primary aliphatic amine-. The copper sulfate reagent also detects amines, when they are formed instead of 2mnionia, and usually gives considerable information ahout their nature. Reagents. T h e soda lime used \vas J. T. Baker U.S.P., low moisture, 20mesh. The methanolic copper sulfate reagent was prepared by dissolving 1 gram of cupric sulfate pentahydrate in 100 nil. of methanol, allowing the solution to stand for 24 to 48 hours, and filtering off any greenish precipitate which had formed on standing. Procedure. Approximately 100 nig. of solid test substance was mived thoroughly \\ith a small amount of soda lime and placed in a 13 X 100 nim. test tube; enough soda lime n a s taken to fill one third or one fourth of t h e test tube. Best results n-ith liquid test substances w i e obtained by putting the liquid in t h e t r s t tube and then adding the soda lime. The test tube was clamped a t a G d e g r e e angle and its mouth closed with a cork containing an L-shaped delivery tube which was drawn out to a fine point that reached to the bottom of 1 ml. of methanolic copper sulfate solution contained in another small test tube. The soda lime was heated. gently a t first and then more vigorously, until any volatile products formed were distilled over into the detecting reagent.
Results. Ammonia produced a nhite turbidity which quickly changed to a purple or blue precipitate, s l o d y settled to t h e bottom of t h e t'est tube. and did not change color appreciably on standing. The following test substances gave satisfactory positive tests for ammonia by this procedure: Amides. Acetamide, adipamide, benzamide, n-butyramide, n-caproamide, achloroacetamide, cyanoacetic acid, formamide, malonamide, p-nitrobenzamide, propionamide, salicylamide, urea. Nitriles. Acetonitrile, acrylonitrile, benzonitrile, n-butyronitrile, n-capronitrile, phenylacetonitrile, succinonitrile. K h e n tested with the niethanolic copper sulfate reagent, ethylenediamine behaved in the same way as ammonia and constitutes the on]>- knon-n interference, although other vicinal diamines would probably behave similarly. o-Phenylenediamine also gave a purple precipit'ate with the reagent, hut this was not stable and lost its color within a fen minutes. Soluble blue or green complexes resulted ivhen the following test substances were added directly t o the methanolie copper sulfate reagent : Primary Aliphatic Amines. 2-Amino-2methyl-1-propanol, 1-amino-2-propanol, benzylamine, n-butylamine, cyclohexylamine, ethanolamine (on prolonged standing 3. few blue crystals formed), ethylamine, methylamine. Secondary Aliphatic Amines. Diethanolamine, morpholine. Pyridine Derivatives. 2-Aminopyridine, pyridine, 2-methylpyridine, 2,4-dimethylpyridine, 2,2'-bipyridine, quinoline, isoquinoline. The same results were obtained by the soda lime pyrolysis of .2'-ethylacetamide, S-(d-hydroxyethyl)-acetamide, and -Tmethylacetamide. d pale green or greenish blue solution from which a flocculent, pale green precipitate slowly settled out was obtained when the following compounds n-ere tested with the metlianolic copper sulfate reagent: Primary Aliphatic Amines. n-Octylamine, n-decylamine, n-octadecylamine, 1,6-hesanediamine. Secondary Aliphatic Amines. Di-nbutyl amine,^ diethylamine, dimethylamine, piperidine. Tertiary Aliphatic Amines. Tri-nbutylamine, triethylamine, trimethylamine. The same results were obtained by
tlroi~ghthe informntion ol)t:iinctl in tiiiq the soc1:i lime pyrolj tylnc~~tniiiitlc, . \ ' , ~ ~ - t l i c t l i y l : ~ i ~ e t ~ i ~ i ipi r~ol c~i~~,l u r cis cwcxiitially :I duplic~:ition of c ~ ) l ) l ~sulcr . \ ' , . \ - d i r t l i y l c l i l o r t ~ ~ ~ t ~ ~ ~ t ~.Y$.\--di~ i i i i t l ~ ~ ~ that given 1)y tlic nic~t11:~noiic~ ttli~lforrnaiiiitlc,antl ~~-,.\'-dinietli?lfor- h t e procedure, on sonic ocwisions it is a most useful supplement to that pro1n:tmide. A very siniilar result, which could not be reliably distinguished from cedure. that just described, was given by Xethylaniline and .Y-methylariiline, either MERCURIC CHLORIDE-BROMOTHYMOL BLUE added directly t o the methanolic copper TEST sulfate reagent or formed by the soda lime pyrolysis of X-ethyl-S-phenylTliiq teqt depends upon the formation aretamide and .T-methyl--Y-phenylacet- of nicrt*ury salts by amides \I Iiich ha1 c a niide. n t lwd onc h ydrogen at om :it t :itahcrl to Heavy, intensely colored precipitates nitrogcn (13): which iisually darkened and tlccomp n s d on standing vere gil-en by tliosc 2 -CO-YTIHgCI. + I prininry aryl amines tested n-itli the nirthanolic~copper sulfate reagent ; f'or-CY b k - H g - S - U )211 'CI tunately, none of these precipitate:7 \!