before reaching the mark Fill remedy this. In earl it^ work ( 4 ,the color of the trioxalatochromium(II1) ion interfered with the end point in the iodometric determination of copper. The incorporation of KTCr in the blank solution in approximately the same concentration as was present in the solutions
( 2 ) Blaedel, W. J., Todd, J. W., ANAL.
being measured corrected for this interference. This procedure is recommended for the determinat'ion of glycine in glycinecopper complex because of its simplicity and speed.
CHEM.32,1018(1960). (3) Schroeder, W.A., Kay, L. & Mills, 'I., R. S., Ibid., 22, 760 (1950). (4) Smith, G. F., McCurdy, W. H., Ibid., 24,371 (1952). (5) Spaulding, G. H., Ibid., 31, 1109 (1909).
LITERATURE CITED
(1) Albert, A., Biochem. J . 47, (1950); 50, 690 (1952).
531
RECEIVED for review September 27, 1961. Accepted November 30, 1961.
Ultraviolet Spectrophotometric Determination of Benzoic Acid in Refined Phthalic Anhydride RAITA MURNIEKS and C. E. GONTER Research and Development Department, Pittsburgh Chemical Co., Neville Island, Pittsburgh 25, Pa.
b Benzoic acid in chloroform can be determined spectrophotometrically at 274 mp. The determination requires complete removal of phthalic anhydride, phthalic acid, and 1,4-naphthoquinone, which also absorb strongly at this wavelength. Standard methods for separation of benzoic acid from phthalic anhydride were found inapplicable at concentrations of less than 0.570 benzoic acid. Good separation was achieved at pH 4.00 b y conversion of phthalic anhydride to the monosodium salt of phthalic acid followed by chloroform extraction. 1,4-Naphthoquinone can be removed b y acid potassium permanganate. The described method determines benzoic acid in refined phthalic anhydride in the concentration range below 0.5y0 with a relative error of =k2Oa/,.
0.1 -
\
L
-
-
253
control of small amounts of impurities in refined phthalic anhydride (PAX) becomes increasingly important when the anhydride is used for the manufacture of plasticizers. Because the odor of the esters of benzoic acid is particularly objectionable, it is necessary to keep this acid impurity a t a minimum in the P=iA-i.e., less than 0.275, Ideally, a spectrophotometric procedure would appear to be the most practical for determining low concentrations of benzoic acid, since the acid shows some absorption throughout most of the ultraviolet region with a me11 defined peak of maximum absorption a t 274 mp. However, PAA, phthalic acid, and 1,4-naphthoquinone also show maximum absorption a t this wavelength (Figure 1) and must therefore be removed. Quantitative separation of amounts greater than 2% of benzoic acid from HE
L
270
L%NE LEhGTY
Figure 1.
T
A
\
&
L
-
U
3lG
233
330
MiLLIVCROhS
Absorption spectra in chloroform
- Benzoic acid - -.- - - - -. Phthalic acid -_1,4-Naphthoquinone phthalic acid can be effected by chloroform extraction and subsequent titration with standard alkali ( 2 ) . The separation proposed by Kappelmeier (3) and refined by Swann, Adams, and Weil (6) employing anhydrous potassium hydroxide is applicable below 2% but is not sufficiently sensitive for complete separation of less than 0.5% benzoic acid from PAA. Aforeover, no means could be found in this procedure for eliminating interference from the basic hydrolysis product of 1,4-naphthoquinone. The present investigation describes an ultraviolet spectrophotometric procedure for the determination of benzoic acid in P A S containing less than 0.5% benzoic acid and up to 50 p.p.m. of (5). Greater 1,4-naphthoquinone
amounts of the latter are removed by pretreatment with acidic potassium permanganate (4). APPARATUS AND REAGENTS
SDectroDhotometer. Beckman hfodel
DK'-2.
A
AbsorDtion cells. silica. 1.0-cm. 6N hydrochloric acid. ' Phthalic acid anhydride, recrystallized from chloroform. Benzoic acid, National Bureau of Standards. Benzoic acid standard solution, 1.0000 gram of NBS benzoic acid in 1 liter of distilled water. CALIBRATION PROCEDURE
Pipet 0.0 (reference), 2.0, 4.0, 6.0, and 8.0 ml. of benzoic acid standard VOL. 34, NO. 2, FEBRUARY 1962
197
oil-
q-c\P-o- e
I
3.0
2.0
4.0
5.0
pH of E X T R A C T I O N
Figure 2. Extraction of benzoic acid from solutions of phthalic acid BA f PA in CHCl3 VI. PA reference 6. PA in CHC13 VI. CHC13 reference
A.
solution into 250-ml. Erlenmeyer flasks each containing 2 grams of recrystallized PAA. Add 25 ml. of 4% sodium hydroxide solution. Fit the flasks with condensers. Reflux for 20 minutes on a hot plate. Remove the flasks from the heat and rinse the condensers lvith minimum amounts of distilled water. Remove the flasks from the condensers and cool to room temperature. Quantitatively transfer the contents of the flasks into 150-ml. beakers. Adjust the p H of each solution to 4.00 with 6N HC1. Quantitatively transfer the solutions into 250-ml. separatory fun-
Table I. Recovery of Benzoic Acid from PAA Containing 1,4-Naphthoquinone
(Each sample contained 2.0000 grams PA.4)
1,4-KQ Added, P.P.M.
