August, 1942
INDUSTRIAL AND ENGINEERING CHEMISTRY
can be reached. The financial arrangement between the canner and municipality is, in the last analysis, the determining factor.
Literature Cited (1) Black, H. H., Canning Age, 23, 325 (May,-1942). (2) Eldridge, E. F., Mich. State Coll. Eng. Expt. Sta. BUZZ.78 and 83 (1938). (3) Halvorson, H. O., “Rept. on Studies of Cannery Wastes”, Minnesota Canners Assoc., 1940. (4) Lee, W. L., and Nichols, M. S., Sewage Works J., 9, 34 (1937).
915
(5) Natl. Canners Assoc. in cooperation with Wis. State Board of Health, unpublished data. (0) New York State Dept. of Health, “Treatment of Canning .. , (7) Sanborn, N. H., Canner, 92, No. 16, 12 (1941). (8) U. S. Public Health Service, “Ohio River Pollution Survey, Industrial Waste Guide, Tomato”, 1939. (9) Warrick, L. F., McKee, F. J., Wirth, H. E., and Sanborn, N. H., Natl. Canners Assoo. Bull. 28-L (1939). (10) Wisconsin Stata Board of Health, “Treatment of Pea Cannery Wastes”, 1926.
_____
PRESENTED before the Division of Water, Sewage, and Sanitation Chemistry at the 103rd Meeting of the AMERICAN CHEMICAL SOCIETY, Memphis, Tenn.
Solubilization of Water-Insoluble Dye in Aqueous Solutions of Commercial Detergents J.
w.
MCBAIN AND R. C. MERRILL, JR. Stanford University, Calif.
HE multiplicity of detergents and wetting agents recently made available has been accompanied by an equally great variety of applications in practically every industry. Comparative measurements on any one of the properties are therefore of great interest. Most of them belong to the class of solutions known as colloidal electrolytes, first defined by McBain in 1918 as electrolytes in which at least one of the ions is replaced by a micelle or colloidal aggregate. Probably all soluble ionizing organic compounds containing more than nine or ten carbon atoms belong to this class.
T
Solubilization One of the most unusual properties of a detergent solution is its ability to dissolve otherwise insoluble materials. This phenomenon has been known and used commercially since 1874 @),Lysol being the most familiar example; but only recently has much attention been paid to the mechanism involved. In 1908 Nottbrack (1.4)used the solvent power of 20 per cent aqueous Turkey-Red oil to obtain solutions of dyestuffs not soluble in water, and found that the amount of sulfonated oil necessary depended on the dyestuff and the concentration desired. Engler and Dieckhoff (3) in 1892 solubilized benzene, toluene, xylene, and turpentine in various soap solutions. Witt (20) in 1915 stated that the alkyl naphthalene sulfonic acids possessed an “astounding capacity for dissolving all manner of substances which are quite insoluble in water-including resinous by-products of sulfonation and the CaSOl formed by neutralizing the reaction mixture”. Since then many other examples have appeared in the literature (2, 6, 6, 7, 16, I?’), notably the work of Smith (18) who showed that 10 per cent sodium
Soaps, soaplike substances, and many others, such as bile salts and the inn umerable detergents now commercially available, have the property of solubilizing waterinsoluble materials, such as an oil-soluble dye, by incorporating the latter in or upon the colloidal micelles that are the distinctive feature of all these colloidal electrolytes. Measurements are given which compare examples of a large variety of such detergents, including some that are nonelectrolytes. Similar observationsare noted for nonaqueous solvents. There is no connection between wetting power and solubilization. Heat increases the amount solubilized, as does the addition of salts in concentrations where the detergent is not yet fully colloidal. In concentrated solutions, added salt decreases solubilization. oleate solutions were able to dissolve all common insoluble organic liquids. McBain and McBain (9) were the first to realize the theoretical importance of this phenomenon for colloid chemistry and critically to establish its actual occurrence. Solubilizing consists of the incorporation of a material in the colloidal micelles of the detergent. These micelles are thermodynamically stable, both before and after solubilization. Incorporation of the insoluble material usually decreases further solubilizing power. Thus, a stable emulsion of benzene may be formed in one per cent sodium lignin sulfonate, but if a dye is already present, the emulsion breaks readily.