-:is blue or purple. Aniline gave a lime The test substance is taken in excess, green precipitate, o-toluidine a n d p so that it is possible to tell whether or toluidine greenish yellon-, l-naplitliylnot the aliove reaction has taken place :mine and p-plicii!.lrnctliaiiiine brown, simply hy inaking the solution alkaline. 2-naphthylaminc~reddish brown, and oIf niercw% chloride is still present, a tolidine hroivnisli I yc~llow-liro\rii precipitate of nicrcuric pyrolysis proccdurc \\-:is trstcd n-ith oside form*. If tlie niercury has all been acetanilitlc, ii-Rcc't'otoluitlc, Iienzunilitle. cwnvertcd t o a n org:rnomercury conip-bronioacetaniliclc, n-caproanilidc, carl)tJlllltl, the solution either !vi11 be clear lianilide, forrnanilidc. malonnnilide, antl or !vi11 contain onlj a sninll amount of propionanilidc. Hydrazinr, n-hen nddctl wliite precipitate, tlcpcnrling on thc directly to the iiirdisnolic copper siilfstr solubility of tlit~ orgnnomwcury cmiireagent. gave a flocculent grayid) Iron-n ~)ountl. rI'lie t w t is c'losrly I precipitate whicli qiiickly turned into a tlesc.rilml 1)y Connor and \'an Cnnipen heavy, clcnse I i r o ~ nprecipitate ; no hy14, 9) for rcactiyr methylene g r o u p ; tlrnzitles were avnilalile for testing. their procedure is reported to lie posiAromatic nitro compounds formed tire for .\-~uisuIistitutetl amides h i t , intense colors-orangr, red, brown, or imlike tliip test, usually fnils with .YI,lack-n-hen the soda lime mixture ivas riionofiulistitutctl amides. lieatc.(l. If tlie heating was done carefully to avoid distilling any of the colored Reagents. T h e mercuric chloridesniatvrial into the copper sulfate reagent, lromothpmol blue I eagent n as p i ('there was usually no interference with I m e d b y dissolving 27 grams of m c i thP detection of ammonia. Khile this cuiic chloride and 0.1 gram of broniothymol blue in 200 nil. of methanol. hehavior is probably not n relialk test' Procedure. Fifty t o 100 mg. of n w for the nitro groupl it is highly suggestin1 test substance n a s dissolved in 2 t,ive of the prcsencc of such a grouping. nil. of methanol. If t h e saniplc did Modification. A variation of t h e not dissolve completely, t h e satuiatetl tcst, employing a n acid wide-range methanolic solution n a s taken. Apindicator mixture as detecting reagent proximately 0.1 ml. of mercuiic chloinstead of t h e methanolic copper sulride-bromothymol blue reagent was fate proved highly useful whenever added and the solution vas agitated there was doubt as t o whether t h e disfor 5 to 10 seconds. Then 0.5X methanolic sodium hydroxide was added tillate contained a n aliphatic or a n dropwise until the solution changed to aromatic amine. T h e acid wideblue or a turbid green; t\yo additional range indicator reagent was prepared by drops of base mere added to ensure dissolving 0.1 gram of phenolphthalein, that the solution was sufficiently nlkn0.2 gram of methyl red, 0.3 gram of line to precipitate any unrenctcrl nicrinethyl orange, 0.4 gram of bromothymol cury as the oxide. hlue, :tnd 0.5 grain of thymol blue in 500 in1. of 95% ethanol ( 8 ) and adding 40 Results. A clear blue solution or a 1111. of 6 S hydrochloric acid. One drop white precipitate suspended in a Iilue of this stock solution \vas diluted with solution constituted a positive test, 10 drops of water to give the detecting which was given by the follon ing comreagent as needed. Ammonia or alipounds: ~rhaticamines, when distilled into this reagent, first neutralize the hydroS-Unsubstituted Amides. Acetamide, chloric acid and then form buffers that adipamide, benzamide, n-htyraniide, nare sufficiently alkaline to turn the indicaproamide, chloroacetamide, cyanoacetamide, formamide, malonamide, p-nitrocator blue or green. The buffers formed benzamide, propionaniide, salicylamide, Iiy aroriiatic amines are yellow or urea. ora.nge, while the reagent remains red in N-~CIonositbstitutrd Amides. Acetanithe absence of any basic distillate. Allide, o-scctotoluide, p-acetotol(iide, p -
+
+
:iniirio:)ct~tnriili~~~., Iie~iza~iili~le, p-Iminor r - c ~ n ~ ~ ~ ~ o : u i i lvi~t Ii vc i, i : ~ i i i l i ( l (-V~, niirlr, fomi:ini\itltx, .V-(o-hyd~oxrt:imitlr, ni~iloiiaiiilitk, .\''j
t:tniiclc., pi,olJiori:triilitlo.
