64
M. Okazaki, I. Hara, and T. Fujiyama
(13) R. M. Barrer and D. L. Peterson, Proc. R. SOC. London, ser. A. 280,466 (1964). (14) G. T. Kerr, J. Phys. Chem., 71, 4155 (1967). (15) P. E. Eberly, Jr., C. N Kimberlin, Jr.. and A. Voorhies. Jr.. J. Catal., 22, 419 (1971). (16) B. I. Mikunov, V. I. Yakerson, L. I. Lafer, and A. M. Rubinshtein, bv. Akad. Nauk. SSSR, Ser. Khim., 449 (1973).
(17) I. V. Mishin, A. L. Klyachko-Gurvich, and A. M. Rubinshtein. lzv. Akad. Nauk. SSSR, Ser. Khim., 445 (1973). (18) I. V. Mishin, G. A. Piloyan, A. L. Klyachko-Gurvich, and A. M. Rubinshtein, b v . Akad. Nauk. SSSR, Ser. Khim., 1343 (1973). (19) R. M. Barrer and E. V. T. Murphy, J. Chem. SOC.A, 2506 (1970). (20)L. I. Piguzova, E. N. Prokofeva, M. M. Dubinin, N. R. Bursian, and Y. A. Shavandin, Kinet. Katal., 10, 315 (1969).
Spectroscopic Studies of Surfactant Solubility. 1. Formation of Hydrogen Bonding between Surfactants and Chloroform Mitsuyo Okazaki, lchiro Hara, Laboratory of Chemistty, The DepaHment of General Education. Tokyo Medical and Dental University, lchika wa, Japan
and Tsunetake Fullyema* Department of Chemistry. Facutty of Science, Tokyo Metropolitan University, Setageya, Tokyo, Japan (Received Ju/y 28, 1975)
Water soluble surfactants which have high solubilities in chloroform are verified to form hydrogen bonds to chloroform by the analysis of infrared absorption spectra. The quantitative analysis of the C-D stretching vibration bands shows that these molecules dissolve in chloroform by forming a complex consisting of several solvent molecules and one solute molecule. A detailed method of determining the composition of the complex in solution is described. The molecules studied are trimethyl- and dodecyldimethylamine oxide, decyltrimethyl-, cetyltrimethyl-, tetraethyl-, and tetra-n-butylammonium chloride, decyl- and octadecylphosphorylcholine, and cetylpyridinium chloride. Pyridine, pyridine 1-oxide, and n-octylamine are also studied as references.
Introduction
and pyridine 1-oxide were purchased from Tokyo Kasei Co., Ltd. and were used without further purification. Solubilities of surfactants in organic solvents have been Absorption Measurements. The absorption spectra were studied by many authors.l-ll The present report concerns recorded with JASCO IR-G grating spectrometer at a resothe study of the solubilities of some surfactants in chlorolution of 1 cm-l. The spectra of chloroform-d solutions form by infrared spectra. Hydrogen bonding of chloroform containing the acceptor in the concentration range from 0 to proton acceptor molecules has been well established, and to 0.5 M were measured with a KBr cell having a thickness various systems have been studied by infrared and NMR of spectra of chloroform and chloroform-d c ~ m p l e x e s . l ~ - ~ ~ 0.1 mm. The thickness of the sample cell was checked by the interference fringe method. Most of the spectroscopic studies were based upon the asSample solutions containing various amounts of the sosumption of 1:1complex formation between solvent and solute molecule were prepared just before measurement by lute molecules. In this study, we determine the number of weighing the solute and chloroform-d in the sample flask. chloroform-d molecules bonded to a proton acceptor by Since all of the solutes are very hygroscopic, they were quantitative analysis of the C-D stretching vibration band dried thoroughly to an anhydrous condition before each a t the dissociation equilibrium between free and bonded measurement. The elimination of water from the sample chloroform-d molecules. solution was confirmed by observing the infrared spectra in the region of 4000-2000 cm-l. Experimental Section The refractive index nD20 and the specific gravity of the Materials. Chloroform-d was