T H E SOLUTION OF INSOLUBLE DYES I N AQUEOUS DETERGENTS'
JAMES W. McBAIN
AND
TS-MING WOO*
Department of Chemistry, Stanford University, California Received July 1, 1958
Our investigations have previously established that many colloidal solutions form spontaneously from their constituents, and that they are thermodynamically stable (9), like ordinary solutions, entering into true reversible equilibria both within the solution and in respect to other phases in contact with them. We showed that, in the presence of stable colloid, other unstable or insoluble substances could likewise dissolve to form thermodynamically stable colloidal systems, comprising true reversible equilibria, the properties of the solutions being independent of previous history and determined solely by composition, temperature, and pressure (10, 11). The present communication extends these observations to solutions of a water-insoluble dye, Yellow AB (benzeneazo-P-naphthylamine), in numerous detergents and mixtures thereof, in an homologous series of pure soaps, unless otherand in a pure hydrogen soap. All experiments are a t 25.0°C., wise stated. COLLOID STABILIZATION
The phenomenon described is that an aqueous detergent solution will take up a definite amount of dye, either from the solid dye itself or from a solution of the dye in an immiscible non-aqueous solvent, setting up a definite equilibrium, losing a portion of its dye to any less saturated nonaqueous solvent, and taking up more from a more nearly saturated nonaqueous solution. The chief non-aqueous solvents used were toluene and benzene. Freezing point measurements show that the dye exists as simple molecules in the benzene solution (molecular weight : theoretical value, 247; value found, 245). A detergent solution, which is originally clear in the ultramicroscope, on taking up dye is still clear in the microscope, but is full of particles visible in the ultramicroscope. I n extremely dilute (a few ten-thousandths normal) solutions of a hydrogen soap, laurylsulfonic Presented a t the Fifteenth Colloid Symposium, held a t Cambridge, Massachusetts, June 9-11, 1938. *Lever Brothers Company Soap Fellow. 1099
1100
JAMES W. MCBAIN AND TS-MING WOO
acid, a small per cent of the particles are so large that they may be centrifuged out in a Swedish “angle” centrifuge. They pass through filter paper. Less dilute solutions are clear and transparent. They are still full of smaller particles, as shown by the ultramicroscope, but none can be centrifuged out. Interesting parallels are found in some of the observations of von Kdthy and Banga (6). The dye is brought into aqueous solution by spontaneous colloid stabilization. Its amount increases with increasing concentration of the detergent or stabilizing colloid. However, it is a remarkable and distinctive fact that a given weight of detergent takes up more dye when it is most diluted. Thus, so far as our studies have gone, the protective solvent power of a definite amount of a stabilizing colloid is increased by addition of the non-solvent)water. This distinguishes the formation of stabilized colloid from the typical cases of Neuberg’s “hydrotropy” or increased solubility in water (3, 4, 6, 8, 13, 17), occurring in general without the presence or formation of any colloid. Again the phenomenon of colloid stabilization is different from “protective action” or “peptization” of preexisting particles in suspensions or gels. THE FORMATION O F STABILIZED COLLOID DYE IN AQUEOUS LAURYLSULFONIC ACID
The especially pure laurylsulfonic acid, ClzH28&H, was prepared by Dr. Marie Louise Koenig by the method of Noller and Gordon (14). The spontaneous colloid stabilization of Yellow AB in aqueous solutions of laurylsulfonic acid was determined in two series of experiments. In the first series a small weighed amount of solid dye was shaken with the aqueous detergent. The undissolved dye was filtered off in a Jena KO.4 sintered-glass Gooch crucible and the excess of undissolved dye weighed after washing and drying at 60OC. The filtrate was likewise analyzed by repeated extraction with purified benzene, from which the dissolved dye was recovered by evaporation, and weighed. The two analyses agreed. A second series was carried out because of our fear lest some very fine particles of solid dye had passed through the filter. Solid dye was completely eliminated by the device of using only the solution in toluene. To 100 cc. of a saturated solution of the dye in toluene 10 cc. of toluene was added to obviate the possibilityof solid dye separating. The aqueous solution was then exposed to the toluene layer, using the device previously described for determining dye numbers, when an extremely slow swirling motion was given to the system with no possibilityof breaking up or mixing the layers. The results of the analyses by extraction and by the colorimeter were then multiplied by 11/10 to represent approximate saturation. KO emulsified toluene was visible in the ultramicroscope either
SOLUTION OF IKSOLUBLE DYES IN DETERGENTS
1101
with or without dye. The Yellow AB contained 0.15 per cent by weight of a water-soluble sulfate and chloride. The data are given in table 1 and figure 1. The solubility of Yellow AB in pure water is so very slight that it is insufficient to color the water even faintly, far less to weigh or TABLE 1 The solubility of Yellow A B in aqueous laurylsulfonic acid ut 25'C., in milligrams of d y e per 100 cc. of solution SECOND SERIES CONCENTRATION OB
Grams of
RSOIH
BY weight
NW 0.00052 0.00104 0.0052 0.0052 0,0104 0.052 0.052 0.104 0.52
Solubility
ext:&on
iye per gram of soap
mo.
