136
ANALYTICAL CHEMISTRY
Table 11. Titrations of Sulfuric Acid in Several Solvent Mixturesa Solvent Mixture, 100 MI. Acetic acid
Sulfuric Acid Content Used, Found, gram gram 0.057 0.053
Acetic acid 50% Acetic anhidride, 50%}
0.057
O.Ob7
0.057 0.171
0.058 0. I72
0.057 0.171
0.056 0.172
Ethyl alcohol 30% Acetic anhydride, 70%}
b
E t h y l acetate, 50% 1 Acetic anhydride, 50%j
Water 30% 0,057 0.057 Acetic'anhydride, 70%} 0.171 0.170 Mixtures were brought t o a boil, then cooled t o room temperature before titrating. b Because of spontaneous reaction of water and ethyl alcohol with acetic anhydride, concentration of each component of solvent was uncertain a t moment of titration.
The data of Table I1 have been collected on a number of mixtures into which a known amount of sulfuric acid had been added. Table I11 gives the quantitative data on the titration of sewmi weak bases in acetic anhydride.
Table 111. Titrations of Weak Organic Bases in .tcetic An hpdride" Purity Found,
*
ditions so obtained give rise to the large potential changes observed a t the end point. Although the conditions under which the sulfuric acid has been titrated seem favorable for dehydration, the titrations have been carried out in the presence of water. Acetic anhydride makes possible the simple and rapid determination of some weak organic bases (Table I ) whose base ionization constants in water are less than 10-12. I n the absence of Kb for allylthiourea the value for thiourea has been included in Table I. It is suspected thst the Kb values for these two substances are about the same. Markunas and Riddick (6) have recommended the use of acetic acid in titrating weak organic bases whose Kb values in water are or larger. Urea, which does not give an insoluble perchlorate in acetic acid, has been listed by Fritz ( 2 )as giving an unsatisfactory end point in acetic acid. The use of acetic anhydride in this instance removes this difficulty (Figure 7).
h
%
Base .kllylthiourea Dimethylaniline p - Aminodimethylaniline Diplienylamine Glycine Pyridine Urea All bases were used as received. Reagent grade materials. Technical or practical grade.
100; 99 98;5C 100
lOOb,
1006 l00.5h
LITERATURE CITED
(1) Hell, K. P., "Acids and Bases. Their Quantitative Behavior," p. 66, London, Methuen and Co., Ltd., 1952.
(2) Fritz, J. S., ANAL.CHEM.,22, 1028-9 (1950). (3) Ibid., 25, 407-11 (1953). (4) Fritz, J. S., and Fulda, M. O., Ibid., 25, 1837-9 (1953). (5) Lange, N. A., "Handbook of Chemistry," 8th ed., p . 1234,
Sandusky, Ohio, Handbook Publishers, Ino., 1952. (6) lfarkunas, P. C., and Riddick, J. A., ANAL.CHEM.,23, 3 3 i - 9 (1951).
(7) Russell, J., and Cameron, 8 . E., J . Am. Chem. Soc.. 60, 1345-8 (8)
(1938). Wagner, C. D., Brown, R. H., and Peters, E. D., Ibid., 69, 2609-10 (1947).
RECEIVEDfor review February 26, 1954. Accepted September 1, 1054. Presented before the Division of Analytical Chemistry a t t h e Regional Conclave of the AMERICASCHEMICAL SOCIETY, New Orleans, La.. December 10, 1 9 3 .
Semimicromethod for Determination of Cyanate Ion in Presence of Interfering Substances WILLIAM
H. R. SHAW
and JOHN 1. BORDEAUX
The University of Texas, Austin, r e x .
The method described employs ion exchange'removalof interfering cations, conversion of cyanate ion to ammonium ion by dilute acid, separation of ammonium ion by ion exchange, and photoelectric colorimetric analysis of ammonium ion with Nessler's reagent.
