210
ANALYTICAL CHEMISTRY
was prepared with the maximum amount of water (consistent with the previously discussed criteria) and the aqueous sample was introduced in a minimum volume. With the silicic acid employed, 15 to 30 mg. of organic acids can be separated very effectively on a 10-mm. diameter column containing 4 grams of silicic acid. Emergence of the acids (as in Figure 2 ) is reproducible to a single tube if care is employed in adhering to standard operating conditions. The recovery from the column of added known acids is 90 to 100%. Advantages of Introducing Sample in Water Phase. The new technique for the introduction of samples in the water phase constitutes a simplification of the generally used methods. It eliminates the tedious and often nonquantitative transfer of the eample from the aqueous to the nonaqueous phase (b). As the sample is introduced in the water phase, acidification of the sodium salts directly on the column becomes possible, and the loss of volatile acids is decreased appreciably. The method permits the eeparation of compounds, such as glyoxylic acid which tend to form hydrates and are not readily extractable by organic solvents. Direct addition of the sample to the column in the aqueous phase should be useful in the routine and exploratory separation of organic acids from such aqueous biological materials as fermentation media, vegetable and fruit juices, plant saps, and deproteinized extracts from animal tissues. This chromatographic technique has been used for the separation of organic
acids, but it may be applied generally to water-soluble organic and inorganic compounds. The new procedure gives a t least as good separation and recovery of organic acids as is obtained when the acids are introduced in an organic solvent. Dehydration of the column, which is often troublesome with samples added in an organic solvent, is eliminated in this method. The only apparent disadvantage in the use of the method described is that skill must be developed in the addition of the samples. Advantages of Introducing Sample on a Paper Disk. Introduction of the sodium salts of organic acids on paper disks followed by acidification has essentially the same advantages as those cited for the introduction of sodium salts in the aqueous phase. Free organic acids introduced as solids in paper diskR are separated better than when they are introduced in the aqueous or organic phase. Compounds soluble only in a large amount of organic solvent can be concentrated in a paper disk, and this decrease in sample volume improves their separation. LITERATURE CITED (1) Bulen, W.
.4.,Varncr, J. E., and Burrell, R. C., Ax.4~.CHEJI.,24,
187 (1952). ( 2 ) Isherwood F. A , Biochem. J . (London),40,688 (1946). R E C E I V E June D 22, 1953. Accepted October 19, 1953. Published with t h e approval of t h e Director of the Wisconsin Agricultural Experiment Station. Supported in part b y the Research Committee of the Graduate School from funds supplied b y the Wisconsin Alumni Research Foundation.
Determination of Oxygen in Sodium 1. C. WHITE, W. 1. ROSS, and ROBERT ROWAN, J R . ~ Analytical Chemistry Division, O a k Ridge National Laboratory, O a k Ridge, Tenn.
.4 method for the determination of sodium monoxide in sodium depends upon the reaction between sodium and excess n-butyl bromide (I-bromobutane) in hexane solution. Sodium monoxide does not react with the reagent and can be determined, after the addition of water, by titration. Both oxygen and other impurities can be determined on the same sample, and the method requires only the simplest equipment and is easily adaptable to the analysis of large numbers of samples. The standard deviation is 0.003 to 0.005%. The method has been applied to sodium that has been sampled in glass and in metallic containers. It is believed that the method will be applicable in the range 0 to 0.02%, if large samples are used.
T
HE oxygen content of sodium is of interest because of the
extreme reactivity of sodium monoxide a t elevated temperatures. The oxide reacts with all the common metals (including the platinum group metals), graphite, and ceramic materials, and because of this extreme reactivity, other impurities besides oxygen are often determined in sodium. Ideally, determinations of both oxygen and impurities should be made on the same sample, thus providing a sounder interpretation of data as well as economy of sample. This investigation was undertaken for the s p e cific purpose of determining oxygen and other impurities on the sample of sodium. A method which has been previously developed for this determination is that of Pepkowitz and Judd (4). Essentially, this method depends upon the extraction of sodium with mercury in an inert atmosphere and the separation of the residual sodium monoxide, which is insoluble in mercury. With this method, however, it is not practicable to determine oxygen and impurities on the same sample. A modification of the Pepkowitz and Judd method has been reported by Williams and Miller (6). A new method has been developed which is based upon the fact t h a t n-butyl bromide (1-bromobutane) reacts with sodium to 1
Present address, Standard Oil Development Co., Linden, N. J.