mo.
grams
6 8 24 25 46 244 250 640
5 7 23 23 43 241 230 650
0.4-0.5 0.27-0.31 0.18 0.18
0.173 0.186 0.184 0.215 0.165
BY
extraction mo.
5.5 7.7 24 42 215 671 1804
' ~
j
B y color mv.
! 1
1 ~
grama
0.42 0.30 23
0.18
44 225
0.17 0.17
638
0.251 0.143
.
1919
i
04
FIG.1. Solubility of Yellow AB in laurylsulfonic acid, in grams of dye per gram of soap.
analyze. It should be noted that, since the molecular weight of the detergent (250.2) is so nearly that of the dye (247), the ratios in grams are equal to the ratios in molecules, as plotted in figure 1. Figure 1 emphzsizes that in extreme dilution the detergent is most effective in bringing into stable colloidal solution almost half of its own weight of dye. This is
1102
JAMES W. MCBAIN AND TY-MXNG WOO
more remarkable because in extreme dilution most of the detergent itself is certainly not present in colloidal form, but is almost completely ionized. Its conductivity is slightly lowered by dissolving the dye. Hartley agrees that here the detergent is almost wholly ionized, but on the other hand he considers that the taking up of dye i s “almost conclusive proof” of the presence of micelles and that the micelles are liquid. The increnbe in solvent power on dilution may bc an important factor in rinsing. The whole curve resembles the iurface tension curve of aqueous lauylsulfonic acid, and the minimum occurs in the same low concentration in each case. The downward slope in the more concentrated solutions in figure 1 corresponds t o the general behavior of very numerous detergents, following the purely empirical rule of McBain and Woo that the amount of
&-- - T r - x - 7 m - * o 20
TEMPERATME, ‘C
--
FIG.2. Solubility of dye in 0.052 N laurylsulfonic acid, a t temperatures from 0°C. to 90°C.
dye stably dissolved is proportional only t o the 2/3 power of the concentration of detergent. Likewise, the greatly increased qolubility of Yellow AB when the temperature of 0.052 N laurylsulfonic acid is raised from 0°C. t o 90°C. shows that the effect bears surprisingly little relation t o the amount of colloid originally in the laurylsulfonic acid. This is largely colloidal at 0°C. and mostly crystalloidal at 90°C. The data are given in figure 2. As regards other detergents, the solubility of Yellow AB in a 1 per cent, or 0,0226 N , solution of pure sodium sulfonate of dioctyl succinic ester (molecular weight 442) is 451 mg. per 100 cc. (determined by weight), 449 mg, (determined by extraction), or 0.45 of the weight of the detergent. Either in weight ratio or mole ratio this is niucli more than in laurylsulfonic acid of the same concentration. The commercial product, supposedly 99.6 per cent pure, twice gaye a d u e of 449 mg. per 100 CC. The solubility in 1 per cent “aliphatic ester sulfate” was 497.5 mg.
