SOME EXPERIMENTS WITH WETTING AGENTS HARVEY A. NEVILLE A N D CHARLES A. JEANSON, 1111
W m . H. Chandler Chemical Laboratory, Lehigh University, Bethlehem, P a . Received April 1, 1988
The surface activities of members of the homologous series of aliphatic acids and their sodium salts have been reported by various investigators (1). These substances show, in general, increasing surface activity, or ability to lower the surface tension of water, with increase in length of the carbon chain in agreement with Traube’s rule. The measurement of the surface activities of some sulfonates of the benzene series was undertaken to show the influence of the nature of the substituent alkyl group and of its position in the benzene nucleus in relation to the polar sulfonate group. Recently new types of, compounds in which the active or polar part of the molecule is a sulfate or sulfonate group have been developed commercially and widely recommended as ideal detergents, wetting and penetrating agents. The stability of solutions of these compounds in the presence of acids and in hard water permits their application under conditions which would prohibit the use of soap. The uses, advantages, and method of manufacture of one class of these products, the “sulfonated” higher alcohols, have been discussed by Killefer (2). Our experiments were extended to measure the adsorption or rate of exhaustion of such compounds from their water solutions by wool, and to study their effect when used as leveling agents in dyeing. I. PREPARATION O F SULFONATES AND SURFACE TENSION MEASUREMENTS
The sulfonation of benzene, toluene, xylene, and cymene was accomplished by the general method of Gatterman (3), using fuming sulfuric acid and the minimum temperature required for each reaction. The sodium sulfonate was precipitated by treating the reaction products with saturated sodium chloride solution, or was obtained by neutralization with sodium hydroxide and evaporation. The sodium sulfonate was then purified by recrystallization from absolute alcohol or acetone until it was free of sulfate. Acetone was the more effective medium for the purification of the higher members of the series. Ethylbenzene, isopropylbenzene 1
Student Research Foundation Fellow, 1931-1933. 1001
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HARVEY A. NEVILLE AND CHARLES A. JEANSON, I11
and butylbeneene were prepared by the Fittig synthesis (4), were then sulfonated, and their sodium salts obtained and purified as described above. Solutions of these salts in distilled water were prepared and their surface tensions were measured over a range of concentrations at a constant temperature of 18°C. These measurements were made by means of an improved torsion balance which was fully described by De Gray (5) in a recent article. The static or equilibrium surface tension values for these solutions are shown in figure 1.
01 0.0
0.1
0.2
0.3
0.9
0.5
CONCENTRATION (MOLES PER LITER)
FIG.1. LOWERING OF SURFACE TENSIONBY SULFONATES OF BENZENE SERIES
In the case of sodium benzenesulfonate the observed lowering of the surface tension of water is roughly proportional to the concentration of the solute. In this its effect is similar to that of the lower members of the aliphatic series of acids or their salts and, in general, of substances in true solution which decrease surface tension. Beyond this first member the curves show increasing tendency to sag or to deviate from the straightline relationship as the alkyl substituents increase in length or complexity. It is of interest to note that although the sulfonates of ethylbenzene (curve 111) and xylene (curve IV) are identical in molecular weight, the. latter is considerably more effective in lowering the surface tension of water.
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This indicates that two substituent groups increase the surface activity of the compound more than a single group containing the same total number of carbon atoms. This point is exemplified further in the curves for the sulfonates of butylbenxene (curve VII) and cymene or p-methylisopropylbenzene (curve VII). These two curves also exhibit a m i n i y n n which is a characteristic of active surface-tension depressants and usually indicates a colloidal condition of the solute. With the exception of sodium benzenesulfonate, the solutes represented by the curves in figure 1 are probably mixtures of isomers.
