INDUSTRIAL
AND
ENGINEERING CHEMISTRY
A N A L Y T I C A L EDITION PUBLISHED
BY
THE
AMERICAN
CHEMICAL
SOCIETY
0
WALTER
J.
MURPHY,
EDITOR
Determination of o-Cresol in Phenol by a Cloud Point Method d
WILLIAM SEAMAN, A. R. NORTON, AND R. T. FOLEY Calco Chemical Division, American Cyanamid Company, Bound Brook, N. J
IPi
THE process of freeing phenol from o-cresol by distillation i t is important t o have a n accurate method for determining low concentrations of the latter in the presence of the former, in order t o evaluate t h e plate efficiency of the column, It is assumed from a knowledge of the compounds involved t h a t only o-cresol is present with the phenol.
from 3 to 5.6 per cent. The method has an accuracy for the loner concentration range which is expressed by a standard deviation of a single value from the true o-cresol content of 10.07 per cent o-cresol and for the higher concentrations of =tO.O9 per cent. The accuracy can obviously be increased by taking the average of more than one determination.
One method for o-cresol in phenol ( 6 , 10) is based upon the formation of a complex between o-cresol and cineole, followed by the determination of the freezing point of this complex. This seems to be more suitable for high concentrations of cresol. Another method which has been recommended by a number of authors (3,7, 8, 11) is based upon the lowering of the freezing point of phenol. Unfortunately, o-cresol freezes out with the phenol in a continuous series of mixed crystals ( 3 ) . This would make it impossible to get very accurate values of o-cresol unless the degree of supercooling were rigidly controlled in relation to the concentration of o-cresol. The extent of this difficulty is obvious from an inspection of the divergent values reported for the lowering of the freezing point of phenol by o-cresol(3,7,8,11). At least one of these authors ( 3 ) recognized this difficulty, and so determined the temperature at which the last crystals melted, instead of the usual freezing point, in order to avoid the effects of supercooling. This would, however, make the procedure less adapted to routine use. Besides, the lowering of the freezing point for a given o-c-resol content is considerably less than the corresponding lom,ering of the cloud point in the method reported below. The statement ( 1 ) that 1 volume of cold liquefied phenol (rendered liquid by the addition of 8 per cent of water) forms, with 1 volume of glycerol, a clear liquid which is not rendered turbid by the addition of 3 volumes of water (absence of creosote and of cresol) suggested the possibility that a cloud point method could be developed for o-cresol in phenol. Dolique (4) has published a study of the systems phenol-water and phenol-glycerolwater, including the effects of a number of impurities. Other papers have also been published on the influence of impurities on the critical solution temperature of phenol-water (2, 5 , 9), but in none did the authors find that o-cresol had been included.
Method of Analysis About 7 to 8 grams of the phenol sample are placed in a dry, tared test tube (2.5 X 15 cm.) and weighed to the nearest milligram. A number of milliliters of distilled water equal to 1.857 times the weight of the phenol sample (this makes a mixture of 35 per cent phenol sample and 65 per cent water) are added from a buret. The tube is placed in a water bath at 75" to 80" C. and its contents are mixed with a glass stirrer (looped to fit around the thermometer to be used later) until the mixture is clear. The tube is then centered by means of a cork in a larger test tube (3.25 X 17.5 em., 1.5 X 7 inches) which serves as an air jacket and is kept in a water bath maintained at about 65" C. A thermometer with 0.1 ' divisions, calibrated for 7.5-cm. (3-inch) immersion, is placed in the solution, which is then stirred vigorously (about 80 to 100 strokes per minute). As the solution cools, a turbidity sets in which serves as a warning of the approach of the cloud point. This turbidity starts at about 1 to 2 O before the cloud point, starting sooner the greater the concentration of cresol, but its onset and the increase in its opacity are not sharp. Finally there is an abrupt increase in the opacity of the mixture. This is taken as the cloud point and the thermometer is read to the nearest 0.05" C. The tube may be reheated and the determination repeated at will if it is desired to increase the accuracy by taking a mean of several values. For cloud points up to 70.25' C., the percentage of o-cresol is calculated by the equation
yo o-cresol
=
cloud point C.) 1.326 ( O
- 66.40
and for cloud points from 70.25' to 73.5" C. by the equation
The authors' first work was done with t h e system phenolwater-glycerol with additions of o-cresol, but this mas abandoned in favor of the phenol-water system because the former involved some difficulties in the precise observation of the cloud point, and had no advantage over the simpler system. )\'orking with mixtures of phenol and o-cresol containing up to 5.6 per cent cresol, and also containing water added i n the ratio of 65 parts by weight to 35 parts by weight of the mixed phenol-cresol, the authors found t h a t each addition of cresol increases the cloud point to a n extent that can be expressed by two linear equations, one for concentrations from 0 to 3 per cent o-cresol and the other for concentrations
yoo-cresol
=
cloud point C.) 1.167 ( O
- 66.81
Development of the Method PHEKOL was urified by distilling c. P. phenol through a acked column, redistiiing the middle cut, redistilling the mid%e cut from this, and collecting three successive cuts which had freezing points of 40.94", 40.93", and 40.93" C., respectively. The freezing points were run in a magnetically stirred enclosed apparatus to protect the phenol from absorption of moisture from the air. There was no significant change in the freezing point when the phenol was boiled in the freezing point tube in order to remove possible traces of moisture. 159
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
160
TABLE I. DEVIATION OF CALCULATED CRESOL VALUESFROM TRUEVALUES Cloud Point (Mean of 10 Values) O
c.