SOLUTION O F INSOLUBLE DYES I N DETERGENTS
1103
(determined by weight) and 496.1 (determined by extraction). That) calculated from the empirical dye number formula is 496.1, showing the useful range of this merely empirical and certainly not general formula. The solubility in a 0.0107 per cent solution of a commercial “75 per cent Turkey red oil” was 13.0 mg. (determined by weight), 12.8 mg. (determined by colorimeter), and 12.0 mg. (determined by extraction), which is much more than the weight of the Turkey red oil. (The dye number in this concentration, which is approximately only 0.0005 N , is a t least 3.) A solution of twice this concentration dissolved 21.0 mg. (determined by weight), 21.0 mg. (determined by colorimeter), and 20.0 mg. (determined by extraction), about equal to the weight of the impure Turkey red oil. Without addition of water the solubility was 7.32 g., in 5 per cent solution it was 0.988 g., and in 1 per cent solution it was 0.291 g. (ll),so that the proportionate weight of dye increases very greatly down to extreme dilution of the Turkey red oil. The following solubilities were determined in 1 per cent aqueous solution: ethyl alcohol, 0.2 mg. (determined by weight), 0.3 mg. (determined by extraction); amyl alcohol, 0.0 mg. (determined by weight), no color; diethylene glycol, 0.1 mg. (determined by extraction), no color; glycerol, 0.0 mg. (determined by extraction), no color. These results are of exceptional interest when compared with the effect on dye numbers .tabulated later. The effect of the presence of 5 per cent Calgon in 1 per cent solution of the Turkey red oil is to change the solubility from 291 mg. to 18 mg. (determined by extraction). In 5 per cent Turkey red oil it is changed from 988 mg. to 296 mg. (determined by extraction). The solubility in 1 per cent Turkey red oil is raised from 291 mg. to 298 mg. by adding 0 2 per cent Calgon. THE DYE NUMBERS O F THE HOMOLOGOUS SERIES O F SOAPS
Dye numbers are determined (11.) by exposing a detergent solution to 2 ec. of toluene containing usually 40 mg. of Yellow AB, for a t least 48 hr., avoiding all emulsification. They are expressed as 100K, where K is the constant from the equation
where D is the concentration of dye in the aqueous and toluene layers, respectively, and S i s the concentration of the soap or other stabilizing colloid referred t o the water present. Concentrations are in grams per 100 g. of solvent, except that for Yellow AB Dtol.is expressed in grams per 100 cc. of toluene. The dye number so obtained is wholly independent of the previous history of the system and its components, provided that a t
1104
JAhlES W. MCBAIN AND TS-MING WOO
least two days have been allowed for equilibrium to be established from either side. In every case the dye number is obtained by approaching equilibrium from both sides, in one experiment always dissolving the dye in the toluene first, and in the other dissolving it in the soap solution first TABLE 2 Dye numbers, loOK,of the soaps (above C,) DYE NUMBER0 I N BOLUTIONB OB CONCENTRATIONS QIVB3W 60AP
0.2
peroent
Potassium Potassium Potassium Potassium Potassium Potassium
1 '
MEAN
0.5
percent
nonylate, CS. , . . . . . . . . (0.38) 0.268 caprate, Clo. . . . . . . . . . 0.809 ' 0 825 2.68 undecoate, C l l , . . . . . . laurate, CIZ. . . . . . . . . . 3 58 I 3.59 3.80 myristate, C I ~ . . . . . . , 3.83 palmitate, C I S . . . . . . , , 3 74
''
I per cent
0.261 0.818 2.69 3.57 3.84
' 3.02 3.06 Sodium laurate, . . . . . . . . . . . . 5.80 Potassium oleate 5.69 Sodium oleate I 1.16 Sodium abietate I Sodium erucate 1526 ________
I
I
per oent
0.257 0.820 3.55 3.71
5.65 1.13
0.265 0.818 2.68 3.57 3.79 3.74 3.04 5.80 5.67 1.14 5.26
__I___
51
I
CARBOY ATOMS
-
FIG. 3. Dye numbers of potassium salts of saturated fatty acids. 0,sodium laurate; A, sodium abietate; 8,potassium oleate; X, sodium oleate; H, sodium erucate.
