Analysis of Mixtures of Terephthaloyl and lsophthaloyl Chlorides ERNEST J. BREDA Easfern Laboratory, E. 1. du Ponf de Nemours & Co., Gibbsfown, N. J. FTerephthaloyl chloride and isophthaloyl chloride are determined in mixtures containing both acid chlorides and the corresponding free acids by dissolving the acid chlorides in iso-octane, filtering off the insoluble free acids, and measuring the absorbance a t 2 2 7 and 2 6 3 mp. The concentrations of the acid chlorides are calculated by simultaneous equations. The average error of the method is +O.6yO absolute for terephthaloyl chloride and +1.3% absolute for isophthaloyl chloride in the 0 to 100% range. The method is best suited for concentrations of 5 to 95% acid chloride.
R
ESEARCH interest in terephthaloyl
and isophthaloyl chlorides has required a method of analysis for mixtures of these acid chlorides which are usually contaminated n'ith small amounts of terephthalic and isophthalic acids. Procedures are available for the determination of phthalic acid (1, 5, 6, 8, I O ) and its isomers ( I O ) in mixtures and in resins. Most published procedures are based on the measurement of ultraviolet absorbance of the acids in suitable solvents. Bryce-Smith (3) reported a procedure for the separation of isophthalic acid and terephthalic acid by means of the thallous salts which might afford a semiquantitative estimation of these acids. Methods
Table I .
are also available for the determination of total acid chlorides in mixtures (2, 7, 9). Although methods are available for the determination of the acids and the total acid chlorides, there has been no procedure that would distinguish the isomeric phthaloyl chlorides. The present method comprises a separation of the acid chlorides from the acids by washing the sample with iso-octane, followed by the measurement of the ultraviolet absorbance of the solution a t two wave lengths. The concentrations of the acid chlorides are calculated by simultaneous equations based on the absorptivities of the acid chlorides and the absorbances of the sample solution a t the chosen wave lengths. Table I shows the conventional structural formulas of the acid chlorides and some of their properties. APPARATUS A N D REAGENTS
Absorbance measurements were made with the Beckman hiIodel D U spectrophotometer and 1-cm. silica cells. A Fisher Filtrator, equipped with a long-stemmed glass funnel, a rubber ring, and tared sintered-glass crucibles, was used to filter the insoluble acids from the iso-octane solutions of the acid chlorides. The iso-octane (2.2.4-trimethvl~entane) was Spectro grade, boiling point 117.7" C. Pure terephthaloyl chloride and isophthaloyl chloride were prepared in
Structural Formulas and Some Properties of Isomeric Phthaloyl Chlorides
/\
c1
State M.P., "C. B.P., "C. Absorbance, Amax,, mp 2020
0
Terephthaloyl Chloride Solid 78-9 259 254, 263
ANALYTICAL CHEMISTRY
Symmetrical hthaloyl Phthaloyl Chloride Ciloride Solid Liquid
Is0
41 276 227
16 281 243
Asymmetric Phthaloyl Chloride Solid 88-9 275 (720 mm.)
...
this laboratory. The acid chlorides were purified by recrystallization from iso-octane and dried in an Abderhalden apparatus. The most probable impurity in a relatively pure acid chloride is the corresponding free acid. Twephthalic acid and isophthalic acid are substantially insoluble in iso-octane and were shown to be absent in the purified acid chlorides by the absence of isooctane-insoluble matter. I n addition, the purities of the acid chlorides were determined by a direct titrimetric method (6) developed in this laboratory; both were 99.9% pure. Terephthalic acid (neutral equivalent 83.16) and isophthalic acid (neutral equivalent 83.04) of high purities were available from research programs at this laboratory. Symmetrical phthaloyl chloride (practical grade, Matheson Co., Inc., East Rutherford, N. J., No. P6155) was purified by distillation, boiling point 281" C. a t 1-atm. pressure. The center one-third fraction of the distillate was used. A fourth isomer, the asymmetric phthaloyl chloride (3,3-dichlorophthalide) was not readily available and was not included. No appreciable amount of this compound was ever found in the materials analyzed and its presence was considered very unlikely.
RECOMMENDED PROCEDURE
Separation of Acid and Acid Chloride. Weigh rapidly and accurately 0.4 t o 0.6 gram of sample in a tared, medium-porosity, sintered-glass crucible. Mount t h e crucible on t h e Filtrator using a 50-ml. volumetric flask t o receive the filtrate. Add 3 t o 5 ml. of Spectro-grade iso-octane t o t h e sides of t h e crucible and slurry t h e mixture with a glass rod. S t a r t the Filtrator. Very slowly and carefully draw the liquid into the 50-ml. volumetric flask. Repeat the slurrying and filtration about seven or eight times. Wash the underside of the crucible and the top and stem of the funnel with a fine stream of solvent. Fill the flask to the neck, insert the stopper, and reserve for the ultraviolet absorbance measurements described below. D r y the crucible in air for 15 minutes, then place in a desiccator for 2 hours, and weigh. Calculate the weight of the insoluble residue as per cent acids, and the loss in weight of the sample as per cent total acid chlorides.
