(16) Holler, -4.C., Klinkenberg, R., ANAL. CHEM.23, 1696-7 (1951). (17) International Nickel Co., 67 Wal!. St., New York, N. Y., “Methods for Chemical Analysis of Nickel and HighNickel Alloys,” Tech. Bull. T-36, 4th ed., p. 22. (18) Kolthoff, I. hf., Elving, P. J., f‘Treatise on Analytical Chemistry,” Part 11, Vol. 7, pp. 1-135, Interscience New York, 1962. (19) Larson, R. P., Ross, L. E., Ingber, N. M., ANAL.CHEX 31, 1596-7 (1959). (20) Luke, C. L., Ibid., 29, 1227-8 (1957).
(21) Nauman, R. V., West, P. W., Tron, F., Gaeke, G. C., Jr., Zbid., 32, 1307-11 (1960). (22) Nydahl, F., Ibid., 26, 580-4 (1954). (23) Ralston, R. R., Chairman ASTM Low Sulfur Task Force, General Electric Co., Pittsfield, Mass., private communication. (24) Rooney, R. C., Scott, F., J . Iron Steel (London) 195, 417-21 (1960). (25) Snell, F. D., Snell, c. T., “Colorimetric Methods of Analysis,” vel. IIA, pp. 654-77, Van Nostrand, New York, 1959.
(26) Steigmann, A,, ANAL, CHEM. 22, 492 (1950). (27) Tyou, P., Humblet, L., Talanta 3, 232-9 (1960). (28) Urone, P. F., Boggs, W. E., ANAL. CHEM.23,1517-19 (1951). (29) Wesley, W. A., J . Electrochem. SOC. 103, 296-300 (1956). (30) West, p. w-, G. c., ANAL* CHEM.28,1816-19 (1956). RECEIVEDfor review May 29, 1962. Accepted October 11, 1962. Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, 1962.
Coulometric Method for the Determination of Traces of Water in Liquid Ammonia W. C. KLINGELHOEFER Nitrogen Division, Allied Chemical Corp., Hopewell, Vu. b A coulometric method for determination of water in ammonia is described. Liquid ammonia is passed through a tube packed with KCI into a glass electrolytic cell with a porous separator. Potassium formed at the platinum cathode reacts with the water in the sample. The end point is indicated by an increase in the electrical conductivity of the solution and this is used to stop the electrolysis. The method is sensitive to less than 1 p.p.m. H20 and is suitable for use up to about 100 p.p.rn. HzO.
met,allic sodium directlv in the liauid ammonia and indicatedthat liquid ^ammonia at 0” C. will dissolve 0.132 wt. % of KCl. Solutions of sodium or potassium in liquid ammonia d S 0 are indicated t o show relatively high electrical conductivity and to be fairly stable.
APPARATUS AND PROCEDURE
The apparatus is shown in Figure 1. The electrolysis cell is made of borasilicate glass and is partitioned by & fritted glass disk of medium porosity, 0 . The cathode side is closed by a ground joint, N , greased with vaseline
i:
S
GRADE commercial anhydrous ammonia is one of the purest large tonnage chemicals. A few industrial operations, such as manufacture of stainless steel plate, benefit, however, through use of an extra-quality ammonia of particularly low water a few p.p.m. Such a content-Le., product poses unusual problems of quality determination, especially in analysis for contained water. To date, no method reliably accurate in lower ranges has been made available. Evaporative procedures (3, 4) whereby water is determined as residue are not suitable for trace quantities. A standard method-Le., determining dew point of the 3H2 N2 gas mixture obtained by catalytic dissociation of the ammonia-is generally considered dependable only when water content is above about 30 p.p.m. The procedure described herein was developed to fill the need for a more sensitive method. It is based on reaction of water in a liquid ammonia sample with potassium produced in situ by electrolysis of potassium chloride dissolved in the sample. Audrieth and Kleinberg (2) state that ammonia cnn be dried by dissolving TANDARD
[ i I
L j
I
+
H
ICM
Figure 1.
