Identification of Amines by X-Ray Powder Patterns of Their Chloroplatinates C. W. GOULD AND S. T. GROSS' Central Research Laboratory, General Aniline & Film Corp., Euston, Pa. The work described w-as undertaken to provide a convenient technique for identifying submilligram quantities of volatile amines which might arise in degradation experiments on more complex substances. The easily prepared chloroplatinate salts, not hitherto considered useful for identification purposes because they have unsatisfactory melting points, are w-ell suited to characterization by their x-ray powder patterns. The diffraction data are given for the chloroplatinates of 25 common aliphatic and aromatic amines. The technique is useful if x-ray equipment is available, and if it is necessary to identify a small sample of a volatile amine, or its salt, without the additional micromanipulations involved in preparing and purifying other derivatives.
I
5-mm. diameter. The cover glass was placed over the 3 X 18 mm. cylindrical depression in a 5 X 25 X 75 mm. microscope slide, so that the drop hung over the center of the depression. Then the cover glass was lifted and 1 to 2 mg. of the amine, or an equivalent of its salt, followed by 1 drop of 5 X sodium hydroxide, were placed in the cell and mixed. The cover glass and hanging drop were replaced immediately. It was helpful if a 1-microliter drop of water was allowed to flow under the edge of the cover glass to keep it from sliding off center over the cell.
N THE degradation of dyestuffs and intermediates it is some-
times necessary to identify submilligram quantities of amines formed by oxidation, reduction, or hydrolysis. Since the most simply prepared derivatives are salts, some method of identification other than melting points is required; the x-ray powder method is appropriate. The chloroplatinates are valuable for this purpose because the gain in weight in the conversion to amine chloroplatinate (thirteenfold in the case of ammonia) facilitates working with very small amine samples, and the high scattering power of the platinum atoms shortens exposure time necessary for good x-ray patterns. The technique of using a micro gas cell for distilling the amine into a hanging drop of chloroplatinic acid vias suggested by Chamot and Mason ( 2 ) who used it in the detection of microgram amounts of ammonium ion by microscopical observation of the ammonium chloroplatinate crystals. While the technique described below is for larger amine samples and the identification is by x-ray patterns, the use of a polarizing chemical microscope is recommended for observing crystal formation and detecting impurities. TEST SUBSTANCES
Alost of the amines tested were Eastman white label preparations; the rest were Baker C.P. reagents, except for morpholine, ~thanolamine, diethanolamine, and phenylethanolamine from Carbide and Carbon Chemicals Co. REAGENTS
Water Repellent for Cover Glasses. A quarter of a gram of paraffin was dissolved in about 20 ml. of carbon tetrachloride. This solution was stored in a wide-mouthed weighing bottle. Platinum Chloride, 25%. The contents of one 1.0-gram bottle of Baker'k platinum chloride (HzP~CIB.GH,O)were dissolved in 3.00 grams of distilled water. The solution was stored in the original bottles, tightly stoppered. For 10% platinum chloride, 1.00 gram of the above solution was mixed b i t h 1.50 grams of wate?. Saturated Sodium Bisulfate. The mixture is in equilibrium with air of 52y0 relative humidity a t 20' C. (4). It also may absorb vapors of amines in excess of the amount necessary to form the chloroplatinates.
Figure 1.
The slide was placed on the microscope stage, and the edge of the hanging drop was observed for 0.5 to 1 minute under the X100 power, for signs of oil droplets, crystal formation, or schlieren. If such an effect was observed, the distillation was allowed to proceed a t room temperature. If no oil, crystals, or schlieren were seen, the slide was gently warmed over a microflame until the cover glass fogged slightly, then was replaced on the microscope stage. If crystals appeared and grew, their shapes, manner of growth, and their polarization colors were observed. Any triangular or octahedral crystals which shorn-ed no birefringence were notedthese were the chloroplatinate of ammonia, a common contaminant of commercial amines or of the reagent exposed to laboratory air. If no crystals appeared in 5 minutes, the cover glass was lifted
PROCEDURE
A cover glass was dipped in the paraffin solution, then shaken to remove the excess, and XTiped with lens paper. Cover glasses were 25-mm. squares, 0.2 mm. thick. -4hout 5 microliters of 25% reagrnt were pipetted onto the center of the cover glass. The invisible paraffin coating on the slide prevented spreading of the reagent drop to more than about 1
