J. Phys. Chem. 1980, 8 4 , 2287-2291
conducted with this in view choosing menadione (MD)vitamin K3as a solute. On photolysis in aerated methanol, this compound produces a product which is fluorescent (A,, = 330 nm, A,, = 455 nm). Photolysis a t -350 nm of MD after solubilization in NaLS and CPC micelles show marked differences. MD solutions in NaLS show product fluorescence after photolysis a t 455 nm whereas CPC solutions do not. The absorption spectra on photolysis show a correspondingly little change a t h = 330 nm in CPC solutions but a large change in methanol and NaLS solutions. Change in [MD] on photolysis was measured by the cysteine method4 arid typically decomposition of MD is -3.5 times higher in NaLS and n ~ 2 . 5times higher in methanol as compared with CPC solutions. This observation clearly points out the influence of host micelle in governing photoreactions in typical biologically important moleculea. Conversely, we suggest that hostmicelle-sensitized photodecomposition of a solubilized solute may also be possible and plays an important role in photobiology.
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E. W. Anacker, J. Phys. Chem., 62, 41 (1958). The authors are very thankful to one of the referees for suggestlng this. Reference 7, pp 90 and 92. M. E. L. McBain and E. Hutchinson, “Solubilization and Related Phenomena”, Academic Press, New York, 1955, pp 75-77. F. H. Quina and R. G. Toscano, J . Phys. Chem., 81, 1750 (1977). D. G. Hall and B. A. Pethlca in “Non-ionic Surfactants”, M. J. Schick, Ed., Marcel Dekker, New York, 1967. T. L. Hill, “Thermodynamlcs of Small Systems”, Vols. 1 and 2, W. A. Benjamin, New York, 1963. P. Mukherjee, J . Pharm. Sci., 60, 1531 (1971). Rwas taken as (radius of micelle) - (radius of pyrene), Le., 2.5nm - 0.3 nm = 2.2 nm. J. B. Blrks, “Photophysics of Aromatic Molecules”, Wiley-Interscience, New York, 1970, pp 532 and 604. (a) A. Nakajima, Bull. Chem. SOC.Jpn., 44, 3272 (1971); (b) Specfrochim.Acta, Part A, 30, 860 (1974); (c) Bull. Chem. Soc. Jpn., 50, 2473 (1977). B. B. Craig, J. Kirk, and M. A. J. Rodgers, Chem. Phys. Lett., 49, 437 (1977). U. Khuanga, B. K. Selinger, and R. McDonald, Aust. J . Chem., 29, 1 (1976). S. C. Wallace and J. K. Thomas, Radiat. Res., 54, 49 (1973). P. Becker and M. Arai, J . Colloid Interface Sci., 27, 634 (1968). A. Henglein and R. Scheerer, Ber. Bunsenges. Phys. Chem., 82, 1107 (1978). S. S. Atik and L. A. Singer, Chem. Phys. Lett., 59, 519 (1978);86, 234 (1979). Pyrene (- lo3 mol/dm3) was sonicated in respective surfactant solutions (0.1 mol/dm3)for 1 h, allowed to settle, and filtered, and then absorption spectra were recorded. To determine exact concentrations, we diluted the surfactant solutions 100 times in ethanol and measuredthe OD at 337 nm. From these OD values, assuming cg3, = 5 X lo4 dm3 mol-‘ cm-I, we calculated the pyrene concentrations. A recent paper, A. Yekta, M. Aikawa, and N. J. Turro, Chem. Phys. Lett., 63, 543 (1979),describes Poisson statisticaltreatment of limiting cases of luminescence quenching which allow an estimation of Ka, n , and the substrate exit and entry rates. Our experiments on P’ quenching by CPC in Brij-35 micelles may be viewed as case I of their treatment, Le., static quenching where the quencher is totally micellized.
References and Notes
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(1) (a) E. J. Fendler and J. H. Fendler, Adv, Phys. Org. Chem., 8,271 (1970); (b) E. H. Cordes and C. Gitler, Prog. Bioorg. Chem., 2, 1 (1973). (2) G. A. Davis, J. Am. Chem. SOC.,94, 5089 (1972). (3) M. A. J. Rodgersand M. F. daSilva E. Wheeler, Chem. Phys. Left., 53, 165 (1977). (4) F. D. Snell and L. S. Ettre, Ed., “Encyclopedia of Industrial Chemical Analysis”, Vol. IO, Interscience, New York, 1970, p 196. (5) N. J. Turro and M. W Geiger, Phofochem. Photobioi., 22, 273 (1975). (6) (a) M. Grakel and J. k:. Thomas, J. Am. Chem. Soc., 95, 6885 (1973); (b) M. Gratzel, K. Kalyansundaram,and J. K. Thomas, J. Am. Chem. SOC.,06, 7869 (1974). (7) J. H. Fendler and E. J. Fendler, “Catalysls in Micellar Macromolecular Systems”, Academlc Press, New York, 1975, p 88.