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z 2 s z
Y
2
i
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lot
0.0
0.I
0.3
0.2
0.4
0.3
CONCENTRATIQN .(MOLES PER LITER)
FIQ.2. COMPARISON OF 0-
AND
p-TOLUENESULFONATBS
In the sulfonation of toluene a mixture of two isomers is obtained. This mixture is composed of approximately 70 per cent of the para and 30 per cent of the ortho isomer. These two isomers were separated by taking advantage of the different melting points of the corresponding toluenesulfonyl chlorides, according to the method recommended by Beilstein (6). The o-toluenesulfonate and p-toluenesulfonate obtained from the separated sulfo&l chlorides were recrystallized from absolute alcohol, and 'surface tension measurements were made upon the solutions of each. These results are shown in figure 2 in rel&tion to the curve for the
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HARVEY A. NEVILLE AND CHARLES A. JEANSON, I11
mixture of the two isomers. It will be observed that the ortho derivative is more effective tha,n the para as a surface tension depressant and that in low concentrations the activity of the ortho isomer predominates in the mixture, while in more concentrated solutions the surface activity of the mixture approaches that of the less active para component. 11. ADSORPTION O F WETTING AGENTS BY WOOL
For these experiments a fine grade of virgin wool was thoroughly degreased by scouring with soap and sodium carbonate, rinsed with distilled water and air dried. It was kept a t constant humidity to attain a moisture content of approximately 13 per cent. Samples of wool weighing 5 g. were soaked for one hour a t 50°C.in 500 cc. of the solutions of the wetting agents. The wetting agents used were the commercial products kpown as “Gardinol C.A.”(compound A) and “Igepon T” (compound B). Both are sodium salts, the former a sulfate of a higher alcohol (2) and the latter a sulfonate of a condensation product. The solutions contained 0.5 per cent of the wetting agents and were made acid or alkaline by the addition of hydrochloric acid or sodium hydroxide. The pH values were determined colorimetrically at the end of the soak by means of standard indscators. The percentage exhaustion of the wetting agent by adsorption was determined, after removing the wool, by evaporating 100-cc. portions of the solutions, drying the residue a t 100°C. in an oven and weighing it. When hydrochloric acid or sodium hydroxide had been used to change the pH of the solution, this was carefully titrated and the weight of the salt formed was subtracted from the weight of the resid’ue. This weight was also corrected for the weight of wool dissolved by the solution in each case. The actual proportion of wetting agent adsorbed by 5 g. of wool from 500 cc. of solution was obtained by comparing the corrected weight of the residue with the weight of residue resulting from 100 cc. of a solution of the wetting agent in which no wool had been soaked. The results, expressed as percentage exhaustion from solution, are represented in figure 3. Since the weight of wool used in each experiment was twice the weight of wetting agent present in the solution, the adsorption percentages based upon the weight of wool will be one-half the values represented by the curves in figure 3. For example, a t pH 1.5 the solution of compound B is 22.9 per cent exhausted; under these conditions the wool has adsorbed 11.45 per cent by weight of this wetting agent. The experiments show that these substances are adsorbed from solution by wool in appreciable amounts only in acid solutions and that the amount of adsorption increases with increase in hydrogen-ion concentration. These results can be interpreted by considering the nature of the com-
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pound in relation to the variation in the electrical charge of wool with change in pH. The wetting agents are sodium salts which, in water solution, produce surface-active anions containing a polar group and a long carbon chain. These negative ions are similar to the color ions of acid dyes and are similarly adsorbed by wool which bears a positive charge in acid solutions. The isoelectric point of wool, as reported by Harris (7), occurs at pH 3.4. Some adsorption of the wetting agent occurs beyond this point, just as the adsorption curves of acid and basic dyes overlap to some extent. However, as the acidity decreases beyond pH 3.4, the negative charge on the wool rapidly increases, and in this condition the wool repels the negatively charged ions so that no measurable adsorption occurs in this region. It is generally recognized that soap is not selectively ad-
OF WETTINQAGENTSBY FIG. 3. THEADSORPTION
WOOL
sorbed from its solution (pH 10-11) by textile fibers; the explanation of this fact is obvious, since the surface-active ion (or ionic micelle) of soap is likewise negatively charged. The practical conclusion to be drawn from these experiments is that, although they are stable in acid solutions, the new types of wetting agents are so strongly adsorbed from solutions of high acidity that they can hardly be employed economically under these conditions. While no compounds furnishing positive ions of high surface activity were available for testing, it may be predicted that such substances would, like basic dyes, be strongly adsorbed by wool from alkaline solutions and negligibly adsorbed from acid solutions.