Filtration and Collection of Chloroplatinates
Present address, Research Laboratory, M. W. Kellogg Co., Jersey City,
N. J.
749
750
ANALYTICAL CHEMISTRY and the hanging drop was scratched x i t h a glass fiber. Some chloroplatinates supersaturate readily (triethylamine) ; others come out first as yellow oils (dimethylaniline). Other chloroplatinates are extremely soluble (dipropylamine), so that it is necessary to dry the hanging drop partially. If scratching did not start crystallization, the hanging drop was placed over concentrated sulfuric acid in the cell of a second microscope slide. Khen the chloroplatinic acid started to crvstallize, the cover glass was placed over saturated sodium bisulfate solution in anothrr cell. The chloroplatinic acid crystals started to dissolve immediately. dfter 5 minutes the mixture was filtered and the yellow or orange chloroplatinate crystals were collected in 3 compact little pile in the center of the cover glass by pushing with a piece of S o . 1 Whatman filter paper held under a second cover glass, as indicated in the diagram, Figure 1. Finally, more mother liquor was removed by squeezing the crystals under the filter paper. The crystals usually adhered to the cover glass rather than to the paper. In some cases-e.g., ammonia, methvlamine, pyridine, morpholine-under the conditions specified, the chloroplatinate formed so iapidly that a crust covered the exposed surface of the hanging drop, and this crust appeared amorphous under the XlOO pon-er. While such chloroplatinates may be suitable for the powder pattern without grinding, they are ugly to a chemist x h o admires beautiful crystals, and their high ratio of surface to volume hinders rcmoval of the mother liquor. This mother liquor causes t n o defects in the final x-ray pattern: weakness from general absorption and diffuse darkening in the center. Secondly, although the hygroscopic chloroplatinic acid in contact with air at humidities of >30% does not give a crvstalline diffraction pattern by itself, it may absorb from laboratory air amines different from the substance under test, and thereby show extra interferences in the pattern. If the chloroplatinate formed too rapidly, the evperiment was repeated mith these changes: (a) a smaller amine sample, ( b ) a drop of lsater along x i t h the alkali and amine, and (c) a hanging drop of 10% reagent. X-RAY EQUIPMEYT AYD TECHVIQUES
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The x-rays used in this laboratory consisted of copper radiation from a Rlachlett type A-2 tube, operated a t 10 ma., filtered through0.001inch nickel foil, Exposures required about 20 minutes. The film was dnsco nonscreen x-ray film. The sample holder was a brass bar 1.52 X 9.52 X 70 mm., with a 6.35 X 0.125 mm. slit cut through then ide faces and centered 19 mm. from one end, with the long axis of the slit parallel to the long axis of the bar. The area around the slit was rubbed with a cloth met with chloroplatinic acid solution to give a black stain on the brass; the hlack stain was then burnished with a dry cloth to give a bright coating of platinum which prevented reduction of chloroplatinates bv the brass. To load the sample, the cover glass was placed on the holder so that the sample lay against the holder at one side of the slit. The cover glass v a s rubbed parallel to the slit in order to crush the sample to the desired particle size. The sample was transferred to the slit by rubbing the cover glass with a circular motion over the slit. S o tamping \vas necessary; it \vas sufficient to
V O L U M E 25, NO. 5, M A Y 1 9 5 3 cover the opening of the slit with a thin layer of powder that transmitted no more than a few pinpoints of light when viewed against a strong light. The sample holder n-as inserted in the side of a special circular camera (3) of 7.0-cm. radius which was constructed in this lahoratory. The 0.125-mm. slit in the sample holder served as the co1limat)ing system 13.0 em. a!yay from the source. S o Iiack collimating pinhole \vas used. The angular range of this cainwa Iyas about 57”. The divergence of the x-ray beam x a s :d)out 0.1”. The cutoff limit for high d values \\-as about 50 -1. .\ fpature of the camera xvhich tended t o decrease the cost of individual patterns as the curved film cassette which could 1)e tmnslated after each exposure so that eight patterns could be ol)tained on a single film. The patterns n-ere measured Kith a transparent, scale prepared photographically on reprolith film, having a scale in Angstrom units for d values c*alculatedfrom the equation
x
= 1.54 = 2 d sin
(3
rvherc R = 7.0 em.. and S was the distance betxveen opposite interference a r e on the film. The accuracy of such measurements \vas zk0.01 d.a t d = 2.00 A,, and about 1 0 . 1 -1. at, 10 A. When greater accuracy ]vas required. i t vias possible to use the ordinary methods of measurement and calculation. T7alues of t i for the chloroplatinates of 25 amines are given in Talilc I. along ~ i t hvisually estimated intensities relative to the strongest interference which is arbitrarily assigned the value of 1.0. 1/11values are given for the principal interferences onl>-: thc &shes in the 1/11 column indicat,e relative intensities 1 c w thnn the loxvwt value stated for each pattern. DISCUSS103
The diffraction data in Table I shon- that the strongest interference;; in each pattern are characteristic of the chloroplatinate measured. Pome less intense lines may arise from the platinized hrass holder: platinum s h o w lines a t 2.27 ( l . O ) , 1.96 (0.86). and 1.18 (1.0) according to the t:il>It,s in (I); the brass showed 2.13
75 1 (1.0) and 1.84 (0.3). according to measurements made in this laboratory. The only previous x-ray diffraction data available for comparison with Table I are for ammonium chloroplatinate (I)-namely, 5.70 (1.00)) 4.93 (0.6), 3.48 (0.2), 2.97 (0.5), 2.46 (0.3), 2.26 (O.l), and 2.20 (0.2),with less intense lines a t smaller d values. It is evident that the use of a distillation step in the method described above Lyill not be possible xvith amines of low volatility. Tests have been made, however, n-hich suggest that the minimum volatility necessary t o obtain crystalline chloroplatinates in a hanging drop placed 3 mm. above the surface of the amine, would correspond t o a boiling point betxveen 250’ to 300” C. if an hour were allowed for the distillation. S o n e of the amines which contained hydrosyethyl groups gave satisfactory chloroplatinates by the method described. Ethanolamine. di- and triethanolamines. S-phenylethanolamine and -Yphenyl diethanolamine were tested. Certain bases, such as hydrazine, phenylhydrazine, and p phenylenediamine, reduced the reagent to platinum. The hanging drop turned black n-ithin an hour. ACKNOWLEDGXIEWT
The authors gratefully acknov-ledge the help of F. K, Mtchell, F. W.Seumann, and R. A. 11acDonald in preparing chloroplatinates, and in obtaining and measuring the diffraction patterns.
