ANALYTICAL CHEMISTRY
432 Routine service consists of daily inspection of instrument operation and addition of water to the saturator and humidifier; weekly changing of the film and inspection of the sample pump; and monthly changing of the recorder chart and lubrication of certain parts. Servicing the recorder normally requires an additional 15 minutes daily, an extra hour once a week, and an extra 2 hours once a month. LITERATURE CITED
(1) Consolidated Engineering Corp., Pasadena, Calif., “Consolidated’s Titrilog,” Bull. CEC 1810D (1953).
(2) Davis Emergency Equipment Co., Inc., Newark, S . J., “Recording Electro Conductivity Analyzer,” Bull. 11-70 (1953), (3) Forbes, J. J., and Grove, G. W., U. S. Bur. Mines, Miner’s Circ., 33 (1938). (4) Hemeon, W. C. L., Sensenbaugh, J. D., and Haines, G. F., Jr., Instruments, 26, 566 (1953). ( 5 ) Rubicon Co., Philadelphia, Pa., “Recording Automatic Hydrogen Sulfide Analyzer,” Bull. 480 (1947). (6) Sayers, U. S. Bur. Mines, Rept. Invest. 2491 (1923). (7) Schaeffer, W. H., Electronics, 22, 85-7 (1949). RECEIVED for review May 26, 1954. Accepted October 6, 1954.
Spot Reaction for Acidic Polynitro Compounds FRITZ FEIGL and VICENTE GENTIL Ministerio d a Agricultura, Rio d e Janeiro, Brazil
Translated by Ralph E. Oesper, University of Cincinnati, Cincinnati, O h i o
When enolizable nitro compounds react with rhodamine B, they give red-violet salts, whose red solutions in benzene fluoresce orange. This finding has been made the basis of a new, fairly sensitive spot reaction for the detection of enolizable polynitro compounds.
E
EGRIWE (1) discovered that the violet precipitates formed in strong hydrochloric acid solution by the amphoteric water-soluble dye rhodamine B with antimony(V), gold( 111), and thallium(II1) ions can be made the basis of sensitive tests for these metals. According to Kuznetsov (?’), these reactions involve the production of salts of the dye, or its quinoidal zwitter ions, with the complex [SbCls]-, [AuC14]-, or [Ticla]- ions. The production of the antimony compound, whose formation may also be used for quantitative microdeterminations (8, 9, 11), can be represented as:
neutral or mineral acid solutions of rhodamine B, violet precipitates appear in many cases. These products are soluble in benzene and the resulting red solutions display an intense orange-red fluorescence in ultraviolet light. The color and the fluorescence reaction can be observed a t dilutions that are too slight to produce a visible precipitate. This behavior, which is completely analogous to that of complex metal halogen acids, is a strong indication that the reaction involves the formation of benzene-soluble salts of rhodamine B with the aci- form of the nitro compounds. When other acid groups are absent, the acidic character of organic nitro compounds is due to the formation of the socalled nitroxy acids (6)-in other words, to the enolization of the NO2 to the NO2H group. I n the case of aliphatic primary and secondary nitro compounds, there is an equilibrium between the tautomeric forms: --CHZ-XOz
n
S --CH=NOnH
CH-NO**
C=NO2H
In the case of aromatic nitro compounds, the acidification results from the rearrangement into quinoidal compounds with development of N02H groups. For example, the following equilibria are established in the case of p-nitrophenol and hexanitrodiphenylamine, respectively:
nCOO-' I
NO2
&() NO1
Analogous reaction schemes apply for the other two metal chloride ions and likewise for [SbIdI- ( 4 ) . Most of the waterinsoluble salts of rhodamine B with metal-halogen acids dissolve in benzene (toluene) to give red-violet solutions ( 5 ) , a finding that was first reported by Webster and Fairhall ( I O ) in the case of the antimony salt. The benzene solutions of most of the rhodamine salts exhibit an orange-red fluorescence in ultraviolet light. The behavior of rhodamine B toward organic acidic compounds with respect to the production of colored benzene-soluble salts has been studied in the present investigation. Enolizable nitro compounds are outstanding in this regard. When not too dilute solutions of such compounds are allowed to react with aqueous
NO2
e
,,0-NH+2
N0z
NO2
dO,H
02N&$NbXOzH NO1
N0z
Enolizable aliphatic and aromatic nitro compounds give yellow solutions in caustic alkali because formation of the water-soluble alkali salt removes the aci- form from the equilibrium. This removal resulting from salt formation with rhodamine B can also occur in the absence of water. This is proved by the fact. that the colorless solution of rhodamine B in benzene (toluene), which contains the lacto- form of the dyestuff, immediately turns red on the addition of nitro compounds which are able to produce nitroxy acids on enolization. This salt formation, beginning with the lacto- form, can be represented schematically as:
V O L U M E 27, NO. 3, M A R C H 1 9 5 5
433
0