before exposing it to the other phase. The results almost always agreed within a few per cent, and the mean was taken to calculate the dye number. The dye number is 0 in the absence of stabilizing colloid. It is likewise 0 for an unstable hydrosol. The dye number is 0 for the potassium salts of the fatty acids from the
1105
SOLUTION O F INSOLUBLE DYES I N DETERGENTS
formate through the acetate, propionate, butyrate, valerate, and caproate to the heptylate inclusive, whether in 1 per cent or 5 per cent solution. Potassium octoate (caprylate) in 5 per cent solution gives a ralue 0.05, but for 1 per cent, 0.5 per cent, and 0.2 per cent solutions it is 0. The dye numbers for the higher soaps are given in table 2 and in figure 3. All these soaps and salts were prepared from Kahlbaum’s and the EastTABLE 3 Dye numbers of commercial soaps or those from technical ingredients 1 per cent solutions SOAPS
DYE NUMBER8
Oleic acid soap. . . . . . . . . . . . . . . . 4.25 Palm oil soap. . . . . . . . . . . . . . . . . 4 , 7 3 Tallow soap, . . . . . . . . . . . . . . . . . . 8 . 5 0 Olive oil soap. . . . . . . . . . . . . . . . 6.98 5.99 Stearic acid soap. . . . . . . . . . . . . Potassium coconut oil soap (dried). . . . . . . . . . . . . . . . . . . . . . 4.80
1 j!
1
1
DYE
SOAP8
NUMBERS
Flakes “ A ” , . . . . . . . . . . . . . . . Flakes “B” . . . . . . . . . . . . . . . Powder “ A ” . . . . . . . . . . . . . . . Powder “B” . . . . . . . . . . . . Powder “C” . . . . . . . . . . . . . .
4.70 3.89 5.25 3.28 3.54
Powder “D” . . . . . . . . . . . . . . .
7.55
TABLE 4 Dye numbers of sulfonated oils ~~~~
I SULFONATED OILS
I 1
“75 per cent Turkey red oil”. . . . . . . . . . . . . . . . . . . . . .
Sulfonated castor oil “B” ,. Sulfonated castor oil “C” . . . . . . . . . . . . . . . . . . “Highly sulfonated olive oil”. . . . . . . . . . . . . . . . . . . . .
~
D Y E NUMBERS
From
1 percent
solution
~
_ 6.22
2.17 6.03 6,18
1
From
5peroent
solution
‘ j
Mean
_ _ 5.96 6.09
2.07 6.24
2.12 6.03 6.21
man Kodak Company’s purest materials, except that the oleic acid was made by British Drug Houses by Lapworth’s method; the sodium abietate was an especially pure specimen prepared by E. I. du Pont de Nemours and Company and preserved under alcohol; the decoic acid was made by Dr. S. Lepowsky, and the undecoic acid by Dr. C. R. Noller. For comparison with the pure chemicals in table 2, we hare given in
1.106
.
.
JAMES W MCBAIN AND TS-MING WOO
TABLE 5 Effect of added substances upon dye numbers ____ BOLWTXONS UBED
DYE KOYBERLI
.1 per cent potassium oleate . . . . . . . . , . , . . . . . . . . . ., . , , . . . . . , . . , I- 1 per cent sodium chloride . . . . , . . , . . . . . . . . . . , , . , , . , , . , . , . , , 5 per cent sodium chloride . . . . . . , . . . . . . . . , , . . , , , , . . . . , . . , 1 per cent potassium carbonate . . . . . . . , . , , . . , , , . , , . . . . . , 0.1 per cent Calgon . . . . . . . . . . ., . . . . . . , . . . . . . ., . . . . . . , , , i0.2 per cent Calgon . . . . . . . . . . . . . , . . . . . . . . . . . . . ,. , . , , . . . , , 0.5 per cent Calgon . . . . . , , . . . . . ., . . . . . . . . . . . . . . . . . . , . 1 per cent Calgon . . . , . . . . , , , , . . , , , , , , . . . . , . , , . , . , , 5 per cent Calgon . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . , . 0.2 per cent trisodium phosphate? . . . . . . . . . . . . . . ,. . . , . . . , . . . 1 per cent trisodium phosphate . . . . . . . . . . . . . . . . ,. . . . . . , 5 per cent trisodium phovphate . . . . . . . . . . . . . . . . . . . . . . . . . , . . 5 per cent sodium metasilicate . , . . . . . . . . . . . . . . . . . . . . . . . . . . 5 per cent, sodium silicate (2.4). . . . . . . . . , . . . . . . , , . , , , . , , , 5 per cent sodium silicate (3.2). , . . . , . . , . , . , , , , , , , . . , , . , . 0.5 per cent, gum tragacanth., . , , . . . . , , . . , , , , . . . . , , , , , . , . , ,
6.1 6.9 6.0 3.9 7.0 7.0 5.2
1 per cent potassium laurate . . . . . . , . . . . . , , . . , . ...... 1 per cent sodium carbonate, . . . . . . . . . , , . . . . , . . . . . . . . . ., , .