The formation of a turbid greenish suspension, which soon separated into a >.ellow precipitate of mercuric oxide and a clear blue supernatant solution, was considered a negative test. This result was obtained n.ith the following test substances : Sitriles. Acetonitrile, acrylonitrile, benzonitrile, n-hutyronitrile, cyanoacetic :wid, phenylacetonitrile, propionitrile, YUCrinonitrile. Iiutylacetamide,
-diethylacetamide ,V-methylacet anilide, AY-methylformanilide, S-methyl, p-nitroacetanilide. -Y,.\'-dimethylfornmmide,
Interferences can result from tlli(, presencc of olefinic or acetylenic niultipl(. bonds or of a-hyirogen atoms, any of diicli inay react with mercuric chloritlr or mercuric oside under the test oonditions. Although such functional groups contain no nitrogen. it is iniportnnt to know their behavior in tlic. nierc.uric~ t.liloride-hromot,liymol I)luc, tost. bet*:iuw tlicly u i n l t l I)(, pwsent in :I test iiilist:rnc.e \vliicli :ilw containi: a nitrogenons fiinctiotial group n u t 1 might thrreforcx Iw iulijcctctl to this procrdiirr. ,Icc.ortlingl!~, n nunil:er of nitrogen-frrr ~ ~ O i i i ~ x J ~ wcre lllt~~ tcstcd to dctcrniinc lion swious tlic intcrf'crrnrc might h. In most s ~ i c l irasw an initial negative trst, was obtainctl, but, witliin n frnseconds or a fcw minutes n f t w thc atldition of h a w the yc~llon.prccipitntt. of nicrcuric oside cithcr t,urncd nliitc n r tlissolved, thereliy trmsfmniing the sult into a pnsitive one. \Tliert. such :1 "pse.udo-positive" result can h cleai-1). tlistinguished froxii the ordinary positive test and correlated with the presence of an "active hydrogen" in the molecule, there is no loss of specificit,y. The following hehaviors were observed for thc aldehydes, ketones, esters, antl unsatur:itcd compounds tested: r(3-
Aldehydes
Positive. Crotonaldrhydr. Pseudopositive. Acetaldehyde, n - b u t w aldehyde, cimiamaldehyde, paraldehyde. Negative. .hisaldrhrde, lienz:ildehyde, fot m:ilclrhyde, sa1icyl:ildrliydr. Ketones
Positive. Acetone, cyclopentnnonc, 2,3pentanedione. Pseudopositive. Acetophenone, cyclohrsnnone, 2,,5-hexanedione,methyl n-amyl ketone, methyl ethyl ketone, methyl isobutyl ketone, methyl isopropyl ketone, methyl n-propyl ketone, methyl p-tolyl ketone. Kegative. Benzoin (on standing a black deposit of mercury formed), benzophenone, camphor, diethyl ketone. VOL. 30, NO. 8, AUGUST 1958
1433
Esters
Positive Diethyl malonate, ethyl acetoacetate. Pseudopositive. Ethyl cyanoacetate. Segative. ti-Butyl acetate, di-n-l)iityl oxalate, diethyl diethylmalonate, diethyl oxalate, ethyl acetate, ethyl benzoate, ethyl n-butyrate, ethyl phenylacetate, methyl benzoate, methyl propionate, methyl salicylate, phenyl a c e t a h npropyl propionate. Unsaturated Compounds
Positive. Vinyl acetate. Pseudopositive. Cyclohexene. Negative. Allyl alcohol, styrene. Cnfortunately, no alkynes were avail-
able for trsting, but they would be expected to give positive or pseudopositive rewlts. DISCUSSION
Possible combiriations of results in the two tests are summarized in Table I. The behavior of ammonia n ith methanolie copper sulfate reagent is highly characteristic; lion ever, the behaviors of the various types of amines formed on uyrolysis are not sufficiently tlistinctivr to identify unambiguously the type of substituent attached t o the amide nitrogen. For the same reason methanolie copper sulfate is not suitable as a general clarsification reagent for amines, al-
Table
l.
Behavior of Nitriles and Amides
Soda Mercuric Lime and Chloride Methand anolic BromoCopper thymol Sulfatea Blue +NH? NH?