form the neutral salt, sodium bromide, but does not react with sodium monoxide. Following this reaction, dissolution of the residue in water yields titratable sodium hydroxide (from the monoxide) in a solution of sodium bromide. The development of this method has, accordingly, entailed a study of the reaction of n-butyl bromide with sodium and with sodium monoxide. REACTION OF n-BUTYL BROMIDE WITH SODIUM
In the Wurtz synthesis of hydrocarbons ( I ) , an excess of sodium is present. A series of tests was conducted to determine whether the reaction proceeds to completion when an excess of the alkyl halide is present. Small amounts of sodium were added to large excesses of propyl, butyl, and amyl chlorides, bromides, and iodides (chloro-, bromo- and iodo-propanes, butanes, and pentanes). 2Na RX +R S a SaX (1) R X -+ S a S R-R RNa (2) In all cases sodium was converted to the halide with explosive violence. The rate of reaction varied little with the halide used. Diluents in the form of hydrocarbons, which are inert to sodium, were added to the halides in order to decrease the reaction rate. Hydrocarbons with boiling points higher than that of
+ +
+ +
211
V O L U M E 2 6 , NO. 1, J A N U A R Y 1 9 5 4 the halide had little effect, even in a solution of 90% hydrocarbon b y volume. Hydrocarbons with boiling points lower than that of the halide reduced the reaction rate to controllable limits. T h e role of the hydrocarbon in the reduction of the reaction rate is evidently t h a t of a heat transfer agent. Dissipation of heat must be rapid enough to prevent the halide from reaching such a temperature that an explosive reaction with sodium occurs. I n this regard, n-hexane, boiling point 67" to 71" C., proved particularly effective. Of the various halides cited, n-butyl bromide, boiling point 101.6" C., was most satisfactory. h solution of 40 to GO volume yon-butyl bromide in hexane reacts suitably ~ i t 0.1 h to 20 grams of sodium. I T hen the bromide concentration is increased to 80 volume %, the hexane is volatilized during the reaction, \T hich then becomes uncontrollable. Concentrations much lon er than 20 volume yo react too slo~vly. r\ five- to sevenfold ewess is optimum for less than 5 grams of sodium. For larger samples a threefold excess is recommended. I n general, when the quantity of bromide is appreciably less than optimum, the time for complete reaction is of the order of 10 to 15 hours. Greater cv,cesses offer little advantage. RE4CTION OF n-BUTYL BROWIDE WITH SODIUllI MONOXIDE
Literature sources yield little information on the reaction of n-butyl bromide n ith sodium monoxide, but it was postulated t h a t the folloiring reactions n ere poqsible:
-
+ +
+
NaLO C4H9Br-+ C4HYOSa S a B r C 4 H 9 0 S a C4HQBr C4H90C4H9 NaBr
+
(3) (4)
Equation 4 represents the Williamson synthesis of ethers ( 2 ) . I n the proposed method, following the reaction of sodium with the halide, the residue of sodium bromide and other products is dissolved in water, and from the alkali formed the monoxide content is calculated. The formation of any organic compound which yields an equivalent amount of hydroxide upon hydrolyqis will not affect the results.