3.57 4.20
+ + + + + + + + + + + + +
+
, , ,
,
, ,
,
,
5.8 3.05 0 8.5 6.0 6.9 5.2 3.9 O*
. . . . . . ., . . . . . . . . . . . 1 per cent “75 per cent Turkey red oil” . 1 per cent sodium chloride . . . . . . . . . . , . . . . . . . . . . . . . . . . . . 5 per cent sodium chloride . . . . , , . . . , . . . . . . . . . . . . . . . . . . 1 per cent sodium carbonate . . . . . . ., , . . . . . , , . . . . , . . . . . . . 0.1 per cent Calgon . . . . . . . . . . . . . ., . . . . . . . . . . . . . . . . . . . . . . 0.2 per cent Calgon . . . . . . . . . . . . . ., . . . . . . , . . . . . . . . . . . . . . . 0.5 per cent Calgon . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . 1 per cent Calgon . . . . . . . . . . . . . . . . . . . , . , . , . , , . . . . . . . . , . , . . 5 per cent Calgon . . .................................. 0.2 per cent trisodiu osphate . . . . . . . . . . . ., . . . . . , . . . . . . . I per cent trisodium phosphate . . . . . , . , . . . . . . . . . . . . . . . . . . . 5 per cent trisodium phosphate. . . . . . . . . . . . . , . . . . . . . . . . . . 5 per cent sodium metasilicate ......... ,.............. 5 per cent sodium silicate (2.4) ....................... 5 per cent sodium silicate (3.2) ....................... 0.5 per cent gum tragacanth., . ....................
6.1 2.0 0 8.5 6.0 6.9 6.0 4.2 O* 6.03 5.94 5.25 6.1 8.6 10.6
5 per cent “75 per cent Turkey red oil” . . , , . . . . . . . . . . . . . . . . . . . . 5 per cent diethylene g . . . . . . . . ., . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ., . . . . . . . . . . . . 5 per cent glycerol . . . . 4- 1 per cent glycerol . . . . . . . . , . . . . . . . , 5 per cent ethyl alcohol, . . . . . . . . . . . , . . . . . . . ., . . . . . . . . . . . . 5 per cent diethyl e t h e r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6.0 9.0 8.8 8.5 1.44 0.92
+ + + + + + + + + + + + +
, ,
,
,
,
,
,
,
+ +
+ + + +
* Salted out .
t Sa3PO~.12H~0.
6.0
1107
SOLUTION O F INSOLUBLE DYES IN DETERGENTS
BOLUTION USED
DYE NUMBERE W H E N PER CEWP OF BILICATE ADDED I5
,
5 percent
+ silicate “S” (3.91). . . . . . . . . . . . . . . . . . . . + silicate “0” (3.15) . . . . . . . . . . . . . . + silicate “X’’ (3.19). . . . . . . . . . . . . . . . . + silicate “K” (2.79), . . . . . . . . . . . . . + silicate “U” (2.41). . . . . . . . . . . . . . . . . . + silicate “C” (1.9). . . . . . . . . . . . . . . . . . . . + metasilicate (1.0). . . . . . . . . . . . . . . . . . .