BA Present, Rig.
4.0 4.0
BA Recovery,
Mg.
%
3.8 4.3 4.5 4.7
108
0.0 20.0 40.0 60.0
4.0 4.0
1
2 3 4
5
Source Samp1es Analysts S-A Exptl. error Total
Figure 3. A.
8. C.
+
nels. Dilute t o 50 ml. with distilled water. Serially extract with three portions of chloroform: 50.0-, 25,0-* and 25.0ml. Combine the chloroform extracts in dry, 100-ml. volumetric flasks and mix thoroughly. To remove the last traces of water filter the solutions through Whatman No. 1 filter paper into dry, 100-ml. volumetric flasks. (Do not dilute to volume.) (Volumetric flasks are used to eliminate loss of chloroform by evaporation.) Determine the absorbances of the solutions a t 274 mp against the reference solution, using matched 1.0-em. silica adsorption cells and a slit width of 0.188 mm. ANALYSIS
ss 0.5329
0.0028
0.0134 0.0054 0.5545
df 4
OF
SAMPLES
Accurately iveigh 2 grams of sample into a 250-ml. Erlenmeyer flask. Treat
2 8 15
29
ANALYTICAL CHEMISTRY
Av. 0.18
0.14 0.13 0.49 0.19
Analysis of Variance MS Estimate of M S 0.1332 U E ~ g(rSA2 rgas2 0.0014 u E 2 $- g U S A 2 cgfl.4' 0.0017 UEz ggSAz 0.0004 UE2
+
+
I. C H C ! 3
BA in CHC13 BA PA in CHCIa, extracted at pH 4.0 BA f PA in CHC13, acid KMnOd treated and extracted a t pH 4
95
112 118
BA/
Calibration and recovery of benzoic acid
Table II. Precision of Method yo Benzoic Acid B B C 0.17 0.18 0.20 0.15 0.18 0.17 0.14 0.18 0.13 0.14 0.15 0.12 0.13 0.13 0.14 0.13 0.13 0.13 0.45 0.46 0.60 0.44 0.47 0.51 0.19 0.18 0.18 0.19 0.18 0.19
Sample
198
BA Recovered,
gm.
++
-F
0.82
according to the procedure for calibration, Determine the absorbance a t 274 mp against a reference solution prepared using recrystallized PAA. EXPERIMENTAL
Since the solubility of benzoic acid is greater in chloroform than in mater (distribution coefficients from 2 to 4), it can be quantitatively removed from aqueous solution by serial estraction with chloroform. Phthalic acid has limited solubility both in water and in chloroform, and small amounts of the acid can be extracted n i t h the organic solvent. However, it u-as found impossible to obtain a constant concentration of phthalic acid in chloroform extracts, thus ruling out the use of a differential technique for determining the benzoic acid spectrophotometrically. Benzoic acid and P.IA can he easily converted into the sodium snlts of the respective acids by addition of sodium hydroxide. The respective acids can be regenerated by the addition of hydrochloric acid. The monosodium salt of phthalic acid is very soluble in n-ater and cannot be extracted from aqueous solution with organic solvents. The dissociat,ion constants of phthalic acid in aqueous solution are 1.3 X 10- a and 3.1 X 10-6. and that for benzoic acid is 6.3 x 10-5. It was therefore expected that at some p H b e h e e n 3 and 5 the phthalic acid would exist as the monosodium salt, and the benzoic acid as the free acid. The optimum working p H of 4.0 was determined (Figure 2) from a series of determinations with recrystallized PAA.
INTERFERENCES
1,4-Naphthoquinone, its adducts and addition products, and o-toluic acid are possible sources of interference in refined PAA. Any maleic anhydride, maleic acid, or fumaric acid present in the material will react similarly to the P h A and will not interfere. 1,4-Naphthoquinone is soluble in alkali with decomposition. Under the conditions of the procedure some naphthoquinone, its decomposition products, or its adducts are extracted and absorb a t various wavelengths between 290 and 240 mp, A series of samples containing 2 grams of recrystallized P.U, 4 mg. of benzoic acid, and various amounts of 1,4-naphthoquinone was treated according to the sample procedure. The data in Table I show that up to 50 p.p.m. of 1,4-naphthoquinone will not cause more than experimental error in the final result. For PAA containing higher concentrations of 1,4-naphthoquinone the following procedure was used.
