V O L U M E 28, NO. 11, NOVEMBER 1 9 5 6
1765
(6) Lahr. T. N.. Olsen. R.. Gleason. G. I.. Tabern. D. L.. J. Lab. and Clin. M e d . 45, 66 (1955). (7) Libby, W. F., ANAL.CHEM.19, 2 (1947). (8) Riegel, B., Hartop, W. L., Jr., Kittinger, G. W., Endocrinology 47, 311 (1950). (9) Schweitzer, G. K., Stein, B. R., AT’ucZeonics 7, No. 3, 65 (1950). (10) Skipper, H. E., Bryan, C. E., White, L., Jr., Hutchison, 0. S., J. B i d . Chem. 173, 371 (1948). (11) Snedecor, G. W., “Statistical hIethods,” 4th ed., Iowa State College Press, A4mes,Iowa, 1946.
(12) Tabern. D. L.. Lahr. T. N.. Science 119. 739 11954) (13j Westphal, U., Firschein, H. E., Pearce,‘E. M:, Am. J. Physiol. 185, 54 (1956). AMRL Rept. (14) Westphal, U. F., Firschein, H. E., Pearce, E. 185, Fort Knox, Ky. (April 22, 1955). (15) Wick, A. N., Barnet, H. N., Ackerman, K.,ANAL.CHEM.21, 1511 (1949). (16) Yankwich, P. E., Norris, T. H., Huston, J., Ibid.,19,439 (1947). (17) Yankwich, p. E., Weid, J. Science 107, 651 (194%. RECEIVED for review April 18, 1956. Accepted July 16, 1956.
w.,
Determination of Di- and Trialkyl Phosphites in the Presence of Each Other D. N. BERNHART and K. H. RATTENBURY Research Laboratories, Victor Chemical Works, Chicago Heights,
In an alcoholic caustic solution dialliyl phosphites are rapidly hydrolyzed to form sodium monoalkyl phosphites, with no interference from trialkyl phosphites. In an acidic alcoholic solution trialkyl phosphites are readily hydrolyzed to form dialliyl phosphites, which may then be hydrolyzed with caustic. Both reactions are stoichiometric and consume one mole of caustic per mole of phosphite.
T
RIALKYL phosphites are generally prepared by the reaction of alcohol and phosphorus trichloride in the presence of a base (Equation 1); without a base, dialkyl phosphites are formed (Equation 2). In the commercial preparation of trialkyl phosphites some dialkyl phosphites are usually formed. Therefore, to determine the purity of trialkyl phosphites, it is necessary to determine each of the two components in the mixture. Relatively few such chemical procedures are reported in the literature. One procedure, which is specific for the dialkyl phosphite content, is the nonaqueous titration of weak acids ( 2 ) . Another procedure for purity only is the determination of molecular weight with alcoholic potassium hydroxide (3). Iodine solutions have also been used to indicate purity (6). There are very few published data on the two latter procedures. The method presented here takes advantage of the rapid hydrolysis of alkyl phosphites. In an alkaline alcoholic medium dialkyl phosphites are instantly hydrolyzed to form sodium monoalkyl phosphites (Equation 3), while trialkyl phosphites react very slowly ( 1 , 4). The rates of reaction of the two components are far enough apart to permit determination of dialkyl phosphites in the presence of trialkyl phosphites by adding an excess of alcoholic sodium hydroxide and immediately titrating the excess caustic nrith standard acid. In an alcoholic acid medium trialkyl phosphites are very rapidly hydrolyzed to form dialkyl phosphites ( 1 ) (Equation 4). The phosphite is then all present as dialkyl phosphite and may be determined by alkaline hydrolysis. 3ROH
+ PCl, + 3 base
-
+ 3 base. HC1
(RO)3P
(1)
0
3ROH
+ PCl,
I/
-+
(R0)zP-H
+ RC1 + 2HCl
II
EXPERIMENTAL
It was found that in an alcoholic medium 1 mole of dialkyl phosphite consumes 1 mole of sodium hydroxide after 1 minute, and this value remains constant for at least 1 hour. Trialkyl phosphite, ranging from ethyl to octyl, consumes no sodium hydroxide for as long as 10 minutes in an alcoholic medium. After 10 minutes of hydrolysis in a slightly acidic alcoholic medium, 1 mole of trialkyl phosphite consumes 1 mole of sodium hydroxide after 1 minute, and this value remains constant for 1 hour. All these reactions were carried out a t room temperature. INTERFERENCES
Alcohols, amine hydrochlorides, and dialkyl alkanephosphonates (the rearrangement isomer of trialkyl phosphites) do not interfere with this method. If acidic compounds such as monoalkyl phosphites, or basic compounds such as amines, are present, they can be compensated by neutralizing the alcoholic solution of the sample with 0.LV acid or base. PROCEDURE
Dialkyl Phosphite. Dissolve 1 to 2 grams of trialkyl phosphite in 50 to 100 ml. of dry ethyl alcohol. Neutralize with 0 . 1 s sodium hydroxide to a light pink with phenolphthalein indicator. .4dd 20.0 ml. of 0.1N sodium hydroxide, mix, add about 10 ml. of a 40/,solution of boric acid, and back-titrate with 0.lN hydrochloric acid until the solution is colorless. Each mole of sodium hydroxide consumed is equivalent to 1 mole of dialkyl phosphite. Sample size and excess caustic may be regulated to suit the particular sample that is to be analyzed. Dialkyl phosphites may also be assayed by this procedure. The boric acid is added to buffer the solution, thus preventing local hydrolysis of the trialkyl phosphite when back-titrating with acid.
