SOME PHYSICAL PROPERTIES OF AQUEOUS HYDROXYBENZENE SOLUTIONS BY LLOYD E. SWEARINGEN
The mono, di- and tri-hydroxybenzenesform a classof substances important and peculiar unto themselves. The mono derivatives, as well as some of the di and tri derivatives are common substances met with in a number of widely different preparations and uses. I n spite of their somewhat wide-spread usage, little work has been done on the physical properties of aqueous solutions of this class of substances. This is especially true of the di- and trihydroxy derivatives. Their solubility in water is known; the water-phenol system has been exhaustively studied; Skraup and Philippi’ have studied the capillary rise of phenol-water solutions; Thiel and Roemer2 have studied the acid properties of the phenols by electric titration methods. Morgan and Egloff3 have measured the surface tension of phenol-water mixtures by the drop weight method. Worley4 has measured the surface tension of phenolwater mixtures by the capillary rise method. More recently, Fergusonj has determined the specific heats, the heats of mixing and the vapor pressures of mixtures of phenol and water. I n view of the small amount of physical data available for solutions of this class, the following measurements have been carried out with the view of contributing something to the knowledge of properties of this class of solutions. The surface tension, the density, the index of refraction and the viscosity of these solutions have been determined.
Experimental Material Water. The water used in these experiments was a good grade of conductivity water, twice distilled from acid permanganate and barium hydroxide, then collected and stored in well steamed and cleaned pyrex glassware. Phenol. Merck and Company. “Absolute Phenol.” C.P. Catechol. E. 8: A. Resublimed. ALP. 103-104°C. Resorcinol. hlallinckrodt. C.P. quality. Free from di-resorcin, phenol and acid. N.P. 108-100~C. Hydroquinol. Merck and Company. Highest Purity. Pyrogallol. Merck and Company. M.P. 128-13 I O C . Phloroglucinol. Merck and Company. Extra Pure. Free from di-resorcin.
* Contribution
from the Chemical Laboratory of the University of Oklahoma. ‘Monatsheft, 32,353-72 (1911). * Z. physik. Chem., 6 3 , 711-61 (1908). J. Am. Chem. SOC.,38, 844 (1916). J. Chem. SOC., 105, 260 (1914). J. Phys. Chem., 31, 757 (1927).
786
LLOYD E. SWEARINGEN
Procedure A quantity of each of the above hydroxybenzenes, sufficient tomake 2 0 0 C.C. of a 0.5 molar solution was accurately weighed out and then dissolved in the required amount of water. I n the case of phloroglucinol, due to the small sample available, the solution prepared was only 0.0836 molar. The surface tensions, densities, indices of refraction and the viscosities of the original solutions were determined. Then a definite quantity of each of the solutions mas mixed with water in such proportion as to decrease the oon-
FIG.I
centration of the solute to 0.8,0.6, 0.4, 0.2 of the original value, so that in this way a series of solutions of 0.5, 0.4, 0.3, 0.2 and 0.1molar concentration was prepared for each of the hydroxybenzenes. The physical properties were then determined for each of the different solutions. Density The density of the different solutions was determined by the pyknometer method, using a Geissler pyknometer. The measurements were made at 2 j°C. and the value of D'$g calculated. Table I gives a summary of the density
A Q r E O C S HYDROXYBENZESE SOLUTIONS
787
determinations. The values given are the averages of three determinations. The separate determinations differed by less than .os% from each other. Correction has been made for the buoyancy of the air. The variation in specific gravity with density is shown graphically in Fig. I . Viscosity The viscosity measurements were taken a t zs0C with a modification of the Ostwald-Poiseuille viscometer. The temperature could be controlled to within a o . I O C . The time of outflow was measured with a stop watch, reading direct
FIG 2
to 0 . 2 second. The usual precautions were taken in cleaning, washing and drying the tube. The viscosity measurements are given in Table 11. The data given are averages of three separate determinations. The time for each determination within a series was reproducible to within 0.4 sec. For all solutions more than IOO sec. was required for outflow. For conversion to absolute units, the value (0.00894 c.g.s. units) of Bingham and Jackson' was used. The effect of concentration on the viscosity is shown graphically in Fig. 2. Index of Refraction The index of refraction was measured a t zs0C with an Abbe refractometer. The temperature was constant a t z 5 T to 0.1'. The indices of refraction are given in Table 111. The readings given are averages of four separate readings. The variation of the index of refraction with density is shown in Fig. 3. 'Bull. Bur. Ftandarda, 14,
(I),
59 (1918.)
