V O L U M E 2 5 , NO. 1 2 , D E C E M B E R 1 9 5 3 Compounds such as diethylene glycol and l,4butylene glycol (1,i-butanediol) do not interfere with the separation and detection of the glycols studied in this work. It is possible that these and other nonvicinal glycols can be separated by partition chromatography, but this study will require the development of an accessory method for their determination. Dichromate oxidation was considered for this purpose but could not be used because of the n-butyl alcohol present in the developing solvents.
1877
H. T. J. Littleton and R. W.Wheatcroft for permission to describe the apparatus in Figure l. The able assistance of Anne Greco also is gratefully acknowledged. LITERATURE CITED (1) Dal Sogare, (1952).
Stephen, and Oemler, A. K.,- 1 ~ 4 CHEM., ~. 24, 902
ACKNOWLEDGMENT
( 2 ) llarvel, C . S., and Rands, R. D., Jr., J . A m . Chem. SOC.,72, 2642 (1950). 1 3 ) Seish, .1.C.. Can. J . Chem., 28, 535 (1950). (4) Ihzd., 29, 552 (1951).
The author wishes to thank John Mitchell, Jr., and L. W. Bafranski for their interest and encouragement in this work, and
RECEIVED for review June 4 , 1963. Accepted September 75, 1953. Presented before the Division of Analytical Chemistry a t the 122nd Meeting SOCIETY, .&tlantic City, S . J.. September 1952 of the . h E R I C A N CHEMICAL
Determination of Elemental Fluorine IR\-ING SHEFT, HERBERT H. HY414N, AND JOSEPH J. KAT% Chemistry Division, Argonne 'l'ational Laboratory, Lemont, I l l . i n connection with an investigation of halogen fluorides, i t appeared practical to adapt the brominefluorine reaction as an analytical method for fluorine. Bromine, dissolved in bromine trifluoride, can be titrated with fluorine gas at room temperature. The reaction is quantitative and the end point is readily detected by the discharge of the bromine color. Using this procedure, the purity of several fluorine samples has been determined to &t%CJ,. The uncertainty of the titration, which is limited by the error in reading the fluorine pressure, should be reducible to about 0.1% by use of a more sensitive pressure-measuring device. It is possible to employ the titration to determine bromine, or substances which yield bromine on reaction with bromine trifluoride. These include metals, oxides, and halides other than fluorides. The titration can also be adapted for the determination of bromine pentafluoride.
sis of the inert components. Bibliographies and additional methods of analysis have recently appeared in the literature (3, 6 ) . In the course of other work, a procedure has been developed r h i c h can readily be applied to fluorine determination. This method depends on the fact that elemental fluorine reacts smoothly and quantitatively with bromine in the liquid phase according to the reaction 3Fz 2Br2 + 2BrF3. Bromine trifluoride (boiling point 127" C.) itself is an excellent solvent for carrying out this reaction. The method involves the titration of a known amount of bromine dissolved in bromine trifluoride with the fluorine gas to be analyzed. -4visual end point, the disappearance of the red-brown bromine color to give the light
+
VACUUM LINE
(L-4
F
LUORISE is usually prepared by the electrolysis of a molten potassium fluoride-hydrogen fluoride bath, using a steel cathode and a carbon anode (1) Fluorine so produced contains hydrogen fluoride from the bath. carbon fluorides from reaction with the anode, and air due to leakage. The hydrogen fluoride is easily removed from fluorine by treatment with sodium fluoride. The other contaminants. hen-ever, are very difficult to remove, and laboratory-generated or commercial tank fluorine will contain variable amounts of these almost unavoidable impurities. For many purposes it is important to know the purity of the fluorine, but many investigators have neglected fluorine purity because of the difficulties of analysis. At present two methods of fluorine determination are commonly used. The first consists of reaction of a known volume of fluorine mith mercury and measurement of the residual gas after fluorine has been converted to mercury fluoride ('7). The second consists of reaction of a known volume of fluorine with sodium chloride and determination of the chloride by absorption in alkaline arsenite (6). The first method has several drawbacks, most important of which is the formation of a mercury fluoride scum on the surface of the mercury. This makes readings of the mercury level difficult and inaccurate, especially where fluorine is a major constitutxnt. This method is primarily useful for the determination of emall amounts of fluorine in other gases inert to mercury. The second method is complicated and involves a rather large number of chemical operations. Loss of some of the residual gases in the various absorbents can lead to error in analy-
FP
CYLl N DER
ITRATION
CELL
Figure 1. Diagram of Apparatus
yellow of a fluorine-saturated bromine trifluoride solution, is easily discernible. The inert components can then be collected if desired for further analysis. This titration analysis is especially useful where fluorine is the major constituent. MATERIALS
The bromine trifluoride was obtained from the Harshaw Chemical Co. and purified by vacuum distillation in a nickel still. Bromine, bromine pentafluoride, hydrogen fluoride, and nonvolatile fluorides are the major impurities. The fraction used (boiling point 95-95.5' C. a t 250 mm.) was pale yellow in color and was stored in a welded nickel container. The fluorine was obtained from the Pennsylvania Salt Co. and was used directly from the tank. The purity of the fluorine in two cylinders employed in this work was greater than 99%. Another
