648
K6z6 SHINODA, TERUKO YAMANAKA AND KYOJI KINOSHITA
Discussion The saturated vapor in equilibrium with solid Liz() contains gaseous Li, o2 and LizO in comparable amounts with LiO as a minor constituent. The composition of the vapor at 1 4 0 0 0 ~is. shown in Table Iv. In addition to the previous results, calculations using the limited data available for the LiONa (mass 46) peak show that ~ p = ~-5.2 ~ kcal./mole-l for the reaction Na(g) + LizO(g) = LiONa(g) + Li(g). The existence of detectable amounts of gaseous NazO molecules Over solid 80dium oxide is thus suggested. The heats of various reactions are given in Table VII. I n order t o see what effect the shape of the molecule has on the third law heats of reaction involving this molecule, a recalculation of the entrOpy a t 1400°K. was made assuming a linear model, but with the same bond constants. The resulting third law entropy for the linear model was 66.82 e.u.,
Vol. 63
compared with 71.35 e.u. for the bent model. At ,140OoK., the difference in AH would be TAS or 6.34 kcal. mole-l. Closer agreement between the slope and third law values of the heats is obtained USing thermodynamic quantities calculated for a bent model. This is to be expected since both covalent and ionic16models predict a bent form for the LizO molecule. In the case of the ionic model this bent ~ ~ 0 form is a result of the large polarizability of.the OXY$en ion and the high polarizing power of the lithium ion. The large amount of polarization in this molecule can also be considered as a large covalent contribution t o the bond. The third law heats are considered more reliable since the slope of the log P vs. 1/T curve could easily be too high if temperature gradients exist in the Knudsencell. (15) F. Hund, z. Physik, 32,1(1925).
STIEtFACE CHEMICAL PROPERTIES IN AQUEOUS SOLUTIONS OF ;PLTONIONIC SURFACTANTS: OCTYL GLYCOL ETHER, CY-OCTYLGLYCERYL ETHER AND OCTYL GLUCOSIDE BY K6z6 SHINODA, TERUKO YAMANAKA AND KYOJI KINOSHITA Department of Chemistry, Faculty of Engineemng, Yokohama National Universitu, Minamiku, Yokohama, Japan Received June $0, 1068
The surface tension, critical micelle concentration (c.m.c.), surface excess, foaminess and foam stability of aqueous solutions of octanol, octyl glycol ether, octyl glyceryl ether and octyl glucoside have been determined. The surface activity and/or c.m.c. values of non-ionic surfactants, containing the octyl group as the hydrocarbon chain, are similar to those of ionic surfactants containing the undecyl or dodecyl group as the hydrocarbon chain. As the foaminess and foam stability of the compounds in the series improved markedly with the increase in the size of the hydrophilic moiety, these properties are probably dependent upon the hydrophilic-lyophilic balance of the molecule.
Experimental
Introduction I n spite of the industrial importance of nonionic surface active agents, few reportsi-a concerning the surface chemical properties of the pure materials have been published, probably because the pure compounds are difficult to obtain; both the synthesis of pure polyoxyethylene alkyl ethers and the purification of commercial non-ionic surfactants are troublesome. We have investigated the surface chemical properties of a series of octyl poly01 ethers to determine the effect of differences in the hydrophilic group. The relatively short hydrocarbon chain, C,, was chosen as the hydrophobic group because (1) the c.m.c. values of these non-ionic surfactants are close to those of ionic surfactants containing the dodecyl group; (2) with Cs as the hydrocarbon chain, the hydrophilic-lyophilic balance changes considerably with an increase in the number of oxygen atoms from 1 to 6; and (3) the synthesis, purification and measurements of longer chain compounds are more difficult.