LLOYD E. SWEARINGEN
788
TABLE I The Density of Aqueous Hydroxybenzene Solutions Concentration in moles/liter
D2s*c
D2~°C
z50c
Concentration in moles/liter
4 T
Phenol I . 0039
I
0.4 0.3
I ,0032
I .0002
I . 0023
0.2
1.0017 I.0008
0.9993 0.9987 0.9978
,0009
0.5 0.4 0.3 0.2 0. I
Phenol 1.0115
I . 0085
0.4 0.3
,009I I . 0066 I ,0046 I . 0024
1.0061 I . 0036 I ,0016 0'9994
0.I
0.2 0. I
I .0106
I .0076
I . 0086
I .0056
I
,0061 ,0042 I . 0024
I
I
1.0012
,003I
0.9994
Pyrogallol
0.5
I
4=c
Hydroquinol
0.5
0.I
d250c
D2~'C 2pc
0.5 0.4 0.3 0.2
Resorcinol
1.0180
I.0149
1.0145 I .0106 I . 0073 1,0035
1.0115 I .
0076
I ,0043 I .0005
Resorcinol
0.5 0.4
I . IO15
I . 0075
0.2
I.0042
1.0012
I . 0085
I . 0055
0.I
1.0021
0.9991
0.3
I. 0061
1.0031
TABLE I1 Relative and Absolute Viscosities of Aqueous Hydroxybenaene Solutions. 2 5 O C Concentration Relative moles/liter Viscosity
Absolute Viscosity
Concentration Relative moles/liter Viscosity
Phenol 0.5 0.4 0.3 0.2 0.1
1.1062 1.0774 1.0480 1.0287 1.0158
Hydroquinol 0.00989 0.00959 0.00935 0.00920 0.00908
0.5
0.4 0.3 0.2 0.1
Catachol 0.5 0.4 0.3 0.2 0.1
1.1126 1.0960 1.0660 1.0398 1.0184
0.3
1.1247 1.0952 1.0580
I . I106 1.0873 1.0655 1.0353 1.0134
0.00993 0.00972 0.00953 0.00926 0.00906
Pyrogallol 0.5 0.4 0.3
0.00995 0.00976 0.00953 0.00930 0.00910
0.1
0.0100~
0.2
0.00979 0.00947
0.1
0.2
Resorcinol 0.5 0.4
Absolute Viscosity
1.1391 1.1119 1.0783 1.0456 1.0186
0.01018 0.00994 0.00964 0.00935 0.00911
Resorcinol 1.0414 1.0191
0.00931 0.00911
AQUEOUS HYDROXYBENZESE SOLUTIONS
789
TABLE 111 The Index of Refraction of Aqueous Hydroxybenzene Solutions. 2 g°C Concentration moles/liter
Index of Refraction
Hydroquinol 1.3422 1.3398 0.3 1,3373 0.2 1.3363 0.I 1.3352
Phenol 0.5
1 ,3419
0.4
I ,3386
0.3
I .3368
0.2
1,3353 1.3343
0.I
0.5 0.4
Pyrogallol
Catechol ,3436 1.3397 1.3373 1'3369 1.3348 I
0.5
0.4 0.3 0.2
0.I
0.4
0.3 0.2 0.I
Resorcinol 1.3443 1.3405 1.3385
0.4
0.3
1.3437 1,3414 I .3388 1,3370 I . 3345
0.5
Resorcinol 0.j
Index of Refraction
Concentration moles/liter
0.2
I . 3366
0.I
1.3353
TABLE IV The Surface Tension of Aqueous Hydroxybenzene Solutions.
2 5°C
Concentration DialReading SurfaceTension Concentration DialReading SurfaceTension moles/liter Units Dynes/cm. rnoles/liter Units Dynes/cm.
Phenol 77.5 82.7 87.35 94.10 103.90
49.1 52.5 55.3 59.6 65.8
0.5 0.4
0.3 0.2
0.I
Catechol 100.80
101.59 105.15 108.20 112.jo
64.0 65.1
0.5
110. j
111.6
116.20
Pyrogallol 113.30 114.75
71.4 71.8 72.5 73.2 73.7 71.8
66.70 68.50 71.3
0.3
115.50
0 . 2
116.1
0.I
117.00
72.60 73.15 73.60 74. I
69.1 70.0 70.6
0.2
Resorcinol 113.15 115.65
71.7 73.2
0.4
Resorcinol 109.I
Hydroquinol 112.7 113.25 114.50 115.40
0.I
7 90
LLOYD E. SWEARINGEN
Surface Tension The surface tension measurements were made with a duNouy Tensiometer. The instrument was calibrated with water a t 2 5 O C , a value of 74.46 dynes/cm being obtained for water a t 25'C. 5 C.C. portions of the different solutions were placed in deep watch glasses and the glasses placed in a water The watch glasses were carefully cleaned and flamed before bath a t 25%. use. The readings given are the averages of six determinations. These readings were reproducible within 0.1scale unit. The measurements are shown in Table IV and Fig. 4.
