Comparison of Methods for Determination uf Sulfamates WILLIAIRI W-. BOWLER AND ERIC -i ARNOLD . Department of Chemistry and Chemical Engineering, Case School of Applied Science, Cleoeland, Ohio The use of standard nitrite solution for the direct titration of primary amino groups has been extended to the determination of sulfamates. The titration of the acidified sulfamate solution with standard sodium nitrite, using an external indicator such as starch-iodide, yields satisfactory results on solutions of known sulfamate content. The method is compared with those in the literature.
S
ULFAMIC acid and many of its salts are p r o t k g to be very useful industrial chemicals for such purposes as fire retardant> and .Ir-eed killers (5). A study was recently undertaken in this laborat,ory on the rate of hydrolysis of sulfamic acid, and a method for determining this acid in the presence of ainnioniuiii sulfate and sulfuric acid was needed. Because of this, it x a s decided to undertake a revie\\- of the methods of analysis for the sulfamate ion with a view to finding a rapid, simple, yet accurate procedure for its determination. A search of the literature revealed that only two methods have been proposed thus far. Baumgarten and Iirunimacher ( 1 ) precipitat'e the sulfates as barium sulfate from a solution surrounded by ice, and filter off and weigh in the usual manner the barium sulfate produced. A second portion of the same solution is acidified xith dilute hydrochloric acid and heat,ed t o boiling with a n excess of sodium nitrit,e solution. The sulfamate ion is quantit,at,ivelyoxidized to sulfate ion and free nitrogen. Barium sulfate is then precipitated, filtered, and weighed in the usual manner. I n t'he first sample, only the sulfates are precipitated, while in the second sample, in addition to the sulfates originally present, the sulfates produced by the oxidation of the sulfamate are also precipitated. From the difference is obtained the \\-eight of barium sulfatc equivalent t o the sulfamate in the original sample. Neuwesen and Merkel ( 4 ) treat the sulfamate solution, acidified with dilute sulfuric acid, with excess sodium nitrite in a special evolution flask, and measure the volume of nitrogen evolved after removing the nitric oxide by bubbling the gas through alkaline permanganate. The volume of nitrogen, after correction to standard conditions, is a measure of tho sulfamate in the sample analyzed.
tion. The sodium nitrite solution should be approximately 0.2 A\- w t h respect to sulfamate, according to the equation
HSO?
T\TH?--SO?-OH
+ Sa
+
Hg0
I t can be seen from the above data that the t e s t concentration is 0.15 to 0.20 gram of sulfamic acid in 100 inl. of solution. The accuracy falls off if there is more than 0.25 gram in this volume. The accuracy ir, the very dilute solutions nould probably be increaqed if more dilute sodium nitrite were used. In order to make a comparison of the tn o previous methods with the direct titration, three commercial samples of ammonium sulfnniate m-ere analy~edby all three methods (Table 11). Samples 1 and 3 n-ere fire retardants for flameproofing fabrics, and sample
Table I. Siilfaiiiic .kcid Taken 0.02002
Determination of Sulfamic Acid 0.2177 S SaSOr .If 1. 2.91 2.92 2.94 2.91
Sulfamic deid Found Gram 0,0205 0 0206 0.0207 0.0205 .iv. 0.0206
0.0606
7.18 7.22 7 24 7.23
0,0505 0.0508 0,0510 0.0509 AY. 0.0508
0 1012
14.44 14.36 14.38 14.40
0.1016 0.1010 0,1012 0,1013 0,1013
0,2025
28.82 28.74 28 76 28 74
0 2531
35.81 35.78 35.91 35.91
0.0898
40.80 40.97 40 99 41.15 40.93
.iv.
Av.
One hundred milliliters of sulfamate solution containing 0.15 t o 0.2 gram of sulfamic acid are acidified with 10 ml. of 10% sulfuric acid, and titrated slowly at room temperature in an Erlenmeyer OT iodine flask with a standard sodium nitrite solu-
f HZ904
After the addition of each 5 or 10 ml. of nitrite solutfon the flask is stoppered and shaken vigorously to aid in the removal of the nitrogen evolved. S e a r the end point the titration must be carried out drop by drop, n-ith shaking after each addition. -4s soon as a drop of the titrated solution causes a blue discoloration of the starch-iodide solution on a spot plate, the equivalcnce point is considered reached. This procedure n as tested on solutions containing known amounts of La Xotte's sulfamic acid, dried to constant weight in EL vacuuni oven a t 35", and titrated with 0.1 A ' carbonate-free sodium hydroxide, using phenolphthalein as an indicator. The results are given in Table I.
Gtwm
Both methods offer disadvantages. The Baumgarten and Krummacher method is s l o ~and tedious like all gravimetric procedures, and the Meuwesen and Merkel procedure, though rapid, is subject to all the hazards of a gas evolution method and requires special apparatus. It was decided to attempt the direct titration of the acidified sulfamate solution with sodium-nitrite, producing a simple, rapid volumetric method, similar t o methods for the determination of primary amino groups. Methods of this type are given in the U. S. Pharmacopoeia ( 5 ) for the analysis of sulfanilamide and sulfapyridine. Cumming and Alexander (8) have recommended the same titration For the reverse purpose, the standardization of sodium nitrite solutions. They add sodium nitrite to the acidified sulfamic acid solution until about three fourths of the sulfamic acid has reacted. They then warm the solution t o 50' C. and continue the titration slowly, using an external indicator such as starchiodide solution or Griess' diazo reagent, a mixture of sulfanilic acid and a-naphthylamine, t o determine the end point. With this background in mind, the following procedure was adopted and found satisfactory.
+
0.2029 0.2024 0.2025 0,2024 0,2025 0.2520 0.2518 0.2527 0.2527
0.2872 0 2884 0.2885 0.2896 0.2881 .Iv. 0 . 2 8 8 4
Difference G Iam
+ O 0004
t o
0002
+o QQOI
i.0
ooocl
-0
0008
- 0 0014
1 mole of SaSOz is equivalent t o 1 mole of NH2SOzOH: 1 ml. of 0.217T N S a S O z is equivalent t o 0.007045 gram of SHzSOzOH.
336