+ +
-
S a 2 0 H20 2NaOH C 4 H 9 0 S a H 2 0 -.c SaOH CaH9OH C4H90C4HQ H 2 0 no reaction
+
+
(5) (6) (7)
I\'o oxygen is lost in Equation 6, since i t can be recovered by hydrolysis and an alkalimetric titration. A loss of oxygen would occur, however, if dibutyl ether, vhich is not hydrolyzed by water, were formed. To determine the extent of ether formation 10 to 50 mg. of sodium monoxide \vas placed in a solution of 50% n-butyl bromide in hexane and allowed to stand for various periods of time at 60" to 65" C. The conditions of the test were selected to approximate those undri Ahich the reaction with sodium is conducted. The residual sodiuin monoxide, which was visibly unchanged even after 72 hours' contact, was filtered and dissolved in water, and the sodium hydroxide formed was titrated. The results of these tests are shonn in Table I. The precision n as not so high as might be desired becaube of the difficulties encountered in the handling of sodium monoxide. The monoxide wm weighed hy diffeience and kept over phosphoius pelitoxide The reagent when received was 97.5% sodium nionoxide and 2.5% sodiuniperoxide. To eliminate the effect of possible changes in the oxide upon standin.;, total basicity deterniinations were carried out simultaneously M ith the butyl bromide tests. The results indicated no formation of dibutyl ether after 36 hours. In only isolated cases was the quantity of base found less than that which was added. I n all tests Mhen the contact time exceeded 24 hours, the base found n-as less than that added, although the losses ere slight and can hardly be considered sipnificant under the conditions of the tests. No dibutyl ether could be detected in the filtrate. The poMible loss of basicity in the filtrate was checked by titrating the hydrolyzed filtrate. In no case was any basicity
Table I. Recovery of Sodium Monoxide after Contact with n-Butyl Bromide Contact Time, Hours 2
Sodium Monoxide, M g . Added Found'
Recovery,
14.0 17.0
Difference (E A) 0.8 -0.5
48.9
20.9 25.0
20.7 25.9 49.0
-0.2 0.9 0.1
99 103 100
24
19.6 52.6
19.8 52.2
0.2 -0.4
99 99
36
22.2 21.5 27.2
22.0 21.3 26.5
-0.2 -0.2 -0.7
99 99 97
72
20.7 34.0 27.1 13.3
20.3 33.4 26.5 11.4
-0.4 -0.6 -0.7
98 98
-1.9
86
16
(A)
(B)
13.2 17.5
-
%
106 97
98
found, even for the trials of 72 hours' contact. I t seems evident that no soluble alcoholate is formed under these conditions. It may be concluded from these tests that sodium monoxide and 50% n-butyl bromide in hexane do not react over a period of a t least 24 hours. PROCEDURE
Purification of Reagents. n-Butyl bromide is purified by washing the commercial grade material with concentrated sulfuric acid until the acid layer v-as clear to remove unsaturated compounds. The residual sulfuric acid in the reagent is neutralized with sodium bicarbonate, and the reagent is subjected to a preliminary drying n ith calcium chloride. It is then distilled and stored in a dark bottle in an argon atmosphere in contact with activated alumina. n-Butyl bromide treated in this manner remained sufficiently dry and free of oxygen for use in the determination for several weeks. Hexane is treated by drying over sodium ribbons, distilling from this medium, and storing in a dark bottle over sodium. I n order to prevent possible oxygen contamination, an atmosphere of oxygen-free argon should be maintained in the hexane container. Some lots of hexane were observed to discolor the sodium upon long standing. Hexane which had been washed with sulfuric acid could be stored for several weeks without evidence of change. The quantity of water in the purified and dried reagents was less than 2 p.p.m. as determined by the Karl Fischer ( 3 )method. Samples Sealed in Glass. A sealed sample normally containing 1 to 2 grams of sodium, is placed in a 4 X 20 em. tube, with a reinforced bottom, containing 100 ml. of a solution of 50 volume yo n-butyl bromide in n-hexane. If the sample size is 15 to 20 grams, the reagent volume and tube size should be increased accordingly. The glass tube is crushed by means of a heavy glass rod (10-mm. diameter), flattened a t one end. As the reaction proceeds, the glam rod is used to continually expose fresh sodium to the reagent. The tube is placed in a sand bath, which is maintained a t GO" to 70" C., to complete the reaction which re uires 1 to 2 hours. Care should be taken to prevent excessive bo?ling of the solution which volatilizes hexane from solution. The reaction of 2 grams of sodium will generate enough heat to obviate long periods of external heating. The reaction may be allowed to stand overnight without adverse effects if an inert-gas blanket is maintained over the