Spot Tests for Detection of N-Nitroso Compounds (Nitrosamines) FRITZ FEIGL and CLAUD10 COSTA NET0 LaboratGrio da f r o d u g a o M i n e r a l , M i n i s t i r i a da Agricultura, Rio de Janeiro, Brazil
Transtated b y RALPH E. OESPER University o f Cincinnati, Cincinnati, O h i o
Procedure. The test is conducted in a micro test tube. One drop of the Griess reagent and 1 drop of hydrochloric acid (1 to 1) are added to 1 drop of the test solution. The mixture is warmed in a water bath. If nitrosamines are present, a more or less intense red-violet color appears a t once or within several minutes, the time and depth of color depending on the amount of ATnitrosamine. This procedure revealed the following:
In contrast to C-nitroso compounds, .\'-nitroso compounds can be hydrolyzed to the corresponding NH compounds by a wet method under mild conditions, and by a dry method by heating with hydrated zinc sulfate or manganese sulfate. The nitrous acid which splits off can be detected by the color reaction with Griess reagent or by the precipitation reaction with sulfaniic acid and barium chloride. In the pyrolytic hydrolysis, the test with the Griess reagent is made on the vapor phase. The detection of nitrosamines can be accomplished within the technique of spot test analysis with identification limits of 0.5 to 15 7.
Compound iV-nitrosodibenzylamine
Formula
Y
CIHLCH~-N-CHGHS
I
10
NO N-nitrosodicyclohexylamine C~HI~I-X-C~HIO
9
I
NO
A
MACRO t e s , discovered by Rosenthaler ( 5 )for acetanilide,
was the starting point in the development of a spot test (S) for acyl derivatives of aromatic amine?, arylurethanes, and inonoalkylureas. I t was observed during this study that, in contrast to C-nitroso compounds, AT-nitroso compounds (nitros:imines) are decomposed by hydrazoic acid (NaNa HCI). This effect, which occurs even at room temperature and is valu'ible for the differentiation of C- and N-nitroso compounds, was ascribed t o a direct denitrification of nitrosamines (Equation 1). However, consideration must be given also to the two partial 1 cxtions that mby be involved in the denitrification. Most nitroaanhes are very slightly but definitely soluble in ivater and it ma?- be assumed that the dissolved material undergoes hydrolysis 8 % shown in Equation 2. The nitrous acid is completely removed from this hydrolysis equilibrium by the wellknown instantaneous reaction with hydrazoic acid ( 6 ) , as shown in Equation 3. C'onsequentljr, the denitrification can be complete, even under the most unfavorable circumstances, if both the solution eqiiilibrium and the hydrolysis equilibrium of the nit1 osamines are re-established rapidly.
iV-nitrosodiphenylamine
/ \S-SO HXO:
+ HS3
+
+ H20 e + HS3
+
+ A - 2 0 + N1
(1)
+ HXO,
(2)
+ KzO + Xz
(3)
)SH
>
Hz0
SH
Summation of Eq,iations 2 and 3 obviously yields Equation 1namely, the representation of the direct denitrification. If the denitrification of nitrosamines by hydrazoic acid proceeds via hydrolytically split-off nitroiis acid, it may be expected that nitrosamines will show the charactelistic reactions of nitrous acid and should be detectable on this basis. Actually this 17 true. If nitrowmines are warmed with Griess reagent (an Lcetic acid Polution of sulfanilic acid and I-naphthylamine), i n many cases there is almost immediate production of the red color because of the formation of an azo dye. I n every case, this result is obtsiined if the mixtiire is Farmed with a little strong hydrochloric acid. DETECTION WITH GRIESS REAGENT
Reagent. ,4 1% solution of sulfanilic acid in 30% acetic acid, and a 0.1% solution of 1-naphthylamine in 30% acetic acid. Equal volumes of these two solutions are mixed to obtain the Griess reagent,
1
I
KO AT-nitrosomethylurea
+
>--KO
CsHj-N-CaHs
0.4
OC/"a
\%CHI
I
KO
CHe-CHz
iV-dinitrosopiperazine
ON-N/
4
>-NO \C H~-C H~
AT-nitrosoacetanilide
CsHs-K-COCHa
I
1
NO
A less sensitive procedure, which is adequate for many purposes, is based on the removal of the nitrous acid from the hydrolysis equilibrium by means of sulfamic acid: HYOz
+ NHzSOaH
+
HzSOa
+ He0 + Nz
(4)
Because the barium salt of sulfamic acid is soluble in water, the occurrence of Reaction 4 is signaled by the precipitation of barium sulfate if barium ions are present. This procedure, which is the basis of the Baumgarten and Marggraff ( 1 ) macro test for nitrite and also of its gravimetric determination, can be translated into spot test technique as follows. DETECTION WITH SULFAMIC ACID
Reagent. Five grams of barium chloride dihydrate and 5 grams of sulfamic acid are dissolved in 100 ml. of a mixture of equal volumes of dioxane and water. Any precipitate should be removed (Pyrex filtering crucible F). The solution becomes cloudy on standing and must be clarified before use. Procedure. A micro test tube is used. One drop of the test solution (aqueous or alcoholic) is treated with 1 drop of the reagent solution and, if necessary, the test tube is gently warmed in hot water. A precipitation or turbidity results if N-nitrosamines are present. A comparison blank is advisable if small amounts are suspected. The procedure revealed 10 y of A'-nitrosodiphenylamine and 10 y of AT-nitrosomethylurea. Equation 2, which represents the hydrolysis leading to nitrous acid, does not show any participation of hydrogen ions, although addition of acid is necessary when nitrosamines are to be denitrified rapidly by the wet method. Obviously, as in so many other hydrolyses, the hydrogen ions hasten the hydrolysis. However, an extensive hydrolysis can be secured in the absence of acids if a dry mixture of a nitrosamine and hydrated zinc 1311