Krafft Points of Anionic Surfactants and Their Mixtures with Special Attention to Their Applicability in IHard Water Kaorui Tsujii, * Naoyukl Saito, and Takashi Takeuchi Tochigi Research Laboratories, Kao Soap Company, Ichikai-machi, Haga-gun, Tochigi 32 1-34, Japan (Received: October 29, 1979)
The Krafft points of the sodium and calcium salts of typical anionic surfactants and their mixtures have been measured to examine their applicability in hard water. The pure model compounds of the linear alkylbenzene sulfonates, a-olefin sulfonates, and alkylpoly(oxyethy1ene) sulfates were synthesized and used for Krafft-point measurements. Among the above three types of surfactant, the alkylpoly(oxyethy1ene)sulfates are shown to be the best surfactant for their practical uses in hard water, since their sodium and calcium salts as well as their mixtures are readily soluble at room temperature. The Krafft point vs. composition curves observed in binary surfactant mixtures have been classified into two groups. In group I, there exists a minimum in the Krafft point at a certain composition, whereas the Krafft point varies monotonously with the composition change in group 11. It is found from the composition analysis of the solid phase that both components are immiscible in group I but are completely miscible even in the solid phase in group 11. The thermodynamic theory for freezing-point depression has been favorably applied to the Krafft point vs. composition curves in group I. Theoretical calculations for the Krafft point vs. composition curve (liquiduscurve) and the corresponding solidus curve in group I1 have also been made, assuming the ideal solutions in both liquid (micellar) and solid phases. The calculated curves are in poor agreement with the observed ones probably because of the nonideality of the solution especially in the solid phase.
Introduction The Krafft points of calcium salts of ordinary anionic surfactants are generally higher than ambient temperature, and they cannot be used in hard water without any sequestering agents. The phosphate builders are well-known to be the most commonly used sequestering agents in
detergent formulations but are now implicated in eutrophication problems in some developed countries. It is then of great importance for practical uses of surfactants to find the agent which is applicable in hard water. In the present work, the Krafft points of the sodium and calcium salts of anionic surfactants and their mixtures have
0022-3654/80/2084-2287$01 .OO/O 0 1980 American Chemical Society
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TABLE I: Surfactant Samples Used in This Work molecular ab brevia. name of surfactant structurea tion'" octylbenzenen-C,H,,PhSO,*M C,PhS.M sulfonate dodecylbenzenen-C,,H,,PhSO,.M C,,PhS*M sulfonate dodecylpol y( oxyn-C,,H,,O(CH,C,,(OE),S.M ethylene) sulfate CH,O),SO,.M 3-hydroxypentadecane- n-C,,H,,CH( OH)- C,,(OH)S.M 1-sulfonate CH,CH,SO,*M 2-pentadecenen-C,,H,,CH= C,,(C=C)S*M 1-sulfonate CHCH,SO,*M a M = Na or '/,Ca.
been measured to examine their applicability in hard water. Linear alkylbenzene sulfonates, a-olefin sulfonates, and alkylpoly(oxyethy1ene) sulfates are chosen as three typical anionic surfactants which are most widely used in detergent formulations. Sodium and calcium salts of pure model compounds of the above three types of surfactant were synthesized and used for Krafft-point measurements. The Krafft points of alkylpoly(oxyethy1ene)sulfate~l-~ as well as the mixtures of their sodium and calcium salts6 have already been reported by several authors. However, reinvestigations have been made to compare the Krafft points of the above three surfactants under the same conditions.
Experimental Section Materials. All surfactant samples used in this work and their abbreviations are listed in Table I. Sodium octyland dodecylbenzenesulfonates were synthesized by ordinary C1S03H sulfonation of 1-phenyl-n-octane and 1phenyl-n-dodecane (99% pure by gas chromatography) purchased from Tokyo Kasei Ltd. After neutralization with NaOH, the crude surfactants were recrystallized twice from ethanol. The corresponding calcium salts of the above alkylbenzenesulfonateswere prepared by metathesis in aqueous CaClz solutions and recrystallized from ethanol. Sodium and calcium dodecylpoly(oxyethy1ene) sulfates were prepared by essentially the same procedures described by Hat6 and ShinodaS6The starting mono- and tris(oxyethy1ene)dodecyl ether obtained from Nikko Chemicals Co. were shown to be more than 98% pure by gas chromatography. Sodium and calcium salts of the final products were purified by repeated recrystallization from 2-propanol/ethanol mixture (3/1 by volume). Sodium 3-hydroxypentadecane-1-sulfonateand sodium 2-pentadecene-1-sulfonatewhich were the model compounds of a-olefin sulfonates were synthesized by the following procedures7
-
CHpCHCHO
Cl2Hz50H
ClzH25Br
C H CHCH=CHZ
H20
OH
OMgBr N ~ H S -
l2
CHCHzCHzS03Na
251OH
C H CHCH=CHz l2 2 5 ~
2 5 ~
C H
CIZH25MgBr
P B ~ ~
C12H25CH=CHCHzBr
% .! %
C,, HZ5 CH=CHCHZSO3Na
The starting dodecanol was purified by distillation under reduced pressure and shown to be more than 99% pure by gas chromatography. The reaction product obtained in each step was checked by IR spectra and gas chromatography. The final products were recrystallized several
Tsujii et
al.