FIG.3
Discussion No irregularity is apparent in the data for the density of the solutione. Two of the three di-hydroxy derivatives, the meta ( I :3) and the para ( I :4) have almost identical densities, while that of the ortho ( I : z ) is but slightly greater a t corresponding concentrations. Reference to Fig. I shows an almost linear relation between concentration and specific gravity. The densities of the different solutions can be calculated very accurately from the law of mixtures. If the equation for a straight line be written as D = m C Do the densities can be calculated very accurately. D is the density to be found, m a
+
AQUEOCS HYDROXYBENZENE SOLUTIONS
791
constant, characteristic for each substance, C the concentration in moles/ liter and Do the value for the average density of the solution a t zero concentration of solute. m is the value of dD:dC, the change in density with concentration. The values of m for the different hydrobenzene solutions are as follows : rn
rn
Phenol Catechol Resorcinol
Hydroquinol Pyrogallol
0.007 j
0.0230
0.0210
0,0350
0 . 0 2IO
FIG.4 Surface Tension-Concentration
Curves
An increase in the number of hydroxy groups in the benzene ring seems to produce an exaltation in the viscosity, as for all concentrations investigated, there is an increase in viscosity in going from the mono- thru the di- to the trihydroxy derivatives. The position of the hydroxyl group seems to have but little influence, as all of the di-hydroxy derivatives possess viscosities very nearly the same, the meta having a slightly higher viscosity than the ortho, which in turn has a viscosity slightly greater than the para derivative. The introduction of the third hydroxyl group tends to cause a considerable increase in the viscosity at all concentrations except the lowest, where all the viscosities are but slightly different from that of pure water. Viscosity con-
792
LLOYD E. SWEARINGEN
centration curves of the type shown in Fig. z are similar in character to those of approximately normal substances, showing little or no association or dissociation in water. The index or refraction exhibits but little change with changes in density or concentration. The change is greatest with phenol, less with the di-hydroxy derivatives and still less with the trihydroxy derivative. The three di-hydroxy derivatives show but slight variation among themselves. The surface tension values of the phenols in water determined by Skraup and Philippi are not available, but the order of decreasing rise given by these workers is as follows: Phenol, catechol and hydroquinol rise to about the same height. Resorcinol and pyrogallol give lower values in the order named. This order is the same as found in the present work, with the exception of the position of hydroquinol and resorcinol. The values of the surface tension of phenol and water in the present work are slightly greater than those reported by Morgan or Worley. The surface tension values show considerable variation depending on the number and position of the hydroxyl groups. Each molecule of phenol is much more effective in lowering the surface tension of water than is a molecule of the di- or tri-hydroxbenzene. The di-hydroxybenzenes stand in the order, ortho, meta and para, in their ability to lower the surface tension of water. This order is the same as their order of increasing melting points. The highest melting point compound lowering the surface tension less than those of lower melting point. Pyrogallol lowers the surface tension of water but slightly. The melting point of pyrogallol is between the melting points of the meta and para di-hydroxy derivative. As we go from benzene, which is but slightly soluble in water to phenol which is moderately soluble a t room temperature, to the di- and tri-hydroxy derivatives, the enhanced solubility of these latter is usually ascribed to an increase in the number of hydroxyl groups in the benzene ring. The fact that water is a polar substance and the polar properties of the hydroxyl group have long been recognized. Surface tensions of a series of similar substances will usually follow the same general order as the melting points, if solids, or the boiling points, if liquids. Other factors being the same, a molecule of phenol should be more effective in lowering the surface tension of water than a molecule of the dior the tri-hydroxy derivative, due to the lower surface tension of the phenol. Fewer phenol molecules than di- or tri-hydroxybenzene molecules would need be concentrated in the surface to produce a given lowering in the surface tension of water. 0.02 mole of phenol produces as great a lowering in the surface tension of water as 2 5 times that much pyrogallol; as 2 0 times the para, 8.5 times the meta and 3.5 times the ortho di-hydroxy benzenes. Undoubtedly more of the highly capillary active phenol molecules are in the surface layer than are the di- and tri-hydroxy molecules a t corresponding concentrations. Otherwise, it would be difficult to account for the appreciable lowering of the surface tension of water by phenol. The di- and tri-hydrobenzenes undoubtedly
AQUEOUS HYDROXPBENZEXE SOLUTIOSS
793
have higher surface tension values than phenol and are incapable of lowering the surface tension of water to such a degree as phenol. But in view of the high concentration of the di- and tri-hydroxy derivatives required to produce a lowering corresponding to a small concentration of phenol, it is logical to assume a much smaller surface concentration of the di- and tri-derivatives than of phenol. Evidently, the increased number of hydroxyl groups encountered in going from the mono to the tri derivatives produces a greater resemblance between the hydroxybenzene molecules and water, with the result that the di- and the tri-hydroxybenzene molecules concentrate less readily in the surface and more readily in the bulk of the solution.
summary The density, viscosity, index of refraction, and surface tension of aqueous solutions of hydrobenzenes have been determined a t 2 goC. 2. Xo pronounced effect due to the number or position of the hydroxyl groups has been found except in the case of surface tension. 3. The monohydric derivative is more effective than the dihydric derivative, which in turn is more effective than the trihydric derivative in lowering the surface tension of water. I.
.Vorman. Oklahoma.
