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
