Volumetric Determination of Hydroxylamine With Ceric Sulfate S. R. COOPER A N D JOSEPH B. MORRIS, IZoward Cnirersity. TTushington, D. C.
l H E ferric salt method is most widely used for t,he deterniinat'ion of hydroxylamine ( 2 ) . In this process, the hydroxylammonium salt is added t o a solution of excess ferric sulfate in sulfuric acid medium. The solution is boiled for 5 minutes, and the amount of ferrous ion obtained is determined by back-titration with 0.1 N potassium permanganate. Hydroxglammonium sulfate was used in the original method. Milligan (3) made a study of the oxidation of hydroxylammonium chloride, using the ferric salt method, and reported two determinations which gave consistent results. Benrath and Ruland (1 ) investigated the oxidation of hydrox>-lammonium sulfate with ceric sulfate solution and found that nitrous oxide and nitrogen were produced, of which 69 t o 73y0 \vas nitrous oxide. They neither gave data nor described a precise niet,hod for their determinations. Ceric sulfate solutions in 1 N sulfuric acid are very stable at boiling temperatures; their concentrations remain constant for months. One tenth normal ceric sulfate in 1A T sulfuric acid has a high oxidation potential ( E = 1.44). Other advantages of wing ceric su1fat.e as an oxidizing agent are n-ell knon-n. PREPARATION OF SOLUTIONS
Anhydrous ceric sulfate and ammonium tetrasulfato cerate \yere obtained from Fisher Scientific Co. and G. F. Smith Co., respectively. One tenth normal solutions in 1 N sulfuric acid were prepared and standardized against 0.1000 K arsenious acid solution, which had been prepared from 99.96% arsenious oxide (Thorn Smith, Royal Oak, Mich.) h 0.01 -If solution of osmium tetroxide in 0.1 N sulfuric acid was prepared for use as a catalyst in all ceric titrations. Phenanthroline (0.025 M ) was used as an internal indicator in the titrations. Hydroxylammonium sulfate and chloride from Eastman Kodak Co. were used t o make 0.05 .If solutions, whose molarities were determined by the met,hod of Trozzolo and Lieher ( 4 ) .
Tahle I.
Reaction of Ceric Sulfate with Iiydroxylammonium Salts a t 100" C. 6 N H2SOa. Water. I v . Reaction Ratio N
0.1032 A11. Ce'-++ t o "SOH, (?;Hi)rCe(SOS4, Ml. kI1. Mmol. 0.0501 -1.iN H ~ O H . ~ / ~ I ~ I ~25.00 S O I ,1111. 50.00 20.0 25.0 1.877 1.964 50,OO 15.0 25.0 2.061 50,OO 10.0 0.0 0 0500 M NHzOH-HCI, 25.00 1111. 50 00 20 0 25 0 1.892 1,944 50 00 15 0 25 0 10 0 0 0 2 091 50 00 ~~~~
ceiic.ion on the reaction ratio. Each reaction mixture a-as heatcd to 100" C., and removed from the heat. Immediately, 25.00 1111. of hydrosylanimonium salt $elution were added. After 3 minutes: the contents of the flask were cooled and diluted to 150 nil. with water. TWOdrops of 0.01 .I! osmium t,etroxide solution ere added for catalysis, and the resulting mixture was titrated with 0.1000 -V arsenious acid solution. S e a r the t s n d point, 2 droli.: of ferroin indicator were ;idded. Table I gives the data for these investigations. Wlien 20 nil. of 6 .V sulfuric acid vias added instead of 15 nil., a decrease in the reaction ratio was obst.rved. However, rvhen the volume of the reaction mixture was decreased by 25.00 ml., therebJ- increasing the concentration of the ceric ion, the reaction ratio n-as greater than 2 to 1. These experiments show that the reaction ratio varied between 2.1 and 1.9 to 1, depending upon the volume of the reaction mixture. the acidit!-, and the concentration of the oxidant. The effect of boiling was studied. The reaction mixture coiitained 50.00 ml. of aninioiiiuni tetrasulfato cerate solution and 15 ml. of 6 S sulfuric acid. Only hydro was used, because prolonged boiling of ceri the chloride ion will oxidize thii; ion. First, 25.00ml. of hl-droxj-Iammonium sulfat,esolution were added to the reaction misture a t room temperature. The contents of the flask were brought to boiling, allowed to boil for 5 minutes, cooled, and titrated n-ith arsenious acid. The reaction ratios varied between 3.4 and 3.7 t.0 1. However, when the reaction mixture was brought t o boiling before the addition of the 25.00 ml. of hydrosylammoniuni sulfate contents of the flask were allowed to boil 5 r, the reartion ratio was about 2.1 to 1. Sinw one of the salts wab hydroxylammonium chloride, a study was made to determine the effect of ceric oxidations on the chloride ion. -1 solution of hydrochloric acid, equivalent, to the amount of hydroxylamine used in the analyses, was added t o ceric solutions and maintained a t 100" C. for 5 minutes. Backtitixtionr nith aweniou3 ac4d inclicated t,hat very little. if an!-.
