12
hlCB.IIS, \TILDER
h 3 D MERRILL, J R .
SOLITBILIZATIOS O F KATER-IKSOLUBLE DYE BY COLLOIDAL ELECTROLYTE8 B S D X O S - I O S I Z I S G DETERGESTS‘ JAMES R. AIcBXIS, .1RTHYIt G WILDER,? Depaitmerit
OSChemislt U , Stnrcfoid I
ah11
R C MERRILL, JR 3
niielsity,
Calzfomza
R e c c i z e t l Aicqitsl 26, 1941
Solubilization (4) consists in the spontaneous passage of an insoluble substance into a dilute solution of a detergent to form a thermodynamically stable colloidal solution. Recent studies from the Stanford laboratory are those of Merrill ( G , 8), Sister Agnes Ann Green (3, 5), and Richards (7). An extensive survey of the relevant literature has been given by Sister Agnes Ann Green (2). The present work describes the solubilization of water-insoluble dye over a complete range of concentration from 0 to 100 per cent detergent, using hexanolamine oleate and two non-ionic detergents. These and other results are contrasted n-ith ordinary solution in mixed solvents. I n each case strong solubilization appears as soon as colloid is present. Other results refer t o solubilization by bile salts and the enhancing effect of added sodium salts thereon. Some comparisons are made x i t h the osmotic behavior of the respective detergents. ZIATEIZI.ILS . I S D METHOD
The experimental method has been described previously ( 5 ) . Well-crystallixed dye \\-as used, measurements being made after the first week of mild agitation on successive samples until constancy indicated that equilibrium was attained. Each sample was centrifuged for 30 min. and allon-ed to stand for 24 hr. before taking clear supernatant liquid for analysis. The hexanolamine oleate u s prepared by mixing equivalent weights of oleic acid (Kahlbaum) and hesanolamine, kindly supplied by the Shell Development Company. Sonaethylene glycol monolaurate was obtained from the Glyco Products Co., Inc. The pure bile acids nere supplied by Riedel de Haen and neutralized n ith carbon dioxide-free sodium hydroxide. Detergent “X” is a condensation product of isooct\-lpheno14 and ethylene oxide. Triton KE (polyalkylene ethyl alcohol) wah supplied by Rohm and Haas. Tlie Catol 607 was especially purified by the Emulsol Corporation ; it has the following formula:
Cii Ha 3 CO 0 C2Hh S H CO CH2-S
/CH-CH
\\
/cH I\ C1 CH=CH 1 Presented a t the Twenty-first Satiorial Colloid Symposium, n-hich v-as held under the auspices of the DiT-ision o f Colloid Chemistry of the Anierican Chemical Society a t Palo Alto, California, June 1s-20, 1947, 2 Preqent address: Pernianente l i e t a l s Corporation, Permanente, California. 3 Present address: Philadrlphia Quartz Company. Philadelphia, Pennsylvania. (2-Met hyl hept yl) phenol.
13
SOLUBILIZATIOS O F TVATER-ISSOLUBLE DYE
The purified Oronite sulfonate was supplied by the Oronite Chemical Company. It is a sodium sulfonate of a trisubstituted benzene having a total of eighteen carbon atoms in the three substituting alkyl groups. I t contained 67.57 per cent active material, 32 per cent water, and 0.40 per cent sodium sulfate. The dyes were supplied by the Calco Company, and were Orange OT (F.D. and C. Orange S o . 2 ; 1-o-tolylazo-2-naphthol) and Yellov AB (F.D. and C. Yellox- S o . 3; phenolazonaphthalamine). RESULTS WITH HEXkIiOL \ M I S E OLE.\TE
The colloidal electrolytic detergent hesanolamine oleate was selected for study because it offered an opportunity to compare solubilization in an isotropic solution with that in an anisotropic solution at moderate temperature, and also because it is miscible with water in all proportions. -An equilibrium temperature TA\BLE 1 S o l u b i l i z a l z r n o j Orange O T ( m o l zct 262 3 ) z7z aqueous soliitions of hexanolamine oleate (mol. ? i f . 4G0 0) at 7'0°C. ~~~
~
DLTTRGEhT
xcighi p e r c e n l
0.5 1.0 5.0 10.0 16.66 20.0 25.0 50.0 90.0 100.0 :,
,I I
i
1. ~
I
1
II I
D Y E P E R LIOLE O F UETERGT>-T
grams
7.56 8.32 8.20 5.30 5.38 5.50 5.44 7.12 12.90 16.20
,
i
I
i I
x
MOLAR R A T I O USE 6O.AP
-
loz
~~
2.86* 3.18* 3.12* 2.02 2.05 2.10 2.07 2.72 4.92 6.18
* 1ndicate-b suspending a c t i o n .