-----Cresol-Calculated
Actual
%
%
Deviation % cresol
By Equation 1 66.39 66.41 (mean of 5 values) 67.00 67.36 (mean of 5 values) 67.70 68.19 68.33 69.18 69.40 70.23
-0.01 0.01 0.45 0.72 0.98 1.35 1.46 2,lO 2.26 2.89
0.00 0.00 0.45
-0.01 +0.01
0.00 f0.05 -0.05 -0.02 0.00 $0.02 -0.07
0.67 1.03 1.37 1.46 2.08 2.33 2.83
f0.06
3.43 4.17 4.71 5.59
-0.04 -0.07 f0.03 +0.07
By Equation 2
70.77 71.59 72.34 73.42
3.39 4.10 4.74 5.66
0-CRESOLwas prepared by diazotizing and decomposing with water o-toluidine which had in turn been prepared from o-acetotoluide that had been recrystallized to a constant melting point of 110.9-111.6" C. (corrected). The o-cresol was distilled under reduced pressure. The middle cut had a freezing point (run in the aforementioned closed apparatus) of 30.99' C. (corrected). The same freezing point was obtained upon redistilling this material under reduced pressure and taking a middle cut. THERMOMETERS. The thermometers were calibrated at an immersion depth of 7.5 cm. (3 inches) by comparing with another thermometer certified by the National Bureau of Standards. GLYCEROL-'WA4TER-PHENOL-cRESOL MIXTURES. Choosing proportions of phenol, glycerol, and water on the basis of data reported by Dolique (4), a number of cloud points were determined for phenol-cresol mixtures containing up to 5.83 per cent o-cresol. The phenol-cresol samples were mixed with an aqueous glycerol solution having a specific gravity a t 300 c' of 1.0218, in 30" C. the ratio of 87.80 ml. of the glycerol solution to 13 grams of the henol-cresol mixture. It m-as possible to get cloud point values For the individual mixtures which agreed within 0.05' C., but when the cloud points were plotted against the cresol content, some of the points fell away from a straight line by as much as 0.2 per cent cresol. The difficulty mas with the determination of the cloud point. This did not appear sharply enough, so that there was a lack of concordance between the point taken as the cloud point for one sample and that for another, although two successive readings on the same sample were concordant. PHEA-OL-KATER-CRESOL MIXTURES. The first mixture which was tried consisted of 32.15 per cent water and 67.85 per cent phenol by weight. Repeated determinations of the cloud point on the same mixture resulted in successive values, each of which was lower than the previous value by about 0.2" C., the initial value being 33.75" C. According t o Dolique's data (4) a change in the water content of the mixture of about 0.07 per cent (or for the size of sample used, about 0.004 ml. of water) would suffice to lower the cloud point by 0.2" C. It would seem most likely that such losses explained the difficulty with this mixture. It was next decided to use a mixture of 35 per cent phenol and 65 per cent water which would be closer to the critical solution temperature of the system, because the system is much less sensitive t o small changes in composition in that region. The method proposed does not pretend t o determine the critical solution temperature, which is the temperature at which the two liquid phases become equal in composition. What is determined is merely the temperature at which a definite clouding phenomenon appears. Because of this fact i t is unnecessary for the use of the method to resolve the divergencies in the critical solution temperatures which have been reported in the literature.
