Determination of Boron in Borine Compounds ANNE L. CONRAD AND
M. S. VIGLER, Standard Oil Company (Ohio), Cleveland 6, Ohio
A rapid method for the analysis of organic borine compounds is accurate to within *0.04% and requires but 3 hours’ total analysis time and a working time of 1 hour. The oxidation is accomplished through use of the Parr oxygen bomb and hot permanganate solution.
A
SUR‘ EY of the literature revealed but two methods of practical value for the determination of boron in borine compounds. Snyder, Kuch, and Johnson ( 4 ) describe a method of oxidation with hydrogen peroxide and a second method of fusion with sodium peroxide in a Parr bomb. The first is very time-consuming; the second may be dangerous when used with low boiling borines. P) 4 W E S T CCNDENSER WllH INDENTED INNER TUBE
sodium carbonate solution and placed upright against the wall in the clean dry base of the bomb. The bomb is assembled and oxygen is admitted equal to 500 pounds per square inch. While immersed in a water bath, the contents of the bomb are ignited electrically. After a 5-minute cooling period the bomb is tipped to allow the sodium carbonate in the vial to come in contact with the combustion gases. The bomb is left in the cooling bath for 0.5 hour. Preparation of Solution. Pressure is released from the bomb slowly to avoid loss of liquid. The bomb contents are washed carefully into a 250-ml. boron-free round-bottomed flask. The solution is adjusted to a pH of 1to 4 with hydrochloric acid. The West condenser is connected to the flask and nitrogen is entered through the 2-way stopcock (Figure 1). The flask contents are heated to boiling under a constant stream of nitrogen, and potassium permanganate solution is added dropwise to the boiling solution until a permanent purple color is maintained after several minutes of boiling; this indicates that oxidation is complete. The saturated sodium sulfite solution is added dropwise until the solution becomes colorless. Boiling and refluxing are continued for 5 minutes. Titration. The flask and contents are cooled to room temperature and the condenser is rinsed with distilled water. The wash a a t e r is collected in the distilling flask. Contents of the distilling flask are washed into a boron-free titrating beaker. The solution is titrated with standardized sodium hydroxide in the presence of mannitol; a pH meter is used to determine the end point. Calculation
-250
ML R B . FLASK
yo boron Figure 1. Detail of Reflux Apparatus
=
ml. of NaOH X N X 0.1082 weight of sample
Table I shows results obtained for boron determination by the above procedure as compared with the hydrogen peroxide digestion method. In all cases the normality of the sodium hydroxide was checked against recrystallized A.C.S. standard sodium tetraborate as described by Hurley (S). Purity of the borine was checked by boiling point and molecular weight determinations.
The method described here is an adaptation of that used by Burke (1)for determining boron in organic borates. The sample is carefully weighed in a gelatin capsule in an atmosphere of nitrogen and is burned in the bomb in oxygen under pressure. Sodium carbonate solution serves as the absorbent. To complete the oxidation, the acidified bomb washings are boiled with potassium permanganate solution until the purple color remains. The resulting boric acid is determined by the standard procedure of removing carbonate and titrating with sodium hydroxide in the presence of mannitol. The total working time of analysis is typically about 1 hour.
Table I.
Tri-n-butylborine
(Theoretical % B, 5.94) Bomb Oxidation Sample, gram 0.2010 0.2172 0.0372 0.1363 0.1514
EQUIPMENT AND REAGENTS
Parr oxygen bomb, oxygen, and gelatin capsule ( 2 ) . ru’itrogen or other inert gas supply. Potassium permanganate solution, 1.5%. Sodium carbonate solution, approximately 5 W . Boron-free distilling flask. West condenser fitted with an entry tube and 2-way stopcock (see Figure 1). Hydrochloric acid solution, approximately 5%. Sodium sulfite solution, saturated. Mannitol, reagent grade. Standardized sodium hydroxide solution.
.4v.
B, %’ 5.95 6.01 5.98 5.92 5.91 5.96
HzOz Digestion (1) Sample, Gram B, % 0.0471 5.92 0.0674 5.97
ACKNOWLEDGMENT
The authors wish to thank E. C. Hughes for suggesting this problem and for many helpful suggestions in the course of this work.
PROCEDURE
LITERATURE CITED
Sampling. A fusion wire, about 10 cm., is looped into the cap-
sule, leaving protruding ends. Capsule and fusion wire are weighed accurately and flushed with nitrogen. The pipet is filled with nitrogen. The sample bottle is opened while flooding with nitrogen. An approximately 0.2-gram sample is drawn into the pipet and transferred into the weighed gelatin capsule. The capsule lid is placed quickly over the looped fusion wire and capsule (Z), and capsule and contents are weighed. Combustion. The protruding ends of the fusion wire are attached’to the bomb electrodes. A 10-ml. vial is filled with 5%
(1) Burke, 147. M.,IND. ENQ.CHEM.,ANAL.ED., 13,50 (1941). ( 2 ) Conrad, A. L., and Lemm, F. J., paper presented before Division of Analytical and Micro Chemistry, 112th Meeting of AM. CHEMSoc., New York, N. Y . (3) Hurley, F. H., ISD.END.CHEM.,ANAL.ED.,8,220 (1936). (4) Snyder, H. R., Kuch, G. A,, and Johnson, G. R., J . A m . Chem. SOC.,60, 105 (1938).
RECEIVED October 16. 1947.
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