Tahle 11. Determination of Hydroxy-lammonium Sulfate 0.1000
.v
.4rsenious Acid,
M1.
PRELIMINARY INVESTIGATIONS
Minol
t.500 496
2870 28.74 28.68 28.73 28.74 28.70 28.68 28.66
~
C Crlr Ion Reduced,
A
2 502
2.497 2.496
2 500 2 502 2 504
Reaction Ratio
C r T + + +to NHnOH,
Mmol.
2 IO00 1.997 2.002 1,998 1.997
+ooo -,
002
2.003 2.000
Mean: .4rninonium t e t r a s u l f a t o c e r a t e , 0.1074 .V SHzOH.'/zH2801. 0.0500 .II
Preliminary investigations showed that the reaction betxccn the ceric ion and hydroxylamine gave nitrous oxide .as the principal product, inasmuch as the react,ion ratio (the number of nioles of ceric ion reduced t o the number of moles of hydroxylamine oxidized) was approximately 2 to 1. Direct titrations of hydroxylammonium salt solutions with ceric sulfate showed that the reaction at room temperature reached equilibrium slon-ly. .kt 50°, 55", and 65' C., the end points were fair, but the results were erratic. Reaction near 100" C. with excess ceric sulfate solution K R S carried out according to the following procedure:
Table 111. Determination of Hydroxylammonium Chloride 0.1000 s 4rsenious Acid, Mi. 25.50 25.55 25.52 25.52 2 5 53
Ceric Ion Reduced. Minol. 2 510 2 505 2 2 2 2
508
Reaction Ratio
C e c r + + t o NHnOII,
Mmol 2 008 2.004 2.OOfi
2,006 2.006 2.005 2.008 25.50 25.52 2 006 >lean 2 006 Arnrnoriiurn tetrawlfato ceratp. 0.1012 N SHzOH-HCI. 0.0500 .ti' 75.54
Fifty-milliliter portions of 0.1032 N ammonium tetrasulfato cerate solution were pipetted into a 500-mI. Erlenmeyer flask. Various amounts of water and 6 -V sulfuric acid were added, to make R study of the effects of acidity and concentration of the
1360
508 507
506 2 ,510 2 508
.
V O L U M E 24, NO. 8, A U G U S T 1 9 5 2
1361
chloride had been oxidized. Upon vigorous boiling of the same t!pe of solutions for 10 minutes, 3.5% of the chloride ion was oxidized.
water to 150 ml. Two drops of osmium tetroxide solution a e r e added for catalysis, and the resulting rnisture was back-titrated with 0.1000 S arsenious acid solution. S e a r the end point, 2 drops of ferroin indicator were added.
METHOD FOR DETERMISATIOh O F HYDROXYLAMINE
Tables I1 and I11 give the data which were obtained for the determination of both hydroxylammonium salts, and support the following equation for the reaction:
thorough stud\- of the effect of acidity, volume of solution, boiling. presence of chloride ion, and concentration of oxidant was made in an effort t o design a procedure to be used in a quantitative deterniination of hydroxylamnionium salts.
2SH2OH
+ 4Ce(SO4j,
+
S,O
+ 2C(:.(S04;3 + fI,O + 2H?SO,
LITERATURE CITED
Fift>-milliliter>of 0.1 ATammonium tetrasulfato cerate solution in 1 S sulfuric acid, which had been qtandardized against 0.1000 -T arsenious acid. were pipetted into a 500-ml. Erlenmeyer flask. Fifteen milliliters of 6 -1-sulfuric acid were added. The mixture was brought to boiling, but not removed from the heat. TThile the solution was boiling gently, 25.00 ml. of hydroxylamine eoluhon n-ere added. The contents of the flask were boiled gently tor 1 minutp. removed from the heat. cooled, and diluted with
(1) Henrath, d..and Rulmd, Ii., Z.anorg. u.allgeni. C h m . . 114,2G777 (1920). (2) Eray, W. C., Simpson, .\I. E., and MacKeneie, A . 1.. J. Am. Chem. floc., 41, 1363--~78(1919). (3) XIilligan, L. H., J. r h u s . Chenz., 28, 544 (1924). (4) l'rozsolo, A. M., and Lieher, E., ANAL.CHEM.,22, 766 (1950). RECEIVED for review February 8. 1952. Accepted hpril 20.
15152,
Isotopic Method for Direct Determination of Oxygen in Fluorocarbon Derivatives A.
I). KIRSHENBAURI, A. G. STRENG, AND A. V. GROSSE Research Institute, Temple University, Philudelphiu, Pa.
GOOD direct method was needed for determining the oxygen The direct methods used for the determination of ovygen in organic compounds are the Schutze-Unterzaucher method ( 1 , 2 , 7 , 11, IS! 14), the ter Meulen method (3, 10, 12, 15), and the elementary isotopic method ( 4 4 ) . Xeither the Gchutze-Unterzaucher method of analysis, based on the thermal deconiposition of the organic compound over carbon, nor the ter Meulen method of analysis, har;ed on the reduction of the organic compound by hydrogen. could be used on fluorocarbon compounds, as they are very stable to thernial decomposition and hydrogenation. The elenientary isotopic method can. hoi
