The 1 1-chelate absorbs light at 380 mp wavelength while the 1,Zchelate absorbs at 435 mk. This complication could not be resolved by using a different transitional metal ion or a different amine. The molar ratio of cupric ion to carbon disulfide can direct the color reaction to either complex as shown in Figure 4. Because of a high baseline resulting from the large concentration of blue cupric ion. the maximum a t 380 mp is inferior. By reacting cupric acetate with carbon disulfide a t various molar ratios while holding the diethanolamine in large escess, it was found that a molar ratio (copper/carbon disulfide) of 0.5 was optimum, Figure 5. It ran be observed that 8501, of the maximum could still be attained between the molar ratios of 0.3 and 2.5, and 95y0 of the maximurn could be attained between 0.4 and 1.5 molar ratio. When analyzing crops of unknown residue concentration a trial sample must be analyzed to determine the ideal copper concentration in the color reagent. If the analytical result does not fall within the range of the solution used, a n appropriate adjustment of
the copper concentration must be made. RESULTS
There is always a n equilibrium between the 1,l-complex and the 1,2complex, even though the equilibrium may be shifted greatly. Because of this equilibrium, the standard working curve does not pass exactly through the origin. The equilibrium is consistent within the range of moIar ratios specified in the procedure. The summary of typical recovery data in Table I shows that essentially theoretical recoveries of the various dithiocarbamates were obtained throughout this investigation. The molar ratio was held between 0.3 and 2.5 to yield an expected range of recoveries of 85 to 1007,. Zineb has a slightly lower range than other dithiocarbamates because of hydrogen sulfide production. The precision of the method is affected by many variables, the most important of which is sampling techniques. As ran be anticipated, a greater variation in recovery is obtained from crops such as tomatoes and cherries which tend to mix and react with dithiocarbamates.
LITERATURE CITED
(1) Aherstrom,
S.,Act. Chem. Scand. 16,
1200-1211 (1962).
(2) Assoc. Offic. Agr. Chemists, “Official Methods of Analysis,” 9th ed., pp. 80-
81, 1960. (3) Ibzd. p. 310. (4) Clark D. G.,Baum, Harry Stanley, E. L., kester, N. F., ANAL.&HEM. 23, 1842 (1951). ( 5 ) Dickenson, D., Analyst 71,327 (1946). (6) Dunning, C. L., J . Assoc. Oj’ic. A9r Chemists 40, 169 (1957). (7) Goksvr, J., Nature 175, 820 (1955). (8) Goksir, J., Physiol. Plantarium 8, 719 (1955). (9) Hauermann. R. F., J . Assoc Ofic Agr. Chemists 40, 264-73 (1957). (10) Lowen, W. K., AXAL.CHEM.23,1846 (1951). (1:) Nebhia, L., Guerrieri, F., Chemica e andustria Milan 35, 896 (1953). (12) Pease, H. L., J . Assoc. Ofic. Agr. Chemists 40, 1133 (1957). (13) Sijpeste n, K. A., Janssen, hZ. J , van der &ea, G. J. M., Biochem. Riophgs. Acta 23,550 (1957). (14) Stanley, E. L., Baum, Harry, Gove, J. L., ASAL.CHEM.23, 1779 (1951). (15) T’iles, F. J., J . Ind. Hyg.Toxicol. 22, 188-96 (1940). (16) Welcher, F. J., “Organic Analytical Reagents,” Vol. 11, pp. 252-5, Van Nostrsnd, New York, 1947. (17) Woeffel, W. C., Anal. Chem. 20, 722 (1948). RECEIVEDfor review Maroh 19, 1963. Accepted October 4, 1963.
