wantitative Determination of Phosphonium Salts and SIR: Recently a wide variety of substituted phosphonium salts and weakly basic phosphoranes have been prepared in this laboratory. During the course of this work it became necessary to develop a rapid, simple method for the quantitative determination of these substances. Titration of the phospholanes in acetic acid with perchloric acid was found to be an eminently satisfactory technique for this determination. This technique may not be satisfactory for all phosphoranes, but suitable modifications as described by Fritz and Hammond (I) can be made to extend the range of applicability. Similarly, phosphonium salts can be analyzed by the addition of excess mercuric acetate to the acetic acid solution, I.
fable
followed by titration of the liberated acetate ion with perchloric acid. These techniques have been used in the past for the determination of ammonium salts and weakly basic amines. They are described in considerable detail by Fritz and Hammond (1). The results of a number of these determinations can be found in Table I. The deviation of the found value from the theory value for the last compound in Table I is due to a small amount of impurity in this sample. Other methods of analysis also indicated that this sample was impure. Phosphonium Salt Determination. An accurately weighed sample of the phosphonium salt, ca. 0.15 meq., is
Theoretical and Experimental Values for Equivalent Weights of Phosphonium Salts and PhosDhoranes
Compound CHr
Equivalent Weight Theory Found
+ I
(CSH,) sP-CHCOaC2HJBr-
+ (CSHJBP-CHZ-
COrG(CHa)a Cl-
+
(CeHa)aP-CHzCHzCQzH C1443
+ (C~HS)SP-CH~CSHS 389 c1K&"%fUF-&Or--C> + Br -
Compound
482 413
Equivalent Weight Theory Found 371
372
445
388
An attempted titration of triphenglphosphine led to an indistinct end point significantly before the equivalence point. It has recently been shown that triarylphosphines can be titrated with perchloric acid in nitromethane (9). Triphenylphosphine oxide could not be titrated with perchloric acid in acetic acid using crystal violet as the indicator. Phosphorane Determination. The method described above was used, except that mercuric acetate was not added. ACKNOWLEDGMENT
Appreciation is expressed by S.T.R. to the Colgate Palmolive Co. for a research fellowship. The authors thank L. C. Smith and J. Vi11 for several of the compounds used in this study.
(l).Frits, J. S., Hammond, G. S. "Quan-
titative Organic Analysis,'J bhap. 3, Wiiey, New Uork, 1967. (2) Henderson, W. A., Streuli, C. A., Buckler, S. A., Abstract?, 137th Meeting, ACS, Cleveland, Ohio, April 1960, p. 47-0.
410,407 0
(CC~H&=J'CH-&CHa
+
401
dissolved in ca. 15 ml. of glacial acetic acid. Mercuric acetate (0.10 gram) is added, followed by 3 drops of a 1% solution of crystal violet in glacial acetic acid. The solution is then titrated to the green end point with a standard solution of 0.02N perchloric acid in glacial acetic acid. The perchloric acid was standardized against potassium acid phthalate. A blank determination was always carried out and this value was subtracted from the volume of standard acid used.
LITERATURE CITED
486,479
0
(CeHs)Q-CBzCHr CHzOHBr-
hosphoranes
318
STEPHEN T. Ross DONALD B. DENNEY
314
School of Chemistry Rutpers, The State Universitv NemBrunswick, PI'. J.
406
-
;fied
CoSo rimet ric
SIR: The dithizone colorimetric method of Friedeberg [ANAL. CEIEM. 27, 305 (1955)l hae been modified and simplified for the determination of microgram amounts of mercury. Friedeberg's method, designed for copper-containing samples, involves a preliminary extraction of mercury dithizonate into carbon tetrachloride from an (ethylenedinitri1o)tetraacetate (EDTA) medium. The mercury and small amounb of extracted copper are then stripped with two portions of 6N hydrochloric acid. The combined acid strips, after neutralization with am0
ANALYTICAL CHEMISTRY
etermination of M monia and further addition of EDTA, are again extracted with dithizone. Though apparently simple, this method involves, because of the relative densities of carbon tetrachloride and the aqueous phases, numerous transfers requiring a t least three separatory funnels. Also, it is not applicable to samples containing high concentrations of cations reactive to EDTA which reduce the effective concentration of EDTA for masking copper. I n the proposed method, mercury dithizonate is extracted into xylene from a duo EDTA-citric acid masking
~
~
~
u
medium buffered with chloroacetate. After stripping with hydrochloric acid, neutralization with ammonia, and addition of EDTA, mercury dithizonate is then extracted into carbon tetrachloride for subsequent color measurement. This modified procedure has been successfully used for determining trace concentrations (as low as 5 X 10-6M) of mercury in dissolved MTR-type, aluminum-uranium fuel elements. In addition to aluminum and uranium, such samples contain the impurities found in 2s or 61s aluminum metal from which the fuel is fabricated.
~