times from ethanol/water mixture (4/1 by volume). The purified samples were checked by elementary analysis and IR and NMR spectra. The calcium salts of the above surfactants were prepared by metathesis in water and recrystallized by the same manner as the above. Krafft-Point Measurements. The Krafft points of the sample surfactants and their mixtures were estimated from the solution temperatures at ca. 1 wt % solutions on gradual heating (at most 1"C/min) in a water bath under vigorous stirring. The reproducibility of the measured Krafft points was within k0.3 "C. When the Krafft point was above 80 "C, the sample solutions were sealed in thick glass tubes after Nz gas bubbling prior to heating. In order to obtain the hydrated solid agents equilibrated with their solutions, the samples were dissolved at high temperature and precipitated by cooling. Sometimes, the crystalline surfactant was not obtained by simple cooling at ca. 0 "C because of supercooling. In such cases, the sample solutions were maintained in a frozen state at ca. -20 "C at least overnight and then thawed to obtain the solid agents. Differential Scanning Calorimetry. Differential scanning calorimetry was performed with a Daini Seikosha Type SSC-544 DSC apparatus.8 The sample solution (60 pL) was put in a sealed aluminum cell and heated at the rate of 0.6 "C/min. The concentration of the sample solutions was usually the same as that of the solutions used in the Krafft-point measurements. Repeated measurements (at least three times) of the transition enthalpy agreed to within 5% of the mean. The DSC measurements could not be carried out at higher temperatures than 100 "C because of the machine limitations. Composition Determinations of the Solid Phase in Binary Surfactant Mixtures. The aqueous solutions (150 mM) of binary surfactant mixtures with a given mixing ratio were maintained at a constant temperature below the Krafft point of the mixture. The precipitated solid phase in equilibrium with the solution was filtered quickly through a sintered glass disk. The composition of the collected solid surfactant was determined by the following methods. Sodium and calcium ion contents were analyzed by flame photometry (Coleman,Model 21 flame photometer) to determine the solid-phase composition of the CI5(OH)S.Na/CIS(OH)S.l/zCamixtures. Proton magnetic resonance (lH NMR) technique was employed to determine the composition of the Cl5(C=C)S-Na/Cl5(OH)S.Na system. The collected solid agent was dissolved to be 10 wt % in deuterium oxide containing a small amount of (DSS) as sodium 2,2-dimethyl-2-silapentane-5-sulfonate an internal reference. lH NMR measurements were carried out with a Varian Type EM-360L NMR spectrometer at 50 "C. The contents of the C15(C=C)S.Na and CI5(OH)S.Na were determined from the lH NMR signal due to the protons of the double bond methine of C15(C=C)S.Na (5.4-5.8 ppm from the DSS signal) and the methylene protons next to the sulfonate group of CI5(0H)S.Na (2.7-3.1 ppm), respectively? The composition analysis of the C8PhS-Na/C12PhS-Nasystem was made by means of high-speed liquid chromatography using a Merck RP-18 column. The solid sample was dissolved to be 10 mg/5 mL in a ethanol/water (3/1 by volume) mixed solvent. The sample solution (2 pL) was injected and eluted with a methanol/water (4/ 1by volume) mixed solvent containing 0.1 M sodium perchlorate. Each component of the mixture was detected by ultraviolet absorption at 225 nm.
Results Krafft Point of Pure Surfactant. The Krafft points of sodium and calcium salts of pure surfactants measured by
The Journal of Physical Chemistry, Vol. 84, No., 18, 1980 2289
Krafft Points of Anionic Surfactant Mixtures
TABLE 11: Krafft 'Temperature of Pure Anionic Surfactant -Krafft point, "C DSC - soln temp surfactant bra salt Ca salt Na salt Ca salt C,PhS 26.0 196.5 25.5 C,,PhS 62.5 269.0 65.0 17.0 C,,(OE )8 9.0 18.7 8.5 C;;(OEj3S
