1886
ANALYTICAL CHEMISTRY
in quantity greater than 5 to lo%, the eflect can be neglected
(1,6). Except when an absorption edge occurs between U L a and ThLa lines, the line of longer wave length, ThLa, is absorbed to a slightly greater extent. The fluorescence yield factors of uranium and thorium are essentially equal. The excitation voltage for the thorium L series is less than for the uranium L series, so that for a given applied voltage the excitation voltage of thorium is exceeded by a larger value. These various effects are compensating, so that no correction was found necessary within the limits of these analyses. The method is based on a linear relationship between line intensities and concentrations of the elements. When the relative amounts of theee elements vary greatly this will be only approximately correct. However, up to about 10% uranium or thorium, this relationship is linear except for matrices of lo^ x-ray density. The x-ray intensities are measured in the linear range of the Geiger tube or a dead time correction is applied. The scintillation counter with its low counting loss is linear up to 3000 to 4000 counts per second and is sensitive to U L a and ThLa. This study indicates that the scintillation counter is the superior detector for this analysis.
ACKNOWLEDGMENT
A number of chemically analyzed samples were supplied by Frank Grimaldi of the U. S. Geological Survey; his cooperation is gratefully appreciated. LITERATURE CITED
(1) Adler, I., and Alexrod, J. iM., Spectrochim. Acta, 7, 91 (1955). (2) Am. Soc. Testing Materials, Philadelphia, Pa., Special Tech. Bull. 157 (1954). (3) Birks, L. S., Brooks, E. J., and Friedman, H., ANAL.CHEM.,25, (4)
(5) (6)
(7) (8)
692 (1953). Campbell, mi. J., and Carl, H. F., Ibid., 26, 800 (1954). Campbell, W. J., Carl, H. F., and White, C. E., Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa., Paper 89 (1955). Campbell, W. J., and Parker, J., Bur. Nines, Inform. Circ. 7725 (1965). Fine, S.,and Hendee, C. F., North American Philips Co., Mount Vernon, N. Y., Tech. Rept. 86 (1954). Grimaldi, Frank, private communication.
RECEIVED for review June 7, 1955. Accepted July 30, 1955. Presented in part, Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa., March 1955, and Fourth Annual X-Ray Symposium, Denver Research Institute, University of Denver, Denver, Colo., August 1955.
Quantitative Infrared Analysis of Alkyl Phenol Mixtures F. V. FAIR and R. 1. FRIEDRICH Research and Development Division, Pittsburgh Consolidation Coal Co., Library, Pa.
A method is described for determining the quantitative distribution of phenol, the three isomeric cresols, the six isomeric xylenols, and several isomeric trimethylphenols in coal tar or tar acid oil. The phenolic compounds are extracted from the other organic compounds present with aqueous sodium hydroxide. After springing the phenols with sulfuric acid, they are dried using benzene in a Dean-Stark apparatus. The dried mixture of phenols is fractionally distilled at 50 mm. of mercury to yield five fractions. The cut points of initial boiling point to 113"C., 113" to 121",121' to 127",127' to 134', and 134' to 144' C.-all column pressures being 50 mm. of mercury-were selected to remove interfering pairs of isomers from samples subjected to infrared analysis. Interferences and analytical wave lengths, as well as details of the procedure, are given.
D
URING research on the low temperature carbonization of bituminous coal, the need arose for a rapid and accurate method for determining the isomer distribution of phenolic compounds in the tar fraction boiling below 230' C. Because of the similar properties of many of the isomers, they cannot be quantitatively separated by distillation, crystallization, or other physical means, Although several methods (3,8, 1 2 ) have been developed based on chromatography, they are applicable only to a small number of isomers and require rigid control of conditions. Chemical methods of analysis are usually limited to the determination of total phenolic compounds. Stevens ( 1 1 ) has published a method for the separation of rn-cresol from p-cresol and 2,4-xylenol from 2,5-xylenol by butylation and debutylation; however, this method does not permit the differentiation of all the tar acids. The limitations of the chemical methods also exist for most instrumental techniques. The very close oxidation potentials prevent the application of electrical methods (6, 7 , 9 ) . Emission spectroscopy is, of couriie, useless, and very little has been reported on the use of a mass spectrometer as applied to this type of problem.
Several authors ( I , 2 ) have used ultraviolet and visible absorption spectroscopy for the analysis of a few mixtures, but the small number of broad absorption bands confines these methods to rather simple mixtures. Ando (I), Friedel (6),and m i e n (13) have shown that infrared spectroscopy is suitable for analysis,
Table I.