A number of mixtures were made up of phenol and o-cresol, ranging from 0 to 5.6 per cent o-cresol, and the cloud points were determined. With each mixture ten separate determinations of the cloud point were made (five in two cases). When the average cloud points were plotted against the known cresol content, it was found that the relationships could be expressed most
Vol. 15, No. 3
conveniently by two straight lines (Equations 1 and 2). Possibly the fundamental relationship could be expressed by a hyperbolic equation, hut the use of two straight-line equations seem more practical. The equations were chosen in such a way that the ercentages of o-cresol, calculated for each of the average cloux points from the equations, would, when compared with the actual percentages of o-cresol, give deviations such that the difference between the sum of the squares of the positive deviations and the sum of the squares of the negative deviations would be at a minimum. The data are given in Table I.
Precision and Accuracy The precision of the method will be determined by t h e degree of agreement between individual cloud point values on a single mixture and the mean. This has been determined for each of the 14 mixtures by calculating for each mixture the average deviation of each value from its respective mean and then multiplying by a factor (1.49 for 5 values and 1.36 for 10 values) to convert to the standard deviation. (The calculation of the standard deviation by means of a factor is not so accurate as by means of the usual root mean square average of the deviations from the arithmetic mean, but i t is felt that the difference in the two methods of calculation is not sufficient t o affect the reported standard deviations in the one significant figure to which they have been calculated.) The latter is then calculated t o per cent ocresol, using Equation 1 or 2. The data are given in Table 11. The accuracy of a single value was determined by calculating by means of Equations 1 or 2 the cloud point value corresponding to each actual percentage of o-cresol, getting the average deviations of the individual determined cloud point
TABLE 11. PRECISION OF CLOUDPOIKT DETERMINATION Average Deviation Cloud Point from Mean (Mean of IO Values)
Corn osition of d'ample % o-cresol
c.
C.
;to
0.45 0.67
66.39 66.41 (mean of 5 values) 67.00 67.36 (mean of 5
3.43 4.17 4.71 5.59
70.77 71.59 72.34 73.42
0.00 0.00
Standard Deviation from Mean C. A % o-cresol
1 '
0.068
0.07 0.10
0.05 0.08
0.045 0.040
0.06 0.06
0.05 0.05
Av. 0.07
0.05
0.07 0.07 0.06 0.09
0.06 0.06 0.05 0.08
0,050
0.052 0.050 0.046 0.065
0.06
Av. 0.07
TABLE 111. ACCURACY OF METHOD Composition of Sample 7' o-cresol 0.00
Calculated Cloud Point
c.
0.45 0.67 1.03 1.37 1.46 2.08 2.33 2.83
66.40 66.40 67.00 67.29 67.77 68.22 68.34 69.16 69.49 70.15
3.43 4.17 4.71 5.59
70.81 71.68 72.31 73.33
0.00
Deviation from Calculated Cloud Point Average Average Standard A % o-cresol A % o-cresol =to C. 0.070 0.053 0.07 0,055 0.041 0.06 0,045 0.034 0.05 0.066 0,050 0.07 0.065 0.07 0.049 0,046 0.035 0.05 0.045 0.034 0.05 0.051 0.068 0.07 0.107 0.081 0.11 0.080 0.08 0.060 Av.
0.062 0.090 0.056 0.091
0.053 0.077 0.048 0.078
0.07 0.07 0.10 0.07
0.11 Bv.
0.09
ANALYTICAL EDITION
March 15. 1943
values from their respective calculated values, recalculating the average deviation to per cent cresol, and converting to the standard deviation as per cent cresol. These data are given in Table 111. The values indicate that the precision is a lit.tle better than the accuracy. By taking the mean of a number of cloud point determinations the standard deviation may be improved by a factor equal to the reciprocal of the square root of the number of determinations.