Sitriles S-Unsubstituted amides A’-MonosubstiAm tilted amides N,A’-DisubstiAm tuted amides a THB. Ammonia in distillate. Am. Amine in distillate, with usually dome indication as to its nature; “acid wide-range indicator” modification of this test is often helpful.
+ + +
1434
ANALYTICAL CHEMISTRY
+ +
though it could be exceedingly useful in certain special cases. As amines interfere in both tests, these procedures cannot be used with basic ubstances. Amines are readily detc.rtable, hoivr\.tJr, b>- their solukdity and their behavior with acid-indicator iiiixtures (6); any difficulties from this source can be eliminated simply by testing first for amines. Khile the soda lime-methanolic copper sulfate test seems to be reliable for amides of low molecular weight, it has been pointed out (11) that some amides having higher molecular weight alkyl groups attached to nitrogen, such as
(czr,),c- CH, - C(CH~)*- ?;H
CO-R,
-
dceomposc on heating to give olefin and .~-uiisuI)stitutctlamide; tlic evolution of ammonia from the latter woiild lead to erroneous results. Berause phenols, primary and sevonrlarj- aliphatic nitro compounds, aritl possihly somi’ carboxylic acids c a n also interfere with the mercuric chlorirlebromothymol blue test, its application m i s t h e limited to neutral compounds. It is probably nise iilso to exclude thow neutral test substancw which oxidize ferrous hylroxide or zinc :rntl aninioniiini chloride (fO),althorigh iionc of the rainpounds available for testing (azol)enzene, azoxybenxene, isoani>-l nitritr, aromatic nitro compounds) interfered. \Ilirri the test is limited to neutral, rionoxidizing test substances, a negative or pseudopositive result is reliable. If a positive test is obtained, a check must be made to ensure that it was not due to carbon-carhon unsaturation or to an a-drogen activabetl by a carbonyl or ter linkage. Suitable tests for these functional groups are descrihed in laboratory manuals (10). JYith the possible exception of the acetylenic bond, these groups do not necessarily interfere with the test for amides. Adtlitionnl information about an unknon-n often makes it possible to conclude that there could be no a-hydrogen with sufficient re:ictivity to give a positive test and therefore that the observed result is or due to the presencBe of a -CO-K€12 -CO-KHgroup. The Zimnierman test (f4),although not ne11 known or widely used, might be particularly useful, as it apparently gives positive tests
itli iiiost neutral compounds hich ha\ e sufficiently acidic hydrogens to mteifere n ith the niercuric chloridebromothymol blue test. The two tests descrihed in this paper, :I, n ell tlic ‘acid M de-range indicator” iiiodification oi the sodj. Iinit. pl rolysis, have been used routinely for the past 3 years in the senior author’s qualitative organic laboratory by approximately 120 students. The tests have given excellent results and contributed greatly to the rapid and reliable identification of neutral nitrogencontaining 01 ganic coinpoundz. \\
LITERATURE CITED
( I ) Uui:kle~;,11. E.> Tlielcn, C. J., .~sAI,. CIIERI.22, ti70 (1950). (2) Caseneuvr, AI., H i t l l . SOC. pha/.iti. Bordyuu.z 6 1 , 153 (192i3). ( 3 ) Cheronis, X. I ) . , Eiitrikiii> J. B., “Seniiniicro Qualitative Organic Analysis,” p. 130, Crowell, S e w York, 19-17. ( 4 ) Connor, It.> Van Campen, J. I i . ,
( 8 ) l l r r c k & Co., “Alerclr Index,
Rah\\-uj., S . J., 5th ecl., p. 601,
1940. (9) Shriner, R. I,., Fuson, R. C., “Systematic Identificatioii 01 Organic Compounds,” 3rd ed., p. 100, JJ-iIey) A-ew York, 1948. (10) Shriner, R. I*.>Fuuori, R. C., Curtin, 1). Y.,“Systemat,ic Identificatiou of Organic: Compounds,” 4th ed., JIYIry, h-erv York, 1956. (11) Soloway, P., priva (12) Soloway, Y., Lip CHEX. 24, 898 (I!152). (13) Williams, J. I\-.> Rainey, IT-. T., Jr., I.eopoltl, R. S., J . -4 t i l . . Cheni. SOC. 6 4 , 1i38 (1912). (14) Zimmermann, JJ7,>%. phyaiol. Chew. 233, 267 (1935).
RECEIVED for review Xovember 18, 1957. Accepted March 12, 1958. Division of Organic Chemistry, 133rd Meeting, ACS, San Francisco, Calif., April 1958.. Work taken in part from a thesis submitted to the faculty of Wesleyan University b y Swiatoslaw Trofimenko in partial fulfilment of the requirements for t h e degree of bachelor of arts with distinction in chemistry.
