V O L U M E 21, NO. 10, O C T O B E R 1949 Henriques (4),Libby (Y), Solomon (8), and Yankwich (9). Parameters IO and 01 were chosen in order to obtain a good fit to the data in the xvorking range of sample thickness from 1 to 50 mg. per sq. em. The value of 01 obtained was 0.216 sq. cm. per mg.
100
5 80 W
u I I :
W
a 60 >-
c 2 tu
1207 data given are well fitted above 4.6 mg. per sq. em. by using 01 = 0.28 sq. cm. per mg. Below 4.6 mg. per sq. em. the experimental curve falls below the theoretical and the extrapolated activity for 0 thickness is 87% of the theoretical. Henriques et al. ( 4 ) employing benzidine sulfate precipitation onto filter paper obtained a value of a = 0.265 sq. cm. per mg., fitting the region from 1 to 11 mg. per sq. cm. Yankwich (IO)and Glendenin (8) have found that the theoretical absorption curve fits the experimental data for sample thicknesses larger than 20’3 of the range, while for thinner samples a departure is observed due to the difference in back-scattering from the planchet material as compared to the carrier material. On this basis one would expect better agreement with the values given by Hendricks et al. and the authors. The value obtained by Henriques for the 1 to 11 mg. per sq. em. range is definitely a function of the backing. The discrepancies noted here are not consistent with the theory in its present state. For accurate work, a self-absorption curve should be run by the experimenter himself. BIBLIOGRAPHY
40
n
w
> E W
cn
20
IO 20 30 40 50 RESIDUE MG. /SQ.CM. Figure 2. Geiger Counter Self-Absorption Curve for Sa6in Barium Sulfate
0
Hendricks et nl. (3) precipitated barium sulfate on brass disks and obtained a self-absorption curve. No theoretical curve was fitted originally but, using their value for the sample area, the
(1) Glendenin, L.E.,.VucZeonics, 2,12 (1948). (2) Glendenin, L. E., private communication. (3) Hendricks, R. H., Bryner, L. C . , Thomas, M . D., and Ivie, J. C., J. Phys. Chen., 47,469 (1943). (4) Henriques, F. C.,Jr., Kistiakowsky, G. B., Margnetti, C . , and Schneider, W. G., IXU. ENG.CHEM.,ANAL. ED.,18, 349 (1946). ( 5 ) Johnson, F., and Willard, J. E., Science, 109,11 (1949). (6) Leslie, W.B., U. S. Atomic Energy Commission, M.D.D.C., 674, (Nov. 15,1946). (7) Libby, W.F., A N ~ LCHEM., . 19,2 (1947). (8) Solomon, A. K., Gould, R. G., and Afinsen, C. B., Phys. Rev., 72, 1097 (1947). (9) Yankwich, P.E.,h’orris, T. €I., andIHuston, J., ANAL.CHEM., 19,439(1947). (10) Yankwich, P. E., and Weigl, J. W., Science, 107, 651 (1948). RECEIVEDFebruary 28, 1949. Work supported in p a r t b y t h e Research Coininittee of t h e G r a d u a t e School from funds supplied b y t h e Wisconsin Alumni Research Foundation. Supported in part from funds received from the UnitediStates Public Health Service.
Rapid Qualitative Method for Acrylonitrile C. E. BROCKWAY B. F. Goodrich Research Center, Brecksville, Ohio Acrylonitrile can be identified by conversion to 8-piperidinopropionitrile, the picrate of which is a suitable derivative. Water and organic solvents, except the stronger acids and bases, do not interfere. Acrylonitrile in concentrations as low as 1% can be detected and identified by this method. Methyl and ethyl acrylate can be similarly characterized by conversion to the picrates of the methyl and ethyl esters, respectively, of 4-piperidinopropionic acid.
I
N CONNECTION with its use in nitrile rubbers the need arose for a rapid and simple method of identifying acrylonitrile. No such method has been described in the literature. A great variety of crystalline derivatives obtained by the cyanoethylation reaction have been described, but the procedures involved do not in general lend themselves to adaptation as simple qualitative methods. Among the most rapid reactions of acrylonitrile are those with certain nonaromatic amines. The aminonitriles obtained are themselves liquids, but may be readily converted into solid derivatives. Such a method for characterizing acrylonitrile has the advantage of greater speed and convenience
than the usual methods for nitriles, and water and various other substances do not interfere. AMINO DERIVATIVES OF ACRYLONITRILE
Piperidine and morpholine (6),certain substituted piperidines (1), and some of the primary aliphatic amines (5)react vigorously with acrylonitrile in the absence of catalyst to give the c o r r e sponding 8-aminopropionitriles. The present study was confined to the use of morpholine and piperidine, particularly the latter. The properties of the two aminonitriles and their derivatives are listed in Table I.
1208 Table 1.
ANALYTICAL CHEMISTRY Properties of Derivatives of .4crylonitrile Beta-Substituted Propionitrile Piperidino Xlorpholino
Nelting Point, Picrate
161-162; 160 ( 6 ) 157 5-158.0 ( 4 ) 158; 152 ( 2 )
Aletliiodidt, Hydrochloride Picrate of parent secondary amine
c' 138-140:.131).5 ( 6 ) 193-195 with drcomp.