tubes. The residue is cooled and powdered to ensure the complete reaction of small particles of sodium, and 100 to 200 ml. of water free of carbon dioxide is added to dissolve the residue and t o form a two-phase system: the aqueous phase, which is a solution of sodium bromide and sodium hydroxide, and the organic phase, which consists of excess reagent and the newly formed octane. The phases are separated in a separatory funnel and the water phase is titrated to pH 7 with 0,OOLV nitric acid using a glass electrode, which responds in solutions of high sodium ion concentration. This volume of titrant is used to calculate the oxygen content. hcid, meq. X 0.008 = oxygen, grams The neutralized solution is diluted to 500 ml., and a 25-ml. aliquot is titrated with 0.5N silver nitrate using eosin as the indicator. The sample weight of sodium is calculated as follows: Silver nitrate, meq. X 0.023 = sodium, grams
ANALYTICAL CHEMISTRY
212 Table 11. Oxygen Content of Double-Distilled Sodium Group
-4 B
Oxygen
Sodium. Grams 2 103 2 212
Mg. 1 12 1 15
0 053 0 052
1.362 1.340 0 946 0 323 0 895
0.344 0 420 0 166 0 327 0 188
0.025 0 031 0 018 0 02.5 0 021
%
Added
0 224 0 101 0 110 0 218 0 145 a
Upper bulb 0 022
0 020
Difference (A B) 0 002
9
0 024 0 023
0 023 0 025
0 001 -0 002
3
0 0 0 0 0 0
0 0 0
0 026 0 02.5 0 027 0 030 0 027 0 029 0 029 0 031 0 033 0 030 0 030 0 032 0 031 0 029 0 030 0 036 0 034 0 034 0 038 0 043 0 039 0 039 0 052 0 054 0 064
- 0 002 0 002 -0 002 - 0 006 0 001 0 000
2.5 26 27
024 027 025 024 028 029 029 027 026 030 030 029 030 032 035 032 034 035 035 038 047 051 053 05,5 052
28
0.063 0.052
0 057 0.061 0.052
Sample 1
1 5 6
Standard deriation = 0.004
Table 111.
Table IV. Duplicate Determinations of Oxygen in Sodium Oxmen, 70
Recovery of Known .4mounts of Oxygen in SodiuniQ Oxygen, % Total (blank Blank b added) 0 054 0 278 0 I55 0 054 0 164 0 054 0 272 0 054 0 054 0 199
+
Found 0 0 0 0 0
Difference 285 +O 007 158 +o 003 161 -0 003 282 +o 010 210 + o 011 Average 0 007
Oxygen added as sodium peroxide.
b .&yerage of three determinations.
This weight is high by the amount of sodium in the sodium hydroxide formed. Hoxever, as this error is insignificant, it may be disregarded in practically all cases. KO holdup of sodium in the organic phase was noted. The remainder of the aqueous solution and the organic layer are available for the determination of metallic impurities. Samples Sealed in Metal Containers. Metallic containers of sodium are treated by melting the contents in n-nonane or 2,2,5-trimethylheptane. These liquids do not react with sodium or sodium monoxide, and have boiling points higher than the melting point of sodium and densities lower than that of sodium. The sample is opened under mineral oil and transferred to the reaction tube containing 50 to 75 ml. of nonane. The tube is heated slightly above 100 C. while covered with dry argon and the sodium melted from the tube. n-Konane must be removed before the halide solution is added. This is accomplished by successive dilution with hexane and withdrawal of the mixture. The remainder of the procedure is as described previously. RESULTS
The range of oxygen concentration extended from 0.001 to 0.1%. I n an attempt to obtain sodium with an oxygen content in the lower part of this range, the metal was double-distilled under high vacuum. Published results for oxygen in sodium prepared in this manner vary somewhat, the general average being about 0.02%. The results of determinations of these samplei: are given in Table 11. Standard samples containing larger amounts of oxygen were prepared by adding known quantities of high purity sodium peroxide to sodium at 300” to 400” C. to form sodium monoxide quantitatively. S a 2 0 a 2Na = 2Kaz0 (8)
+
This reaction proceeds with considerable violence if the teniperature is increased rapidly; however, with the use of a sand bath for heating and a high ratio of sodium to sodium peroxide (approximately 100 to 1) a smooth reaction occurred. Mineral oil, previously conditioned by heating under argon to 400” C. in contact with sodium, was used as inert medium for the reaction. Typical results are shown in Table 111. further evaluation of the method has been made on the basis of the result8 of 31 duplicate determinations, the results of lvhich are shown in Table IV. These samples were contained in two-bulb glass sample tubes which were filled by drawing molten sodium into the tubes. The desigqations “upper” and “lower” refer to the position of the bulbs during filling; the sodium entered the tube, passed through the lower bulb and on into the upper bulb. The two bulbs were then separated to provide duplicate samples.