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HARVEY A. NEVILLE AND CHARLES A. JEANSON, I11
111. THE INFLUENCE O F WETTING AGENTS UPON THE ADSORPTION O F ACID
AND BASIC DYES BY WOOL
The wool used for these experiments was a fine, white worsted knitting yarn. It was maintained a t constant humidity, and one meter (about 0.5 g.) was accurately weighed for each test. Methylene blue was used as the basic dye at a concentration of 0.2 per cent; the acid dye was Orange 11, and the concentration of the dye solution was 0.1 per cent in this case. Series of experiments with each dye were also performed in which Gardinol was added to the extent of 0.1 per cent and 0.5 per cent of the weight of the solution. The samples of wool were boiled for 2 minutes in 50-cc. portions of the dye solutions, which were made acid or alkaline with sulfuric acid or sodium carbonate respectively. Each sample of wool was transferred from the dye bath to distilled water and boiled for 2 minutes. It was then placed in an Erlenmeyer flask, covered with distilled water, and the air was displaced by carbon dioxide. The contents of the flask were heated to boiling and the dye on the wool was titrated with titanous chloride, using a slight excess of this reagent. The boiling was continued until the color was completely discharged and the excess of titanous chloride was then titrated wit)h a solution of the same dye which served as its own indicator. A steady stream of carbon dioxide was passed through the flask throughout the titration. The pH values of the dye baths were obtained, after removing the wool, by means of a quinhydrone electrode. The results for the acid dye are shown in figure 4 and for the basic dye in figure 5. The percentages are based upon the weight of the wool. Quantitative data for the adsorption of acid and basic dyes have been published by Briggs and Bull (8), who also studied the effect of the addition of salts to the dye bath. The results represented by curve I for each dye are consistent with the data of Briggs and Bull and with Bancroft’s generalizations for the adsorption of dyes (9). With regard to the influence of the wetting agent or leveler, this can again be interpreted from a consideration of the nature of the surface-active ion in relation to the electrical condition of the wool. As shown in figure 3, Gardinol is strongly adsorbed by wool in acid solutions and, since its active ion is negative, this interferes with and decreases the adsorption of an acid dye in which the surface-active ion is also negative. In the case of the basic dye in which the active ion is positive, its adsorption is increased in acid solutions by Gardinol because of the strong adsorption of the negative ion of Gardinol. This is entirely consistent with Bancroft’s statement that a readily adsorbed anion will increase the adsorption of a basic dye and decrease the adsorption of an acid dye. However, in alkaline solutions the adsorption of the basic dye is decreased by the Gardinol. This is apparently in contradiction to the rule just stated, but is not so in reality
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since, of course, an anion is not “readily adsorbed” by wool in an alkaline solution. The ability of Gardinol to decrease the adsorption of the basic
1
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ADSORPTION O F A N ACID DYE 0
I D Y E ( O R A N G E nl II D Y E + 0.1% GARDINOL lU D Y E + 0.5-/. G A R D I N O L
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2
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4
3
5
6
8
7
9
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pH VALUEJ
FIG.4. THEINFLUENCE OF A LEVELINGAGENT UPON DYEBY WOOL
I
THE
ADSORPTION OF
ACID
AN
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bY
-4-
ADSORPTION O F A BASIC D Y E
w I. D Y E ( M E T H Y L E N E O L U E ) 2 DYE 0.1% GARDINOL 3. D Y E 0.5% G A R D I N D L
+ +
7
0
9
IO
pH VALUES
FIG.5. THEINFLUENCB OF
A
LEVELING AGENTUPON THE ADSORPTIONOF DYEBY WOOL
A
BASIC
dye in alkaline solutions may be attributed to its peptizing or detergent action, or its negative ion (or micelle) may be thought of as competing with the negatively charged wool for the dye cation.
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HARVEY A. NEVILLE AND CHARLES A. JEANSON, 111
SUMMARY
1. A number of the sulfonates of the benzene series have been prepared and the effect of the nature and position of substituent groups upon their surface activities has been studied. The surface tension-concentration relations of these products are compared with those of soap and other wetting agents. 2. The adsorption of some commercial wetting agents by wool has been measured in solutions having various hydrogen-ion concentrations. It is shown that, for substances of this type, the adsorption parallels the potential curve of the wool in acid solutions and is negligible in alkaline solutions, 3. The influence of wetting agents upon the take-up of acid and basic dyes by wool a t various hydrogen-ion concentrations has been determined quantitatively. These agents increase the take-up of basic dyes in acid solutions and decrease dyeing under other conditions. The results are interpreted in terms of the electrical condition of the fiber and the adsorption of the surface-active ions. REFERENCES (1) FREUNDLICH: Colloid and Capillary Chemistry, pp. 61-71. E. P. Dutton and Co., New York (1926). (2) KILLEFER:Ind. Eng. Chem. 26, 138 (1933). (3) GATTERMAN: Practical Methods of Organic Chemistry, p. 280. Macmillan and Co., New York (1915). (4) Reference 3, p. 276. ( 5 ) DE GRAY:Ind. Eng. Chem., Anal. Ed. 6,70 (1933). (6) BEILSTEIN:Handbuch der organischen Chemie, 4th Ed., Vol. XI, p. 83. (7) HARRIS:Bur. Standards J. Research 8,779 (1932). Research paper No. 451. (8) BRIGGSAND BULL:J. Phys. Chem. 26, 845 (1922). (9) BANCROFT: Applied Colloid Chemistry, pp, 133-6. McGraw-Hill Book CO., New York (1926).