181-182
210-211
150-131
148-150
For such application the mixture should first be freed of acid or strong base by any appropriate neutralization, extraction, or distillation procedure. A sample of 0.5 to 5.0 ml. of the neutral mixt,ure is treated with 0.10 ml. of piperidine and the mixture is a!lo!ved to stand 10 minutes before being added to about 5.0 ml. of picric acid solution. If no precipitate is obtained a t once, the mixture should be allowed to stand a few minutes. An alternative procedure, useful for detecting as little as 1% acrylonitrile in a solvent more volatile than P-piperidinopropionitrile, is as follows: T o 20 ml. or more of solution is added about 0.20 ml. of piperidine, and the mixture is refluxed or heated to 100" for 10 minutes. Solvent is then removed by distillation until the distillation residue has been reduced in volume to 2 to 3 ml. A few drops of the cooled residue are added to picric acid solution and the precipitate is treated as above. EXPERIhlENT.4 L
Of the derivatives listed, the picrates are much the simplest to prepare. Addition of either aminonitrile to a saturated solution of picric. acid in ethanol results in an immediate precipitate of the picrate. -4fter recrystallization from ethanol, the picrates have i,eproducible melting points. The piperidino derivative is pref r i w d because its picrate has a higher melting point than that of the parent secondary amine, whereas the reverse is true of morpholine. Hence, there is less chance for uncertainty with piperidine if in case of a negative test for acrylonitrile the picrate of the secondary amine happens to be obtained. However, morpholine h:ls been successfully used t o characterize mmples of :irryloniti,ile.
The effect of varying the ratio of piperidine to acrylonitrile is illustrated in Table 11. Samples of 0.10 ml. of acrylonitrile were treated nith various volumes of piperidine, and the mistures were :illo\ved t o stand 30 seconds and then poured into 5.0 ml. of picric acid solution.
Table 11. iO.10 \-ul.
(if
PROCEDURE FOR QVTALIT.iTIVE TEST
For an unknonm rvhich is suspected to consist chiefly of acrylonitrile, the recommended procedure is tis follows:
-4sm:rll volume (0.1 to 1.0 ml.) of unknown is treated with ji somewhat less than equal volume of piperidine. The misture I$ allo~vedto stand 2 minutes and then added to 5 to 20 nil. of picric acid solution. The resulting precipitate is recrystallized once from ethanol, filtered, and washed with a little ethanol. The product i:, tlried for a few minutes on the suction funnel and the melting point is determined. If the melting point falls in the range of :il)out 161" to 162" C., this n-ill serve to identify the sample :is
I'iueridinr. 111. 0 023
3
1111.
of picric acid noliltion)
Effect Iuiiiiediate turbidity. voluniinoiir precipitate after 5 ininuter: Irninediate dense precipitate Ininiediate dense precipitate Iniiiiediate slight precirJitate N o urecivitate
The effect of escess piperidine :tnd of other amines was further il1ustr;ited by a series of tests in which a niisture of 0.10 ml. each of acrylonitrile and piperidine \vas added to 5 ml. of picric acid solution, nnd the slurry of picrate in mother liquor was treated \\it11 just sufficient amine to redissolve the precipitate. The following volumes were required: piperidine, 0.10 ml. : morpholirie. 0.15 nil. : tii-rc-t,ut?.l:Iiniiic, 0.20 nil.: nriiline, no effect with 5.0 nil. Table TIT. (.\rs~lonitrile.0.10
1111.
Solvent
~
Effect of Solvents
Piperidine, 0.10
\Vatern Ethanol n-Butanol ,,-Hexane .. n-Hexane Light mineral oil E t h y l ether Isopropyl acetate Ibopropyl acetat? E t h y l chloride E t h v l chloride .iceionitrile Propionitrile .\crylonitrile .\lethacrylonitrile M e t hacrylonitrile Acetone Acetone .\Iethyl ethyl ketone l l e t h y l ethyl ketone l l e t h y l isobutyl ketone Methyl isobutyl ketone Formalin, 37% 1:ormahn. 37'3 Leetic acid ~~
Notes. Heat is evolved when piperidine is added to ticrylonitrile. ..\ little spontaneous boiling may occur, but with small samples cooling is not necessary. Heat is also evolved when piperidine is added to various other compounds, notably acids :lnd certain aldehydes. However, if the sample of unknown is ~y~:isonablypure, failure to observe a temperature rise virtually constitutes a negative test. Dilute solutions of acrylonitrile in inert solvents may not give :I noticneable temperature rise when i rwted with piperidine. \Then the piperidine-acrylonitrile reaction mixture is added to picric acid solution, the picrate comes down immediately as an intense yellow powder or as flat yellow platelets. The product is only sparingly soluble in boiling ethanol. Recrystallization can be accomplished quickly by simply leaching the solid for 1 to 2 minutes with about 20 ml. of boiling ethanol, filtering by gravity wliile the mixture is still hot, and chilling the filtrate to rerover tlie purified product. By this procedure picrates melting at 161-162' C. were obtained. The melting points were not :tltc!red hy further recrystallization. From the data in Table 111 it is oppnrent that the method can I)e used t o detect relatively small :tniounts of acrylonitrile in :L wriety of mixtures.
Effect of Amount of Piperidine
of arrylonitrilta.
0.050 0.10 0.50 0.25
REAGENTS
Piperidine. Eastman Kodak Company white l a t d gr:ttlc 01' other material of similar quality is satisfactory. Picric Acid Solution. Excess reagent grade picric acid (containing 10 to 1 2 5 of water) is shaken with commercial denatured vthanol and the solution saturated at Toon1 temperature i. drc:inted from the undissolved solid.
1111.
Picric acid, j . 0 1111.) 11.11. of precipitate Voluiiie, 311. "C 1111.
10.0
159-161
10.0 10.0 2.0 10 n 1 0
158-160 139-162
1 0 1 .