Apparatus for determination of water in ammonia
A . Stop clock, Standard Electric Time Co. Model S-10 B. DPST relay C. Vacuum tube relay D. Battery, 90-volt, with 20,000-ohm rheostat E. Meter, 25 ma. F . Weston DC Miniature Relay, Model 634 G. Ammonia sample cylinder H . Anode outlet I. Anode, graphite
Cathode outlet Sample valve Dewar flask with liquid ammonia Tube packed with KC1 Ground joint Fritted glass partition P. Cathode, platinum &. Magnetic stirrer in glass R1. 10,000-ohm Rz. 400-ohm Rs. 100-ohm S. Platinum electrodes for conductivity J. K. L. M. N. 0.
VOL. 34, NO. 13, DECEMBER 1962
1751
and wired in place. Three platinum electrodes are attached to leads sealed through the small end of the inner part of the ground joint. The cathode, P, is about 2 X 5 mm. and is close to the partition. The other two electrodes, 8, are used to indicate the electrical conductivity of the mixture and are about 4 X 6 mm. spaced about 1 mm. apart. A glass-covered magnet stirrer, &, runs on glass bearings in the cathode section and is driven by an external magnet and motor. The cathode inlet and outlet tubes are of 1-mni. capillary tubing. The outlet, J , is connected to rubber tubing closed by a screw clamp. The anode, I , is a pencil lead about 2 mm. 0.d. The anode section is closed by a rubber stopper which carries the anode and an outlet tube, H . The cell is held in a 70-mm. i.d. x 200-mm. deep clear glass Dewar flask filled with liquid ammonia. Air is bubbled through the ammonia to keep the temperature a t about -40' C. The ammonia sample is held in a stainless steel cylinder, G, a t room temperature. The cylinder is connected to a special long stemmed needle valve, K , in the cold bath. Liquid ammonia sample passes from the valve outlet through a short rubber connection to a glass tube, M , filled with KCl crystals held between glass wool plugs. The ammonia dissolves some KC1 and then passes to the electrolysis cell. The cell is flushed with sample, part being removed from the cathode outlet and part passing through the separator and out the anode side. The system holds about 50 ml. of liquid ammonia, with about 8.5 ml. in the cathode section. Current is supplied from a 90-volt battery, D, and passes through 20,000ohm rheostats, then through the relay contacts and a 25-ma. meter, E , to the anode. The current passes through the ammonia-KC1 solution to the cathode and back to the battery and ground. The conductivity electrodes in the cathode section are connected to the moving coil of the sensitive relay, F . A potentiometer and battery in the circuit supply about 0 to 0.3 volt and allow adjustment of the end point. A 10,000-ohm resistor, R1, is shunted across the electrodes. The solution resistance a t the end point is about 5000 ohms. The contacts of the moving coil relay are connected t o a vacuum tube relay, C, and this in turn is connected t o a double pole relay, B. One side of this relay controls the electrolysis current, while the other side controls the clutch circuit of the electric stop clock, A . The apparatus is adjusted in a preliminary test. The Dewar is filled with ammonia and is brought to about -40' C. The cell is filled 7%-ithammonia. The sample valve and cathode outlet are closed. The electrolysis current is turned on and is cut off when the solution in the cathode section becomes a faint blue color due to the presence of potassium dissolved in the ammonia. The potentiometer then is adjusted to operate the relays. In making an analysis, the cell is flushed with ammonia sample and closed
1752
ANALYTICAL CHEMISTRY
as before. The electrolysis current is started and adjusted. When the relays cut off the current, the time is noted. The water content of the sample is calculated as follows: 18 (10)O it p.p.m. H20 (uncorrected) = 96,500 vd
-
where molecular weight of water is 18, the Faraday equivalent is 96,500 coulombs, i is the electrolysis current in amperes, t is the time for electrolysis in seconds, V is the volume of sample in cathode section in cubic centimeter, and d is the density of liquid ammonia a t operating temperature. The hydrogen formed from reaction of the water with potassium forms a bubble in the ammonia in the cathode section. At -40' C. and 1 atm., the Hz, NHs vapor mixture amounts to about 0.3 cc. per coulomb. This gas displaces part of the sample through the separator and leads to low results. A correction for this factor would vary nith the water content as follows: HzO, p . p m Correction t o add,
0 40 50 75 100 0
p.p.m.