purchased from Merck and solution were measured with an Abbe refractometer and a Co., Ltd. and was used without further purification. picnometer, respectively, a t the same time as the absorpDecyl- and octadecylphosphorylcholines were synthetion measurements. sized by the authors. An aqueous solution of decyldimethAll the measurements were done at 20 f 2OC and the abylamine oxide was supplied from Kao Atras Co., Ltd. and sorption spectra of the C-D stretching vibration for the frewas used after a crystallization from acetone. Cetyl- and quency region of 2500-2000 cm-l were measured with a decyltrimethylammonium chlorides and cetylpyridinium resolution of 1cm-l and scanning speed of 33.3 cm-l/min. chloride were purchased from Tokyo Kasei Co., Ltd. and purified by recrystallization from acetone. The purities of Results and Discussion these samples were checked by thin layer chromatography. Infrared Spectra of Chloroform-d Solution. Table I Trimethylamine oxide, tetraethylammonium chloride, shows the structures of the molecules studied in the tetra-n-butylammonium chloride, n-octylamine, pyridine, The Journal of Physical Chemistry, Vol. 80, NO. 1, 1976
65
Spectroscopic Studies of Surfactant Solubility TABLE I: Molecules Studied and Spectral Characteristics for C-D Stretching Vibration of Chloroform-d Acceptor a R
CH3 I+ R-N-0-
Trimethylamine oxide Dodecyldimethylamine oxide
I
-7 7
68
-8 2
68
-5 9
42.5
-5 9
43.5
-62
43.5
-68
49.5
-46.5
44.5
-45.5
44
-5 6
40
CH, Decyltrimethylammonium chloride Cetyltrimethylammonium chloride R
I R-N+-R. I
Tetraethylammonium chloride Tetra-n-butylammonium chloride
ci-
R 0
II
Decylphosphor ylcholine Octadecylphosphorylcholine
ROPO-
I
R
Cetylpyridinium Chloride
CI -
aThe acceptor concentration is 0.45 M.
Chloroform-d
T f
Y
V
v1 bonded
4000
3?00
2000
"2 bonded
1600 wavenumber
1200 (
L' 800
v'v3
bpndod 400
0-l )
Figure 1. Infrared spectra for the chloroform-6C12A0system. CqzAO concentration is 0.70 M.
-#-+
present work. All the molecules have the structure with zwitterionic or ammonium salt form and show high solubilities in both water and chloroform. As these substances are hardly soluble in nonpolar solvents and slightly soluble in non-hydrogen-bonding polar solvents, the solubilities in chloroform suggest the existence of some intermolecular interactions between the solute and solvent mol-
ecules. Actually, the infrared spectra of chloroform-d show remarkable changes in the fundamental bands of chloroform-d; the C-D stretching, the C-D bending, and the C-Cls symmetric stretching vibrations. The v1 vibration changes its frequency about -45 to -82 cm-' from that of pure liquid chloroform-d, while the u2 and u3 vibrations shift about 20 and -15 cm-l, respectively. These observaThe Journal of Physical Chemistry, Vol. 80, No. 1, 1976
M. Okazaki, 1. Hara, and T. Fujiyama
TABLE 11: Relative Intensities of the C-D Stretching Vibration for the Chloroform-d-C, , A 0 System Sample Wt % no. C,,AO
.I
I
F
B
0 1
2400
2300
2200
wavenumber
(
2100
J
2000
cm-1 )
0
0
1 2 3 4 5 6 7
0.2569 1.0106 1.4062 1.7816 2.8574 2.8608 5.2304 6.4981 8.7316
~ D Q
d
Ib *
If*
1.4470 1.4471 1.4472 1.4473 1.4474 1.4476 1.4476 1.4481 1.4486 1.4488
1.48 0 1.302 1.478 0.186 1.279 1.472 0.629 1.262 1.469 0.886 1.252 1.465 1.064 1.216 1.457 1.709 1.209 1.457 1.647 1.189 1.438 2.943 1.120 8 1.428 3.610 1.068 9 1.411 5.029 1.010 Q n p is refractive index and d is specific gravity for the
solution. Ib * and If* are relative intensities defined by the eq 2. (See text.)
Figure 2. Infrared spectra for chloroform-d solutions in the C-D stretching region (F. free; B. bonded): - chloroform-d (pure),C12A0, - - - octadecylphosphorylcholine,- - - - cetyltricetylpyridinium chloride, methylarnmonium chloride, - tetra-n-butylarnrnonlumchloride.