COLORIMETRIC method for the determination of cyanate ion in the presence of interfering substances has been developed. The mixture containing cyanate ion is passed through a cation exchanger; the effluent is collected; the column is eluted with a sodium hydroxide solution and rinsed, thus freeing it from all cations except the sodium ion. The original effluent containing only anions, sodium ions, and neutral molecules is acidified, and cyanate ion is rapidly converted to ammonium ion. The resultant solution is again passed through the cation cxchanger. Ammonium ion is quantitatively retained, and the anions, exchanged sodium ions, and neutral molecules are rinsed from the column and discarded. Ammonium ion is eluted, the elutriate is treated with Sessler's reagent, and the absorbance is determined. A calibration curve relates absorbance to the cyanate ion concentration. Interference may be expected from a rather limited number of substances that react with dilute acid t o
produce cations which, in turn, interfere with the Sewler's reaction. -kt elevated temperatures in aqueous solutions, urea tiwomposes according to the following reaction
+ CNO-
CO(NHz)z - NH:
(1)
In the course of a kinetic study of this reaction (Is),an e l tremely rapid conversion of cyanate ion to ammonium ion h!dilute sulfuric acid was observed.
CNO-
+ 2H+ + 2H20 -
'4"
+ H&Os
(2)
This same reaction had been employed by Hertig (4, 5, 1 4 ) qand others a t elevated temperatures for the quantitative determination of cyanate. Previous work (6-8, 1 2 ) had established a convenient method ior the determination of the ammonium ion based on an ion exchange separation and subsequent colorimetric analysis with Sessler's reagent. Consequently, if Reaction 2 were quantitative a t room temperature, cyanate ion could be easily determined by a technique similar to that employed for ammonium ion. Since this method had proved useful in the presence of interfering substances, and treatment of complex mixtures containing
V O L U M E 2 7 , NO. 1, J A N U A R Y 1 9 5 5
137
cyanate a t a lower temperature than that employed by Hertig Iernied desirable, the proposed technique was subjected to Further investigation. APPARATUS AND REAGENTS
('olorimeter. A Lumetron photoelectric colorimeter Model 402E: equipped with a blue glass filter 31 440 and 10-mni. rectangular cuvets was employed. Ion Exchange Columns. A convenient column may be prepared by joining a 38 X 200 mm. test tube to 32 em. of 15-mm. Iiorosilicate glass tubing. A 2-mm. stopcock is attached to the tubing to regulate the drop rate. Twelve columns were used in the work.
-I
.500F ,400 W
I
/
I
I
,3001
40
00
120
160 200 240 200
NITROGEN, MICROMOLARITY
Figure 1. Absorbance as a Function of Nitrogen Content 0 Standard ammonium chloride 0 Standard potassium cyanate
1t d e r ' b Reagent. The preparation of this reagent has been tlcs.-cribed ( 1 ) . Ion Exchange Resin. For each column 11 ml. of low color Dowex 50 (20 to 50 mesh) was employed after it had been purified l)y recycling three times from the hydrogen to the sodium form. ?Immonia-Free Water. Distilled water passed through a large c,apacity Dowex 50 exchanger was used throughout the work. .ill other reagents were of analytical reagent grade and con1 ormed to A.C.S. specifications.
12. Add approximately 90 ml. of water and 10 drops of 4;21 sodium hydroxide. 13. Elute into a 100-ml. flask a t a rate of 1 drop every 2 seconds. 14. Add 4 ml. of Nessler's reagent and dilute to mark. 15. Allow to stand 15 minutes, and determine absorbance. When interfering substances are known to be absent, only steps 6 through 15 need be followed. RESULTS
Figure 1 shows a representative calibration curve obtained with both standard potassium cyanate and standard ammonium chloride. Figure 2 demonstrates the effect of increasing acid concentration with a fixed cyanate concentration. Complete conversion requires a mole ratio of acid to cyanate of a t least 2.5 X lo3. -4t high acid concentration a slight decrease in the apparent concentration of cyanate is observed. This presumably occurs because of the very high sodium content of these solutions after neutralization (step 10 in procedure). A competition of the sodium ion and ammonium ion for the resin takes place, producing the observed effect. No interference from urea, ammonium ion, or common cations and anions a t moderate concentrations was observed (6). A series of experiments showed that the conversion of cyanate ion to ammonium ion in 0 . l A sulfuric is complete in 10 minutes or less (step 8). The range of the method as described is approximately 40 to 200 micromoles of cyanate per liter of nesslerized solution (step 14). hppropriate dilution before adsorption (step 3) can readily be made to cover a wide range of concentrations. The standard deviation of a set of ten duplicate analyses of a solution containing 170 micromoles per liter was 1.5%. DI scus SIOn
A search of the literature has revealed several methods for cyanate determination; a gravimetric method (3)based on the comparative insolubility of silver cyanate, argentometric methods (10, l l ) ,and two colorimetric methods (9, 2 ) .