Table I.
+ NaOH
4
J
(RO)(NaO) -H
Added
1.0 3.0 5.0 10.0 15.0 20.0
?To Tria Found Added Di- and Tributyl Phosphites
0.9 3.0 5.1 9.9 14.8 19.7
99.0 97.0 95.0 90.0 85.0 80.0
Found
99.1 97.0 94.7 89.9 84.8 80.2
Di- and Triiso-octyl Bhosphites
+ ROH
(3)
0
(RO)IP
Typical Results with Synthetic Mixtures % Di
0
0
(RO)J’-H
(2)
111.
II + HOH %(RO)*P-H + ROH
7.0 10.0 15.0 20.0
7.0 9.8 14.7 19.9
93.0 90.0 85.0 80.0
Standard deviation of tri-component, 2 parts per thousand.
(4)
92.7 90.2 84.8 79.8
ANALYTICAL CHEMISTRY
1766 Total Phosphite. Dissolve a sample containing 0.002 to 0.003 mole of phosphite in 100 ml. of 95% ethyl alcohol. Keutralize immediately to a light pink with phenolphthalein indicator. Add 5.0 ml. of 0.1N hydrochloric acid, mix, and allow to sit for a t least 10 minutes. Add 40.0 ml. of O.IN sodium hydroxide, mix, and titrate with 0.LY hydrochloric acid until the solution is colorless. The net moles of caustic consumed are equivalent to the moles of phosphite present. The trialkyl phosphite content is calculated by subtracting the dialkyl phosphite from the total phosphite. Sample size, strength of solutions, and the amount of alcohol used as solvent may be regulated as desired. The authors prefer using aqueous acid and base with enough alcohol to keep a clear solution rather than alcoholic acid or base. RESULTS
The method is simple, rapid, and accurate. It is applicable to alkyl phosphites ranging from ethyl to octyl alkyl groups, with little interference from materials commonly found in commercial trialkyl phosphites. Table I shows typical results ob-
tained from synthetic mixtures of pure fractionated di- and tributyl and di- and triiso-octyl phosphites. ACKNOWLEDGMENT
The authors wish to express their‘thanks to Betty Bruns for assisting in compiling the analytical data. LITERATURE CITED (1) hrbuzov, A. E., J. Russ. Phys. Chem. SOC.46, 291-4 (1914). (2) Deal, V. Z., Wyld, G. E. A , , ANAL.CHEM.27, 47-55 (1955). (3) Landauer, S. R., Rydon, H. K.,J . Chem. Soc. 1953, 2224-34. (4) NylBn, P., “Studien uber organische Phosphorusbindungen,” thesis, p. 130, Alniquist och Wiksells Boketryckeri, A.B., Uppsala, 1930; Ber. 57B, 1023-38 (1924); 59B, 1119-28 (1926). (5) Shell Development Co., “Organophosphorus Compounds for Department of the h’avy,” Tech. Rept. 8 (March l , 1950, to hIay 31, 1951).
RECEIVED for review May 19, 1936. -4ccepted July 10, 1956. Division of .4nalytical Chemistry, 129th Meeting, 9CS, Dallas, Tex., April 1956.