10.51 10.5 10.6 6.1 8.5 6.0
1
I permt
0.2percent
6.84 6.81 6.84 6.08 6.01 6.87 6.01
6.08 6.01 6.03 6.01 6.00 5.99 6.87
6.1)
5.2
table 3 the dye numbers of five soaps made from single technical materails, kindly supplied by the National Oil Products Company, ,four commercial soap powders from different makers (one possibly containing a portion of syiithetic detergent), two coinmercial soap flakes, and a potassium coconut oil soap supplied by the Davies-Young Soap Company. THE DYE NUMBERS O F THE SULFONATED VEGETABLE OILS
In table 4 are listed the dye numbers of sulfonated oils, some of which, like sulfonated olive oil and sulfonated castor oil (Turkey red oil), have been known and used in the dye industry for nearly a century, but whose manufacture has in recent years been improved as regards control and degree of sulfonation. Our thanks are due to the many firms in this and other countries who kindly supplied or obtained for us these and our very varied assortment of detergents. A few were synthesized under the supervision of Dr. C. R. Noller a t Stanford University. The dyes were given to us by the Calco Company. In table 4 degree of sulfonation appears to be a minor factor as compared with the dilution of the original material. SOLUTIONS LACKING DYE NUMBER OR PROTECTIVE SOLVENT POWER
The following substances leave water a complete non-solvent for Yellow AB when they are added to the extent of 1 or 5 per cent, and their dye number is 0: sodium alginate (pure), sodium silicates (all), sodium hexametaphosphate (Calgon), trisodium phosphate, gum tragacanth, ethyl alcohol, amyl alcohol, diethylene glycol, glycerol, casein. It is all the more interesting that some of these substances enhance the dye numbers of Turkey red oil and of potassium oleate.
1108
JAMES W. MCBAIN AND TS-MING WOO
EFFECT OF ADDED SUBSTANCES UPON DYE NUMBERS
The experiments in table 5 were performed by adding various substances t o solutions originaily containing either 1 per cent of potassium oleate or 1 or 5 per cent of “75 per cent Turkey red oil.” The effect of admixtures in enhancing the formation of stabilized colloid is noteworthy, TABLE 6 Dye numbers of synthetic electrolytic detergents DYE NUMBER0
___
DETERGENTS
From
Iper cent
solution
From 6 per cent solution
Trimethyldodecylammonium bromide (pure), , . , . 6.74 A technical cat.ionic active detergent. . . . . . . . . . . . . . . 2.07 A quaternary ammonium base, . . . . . . . . . . . . . . . . . . . . . 1.16 Another quaternary ammonium base, . . . . . . . . . . . . . . 1.22 An imidazole compound. . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.26 Sodium alkylated naphthalenesulfonate . . . . . . . . . . . . 3.28 Sodium monosulfonate of dioctyl succinate (pure). , 8.15* 1 per cent glycerol. . . . . . . . . . . . . . . . . . . . . 10.23 1 per cent diethylene glycol. . . . . . . . . . . . . . . . . . . 10.30 Sodium secondary-tetradecyl sulfate . . . . . . . . . . . . . . Sodium secondary-octyl sulfate . . . . . . . . . . . . . . . . . . . . Sodium secondary-heptadecyl sulfate. . . . . . . . . . . . . . . 0.39 An Igepon product.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.85 4.16 Technical sodium oleyl sulfate, . . . . . . . . . . . . . . . . . . . . ......... 9.74 Technical sodium stenyl sulfate. . . . Technical sodium lauryl sulfate. . . . . . . . . . . . . . . . . . . 3.94 2.96 Technical sodium octyl sulfate. . . . . . . . . . . . . . . . . . . . . 5.06 Sodium lauryl sulfate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.93 Ammonium lauryl sulfate. ....................... Diethanolamine coconut oil dimethyl sulfate. . . . . . . . 3.89 A sulfated fatty alcohol.. . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.99 A technical alkyl sulfate powder. . . . . . . . . . . . . . . . . . . 4.21 , , ,
6.72 1.12 1.21 1.22
+ +
1.47 0.13 0.38 6.92 4.14 9.81 3.90 2.94 5.18 6.04 3.65 5.44
Mean
6.73 2.07 1.14 1.22 1.24 3.28 8.15* 10.23 10,30 1.47 0.13 0.38 6.89 4.15 9.78 3.92 2.95 5.12 5.99 3.8 5.7 4.21