ANALYTICAL CHEMISTRY
1312 sulfate or manganese sulfate is heated to 200" C. Nitrous vapors are evolved because the following reaction takes place. When these sulfates are heated to 150" to 200' C. and 154' to 300" C. respectively, they are changed into the anhydrous sulfates ( 2 ) . Superheated steam results %hen the water is lost. The steam reacts, a t the place of its release, n i t h the nitrosamine with which i t is in contact, and hydrolysis of the latter occurs. Nitrous acid can also be produced without the addition of any water-releasing material, if nitrosamines are heated t o incipient charring with access of air. I n this case, the superheated steam resulting from the decomposition of the organic compound brings about the hydrolysis of the nitrosamine. These instances are additional evidence of the analytical value of hydrolyses occasioned by superheated steam, a matter that has been discussed elsewhere ( 4 ) . This pyrolytic splitting off of nitrous acid when a dry mixture of a nitrosamine and hydrated zinc sulfate or manganese sulfate is heated can also be utilized as a test for these organic compounds. S o nitrous acid is J ielded when C-nitroso compounds are subjected t o the pyrolytic procedure. DETECTION BY HEATING WITH HYDRATED 3IANGANESE (ZINC) SULFATE
Reagents. Hydrated manganese sulfate or hydrated zinc sulfate and Griess reagent (prepared as described previously).
Procedure. The test is made in a micro test tube. One drop of the test solution or a tiny bit of the solid is mixed with several centigrams of hydrated manganese or zinc sulfate, and taken t o dryness if need be. The mouth of the test tube is covered with a disk of filter paper that has been moistened with a drop of Griess reagent, and the tube is heated in the flame of a microburner. A red-violet stain appears on the colorless paper if N-nitroso compounds are present. A positive response F a s given by 10 y of S-nitrosodicyclohesylamine, 5 y of N-nitrosodiphenylamine, and 1.5 y of iY-dinitrosopiperazine. ACKNOWLEDGMENT
This study x a s kindly supported by the Conselho Sacional dr Pesquisas. LITERATURE CITED
Baumgarten, P., llarggraff, J., Ber. 63, 1019 (1930). (2) Duval, C., "Inorganic Thermogravimetric .halysis," pp. 190, 277, Elsevier, Xew York, 1955. (3) Feigl, F., ANAL.CHEM.27, 1316 (1955). (4) Feigl, F., lIoscovici, R., Analyst 80, 803 (1955). ( 5 ) Rosenthaler, L., Pharm. Acta Helc. 25, 365 (1950). (6) Sommer, F., Pincus, H., Ber. 48, 1963 (1915). (1)
RECEIVED for review February 13, 1956. Accepted April 18, 1956.
Rapid Determination of Carbonyl Content in Acrylonitrile ROBERT L. MAUTE and M. L. OWENS, JR. Monsanto Chemical Co., Texas City, r e x .
Low concentrations (0 to 0.2$%)of aldehydes and ketones in acrylonitrile can be rapidly determined by a modified hydroxylamine hydrochloride method employing a unique nonaqueous system. -4ccurate acetaldehyde content is found by allowing the sample to react with an alcoholic solution of the reagent for 1 minute before titration of the liberated acid with methanolic caustic to the thymol blue end point; total carbonyls are determined by increasing the reaction time to 5 minutes. The precision of the method for acetaldehyde is within A0.003y0 in the range from 0 to 0.1%. For the higher molecular weight ketones which react more slowly, or for mixtures of carbonyls, the precision is within =k0.005%.
hydes was modified in an attempt to apply it to low concentrations, but it was also found to be unsatisfactory. A widely used method for total carbonyl determination is the hydroxylamine hydrochloride method, which was used for fornialdehyde as early as 1895 ( 8 ) and has been improved by using pyridine as the osimation catalyst for quantitative determination of pure compounds ( 3 ) . A hydroxylamine hydrochloride procedure has been employed using mised aqueous-alcoholic reagents (1, 10, 14), with the end point detected by pH determination or by use of indicators (3, 14).
Table I.
Determination of -4cetaldehyde Weight %
Taken
ARIOUS carbonyl impurities are produced in the manufacture of acrylonitrile from acetylene and hydrogen cyanide. Among these are acetaldehyde (6, 8, 16), methyl vinyl ketone (6, 16), and paraldehyde (8). Because of their chemical and physical properties some of these carbonyl compounds may not be completely removed during purification of crude acrylonitrile; hence, rapid methods for the determination of aldehydes and ketones in product acrylonitrile became necessary. Many methods are available for the determination of carbonyl compounds, but few can be applied for trace amounts. One widely used method for the detection and determination of aldehydes (11, 16)is the fuchsin procedure. However, for quantitative results the reagent must be freshly prepared and kept in an inert atmosphere (11); a calibration curve must also be prepared for each batch of reagent for best results. Different aldehydes give varying color intensities and hence, the method is poor for mistures of aldehydes. The silver oside method (It)for alde-
0.135 0.170 0.123 ?.235
Found 0 . 14.5 0.176 0.125
1.LU