PROCEDURE
-7
The separation and determination of cyanate, when interfering substances are present, are accomplished by the following steps: 1. To an appropriate aliquot of the solution containing yanate add several drops of citrate buffer, to effect easy attainiiient of a sharp end point, and enough bromothymol blue to vnsure a good color change. 2. Titrate the solution to a light green end point with dilute d f u r i c acid or sodium hydroxide. Proper p H is essential for quantitative adsorption on the column, 3 . Quantitatively transfer the solution to the ion exchange volumn (sodium form). 4. -4dsorb a t the rate of 1 drop every 3 seconds, retaining the effluent in a 100-ml. volumetric flask. Interfering cations are retained on the column; anions, including the cyanate ion, exchanged sodium ions, and neutral molecules are in the effluent. 5 Wash, retaining washes until total volume is about 90 (
1111.
6. Fill the columns with about 90 ml. of water and add 10 drops of 4-51 sodium hydroxide. Allow to flow a t full rate and rinse thoroughly with water. This removes the interfering vations trapped in step 4. 7 . To the retained effluent (steps 4 and 5 ) add 10 ml. of 1.0,V sulfuric acid. S Dilute to volume, mix, and let stand 10 minutes or more. anate ion is converted to ammonium ion. 9. Pipet appropriate aliquot into a beaker. 10 Repeat steps 1, 2, 3, and 4, but do not retain the effluent. Iritrrfering anions and neutral molecules are discarded in this 9trp.
I I.
Wash until effluent is free of indicator color.
H2S04 MOLARITY
Figure 2. Effect of Acid Concentration on Cyanate-Ammonium Conversion Dashed line represents complete conversion
The gravimetric and argentometric methods were not well suited to semimicrodeterminations,and, like the first colorimetric method, had not been extensively evaluated in the presence of interfering substances. Dodge and Zabban ( 2 ) , however, employed a method similar in some respects to the one reported here. In their determination cyanate ion was converted to ammonium ion by digestion with sulfuric acid ( 4 , 6, 14), for 0.5 hour, keeping the solution near the boiling point. The ammonium ion formed was analyzed with Nessler's reagent. If interfering substances were present, the method was somewhat difficult to apply. In the presence of ammonium salts or other nitrogenous materials cyanate was precipitated as silver cyanate,
138
ANALYTICAL CHEMISTRY
which was subsequently digested with acid. Before analysis, the silver ion had to be removed t o prevent reaction with the Nessler’s reagent. If interfering cations were present a Rochelle salt solution was used to complex them. This procedure, however, could be applied to only a limited number of cations present in low concentration. I n some instances, a modified Kjeldahl method was employed to separate the ammonia. The present method is well suited to the analysis of mixtures. The preliminary pass through the column removes interfering cations, which are subsequently eluted and discarded. The comparatively gentle treatment of the elutriate containing the anions, including cyanate, exchanged sodium ions, and neutral molecules with O . 1 N acid a t room temperature for 10 minutes should convert only the most easily hydrolyzable substances to ammonium ion. The second pass of the solution through the column retains only sodium ion and anions or molecules that are converted by mild acid treatment to cations. Of these cations only those that on elution interfere with the Nessler’s reaction will prove troublesome. It seems unlikely that many substances other than the cyanate ion will exhibit this sequence of chemical behavior. Ammonium ion and cyanate ion can be readily determined in solutions containing both, without resorting to a method of differences. The procedure is easy to perform and fairly rapid. In the
current atudy, 24 analyses per day are made routinely by a single analyst. ACKNOWLEDGMENT
The authors gratefully acknowledge the generous grant from the Research Corp. of New York which made this study possible. LITERATURE CITED
ilmerican Public Health Association, New York, “Standard Methods for the Examination of Water and Sewage,” 1933. Dodge, B. F., and Zabban, W., Plating, 39, 381 (1952). Duval, C., Anal. Chim. Acta., 5 , 506 (1951). Hertig, O., J . SOC.Chem. I n d . (London), 20, 838 (1901). Hertig, O., Z . angew. Chem., 14, 585 (1901). Kistiakowsky, G. B., Manglesdorf, P. C., Rosenberg, A. J., and Shaw, W. H. R., J . Am. Chem. SOC.,74, 5015 (1952). Kistiakowsky, G. B., and Shaw, W. H. R., Ibid., 75,866 (1953). Ibid., p. 2751. Martin. E. L.. and McClelland. ANAL.CHEY..23.’ 1519 (1951). Ripan-Tilici, R., Z . anal. Chem.,’ 99, 415 (1934). Ibid., 102, 32 (1935). Rosenberg, A. J., thesis, Harvard University, 1952. Shaw, W. H. R., and Bordeaux, J. J., work in progress. R‘illiarns, H. E., “Cyanogen Compounds,” pp. 400-2, London, Edward Arnold and Co., 1948. 1
,
R E C E I V for ~ D review J u n e 14,1864. Accepted October 1, 1954.
