100% and the sum of the two acid chloride figures roughly represents the acid content.
absorbs a t 290 nip. At 227 and 263 nip the absorbance is too low to interfere significantly.
DISCUSSION
LITERATURE CITED
If phthaloyl chloride is also present, it is necessary to measure the absorbaiice of the solution a t three nave lengths and derive three appropriate equations. I n this TT ork, however, only mixtures of terephthaloyl chloride and isophthaloyl chloride were of concern. Thionyl chloride, S0Cl2, a chemical used to convert acids to acid chlorides,
(1) Am. SOC.Testing Materials, .‘ASThI
Standards,” designations 1) 1307 and D 1306, 1951. ( 2 ) Bauer, S. T., Oil & Soup 23, 1 (1946). (3) Bryce-Smith, D., Cheni. R. Znd. (London1 1953. 2-14. --
(6) Lohr, L. J., private comniunication. (7) Pesez, 11,,Killemont, R., Buli. soc. chir?~.France 15, 479 (1918). ( 8 ) Shreve, 0. I),, Heether, 11. E., - 4 x . l ~ CHEX . 23, 441 (1951). (‘3) Siggiu, S., ”Quantitative Oryaiiic .Innlysis via Functional Groups,” 2nd ed., p. 56, Kiley; S e w Tork, 1954. (10) Swsnn, 11. H.!Adanis, 11. L., \Veil, 1). J., .%SAL. CHEX 27, 1604 (1955). (11) Viughn, R. T., Stearn, -4, E,, Zhid., 21, 1361-3 (1949).
I
(-i)’-Furman, S . ’H., Bricker, C. E., J . d i n . rhein. Soc. 64, 660 (1942). ( 5 ) Garn, P. D., Ha!line, E. IT.,AXAL. CHEM.27, 1563 (1955).
RECEIVEDfor revieiv May 9, 1958. Accepted August 2, 1958. Delatvare Valley, Second Regional Meeting, rlCH, Philadelphia, Pa., February 5, 1958.
Determination of ToIuenesuIfonic Acids in Presence of an Excess of Sulfuric Acid SHRAGA PINCHAS and PINCHAS AVINUR The Weizrnann lnstitufe of Science, Rehovoth, Israel
Mixtures of the three isomeric toluenesulfonic acids, obtained from toluene and sulfuric acid a t room temperature, can b e determined spectrophotometrically in the presence of a large excess of sulfuric acid on the basis of their absorption a t 2220 A. Satisfactory results are obtained for the total amount of acids by using a mean absorptivity. The ultraviolet absorption curves of the individual isomers are given.
is in agreement with that given in the American Petroleum Institute catalog of ultraviolet spectra ( 2 ) . The concentrations in the A P I curve are however in error by a factor of about 4 (9), as is also evident from the absorptivities a t 2220 and 2610 A , calculated froin them. They appear to be too high and are also contradicted by Figure 1. Figure 2 s h o w the ultraviolet absorption of o- and m-toluenesulfonic acid. EXPERIMENTAL
I
with a n investigation aimed to find the optimal conditions for the exchange of tritium between sulfuric acid and toluene a t room teniperature ( I ) , a n easy method was needed for the quantitative determination of the total amount of the three isomeric toluenesulfonic acids, formed as a by-product, in the presence of a large excess of sulfuric acid. A search of the literature revealed that no such method existed. Toluenesulfonic acids or benzenesulfonic acid in the presence of sulfuric acid are determined by measuring the total acidity and correcting for the sulfuric acid ( 3 , 5 ) . The possibility of solving this problem by ultraviolet spectroscopy was therefore investigated, all the isomeric toluenesulfonic acids being expected to absorb strongly in this region. Figure 1 s h o w the absorption of p-toluenesulfonic acid in solution in distilled water; the absorption peak a t 2220 A. is strong enough to enable a spectrophotometric determination of this acid, in the presence of an excess of sulfuric acid. The shape of the curve N CONKECTION
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ANALYTICAL CHEMISTRY
The p-toluenesulfonic acid usrd for the absorption measurements was of a commercial, pure grade and \\-as further purified by recrystallization from hydrochloric acid. After drying in a desiccator over calcium chloride and pellets of potassium hydroxide its melting point was 105” to 107’ C. It was then in the form of monohydrate (6) as was also evident from a Karl Fischer mater content determination. The o-toluenesulfonic acid was prepared in solution by sulfonating toluene in the usual way, precipitating the niixture of the acids with barium chloride. recrystallizing the barium toluenesnlfonates repeatedly from vxiter, accorcling to Holleman and Caland ( 7 ) . drying a t 100” C., and finally acidifying the solution of the pure barium o-toluenesulfonate thus obtained. The purity of this salt was proved by the identity of the infrared spectra taken in a Kujol mull before and after a further recrystallization. The m-toluenesulfonic acid used was synthesized by oxidizing m-thiocresol ( 8 ) ,according to Holleman and Caland ( 7 ) , precipitating the acid with barium chloride, recrystallizing the salt from water, drying a t 100” C., and acidifying its solution in distilled mater.
