Volumetric Estimation of 5-Bromo-2-Furoic Acid .with Standard Bromate ELIZABETH E. HUGHESAND S. F. ACREE,Bureau of Standards, Washington, D. C. tures mentioned above are subject to fluctuations of not more than 2' C. The potassium bromate solution was introduced from the side arm into the acidified 5-bromo-2-furoic acid b tilting and the solutions were mixed b swirling the flask gent$. The reaction was allowed to proceelfor definite time eriods, at the end of which the potassium iodide was added. I t ordinary laboratory temperature about 10 minutes seems to be ample duration for the reaction. The contents were shaken vigorously and the liberated iodine titrated with 0.1 N sodium thiosulfate using starch indicator (0.5 grams of soluble starch in 250 ml. of boiling water).
N A PRECEDIYG article (4) the authors described the
I
equipment, technic, and conditions for allowing furfural to react quantitatively with one molecule of bromine from standard bromate within 5 minutes a t 0" C. with errors less than 0.5 per cent. The method is especially useful in the analysis of farm wastes for pentosan content. The usual procedure ( 1 ) is to distill the fibers with 12 per cent hydrochloric acid and determine the volatilized furfural with phloroglucinol, thiobarbituric acid, or with excess bromine by the method of Powell and Whittaker ( 5 ) . The errors, even with empirical corrections, may be 2 to 4 per cent. The technic of the bromination method cited above is more nearly accurate and takes much less time. In a n attempt to apply this method to the analysis of products of bromination and oxidation of furfural, the present investigation was undertaken to see whether 5bromo-2-furoic acid can be determined quantitatively both by titration with standard alkali and by addition of molecular equivalents of bromine.
TABLE I. REACTION OF 5-BROMO-2-FUROIC ACID WITH BROMINE TIME 103 mg.
OF REACTION
Sec. 30 Min. 1 2 3 4 5 6 8 10 20
EXPERIMENTAL PROCEDURE The 5-bromo-2-furoic acid was first described by Hill and Sanger (3) with melting point of 184" to 186" C. It is isomeric with a monobromo derivative having the bromine in the 3 or /3 position with melting point of 128" to 129" C. The acid used in these experiments was kindly made for the authors by J. A. V. Turck by the method of Gilman and Wright (i?),and was a white crystalline substance melting at 184' to 186" C. The purity based upon acidity by titrating with 0.1 N or 0.02 N sodium hydroxide using phenolphthalein as indicator was 100 per cent (+0.1 per cent). T h e s o l u bility in water was determined a s a p proximately 2.5 mg. per ml. a t ordinary room temperatures. For these experiFIGURE1. DIAGR.4M OF FLASK ments the solution of the acid was prepared by dissolving 2 grams of the acid in 1liter of boiling water which was kept warm until solution was complete, then cooling to room temperature. An aliquot portion of the solution was transferred to the body of a special side-arm titration flask (Figure 1) containing 200 ml. of 3 per cent hydrochloric acid (prepared by diluting 1 part of 36 to 38 per cent concentrated hydrochloric acid with 11 parts of water). In one side arm were placed 25 ml. of 0.1 N aqueous solution of potassium bromate containing 50 grams per liter of potassium bromide. In the other side arm were placed 10 ml. of an aqueous solution of 10 per cent potassium iodide. A second flask was similarly prepared but omitting the 5-bromo-2-furoic acid. The flasks were sealed by placing a drop of phosphoric acid on the ground-glass stopper; the flask and contents were allowed to come to constant temperature. The experiments at 0" C. were made with the flasks suspended in an ice bath for the short time periods and placed in an ice box maintained at 0" C. for the longer ones. Experiments at 21' C. were conducted in a constant-temperature room. The tempera-
W E I Q H T OF
85 mg.
50mg.
SAMPLE 62 mg.
7 -
210 C-.
61.7
63.2
...
81.6 92.3
83.8 95.7
99.0
...
...
7 -
...
...
...
26 mg.
...
... ... ... ... ...
... ...
98.9
100.0
99.8 100.0 100.2 100.6
100: 1 100.1 100.1 100.6
98.3
30 40
100.0
...
100.5
100.6
...
...
...
...
60
100.0
100.6
102.3
90
...
...
...
Hre. 2
101.1
...
...
,..
92.8 (85.3)
...
...
99.6
...
(93.7)
100.6 (75,8)
...
...
... ... ...
...
5 18
...
103:3
20 Days 3
101.2
102.1
...
...
103.0 105.2
... ...
... ...
...
...
c.-
...
63.1 65.9
99.0 99.8 100.0 100.1
...
00
...
97.7
7
46 mg.
P E R C E N T OF THEORETICAL AMOUNT F O U N D
...
...
... 100.1 (97.8) i0i:g 100.5
...
...
...
52.4
... ...
86.3
...
93.6 97.8 99.3
...
99.8 99.7 98.5 100,6 99.9 100.7
... 103.4 102.9
... ...
...
The results at 0" and 21" C. are shown in Table I and Figure 2 and express the extent of the reaction with respect to time. The addition of 2 moles of bromine to 1 of 5-bromo2-furoic acid is represented by 100 per cent. The number of
TIME O F REACTION
-
MINUTES
FIGURE 2. REACTION OF ~-BROMO-~-FUROIC ACIDWITH,BROMINE
milliliters of 0.1 iV thiosulfate required for the blank less that required for the sample multiplied by 0.004775 gives the number of grams of 5-bromo-2-furoic acid.