INDUSTRIAL AND ENGINEERING CHEMISTRY
916
TABLEI. SOLUBILITY OF O R ~ N G E OT IS ONE PER CEST AQUEOUSSOLUTIONS O F P U R E AXD CohlVERCI.4L SOLUBILIZIXG S O A P L I K E DETERGENTS 4T 25" c. N g . Dye/
Soap or Detergent
100 Cc. Goin.
Aerosol O T Aerosol MAa Aerosol 4 Y a Aerosol I B a -4nhydrous Wettal Aquasol AR 75% Bozetol Catylon D Cetyl pyridinium chloride Damol Daxad X o . 11 Duponol WA Emulphor Hytergen Igepal C Igepal CTA Lamepon 4C Laurel concd. textile oil Lauryl pyridinium iodide X-171, nonelectrolytic 11-885,nonelectrolytic 11. P. 191 Monopol oil Alonosulph Morpel oil No. 501 Morpeltex B Nacconol FSNO Nacconol N R Nopco 1440 r1 olyphosphete
I:%;
8
Petronate
Soap or Detergent Product P Product QB Product Q b Santomerse D Santomerse No. 3 Sapamine A Sapamine CH Sapamine LIS Saponin Sodium cholate Sodium deoxycholate Sodium lignin sulfonatec Sodium novenate Sodium taurocholate Supratol Syntex Teieitol 08 Tergitol 4 Tergitol 7 Triton B d Triton 720 Triton K12 5OYc Triton I i l 2 , 50Y0 Triton 720 50% Triton 720, 50% &I-171 Triton NE Turkey-red oil A S , a nonelectrolytic polymer Zephiran
1.61 0.40 0.04 0.01
10.4 10.0 1.83 2.19 22.7 12.7 2.87 8.3 4.9 0 47 1.87 1.80 1 . 10 9.9 12.4 0.35 3.14 1.53 4.50 8.6 8.5 3.80 3.8 18.1 7.7 0.27 1.10 1.94
318. Dye/ 100 Soh.
cc.
Vol. 34, No. 8
3Ieasurements of Solubilization in Detergent Solutions Table I gives the solubility of the water-insoluble dye Orange O T (1-o-tolylazo-@-naphthol) in 1 per cent solutions (actually 1 gram in 100.0 cc. of water) of various pure and commercial solubilizing soaplike detergents a t 25 C. This dye is insoluble in pure water and solutions of ordinary electrolytes. The data were obtained by shaking recrystallized dye with the solution a t least 24 hours (although much less time would ordinarily have been sufficient to obtain equilibrium), allowing all solid particles to settle, carefully removing the clear supernatant liquid with a pipet or medicine dropper, and analyzing it iu a Klett-Summerson photoelectric colorimeter. The amount given is only that truly dissolved (solubilized), since great care was taken to eliminate any peptized or dispersed colloidal dye. The detergents were kindly supplied by the manufacturers, to whom appreciation is expressed. They were used as 1eceived without further purification, so that they varied nidely in the amount and nature of the active constituent and salts contained. Some had been specially purified. For this reason only semiquantitative conclusions can be reached in many cases. It must also be kept in mind that these data apply only to the particular dye, and in view of the recognized specificity in the relativr effectivrness of these types of compounds, the order of effectiveness might not be the same for other dyes. Table I of Merrill and McBain (IS) shows that even for dyes differing only slightly in structure, O
0.82 1.2 17.7 4.86 7.0 0.63 0.34 8.5 0.70 0.29 1.5 0.85 4.7 1.45 1.44 3.65 0.10 0.38 0.94 0.13 1.12 4.72 4.0 0.74 1.67 13.5
4 . 87 0.40
a Value obtained from Figure 1. b Solution supersaturated as regards detergent. although in equilibrium with dye. c Value by extraction w-ith benzene, 0.81. d Solubility of Yellow AB in a 2% solution is 40 mg. per 100 cc.