7 8 9 10
11 12 13 14 15 16 17 18 19 20 21 22 23 24
(4
0
0 0
0
0
0
0 0 0 0 0 0 0 0
0 0
0.059
Lower bulb
(B)
Algebraic sum Average difference Xumber of cases in which -4 > B = 13 S u m b e r of cases in which A < B = 13 Standard deviation. Calculated from arerage range -0.0030 Calculated from sum of variance -0 0034
-
0 000
-0 004 -0 007 0 000 0 000 -0 003 -0 001 0 003 0 005 -0 004 0 000 0 001 -0 003 -0 005 0 008 0.011 0.001 0.001 -0.012
0.006 -0.009 0.007 -0.012 0,003
DISCUSSION
The oxygen values are all higher than usually found for carefully distilled and handled sodium. The samples were possibly contaminated by sodium hydroxide and sodium carbonate. .4s neither of these reacts with n-butyl bromide. they would be included in the titration step as 0x1 gen. The recovery of oxygen added as sodiuni peroxide provides a check on the method a t higher concentrations of oxygen. In general, such high values mould rarely be encountered in high grade sodium. The average difference of 0007% is eatisfactory under such conditions. .k comparison of the results obtained on identical samples by the Pepkowitz and Judd method shoirs an average difference of O.OOS%, and in only a few cases a difference greater than 0.01%. I n general, there is no indication that on? method tends to vield higher or lower results than the other. The standard deviation for the results of duplicate determinations listed in Table IV is 0.0034%. The precision in this case was better than for any of the other iesults reported. The probable elplanation is that the precision of the method is actually as good as is indicated and that the poorer precision observed for the other tests is a result of sample heterogenity. However, the duplicate determinations listed in Table IV were made at the same time, side by side; such it procedure often effects an improvement, which is artually fictitious, in the apparent precision of a method. I t is evident from the data in Table IV that there was no consistent tendency toward segregation; both upper and lower sample bulbs contained, on the aversge, the same quantity of oxide. The standard deviation of the present method is in the range 0.003 to 0,005’% which compares favorably with that for the Pepkowitz and Judd method. Modifications in the amalgamation procedure by Pepkowitz, Judd, and Downer ( 5 ) have led to increased precision of the order of 0.0016%. The present method is satisfactory for samples of sodium containing more than 0.02% oxygen. Becauw of the lack of sam-
213
V O L U M E 2 6 , NO. 1, J A N U A R Y 1 9 5 4 ples of suitably low oxygen content, the method has not been sufficiently investigated with respect to lower ranges of oxygen concentration. Samples as large as 20 grams have been handled by this method, indicating the wide range of sample size which can be tolerated. Such large-sized samples are not practical for routine analytical use because of the volume of reagents required and excessive reaction time.
LITERATURE CITED
(1) Fieser, L. F., and Fieser, Ll., ”Organic Chemistry,” p. 38, Boston, D. C. Heath and Co., 1944. (2) Ibid., p. 141. (3) Mitchell, J., Jr., and Smith, D. M., “Aquametry,” p. 103, Sew
4 C K N O R LEDGXIENT
York, Interscience Publishers, 1948. 14) Pepkowita, L. P., and Judd, IT, C., AN.%L. (‘HEM., 22, 1283 11950). (5) Pepkowita, L. P., Judd, W. C., and Downer, R. J., Ibid., 26, 246 (1964). (6) Williams, D. D., and lfiller, R. R., Ibid., 23, 1865 (1951).
The authors acknowledge the contributions of H . H. Willard, C. D. Susano, and L. J. Brady, who made helpful suggestions during the course of this investigation.
Received for review May 11, 1953. Accepted October 13, 1953. Work carried out under Contract S o . W-7405-eng-26 a t Oak Ridge h-ational Laboratory, operated by Carbide and Carbon Chemical Co., a division of Union Carbide and Carbon Corp., for the Atomic Energy Commission.