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LITERATURE CITED
i l ) ;Im. Soc. Testing llaterials, “llphabetical and Sumerical Indexes of S-Ray Diffraction Patterns,” 1950. ( 2 ) Chamot, E. XI., and Mason, C. W., “Handbook of Chemical lficroscopy,” 1-01, 11, 2nd ed., pp. 74-5, K e a York, John
TTiley 8: Sons, 1940. ( 3 ) Gross, S.T., U. S.Patent 2,584.962 (Feb. 5, 1952). (4) Hodgman, C. D., Editor, “Handbook of Chemistry and Physics,”
30th ed., p. 1925, Cleveland, Ohio, Chemical Rubber Publishing Co., 1949.
RECEIVED for review September 1 2 , 1952.
.Iccepted January 21. 19.33.
Oxidation of N-Alkylarylamines Identification of N-Alkyl Groups F R E D W. SEUMANN AND C. T. GOULD Central Research Laboratory, General . h i l i n e &: F i l m Corp., Easton. Pa.
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HIS paper is an account of a study of the scope and limitations of oxidation of AV-alkylarylamines by dichromate in a sulfate-bisulfate buffer, and of simple methods for identifying the carbonyl compounds, quinones, and simple aliphatic amines formed to characterize the S-alkyl groups. The formation of aldehydes and ketones as oxidation products of .V-alkyl groups in amino acids (34, 37), amino alcohols ( 3 8 ) , and aliphatic aniines ( 2 , 3. 11, 13, 21, 22, 27, 33, 40, 47.48,50, 5 1 ) has been txtensively studied. The oxidative loss of ;\--alkyl groups, as the corresponding carbonyl compounds, from arj-Iamines is less ivell knon-n. Previous work has concerned the production of form:ild~liydc(,$, 1 7 ) and substituted benzaldehydes ( 18. 19. 33) by osidation of S-methyl and S-benzj-lanilines. Diepolder (I,?) in 1898 identified ethylamine as an oxidation product of o-ethylaminophenol. S o previous work has covered the systematic study of alkylated ary1:imines. using one oxidant and a large number of amines variously sulistituted on the S-atoms and the aromatic nuclei. The proerrlure is very selective in action to the aromatic bases, and miniinizes positive tests sometimes given hy other func-
tional groupe--c.p.. aliphatic amineP.
ethers, esters, olefinic linkages, and simple APPLICATIOS S
The, extensive testing (listed in Table I ) of the procedures offers a basis for their application in the milligram degradation of commercially important S-alkylated arylamines. I n the general case, whenever a mixture of aldehydes and ketones is expected from different -\--alkyl groups, the 2,Cdinitrophenylhydrazine reagent is recommended as carbonyl precipitant. The chromatographic separation (23. 26, SI! 35, 43, 44.54) of 2,4-dinitrophenylhj-drazone mixtures is amply described in the literature. However, in vietv of complications arising in the dinitrophenylhydrazone series-stereoisomerism and polymorphism-identification as dimethones is preferable when possible. [The aldehyde as derivatives obtained using 5,5-dimethyl-1.3-c~-clohexanedione reagent is referred to here as dimethone derivatives-e.g., 2,2’methylene bis-(5,5-dimethyl-l,3-cyclohexanedione)as formaldehyde dimethone; 2,2’-ethylidene tiis-(5,5-dimethyl-l,3-cyclohesanediont) as acetaldehyde dimethone. etc. The reagent,