TABLE 11. DATA os DETERGEKTS ISTABLE I Commercial Name Aerosol OT Aerosol MA Aerosol AY Aerosol I B Anhydrous Wettal
Type of Material Dioctyl (2-ethyl hexyl) ester of Nasalt of sulfosiiccinic acid, 99.0y0; SaHS03, 0.2yo: moisture, 0.8% Dihexyl (methyl amyl) ester of N a salt of sulfosuccinic acid, 99.0% Diamyl (mixture of 2- and 3-methyl butyl) ester of N a salt of sulfosuccinic acid, 99% Diisobutyl ester of Na salt of sulfosuccinio acid, 99% Complex mixt. with active ingredient of formula: 0
Manufacturer American Cyanamid and Chemical Corp. Same Same Same Emulsol Corp.
I/
R-C-0-CHzCHz-O-CH~CHz-OS-O-SHzCHzCHz0H
II
0
Aquasol AR 7570
Bozetol Catylon D Cetyl pyridiniuni chloride Damol
Daxad No. 11 Duponol IT-4 Emulphor 0 Hytergen
0
/I
(I 0
where R - C 4 = coconut oil fatty acids; also substantial proportion of unsulfated esters of diethylene glycol and ethylene dichloride Sulfated castor oil (4.370SOa, 29.6% H20) Sulfated castor oil derivatire Formate of condensation product of stearic acid and hydroxyethyl ethylenediamine mixed with a fatty acid amide. May contain sodium sulfate Technical grade ,~~,',N,N,.?'-tetramethyl-?\r,Iv-didodec~~l-~-hydroxypropylene diamnioniuni broniide, 99.5% pure: CH,
L
CHa CHa (Na alkyl sulfonate or S a naphthalene sulfonate polymer?)
American Cyanamid and Chemical Corp. Hart Products C o ~ p H a r t Products Corp. Wm. S.Merrell Co. Alba Pharmaceutical Lab.
Dewey and Almy Chemi. cal Co. Du Pont C o . General Dyestuff C o ~ p Hart Products Corp.
N a sulfate of technical lauryl alcohol Polyethylene glycol condensate (?), nonelectrolyte Sulfated fatty acid amide 0
Igepal C , Igepal CTA Lamepon 4C Laurel concd. textile oil Lauryl pyridinium iodide (Emulsol BBOB) M-171 M-885 M. P. 191
I1
Cis imported, C T d is domestic; ethylene oxide polymer of general formula RlCO-Rz-(O-R~),-OH, where R1 is a hydrophobic aliphatic chain, R Zis a short hydrocarbon residue, usually CzHn Condensation product of protein derivatives and fatty acids; no free fatty acids or soap: not sulfated Sulfated oil From commercial lauryl alcohol (70% n-dodecanol-l), slight excess of pyridine
Laurel Soap Mfg. Co Emulsol Corp.
Technical sodium lauryl sulfate Condensate of isooctylene, phenol, and polyethylene oxide True sulfonate from pure heptadecane; 50% NaCl containing some NazSO4
D u Pont Co.
Same Chemical Marketing Co.