292
July 15, 1934
INDUSTRIAL AND ENGINEERING CHEMISTRY DISCUSSIONOF RESULTS
Table I and Figure 2 show the rate of addition of bromine under specified conditions upon which basis the percentage of the theoretical amount found is calculated. It is found that bromine adds so rapidly to 5-bromo-2-furoic acid that, in contrast to furfural (4, it is not practical to stop the reaction short of two molecular equivalents of the halogen. Over a period of several hours and days the tetrabromide addition product of the normal reaction apparently loses hydrobromic acid very slowly to form more double bonds and the bromine used in subsequent reaction may reach 0.1 mole or more. According to the mass law and verified in Table I and Figure 2, the percentage of normal and of further reaction with the same amount of bromine for a given short time period should increase with decrease in size of sample. At 0' C. the results are not always reproducible, as shown
293
by the percentages given in parentheses. Experiments to be reported later show a small photochemical effect which is not, however, responsible for the discrepancies in the analyses, especially a t 0" C. At 21" C., however, the results are concordant and the reaction, regardless of the size of the sample, is complete within 8 to 30 minutes. LITERATURE CITED (1) Assoo. Official Agr. Chem., Methods of Analysis, p. 284 (1930). (2) Gilman, H., and Wright, G. F., J . Am. Chem. Soc., 52, 1170 (1930). (3) Hill and Sanger, Ann., 232, 100 (1885). (4) Hughes, E. E., and Acree, S. F., IND.ENG. CHEM.,Anal. Ed., 6 , 123 (1934). ( 5 ) Powell, W. J., and Whittaker, H., J . Soc. Chem. Ind., 43, 35T (1924).
RECEIVED March 17, 1934. Published by permission of the Director, National Bureau of Standards.
Continuous Determination and Recording of Carbon Dioxide Content of Gas Mixtures Apparatus Used in the Bureau of Mines Helium Plant ALLENS. SMITH,U. S. Bureau of Mines, Amarillo, Texas H E d e t e r m i n a t i o n of I n designing a n apparatus to give a continuous and bicarbonate s a l t s o f t h e carbon d i o x i d e in gas record of the carbon dioxide content of heliumOr as affected by the partial pressure mixtures by absorption bearing natural gas processed in the Amarillo of carbon d i o x i d e in equilibin alkaline media has occupied Helium Plant of the Bureau of Mines, three rium w i t h t h e solution, have the attention of a large number methods were investigated. One, described by been developed. The e a r l i e r of investigators since D a l t o n White, based on conductance measurements, was process determined the equilibo r i g i n a t e d the method. The rium by measureliterature has been adequately selected as being most suitable for the application ment of the p H of the solution. r e v i e w e d , m o s t recently by desired. A modification of this method, which The relatively low a c c u r a c y Thomas (9) and by Martin and improves its operation and adaptability in plant i n h e r e n t in this method has Green ( 3 ) . The latter authors installation, is briefly described. The apparatus, been improved upon by the use also classify a n d discuss of the glass electrode t o deteras modijed, has given satisfactory service in a briefly the methods which have mine the PH Potentiometrically been used. An improvement plant installation for recording concentrations of (II), adding rapidity and simin p H measurement h a s b e e n carbon dioxide f r o m 0.1 to 1.0 per cent in sweet plicity. to a method which has published by Wilson, 0 r c u t t , natural gas. advantages in being independent and Peterson (11), who describe of gas flow. a potentiometric m e t h o d for Continuous measurements of the p H of a solution are determination of carbon dioxide. At the Amarillo Helium Plant of the Bureau of Mines the practicable only with the quinhydrone and antimony elecneed arose for an accurate apparatus to record continuously trodes.' The latter has the advantage of not requiring the and automatically the carbon dioxide content of helium- addition of any reagents for the measurement but offers some bearing natural gas. The average carbon dioxide content difficulties in preparation and calibration for use with alkaline of the unprocessed gas is about 0.7 per cent, and the hydrogen solutions which are in motion and are not in contact with air. sulfide content less than 0.002 per cent. The other constitu- The quinhydrone electrode has a limited range because of ents vary somewhat, depending upon the proportion of the decomposition and oxidation which occur in the system when total flow produced from each of the government's gas wells subjected to alkaline solutions. It has been applied without and upon temperature conditions in the pipe line. Because success in an attempt to measure carbonate-bicarbonate of this low concentration of carbon dioxide and variation in equilibria (11). This type of electrode is not suitable for use other constituents the gasometric methods and those based in unbuffered solutions, but since a decided change in pH on physical properties of the gas could be eliminated a t once will be caused by a trace of carbon dioxide in a perfectly in considering the known continuous, recordable processes. neutral salt it seemed desirable to make some very brief tests Three types of electrolytic methods offered possibilities and of the pH in unbuffered solutions. The results of this limited study were not satisfactory, showing excessive drifting of the were investigated.
T
MEASUREMENT OF CARBONATE-BICARBONATE EQUILIBRIA FIRSTMETHOD. Two variations of a method depending upon measurement of the equilibrium between carbonate
1 After completion of the experimental work on which this paper is based, a n article by Vickers, Sugden, and Bell appeared in Chemirlry & Industry, 51, 545 (1932), reporting an apparatus for the continuous recording of p H in which a glass electrode is used.
