Colorimetric Determination of P,4=DinitroanisoJe MILTON S. SCHECHTER AND H. L. HALLER
U. S.
Department of Agriculture, Agricultural Research Administration, Bureau of Entomology and.Plant Quarantine, Beltrville, Md.
T
The results for the standards may be plotted as per cent transmission against concentration on semilogarithmic paper, or as log
H E development of insecticidal dusts (8, 5) containing 2 , 4 dinitroanisole has raised the problem of a suitable method for the determination of this compound in insecticidal compositions. The presence of a yellow color in some preparations due to other materials, such as pyrethrum oleoresin, made i t impractical to use the yellow color of 2,4dinitrophenol produced by the action of alkalies on 2,4dinitroanisole as the basis of a photometric method. Use was made of the purpuric acid reaction (1, 3,4), in which potassium cyanide reacts with m-dinitro compounds to give red-brown to violet colors. Bylanalogy, the reaction with 2,4dinitroanisole is presumed to be similar to that for 2,4dinitrophenol, which is as follows: OH
OH
I
I NOz
N0z
(yo
)
against concentration on ordinary graph paper. transmission loo The concentration of 2,4-dinitroanisole in the unknown may then be read off this graph. The color follows Beer's law, as shown in Figure 1. Acetone was used as the solvent in order to obtain a rapid and complete solution of the constituents of the powder without having to resort to a Soxhlet or other extractor. However, potassium cyanide is not soluble in acetone, and a 0.5% aqueous solution of this reagent had to be used. The amount of water thus added to the acetone solutions wm found to be sufficient to keep the potassium cyanide in solution without precipitating any of the dissolved organic substances. As a n example of the precision to be expected, a commercial sample of dust supposed to contain 2y0 of 2,4--dinitroanisoleplus
[The equation given by Anger (I) and reproduced by Feigl(4) is not balanced and could be made to balance only if potassium carbonate is a product rather than potassium bicarbonate, w given by Feigl.] Feigl (4) described this test for a number of m-dinitro compounds but did not list 2,4-dinitroanisole, which the authors found to give a red color with the potassium cyanide reagent. He did list l-chloro-2,4-dinitrobenzene,which sometimes occurs as an impurity in 2,4dinitroanisole and would therefore interfere. However, a specific method for determining l-chloro-2,4-dinitrobenzene in 2,4dinitroanisole has been developed (6). I n the case of 2,4dinitroanisole (and 1-chloro-2,Pdinitrobenzene) heating was not found to be necessary for rapid development of the color, but does seem to be necessary for many of the othei mdinitro compounds, such as 2,4-dinitrophenol and dinitrocyclohexylphenol. The following procedure ~ t t developed s for a n insecticidal dust (2) containing 2% of 2,4-dinitroanisole, 2% of N-isobutyl undecylenamide, enough pyrethrum oleoresin to give 0.2% of total pyrethrins, and I % of an antioxidant, with pyrophyllite as the diluent:
Figure 1.
Weigh 2.000 grams of the powder into a small beaker. [For dusts containing 10% of 2,4-dinitroanisole, such as is recommended by Gould (5), about 0.400 gram suffices.] Stir the sample with four or five portions of acetone, decanting each time through a Gooch crucible that contains an asbestos mat and is held in an all-glass Gooch funnel. With care, the solution may be filtered directly into a 100-ml. volumetric flask, if a large enough filtering bell jar is used. Continue to wash with acetone until the volume is nearly 100 ml. and then make up to volume and mix. The solution should be perfectly clear and will have a yellow color due to the pyrethrum oleoresin and other constituents. Take a 10.00-ml. and a 15.00-ml. aliquot, and add 5.00 ml. of acetone to the 10.00-ml. aliquot. Prepare comparison standards containing 2, 4, and 6 mg. of pure 2,4-dinitroanisole and dilute each to 15.00 ml. with acetone. These standards are conveniently prepared from a standard solution containing 40 mg. of 2,4-dinitroanisole per 100 ml. of acetone. Add 5.00 ml. of 0.570 a ueous potassium cyanide to each of the solutions, mix, let stand ?or one hour, and measure the color in a photometer, using acetone as the blaqk. An Aminco photometer, t y F, using photometer test tubes and a No. 58 yellow filter g a v e length of maximum transmission a t about 580 millimicrons) is suitable. It was found by ex eriment that if a No. 58 filter is used there is no interference ;om the other constituents in the amounts in which they are present in the in$ecticide dust, even though they contribute a yellow color to the acetone solution,
Determination of 2,CDinitroanirole Using Potassium Cyanate as the Reagent
YlLLlGRAYS
Figure 2.