ANALYTICAL CHEMISTRY
1878 cylinder which was analyzed contained 95% fluorine, and an isolated shipment of two cylinders has been found to contain less than 80% fluorine. APPARATUS
The titrations were carried out in the nickel apparatus shown in Figure 1. The fluorine-measuring tank is a welded nickel tank fitted with Hoke nickel-alloy diaphragm valves (Sos. 411 and 413). An 81/2-inch K-Monel Bourdon tube Helicoid gage (So. 462), 0 to 1500 mm. absolute, was used to measure the fluorine pressure in the tank. The volume of the tank and gage was determined a t several pressures by expanding gas from a standard volume into the tank and noting the pressure change. After correction for the connecting tubing, the volume was found to be 1125 f 2 ml. a t 25' C. The tank \vas enclosed in a Lucite box to minimize temperature fluctuations. The titration cell is a molded Kel-F (chlorotrifluoroethylene high olymer) (8) tube, "4 inch in outside diameter, \$-itha standard g.A.E. 3/4 inch flare. These tubes are transparent and have been made in several ways. Machining from commercially available 1-inch rod is simplest, but gives the least transparent tubes. The Argonne Plastics Shop has produced reasonably clear tubes by molding directly from Kel-F powder, but with only intermittent success. hlolding bottoms and flares on lengths of commercially available extruded tubing, 3/4 inch in outside diameter, gives the clearest tubes, but the technique is not yet fully developed. Directions for preparation of suitable tubes will be published when the methods have been fully explored. The fluorine delivery tube is an inch nickel tube, long enough to dip below the surface of the solution in the cell. TITRATIOX PROCEDURE
The bromine used in the titration was measured either by weighing, or from micropipets calibrated "to deliver." The bromine-bromine trifluoride solution can be prepared in various ways. For example, bromine trifluoride may first be placed in the titration vessel, either by pipetting or from the storage vessel. The authors have found a volume of about 8 ml. to be convenient. The bromine trifluoride is then pumped on for a short time a t room temperature to remove any traces of volatile impurities such as bromine or bromine monofluoride (boiling point 15" C.) which may have formed since the initial purification. The titration vessel is then filled with dry nitrogen and removed momentarily from the line, and a known volume of bromine is added by pipet. The titration vessel is then replaced on the line, the contents are frozen in liquid nitrogen, and the system is evacuated. After warming to room temperature, fluorine is added from the fluorine reservoir until the deep bromine color is discharged. The end point is sharp and is readily detected by visual comparison of the reaction mixture 1%ith pure bromine trifluoride in a similar Kel-F tube. Alternatively, bromine may be weighed into the empty titration vessel, which is then attached to the line and frozen with liquid nitrogen, and the vessel is evacuated. Bromine trifluoride is then delivered from the storage vessel by application of helium pressure. The volume between the two valves is about 8 ml., and after this portion of the line has been filled with bromine trifluoride, the lower valve is opened and the proper amount of bromine trifluoride allowed to flow into the titration vessel. The titration can then be carried out as before. This procedure was used in samples 1 and 4. \T7hen the fluorine contains large amounts of inert gases, it may be necessary to bleed the inert gases from the titration cell in order to add enough fluorine to reach the end point. This may be done by interrupting the titration, venting the gases, and continuing the titration until the end point is reached. The inert gases may readily be allowed to expand into an evacuated container and submitted for mass spectrographic analysis. The reaction of fluorine with bromine dissolved in bromine trifluoride is rapid, smooth, and complete at room temperature. At temperatures above 50" C., the reaction of fluorine with bromine trifluoride to yield bromine pentafluoride becomes appreciably fast. To avoid error as a result of this side reaction, it is important to carry out the titration a t temperatures below 30" C., where the rate of bromine pentafluoride formation is negligibly small. RESULTS AYD DISCUSSION
The results of a number of determinations are given in Table I. The accuracy of the titration is limited by the 2- to 5-mm. error in reading the fluorine pressure. With a fluorine consumption
corresponding to a 300-mm. change in pressure, an uncertainty of about 2% may be anticipated. Khen greater accuracy is desired, a balancing device such as a differential pressure transmitter or a Booth-Cromer gage (2, 4) may be employed. A sensitive gage or manometer may be used to measure the inert gas side and determine the fluorine pressure to *O.l mm. Using such equipment and bromine samples of about 1 gram, the uncertainty in the titration should be readily reducible to about 0.1%. To illustrate a complete analysis of commercial fluorine, the inert gases from a sample of the 95% fluorine nere collected and analyzed mass spectrographically by the Consolidated Engineering Corp , Pasadena, Calif., nith the foIlov?ng results: nitrogen 62.8%, oxygen 28.070, carbon monoxide 3.2%, argon 0.6%, hydrogen < O . l l % .