To the 2-gram sample of PAA add 25.0 ml. of 1 to 19 (by volume) sulfuric acid solution. Heat the mixture under reflux to 75’ to 80’ C. on a steam bath. .4dd 5 ml. of 5% potassium permanganate solution and continue heating for 30 minutes. Neutralize the mixture with 5 ml. of 10X sodium hydroxide solution and heat for 10 minutes or until all of the PAA is in solution. Cool to room temperature. Adjust the pH of the solution to 4.0 with 6.V HC1. Filter through Whatman KO.1 filter paper. Dilute, extract, and measure the absorbance as directed in the procedure. Prepare the blank and calibration accordingly. By this pretreatment benzoic acid has been suc-
cessfully determined in P.4A containing as high as 500 p.p.m. of 1,4-naphthoquinone. o-Toluic acid was found to exhibit the same properties as benzoic acid, in that it can be extracted under the conditions of the test, and its absorptivity in chloroform is of the same order as that of benzoic acid. Claims have been made (1) that i t can be converted into phthalic acid by heating with basic potassium permanganate. Ten milliliters of a solution containing 0.5 gram of o-toluic acid per liter, 5 ml. of 1.OM sodium hydroxide, and 5 ml. of 570 potassium permanganate were refluxed for 30 minutes. The solution was cooled, filtered, and treated according to the procedure. There was no absorbance in the 300- to 250-mp region, which indicates that the interference of o-toluic acid was removed. Using the above data the recovery of benzoic acid in the hydrolysis-extraction procedure is 92%, and with the permanganate pretreatment is 84Y0. Since no equivalent methods were available for the determination of these quantities of benzoic acid, the respective absorptivities were used with each procedure, and the relative recovery of benzoic acid was assumed to be 100%. A statistical study of the hydrolysisextraction procedure was conducted by three analysts on 2 days. Benzoic acid was determined in two production and three competitive samples of refined PAA which were manufactured from both naphthalene and mixed (0-xylenenaphthalene) feeds (Table 11). Since the ratio 0.0014/0.0017 from the analysis of variance is less than I,
the analyst error is obviously not significant when the F test is applied. The “experimental error,” u E 2 , is an estimate of the reproducibility of duplicates by a given analyst. As usuaI, it is a gross understatement of the true error of the method. For this reason the effects are tested against the interaction error. The precision of the method obtained from the pooled error mean squares is estimated a t &0.04% or 25% of the amount present. The standard deviation of duplicate determinations is &0.02%; the standard deviation for the method is = ! ~ 0 . 0 4 ~ ~ , which amounts to 20% relative error in P A 4 containing less than 0.2% benzoic acid. ACKNOWLEDGMENT
The authors acknowledge the technical assistance of J. R. Lutchko, Milton Manes, and J. J. Petty. LITERATURE CITED
(1) Claus, A., Pieszcek, E., Ber. 19, 3085 (1886). (2) Gilman, H., Kirby, J. E., J. Am. Chem. SOC.54,345 (1932). (3) Kappelmeier, C. P. A., Farben-Ztg. 40, 1141 (1935); 41, 161 (1936); 42, 561 (1935); Paint Oil Chem. Rev. 6 , 10 (1937). (4) Miller, O., Chern. Zentr. 1914, I, 790. (5) Peters, H., ANAL. CHEAI.31, 1326 (1959). (6) Swann, M. H., Adams, M. L., Weil, D. J., Ibid., 28,72 (1956). RECEIVEDfor review .4ugust 2, 1961 Accented October 30. 1961. Division of Analitical Chemistrk, 139th Meeting, ACS, St. Louis, No., March 1961.
The Spectrophotometric Determination of AbieticType Dienoic Rosin Acids ROBERT L. STEPHENS and RAY V. LAWRENCE Naval Stores laboratory, Olustee, Fla.
b A
procedure employing a modified Liebermann reaction for the quantitative determination of abietic-type dienoic rosin acids is presented. The acids are determined spectrophotometrically at a wavelength of 570 mp in the concentration range of 30 to 150 pg. The behavior of related compounds under the test conditions is discussed.
T
HE PRESENCE of many organic compounds in natural and synthetic mixtures can be demonstrated by qualitative color tests which vary in
degree of selectivity and sensitivity. In the field of rosin chemistry, several tests have been used to detect rosin and rosin derivatives under a variety of conditions. A discussion of these tests has recently been presented by Conner (2). The Liebermann reaction (4) with modification by Storch (6), Burchard ( I ) , and other investigators (2, 3) has been widely applied to the detection of rosin and rosin derivatives. In general, a positive t,est is based on the formation of a “fugitive or transient violet” color when the sample, in acetic anhydride,
is treated with concentrated sulfuric acid. In most cases, the violet rapidly changes to a nondescript brown which is not specific for this group of constituents. Swann (6) has modified the general test and applied it to the qualitative and quantitative determination of rosin and rosin derivatives in surface coatings. Since the Liebermann reaction is highly sensitive, there is some danger in the application of this test to complex materials, for even trace impurities may produce colors which are similar, therefore creating some confusion with respect VOL. 34,
NO. 2,
FEBRUARY 1962
199
