(8) Haagen-Smit,
A. J., Brunelle, Margaret F., Haagen-Smit, J. W., Rubber Chem. Technol. 32, 1134 (1959). (9) Hommel, C. O., Chleck, D., Brousaides, F. J., Nucleorics 19, 94, (1961). (10) Littman, F. E., Benoliel, R. W., ANAL.CHEM.25, 1480 (1953). ( 1 1 ) McCully, C. R., Roesler, J. F., Gordon, E. S.; Van Scoyoc, J. N., Carrigan, R. A., IRE Trans. Znstr. 1-10, 89 (1961).
(17) Smith, R. G., Diamond, P., Am. Znd. Hyg. Assoc. J . 13, 235 (1952). HUMBERTO A. BRAVO JAMES P. LODGE, JR. National Center for Atmospheric Research
(12) Regener, V. H., J. Geophys. Res. 65, 3975 (1960). (13) Regener, V. H. in Ozone Chemistry and Technology, Am. Chem. SOC.,Adv. Chem. Series 21. 124 (1959). (14) Renzetti, N. 'A., Romanovsky, J. C., J. Air Pollution Control Assoc. 6 , 154 (1956). (15) Saltzman, B. E., Gilbert, N., Am. Ind. H y g . Assoc. J. 20,379 (1959). (16) Sawicki, E., Stanley, T., Hauser, T., Chemist-Analyst 47,31 (1958).
Boulder, Colo. RECEIVED for review October 14, 1963. Accepted December 20, 1963. Division of Water and Waste Chemistry, 145th Meet.ing,ACS, New York, N. Y., September 1963.
Spectrophotometric Determination of Traces of Acetic Acid in Acetic Anhydride SIR: Some dye reagents have lately been developed in this laboratory for the detection of minute traces of acids, bases and salts to 10-6N) in benzene (2). The present paper reports the application of such a technique to the development of EL simple method for determining acetic acid content of acetic anhydride. The method in essence consists of dissolving acetic anhydride in dry benzene and measuring its acid content spectrophotometrically after reacting with a suitable dye reagent in benzene. EXPERIMENTAL
Reagents. A. Stock solution. One-tenth gram of the acetic anhydride sample (97% B.D.H. Laboratory Reagent) t o be analyzed is dissolved in exactly 10 ml. of dry benzene t o make ZL nearlv 0.1M solution. B. Acetic acid solution. Pure glacial acetic acid (not less than 99.5yo B.D.H. Laboratory Reagent) (0.06 gram) is taken in exactly 10 ml. of dry benzene t o make a 0 . 1 N solution. C. Acetic anhydrjde solution of known acetic acid content (for checking the result). A known amount of water-Le., 0.5%, 1% 275, 3%, 4%is added to definite quantities of acetic anhydride (same sample as for A) in separate volumetric flatjks and is left for 7 days t o let the reaction go to completion. Rhodamine Reagenl . (Calcozine) Rhodamine 6Gx conclmtration (Color Index 45160) 3 to 4 ing., is dissolved in 2.5 ml. of a buffer (sodium hydroxidesodium phosphate) of pH 10 to 12 and is extracted immediately with 100 ml. of benzene. The reagent is preserved over solid caustic soda in the dark ( 2 , 3). For convenience in comparison, the absorbance of the rhodamine reagent is always adjusted t o 0.40 =k 0.005 a t 515 mp. The reagent does not de-
electric spectrophotometer contain ing a similar cell filled with benzene as reference. The absorbance is read at 515 mp. The measurement should be done quickly since the coefficient of expansion of benzene is very high. The dilution and mixing operation (with the dye reagent) should be done in a closed box saturated with benzene vapor. This is done a t a number of dilutions of the anhydride solution, A, t o have a linear curve of absorbance against concentration (Figure l a ) . Similar measurements are made on solution B a t various dilutions to obtain a standard curve for acetic acid (Figure
teriorate over months. This reagent can easily detect acetic acid as low a concentration as 10-5 molar in benzene. Procedure.
ESTIMATION
OF ACETIC
The stock solution A is first diluted with dry benzene to a concentration (about lO+M acetic anhydride) such that the pink color developed with the dye reagent is not too intense. Two milliliters of this diluted anhydride solution is mixed with 2 ml. of the dye reagent in a clean test tube and a pink color is developed immediately. For control, 2 ml. of benzene is mixed with 2 ml. of the dye reagent. The colored solution and the blank are then transferred in two separate 1-cm. cells to the cell compartments of a Hilger Uvispek photoACID CONTENT.
lb). Calculation. From the slopes of the
curves for A (anhydride) and B (acetic acid) (Figure l a and b) the
Figure 1. Absorbance a t 515 rnp vs. concentration of ( a ) Macetic anhydride, (b) 1 O-4M acetic acid
t
01
I
I
I
I
I
I'0 1'5 2 '0 C O N C E N T R A T I O N , < ~ > ~ I O ' ~ / I (b) x i 0 4 m/l.
0'5
VOL. 36, NO. 3, MARCH 1964
673
Table 1.