Bravimetric Determination of Tetramethylphosphonium Ion Use of Chloroplatinic Acid as Precipitant C. J. ANDERSON and R. A. KEELER Vitro Corp. o f America, West Orange,
N. J.
.4 need arose for the determination of the tetramethylphosphonium ion. As the ion behaved like the potassium ion, this resulted in the development of a method of analysis based on the formation of an insoluble chloroplatinate which can be weighed. When pure materials are used, the method has an accuracy of better than 99.5% and a precision of 2 parts per thousand. An ionexchange method has been developed for the separation of tetramethylphosphonium ion from anions using Rohm 8: Haas IR 100 H cation exchange resin.
I
N RECENT years the chemistry of organic phosphorus com-
pounds has become a field of numerous investigations and research. Of particular importance has been the interest in organic onium salts because of the possible application of their biocidal and surface active properties. Kosolapoff ( 1 ) has compiled most of the literature available on this subject. -4 search of this and the literature in general yielded no specific method for the analysis of such compounds and in particular tetramethylphosphonium ion (TMP). Because of this, a procedure for its analysis was devised. The tetramethylphosphonium ion has four phosphorus-tocarbon links which account for its unusual stability. Investigations have shown that it is resistant to oxidation. When its chloride salt (TMPC) was evaporated with a mixture of nitric and perchloric acids to dense white fumes, the resulting solution yielded none of the usual reactions of the orthophosphate ion. Additional experiments showed that the tetramethylphosphonium ion remained unaltered and intact after treatment with nitric and perchloric acids. Phosphine may be distilled from alkaline solutions of phosphonium (PHa+) salts; however, all attempts to distill trimethylphosphine from an alkaline solution of tetramethylphosphonium ion failed. A resemblance between the tetramethylphosphonium ion and both the potassium and the ammonium ions was observed. Many of the reagents (chloroplatinic acid, perchloric acid, 2,2‘,4,4‘,6,6 ‘-hexanitrodiphenylamine, picric acid, and silicotungstic acid) which precipitate potassium and ammonium ions also precipitate tetramethylphosphonium ion. Because chloroplatinic acid is a common laboratory chemical and is available in a pure state, it was tried first as a quantitative precipitating agent. CHLOROPLATINATE METHOD
The procedure described has been used successfully in this laboratory for the det,ermination of the tetramethylphosphonium
ion for over a year. This method is based on the insolubility of tetramethylphosphonium chloroplatinate, [(CH&P)]ZP~CII), in ethyl alcohol. The sample in the chloride form, free from other substances, is treated with an excess of chloroplatinic acid and evaporated to a small volume. (CHz),PCI
+ H2PtCI6
-t
[(CHi)rP]&Cls
+ 2HC1
The residue is extracted with ethyl alcohol, filtered, and weighed after washing and drying. Ammonium, potassium, rubidium, and cesium ions all form ethyl alcohol-insoluble chloroplatinates, thereby contaminating the precipitate. Moderate amounts of calcium, strontium, and magnesium chlorides can be tolerated. Because of the cost of the chloroplatinic acid a series of experiments was carried out to determine the optimum ratio of reagent to the chloride salt necessary for quantitative precipitation (Table I). It was found that 0.32 gram of chloroplatinic acid is the minimum quantity of reagent required for a quantitative recovery of 0.2 gram of tetramethylphosphonium chloride. This represents a ratio of 1.6 to 1. The procedure prescribes a 2 to 1 ratio which permits slightly larger samples.
Table I.
Ratio of Chloroplatinic Acid to Tetramethylphosphonium Chloride (TMPC)“
TMPC Added, Recovered, Recovered, Ratio of H2PtCls Ratio of P t gram gram % t o T.MPC to T M P C 0.38 0.79 0.1940 0,1008 51.96 0.56 0.1940 0.1486 1.18 76.60 0.75 1.58 0.1940 0.1939 99,g.j 0.94 0.1944 1.97 0.1940 100.21 1.12 0.1940 0.1939 99 95 2.36 1.31 2.75 0.1940 0.1936 09,79 a 5-ml. aliquot of standard solution of tetramethylphosphonium chloride used in each case.
