ing Materials, E-14 Meeting, San Francisco, 1955. (3) Beelhouwer, C., Riemskijk, A. J. van, Steenis, J. van, Waterman, H. I., Anal. Chim. ... . Acta 6 . 476 - 11952). ~
- I
\ - - -
~~
(4)Brook, B. M., Whitman, B: T., J. Inst. Petrol. 44, 212 (1958). (5) Ferguson, W. C., Snyder, L. R., Am. SOC. Testing Materials, E-14
Meeting. New Orleans, 1962. (6) Fitzgerald, M. E., Cirillo, V. A., Gal-
braith, F. J., ANAL. CHEM.34, 1276 (1962). (7) Hamway, P., Cefola, M., Nagy, B., Ibid., 34, 43 (1962). ( 8 ) Karr. C.. Jr.. Weatherford. W. D.. Jr., Ca' ell,'R. G., Ibid., 26, 252 (1954): (9) Kniggt, H. S., Groennmgs, S., Ibid., 28, 1949 (1956). (10) Lipkin, M. R., Hoffecker, W. A., Martin, C. C., Ledley, R. E., Ibid., 20, 130 (1948):
.-,
-
_ ,
(11) ?;orris, T. A., Shively, J. H., Constantin, C. S., Ibid., 33, 1556 (1961). (12) Schmrtz, R. D., Brasseaux, D. J., Zbid., 30, 1999 (1958). (13) Snvder. L. R.. Ibid.., 33.. 1527 (1961). , . (14) Zbld., p: 1535.' (15) Ibid., p. 1535. (16) Zbid., 34, 771 (1962).
RECEIVEDfor review June 3, 1963. Accepted October 7 , 1963.
Spot Tests for Aromatic and a,P-Unsaturated Aldehydes FRITZ FEIGL and ESTHER LlBERGOTT laboraforio da ProduSGo Mineral, Ministirio das Minas e Energia, Rio de laneiro, Brazil (Translated by RALPH E. OESPER, Cincinnati 19, Ohio)
b The condensation of aromatic aldehydes with thiobarbituric acid to yield orange products can be utilized in spot test analysis for the detection of aromatic and a,@-unsaturated aliphatic aldehydes. The highest sensitivity is attained by warming the reactants in sirupy phosphoric acid. Compounds which are cleaved by acids to yield aromatic aldehydes act like the latter with respect to this test. Such compounds include polysaccharides, pentoses, hexoses, cellulose, ethers and esters of cellulose, and N-arylidene compounds. As an Nbenzylidene compound, hydrobenzamide behaves like benzaldehyde, whereas the isomeric more strongly basic compound, amarine, remains unchanged. It is therefore possible to differentiate between these isomers and to detect them in mixtures with each other. All tests based on condensation with thiobarbituric acid have microanalytical detection limits.
D
ox and Plaisance (8) have based a
method for determining furfural and methylfurfural on the fact that 10% HC1 solutions of these aldehydes yield an orange precipitate on the addition of thiobarbituric acid; the precipitate can be dried and weighed. Through isolation and analysis of the reaction products these authors showed (3) that the behavior of these furfuraldehydes is a special case of the general condensability of aromatic aldehydes (including cinnamaldehyde) with thiobarbituric acid: OC-NH ArCHO
+ H2k AS
drops of sirupy phosphoric acid, are added. After removal of the solvent (if need be), the contents of the test tube are warmed in a glycerol bath. An orange product will appear a t once or within 1 to 2 minutes, depending on the nature and amount of aldehyde present, if the temperature of the bath is 120' to 140' C.
requires the presence of a =C-CHO group. The latter occurs in purely aromatic aldehydes and also in the above-noted &unsaturated aliphatic aldehydes. The finding that condensation with thiobarbituric acid in sirupy phosphoric acid occurs even with minimal amounts of reactive aldehydes led to the expectation that this method would permit the detection of compounds which yield aromatic aldehydes on warming with mineral acids. This expectation was realized and the reaction provided the basis of tests for pentoses, hexoses, and N-arylidene compounds (Schiff bases, oximes, and hydrazones of aromatic aldehydes). The utilization of this reactivity of the N-benzylidene group led furthermore to a reliable differentiation of the isomers hydrobenzamide and amarine.