RESULTS
OF
1
2
4
7
ANALYSES
The operation of the analyzer waq checked by testing ammonia samples before and after addition of known amounts of water. The water was placed in a short piece of '/,e inch bore stainless steel tubing and flushed with liquid ammonia into the evacuated and cooled sample cylinder. A sample of ammonia was tested nith a current of 5 ma. and required i 6 seconds to reach the end point. With a sample of 8.5 ml. and a density of 0.69 gram per milliliter, the sample was indicated to contain 12 p.p.m. H:O. X sample was made from 1009 grams of the above ammonia and 0.044 gram of water to give a sample containing an expected 56 p.p.m. HLO. Tests on this material gave 54 p.p.m. H2O. A correction of 2 p.p.m. H 2 0 could be added to allow for the effect of the hydrogen formed, a$ indicated above. .A similar test was made with ammonia that gave a value of 25 p.p.m. HzO. After addition of m t e r corresponding to 21 p.p.m., the mixture was tested and gave a value of 46 p.p.m. H 2 0 , in perfect agreement without correction. Applying the correction of about 2 p.p.m. would make the result slightly high. Another sample was prepared by adding 54 p.p.m. HzO to the ammonia which showed 25 p.p.m. H?O. This mixture showed 65 p.p.m. H?O. Even with a correction of about 3 p.p.m., this result is substantially loxer than the value expected (68 19s. 79 p.p.m.).
Another test was made using ammonia which had been treated with sodium. Samples taken from the vapor phase of this ammonia showed 1.6 p.p.m. HzO. Ammonia distilled from this sodium-treated material and collected in a sample cylinder showed 6.4 p.p.m. H20 on analysis. A sample prepared by addition of 14.3 p.p.m. HzO t o the latter sample was analyzed and gave 19.3 p.p.m. H20. I n this low range of water content, no correction vas applied leaving the result slightly below the indicated value (19.3 us. 20.7 p.p.m.). DISCUSSION
Akhumov (1) reported that electrolysis of KBr in liquid ammonia gave KKHr a t the cathode. In the present work the blue solution of potassium in ammonia forms at the cathode and this solution is fairly stable. KNHz can be formed by reaction of potassium with ammonia, but under the conditions used here this reaction is very slow and does not interfere. The anode products probably are NH2C1, NHIC1, and some N2H4, Nz, and H2. A platinum anode was used for a while but gave poor results and led to formation of a dark deposit on the fritted glass partition. When the graphite anode was used, no deposit formed on the partition and results were more consistent. The solution of KC1 in ammonia passes very little current when less than the decomposition voltage is applied to the conductivity electrodes. When potassium is present, the solution exhibits metallic-type conduction and passes enough current to operate the relay even when only about 0.1 to 0.3 volt is applied. Increasing the concentration of potassium increases the conductivity and also increases the intensity of the blue color of the solution. It is desirable to stop the electrolysis when only a small excess of potassium is present, such as when a very pale blue color is noted. ilt that point the excess appears to correspond to about 1 p.p.m. HzO. The end point adjustment could be made on the basis of conductivity alone, if desired. Analyses also have been run without the conductivity system, cutting off the current when the blue color developed in the cathode section. This procedure has given good results. Control of the unit with a light beam and photocell system gave poor results because of the formation of a suspension of very small crystals of KOH in the cathode section. The KOH does not affect the conductivity end point detection. Flushing part of the ammonia sample through the cathode outlet removes some of the KOH.
Oxygen has given serious interference because it reacts with the potassium. Oxygeii present in a n ammonia sample cylinder can be removed by venting the vapor space. The method gave consistent results with ammonia samples containing as little as 2 p.12.m. H20 and up to at least 100 p.1i.m. H20. At about 150 p.p.m. H20 and higher, the results became irregular and sometimes no end point could be obtained. The reason for this effect has not been established
LITERATURE CITED
but may be due to depletion of potassium ion and build-up of ammonium ion. KC1 is only slightly soluble in liquid ammonia and the sample may not be saturated after passing through the KC1 tube. Ammonia appears to dissolve only a few p.p.m. of KOH. The method probably could be applied to the aliphatic amines. Similar results were obtained by using KaC1 in liquid ammonia, but this requires a different method of addition of salt and sample.