-.-.
-
-
e
- . . _ a .
1.0
2400
2300
2200 wavenumber I cm-1 1
2100
1;
Flgure 3. Concentration dependence of the C-D stretchlng vibration of chloroform-d for & A 0 solution. tions indicate the formation of hydrogen bonding between the solute molecule and chloroform-d. As an example, the infrared spectra for the chloroform-d solution of dodecyldimethylamine oxide (C12AO) are shown in Figure 1. Intensity Measurements of u1 Bands. The absorption spectra for the chloroform-d solutions in the frequency region from 2500 to 2000 cm-l are shown in Figure 2. Bands of the C-D stretching vibration corresponding to the free and the bonded states are observed separately. All of the bonded bands for various solutes show large frequency changes to the low-frequency side and increased band width or absorption intensity. The half-band width, Au112, and the frequency shift, u - yo, are listed in Table I, where the concentration of the solute is 0.45 M and uo is the maximum absorption frequency of the C-D stretching vibration of pure liquid chloroform-d (uo = 2254 cm-l). The values of u - uo and Au1/2 of Table I are much larger than those observed for diethyl ether, acetone, and pyridine solutions,13 which may indicate the formation of stronger hydrogen bonding in the present systems. The absorption spectra for the C-D stretching vibration of chloroform-d containing various amounts of the solute molecule were measured in each system. The spectra obtained for chloroform-dCl2AO system are shown in Figure 3. As the concentration The Journal of Physical Chemistry, Vol. 80, No. 1, 1976
Figure 4. It,' vs. Table 11).
/f'
(
cm-1 I
plot for the c$Ioroform-d-C12AOsystem (see
of the acceptor molecule increases, intensities of bonded bands increase remarkably, while those of free bands decrease. One of the results is listed in Table I1 (chloroformd-ClZAO system). Analysis of Intensity Data. The relative intensities of the free and the bonded bands are defined, respectively, as
and
in cm-I, where 1 is the thickness of the sample, 10the energy of incident light, I the energy of transmitted light, and u the frequency of light. Hereafter, the subscripts b and f refer to the bonded and free states, respectively. The molar concentration of chloroform-d in the solution was determined from the observed weight concentration and density of the solution. After being corrected for the local field effect,12the relative intensities, z b and If,are re-
Spectroscopic Studies of Surfactant Solubility
67
TABLE 111: Final Results for Intensity Data rb
Acceptor Trimethylamine oxide Dodecyldimethylamine oxide Decylphosphorylcholine Octadecylphosphorylcholine Decyltrimethylammonium chloride Cetyltrimethylammonium chloride Tetraethylammonium chloride Tetra-n-butylammonium chloride Cetylpyridinium chloride n-Octylamine Pyridine Pyridine 1-oxide
1.2
9
rf
9
Intensity ratio,
Flgure 5.
6'
vs. If'
rf
cm2/mol
3177
106
30
2.5
75
1726
106
16
5
80
1944
108
18
3-3.5
54-63
1460
104
14
4-5
56-70
1906
106
18
4-4.5
72-81
1930
106
18
4-5
72-90
4468
114
39
2-2.5
78-98
5483
112
49
2
98
2310 1824 1780 1850
105 103 107 106
22 18
3-4 1 1 2
66-88 18 17 35
rb/rf
17 17.4
(rb
1.3 I f * [ crn-1 )
ne system.
Solvation no., n
cm*/mol
If*
plot for the chloroform-d-decylphosphorylchoii-
duced to the values a t the molar concentration of pure liquid chloroform-d, COCDC~~ = 12.30 M, thus
cm-1 )
plot for the chloroform-d-pyridine system.