Citral Crotonaldehyde Acrolein
I
DETECTION OF AROMATIC AND a,8-UNSATURATED ALDEHYDES
+
Ok-NHI
OC-NH ArCH-A
Ob-" 132
A study of the above reaction revealed that if conducted as a spot test it permits the detection of aromatic aldehydes. The highest sensitivity is attained by warming the reactants with sirupy phosphoric acid. This fact may be attributed to the dehydrating action of the latter and to the fact that it allows the temperature to exceed 100" C.; both facilitate the condensation. Furthermore, benzoin, benzil, benzophenone, and acetophenone-i.e., compounds which contain a GH&O group-do not react with thiobarbituric acid, whereas cinnamaldehyde and pyridine aldehydes as well as the aliphatic unsaturated aldehydes, citral, acrolein, and crotonaldehyde, do react. Accordingly, the condensation with thiobarbituric acid
ANALYTICAL CHEMISTRY
+ H,O
Procedure. A small quantity of the test material is placed in a micro test tube or 1 drop of the solution in ether is used. Several centigrams of thiobarbituric acid, along with 1 or 2
FOVND, pg.
Benzaldehyde o-Hydroxybenzaldehyde m-Hydroxybenzaldehyde
5 2.5 5
Anisaldehyde Cinnamaldehyde Pyridin-(2,3,4)aldehydes p-Dimethylaminobenzaldehyde o-Nitrobenzaldehyde Chlorobenzaldehyde g-enzaldehyde sulfonic acid (o-
0.1
p-hydroxy benzaldehyde
and m-)
0.5
0.5
500 25
5 25
10 50 10
10
DETECTION OF PENTOSES AND HEXOSES
Di- and polysaccharides are hydrolytically cleaved by warming with mineral acids and the resulting monosaccharides (pentoses and hexoses) are dehydrated to furfural or hydroxymethylfurfural. Spot test analysis has employed these facts for the detection of carbohydrates, and likewise of cellulose and cellulose esters (C), since the steam-volatile furfurals give red polymethine dyestuffson contact with aniline acetate ( I , 7). If compounds of the kinds just noted are subjected to the procedure described above, the resulting furfurals react directly with thiobarbituric acid to produce the orange condensation products. FOUND, pg. Xylose 5 Arabinose 10 Glucose 5 Levulose 0.5 1 Mannose Saccharose 0.5
A positive responE$e %-as obtained likewise with very sinall amounts of solid cellulose, nitrocellulose, and cellulose ester and ether. DETECTION
OF N-ARYLICENE COMPOUNDS
If Schiff bases, oximes, and hydrazones of aromatic aldehydes-Le., N-arylidene compounds containing the ArCH=NR-atom grciup are subjected to the procedure described above, hydrolysis occurs:
+
+
ArCH=NR HZO 3 ArCHO NHiR (R = H, OH, NH2, etc.) and the aromatic aldehyde split off in this manner will condense with thiobarbituric acid. Pertinent compounds therefore behave in the same manner as aromatic aldehydes.