of 70°C'. v a s chosen for most of the studies vith this detergent, since solutions above approximately 10 per cent are viscous solutions, or even jellies, a t room temperatures. The data obtained are summarized in table 1. The solubilixation decreace. .mootlily from 100 per cent detergent don n t o 10 per cent; that i., from an isotropic phase through t n o liquid-crystalline phases, and the ordinary isotropic ~ o a psolution. Belon- 5 per cent the values appear erratic, oning to suspending action on small particles or fragments of dye. The phase diagram of Gonick and JlcBain (1) had to be partially revised, in that it v a - found that a t 70°C. the heterogeneous region betn een isotropic solution and the first liquid-crystalline phase estended from 15 per cent to 30 per cent instead of from 28 per cent to 34 per cent. The revised phase diagram is given in figure 1. The circles represent the points originally established by Gonick and IfcBain, and the crosses the values which were obtained by sealing samples of various concentrations in evacuated tube5 and observing them be-
14
MCBAIS, WILDER AXD MERRILL, JR.
tn-een crossed polaroids while gradually raising the temperature and keeping the contents stirred. =It 25"C., solutions of hesanolamine oleate \yere studied over a concentration range from about 5 per cent don-n to 0.025 per cent. To aroid suspension in the
200
t
t
PBCEWTACE
COMPOSITION EY YtEICHP
i , ' r ( ; , 1. Phase diagram for hexanolamine oleate
, %,eight 9 e r cent
I
mg.
0.04
1
mg.
1.53
0.23
dilute solutions the method developed by Sister _ignes Ann Green (5) was used, in which the dye was dissolved in n-hexadecane. The n-hexadecane itself is not solubilized (7). Results are set forth in table 2 and plotted in figure 2. The milligrams of dye solubilized and the molar ratio of dye t o soap both sholv an increase over this range. The increase is rapid a t first, trebling lietween 0.0255
SOLUBILIZATIOS O F WATER-INSOLUBLE DYE
15
and 0.1265, and then it slopes into a nearly linear increase with concentration up to 3 per cent detergent. Solubilization appears to follow the usual course of beginning distinctly below the so-called critical concentration for micelles, owing to promotion of formation of micelle through interaction of detergent with the solubilized material. For hexanolamine oleate the critical concentration is approximately 0.12 per cent. The solubilization curves and the osmotic coefficients for hesanolamine oleate appear to he very similar to those for potassium oleate. For 3 per cent hexanolamine oleate the solubilization at 70°C'. is trike that at 2.5"C. S o adequate explanation has yet been given of this usual temperature coefficient of solubilization.
E'rc; 2 . Solubilization of Orange OT by dilute aqueous solutions of hexanolamine oleate arid thr. iioii-ioriic I h t e r g e n t "S",at 25'c'.
Whcw IO ecpiralents per cent excess of the amine is added to a I per cent solution of hcsnnolamine oleate, the solubilization is scarcely affected; it falls from a molar ratio of 0.65 to 0.63 X lo?. RERI-LTS JVITH
CATOLGO7
The cation-actire detergent C'atol GO7 (mol. \\ t . 394.8) solubilizes Orange OT a t 0"('., a:: &o\vn in table 3. Table 4 shows the solubilization at 25°C. and also shoi\\ ho\v greatly it is enhanced by the addition of progressive amounts of pota-ium chloride. ,111 these results are compared in figure 3. RESL-LTh J\.ITH S O S - I O S I Z I S G DETCHGESTS
Son:iethylene glycol monolaurate (mol. wt. GOO), Triton NE (mol. wt. not mea.mretl), and Detergent "X" (mol. wt. 636) are non-ionizing detergents miscible with ivatrr in all proportions. Cnlike hexanolamine oleate, which is also miscible
16
M C B - U S , WILDER -4PI-D MERRILL, JR.