Determination of Solubility of Several Phosphine Oxides in Aqueous Solutions Using CI N e w Spectrophotometric Procedure JEROME W. O’LAUGHLIN, FLOY W. SEALOCK, and CHARLES V. BANKS Institute for Afomic Research and Department of Chemistry, Iowa Stafe University, Ames, Iowa
b The solubilities of bis(di-n-hexylphosphinyl)methane, HDPM; bis(di-nhexylphosphinyl)ethane, HDPE; bis(din-hexylphosphinyl)propane, HDPP; bis(di-n-hexylphosphinyI)butane, HDPB; and tri-n-octylphosphine oxide, TOPO, in water were determined as a function of temperature. The solubility of HDPM in hydrochloric and perchloric acids at 25’ C. was also determined. A new spectrophotometric procedure for the determination of phosphine oxides is based on the extraction of a yellow adduct of the phosphine oxide with titanium(1V) and a thiocyanate salt from an acidic medium into chloroform.
I
with an investigation of various bifunctional phosphine oxides 84 metal extractants (3-6) it became necessary t o find a method for N CONNECTION
224
0
ANALYTICAL CHEMISTRY
the determination of the solubility of these compounds in various aqueous phases. Young and White (7) have described a method for the determination of titanium based on the measurement of the absorbance at 412 mp of the titanium-thiocyanate complex extracted from an acidic, aqueous phase into tri-n-octylphosphine oxide, TOPO, in cyclohexane. It was observed that a similar yellow-colored complex was extracted when bis(di-whexylphosphiny1)methane, HDPM; bis(di-n-hexylphosphinyl)ethane, H D P E ; bis (di-nhexylphosphinyl)propane, H D P P ; or his (di-n- h e x y l p h o s p h i n y 1) b u t a n e, HDPB, was substituted for TOPO in the above procedure and it seemed possible that a modification of this procedure in which the titanium concentration was held constant could be used for the determination of phosphine oxides. This wm found to be the case and a pro-
cedure is given for the determination of these compounds and TOPO. The solubilities of HDPM, HDPE, HDPP, and H D P B in water were determined as a function of temperature. The solubility of TOPO in water was determined at 0’ and 25” C. and the solubility of H D P M in hydrochloric and perchloric acids was determined a t 25” C. EXPERIMENTAL
Rea ents.
The preparation of HDPG h as been described (6). The preparation and properties of HDPE, HDPP, and H D P B will be given in another publieation (3). The TOPO was obtained from the Eastman Kodak Co. and used without further purification. The other chemicals were all reagent grade and not further purified, except for potassium titanyl oxalate which was recrystallized from ethanol. Apparatus. Spectral measurements were made with a Cary 1 4 recording
spectrophotometer. Absorbance measurements for the analytical work were made with a Beckrnan Model DU spectrophotometer. A Burrell wristaction shaker was used for all extractions. A Precision Scientific Co. electronic relay was used to control a constant temperature bath to within A0.l0 c. Standard Spectrophotometric Procedure. For the preparation of a standard curve i t irr convenient to take 2- to 15ml. aliquots of lO-'M solutions of the bifunctional phosphine oxides in chloroform. Add enough chloroform to the sepwatory funnel to bring the total volumi: to 10 to 15 ml. Add 40 ml. of an ,tqueous solution 2M in hydrochloric acid and 2M in magnesium chloride, and then just prior to equilibration add 0.5 gram of potassium titanyl oxalate and 2.0 grams of sodium thiocyanate. Shake this mixture for 3 minutes and transfer the chloroform phase to a 25-ml. volumetric flask. Extract the aqueous phase with two additional 3- to Sml. portions of chloroform and add these chloroform phases to the first portion. Dilute to volume with chloroform and read the absorbance within 30 minutes a t 390 mp in I-cm. cells against a reagent blank prepared in exactly the same manner. In the case of TOPO, use carbon tetrachloride as the solvent and read the absorban:e a t 412 mp.
