to complete dryness, chromate helps to prevent iodine loss.
(2) Moran, J. J., ANAL. CHEW 24, 378
(1952). (3) O'Neal, L. W., Simms, E. S., Am. J . Clin. Pathol. 23, 493 (1953). ( 4 ) Van ZYlt A.7 8. African J . Sci. 16, 95 (1951). (5) Zak, B., Willard, H. H., Myers, G.
LITERATURE CITED
(1) Leffler, H.H., Am. J . Clin. Pathol. 24, 483 (1954).
B., Bogle, A. J., ANAL. CHEW
24, 1345 (1952).
RECEIVED for revieJv February 2, 1957. -4ccepted July 25, 1957. Supported by a grant from the Michigan Heart dssociation.
Titrimetric Determination of Sdfamic Acid C. L. WHITMAN Research and Development Department,
U. S.
b A method has been developed for the titrimetric determination of small amounts of sulfamic or nitrous acid in the presence of nitric acid. The procedure involves the reaction of sulfamic acid with sodium nitrite, oxidation of excess nitrite with cerium(lV) ammonium sulfate, and titration of excess cerium(lV) ion with iron(l1) ammonium sulfate. From the relation between the amount of iron(l1) ion required for the sample, and that required for two different blanks, it can b e determined whether nitrous or sulfamic acid is present, and the amount of either can b e calculated.
A
was sought for the determination of small amounts of sulfamic acid. The expected concentration was 0 to 10 ml. of 0.01M sulfamic acid per 100 ml. of solution. If no sulfamic acid were present, free nitrous acid would be present and this would have to be determined instead. Two gasometric methods for the determination of sulfamic acid have been described. Meuwesen and hlerkel (4) treated sulfamate solutions with dilute sulfuric acid, added sodium nitrite, and measured the nitrogen evolved after absorption of any nitric oxide in alkaline permanganate solution. The method devised by Carson (3) involves the reaction of the sulfamic acid with sodium nitrite, absorption of nitric oxide in bromine and water, and measurement of the volume of nitrogen. The gravimetric method of Baumgarten and Krurnmacher (1) is based on the precipitation, as barium sulfate, of any sulfates present in the sample, reaction of the sulfamic acid with sodium nitrite in acid solution and a second precipitation as barium sulfate, of original sulfate plus that from the oxidization of sulfamic acid. A titrimetric method developed by Bowler and Arnold ( 2 ) uses the reaction of sulfamic acid with nitrous acid and detection of excess nitrite ion with starch-iodide indicator. The method developed in this work METHOD
1684
ANALYTICAL CHEMISTRY
Naval Powder Factory, Indian Head,
Md.
was a titrimetric determination of small amounts of sulfamic or nitrous acid in the presence of nitric acid. This method is valid, even though it is not known which of the two constituents is present. However, a qualitative test for nitrous acid may be made with starch-iodide paper. Among the methods tried &-as the addition of excess nitrite ion and determination of the unreacted nitrite colorimetrically with 1-naphthylamine m d sulfanilic acid. The color was slow in forming, a precipitate was formed a t high concentrations, and the accuracy was not high enough. The gasometric method had the drawbacks that the amount of gas released might be extremely small, and the presence or absence of nitrites was not determined. Attempts to break dona sulfamic acid with sodium hydroxide were not successful. The method which gave the most satisfactory results involves the following series of reactions: NHzS03H
+ T\TaN02
+ NaHSOh
+ XZ+
Hz0 (1)
+ S O 2 - - + KO3- + 2 Cef3 Ce+4 + Fe+2+ Ce+3 + Fe+3
2 Ce+4
(2)
(3)
To allow for the fact that in a given solution either nitrites or sulfamic acid may be present, two blanks are used. Blank 1 indicates the amount of cerium(1V) used and also furnishes data for the standardization of the iron(I1) solution. Blank 2 shows the amount of nitrite used. The relationship between the volume of the blank and the volume of standard iron(I1) solution indicates which of these two constituents is present. As indicated in the equations, the method is based on the reaction of sulfamic acid (if present) with acidified sodium nitrite. Nitrite originally present if sulfamic acid is absent, plus any unreacted nitrite that is added later, is oxidiEed with cerium(1V) and the excess cerium(1V) titrated with standard iron(I1) using o-phenanthroline iron(I1) sulfate as the indicator.