Table I. Determination of Fluorine by Titration with Bromine in Bromine Trifluoride Solution Fluorine Sample % Fz Used. In Cc. (STP) Cc. (STP) Sample 638 63 1 101 0 255 259 98 5 255 256 99 6 255 261 97.7b 255 258 99 0 0.609 271 255 93 7 0.609 264 255 96.5 0.609 255 267 95,5 a Samples taken from three different fluorine cylinders obtained from Pennsylvania Salt Manufacturing Co. Samples 1, 2, and 3 came from one cylinder, 4 and 5 from a second, and 6, 7, a n d 8 from a third. b A sample of fluorine from this tank was also analyzed by the mercury absorption method a n d found to contain >99% fluorine (9). Fluorine Samplea
Bromine, Grams 1.520 0.609 0.609 0.609 0.609
Fluorine Equivalent to Bromine,
The bulk of the inert impurity is obviously air. The presence of carbon monoxide is rather surprising, and illustrates the desirability of detailed information about fluorine used in experimentation. OTHER AVALYTICAL APPLICATIONS
Using fluorine of known purity, it is possible to employ the titration to determine bromine, or substances that yield bromine by reaction with bromine trifluoride. These include metals, oxides, and halides other than fluorides, all of which yield bromine on reaction with bromine trifluoride. Some of these reactions liberate substantial amounts of heat and are best performed in a metal (nickel or hfonel) titration tube. Khen the titration is carried out in metal tubes, an alternative to the disappearance of bromine color as a criterion of the end point is used. In this procedure, fluorine is added until uptake ceases. The excess fluorine is then pumped out, and the cell is again filled with fluorine. This latter amount of fluorine is then an overtitration correction, and by subtraction from the first amount of fluorine used, gives the fluorine actually used in the titration. The fluorine must be of such purity that the back-pressure of the inert gases does not exceed the fluorine pressure in the measuring tank. The titration can also be adapted for the determination of bromine pentafluoride. It has been shown that bromine will react quantitatively with bromine pentafluoride a t temperatures above 150" C. I t should be possible, therefore, to add excess bromine to the sample in a nickel titration tube which is frozen and evacuated as described. The tube is then heated a t 150" to 200" C. to complete the reaction 3BrF6 -t Br2-* 5BrF3 The residual bromine is back-titrated a t room temperature with fluorine. Presence of bromine trifluoride, a common impurity in bromine pentafluoride. obviously will not interfere with the analysis, and this procedure then becomes particularly useful in determining bromine pentafluoride iii bromine trifluoride.
V O L U M E 2 5 , NO. 1 2 , D E C E M B E R 1 9 5 3 LITERATURE CITED
(1) Cady, G. H., “Preparation of Fluorine,” Chap. 8 in “Fluorine Chemistry,” Vol. I, J. H. Simons, ed., New York, Academic Press, Inc., 1950. (2) Cromer, S., ”The Electronic Pressure Transmitter and SelfBalancing Relay,” Oak Ridge, Tenn., U. S. Atomic Energy Commission, MDDC-803 (1944). (3) Guerin, H., ”Trait6 de Manipulation e t d’dnalyse des Gas,” p. 319, Paris, lllasson and Co., 1952. (4) Katz, S., and Burr, J. T., ASAL. CHEM.,25, 619 (1953).
