Determinalion of Formic Acid in Presence of Formaldehyde Bisulfite LARS AHLhN AND OLOF SAMUELSON Department of Engineering Chemistry, Chalmers Tekniska Hogskola, Goteborg, Sweden ion exchange method can be used for the separation of T aldehydes from alcohols, ketones, and organic acids. The results are summarized in a recent monograph (6). The method HE
has been applied t o the determination of various volatile compounds in sulfite waste liquor. A modification of the technique for determination of formic acid in the presence of formaldehyde bisulfite, adapted to the analysis of sulfite waste liquor, is described. In the common method for the determination of formic acid by the reduction of mercuric chloride ( 2 , 3), the presence of formaldehyde and sulfur dioxide causes considerable errors. Some results are presented in Table I. Tahle I.
Influence of Formaldehlde and Sulfur Dioxide on Formic Acid Determination HCHO
Added, M e .
SOP
HCOOH
Found, M g . HCOOH
~
If no sulfur dioxide is present it should be possible to carry out a separation of formic acid and formaldehyde by means of an anion exchanger in the bicarbonate form ( 5 ) . I n the presence of sulfur dioxide the formaldehyde is taken up as a-oxysulfonic acid (formaldehyde bisulfite). Consequently the sulfur dioxide must be eliminated before the ion exchange separation. Because of the high stability of the formaldehyde bisulfite it is rather difficult to remove the sulfur dioxide from the solution by oxidation, precipitation, or distillation. It is not possible to perform the separation by extracting the formic acid by means of ether. Formaldehyde. as well as sulfur dioxide, partly enters the ether phase. iimong the methods investigated the precipitation as barium sulfite was found to give satisfactory results. The decomposition of the bisulfite addition compound is favored by a high pH of the solution. At pH values of 11.5 and higher, a Cannizzaro reaction occurs ( 4 ) a t such a rate that the formation of formic acid from formaldehyde can cause a considerable error. Satisfactory results can be obtained XT-orking a t p H 10, provided a slight excess of barium chloride i q present to depress the solubility of the barium sulfite. In the ion exchange separation it is favorable to have the lowest possible amount of electrolytes in the solution. .4n increased amount of chloride decreaqes the break-through capacity of the ion exchange column for formic acid and makes it necessary to increase the column length. For this reason it would be preferable to make the solution alkaline by means of barium hydroxide. In this case the barium sulfite is obtained in a form which is difficult to remove by filtration. If instead, sodium hydroxide is added, and the precipitation is performed by the addition of barium chloride after heating the solution to 60" C., the filtration goes quickly. After removal of the barium sulfite the solution can be acidified by means of a cation exchanger in the free-acid form. Subsequently formaldehyde and formic acid can be separated by the ion exchange method (combined batch and column operation) described in an earlier paper ( 5 ) . This separation method was worked out for analyses xhere the acid was determined by alkalimetric titration. In the present investigation 1Thei-e the formic acid has been determined by the mercuric chloride method the technique has been simplified. The alkaline solution is passed directly through a column containing an anion exchange resin
in the acetate form. Formic acid is taken up by the resin whereas formaldehyde passes into the effluent. After washing with water the formic acid is eluted by means of sodium carbonate. Before treatment with mercuric chloride the solution has to be acidified to remove the carbonate which interferes with the determination. PROCEDURE
A water solution containing formic acid, formaldehyde, and sulfur dioxide is made alkaline (pH 10) by the addition of 0.1 J4 sodium hydroxide. After heating to 60" C. a slight excess of 0.5 Ji barium chloride solution is added. During the precipitation the pH value is lowered, which is compensated for by further additions of sodium hydroxide. The solution is allowed to stand at 60" C. and p H 10 until the barium sulfite has settled (about 0.5 hour). ilfter filtration and washing with a slight amount of hot water, the filtrate is cooled. The alkaline solution is passed through an ion exchange column of standard type (6) filled with a strongly basic anion exchanger (Amberlite IR9-400, particle size 0.12 to 0.30 mm. in air-dried condition, Rohm & Haas Co., Philadelphia). The resin has previously been transformed into the acetate form, by treatment with 400 ml. of 1 'TI sodium acetate solution and washing with water. With the amounts of acid used in the experiments presented in Table 11, the following dimensions of the resin bed are recommended: height, 180 mm.; diameter, 10 mrn. These dimensions are satisfactory provided that not more than 8 ml. of barium chloride have been added. ,4 suitable flow rate is 3 ml. per minute. After washing with 200 ml. of water the formic acid is eluted with 40 ml. of 0.5 JI sodium carbonate solution folloTyed bv 40 ml. of water. Table 11. Determination of Formic Acid by the Ion Exchange Method
a
Added, l l g . a HCHO $02 HCOOH 27 109 29.25 27 109 29.25 27 109 29.25 27 109 11.70 27 109 11.70 27 109 5.86 27 109 5.85 27 109 5.83 Volume of sample solution is 60 ml.
Found, h9g. HCOOH 29.17 29.25 29.33 11.80 11.71 5.87 5.87 5.93
Relative Error,
%
-0.3 0.0 f0.3 +0.9
+o.