(1) A4khunlov, E. I., J . Gen. C‘hem. C‘SSR (Eng. Tranl.) 7, 298-304 (1937); C. A . 31,4601’ (193‘7).
(2) ‘kudrieth, L. F., Kleinberg, J., ‘‘Yonaqueous Solvents,” pp. 43-6, 94-115, pviley, 1953, (3) Fudge, J. F., J . Assoc. O$k. Agr. Chenizsts 39, 558-62 (1956). (4) Kirk, R. E., Othmer, 1).F., “Encyclopedia of Chemical Technology,” Vol. 1, 805, Interscience Encyclopedia Co., 1947. R~~~~~~~ for review june14, 1962. Accepted September 21, 1962.
Isotope Effect in the RecrystaIIization of D-Mannose-1-t Phenylhydrazone FRIEDRICH WEYGAND, HELMUT SIMON, and K. D. KElL Organisch-chernisches lnstitut der Technischen Hochschule, Munich, Germany
H. S. ISBELL and L. T. SNlEGOSKl National Bureau of Standards, Washington, D.
b An isotope effect previously reported in the recrystallization of Dmannose-1- t
phenylhydrazone
Table 1.
has
been reinvestigated and confirmed. The ratio of the rate of crystallization of the isotopic to that of the nonisotopic form (k*/k) was 0.89.
I
C.
1 PRIOR publication, Keygand, Simon. and Keil (10) reported that, n heri rmiannose-1-l phenylhydrazone is fiactionally recrystallized from 60y0aqueous ethanol, the crystals that separate initially have a Ion er specific activity. and those that separate later, a higher specific activity, tlian that of the original D-mannose-1-t phenylhydrazone. A small isotopeeffect was also observed in the fractiona! recrystallization of D-glucose-1-t equilibrated n-ith aqueous ammonium hydroxide. Subsequently, Ishell, Frush, and Holt ( 1 ) reported the absence of an isotope effect in the recrystallization of a-D-gluC0Sf-l-t under conditions ordinarily used for purification of the sugar; this observation was confirmed by Weygand, Simon, and Keil. I n view of the importance of fractional recrystallization for the purification of labeled compounds, a collaborative project was arranged to reinvestigate the recrystallization of D-mannose-1-t phenylhydrazone. Two series of measurements were made, one in each laboratory. The results, given in Table I, clearly show an isotope effect in the recrystallization of D-mannose-1-t phenylhydrasone. The existence of the isotope effect was also confirmed by another series of
Distribution of Radioactivity in the Fractional Recrystallization of DMannose-1 -t Phenylhydrazone
Relative Relative activity activity of
of
Yield Product
mg.
x
D-Mannose-I-t D-Mannose-1-t phenylhydrazone (crude) a. Fractional recrystallization Fraction 1 Fraction 2 Fraction 3 b. Fractional recrystallization of a-1
Fraction 1 c. Fractional recrystallization of b-1 Fraction 1 Fraction 2
Radioactivity
70 Av. Weygand, Simon, and Keil (c.p.m./pM) 343.4, 342.3 342.9
( y ) 67.0
productja product,
%
%
100.0
345.9
345.9
100.9 95.0 103.7
73 26
18.2 6.5
324.7, 327.2 355.6 422.6. 419.8
325.9 355.6 421.2
(200) 123
61.5
308.1
308.1
94.5
89.9
(‘i:) 10
86 10
301.6, 296.8 377.7
299.2 377.7
97.1 122.6
110.1
122.8
87.3
Isbell and Sniegoski (pc./mM ) 173.3, 173.3
n-Mannose-1-t D-Mannose-1-t phenylhydrazone (crude) a. Fractional recrystallization Fraction 1 Fraction 2 Fraction 3
(;g) 82 14
69.5 20.5 3.5
173.3
100.0
171.1, 171.1, 171.6
171.4
98.9
162.7, 160.3 185.1, 181.9 182.7
161.5 183.5 182.7
93.2 105.9 105.4 ( Continued)
VOL. 34, NO. 13, DECEMBER 1962
1753