Effect of Variations i n Water Content Since the sample must be made up by adding water, it is important to know how changes in the water content of the prepared sample will affect the cloud points. This is particularly necessary because of the hygroscopic nature of phenol. If the accuracy of the method were affected by small changes in water content, it would be difficult to use. Dolique ( 4 ) published data on the change of the critical solution temperature of phenol-water with changes in composition : Wster 7u 61.16 64.13 65.00 65.69 68.46
Critical Solution Temperature
Phenol
c.
70
66.4 66.5 66.5 66.5 66.4
38.84 35.87 35.00 34.31 31.54
It is seen that near the region of concentrations with which this method is concerned, the cloud point of pure phenol is insensitive to small changes in water concentration. To two mixtures of cresol in phenol, 1 per cent less and 1 per cent more, respectively, than the usual 65 per cent of water were added, with results as follows: a-Cresol Content
Water Content
%
7%
1.14
64 65 66 64 65
2.63
66
Cloud Point
c.
67.78 67 91 (calcd.) 67.88 69.61 69.88 (calcd.) 69.84
o-Cresol Found
(4) Dolique, R., Bull. sci. pharmacol., 39, 129-47 (1932). (5) Duckett, J., and Patterson, W. H., J . P h y s . Chem., 29, 295-303 (1925). (6) Dull, H., A r c h . P h a r m . , 274, 283-92 (1936). (7) Fox, J. J., and Barker, M . F., J . SOC.Chem. I n d . , 37, 268-72T (191s) (8) Knight, G. W., Lincoln, C. T., Formanek, G., and Follett, H. L., J. IXD. EXG.CHEY.,10, 9-18 (1918). (9) MacKinney, G., Trans. Rou. Soc. Can., [3] 21, Sect. 3 , 265-6 (1927). (10) Potter, F. XI., and TVilliams, H. B., J . Soc. Chem. I n d . , 51, 5960T (1932). ESG. CHEM.,9, 569-80 (11) Weiss, J. Xf., and Downs, C. R., J. IND. (1917). PRESENTED before the Division of Analytical and JIicro Chemistry a t the 104th Meeting of the AJIERICAN C H ~ M I C SOCIETY, AL Buffalo, N . Y.
A New Gas Generator SIDNEY KATZ Goldsmith Brothers Smelting 62 Refining Company, Chicago, 111.
T
HE writer has frequently required a compact, portable form of gas generator. The instrument described here was finally adopted as being satisfactory from the standpoints of simplicity of manufacture and operation and ease of cleaning.
Error
To
7uo-cresol
1.05
-0.09
i:i3 2.46
-0.01
2:62
-0.01
~
161
....
-0.17
....
It can be seen that 1 per cent additional water causes a negligible error. If about 15 ml. of water are measured from a buret for a single mixture, an excess of even 0.2 ml. will cause an error of no more than 0.01 per cent o-cresol. A deficiency of water may be more serious, but that can be avoided with considerable certainty. Summary
A method has been devised for the determination of ocresol in phenol in concentrations up to 5.6 per cent, by measuring the cloud point of a mixture of the sample with water. The relationship between the cloud point and the o-cresol content is expressed by one straight-line equation up to 3 per cent and another from 3 to 5.6 per cent. The accuracy of the method is indicated by the standard deviation of a single value from the true o-cresol content; this equals *0.07 per cent o-cresol up to 3 per cent and hO.09 per cent from 3 to 5.6 per cent. Literature Cited (1) “Allen’s Commercial Organic Analysis”, 4th ed., Vol. 111,p. 292, Philadelphia, P. Blakiston’s Son & Go., 1914. (2) Boutaric, A., and Nabot, Y . , Compt. rend., 176, 1618-20 (1923). (3) Dawson. H. M.,and Mountford, C. A., J . Chem. Soc., 113,92344 (1918).
For ordinary operations, a 300-ml. Erlenmeyer flask waa employed, t o the base of which were sealed three 5-em. lengths of 8- to 9-mm. tubing, as illustrated. These legs were sealed off and a small hole was blown into each of them near the base. A stopcock side arm was sealed t o the neck of the flask, as shown, though in a simpler modification the stopcock was simply inserted in the stopper. The instrument fits nicely into a 1-liter beaker. In operation, the solid reagent is placed in the flask, while the acid is poured into the beaker, to within an inch of the brim. Opening the stopcock admits acid through the legs of the flask, generating the gas. When the stopcock is closed, the gas pressure displaces the acid from the flask and the reaction ceases.