August, 1942
INDUSTRIAL AND ENGINEERING CHEMISTRY
large differences are found in the effectiveness of various types of detergents. Table I1 summarizes the available information regarding the nature and purity of the detergents. The data are interesting because of the large number of types of compounds which act as solubilizers. Because of the correlation between effectiveness as a solubilizer and other indications of micelle formation (such as freezing point, conductivity, transport number, x-ray evidence, etc.), the data indicate that they form micelles in solution, are therefore colloidal, and thus tend to confirm a prediction made in 1920 (12) that the then new class of colloidal electrolytes would be more numerous than all acids and bases. The increase in solubilizing action with increasing chain length shown by the Aerosols, Tergitols, and Santomerses, together with the data on a series of 0.01 N pure long-chain sulfonates and sulfates presented in another paper (13) show that, in general, solubilizers containing a large proportion of hydrophobic material are best. Those which are anion-active such as the Aerosols, Tergitols, and bile salts, cation-active such as the pyridinium and other quaternary ammonium halides, and nonelectrolytes such as polymers of ethylene oxide, fatty acids, and alcohols, are all possibly of the same order of effectiveness as solubilizers if they are comparable in purity and hyd-rophobic character. The series of Aerosols (of which there are conceivably over a million individuals) are of special interest because some are available as practically pure sodium salts of different sulfosuccinic acid esters. Their effectiveness in solubilizing
917
30
-
%25
x 20
3 0 v) 0
IS 4
w
v)
g 10
?i s 5
z
-I 0
55
FIGURE 1.
0.1
0.2
0.3 0.4 0.5 0.6 0.7 NORMALITY O F AEROSOL SOLUBILITY OF ORANGEOT IN AEROSOLSOLUTION AT
25” C.
Orange OT in aqueous solution is shown in Table’III and Figure 1. When solubilizing power is plotted against concentration as in Figure 1, the curves parallel those obtained by 0. E. A. Bolduan in this laboratory for the osmotic coefficient; this shows again that the micelles of the detergent are responsible for solubilization. His measurements indicate that with Aerosol IB the freezing point lowering up to 0.3 or 0.4 M is
TABLE I1 (Continued) Commercial Name Monopol oil Monosulph Morpel oil No. 501
Type of Material 35% s o h . of 39% sulfated oil (?) Highly sulfated castor oil (30% HeO), ricinoleyl sulfate Highly sulfated castor oil: 67% fat and 8-8.5% sulfonated on 100% fat basis
Morpeltex B Nacconol FSNO
32.5% SO8 on 100% fat basis Nearly pure alkyl aryl sulfonate; alkyl group has about 13 carbon atoms and is largely branch-chained Na alkyl benzene sulfonate, where alkyl is between CIZand Cl8; contains NatSOs Soluble pine oil Ester of octyl alcohol with phosphoric acid Condensation product of octadecyl alcohol and ethylene oxide, nonelectrolyte, free from salt A petroleum product 22% aqueous soln. of a polyhydroxy ether Paste of technical stearyl trimethyl ammonium bromide (also called “Du Pont Retarder A”) Paste of technical lauryl trimethyl ammonium bromide Essentially decyl benzene Na sulfonate, mixt. of branched and straight-chain radicals: 99.570 pure through alcoholic purification Essentially dodecyl benzene Na sulfonate : alcohol-purified to 99.5% pure Diethylamine ethyl oleyl amide acetate, 95% anhydrous Diethylamine ethyl oleyl amide hydrochloride, 16.3% anhydrous Diethylamine ethyl oleyl amide methyl sulfate Natural product Pure bile salt Pure bile salt 90% pure lignin sulfonate, balance associated filter-cake products, hydrolyzed pentoses, hemicellulose, etc. Naphthenic acid salt Pure bile salt Highly sulfated castor oil
Nacconol NR Nopco 1440 Octyl tripolyphosphate Peregal 0 Petronate Product P Product Q Product QB Santomerse D Santomerse No. 3 Sapamine A Sapamine CH Sapamine MS Saponin White Sodium cholate Sodium deoxycholate Sodium lignin sulfonate Sodium novenate Sodium taurocholate Supratol Syntex (Igepon T )
CHI-(CHZ)~CH=CH(CHZ)~-CON(CHI)-CH~-CHZ-S~~N~
Tergitol 08
40% dispersion of Na 2-ethyl hexyl sulfate
Tergitol 4 Tergitol 7 Triton B Triton K12 Triton N E Triton 720 Turkey-red oil A Zephiran
25y0 liquid dispersion of Na sec-tetradecyl sulfate 25% liquid dispersion of Na sulfate of 3,9-diethyl-6-tridecanol 40% aqueous soh. of dibenzyl dimethyl ammonium hydroxide Chiefly lauryl dimethyl benzyl ammonium chloride, 27.6% anhydrous Polyalkylene ether alcohol Na salt of alkyl phenoxyethyl sulfonate F a t content, 61.4% by wt. 10% soln. of alkyl (from coconut oil) dimethyl benzyl ammonium chloride
Manufacturer General Dyestuff Corp. National Oil Products Co. Textile Chemical Products co. Same National Aniline and Chemical Co. Same National Oil Products C o . Victor Chemical Works General Dyestuff Corp.