aone, C6HaCHNNH2,which is isomeric with benzamidine, behaves in the same manner as other N-benzylidene compounds. Therefore it is possible t.0 distinguish between the two isomers by the test described above. DIFFERENTIATION OF HYDROBENZAMIDE AND AMARINE
Hydrobenzamide (I) and the isomeric heterocyclic amarine (11) formed from (I) by heating to 120°C. are condensation products of 3 moles of benzaldehyde and 2 moles of ammonia
I (m.p. 101’ C.) ACKNOWLEDGMENT
FOU~D /Lg. , Benzalazine Benzaniline Resorcylaldoxime Salicylaldszine PHydroxybenzaldoxime m-Xitrobenznldazine
5 10 2.5 2.5
2.5
10
The test for N-arylidene compounds just given assumes the absence of aromatic aldehydes. The presence of the latter can be detected by the spot test procedures commonly employed (6). Benzamidine, Cd&C(NH)NHt, proved to be completely inactive. This was to be expected, since this compound contains no benzylidene group and when saponified yields no benzaldehyde but instead the nonreacting benzamide. Howevw, benzalhydra-
Another way to distinguish between these two water-insoluble isomers is based on the finding that amarine, in line with its constitution, is a stronger base than hydrobenzamide. Both isomers respond to the test characteristic of basic inorganic and organic basic compounds-namely, the formation of a red precipitate on contact with nickel dimethylglyoxime equilibrium solution (6). However, this reaction proceeds much more rapidly with amarine than with its isomer. If 0.5 mg. of amarine is used, the reaction with the equilibrium solution is immediate, whereas the same weight of hydrobenzamide yields either no precipitate or a barely visible amount of nickel dimethylglyoxime.
semihgdrate, 106’ C.)
II(m.p. 130” C.; as
Inspection of structural formulas I and I1 reveals that only hydrobenzamide contains a -N=CHC&group and accordingly reacts in the manner discussed above. Therefore hydrobenzamide can be detected through the positive outcome of this test and thus be differentiated from amarine. The procedure used for detection of n-arylidene compounds was followed. Identification limit is 5 bg. of hydrobenzamide. The results were positive in the presence of any reasonable amount of amarine.
The aut’hors are grateful for the support of this work by the Conselha Nacional de Pesquisas. LITERATURE CITED
e, G. P., J .
(1916). (3) Ibid., p. 2164. ( 4 ) Feinl. F.. “ h o t Tests in organic Anal;s!s.” 6th ed.. DD. 426.591. Elsgvi \
I
~,
38,3824’(1905).
RECEIVED for review January 7, 1963. Accepted July 15, 1963.
S pect rophioto met ric Dete rmina ti on of Platinum with 2,3-CJuinoxalinedithiol GILBERT H. AYRES arid RAYMOND W. McCRORYl Department of Chemisfry, The University of Texas, Austin, Texas
b Platinum(lV), after reaction with tin(1l) chloride in hydrochloric acid, gives a blue color with 2,3-quinoxalinedithiol in N,N-dimethylformamide solution. The color develops rapidly and is stable for many hours. Absorption peaks occur at 624 and 585 mp. The system con‘orms to Beer’s law, and spectrophotometric results are reliable to a relative error of less than 1.5% over the ciptimum concentration range of about 1.4 to 5 p.p.m. of platinum for measurement at 1.00cm. optical path. The? absorbance is not highly sensitive to the concentration of reagent, of tin(1l) chloride, or of hydrochloric acid. Copper, cobalt, nickel, and rhodium interfere and require separation from platinum.
Spectrophotometricsolution studies and precipitate analyses show that platinum and 2,3-quinoxalinedithioI react in a 1 to 2 ratio to form a blue, uncharged complex in acid solution. This complex is a weak diprotic acid that ionizes in alkaline solution to give a red divalent anion having maximum absorption at 519 mp.
R
EVIEWS O F THE SPECTROPHOTOMETRIC methods for the platinum
metals were published by Beamish and McBryde (4) in 1953 and in 1958. Of the several methods then available for platinum, the tin(I1) chloride method (3, 6, l a ) and the p-nitrosodimethylaniline method (12) were favored.
More recently, platinum has been determined spectrophotometrically with tin(I1) bromide ( I @ , with o-phenylenediamine (l?), and with N,N‘-bis(3dimethylaminopropyl) dithiooxamide (9). The preparation of 2,3-quinoxalinedithiol by Morrison and Furst (14), and their observation that it formed colored products with a number of metal ions, has led to the use of this reagent for the spectrophotometric determination of some of the transition elements. Nickel in ammoniacal solution was determined by Skoog, Lai, and Furst (18). Ayres and Janota (2) Present address, Jackson Laboratory,
E..I. du Pont de Nemours & Co., Wilmngton, Del.
VOL. 36, NO. 1, JANUARY 1964
133