0.9j
I
I
I
400
450
I
06 07L
00
350
WAVELENGTH, mp
Figure 1. Absorption spectra for HDPM complex with titanium(lV) and thiocyanate Standard procedure:
a , b, and c for 27, 18, and 9 pg. of HDPM per mi. of tlnal soiution
spectrum of the complex changed with time. The shoulder on the ultraviolet side grew and after 24 hours the valley around 360 mp had disappeared. The increase in absorbance was assumed to be due to an increasing contribution from decomposition products of the thiocyanate. A 30-minute period after extraction and before reading the samples was arbitrarily chosen. Solubility of Phosphine Oxides. An excess of the organophosphorus compound was equilibrated with water by stirring a t least 15 hours with the container immersed in a constant temperature bath controlled to within *O.Io C. An exception to this was made in the 0" C. case where an ice bath was used to control the temperature during a 4-hour equilibration period. With longer equilibration times a t 0' C. the aqueous phase became cloudy and phase separation was very difficult. Aliquots of the equilibrated aqueous phase were taken and the amount of phosphine oxide was determined using the spectrophotometric procedure. The solubility of these compounds is an inverse function of the temperature and it was necessary to cool the pipet to the temperature of the solution being pipetted to prevent loss of the organophosphorus compound on the walls of the pipet. In the spectrophotometric procedure given for the preparation of the standard curve, the phosphine oxide was initially in the organic phase. If equilibrium is established between the aqueous and organic phases, it should make no difference whether the phosphine oxide was initially in the aqueous or organic phase. Therefore, the necessary reagents n-ere added directly to the aliquot
EFFECTOF SoLmwr. Cyclohexane, between the limits of 2 to 5M did not the solvent used by Young and White, change the absorbance of the complex so and carbon tetrachllride were unlong as the total concentration of suitable for use with the bifunctional chloride remained a t 6M. The absorpphosphine oxides because a third phase tion increased somewhat when the formed which adhered to the funnel chloride concentration was increased. walls. Chloroform and 1,2-dichloroEFFECTOF TIME. The absorbance for benzene were satisfactory. The former B 10-ml. aliquot of a lO-4M HDPM mas used because it gave slightly solution using the standard procedure superior phase separations, although the was 0.545 after 30 minutes, 0.600 after molar absorptivity of the complex is 1 hour, and 0.750 after 24 hours. The lower in chloroform than in I,!& dichlorobenzene. EFFECTOF TITANIUM CONCENTRATION. The absorbance given by a 10-ml. aliquot of the lO-4iM HDPM Table 1. Recovery of HDPM and TOPO Using Standard Procedure solution using the standard procedure changed only slightly ES the amount of HDPM, p g . / d . TOPO, ug./ml. titanium added (as p3tassium titanyl Cslcd. Found Diff. Calcd. Found Diff. oxalate) was varied from 0.2 to 2.0 27 2i. 06 -0.3 +O. 06 23 22.6 grams. The 0.5-grain amount was t0.51 26.31 -0.69 15 15.51 chosen arbitrarily. 27.91 +o. 91 15 +o. 8'2 15.82 EFFECT OF THIOCYANATE CON28, OS +1.08 15 $0.82 15.82 CENTRATION. The amount of thio28.93 +1.93 -0.49 7.7 7.21 28.02 -0.27 +1.02 4.6 4.33 cyanate added was varied from 0.5 to 26.70 -0.30 4.0 grams and the atlsorbance (for a 29.50 +2.50 10-ml. aliquot of the 10-4M HDPiM 1s 16.58 -1.42 solution using the standard procedure) 17.26 -0.74 increased steadily from 0.415 to 0.650. 17.93 -0.Oi The presence of a large absorption band 16.75 -1.25 in the ultraviolet region due to the thio17,49 -0.51 16.98 -1.02 cyanate made an increasing contribu15.47 + O . 47 tion to the absorbance :it 390 mp as the 18.41 +0.41 thiocyanate concentnition was in18.41 +0.41 creased. Consequently the %gram 9 8.96 -0.04 amount of thiocyanate was arbitrarily 9.47 +0.47 chosen. 8.63 -0.37 EFFECTOF ACID CONCENTRATION. 8.56 -0.44 The amount of hydrogen ion present VOL. 34, NO. 1, JANUARY 1964
225
taken for analysis, so that the resulting solution had the same composition as the aqueous phase in the standard procedure and the titanium(1V)-thiocyanatephosphine oxide complex was extracted into chloroform. The aliquot and the reagents were placed directly in the separatory funnel since the complex is water insoluble and might have been lost in any transfer prior to extraction. Several standards, which bracketed the concentration of the sample, were run aiong with each sample in the solubility studies. The concentration of the sample was calculated based on the absorptivity of these standards.