* Calculated from the solubility of the dye in 1 per cent solution (0.449 g. per 100 cc.) is 8.01; dye numbers with 1 per cent and toluene tend to give a higher result, and the experiment with 5 per cent is precluded by the complete emulsification of the toluene. even when some alone exhibit no dye numbers and have no hydrotropic actions in the dilutions considered. This is especially clear with such added substance as diethylene glycol and glycerol, as well as some of the sodium silicates. The addition of small quantities of Calgon is favorable, but large additions spoil the detergent. DYE NUMBERS O F SYNTHETIC DETERGENTS
The names given for the synthetic detergents listed in table 6 are those of the pure chemical or of the main constituent when thus stated and
SOLUTION O F INSOLUBLE DYES I N DETERGENTS
1109
supplied by the maker. In many cases only an indication of the type of a commercial product can be given. The proportion of active material and of other materials in the technical preparations varies greatly and in many cases is unknown to us. Some of these data are included from a previous communication (11). Where the technical constituent is diluted or where it contains also salts or substances such as alcohol, the dye number suffers accordingly and the value recorded here is too low. DETERGENTS THAT ARE NON-ELECTROLYTES
Colloid stabilization may be brought about by substances that are very different from the soaps or other salts, acids or bases, such as have been
TABLE 7 Dye numbers of non-electrolytic detergents DYE NUPBBRB DETERQENTS
From I par cent solution
Konyl glucoside (pure). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Synthetic non-electrolytic polymer. Another non-electrolytic polymer. . . . . . . . . . . . . . . . . .
5.24 6.60
...........................
nical . . . . . . . . . . . . . . . . . . . . . . A polyether alcohol,, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Polyethylene glycol condensate (7) . . . . . . . . . . . . . . . . . . Condensate of Cls.alcoho1 and ethylene oxide. . , , . . , Another condensate or polymer Diglycol laurate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Saponin Quillaia, Merck, purified . . . . . . . . . . . . . . . . . Diethanolamine fatty acid, . . . . . . . . . . . . . . . . . . . . . . . . Diethanolamine coconut oil. . . . . . . . . . . . . . . . . . . . . . . Another diethanolamine coconut oil, , , , , , . . , , , , . , Diethanolamine oleic acid. . . . . . . . . . . . . . . . . . . . . . Diethanolamine stearic acid. , . , , , , , . , . , , , , , , , , ,
,
,
, ,
1.81 5.97 1.96 1.89 5.63 0.54 4.21 6.01 5.97 3.86 3.57
From
5 per cent
solution
6.58 7.33 4.15 3.62 5.29 5.63 0.54 3.53 5.39 5.49 3.66 3.62
Mean
5.24 6.59 7.33 4.15 3.62 1.81 6.63 1.96 1.89 5.63 0.54 3.9 5.7 5.7 3.8 3.6
enumerated in the foregoing tables. It is of very great interest that detergent power is independent of both dissociation and hydrolysis, although both of these affect the electrolytic detergents. The non-electrolytic detergents cover the same range of dye numbers as the electrolytic ones. Table 7 lists a few of these. DISCUSSION
Considerations of space preclude Lny detailed discussion here. The newer trend of the results is quite clearly in the further direction of surmising that a stabilized particle, that is, an unstable particle merely cbated with stabilizing agent, may possibly be stable as compared with the sepa-
1110
JAMES W. MCBAIN AND TS-MING WOO
rate constituents of which it is composed. This has not yet been proven. However, in the cases here studied i t seems probable that, especially in very dilute systems, there is comparatively little stabilizing agent a5 compared with the insoluble stabilized material. This would lead to the point of view that the molecules of dye associate statistically to particles whose formation is less and less probable as the size increases, but once formed are stabilized by the protective colloid. This presents the conception of a statistical equilibrium. This paper deais only with proven true reversible equilibria, reached equally from both sides. It is thus distinguished from the experiments of Pickering (15), Bailey (l),Lester Smith (16), Hartley ( 5 ) , and Lawrence (7), where the usual