Determination of High Molecular Weight Ketones L. D. METCALFE and A. A. SCHMITZ Research Division, Armour & Co., Chicago,
111.
A simple rapid method for the determination of high molecular weight ketones uses hydroxylamine hydrochloride and a high molecular weight amine in nonaqueous solvents. The method has been used to determine varying amounts of carbonyl compounds in mixtures, and has been used successfully as a control procedure.
H
YDROXYLAMISE hydrochloride has been used as a reagent for the determination of aldehydes and ketones in analytical procedures for a number of years. The reactions involved are
+ NHzOH*HCl-+ RCH=KOH + HzO + HCl RCOR‘ + NHZOH*HCl-+ RR’C=NOH + H20 + HCl RCHO
(1) (2)
The use of the reagent was reported by Brochet and Cambier (2)as early as 1895 for the quantitative determination of formaldehyde. Bennett and Donavan (1) and Marasco ( 5 ) later used it to determine acetone. The procedures employing hydroxylamine reagent to determine carbonyl compounds are of four general types: titration of the hydrochloric acid produced as shown in the above equations ( 3 , 9); neutralization of the hydroxylamine hydrochloride liberating free hydroxylamine to react with the carbonyl groups, followed by titration of unreacted hydroxylamine (10, 11); determination of the water produced in the reaction using Karl Fischer reagent ( 7 ) ; and measurement of the change in pH caused by the liberation of hydrochloric acid as indicated in Equations 1 and 2 ( 4 , 8). An excellent summary of hydroxylamine procedures has been prepared by Mitchell (6). -4procedure has been developed t o fill the need for a rapid and simple determination of high molecular weight aliphatic ketones
in the presence of varying amounts of free fatty acid. S o previously mentioned method could be applied to the determination of such ketones as stearone and palmitone, because of their limited solubility in all but a few suitable solvents. Using as the reagent 0 . 5 5 hydroxylamine hydrochloride in a mixed solvent of 65% isopropyl alcohol and 35y0 methanol, the analytical procedure has been used effectively to determine these ketones. X measured excess of an organic base (octadecenylamine) in isopropyl alcohol is added to facilitate complete reaction between the ketone and hydroxylamine hydrochloride by combining with the hydrochloric acid liberated. At the end of the reaction period, unreacted amine is titrated m-ith standard hydrochloric acid solution in isopropyl alcohol to a bromophenol blue end point. A titration is run on a blank containing the exact quantities of hydroxylamine hydrochloride and octadecenylamine used with the sample. The difference between blank and sample titrations gives a direct measure of the carbonyl groups present in the sample. Since hydrochloric acid formed in the reaction is never liberated and is constant, it does not, affect the titration of either the sample or the blank. Under these conditions, any free fatty acid present mill not affect the tit,ration. If amine salts of the fatty acid are formed, they will titrate as free amine. -4 procedure using free hydroxylamine in a proper solvent mixture, omitting the organic base, may be used. However, since the stability of a solution of free hydroxylamine is poor, this procedure is impractical where a great number of control analyses must be made constantly. -1lthough the results of this paper deal entirely with ketones, the procedure has been applied successfully to some high molecular weight aldehydes. REAGENTS
Hydroxylamine Hydrochloride Reagent. Dissolve 35 grama of hydroxylamine hydrochloride (reagent grade) in 350 ml. of