The ultraviolet absorption measurements nere carried out in a 1-em. cell in a Beckman DE spectrophotometer and the difference in absorbance between the solution cell and the blank cell was taken into account in the calculations. Solutions of p-Toluenesulfonic Acid. p-Toluenesulfonic acid solutions of various concentrations \\-ere examined a t their maximum absorption peak a t 2220 A. It was found that they obey Beer’s law, their absorptiyity being alnays 55.6 f 1.3 (calculated for a 1-gram per liter of monohydrate solution). Table I summarizes the results obtained. Table I s h o w clearly that even a very large excess of sulfuric acid (of over 600 to 1) would not interfere with the spectrophotometric determination of p-toluenesulfonic acid on the basis of its absorption a t 2220 A. It can be further seen from the table that although moderate amounts of toluene do not change the absorbance of the p-toluenewlfonic acid solution appreciably, larger concentrations make i t unreliahle for quaiititative analysis, unless the evact amount of toluene present is knon n and the absorbance of the solution is corrected for it. That toluene has indeed a relatively low, but still definite, absorption a t about 2220 A. is also evident from its published spectrum (4). DETERMINATION OF MIXED TOLUENESULFONIC ACIDS
As can be seen from Figure 2, the intensity of the absorption of o-toluene-
4 2
38
3 4
30 A
I
2 6
u, 0
0
2 2
18
\
14
I
I 1
10
2100
I
2300
I
I
I
2500
I
I
I
I
I
I
2500
I
I
2 700
I 2 9 0 0 A.
2 9 0 0 A.
2700
-1-. . Figure 1. Ultraviolet absorption of p-toluenesulfonic acid monohydrate
sulfonic acid a t 2220 A. is almost equal to that of p-toluenesulfonic acid. Thus the absorptivity of the dry ortho isomer is equal to 59, while it is 55.6 in the case of the para isomer monohydrate and 61.5 for the dry acid. The absorptivity of the meta isomer a t this frequency was found to be 44. The amount of this isomer in the mixture of toluenesulfonic acids obtained by the sulfonation of toluene a t room temperature is about 4 to 6% (7). The ortho isomer is formed to the extent of 30 to 35%; it seems therefore that taking a mean value of 80 for the absorptivity of all the dry isomeric acids will cause no mistake in their quantitative determination in the products of a room temperature reaction. I n fact, various samples of known toluenesulfonic acids content were measured and their concentration calculated from the absorbance a t 2220 A , using this value as the mean absorptivity. Table I1 shows t h a t the agreement with the known concentration n as satisfactory. T h e n the absorption was measured :it the absorption peak of the examined solution (even if this point actly a t 2220 A.) and this value was used for the calculation, better agreement with the actual concentration was obtained. It was also found that moderate amounts of toluene and even a high concentration of sulfuric acid did not interfere with the determination of the mixed toluenesulfonic acids by this method, just as in the case of p-tolucnesulfonic acid. Many samples, containing mixed toluenesulfonic acids. were analyzed (1) by this method, after being dissolved in distilled rrater to form solutions of about 0.01 g r m i per liter.
2300
2100
*
Figure 2. Ultraviolet absorption of rn- and o-toluenesulfonic acids
Table 1. Absorption of Various Aqueous Solutions of p-Toluenesulfonic Acid Monohydrate a t 2220 A.
Concentration, Gram/ Liter 0.00708 0.00885 0.00912
0.01058 0.0112 0.00579 0.0089
Additional Constituents
... ... ...
...
H~SO;\dilute solution) 1.8 8.A.
Absorbance. 0.403 0.485 0.515 0.587 0.61
Absorp-
tivity 56.9 54.8 56.5 55.5 54.5
0.325 5 6 . 1
H 3 0 4 0.50 12 g./l. HiSOi 0.895 0.0160 0.01058 0.014 E./]. toluene 0.571 0.01175 0 . 1 g./l. toluene 0.69 0.0023 Toluene (sat-
Actual Concentration, Gram/ Liter 0.00257 0.00433 0.00512 0.00730 0 00797
Absorbante
Calcd. Concn.
0.15 0.265 0.315 0.44 0.485
0.00250 0.00441 0.00525 0,00733 0.00808
Mean deviation
Deviation,
% -2.8 $1.8 $2.5 $0.4 $1.4 1.8
56.1 55.9 540 58. ia
urated solution diluted a
Table II. Analyses of Mixtures of Isomeric Toluenesulfonic Acids Dissolved in Water
1:5) 0.18 78“ Not corrected for toluene content.
The results checked well with those obtained from the decrease in the volume of the toluene. When samples from a reaction mixture were taken out a t different times, the plot of their spectrophotometrically determined content of sulfonic acids against time was in agreement with theory. K h e n such samples are analyzed, i t is important to take care that they are homogeneous, as one of the isomers often crystallizes out on standing. They must also be weighed and dissolved in distilled water as rapidly as possible, because upon standing undiluted such samples tend to undergo a chemical change as evidenced by the black color they develop.
LITERATURE CITED
(1) Avinur, P., Nir, A., Bull. Research Council Zsrael ”A, 73 (1958). (2) California Research Corp., “Ultra-
violet Spectral Data Catalog,” American Petroleum Institute, curve 114,
1945. (3) Englund, S. K., Aries, R . S., Othmer, D. F., Znd. Eng. Chem. 45, 189 (1953). 14) Ethvl Corm. “Ultraviolet Saectral
Data “ Catal6g,” American Pet;oleum Institute, curve 19, 1945. ( 5 ) Harvey, A. W., Stegeman, G., Ind. Eng. Chem. 16, 842 (1924). (6) Heilbron, I. M., Bunbury, H. RI., “Dictionary of Organic Compounds,” Vol. 111, p. i i 5 , Eyre and Spottifiwoode, London, 1937. ( i )Holleman, A. F., Caland, P., Ber. dezct. chem. Ges. 44, 2504 (1911). (8) Tarhell, T. S., Fukushima, D. K., “Organic Syntheses,” Coll. Vol. 111, p. 809, Wiley, New York, 1955. (9) California Research Corp., private communication from R. L. LeTourneau.
RECEIVEDfor review February 4, 1058. Accepted August 4, 1958. Division of Analytical Chemistry, 4th Meeting, Israel Chemical Society, Tel-Aviv, Israel. VOL. 30, NO. 12, DECEMBER 1958
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