2.0
solution, the absorptivities were:
I I
I
A
227
mr Terephthaloyl chloride 0.226 Isophthaloyl chloride 3.500
263 mfi
2.121 0.037
EQUATIONS FOR CALCULATION OF COMPOSITIONS FROM ABSORBANCES
The absorptivities were used to set up simultaneous equations for absorbances at 227 and 263 mg in terms of concentrations of terephthaloyl chloride and isophthaloyl chloride. These simultaneous equations were solved to give expressions for concentrations in terms of absorbances. The equations for calculation of compositions from absorbances a-ere developed from the additive form of the Bouguer-Beer equation for two-coniponent mixtures according t o the method used by Vaughn and Stearn (11). The final equations for the calculation of concentrations are
Figure 1. Ultraviolet spectra of terephthaloyl, isophthaloyl, and phthaloyl chlorides in iso-octane
1.0 mg. of acid chloride in 100 ml. A . Isophthaloyl chloride B. Terephthaloyl chloride C . Phthaloyl chloride Preparation of Calibration Curves. Weigh 0.0500 gram of acid chloride in a tared, sintered-glass crucible. Extract and dilute t o 50 nil. as in t h e separation of acid and acid chloride. D r y and weigh t h e crucible t o determine t h e actual weight of acid chloride transferred. Dilute 5 ml. of t h e stock solution t o 100 ml. with iso-octane. Transfer suitable (1-, 2-. 3-, 4-. and 5-ml.) aliquots of the second solution into 50-ml. vol1:metric flasks and adjust the volume to 50 ml. a t 25" C. (or other convenient constant temperature) with iso-octane. Determine the absorbance a t 227 and 263 mp and plot both against the milligrams of acid chloride in 50 ml. on coordinate graph paper. From the slopes of the straight lines, calculate absorptivities and thence the equations for the concentrations of the two acid chlorides. Analysis of Sample. Measure t h e absorbance of t h e filtrate from t h e free acids a t 227 and 263 mp, a t an appropriate dilution ( A = 0.025 to 0.800) and adequately controlled temperature. Calculate the concentrations of the two acid chlorides in the final solution and thence the percentages of the two isomers in the original sample.
ULTRAVIOLET SPECTRA
The ultraviolet spectra of terephthaloyl, isophthaloyl, and symmetrical phthaloyl chlorides in iso-octane were determined and are shown in Figure 1. The maximum absorbance of isophthaloyl chloride is at 227 mp, where the absorptivity of terephthaloyl chloride is only about one fifteenth that of isophthaloyl chloride. Terephthaloyl chloride shows absorbance peaks a t 254 and 263 mp. The smaller peak at 227, 263 mp was chosen for this work because there is less interference by isophthaloyl chloride a t 263 than a t 254 mp. At 263 mp the absorptivity of isophthaloyl
chloride is only about one fiftieth that of terephthaloyl chloride. Solutions containing different concentrations of terephthaloyl chloride were prepared by dissolving 50.0 nig. in 50 ml. of iso-octane and diluting suitable aliquots to 50 ml. in volumetric flasks. Absorbances were measured a t 227,243, and 263 mp. Both the terephthaloyl and the isophthaloyl chloride data show substantial conformation to the Bouguer-Beer law. Absorbance measurements a t 243 m p were made to determine the extent of interference by terephthaloyl and isophthaloyl chlorides in a possible determination of phthaloyl chloride by this method. A t a cell depth of 1.000 em. and a concentration in milligrams per 50 ml. of
= 0.2860 AZ1 - 0.0305 AZB3= mg. of isophthaloyl chloride per 50 ml. of
C,
final solution Ct = 0.4720 Anea- 0.0049 A22i = mg. of tere hthaloyl chloride per 50 ml. of final soition ANALYSIS OF KNOWN MIXTURES
T o test the equations, known mixtures of terephthaloyl and isophthaloyl chlorides were analyzed by the spectrophotometric method (Table 11). The results were not highly accurate but were adequate for the purpose. Table I11 shows typical results obtained on knoivn mixtures containing some acid. The difference betreen
Table 11.
Terephthaloyl and Isophthaloyl Chloride Recoveries on Known Mixtures Containing No Acid
Mixture KO.
Terephthaloyl Chloride, Yo Taken Found Error
1 2 3 4 5 6 7 8 9
98.6 94.1 86.0 78.9 49.8 29.4 9.5 5.5 2.5
99.0 94.9 86.3 79.6 49.4 29.5 9.8 4.9 1.0 Av. error, 70
Isophthalogl Chloride, 7c Taken Found Error 1.0 5.1 13.6 20.4 50.6 70.5 90.2 95.1 99.0
-0.4 -0.8 -0.3 -0.7 +0.4 -0.1 -0.3 +0.6 f1.5 +O. 56
2.4 (3.7 15.2 21.9 51.4 71.3 91.3 96.1 101.1
+1.4 $1.6 +1.e +l.5 +0.8 $0.8 +1.1 +1.0 +2.1 $1.32
Table 111.
Analysis of Known Mixtures of Terephthaloyl and lsophthaloyl Chloride after Separation of Acids
hlixture No.
Terephthaloyl Chloride, yo Taken Found Error 5.i 2
55 1
Isophthaloyl Chloride, yo Taken Found Error
-n. 1_
44.8 -0.3 28.9 +0.4 61.9 38.1 38.5 54.6 44.8 55.2 -0.6 21.0 21.4 $0.4 9.9 30.1 60.2 -0.3 59.9 75.4 24.0 24.1 +o. 1 First four mixtures contained less than 0.1% total acid taken. 1
7i.i
70.8
~~
43 2 28.9 60.6 42.6 9.2 30.7 75.9
VOL. 30, NO. 12, DECEMBER 1958
-1.6 0.0 -1.3 -2.2 -0.7
+o.e $0.5
2021
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.
(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)
DISCUSSION
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,
LITERATURE CITED
(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. -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).
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).
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
2022
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-