Preparation of Pure Compounds for Calibration
Compound Benzene Phenol o-Cresol m-Cresol p-Cresol 2 6-Xylenol 2'4-xylenol 2'5-~ylenol 3:4-~ylenol 3,5-Xylenol
Original Source Thiophene-free 9 C S grade Mallinckrodt C.P. Reilly Co., 98% Reilly Co., 98% Hercules Co., synthetic Pgh. Cons. Coal Co., R & D Reilly Co. Reilly Co. Reilly Co. Reilly Co.
Treatment Azeotropically dried Redistilled Redistilled, heart cut Butylated, distilled Redistilled, heart cut Synthesized Butylated, distilled Butylated, distilled Butylated, distilled Distilled, recrystal-
2 3-Xslenol o:E t hylp henol m-Ethylphenol p-Ethylphenol 2 4 6-Trimethylphenol 2:3:6-Trimethylphenol
Pgh. Cons. Coal Co., R & D U. S. Bureau of Mines Reilly Co. U. S. Bureau of Mines Shell Development Shell Development
Sy%kzed Xone Redistilled, heart cut None None None
Table 11.
1;v-A
Boiling Point and Absorption Bands of Methyl Substituted Phenols
Compound Benzene Phenol o-Cresol Z16-Xylenol m-Cresol p-Cresol o-Et hylp henol 2,4-Xylenol 2,5-Xylenol 2 3-Xylenol 2'4 6-Trimethylphenol ;-Ethylphenol p-Ethylphenol 3,5-Xylenol 3 4-Xylenol 2:3,6-TrimethylphenoI
Distillation Fraction 1
2
3 4
5
Boiling Point C. a t 50 M m . of H g O
109 113 115 121 121 123 127 127 132 132 134 134 137 142 144
Absorption Analytical Band, Microns 14.89 9.34 9.04 13.09 12.85 12.22 13.30 12.27 IO.04 9.37 11.70 11 03 12.07 14,68 9.95 9.22
V O L U M E 27, NO. 12, D E C E M B E R 1 9 5 5
1887 ences of near-boiling compounds, are strong absorption bands, and, with the exception of the 9.04-micron band of o-cresol, the absorbance is proportional to concentration. o-Cresol exhibited no absorption which obeyed Beer's lm-; however, experience has shown that for the concentrations of o-cresol usually found, the deviation from linearity a t 9.04 microns is not a limiting factor in the precision of the analysis. Figure 1 illustrates the spectra of p-cresol and 3,4-xylenol and points out the necessity of separating these two compounds before analysis, as both compounds have strong absorption bands in the 12.2- to 12.4-micron region. 4 s shown in Figure 2, 3,4-xylenol must not be present with 2,4- and 2.5-xylenol. The spectra of the ethyl phenols are very similar to those of their corresponding cresol analogs, and these pairs should not be present in the same cut. Examination of the boiling points a t 50 mm. of mercury (see Table 11)indicates that a precise distillation prevents the mentioned interferences, especially if an appreciable amount of methylphenol is present to provide a "flat" between 2,4xylenol and 3,4-xylenol. The distillation cuts selected were initial boilingpointto 113" C., 113" to 121°, 121Oto 127', 127" to 134', and
s W
0
WAVE LENGTH IN MICRONS
Figure 1.
TTirf7
Comparison of spectra ofp-cresol and 3,4-xylenol
80
2.4-XYLENOL
and Woolfok, Golumbic, Friedel, Orchin, and Storch ( 1 4 ) have applied their data to the analysis of many of the isomers found in coal tar. Essentially an extension of Friedel's work, the method detailed here includes all of the isomers boiling below 230' C. EXPERIMENTAL
The methods shown in Table I were used to prepare high purity compounds for calibration. The distillations were made on a column, 1 inch by 4 feet (about 30 theoretical plates), which was fitted with Cannon packing and operated a t a reflux ratio of 5 to 1with a boilup of 8 ml. per minute. The butylations were carried out as described by Stevens (11). The infrared absorption spectra of the pure materials were obtained using a Baird double beam recording infrared spectrophotometer equipped with sodium chloride optics. All work described in this paper was carried out using approximately 2% (by weight) solutions of the phenols in carbon disulfide with 0.1-mm. cells. The reference cell was filled with carbon disulfide. Bakers Snalyaed C.P. carbon disulfide is suitable without any treatment. Comparison of the spectra with those listed in the literature cited showed no extraneous bands.
I-
W z V
El n 1.81% IN CS2
Table 111.