mechanisms for producing unstable von Weimarn types of sols and emulsions are not guarded against and in many cases are certainly operative; these have long been the usual methods of exceeding equilibrium concentrations. The present results deal only with moderately dilute systems, and not with the exceedingly complex relations observed in concentrated systems illustrated by the phase rule diagrams of Booth (2) or of Weichherz (18), or with the very concentrated systems in which hydrotropy is so often studied (such as 75 to 250 per cent sulfosalicylic acid). A detergent might almost be defined as a substance which achieves in very dilute solution a solvent action comparable to that of a highly concentrated organic solvent. I t must again be emphasized that the 2/3 power rule is valid only over a limited, moderately dilute range. It serves as a reminder that the proportion oC dye to Turkey red oil is eighteen times greater in extreme dilution than in pure Turkey red oil itself. The solubility of an azobenzene dye was likewise found by Hartley and Miss Parsons to be fivefold more in a given amount of paraffin-chain salt present than in an equal weight of pure hexadecane. The facts here recorded for these numerous detergents do not accord with the interpretations suggested by Hartley ( 5 ) and Lawrence (7). The 2/3 power rule for these detergents may, as shown by calculations of Dr R. D. Told and Dr. M. J. Vold, equally well be replaced by a formula based upon calculations of Meyer and van der Wyk (12), assuming that particles are built up stepwise, each step (the addition of one more molecule) involving tlie same energy, provided that it is further assumed that each particle, irrtlependent of size, has the same average power of stabilizing a Inoleclile of dye within the detergent solution. This, like the original calculations of Meyer and van der \Vyk, is an interesting opposite extreme from the views of Hartley and Lawrence. It should he emphasized again that the dye numbers and the dye solubilit,ies mrasiire one, but only one, of the factors involved in detergent
SOLUTION O F INSOLUBLE DYES
IN
DETERQENTS
1111
action. Further work is needed with systems including fabrics, where dye and detergent compete for the surface of the fabric as well as for each other. SUMMARY
1. The spontaneous formation of stabilized colloid involving true reversible equilibrium has been further studied. 2. The colloid stabilization appears to be more closely related to the surface activity than to the colloidality of the detergent. 3. Dye numbers of many types of modern and synthetic detergents, including pure soaps and other compounds as well as commercial products, have been measured. 4. Detergents that are anion-active like soaps and sulfonates, cationactive like substituted ammonium derivatives, and, most interestingly, non-electrolytic detergents cover the same range of dye numbers. 5. Blends and mixtures, even with materials which possess zero dye number, such as silicates and phosphates, may noticeably enhance the dye numbers of detergents. REFERENCES
(1) BAILEY:J. Chem. SOC.123, 2579 (1923). (2) BOOTH:Chemistry & Industry 66, 1120 (1937). (3) FREUNDLICH AND KRBQER:Biochem. 2. 206, 186 (1929). (4) HADJIOLOFF: Naturwissenschaften 26, 762 (1937). (5) HARTLEY:Symposium on Wetting and Detergency, London (1937). (6) KIITHY,A. VON, AND BANGA:Biochem. Z. 230, 458;257, 380 (1931); 244, 317 (1932). (7) LAWRENCF,: Trans. Faraday Soc. 33, 325, 815 (1937). (8) LINDAR:Naturwissenschaften 20, 396 (1932). (9) MCBAIN:Kolloid-2. 40, 1-9 (1926);Colloid Symposium Monograph 4,7 (1926). (10) MCBAINAND MCBAIN:J. Am. Chem. SOC.68,2610 (1936). (11) MCBAINAND Woo: J. Am. Chem. SOC.60, 223 (1938). (12) MEYERAND VAN DER WYK: Helv. Chim. Acta 20,1313 (1937). (13) NEUBERQ:Biochem. Z. 76, 107 (1916). (14) NOLLERAND GORDON:J. Am. Chem. SOC.66, 1090-4 (1933). (15) PICKERING: J. Chem. SOC.91,2001 (1907);ill, 86 (1917). (16) SMITH:J. Phys. Chem. 36, 1401, 1672,2455 (1932). R KIITHY,A. VON: Biochem. Z. 226, 267 (1930). (17) V E R Z ~AND (18) WEICAERB:Kolloid-Z. 47, 133;49, 158 (1929);68, 214;60, 192, 298 (1932).
