NOTE ON ANALYTICAL PROCEDURES Analysis
OF
Boron Trifluoride in Organic Liquids (Ethers) S.
L. WALTERS AND R. R. MILLER
Naval Research Laboratory, Office of Research and Inventions, Anacostia Station, Washington, D. C.
C
ONSIDERABLE difficulty is encountered in analyzing boron trifluoride in organic liquids by conventional methods for boron and fluorine. This is due in part to the fact that the hydrolysis of boron trifluoride gives not only a mixture of boric and hydrofluoric acids, but some fluoboric acid, HBF,, in addition. Several methods of decomposition have been used. Pflaum and Wenzke (I first )made a fusion in a Parr sulfur bomb and determined boron and fluorine in the products of fusion. Bowlus and Nieuwland (I) heated with fuming nitric acid in a closed tube to decompose the sample. Vaughn and Xieuwland (3) determined fluorine in organic compounds by the use of liquid ammonia and sodium, but did not report any results for boron. A problem in this laboratory required the routine determination of boron trifluoride dissolved in various low-boiling ethers. These solutions contained no nonvolatile matter. A convenient method of analysis was developed based on the reaction of boron trifluoride with sodium fluoride to form sodium fluoborate. This compound is stable and can be heated to 200" to 300' C. with no appreciable decomposition; therefore, the method should apply t o organic solvents with rather high boiling points.
pered and weighed. Approximately 2 grams of the sample were placed in a tared 15 X 40 mm. weighing bottle and weighed. Samples were conveniently transferred with a small hypodermic syringe and in a dry-box, since boron trifluoride compounds are very hygroscopic. The weighing bottle and sample R-ere placed in the Bask with tweezers, the stopper was removed, and the flask was attached to a reflux condenser. After refluxing for about 30 minutes, the flask was removed and the liquid evaporated on a hot plate. The flask was stoppered, cooled, and weighed. The gain in weight minus the tare of the weighing bottle gave the weight of boron trifluoride in the sample. Analysis by this method was found to be reliable and accurate within o.50/0. Three analyses on a single sample of boron trifluoride ethyl etherate gave 48.3, 48.1, and 48.5y0 boron trifluoride; the theoretical boron trifluoride content was 47.8%. Additional work on mixed butyl and ethyl etherates indicated satisfactory results with this method. LITERATURE CITED
PROCEDURE
About 5 grams of anhydrous sodium fluoride were placed in a 100-ml. wide-mouthed extraction flask, and the flask was stop-
(1) Bowlus and Nieuwland, J. Am. Chem. Soc., 53, 3835 (1931). (2) Pflaum and Wenzke, IND. ENG.CHEY.,ANAL.ED.,4 , 3 9 2 (1932). (3) Vaughn and Nieuwland, Ibid., 3, 274 (1931).
CORRESPONDENCE Effect
OF
A c e t i c A c i d on the Spectrophotometric Estimation Gossypol in Aqueous Alcoholic Solution
SIR: Since publication of an improved rapid method for the determination of gossypol ( 1 ) it has been found with different lots of alcohol that the intensity of the color and the precision of the analyses depend upon the acidity of the alcohol used. Very satisfactory results are obtained when sufficient acetic acid (0.1 to 0.2 ml. per liter) is present to give the 95% alcohol an acidity
Table
1.
Effect of Acetic A c i d on Development of Color of Dianilino Gossypol in Aqueous Alcohol [As measured b y per cent transmittance= at 445 mp (6 determinations each concentration) ] Per Cent Transmittance 0.025 Mg. of Gossy- 0 . 1 0 0 M g . of Gossy- 0.175 hlg. of Gossypol per 25 M1. pol.per 25 hI1. pol per 25 MI. 0 . 2 M1. 0 . 2 M1. 0 . 2 M1. No of AcOH No of AcOH No of AcOH per liter AcOH per liter per liter AcOH AcOH 30.4 E 6 12.4 74.0 39.7 Lowest 77.4 13.0 31.6 24.5 Highest 92.0 76.4 47.5 12.96 Mean 82.38 30.93 22.32 74.96 41.03 Coleman double monochrometer spectrophotometer.
OF
of 0.002 to 0.004 N . The upper limit of acidity is not critical, since as much as 6 ml. of glacial acetic acid per liter may be used. Table I shon-s that the addition of only 0.2 ml. of glacial acetic acid per liter of alcohol increases the intensity of the color and greatly reduces the variation between replicate determinations. The acid added increased the normality from 0.0003 to 0.0037. The equation for the concentration-log transmittance curve for all data with 2 - log T acidified alcohol is: mg. of gossypol in 25 nil. = This ~
5.017
.
equation agrees with that previously found and published. It is recommended that in the determination of gossypol by the Dreviouslv published method ( 1 ) the alcohol used for the extraction b e adjustkdto an acidity between 0.002 and 0.004 N with acetic acid. LITERATURE CITED
(1) . . Smith. F. H.. IND.ENG.CHEM., ANAL. ED.. 18. 43-5 (1946). . , .
~
I
F. H. Department of Animal Industry North Carolina Agricultural Experiment Station Raleigh, N . C.
658
SMITH