TABLE 3 S o l u b z l i z a f i o n of Orange OT an aqueous soluiions of C a f o l 607 at 0'C. cc OF
D I E PER 100
IORYALIT'I
SOLZ'TIOU~
D I E P E R GRAY O F
LIOLAR RATIO
~
x
IO4
DYE/C~TOL
DETERGEPIT
w. 0 0002 0 0005
I
0 0010 0 0025 0.0050 0.0075 0 0090 0 0120 0 0150 0 0180 0 0220 0 0325 0 0600 0 0900
I
I
I I I
I
0
0
0.003 0.02 0.04 0 13 0.30 0.51 0.75 1.12 1.36 1.77 3.10 5.72
0 40
0 6
8.71
I
TABLE 4
Solubilization of Orange 01'in ~riolesd y e X 103 p e r mole o j Catol 60Y solutions at 25"C., as influenced b y p o t a s s i u m chloride
I SORMALITY OF CATOL
I I
0.0002 0.0005 0 0010 0.0025 0.0050
0.0075 0 0090 0 0120 0.0180 0.0180 0 0220 0 0280 0 0325 C 060 0 090
j
, ~
P O T 4 S S I U Y CHLORIDE
~
I'vITHOUT SALT
0 2.4 1.9 1.6 2.7
1
0.010
s
1.9 2.6 2.3 4.7
i
0.030 s
1
2.3
-I 1
5.7
1
I I
0 0448 \
1 9 5 3 1
4 0
, '
1
0.1468
S
1
5.i
0.4468 .?:
2.8 5.3
~
i 1
l
7.5 s.2
6 6 I
2.5 3.6 4.6 5.1 5.3
4.5 4.9
5.9 6.1 5.7
6.1 6.3 8.9
5.6 5 .7
6.2
~
l
I
I
6.4
1
6 6
6.0
6.7
7 2
6.0
I
s.1
I
I
i.5
!I . 0
7.4 7.4
9.2 S.0
I
I
,
,
6.9 6.6
7 0 7 1
I
, I
!LO 7.1 7.6
!l.O
'3.4
with water but passes through tivo ranges of liquid-crystalline phases, all these solutions are free-flowing isotropic liquids over the \\hole concentration range a t 25°C. Solubilization by nonaethylene glycol monolaurate a t 25°C. is much greater
SOLUBILIZAiTIOS O F JV.\TER-ISSOLL-BLE
17
DYE
than by hexanolamine oleate a t 25°C. but is very simiilnr to that of hesanolamirie oleate a t 70°C. The results are shon-n in table 5 . Sonaethylene glycol monolaurate is a better solubilizer than potassium laurate, solubilizing tn-ice as much
11.0
1
10.0
9.0 m
2
0.0
a.
5”
i 3
El
7.0
6.0 5.0 4.0
3.0 2.0
1 .c
R O W L I T I SP C A I C L AO. bC7
FIG.3. Solubilization of Orange OT by solutions of a cation-active detergent with and without added potassium chloride.
T.4BLE 5 Solubilization of Orange OT b y nonaethylene glycol monolaurate at 25°C. DETERGEKT
\E P E R 100 C C . OF S O L V T I O S
1
D’E
PER G R A M OF DETERGEYT
%,eight9er cent
mg.
mg.
0.06 0.12 0.21 0.25 0.49 1.32 5.0 7.95 11 .o 15.46 20.98 28.10 37.49 s9.95 loo. 00
0.34 0.81 1.81 2.11 4.19 11.45 42.5 70.6 97.5 130 1so 245 365 2055 3075
5.52 6.60 8.31 8.51 8.55 8.68 8.49 8.88 8.77 8.11 8.57 8.71 (3.72 22.74 30.75
x
MOLAR RATIO DYE/SOAP
102
1.26 1.51 1.93 1.95 1.96 1.99 1.94 2.03 2.01 1.93 1.97 2.00 2.23 5.21 7.04
on a weight basis and five times the amount on the basis of mole ratio. Its critical concentration is also lower than that of potassium laurate. The results for Detergent “X” are given in table 6 and in figures 2 and 4. It,
18
MCBAIN, WILDER A S D JIERRILL, JR.
