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. 4CKNOR LEDGXIENT
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.
LITERATURE CITED
(1) Fieser, L. F., and Fieser, Ll., ”Organic C h e m i s t r y , ” p. 38, Boston, D. C. H e a t h a n d Co., 1944. (2) Ibid., p. 141. (3) Mitchell, J., J r . , and S m i t h , D. M., “ A q u a m e t r y , ” p. 103, Sew Y o r k , Interscience Publishers, 1948. 14) Pepkowita, L. P., a n d J u d d , IT, C., AN.%L. (‘HEM., 22, 1283 11950). (5) Pepkowita, L. P., J u d d , W. C., a n d Downer, R. J . , Ibid., 26, 246 (1964). (6) Williams, D. D., a n d lfiller, R. R., Ibid., 23, 1865 (1951). 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. Added, gram
Ratio of Chloroplatinic Acid to Tetramethylphosphonium Chloride (TMPC)“ TMPC Recovered, gram
Recovered, %
Ratio of H2PtCls to T.MPC
Ratio of P t to TMPC
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.
ANALYTICAL CHEMISTRY
214 Since the mode of evaporation may vary with the operator and
thus affect the actual ratio of alcohol to water in the final solution, samples were run using alcohol solutions of varying strength for diluting and subsequent washing (Table 11). The results indicate that the evaporation must be carried out so that on cooling a solid mass forms. Failure to do this tends to dilute the alcohol, which increases the solubility of the precipitate.
Table 111. Recovery of Tetramethylphosphonium Chloride (TlMPC) Added, gram
TMPC Recovered, gram
0.1289 0.1788 0.1953 0,2055
0.1284 0.1782 0.1942 0.2051
Table 11. Effect of Alcohol Strength on Recovery of Tetramethylphosphonium Chloride (TMPC) Alcohol, % 95 S5 7.i 65
Reagents.
Added, gram 0.4131 0.4131 0.4131 0.4131
TMPC Recovered, gram 0.4131 0.4125 0.4103 0.4058
Table IV.
Recovered, %
Deviation, 5% -0.03
99.61 99.66 99.48 99.81 Av. 99.64
+0.02 -0.16 +O. 17 f O . 10
Analysis of Unknowns
First Analysis, %
Second Analysis, %
Difference, %
Recovered, '%' 100.00 99,85 99.32 98.23
Chloroplatinic acid hexahydrate (HJ'tC'16
6Hz0),
1 0 5 solution.
Rthyl alcohol, c.P., 95%. Nitric acid, c.P., concentrated. Perchloric acid, c.P., 60%. Hydrochloric acid, c.P., concentrated. Procedure. Dissolve the sample (about 0.2 gram of tetranwthyiphosphonium chloride) in 10 ml. of water. If organic matter is present, add 5 ml. of nitric acid and 5 ml. of perchloric acid, ubwrving the usual safety measures for handling perchloric acid ( 2 ) . Evaporate to dryness. Dissolve the perchlorate using a minimum amount of water, and add 0.5 ml. of hydrochloric acid. Add, with stirring, 5 ml. of chloroplatinic acid. Because tetrameth] lphosphonium chloride is very hygroscopic, care should be esercised in weighing. The precipitation should be carried out in a place free from ammonia fumes, for they will a130 be precipitated if present. Evaporate the solution to a sirupy consistency, which upon cooling forms a solid mass. The sample should not be evaporated to complete dryness or at too high a temperature. Cool, add 10 ml. of 95% ethyl alcohol, and break up the residue with a stirring rod. Filter the solution through a tared sintered-glass crucible (medium . Wash the residue free of impurities with 95% e t h y r g % z ! until the filirate comes through clear. Dry at 120' C. for l hour, cool, weigh, and make the following calculations. Tetramethylphosphonium chloride, grams = 0.4289 X weight of precipitate, grams. Tetramethylphosphonium ion, grams = 0.3087 X weight of piecipitate, grams. Phosphorus, grams = 0.1050 X weight of precipitate, grams. Recovery of Platinum (3). RESIDUES.Add the iesidue to about 500 ml. of water. Add a slight excess of formic acid and let stand until the supernatant liquid becomes clear. This usually requires a few days. Filter, and wash with hot water. FILTRATES.Evaporate the ethyl alcohol and then treat as a residue. Preparation of Chloroplatinic Acid. Dissolve the platinum in aqua regia and evaporate to a thick sirup. Evaporate alternately with hydrochloric acid and pyvater three times. To convert any chloroplatinous acid to chloroplatinic acid, saturate the warm solution with chlorine gas until it becomes yellow. Evaporate to a sirup to remove the chlorine and dilute to a 10% solution. Accuracy and Precision. An examination of the results contained in Table I11 indicates that the error of the method is less than 0.5%. The precision of the method may be judged by the agreement between duplicate determinations on unknown samples. Table IV gives some typical results. ION EXCHANGE SEPARATION
Since the tetramethylphosphonium ion is a cation, it can be removed from a solution with cation exchange resina. About 5 nil. of Rohm & Haas cation exchange resin IR 100 H in a 10-ml. buret. using a slow flow rate, proved to be satisfactory for
the separation of approximately 0.2 gram of the ion from a neutral water solution of the chloride. 0
(CH,),PCI
0
It
+ HO-S-R
+
(CH3)aP-0-S-R
0
I1 I1
+ HCI
0
The hydrochloric acid liberated in the reaction was titrated quantitatively in the effluent with 0.1N sodium hydroxide (Table V). When the column is leached with about 50 ml. of 1 to 1 hydrochloric acid, tetramethylphosphonium chloride is found in the eluate and may be determined by the method described.
Table V. Separation of Tetramethylphosphonium Chloride (TMPC)
EL,:
Gram 0.1939 0.1939 0.1939 0.1939
NaOH Titration of Effluent T,MPC, gram TMPC, % ' 0.1927 0.1914 0.1926 0.1926
HIPtCls Precipitate after Leaching TMPC, gram TMPC, 5%
99.38 98.71 99.33 99.33
...
...
0 .'I963
ioi: 1
0.1955
100.8
This technique may be eytended to the estimation of tetramethylphosphonium ion in the absence of other cations. I t would, of course, be necessary to correct for any acidity or basicity initially present in the sample. The use of a cation exchange resin also offers a clean cut method for the gross separation of the ion from anions. ACKNOWLEDGMENT
The authors wish to express their appreciation to C. A. Kamser for his interest and cooperation in this investigation. LITER4TURE CITED
(1) Kosolapoff, G. XI., "Organophosphorus Compounds," Se-iv York, John Wiley & Sons, 1950. (2) Sax, 9. I., "Handbook of Dangerous Materials." p. 296, New York, Reinhold Publishing Corp., 1951. (3) Swiches, M C., and H u m m e , F. F., IND.ENG.CHEM.,ANAL.ED., 11, 162 (1939). RECEIVED for review January 8 . 1953. A c c ~ p t e dOctober 26, 1953.