Spectrophotometric Determination of Acetic Acid in Acetic Anhydride Samples
Composition Acetic anhydride Acetic anhydride 0 . 5 % water Acetic anhydride 1.OY0 water Acetic anhydride 2 .O% water Acetic anhydride 3 . 0 % water Acetic anhydride
+ +
+ + + 4 . 0 % water
Moles of acetic acid/mole of acetic anhydride, total
Moles of acetic acid/mole of anhydride (due t o added water)
Water, % Added Found
0.0685 0.1285
0.0600
0.502
0.52
0.1780
0.1095
1.046
0.97
0.2900
0.2215
2.023
1.85
0.4320
0.3635
3.054
3.20
0.5100
0.4415
4.028
3.89
acetic acid present due to added water will be the total acetic acid minus the acid originally present in the anhydride solution. The measured acetic acid content and the amount actually present due to the added water are shown in the table as per cent water to give an idea of the accuracy claimed by this method. Acetic acid content in acetic anhydride has also been checked up by a second method (1) and is found to be 3.36y0 by weight. The latter method works smoothly but the accuracy regarding the acid content of the anhydride may not be as good as the present method a t this range because it is dependent on the difference between the tw7o fairly large titer values. LITERATURE CITED
(1) Critchfield. F. E.. Johnson.' J. B.. >
acetic acid content of the acetic anhydride solution is easily calculated. As an independent check of the result, known weights of water are added to acetic anhydride to obtain a series of solutions of known extra acetic acid content (reagent C). Measurements are made on them by a similar procedure and separate Curves (not shown) are drawn for each solution and the total acetic acid (for solutions c) are calculated by the same procedure as above.
RESULTS AND DISCUSSION
As obtained by this method, acetic acid present in the anhydride sample is found to be 0,0685 mole per mole of acetic anhydride or 4.03% by weight (Table 1). To have an independent check of the accuracy of this Procedure, different percentages Of water are added to the anhydride and allowed to generate equivalent quantities of the acid. The
,
ANAL.C H E ~28, . 436 (1956). (2) Palit, S. R., ANAL. CHEM.33, 1441 (1961). (3) Palit, S. R., Chem. Ind. London 1960, p. 1531.
BHAIRAB CHANDRA MITRA PREMAMOY GHOSH SAKTIR. PALIT Indian Association for the Cultivation of Science, Jadavpur, Calcutta-32, India ONEof the authors (B. C. M.) received a scholarship from the Council of Scientifir & Industrial Research, Government of India.
Dissolution of Elemental Boron SIR: Elemental boron is generally dissolved by either a sodium carbonate fusion or by treatment with nitric acid with or without hydrogen peroxide and fusion of the insolubles remaining with sodium carbonate. Other less frequently used methods involving the use of solutions of such oxidizing agents as ceric sulfate, potassium periodate, iodate, permanganate, or dichromate are summarized by Vasilieva and Sokolova ( I ) , who also describe a hydrogen peroxide-potassium persulfate procedure. In work being carried out by the authors on the analysis of boron, none of these methods has been found to be completely satisfactory. The carbonate fusion is slow and is ordinarily limited to less than 300-mg. samples. Unsuccessful fusions are often obtained as a result of flaring, creeping, etc. Nitric acid dissolution results in the presence of nitrate in the final solution, and nitrate interferes seriously in one of the methods being developed for the determination of boron. Early in the present work, a composite method was 674
ANALYTICAL CHEMISTRY
devised in which the sample is treated with slightly less than the calculated amount of nitric acid, then sodium carbonate is added and, after evaporation, the residue is fused in platinum. A solution essentially free of nitrate is obtained but significant quantities of platinum, which also interfere, are present. The method, however, is convenient and potentially useful. Of the remaining dissolution methods, only the hydrogen peroxide-potassium persulfate mixture (1) was considered suitable for testing. Samples of finely divided pure boron weighing less than 200 mg. dissolved satisfactorily within an hour leaving only traces of residue that had to be fused with carbonate. However, with samples consisting of coarser particles or containing relatively large amounts of carbide, dissolution proceeded with difficulty and roughly half of 200-mg. samples remained undissolved after repeated reagent addition and prolonged boiling up to several hours. I n these cases, fusing the insolubles is nearly as troublesome as fusing the entire sample.
Powdered elemental boron can be dissolved smoothly and rapidly by fusion with potassium persulfate for 15 to 20 minutes in a quartz flask. KOattack on the quartz is apparent. Large quantities of persulfate must be used: 50 grams for 400-mg. samples; 60 grams for 800-mg. samples. Boron carbide in the sample dissolves readily but a slightly longer heating period is necessary. I n fusions made with boron carbide, 300-mg. samples dissolved satisfactorily in 50 grams of persulfate. High-temperature carbide, fired at greater than 2400" C., merely required longer heating periods. In an occasional sample, traces of material remaining undissolved when the cooled melt was taken up in water have been identified by x-ray diffraction as boron nitride. When nitride is present, the solution is filtered, the paper is moistened with sodium carbonate solution and ashed, and the residue is fused with 2 grams of sodium carbonate. This fusion presents none of the problems associated Tvith the original sample. Powdered samples must be used but