J 1
RESULTS A N D DISCUSSION
Spectrophotometric Procedure. The absorption spectra for the complex formed with H D P M using the standard procedure are given in Figure 1. The absorption maximum a t 390 mp was found to follow Beer's law a t least up to 27 pg. of HDPM per ml. in the final solution. The molar absorptivity, based on the concentration of HDPM, was found to be 13,300 liters per molecm. with a relative standard deviation of 4.7y0 for the 21 determinations of HDPM given in Table I. The recovery of HDPM or TOPO shown in Table I mas calculated using the molar absorptivities for HDPM or TOPO obtained from averaging all the results. The molar absorptivity of TOPO was 14,200, with an average relative standard deviation of 4.94%. In the case of TOPO carbon tetrachloride was used as the solvent but otherwise the same procedure was used. Cyclohexane also appeared to be suitable as a solvent for TOPO. Young and \Yhite (7) reported a molar absorptivity of 41,000 liters per molecm. for the titanium-thiocyanate-TOP0 complex based on the titanium concentration. This suggests, as might be expected, that the combining ratio of TOPO or HDP,M to titanium in the complex is greater than 1. A combining ratio of TOPO to titanium of 3 would give a value of 42,000 liters per molecm. for the molar absorptivity of the complex formed in the presence of excess titanium. This similarity to the value given by Young and White, plus the fact that the spectrum of the complex formed using excess titanium is identical to that published by these authors, suggests that only one species with a c o m b i n g ratio of 3 is formed. The molar absorptivity of the HDPM corn-
226
ANALYTICAL CHEMISTRY
TEMPERATURE. ' C
Figure 2. Solubility of HDPM, HDPE, HDPP, and HDPB in wafer as a function
of temperature
plex suggests a similar combining ratio but the change in solvent makes this less certain. The spectra of the complexes for HDPE, HDPP, and HDPB were very similar to that of HDPM with the maximum absorbance at 390 niM, Tri-n-butyl phosphate, TBP, failed t o extract the titanium-thiocyanate complex (at least there was no color development). The effect of other organic substances on the color reaction was not investigated, but it is known the color reaction is not unique. A very sensitive reagent for the detection on paper of a large number of organophosphorus compounds can be prepared by adding 0.5 gram of potassium titanyl oxalate, 5.0 grams of potassium thiocyanate, and 5.0 ml. of concentrated hydrochloric acid to 100 ml. of water. Following their separation using paper chromatography, a large number of organic phosphates, phosphonates, phosphinates, phosphine oxides, and acidic organophosphorus compounds showed up as bright yellow- to orange-colored zones after spraying with the above reagent (5). Not all of these compounds could be determined by the proposed procedure or would necessarily interfere, however; TBP, for example, gave a bright yellow color reaction on paper but did not show any color reaction when substituted for HDPhI in the proposed procedure. Solubility Studies. The solubilities of H D P M , H D P E , H D P P , and
H D P B in water as a function of temperature are shown in Figure 2. The solubility of TOPO was 1.5 mg. per liter a t 25' C. and 2.8 mg. per liter a t 0' C. The solubility of H D P M a t 25' C. in 1M hydrochloric acid was found to be 26.5 mg. per liter but rose to 64.1 mg. per liter for 6M hydrochloric acid. The bis(dialky1phosphiny1)alkanes formed viscous acid adducts when equilibrated with aqueous perchloric acid and very little of t,he organophosphorus compound was found in the aqueous phase (