14
13
12
II
The individual isomers were run a t several concentrations (1.5 to 2.5%), and the wave lengths listed in Table I1 Fere selected for analytical use. All of the bands selected are free from interfer-
WAVE LENGTH IN MICRONS
Figure 2. Comparison of spectra of 2,4xylenol, 2,5-xylenol, and 3,4-xylenol
Analyses of Synthetic Mixtures Mixture Number
1 Act., S n a l . , Dev.,
Benzene Phenol +Cresol 2,6-Xylenol m-Cresol p-Cresol o-Ethylphenol 2,4-Xylenol 2,5-Xylenol 2,3-Xylenol 2,4,6-Trirnethylphenol rn-Ethylphenol p-Ethylphenol 3,5-Xylenol 3 4-Xylenol 2:3,6-TrimethyIphenol
%
%
%
48.7 25.7 25.6
49.3 25.5 25.2
+0.6 -0.2 -0.4
2 A c t . , .4nal.,
%
%
17.1
18.0 34.3 8.2 17.6 21.9
33.8
8.3 18.6 22.5
Dev.,
%
S0.9 +0.7 -0.1 -1.0 -0.6
3 S o t . , Bnal.,
%
%
9 . 9 10.3 17.2 18.0 23.7 24.0 26.9 25.0 22.3 22.5
Dev.,
%
-A c t . , 9t
4 Anal., Dev.,
70
%
14.4 9.2 20.5 15.1 25.4 15.4
+0.8
5 Act., Anal.,
%
%
Dev.,
%
+0.4 +0.8
f0.3 -1.9 -0.2
13.6 10.1 19.8 16.1 25.4 15.1
-0.9 +0.7 -1.0 0.0 SO.3
50.3 51.0 f 0 . 7 13.8 14.7 +0.9 1 1 . 4 11.4 0.0 1 6 . 3 15.1 - 1 . 2 8.1 7 . 8 -0.3
ANALYTICAL CHEMISTRY
1888 134’ to 144’ C.-all column pressures being 50 mm. of mercury. These cuts result in the distribution of isomers as shown in Table JI. Synthetic samples were made up to contain the materials predicted in each fraction. These samples were analyzed by the method described here. The results given in Table I11 indicate a n accuracy of one absolute per cent. Ah-.4 LYTICAL METHOD
Sufficient tar or tar acid oil to give at least 50 grams of tar acids is weighed into a separatory funnel and estracted four times with an equal volume of a 10% aqueous solution of sodium hydroxide. The combined aqueous phases are acidified with 30% sulfuric acid, and the sprung phenolic compounds separated. The aqueous phase is extracted four times with C.P. benzene, and the benzene phase added to the wet tar acids. The resulting mixture is dried using a Dean-Stark azeotropic drying apparatus and most of the benzene is stripped off. If the sample contains less than 5% m-ethylphenol, 5 grams of this compound are added to the weighed dry tar acids. Ten grams of acenaphthene (l,2-dihydroacenaphthalene) are added to act as a “backer” to ensure the distillation of all the phenolic compounds. The misture is then distilled at a pressure of 50 mm. of mercury on an efficient column having a t least 25 theoretical platos, and the ment,ioned fractions are collected, weighed, and set aside for infrared analysis. Using an analytical balance, samples of the distillation cuts are weighed in 2-ounce vials, and sufficient carbon disulfide is added to give approsimatelj- a 274 solut,ion of the tar arids. Usually 0.2 gram of sample and 10 grams of carbon disulfide are used. Aluminum foil liners in the caps of the vials prevent contamination and evaporation of the solution. The absorption spectrum of the solution from 9 to 1.5 microns is obtained using 0.1-mm. cells with carbon disulfide in the reference cell. Transmittance values are read from the chart a t the wave lengths tabulated in Table 11. After converting transmittance to absorbance, t.he concentration of each component is determined using matrices (4>10) prepared from the spectra of the pure compounds. The sum of t,he components in each cut may not tots1 1007,; however, if no estraneous absorptions are noted, t,he analysis is normalized to place it on a 100% basis. Experience of the authors has shovin that when the unnormalized t3tals consistent’ly fall belon 957‘, the analysis is not trustworthy, and recalibration of the cell is necessary. The calibration may he checked a t any time by the use of a synthetic sample made up from the pure isomers, Tvith recalibration usually being necessary every 2 to 4 months. Calculation of the isomer distribution in the original sample is straightforward once the analysis and weight of each distillation fraction is known.
The viale used for weighing may be reused after washing with a detergent and then acet,one, but the caps and liners should be discarded after one use since they cannot be easily cle,zned. Although the method described seems to be time-consuming, a complete analysis can be obtained in 24 man-hours. If desired the method can be applied t o tar acid mixtures containing only tn.0 or three isomers with a resalting increase of precision to about 0.5% absolute. The method has been in use for a period of 4 years in this laboratory with satisfact,ory results. ACKNOWLEDGMENT
The authors wish t o thank 11.B. Seuwortli for his aid and advice in establishing the conditions for fractionating the tar acids and for the syntheses of several of the pure compounds used for calibration purposes. LITERATURE CITED
(1) .Indo, S., and Uchida, AI., Coal Tar (.Tumm), 5, 14, 1953. ( 2 ) Carney. G. E., and Sanford, J. I