1879 (5) Kimble, R. H., and Tufts, L. E., “Complete Analysis of Fluorine Gas,” Oak Ridge, Tenn., U. S. Atomic Energy Commission, MDDC-195 (1945). (6) McKenna, F. E., Nucleonics, 9, 51 (August, 1951). (7) Miller, W. T., and Bigelow, L. A., J. Am. Chem. SOC., 58, 1585 (1936). (8) Schildknecht, C. E., “Vinyl and Related Polymers,” pp. 47583, New York, John Wiley & Sons, 1952. (9) Stein, L., Chemical Engineering Division, Argonne National Laboratory, private communication. RECEIVED for review July 11, 1953. Accepted October 23, 1953.
Determination of Maleic Hydrazide Residues in Plant and Animal Tissue PAUL R . WOOD Naugatuck Chemical, Division of United States Rubber Co., Naugatuck, Conn. 31aleic hydrazide, l,Z-dihydropyridazine-3,6-dione,is a growth regulant or retardant. Because it is useful on certain food crops, it is important to determine the residues in a large number of plant and animal tissues as a prerequisite to registration of the chemical for agricultural use. A method is presented whereby the hydrazide is reduced and hydrolyzed in water, alkali, and zinc, to split off hydrazine, which is then distilled and determined colorimetrically using p dimethylaminobenzaldehyde. Residue determinations of below 1 p.p.m. are possible. The procedure can probably be used without major modifications for other compounds that will form hydrazine under the conditions of this method.
ALEIC hydrazide ( 8 )(1,2-dihydropyridazine-3,6-dione) is a growth regulant or retardant. Because i t is useful on certain food crops, it is important to determine the residues in a large number of plant and animal tissues as a prerequisite to registration of the chemical for agricultural use. Maleic hydrazide(1) probably exists in tautomeric equilibrium. OH I
c1
/-\
HC
’C‘
/-\
HC
NH
S
red (yellow in dilute solution), Solutions of these water-soluble salts obey Beer’s lam and are stable after maximum color is developed in 10 to 15 minutes. The p-dimethylaminobenzalazine formed in alkaline solution gives canary yellox crystals, insoluble in water and slightly soluble in alcohol, melting point 264-6”. I n an acid, HX, isomerization to a p-quinone structure(I1) occurs, giving dark red crystals, melting point 224”; it is a reversible reaction. This method is sensitive to 0 . 1 ~ per ml. Based on this information, absorption and concentration curves n w e made from purified hydrazine monosulfate and p-dimethylaminobenzaldehyde. ( C H , ) , N~H=N-NH-CH=
/I
I
0
OH
I It is stable to both acidic and basic hydrolysis, as evidenced by the fact that heating for several hours a t temperatures up to
200” C. in 18N sulfuric acid or concentrated sodium hydroxide causes no breakdown. Some decomposition does occur in concentrated sodium hydroxide a t higher temperatures. However, after reduction, ring opening by hydrolysis readily occurs, yielding a quantitative amount of hydrazine which can be distilled out under favorable conditions. Many reduction-hydrolysis systems were evaluated, resulting in the present selection of zinc plus alkali in water. Of the possible quantitative methods for determining small amounts of hydrazine, the colorimetric method of Pesez and Petit ( 5 ) was selected because of minimum interference from naturally occurring substances. A recent publication by W a t t and Chrisp ( 7 ) also describes use of this method. According to Pesez and Petit, hydrazine reacts with p-dimethylaminobenzaldehyde to give an azine, the acid salts of which are a n intense
O $ ( C H & X -
I1 REAGENTS
Reagent grade p-dimethylaminobenzaldehyde was further purified by the procedure described by Adams and Coleman ( 1 ) . The purified product was washed free of chloride and dried t o a constant weight in a vacuum desiccator over calcium chloride. If passed through a 60-mesh screen prior to final drying, the resulting product will dissolve more rapidly. The dried compound or dissolved reagent should be stored in the dark. The reagent should be prepared fresh daily by dissolving 0.20 gram in 5 ml. of 2N sulfuric acid. Purified maleic hydrazide available from Naugatuck Chemical, Division of U. S. Rubber Co., Naugatuck, Conn. Hydrazine monosulfate, c.P., freshly recrystallized from water. p-Dimethylaminobenzaldehyde, practical grade, purified according to (1). Sodium hydroxide, analytical reagent grade pellets. Sulfuric acid, analytical reagent grade. Nitrogen, oil pumped. Benzene, analytical reagent grade. Oxygen-free water, freshly boiled distilled water, used while still hot. Zinc, analytical reagent grade, 30-mesh granular.