addition of an acid (6) makes possible a new test for aci-nitro compounds with rhodamine B as reagent. I n the procedure, it is necessary to bring together a weak alkaline solution or suspension of the test material and a
-COOH
II 1 + HO-.N=C--, ,
1
/
(CzHiLK
co3\ r
Because most nitro compounds are far more soluble in benzene than in water and the colorless lacto- form of the dyestuff can be extracted by benzene from the a-ater solution of rhodamine B, it is probable that the reaction given above is likewise involvedLe., the reaction theater is transferred to the benzene solution when neutral or acid suspensions of nitro compounds in water solutions of rhodamine B are shaken out with benzene. The possibility that the color and fluorescence reaction with rhodamine are due to the formation of molecular compounds with participation of NO1 groups can be excluded, because nitro compounds which are not capable of an enolization do not react with rhodamine B. This xas demonstrated by the negative results obtained with o-nitrophenol, p-nitrotoluene, m-6itroaniline, 6nitroquinoline, nitroguanidine, p-nitrobromobenzene, p-nitroacetamide, p-nitromandelic acid, nitrobarbituric acid, p-nitroalizarin, and trinitrotoluene. Very small amounts of many enolizable nitro compounds can be detected directly through the salt formation on treatment with a benzene solution of rhodamine B. However, this procedure is not reliable. Some phenols, mercapto compounds, carboxylic acids, and sulfonic acids give red solutions; others are tinted red when treated with a benzene solution of rhodamine B. Obviously, here again there is some production of a rhodamine B salt. Acidic compounds which are not soluble in benzene nevertheless produce benzene-insoluble salts with rhodamine B via topochemical surface reactions. Solid monobasic fatty acids are not colored by benzene solutions of rhodamine B. The aliphatic dicarboxylic acids-oxalic, malonic, maleic-give a pronounced reaction, whereas succinic, glutaric, and adipic acids show no reaction. An intense color is obtained with a-hydroxycarboxylic acids such as tartaric and (anhydrous), mandelic acid and its derivatives, malic acid, and citric acid (including the hydrated variety). The following are colored irreversibly: 2,7-dihydroxynaphthalene,, gallic acid, dimethylglyouime, benzoinoxime, alizarin, nitroalizarin, 8-quinolinol5-sulfonic acid, and barbituric acid. Powdered phenol resins are tinted red on contact with benzene solutions of rhodamine B. Frequently the tinted products give the same fluorescence color in ultraviolet light as the salts of rhodamine B. Rlany inorganic compounds likewise yield red or red-violet colors when treated with a colorless benzene solution of rhodamine B. Instances of this behavior are: sulfates of the alkaline earths, anhvdrous sulfates of copper, manganese, and cobalt, cuprous iodide, silver halides, and oxides of aluminum, zirconium, titanium, columbium, and tantalum. I n these cases it is likely that there is an irreversible adsorption of the dye, whose lacioform is thus rearranged into its corresponding quinoidal form. Perhaps the adsorptive binding of the dye molecule involves its trivalent nitrogen atom or the oxygen of the pyrone ring. Furthermore, some enolizable nitro compounds do not react directly with rhodamine B dissolved in benzene, because the quantity of the mi- form in the tautomerism equilibrium is insufficient. The red solutions of rhodamine salts of mi-nitro compounds in benzene can be lightened in tone considerably by adding an equal volume of ether. This result is due solely to dilution; the red benzene solutions of rhodamine salts with phenols and the like are decolorized by this treatment. I t may be assumed that the ether causes a splitting of the rhodamine B salts into their lactone colorless phenol components. The utilization of this finding together with the fact that alkaline solutions contain only ions of the mi- form of the nitro compounds, from which the respective nitroxy acids are liberated transiently on the
if
mineral and to extract acid solution the mixture of rhodamine a t once with B ether-benzene. A red color in the supernatant layer is characteristic of enolizable nitro compounds. The sensitivit,ies attained are adequate for micro or semimicro tests, especially for enolizable nitro compounds. More than 80 acidic compounds of the most varied classes were subjected to this test in amounts from 5 to 10 mg. per ordinary drop. Only thio compounds, such as mercaptobenzothiazole and thioglycolic acid aminonaphthalide, show a behavior with this reagent analogous to that of acidic polynitro compounds. However, thio compounds are easily revealed by the iodine-azide t’est ( 2 ) and furthermore they are readily oxidized to noninterfering disulfides by evaporation with hydrogen peroxide, a treatment which leaves nitro compounds unchanged. Accordingly, the test with rhodamine B in the form given here can be regarded as characteristic for polynitro compounds ( 3 ) .