and (Cb*
+ cf*)= f c ( C b + cf) = C°CDC1:~
(5)
Equations 4 and eq 5 give the relation
If* = f d d f zb*
Flgure 6. I!," vs. If*
[
= fdfcIb
and fc fd
or
= 12.30/CCDC13
= 9nD/(nD2
+ 2)2
(3)
Ib*
= -(rb/rf)If*
+ rbC'CDCI,,
(6)
By plotting Zb* against Zf* a t a series of concentrations, a where n D is the refractive index of the solution and COCDC~:~ straight line with a slope of - @ b / r f ) is generated so far as is the molar concentration of chloroform-d. the absolute intensities, I'f and r b , are constant over the Now, the absolute intensities, rfand r b , are defined as concentration range employed. The extrapolated If*value at I b * = 0 corresponds to the rfvalue of pure liquid chloroc b * r b = zb* form-d, and may be compared with the rf value directly (4) cf*rf= If* observed for pure liquid chloroform-d. The Journal of Physical Chemistry, Vol. 80, No. 1, 1976
68
M. Okazaki, I.
TABLE IV: Calculation of Solvation Number, n, for the Chloroform-d-C, , A 0 System
chloroform-d and the acceptor molecule, the product of the ratio, I'b/I?f, and the solvation number, n, is an appropriate estimate of the stabilization energy of one acceptor molecule through hydrogen bond formation in solution. In other words, the product is a good way to estimate the solubility of an acceptor in the solvent. The last column of Table 111shows the calculated n(rb/ I'f) products. The results indicate that the product takes almost similar values for all the surfactants studied. This may correspond to the fact that the stabilization energy necessary for the acceptor to be dissolved in chloroform-d is almost the same. In case weak hydrogen bonding is formed, e.g., octadecylphosphorylcholine, a large number of solvent molecules are necessary to dissolve the acceptor. In case strong hydrogen bonding is formed, e.g., tetra-n-butylammonium chloride, only a few solvent molecules are necessary to form a stable complex in solution.
lo3 x C,, Solvation mol/cm3 mol/cm3 no., n 1 0.108 0.017 6.47 2 0.364 0.066 5.52 3 0.513 0.092 5.56 4 0.616 0.117 5.25 5 0,990 0.190 5.21 6 0.954 0.190 5.01 7 1.705 0.357 4.78 8 2.092 0.449 4.66 9 2.914 0.619 4.71 a cb is Ib/rb, C, is the concentration of the acceptor molecule. Solvation number, n, is Cb/C,.(See text.) Sample no.
Hara, and T. Fujlyama
l o 3 x Cb ,
In Figures 4-6, plots of Ib* vs. If* for chloroform-dC12A0, chloroform-d-decylphosphorylcholine,and chloroform-d-pyridine systems are shown. It can be seen from References and Notes these figures that linear relationships exist between Ib* R. A. Reck, H. L. Harwood, and A. W. Ralston, J. Org. Chem., 12, 517 and If*.Consequently, the validity of Lambert-Beer's law (1947). R. S. Sedgwick, C. W. Hoerr, and A. W. Ralston, J. Org. Chem., 10, 498 was verified in these concentration ranges. I t is also seen (1945). from the figures that the extrapolated If*values a t Ib* = 0 H. J. Harwood, A. W. Ralston, and W. M. Selby, J. Am. Chem. SOC.,63, are almost same for those systems. For the chloroform-d1916 (1941). C. W. Hoerr. H. J. Harwood, and A. W. Ralston, J. Org. Chem., 9, 201 ClzAO system the I'f and I'b were 106 and 1726 cm2/mol, (1944). respectively. The observed absolute intensities by this A. W. Ralston, C. W. Hoerr, W. 0. Pool, and H. J. Harwood, J. Org. Chem., 9, 102 (1944). method are summarized in Table 111. The values of I'f are A. W. Ralston, H. J. Harwood, and E. L. DuBrow. J. Org. Chem., 9, 239 fairly identical for all systems. r b values are approximately (1944). equal for all acceptors except tetraethyl and tetra-n-butylS. H. Shapiro, "Fatty Acids and Their Industrial Applications", E. S. Pattison, Ed., New York, N.Y., 1968, pp 109-119. ammonium chloride, and trimethylamine oxide. C. C. Addison and C. R. L. Fumidge, J. Chem. SOC., 3229 (1956). Determination of Solvation Number. At a low concenJ. H. Hildbrand and R. L. Scott, "Solubility of Non-electrolytes", Reinhold, New York, N.Y., 1950. tration of the proton acceptor, all acceptor molecules are F. K. Brown and H. J. Harwood, J. Am. Chem. SOC.,72,3257 (1950). considered to be bonding to chloroform-d mole~ules."~ C. W. Hoerr and H. J. Harwood, J. Am. Chem. SOC., 74,4290 (1952). Therefore, the ratio of the concentration, c b , of the bonded S. R. Polo and M. K. Wilson, J. Chem. Phys., 23, 2376 (1955). R. C. Lord, B. Nolin, and H. D. Stidham, J. Am. Chem. SOC., 77, 1365 chloroform-d to the concentration, c,, of the solute, c b / c , , (1955). corresponds to the number of chloroform-d molecules atC. M. Huggins and G. C. Pimentel, J. Chem. Phys., 23,896 (1955). C. M. Barrow and E. A. Yerger, J. Am. Chem. SOC., 76, 5247 (1954). tached to an acceptor molecule. Using the observed I'b R. E. Glick, Chem. lnd., 413 (1956). value, c b is determined as C. M. Huggins and G. C. Plmentel, J. Chern. Phys., 23, 1244 (1955).