L. Sonneborn Sons, Inc. (Unilever Limited?) Du Pone Co Same Monsanto Chemical Co. Same Ciba Co., Inc. Same Same British Drug Houses, Ltd. Riedel de Haen Same Marathon Chemical Co. Boake, Roberts and Co. Eimer and Amend Hart Products Corp. Colgate - Palmolive Peet c o. Carbide and Carbon Chemicals Corp. Same Same Rohm and Haas Co., Inc. Same Same Same General Dyestuff Corp. Alba Pharmaceutical Co. and General Dyestuff Corp.
-
INDUSTRIAL AND ENGINEERING CHEMISTRY
918
OF ORANGEO T IN AQUEOUSAEROSOL TABLE 111. SOLUBILITY SOLUTIONS AT 25" C.
Normality -Aerosol 0.800
0.700 0.600 0.400 0.300
0.200 0.100 0.005
--
0.780 0.700 0.600 0.500 0.400
0.361 0.300 0.200 0.100 0.070
0.040 0.010 0.005
Mg. 100Dye/ cc. Soh.
17.5 I B 12.25 8.75 3.78 0.15 1.11 0.03 0.00
ole
":p,b~e/
Aerosol
Kormality
0.00083 0.00067 0.00056 0.00036 0.000029 0.00011 0.000006 0.000000
-Aerosol 0.800
0.700
0.600
0.500 0.400 0.300 0.200 0.100
0.050 0.010 Aerosol MA-
65 58.6 38.7 50.2 27.5 24.1 19.5 9.5 3.29 1.53 0.85 0.20 0.05
7 -
0.00070
0.0330 0.0300 0,0225 0.0250 0.0200 0.0150 0.0125 0.0100 0.0075 0.0050 0.0037 0.0020
0.00038
o.oolo
0.0032 0.0032 0.0029 0.0032 0.0026 0.0025 0.0025 0.00182 0.00126 0.00083 0.00081
Soh.
D$y$ole Aerosol
50.2 A\'------?0.0024 40.3 0.0022 28.3 0.0018 22.0 0.0017 15.2 9.75 0.0014 0.0012 4.85 0.00093 0.36 0.00013 0.07 0.000005 O.Oo AerosolOT-
2.48 2.32 1.55 1.82 1.25 0.88 0.64 0.47 0.31 0.14 0.07 0.04 0.02
o.oooooo 0.0029 0.0029 0.0026 o.oo28 0.0024 0.0022 0.0019 0.0018 0.0016 0.0011 0.00072 o.00038 0.00038
practically the same as that of potassium chloride. Even
in the most concentrated solutions obtainable a t 0" C., the
,
average ion aggregate probably contains only four or five ion pairs. However, with increasing chain length, the micelles rapidly increase in size and amount. Valkd (19) considers that the average aggregate in micelles of Caledon Jade Green, an Indanthrene dye, is increased from 3 to 420 by the nonelectrolytic detergent, Peregal 0. It is important to note that solubilizing is a much more sensitive test than freezing point for the presence of micelles or, more likely, the dye itself promotes the formation of mixed micelles. The fact that detergent solutions, originally clear in the ultramicroscope, are usually found when solubilizing dye t o contain minute ultramicroscopically visible particles might be taken as another indication that the dye has in some manner increased the size and number of micelles. The Aerosols solubilize one another and can then solubilize dye. Thus, although a t 25" C. the solubility of Aerosol OT is only 0.033 M , this is increased to 0.0585 iM in 0.274 M Aerosol MA, and the mixture solubilizes 21.2 mg. of Orange OT per 100 cc. of solution. The data for the Aerosols indicate that with increasing dissymmetry, such as branching of hydrocarbon chains, and heterpolarity of the ions involved, micelle formation is much more gradual. It begins a t more concentrated solutions and extends over a wider range of concentrations than for the symmetrical or straight-chain compounds containing only one lyophilic group, which has been the only type much studied.