1
+0.3 +0.3 +1.4
The eluate which is taken up in an Erlenmeyer flask is neutralized against methyl orange by means of 2 111 hydrochloric acid. Carbon dioxide is removed by shaking the flask vigorously. rlfter addition of 3 grams of sodium acetate and 25 ml. of a 5% mercuric chloride solution (another 3 ml. for every 10 mg. of formic acid exceeding 50 mg.) the flask is covered by a watch glass and placed for 2 hours on a steam bath. The solution is filtered through a sintered-glass filter crucible (Pyrex M or Jena G 4), and the precipitated mercurous chloride is washed with water a t 40 to 50" C. and finally with ethanol. After drying for 1 hour a t 100' C., the precipitate is weighed. The weight multiplied by 0.0975 gives the amount of formic acid in the sample. SUllM4RY AND RESULTS
A method has been worked out for the determination of formic acid in the presence of formaldehyde bisulfite. The sulfur dioxide is removed by precipitation as barium sulfite. Subsequently formic acid and formaldehyde are separated by means of an anion evchanger in the acetate form. After elution the acid is determined according to the mercuric chloride method. The experimental results presented in Table I1 show that a good agreement has been obtained between the added and found amounts of formic acid. The maximum relative error is 1.4%. Similar accuracy has been obtained with solution8 which besides 1263
ANALYTICAL CHEMISTRY
1264
formic acid contain excess acetic acid. The method has been adopted in the determination of formic acid in sulfite u,asteliquor ( 1 ) . ACKNOWLEDGMENT
Support of this investigation by the Foundation for Forest Research is gratefully acknowledged. LITERATURE CITED
( 1 ) AhlBn, Lars, and Samuelson, Olof, Suensk Pnpperstidn., in press.
(2) Auerbach, F., and Zeglin, H., 2. physik. Chem., 103, 161 (1923). (3) Bed, Ernst, ed., “Berl-Lunge, Chemisch-technische Untersuchungsmethoden,” 8th ed., ‘Vol. 111, p. 764, Berlin, Julius Springer, 1932. (4) Euler, H. von, and Lovgren, T., 2.anorg. u. aZZgem. C h e m , 147, 123 (1925). ( 5 ) Gabrielson, G., and Samuelson, O., Acta Chem. Seand., 6 , 729 (1952). (6) Samuelson, O., “Ion Exchangers in Analytical Chemistry,”
New York, John Wiley and Sons, and Stockholm, Alniqrist and Wiksell, 1952. RECBIVED for review Fehruary 6, 1953. Accepted April 10, 1953.
Colorimetric Microdetermination of Boron by the Curcumin-Acetone Solution Method LOUIS SILVERMAN AND KATHERINE TREGO Atomic Energy Research Department, North American Aviation, Inc., Downey, Calif. I1 0 0
of variations of the amounts of reagents used in Tthe effects boron-curcumin reaction, as applied to the colorimetric HE
determination of boric acid or borate in solutions of low solids content, were studied. The procedure is effective in water solutions for determination of detectable amounts of boron (0.027, contained in a 10-ml. standard volume of solution plus reagents). Precautions are described which must be observed with reagents and apparatus in order to avoid contamination a t low boron contents (0.17 or less). Reaction of Boric Acid with Specific Organic Reagents. Korenman ( 4 ) reviewed the action of boric acid with several hydroxy derivatives of anthraquinone. It was shown that the colors of the sulfuric acid solutions of the selected quinones were changed when boric acid was added, and that these solutions become fluorescent. These quinones were characterized as having hydroxyl groups in peri-position with the carbonyl groups of the quinones. I n the case of anthraquinone, the hydroxyl group may be in the 1, 4, 5 , or 8 position.
LLU II
I
II
H 0 I
HO-
Curcumin is also found to have this basic structure, sinw it is believed that curcumin exishs in tautomeric forms:
0 I
0
h
H
eH
ci
I3
I
‘I
HC
H CH
HC
CH
II
HC
H 0
0
0
H
II
0
H
0 The boric acid reaction has been visualized as follows:
0.‘ Curcumin, which is pale1 yellow in acetone solution, is colored orange in the presence of boric acid, and the color is intensified in the presence of oxalic acid. Present Usage of Boron-
wherein the six-membered ring
or
forms, the boron being joined to the carbonyl oxygen by an auxiliary valence, or by chelate formation. Morin, the reagent which has been most used for the determination of boron, has a similar basic structure, with the hydroxyl group in pa’-position.
\
0
nn HaCO-(,,
O-OCH’ Curcumin-Oxalic tem. Allen and Acid Zies Sys(1) I 1 dipped strips of turmeric 0 0 paper in test solutions and H H dried the strips. The length and spread of color gave quantitative results for boron. Cassal and Gerrans ( 9 ) introduced oxalic acid but used solutions in place of paper. I n an improved method, Naftel(6) determined insoluble and soluble boron in soils and plants by fusing with calcium hydroxide, acidifying with hydrochloric and oxalic acids, adding cureurnin, and extracting with alcohol. The American Society for Testing Materials ( 2 ) uses a similar eystem for the determination of boron in steels, in conjunction with the methyl borate distillation. In this method, close control