Materials.-Octanol obtained from the Ka6 Soap Co. Ltd. was purified by fractional distillation through a 100 cm. column to give a product boiling at 96' (16 mm.). Octyl glycol ether, synthesized4 from octyl bromide (b.p. 94-95" a t 20 mm.), and ethylene glycol (b.p. 116' at 40 mm.), wm purified by fractional distillation through a 60 cm. column, b.p. 132' (21 mm.); TPD 1.4355, n Z 0 D 1.4357.4 or-Octyl glyceryl ether prepared6 from glycerol a-monochlorohydrin b.p. 125-130' at 21 mm.) and sodium octylate, was puri ed by distillation, b.p. 132-133' (0.5 mm.); d20 0.9614; ~ 9 1.4517. 0 ~ 8-D-Octyl Glucoside.-Glucose was acetylated to give (3pentaacetyl glucose (m.p. 127.5-128.5') which upon bromination yielded acetobromoglucose, m.p. 87-88". This bromo compound reacted with octanol in the presence of silver oxide to give 8-tetraacetyl octyl glucosidesJ (m.p. 61.5-62.5'), which was deacetylated in sodium methylate solution in 24 hours a t 10-20' to yield P-octyl glucoside; m.p. 63.8-65'. (62-65',7 65-9906); [ C ~ ] ~ O D -33.8' in 4% aqueous solution ( [ a ] 2 0 ~ -34').7 Careful purification, drying and crystallization were indispensable in the synthesis of this compound. Procedures.-Surface tension was measured by the drop weight method, with a tip 0.249 cm. in diameter, in an air thermostat at 25 i 0.2". There was no appreciable change of surface tension with time within two minutes after the
(1) C. R. Bury and J. Browning, Trans. Faraday Soc., 49, 209 (1953). (2) T. Nakagawa, et al., J. Chem. SOC.Japan, 77, 1563 (1956); 79, 345. 348 (1958)(in Japanese). (3) L. M. Kushner, W. D. Hubbard and A. S. Doan, THISJOURNAL, 61, 371 (1957).
(4) F. C. Cooper and M. W. Partridge, J. Chem. Soc., 459 (1950). (5) G. G. Davies and W. M. Owens, ibid., 132, 2542 (1930). (6) C. R. Noller and W. C. Rookwell, J. A m . Ckem. SOC.,60, 2076 (1938). (7) W. W. Pigman and N. K. Riohtmyer, ibid., 64, 369 (1942).
x
May, 1959 SURFACE CHEMICAL PROPERTIES IN AQUEOUS SOLUTIONS OF NON-IONIC SURFACTANTS 640 TABLE I
a
RsOH RaOCHzCHzOH RsOCHzCHOHCHzOH RsOCH-( CHOH)& RaNCsH6CI R I?OS03Na RizO(CH2CHzO)r.sH Ref. 1. b Ref. 11. Ref. 12.
...
...
(R.9 30 32 32 41 34" 33,b 40c 34d
5.6 5.2 5.2 4.0 4.95 4.0c 4.9d
... .0013
Area per molecule
Surface excess (mole X 10 - 10)
0.0038 .0075 ,012 .I+
0.0049 ,0058 ,025 .23" ,0081b .00025d
+
Ref. 2.
formation of droplets. The correction of Harkins and Browns was applied. The foaming properties of a given surfactant are characterized by at least two parameters; one is the foaminess and the other the foam ~ t a b i l i t y . The ~ foaminess was measured by the procedure described previously.10 The foam stability was expressed as the time required for the foam height to decrea.se to one-half of the initial height in a closed test-tube.
Results The surface tension-log concentration curves are shown in Fig. 1. For #e sake of comparison, the data for polyoxyethylene dodecyl ether2and sodium dodecyl sulfate" were included. The value of octyl glucoside obtained by Bury and Browning' is in excellent agreement with our value. The inflections in the curves correspond to the c.m.c. values (or the maximum concentration of molecular dispersion) of non-ionic surfactants. Because the activity of solute is constant over the flat portion of the surface tension-concentration curve for a two compbnent system, the concentration of molecularly dispersed solute stays approximately constant over the flat portion, provided the solution is dilute. The c.m.c. values thus obtained from Fig. 1 are given in Table I. The flat portions of the surface tension-log concentration curves increased remarkably with the size of the hydrophilic group, i.e., the larger the hydrophilic group, the larger the ratio of solubility to c.m.c. This flat portion (micellar region) is very significant, since surfactants, which do not show this phenomenon, possess little solubilizing power, detergent action, etc. Table I gives the c.m.c., surface excess and residual mea per molecule estimated from the data in Fig. 1 under the assumption that b In a / b In c = 1. The values for octylpyridinium chloride' were included for comparison. The solubility was obtained from the turbidity change. The surface tension measurements were extended to the emulsified solution in some cases in order to obtain a clearer flat portion. Foaminess and foam stability are plotted as functions of the concentration in Fig. 2. The foaminess of octanol (30 seconds after shaking) was zero over the concentration range examined. The arrows indicate the c.m.c. values. It is evident that there is a close relation among foaminess, foam stability, c.m.c. and hydrophiliclyophilic balance. (8) W. D. Harkins and F. E. Brown, J. Am. Chem. SOC.,41, 519 (1919). JOURNAL, 62, 159 (1958). (9) W. M.Sawyer and F. M. Fowkes. THIS (IO) M. Nakagaki and I