Vol. 34, No. 8
the National Oil Products Company, were pure sodium soaps free from sodium chloride, silicate, or other fillers and contained a maximum of 1 per cent water and 0.1 per cent free alkali. It was found that 0.1 per cent olive oil soap solubilized 1.51 mg. of Orange OT; that from oleic acid, 1.72 mg.; that from palm oil, 1.62 mg.; and that from t'allow, 2.43 mg. per 100 cc. Again this demonstrates the superiority of longer chain compounds as solubilizers. A comparison of the solubility of pure recrystallized Orange OT (1-o-tolylazo-6-naphthol) and Yellow AB (phenylazo2-naphthylamine) in 1 per cent solutions of pure and commercial anionic-cationic and nonelectrolytic detergents was given in Table I of a previous paper (11). Three different sulfated oils were also included as well as four pure bile salts. With the bile salts, mere oxidation of the three hydroxyl groups of the four-ring compound (sodium cholate) to three ketone groups (sodium dehydrocholate) caused a fairly efficient solubilizer to become noneffective. In all cases except one, the more hydrophobic Yellow AB was solubilized to a greater extent and illustrated the general principle of like to like. However, even with such closely similar dyes the amount varied from three to ten times as much, which indicates that the relative effectiveness of a group of solu' bilizers might vary with the dye used. TABLE V. SOLUBILITY OF ORANGE O T IN 0.5 PERCENTAQUEOUS SOLUTIONS OF PUREASD COMMERCIAL SOLUBILIZING SOAPLIKE DETERGENTS AT 25' C. Solubilizer Lauryl ester of glycine hydrochloride Lauryl ester of alanine hydrochloride Lauryl ester of a-amino isobutyric acid hydrochloride
htg. Dye/100 Cc. Soln.
C~~HZ~COOCZHI~XH--CO-CHZ-N-(CH~)~
4.24 3.97 3.70 2.51
61 Impure diethanolamine oleate Mainly diethanolamine laurate Mainly sulfated diethanolamine laurate A polyglycerol ester
4.55 2.97 3.14 3.0
TABLEVI. EFFECTOF INCREASING SULFATION UPON TEE SOLUBILIZING ACTIONOF SULFATED CASTOROILS IN ONE PER CENT h Q U E O U S SOLUTION hfg. Dye/100
Dye Orange OT
Detergent Aquasol AR-75% Morpel oil h 0 . 501 Morpeltex B
Yellow AB
Aquasol A R 75% Morpeltex B
Cc. Soln. 14.2 12.0 7.7 82.6 74.0
Per Cent Sulfation
4.3 8.5 32.5 4.3 32.5
These data are now supplemented by the further data of Table V, using the less soluble detergents a t 0.5 per cent. The lauryl amino acid esters were pure products obtained from the Emulsol Corporation; when compared a t equivalent normalities they are, as expected, about equally SOLUBILITY OF YELLOW AB IN AQUEOUS POTASSIUM TABLE IV. effective solubilizers. OLEATESOLUTIOXS AT 25" C. I n Table VI the values for the one per cent sulfated castor Normality of Mg. Dye/100 Mole Dye/ K Oleate Soln. Cc. Soln. Mole K Oleate oils have been corrected for the different percentages of 0.004 141 0.134 water in the original product and involve the assumptions 68 0.004 0.067 3s 0.004 that the original oils were comparable and that the ratio of 0.033 19 0.004 0.016 moles of dye to moles of sulfated oil is approximately con0.002 5.6 0.001 stant in this range. They show the decrease of solubilizing action with decreasing lyophobic character or increasing sulfation. To illustrate the contrast with an excellent detergent The lauryl esters of amino acid hydrochlorides also soluoperative even in dilute solution, the data of Table IV are bilize Pellow AB (about 8-12 mg. per 100 cc.). The digiven for potassium oleate. The results are comparable ethanolamine compounds were prepared by the Rit Products with those for sodium oleate, although somewhat affected by Company and were condensation products of 2 moles of hydrolysis. diethanolamine with 1 mole of oleic and coconut oil fatty Other less soluble soaps were tested in 0.1 per cent soluacids, respectively. The third product of this group had tion, as in practical washing. The soaps, obtained from
August, 1942
INDUSTRIAL AND ENGINEERING CHEMISTRY
also been treated with dimethyl sulfate. All the compounds in Table V apparently form micelles in solution and, except for the nonelectrolyte polyglycerol ester, are also to be classed as colloidal electrolytes.