Decomposition of Organic Fluorine Compounds by Wickbold Oxyhydrogen Flame Combustion Method P. B. SWEETSER Chemical Department,
E. 1. du Pont d e Nemours & Co.,
/nc.,Wilmington, Del.
The Wickbold oxyhydrogen combustion method is an excellent way of decomposing organic fluorine compounds for determination of fluorine. In this method the vaporized organic fluoride or its partial combustion products are passed through an oxyhydrogen flame which decomposes the sample to carbon dioxide and hydrogen fluoride. The hydrogen fluoride is absorbed in dilute sodium hydroxide solution and subsequently titrated with thorium nitrate. This method is rapid and eliminates the difficulty resulting from high salt content normally present after a Parr bomb-type decomposition.
0
VER 500 references have been listed by McKenna (8-4)
on methods of decomposition and analysis of fluorine compounds. However, none of the procedures given in the above reference are entirely satisfactory. The two main sources of error encountered in fluorine analysis are: (1) Difficulty in obtaining quantitative conversion of the organic fluorine to ionic fluoride. It is usually necessary to employ more drastic decomposition conditions than those required for other organic compounds, and even then some organic fluorides give low results due to incomplete decomposition. ( 2 ) The quantitative determination of fluoride in the decomposed sample. Volumetric methods based on formation of complexes and precipitates are complicated by the difficulties of end point detection, slow reactions, and general nonstoichiometric conditions caused by pH and salt effects. Gravimetric determinations generally are not suitable because of the solubility of metallic fluorides and the difficulty in filtering precipitates. Probably the most widely used method for fluorine analysis is a Parr bomb decomposition, followed by titration of the fluoride with thorium nitrate usiqg alizarin red as indicator. A Parr bomb method has proved satisfactory in this laboratory for the decomposition of most organic fluorides; only in the case of highly volatile compounds and compounds with high fluorine content has there been difficulty in the decomposition step. The nature of this decomposition, however, makes the final deter-
mination of fluoride difficult because of the large amount of salt residue from the Parr bomb fusion. This high salt content not only has a detrimental effect on the sharpness of the end point, but also changes the stoichiometry of the reaction. In an effort to avoid these difficulties, a study has been made of the decomposition of organic fluorides by a Wickbold-type, oxyhydrogen flame combustion apparatus (5, 6). APPARATUS
The quartz flame combustion apparatus (Figure 1 ) is similar to that described by Wickbold (6) and consists of five main parts: the vaporization tube, A , the burner, B, the flame chamber, C, the condenser, I , and the absorption receiver, D. Absorption receiver and Reitmeyer attachment, E, are of borosilicate glass; all other parts are of quartz or Vycor (96% silica glass) glass. The vaporization tube is the section in which the sample is heated to give partial combustion or vaporization. Gaseous products then pass from the vaporization tube via a capillary tube into the burner head at B. The oxygen and hydrogen are supplied to the burner from the two tubes, x and g, so that the capillary from the vaporization tube is surrounded by the hydrogen and oxygen tubes ahich end at the burner head. The burner section is connected to the flame chamber, C, by a 19/38 joint at B. The flame chamber is surrounded by a water jacket to prolong the life of the quartz tube and t o prevent possible melting of the quartz. The flame chamber tapers down a t the end to about 6 mm. and is connected to a spiral enclosed in a water condenser, which in turn is connected at J to the absorption receiver with a 10/30 joint. The apparatus is mounted on a Transite panel. The flows of the flame oxygen, sweep oxygen, hydrogen, and exhaust lines are controlled by needle valves, mounted on the front of the panel, which are connected to the Brooks multitube Flowmizer flow meters mounted in a single four-unit mount. The apparatus is surrounded by a Lucite acrylic resin safety shield. A probe burner, 11/2 X 20 cm., P , is made of Vycor glass. The oxygen is supplied to the burner through the outer tube and the gas by the inner tube, both of which taper down at the burner head. A platinum boat, 1 X 4 X 1 cm., was used in the vaporization of solid samples and high boiling liquids. A quartz pig similar to that used by Wickbold was used for the volatile liquid samples. The illuminator for the titrations is an H-3, 85-watt Westmghouse mercury lamp with a vapor lamp transformer. The lamp is housed in a mount that directs the ultraviolet light a t an angle