REAGENTS
Iron(I1) ammonium sulfate solution is prepared by adding 8 grams of the hexahydrate to 20 ml. of sulfuric acid (1 to 1 by volume) and diluting to 1 liter. The resulting solution is a p proximately 0.02N. Cerium(1V) sulfate solution. The 0.02N solution is made by taking 13 grams of the dihydrate, adding 40 ml. of sulfuric acid (1 to 1 by volume), and diluting to 1 liter. Sodium nitrite, 0.01M. Exactly 0.6901 gram of dried sodium nitrite are dissolved in water and the solution is diluted up to the mark in a 1-liter volumetric flask. o-Phenanthroline iron(I1) sulfate indicator, 0.02511f. Fisher P-69 or equivalent is satisfactory. STANDARDIZATION
The 0.02N cerium(1V) sulfate solution is standardized against a standard solution of sodium thiosulfate. A 25ml. sample of cerium(1V) sulfate solution is pipetted into an iodine flask and 5 ml. of 15% potassium iodide and 10 ml. of hydrochloric acid (1 to 1 by volume) are added. After standing for 5 minutes, the solution is titrated with sodium thiosulfate to a starch end point. The normality, N , of the iron(I1) solution is obtained from blank 1 as
where VI is the milliliters of cerium(1V) solution, and N I its normality, while V z is the milliliters of iron(I1) solution. The normality of the sodium nitrite is not used in the calculations and therefore it is not necessary to have an exact value for its normality. If desired, its concentration may be calculated from one of the values of the blank. PROCEDURE
A 100-ml. sample of the material to be analyzed is placed in a 500-ml. iodine flask and 20 ml. of 1 to 1 sulfuric acid (by volume) are added. A known volume of 0.01M sodium nitrite, in excess of the amount required for the
reaction, is added from a pipet. The flask is stoppered and allowed t o stand for 30 minutes. A known volume (an excess) of 0.02N cerium(1V) sulfate solution is added, and the solution is titrated with iron(I1) sulfate, using o-phenanthroline iron(I1) sulfate as the indicator. For these titrations a buret graduated to 0.02 ml. should be used. It is desirable to run two blanks. Blank 1 is a solution of cerium(1V) sulfate of the same volume as t h a t required for the sample. This is titrated with standard iron(I1) ammonium sulfate mixture. Blank 2 is a solution prepared by using the same volumes of sodium nitrite and cerium(1T’) sulfate solutions as required for the sample. The excess of cerium(1V) sulfate in this solution should not be less than 5 ml This amount was determined as the smallest excess that mould gire a sufficient concentration to ensure quantitative oxidation. Calculations. I n cases where the sample titration, in terms of iron(II), is less than blank 2 . t h e sample contains no sulfamic acid b u t does contain free nitrite ion. Then %; HXO? =
(Bz - V ) X N X 2.351 grams of sample
where Bz = nil. of blank 2 V = ml. of iron(I1) solution for test sample N = normality of iron(I1) solution K h e n the sample titration, in terms of iron(II), requires more solution than blank 2, sulfamic acid is present. Then X 4.855 B,) X yosulfamic acid = i T ’ grams of sample Blank 2 should be, in terms of iron(II),
Table I.
NaNO1,
famic acid that can be detected is the amount n-hich is eauivalent to the difference between blahk 1 and blank 2 . Data obtained for the duplication of blanks 1 and 2 are given in Table I.