(7) As c, is known, the ratio, c b / c , , is easily determined. We call the ratio solvation number, n. The calculated results for n are summarized in Table 111. As an example, the detailed data for C12AO system are shown in Table IV. The solvation number obtained in this case is 4.71-6.47.Therefore, it is concluded that about five chloroform-d molecules and one ClzAO molecule form a complex molecule in solution. Spectroscopic Information and Solubility. Table I11 shows the absolute intensities and the solvation numbers observed for various acceptors. I t is seen from Table 111 that a complex consisting of several solvent molecules and one acceptor molecule is formed in the solution. Only when an acceptor is pyridine or n-octylamine is the existence of a 1:l complex verified. The solvation number is largest in the octadecylphosphorylcholine system and smallest in the tetra-n -butylammonium chloride system. The absolute intensity of the hydrogen bonded chloroform-d, on the other hand, is largest for the tetra-n-butylammonium chloride system. If the intensity ratio, I ' b / r f , can represent the strength of hydrogen bonding between
The Journal of Physical Chemistry, Vol. 80, No. 1. 1976
G. J. Korinek and W. G. Schneider, Can. J. Chem., 35, 1157 (1957). L. W. Reeves and W. G. Schneider, Can. J. Chem., 35,251 (1957). M. F. Rettig and R. S. Drago, J. Am. Chem. SOC.,88,2966 (1966). M. W. Hanson and J. B. Bouck, J. Am. Chem. SOC.,79,5631 (1957). E. Halpern, J. Bouck. H. Finegold, and J. Goldenson, J. Am. Chem. SOC., 77, 4472 (1955). B. N. Khore, S. S. Mltra, and G. Lengyel, J. Chem. Phys., 47, 5173 (1967). P. J. Berkeley, Jr., and M. W. Hanna, J. Chem. Phys., 41, 2530 (1964). P. J. Berkeley, Jr., and M. W. Hanna, J. Phys. Chem., 67, 846 (1963). A. L. McClellan, S. W. Nlcksic, and J. C. Guffy, J. Mol. Spectrosc., 11, 340 (1963). J. Devaure, G. Turrell, P. Van Huong, and J. Lascombe, J. Chim. Phys. Physicochim. Biol., 65, 1064 (1966). P.Bacelon, J. Corset, and C. De Loze, J. Chim. Physicochim. Biol., 70, 1145(1973). R. Mierzeckl, Rocz. Chem., 46, 1375 (1972). W. E. Thompson and G. C. Pimentel, 2.Nektrochem., 84, 748 (1960). L. Segal, J. Phys. Chem., 65, 697 (1961). K. Szcrepaniak, Bull. Acad. Pol. Sci. Ser. Sci. Math., Astron Phys., 12, 189 (1964). K. Szczepaniak and A. Tramer, Bull. Acad. Pol. S d Ser. Sci. Math., Astron Phys., 13, 79 (1965). W. 0. Paterson and D. M. Cameron, Can. J. Chern., 41, 198 (1963). R. Kaiser, Can. J. Chem., 41, 430 (1963). V. V. Bhujle and M. R. Padhye, lndian J. Pure Appl. Phys., 10, 867 (1972). J. R. Baker, I. D. Watson, and A. G. Williamson, Aust. J. Chem., 24, 2047 (1971). Wel-chuwan Lin and Shyr-JlnTsay, J. Phys. Chem., 74, 1037 (1970). It is ascertained that the C-D stretching band corresponding to the free state completely disappears at saturation.