TABLE 6 Solubilization of Orange OT by Deteryent " X " ( m o l . ut. 696) at 25°C. COUPOSITION BY WEIGHT
I
YE PER 100 cc. OF SOLUTIOK~
p e r cent
ms .
0.0169 0.0292 0.0562 0.1401 0.2566 0.509 1.003 2.011 4.392 4.550 7.262 14.489 26. 047 19.367 74.785 100.0
0.032 0 .os5 0.177 0.510 0.961 1.93 3.66 10.38 23.45 25.00 11.80 78.75 118 33i 850 3250
1 1 I I
DYE PER G R A Y OF DETERGENT
x
MOLAR RATIO
101
DYE/SOAP
mg .
1.89 2.91 3.15 3.66 3.75 3.83 3.99 5.li 5.30 5.49 5.73 5.47 5.68 6.83 11.36 32.49
0.46 0.71 0.76 0.89 0.91 0.93 0.99 1.25 1.30 1.33 1.40 1.32 1.38 1.66 2.76 7.89
TABLE 7 Solubalzzation of Orange OT in aqueous solutzons of Traton X E (assumed m o l . wt.600) at 25°C. TRITON NE PER 100 CC. OF SOLUTION
grams
0.008 0,010 0.050 0.10 0.50 1.oo 2.07 3.00 4.1.5 5.0 6.0 8.3 10.0 11.07 14.76 19.68 19.69
26.25 35.00
1
S E PLR 100 CC. OF SOLUTION
0.06
I I I I
I I ~
99.
99. 129. 173.
I ,I
x lo2
MOLAR RATIO DYE/TRITOH
.
7.5* 10.0* 6.0" 6.2* 5.0" 5.4* 4.7
~
-3
I t .
TRITOS SE
mg
mg.
0.3 0.62 2.5 5.1 8.7 11.3 18.0 25.7 30.5 36.5 50.4 52.
DYE PER GR41* OF
4.7 4.8 5.1 5.0 4.0 5.0 5.1 5.2 6.0 5.0 5.1 4.9
1.72 2.29 1.37 1.42 1.15 1.24 1.08 1.08 1.10 1.17 1.15 1.12 1.15 1.17 1.19 1.17 1.17 1.17 1.12
-~__
' Rcsults
high, owing t o suspendiug of finc particlm of d y e .
critical concentration is ahout the same as that for the other two non-ionizing detergents studied. The results with Triton N E are given in table 7.
SOLUBILIZ.1TIOS OF SOLUBILIZATIOS
OF
Jv-ITER-ISSOLUBLE
ORASGEOT
19
DYE
I-ELLOW h B BY BILE
ASD
SALT^
Yellou- AB is about 3.5 times more soluble than Orange OT in solutions of bile salts. Sodium cholate is not as effective as sodium deoxycholate but sodium dehydrocholate is of a lower order of magnitude altogether, solubilizing only 1/85th as much as the deoxycholate. Conductivity and osmotic coefficient shoir that sodium dehydrocholate contains very little colloid. The results are given in tables 8 and 9, where it is also shown that in every case the solubilization is enhanced by the presence of 0.025 S sodium salt. This corrects the opposite indication given in reference 6. TABLE 8 Solubilizaiion of Orange 0 2 ' a n d Y e l l o w A B at 25°C. bii 0.1 .I-s o d i u m deoxvcholate XIITBOUT SALT
~
.V Sac1 I WITH o 025 .V KazSOI
N I T R 0.025
orange OT Yellow AB,Orange OT,Yellow AB ~
1
)range OT Yellow AB --1-1--1
Milligranis of dye per 100 cc.. . . . . . . . 14.87 Grams of dye per m o l e . , . . . . . . . . . 1.487 Mole ratio X l o 3 dyeldetergent . . . . 5.66
47.50 4.750 1.92
1 I
1i.15 1 715 6 52
i
51.50 5.150 2.08
1 16.75 1 50.50
1
,
1.675 6.38
5.05 2.04
TABLE 9 Solubilization of Orange 02' at 85'C. b y 0.1 -Y s o d i u m cholate a n d s o d i u m dehydrocholate
Sodium cholate hlilligranis of dye per 100 cc. . Grams of d j e per mole Mole ratio X l o 3 dyeldetergent
. . . . . .I
11.53 1.153 4.90
10.45 1.045 3.98
Sodium dehydrocholate ~
~
Milligrarris of dye per 100 cc. Grams of dye per mole Mole ratio X l o 3 dye/detergent PURIFIED
~~~~
I
I
0.174 0 0174 0 0664
I
1
0.226 0 0226 0.0860
OROKITESULFOSATE