Effect of Added Salts on Solubilizing Table VI1 shows the influence of added salts, which by themselves are nonsolubilizing, upon the solubilizing action of 0.1 N sodium deoxycholate. Previous work (4, 11) has shown that in concentrations where the solubilizer is not fully colloidal, addition of salts increases the amount of .dye solubilized due to its action in increasing the number of micelles in the solution. It is necessary to have anion concentration sufficient to form an appreciable number of micelles. Concentrations of sodium chloride up to 0.7 N , where the detergent is salted out of solution, do not produce solubilizing action by 0.005 N sodium decyl sulfonate. However, 0.1 N sodium deoxycholate already contains the maximum proportion of colloid, and added salt materially reduces the amount of dye solubilized, probably as a result of partial salting out or coagulating action or to a displacement of the sorption equilibrium. The ratio, moles of dye solubilized per mole of sodium deoxycholate, a t 25’ C. is 0.0271, which agrees well with previous data (11).
919
the solubilizer itself in solution), effectiveness as a wetting agent shows a maximum at around seven to twelve carbon atoms ( I ) , depending on structure. Also, compounds such as Daxad No. 11, which lower the surface tension only a dyne or so, are fairly good solubilizers. Suspending action was defined and a hypothetical explanation set up in a previous review article (8). We ascribe i t to the ionic atmosphere around the charged particles, which must be inseparable from them on account of the necessity of electroneutrality. These gegenions, therefore, lessen the sedimentation of the particles. Such suspending action is distinct from wetting, solubilization, or protective action and from many other different factors in detergency. Solubilization is differentiated from hydrotropy in that the latter refers to solutions so concentrated that the thermodynamic environment is changed and usually no colloid is involved. Powney and Noad (16) found that the soaps have an optimum action in suspending ilmenite particles at concentrations decreasing rapidly with increasing chain length.