Dudication of Blanks
Ce(IV), 111. Blank 1
Fe(II), Ml,
10 10 15 15 20 20
10.50 10.45 15.00 15.00 20.90 20.95
DISCUSSION
The recovery of sulfamic acid from solutions containing a known amount in the 1 t o 10 mg. range was around 99%. The values obtained are summarized in Table 11. This method can be applied to solutions containing small amounts of either nitrous or sulfamic acid. requires no complicated apparatus, and can readily be applied t o control Lt-ork.
Blank 2
M1. 5
5 5 10 10
in
5.02 5.04 10.04 5.00 5.02 10.00 10.04 4.98 5.02 10.00
10 10 15 15 15 20
Table It.
1
8
0.97 0.97 1 (74
9.70
(1) Baumgarten, P., Krummacher, H., Ber. 67, 1257-60 (1934).
A.
Determination of Sulfamic Acid in Known Solutions
Sulfamic Sample iicid Taken, SaKOz, KO. Rlg. RI1. 2
LITERATURE CITED
Ce(IV),
Fe(II!,
5
in
111. 6 10 6.12 7 20
20
25
15.8.5
3
5
311. 10 10
about one half of blank 1. This is desirable, as the calculations involve the difference ( B , - V ) or (17 - &), which must be neither too large nor too small. Blank 1 supplies data for the calculation of the normality of the iron(I1) solution. The total amount of SUI-
Sulfamic Acid Found, N g . 0.96 0 98
Error, %
1.95
-1.0 f1.0 +0.5
9.74
+0.4
IT.W., Arnold, E. -I., ANAL. CHEX. 19, 336-7 (1947). (3) Carson, W. S . , Jr., Ibid., 23, 1016(2) Bowler,
19 (1951). (4) lleuwesen, 8 . ,Merkel, H., 2 nnorg. Chem. 244, 89-93 (1940).
RECEIVEDfor review Alarch 14, 1957. Accepted July 10, 1957.
Titration of Nitroaromatic Amines as Acids JAMES S. FRITZ, ANTHONY J. MOYE, and MARLENE JOHNSON RICHARD lnsfitufe for Atomic Research and Deparfrnent of Chemistry, Iowa Sfate College, Ames, Iowa Anilines substituted in the 2, 4, or 2, 4, and 6 positions with a t least two nitro groups, or with one nitro group and one or more chloro groups, can b e titrated as acids in pyridine, with triethyl-n-butylammonium hydroxide as the titrant. Diphenylamine derivatives with a t least one nitro group in the 4 position can b e titrated in a similar manner, Trinitrotoluene and trinitrobenzene can also b e titrated as monobasic acids. In several cases a selective determination of the different components in a mixture is possible.
D
a study of various nitro derivatives of aniline for possible use as acid-base indicators, it was found URIXG
that certain compounds of this type can be titrated quantitatively as acids. The titrations were carried out potentiometrically in pyridine, by using triethyl-n-butylammonium hydroxide ( 4 ) as the titrant. It then became of interest t o study in some detail the potentiometric titration of nitro aromatic compounds that are acidic yet do not have a functional group that is geiierally considered to be acidic. This paper presents the results of that study. Some analytical use has been made of the acidic properties of nitroaromatic amines and polynitroaromatic compounds. Moss, Elliott, and Hall ( 6 ) used 1,3,5-trinitrobenzene as an indicator in the titration of phenol with $0-
dium aminoethoxide in ethylenediamine. Fritz and Keen (3) found that 2-nitroaniline behaves as a weak indicator acid in ethylenediamine and is suitable for use as an indicator in the alkalimetric titration of phenol. Takiura and Takino (‘7) used 4-nitro-i’-aniinoazobenzene as an indicator in the same titration. Brockmann and 1Ieyer ( I ) titrated several aromatic polynitro compounds potentiometrically as acids in ethylenediamine. They found that 3dinitrobenzene gives two definite potentiometric breaks, the second coming after 2 equivalents of base (sodium aminoethoxide) per mole of 3-dinitrobenzene has been added, that picric acid consumes 3 equivalents of base per mole, VOL. 2 9 , NO. 1 1 , NOVEMBER 1957
1685