325
2.I-DINITROANISOLE
Determination of P,+Dinitroanirole Using Acetone and Alkali
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
326
the other constituents named above, when analyzed by the proposed method gave, as an average of 10 determinations, 2.17% with an average deviation of 0.05 and a maximum deviation of 0.12% when the 10-ml. aliquots were used, and 2.11% with an average deviation of 0.04 and a maximum deviation of 0.11% with the 15-ml. aliquots. A more sensitive color reaction took place when 25 ml. of an acetone solution of 2,4-dinitroanisole were shaken with 5 ml. of concentrated sodium hydroxide solution (about 35%), with which it is immiscible. After the solution has been shaken for several minutes in a glass-stoppered cylinder and has stood for 30 minutes, a beautiful violet color develops in the acetone layer. The acetone may be decanted into a photometer tube and the color measured photometrically (a No. 58 filter on the Aminco photometer, type F, was suitable). Some data to illustrate the sensitivity of the method are plotted in Figure 2. The test was found to be too sensitive to obtain concordant results in the analysis of dusts containing aa much as 2% of 2,4-dinitroanisole, possibly because of the greater effect of interferences on such a sensitive reaction. However, this method would certainly be useful where very small amounts of
Vol. 16, No. 5
2,4-dinitroanisole had to be deteruiiried. This ieaction is similar to that described for the analysis of in-dinitrobenzene ( 7 ) . 1Chlorc-2,4-dinitrobeneene, which sometimes occurs as an impurity in 2,4dinitroanisole, also gives this color reaction. One of the interferences which must be scrupulously avoided is the presence of even traces of sulfur, such as contamination from the sulfur in rubber stoppers. Sulfur destroys the violet color, produring a greenish coloration instead. LITERATURE CITED
(1) Anger, V., Mikrochin. Acta,2, 2 (1937). (2) Anon., Soap S a d . Chemicale,18 (111,105 (1942). (3) Beilstein, “Handbuch der organischen Chemie”, Aufl..4,Bd. 15, p. 68, Berlin, Julius Springer, 1932. (4)Feigl, F., “Qualitative Analysis by Spot Tests, Inorganic and Organic Applications”, p. 270, New York, Nordemann Publishing Co., 1939. ( 5 ) Gould, G . E.. Soap S a d . Chf37n2&l3, 19 (8), 90 (1943). (6) Schechter. M. S., and Haller. H. L., IND.ENQ.CEQM..ANAL, ED.,16,326 (1944). and Snell, C. T., “Colorimetric Methods of Analy(7)Snell, F.D., ab”,Vol. 2,p. 5, New York, D. Van Nostrand Co., 1937.
Colorimetric Determination of I-Chior0-2~4-dinitrobenzene as an Impurity in ~!~4=Dinitroanisole MILTON S. SCHECHTER
U. S.
AND
H. L. HALLER
Department of Agricdture, Agricultural Research Administration, Bureau of Entomology and Plant Quarantine, Beltsville, Md.
0
RDINARILT 2,4-dinitroanisole is manufactured either by the methylation of 2,4-dinitrophenol or by the reaction of
alkali and methanol with l-rhloro-2,4-dinitrobenzene. I n the latter process some of the chlorodinitrobenzene may be left in the final product, even after recrystallization. In fact, all commercial samples of 2,4-dinitrosnisole made from I-chloro2,4-dinitrobenzene which have been examined by the authors, even those that were supposedly purified by recrystallization,
when analyzed by the colorimetric method outlined below proved to contain about 0.5% of l-chloro-2,4-dinitrobenzene. Procedures for determining l-chloro-2,4-dinitrobenzenein 2 , 4 dinitroanisole based on the conversion of the chlorine t o chloride by heating in alkaline solution and gravimetric or titrimetric determination of the chloride are unsuitable for small concentrations of the chlorodinitrobenzene, since a large sample has t o be used and a correction also has to be made for inorganic chloride derived from salt left in the compound in the process of manufacture. 2,PDinitroanisole is used as an insecticide (1, &’), and a method for its analysis in insecticidal powders is described (4). Since l-chloro-2,4-dinitrobenzeneis a powerful skin irritant and repeated contacts may cause hypersensitization (5, g), i t is desirable t o have a sensitive colorimetric method of analysis for thk compound in dinitroanisole. The procedure developed is based on the Vongerichten reaction (7,9):
aqueouyf N o, < H\Or e d (aldehyde form) A
0
+
RC1
Per Cent 1-Chloro-9,4-dinitrobcnzene
Fisure 1.
Determination of l-Chloro-P,4-dinitrobenzene Dinitroanisole
in
P,4-
R = 2,Cdinitrophenyl
/
R