Solubilizing in Nonaqueous Solvents
Recently (10) it was demonstrated that solubilizing occurs in nonionizing media such as heptane, benzene, and toluene, indicating that micelle formation also takes place in nonaqueous solvents. We have since found that less than 2 mg. of aluminum oleate, magnesium ricinoleate, lead stearate, a commercial product called “Dissolvo”, or glyceryl monoTABLEVII. SOLUBILITY OF YELLOW AB IN 0.1 N SODIUM ricinoleate in 25 cc. of toluene is able to solubilize Methylene DEOXYCHOLATE AS INFLUENCED BY TEMPERATURE AND ADDITION OF SALTS WHICHARE BY THEMSELVES NONSOLUBILIZINGBlue and Crystal Violet, although the dye is insoluble in the pure solvent. Similarly, glyceryl monooleate and sorNormality of Salt Soh. 25’ C. 62’ C. bitol dilaurate dissolved in n-heptane solubilize both of these 71 175 Na deoxycholate alone +0.025 NazS04 42 128 dyes in dilute solution; ethylene glycol monoleate and 37 113 +0.025 NaaPOl +0.025 NazCOa 44 144 propylene glycol monolaurate solubilize in concentration 41 119 + O . 025 NaCl greater than about one per cent, whereas butyl Cellosolve 32a 121“ + O .0256ucro8e laurate, o-hydroxydiphenyl, methyl caprylate, methyl steara Values doubtful because of bacterial decomposition. ate, palmityl amide, methyl linoleate, and refined cottonseed oil are completely ineffective as solubilizers. Congo Red was also tested with the last five compounds, and they were Whereas a t 25’ C. 30-35 molecules of bile salt are necesfound to be ineffective. A 0.2 per cent toluene solution of an impure lecithin solubilized both Crystal Violet and sary to solubilize 1 molecule of Orange OT, only about 10-12 molecules are necessary at 62’ C. This increase in solvent Methylene Blue as did a small amount of guaiacol in 40 cc. Preliminary results indicate that warm heptane solutions of power with temperature is a t first rather surprising since solubilizing action is almost surely connected with micelle diglycol laurate, sorbitol dilaurate, and magnesium ricinformation, which is known to decrease with rise in temperaoleate are able to solubilize small amounts of an oil sludge soluble in hot Nujol. ture. However, the presence of dye apparently alters considerably the equilibria involved. It is possible that heating Literature Cited in the presence of dye favors the existence of a larger number of smaller micellgs which, because of the increased surface (1) Caryl, IND.ENG.CHEM.,33, 731 (1941); Swan, “Synthetio exposed, are relatively more effective than larger micelles. Organic Chemicals”, Vol. 13, No. 3, Rochester, Eastman Methylcellulose and two starch derivatives, kindly supKodak Co., 1940. (2) Dietze, U. S.Patent 1,405,902(1922). plied by L. Zakarias, have a negligibly small solubilizing (3) Engler and Dieckhoff, Arch. Pharm., 230, 561 (1892). action but become fairly effective in the presence of large (4) Hartley, J. Chem. Soc., 1938, 1972. amounts of salts and alkali. However, the two starch (5) Heuter, Kunststoffe, 13, 13 (1923). derivatives alone can remove Methylene Blue from glass, (6) Heyden, von, German Patent 57,842 (1890). (7) Link, German Patent 35,168 (1885); Friedlaender, P., “Fortand they are used as laundry detergents.
Solubilization vs. Wetting Within solutions of detergents and wetting agents there exist complex equilibria between free ions, various types and sizes of ion aggregates and micelles, and the oriented layer of ions a t the surface and at solid and liquid interfaces which is responsible for the reduction of surface and interfacial tensions. Since the existence of micelles is responsible for solubilizing action, no correlation would be expected between the effectiveness of a substance as a solubilizer and as a wetting agent. That none exists is shown by the fact that, whereas effectiveness as a solubilizer increases with chain length (to a limit fixed only by the necessity for having
schritte der Teerfarbenfabrikation”, Vol. I, p. 11 (187787). (8) McBain, “Advances in Colloid Science”, Vol. I, pp. 99-142, Interscience Publishers, 1942. (9) McBain and McBain, J. Am. Chem. SOC.,58, 2610 (1936). (IO) McBain, Merrill, and Vinograd, Ibid., 62, 2880 (1940). (11) Ibid., 63,670 (1941). (12) McBain and Salmon, Ibid., 42, 426 (1920). (13) Merrill and McBain, J. Phys. Chem., 46, 10 (1942). (14) Nottbrack, Chem.-Ztg., 32, 100 (1908); Chem. Zentr., I, 778 (1908). (15) Otto, Ber., 27, 2131 (1894). (16) Powney and Noad, J. Teztile Inst., 30,T167 (1939). (17) Rappenstrauch, Arch. Pharm., 229, 201 (1891). (18) Smith, J. Phys. Chem., 36, 1675, 1684 (1932). (19) Valk6, Trans. Faraday SOC.,31, 254 (Jan., 1935). (20) Witt, Ber., 48, 747 (1915).