Solubilization of Orange OT by 1 per cent solutions of purified Oronite sulfonate (mol. Tvt. 432.6) a t 2 5 O C ' . is as follows, where the milligrams per gram and the molar ratio have been calculated on the basis of the active constituent in this commercial sample: hlilligrams of dye per 100 cc. of solution . . . . . . . . . . . . . . . . . . . . . . nlilliyrams of Jj-e per g r a m . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i Alole ratio dye soap.. . . . . . . . . . . . . . . . . Grams o f dye per mole. . . . . .
i
8.40 12.4 j,:jg 2.04
x
10"
20
McBAIX, WILDER AXD MERRILL, J R . DISCUSSION
It is of interest to compare and contrast ordinary molecular solutions of dye by mixed solvent with solubilization by aqueous colloidal electrolytes. This is done in figure 4. The solubility of Orange OT at 25°C. in aqueous acetone is excessively small until there is a preponderance of acetone: Per cent acetone Grams of dye per niolc
1
16 5 0 0Uil
8.1 0 0020
1 ,
34.6 0.0066
51.3 1 76.1 0.055 0 37
~
1
100 13.6
20
I -
15
-
2or
I
E
I
PWCEN'IACE CGWOCI?iOI 3 Y YEISP?
FIG.4. Solubilization of Orange OT by one anion-active detergent and three non-ionic detergents over the whole range from 0 t o 100 per cent, as compared with mere solubility in mixtures of water with acetone or ethyl alcohol.
Similarly in ethyl alcohol, which is a much poorer solvent, the values are: Per cent ethyl alcohol Grams of dye per mol?
1
7.6
1
0
' ~
15.5 0.0015
~
32.3 0.0022
,
50.8 0 013
'
i1.0 93 7 0 0551 0 17
For 7.35 per cent butyl alcohol the solubility is 0.0011 g. per mole, since butyl alcohol is a better solvent than acetone, *I11such data shon- that n very large proportion of good solvent is required to make the dye soluble in the aqueous mixture and, conversely, a very small amount of water seriously cuts down the solubility in the organic solvent.
SOLUBILIZ.LTION O F WATER-IKSOLKBLE
21
DYE
In complete contrast, a very low percentage of colloidal electrolyte produces a high relative solubilization by the detergent in water. However, the solvent power of the 100 per cent pure liquid detergents is several times greater than the solubilizing power of the same weight of detergent in aqueous solution. It is also of interest to compare solubilization with the osmotic coefficient, because the osmotic coefficient clearly shows the onset of micelle formation. An example of this is given in figure 5 . The osmotic coefficient of the ratio of the observed Ion-ering of freezing point to that of fully dissociated ideal electrolyte is g = 8'3.716 m. The curves in figure 5 are antibatic. However, as in all cases on record, it is seen that the so-called critical concentration for micelle formation is distinctly anticipated in a lower concentration by a small amount of solubilization. This is significant because it shows that the colloidal complex between
r
1
3Y.O
--
05rnTIC C O B p P i C I B s
nmLL*LITy OF CAIOL
FIG.5 . Solubilization of Orange OT by the cation-active detergent Catol a s compared with the amount of colloid, indicated by the departure of the osmotic coefficient from the value of unity.