N( C2HS)z 0--rU -C
L
1 -I
EXPERIMENTAL
Reagent. A 0.1% solution of rhodamine B in 4% hydrochloric acid. Procedure. One drop of the weakly alkaline test solution is placed in a micro test tube and 5 drops of the rhodamine B r e agent solution is added. Five drops of 1 to 1 ether-benzene mixture is introduced and the system shaken vigorously. A red or pink color in the upper layer and an orange fluorescence in ultraviolet light signify the presence of enolizable polynitro compounds. DISCUSSION RESULTS
.
The following mononitro compounds, which are capable of enolizat’ion, were tested with the colorless reagent solution: nitromethane, nitroethane, the three isomeric nitrophenols, p-nitroaniline, and 5-nitrosalicylic acid. With the exception of the lat,ter compound, the color and fluorescence reaction were not evident with amounts below 2500 y . o-Nitrophenol does not show any reaction belom- 0.5 gram. Furthermore, and again with exception of 5-nitrosalicylic acid, the stability of the red benzene solution toward ether is distinctly less than in the case of enolizable polynitro compounds. Consequently, i t appears that nitro and carboxyl groups in enolizable nitro compounds exert a positive influence on the occurrence of the reaction with rhodamine B. IDENTIFICATION L I M I T S 0 . 2 3 y of dipicrylamine (2,4,6,2’,4’,6’-hexanitrodiphenylamine) 0 . 5 y of picric acid ( 2 , 4, 6-trinitrophenol) 1 y of picrolonic acid [3-rnethyl-4-nitro-l-(p-nitrophenyl)5-pyrazoIone] 4 y of 5-nitrosalicylic acid 10 y of hfartius yellow (alkali salt of 2,4-dinitrophenol) 10 y of naphthol yellow (alkali salt of 2,4-dinitro-l-naplitholsulfonic acid) 500 y of 2.4-dinitrophenol 2000 y of p (4-nitrophenol
LITERATURE CITED
(1) Eegriwe, E., 2. anal. Chem., 70, 400 (1927).
(2) Feigl, F., Mikrochemie, 15, 1 (1934). (3) Feigl, F., “Qualitative Analysis by Spot Tests,” 4th ed., Vol. 11,
p. 340. Elsevier PublishingCo., Amsterdam, Netherlands, 1954. (4) Ibid.,p. 342. (5) Feigl, F., Gentil, V., and Goldstein, D., Anal. Chim. Acta, in press. (6) Karrer, P., “Organic Chemistry.” 2nd ed., p. 132, Nordemann Publishing Co., Yew York, 1946. (7) Kuznetsov, V. J., Compt. rend. mad. sci. U.R.S.S., 52, 231 (1946). (8) Luke, C. L., ANAL.CHEM.,25,674 (1953). (9) Maren, T. H., IND.ENG.CHEM.,ANAL.ED., 19, 487 (1947). (10) Webster, S. H., and Fairhall, L. T., J.Ind. Hug. Toxicol., 27, 183 (1954). (11) White, C. E., and Rose, H., ANAL.CHEM.,25, 351 (1953). RECEIVED for review July 28, 1954. Accepted November 8. 1954.