detergent and solubilized material is formed with positive affinity, and therefore the presence of even this small amount of dye promotes the formation of micelles in a solution othern-ise too dilute for the presence of colloid. I t clearly follows that the method of determining critical concentration for the formation of micelle by titration n-ith dyes such as pinacyanol, etc., must lead to concentrations slightly but definitely lover than the true values. SCMMART
The solubilization of n-ater-insoluble dye in aqueous systems by four nonionizing detergents and one ionizing colloidal electrolyte, hesanolamine oleate, has been determined oyer the whole range of concentration from 0 to 100 per cent detergent, and contrasted n-ith the behavior of solutions in mixed solvents. Added salts strongly promote solubilization by bile salts and the cationic
22
I. 12. KOLTHOFF I S D W.4RRES- F. JOHSBOS
detergent Catol 607, but sodium clehyclrocholatc is a far poorer solubilizer than lutions are recorded. T h e solubilization of dyc per gram of detergent is far from being eclual to the d u b i l i t y of the dye in that ~ I I I ’ Panhydrous detergent. l!k:FE;ItE:S
(
(1) GONICK, E., AND Mr13.~1x,.I. W.:, J . Ani. PI: S N : Ph.11. Dissertation, Stanford I.tiiversity, 19.16. ( 2 ) GREEN,SISTERA (3) GREEN,SISTER . ~ C ; K E SAss. A S I ) l r ( 3 I 3 ~ 1 9 J, . W.:.J. PIiys. (’hem. 51, 286 (1947). (4) JICRAIN.J . W.:Sdrnrcccs iri (‘olloitl Sc.ic.ricc , \.ol. I . pp. !19-142. Intersrirnce P u b lishers, Inca.. S e x R ACSKS .%Ns:.I. .\in. Chrtii. Soc. 68, 1731 (1046’1. ( 5 ) L f c R a r s , J . R., .GI) is) ,\fC13,41N; .I. .44s1) J f E R R I l , I , $ 11, c.,J R . : Ind.I:Ilg. C‘h~111.34, 915 (1942). ( 7 ) ~ I C B A IJN. , . ~ S DRICHARDS, 1’. 11.: Ind. h g . (‘hem. 38, 612 (1946). ( 8 ) MERRILI,,R . (”., JR.:.$SI) X l c U ~ r s .J. . W.:J. Pliys. (‘hem. 46, 10 (1912).
w., w.,
I. 11. 1iOI~THOE’I~ . 4 m W A I i R E S 1;. JOIIXSOS School oj’ (‘hcriiissfrjy, r-nicersity of .lfinr~e.sotu,.lIiriticupdis, Sfinnesotti
Kecei red -4u g u s t 26, i.947
In a recent publicat’ion (4)results of t’he measurement of the sodium-ion activity in aqueous solutions of va,rious anionic ‘detergents have been reported. Vse has been made of negatively charged collodion membranes, the potential difference b e t m e n the inside and the outside of the membrane being determined by the ratio of the cation activities of the solutions inside and out,side of the membrane ( I , 2 , 3, 5 ) . The method gives excellent results as long as \\-e are (lealing with one kind of cation only and not with a mixture of cations. It \vas fount1 that the sodium-ion activity in solutions of sodium salts of‘ detergents decreases slightly wit’h increasing detergent concentration in a way similar to the deereast: of the sodium-ion activity in solutions of sodium salts of strong electrolytes. Howeyer, at the critical concentration of the detergent, where marked micellization occurs, the sodium-ion activity was found to decrease abruptly. In the micelle the detergent anions are associated and a r closely ~ packed together. The net, negative charge of the micelle is equal t o the sum of the charges o f tlie sodium 1 Presented at t h e Twciit>--first Stttional Colloid Symposium, which was held under the auspices of the Division of Colloid (’hemistry of t h c . h e r i c a n Chemical Sorirty a t Palo A l t o , c’aliforiiia, Juiic 15-20, 1047. 2 This investigatioti \vas c a r r i d out u n d e r the sponsorship of t h e Office of Rubber Reserve, Reconstruction 1:iiiance (’orporation, in c*onnc,.ction\\-it11 the synthetic, rubber prograiii of t h e 17tiitedStates Government.
