ADSORPTION AT CRYSTAL-SOLUTION INTERFACES. X A STUDYOF THE ADSORPTION OF MONOAZO DYESBY CRYSTALS OF POTASSIUM SULFATE DURING THEIR GROWTH FROM SOLUTIOW~ MERLE D. RIGTERINK
AND
WESLEY G. FRAECE
Department of Chemistry, The Ohio State University, Columbus, Ohio Received July 14, 1938
This paper is a continuation of previously reported studies made in tKis laboratory on the adsorption of foreign substances by growing crystals (1, 3, 5, 6, 7, 8, 10, 11, 15, 16). Attention has been focussed especially on one point which has received very little previous study,-the presence and distribution of polar groups in the foreign molecules. Only a few cases of closely related dyes where one was adsorbed and the other was not have been observed in the earlier work. Buckley (2) investigated a large number of closely related dyes but only a rather limited number which were isomeric; consequently he was unable to arrive a t any general conclusions which would predict the behavior of a dye not previously investigated. Fortunately samples of the members of two series of dyes which were admirably suited for such an investigation were obtained. These were originally prepared by Dr. Wallace R. Brode and two of his former students (4,9) for spectroscopic investigations, and therefore are of a higher purity than the usual commercial products. These dyes were prepared by coupling aniline and the ortho-, meta-, and para-sulfonated anilines by the usual method of diazotization with a series of mono- and di-sulfonic acid derivatives of a- and /3-naphthols and a- and P-naphthylamines. They will be referred to in the tables by abbreviations which are derived from the intermediates used in their preparation. These intermediates were as follows : aniline (A), ortho-sulfonated aniline (0),meta-sulfonated aniline (M), para-sulfonated aniline (P), a-naphthol (a-OH), @naphthol @-OH), a-naphthylamine (a-NH2), and &naphthylamine (P-KH2). The numbers given in the tables after the abbreviations refer t o the positions of the -S03Na groups attached to the naphthalene rings. The dyes which are starred in the tables possess the nucleus
O"="8
Presented at the Fifteenth Colloid Symposium, held at Cambridge, Massachusetts, June 9-11, 1938. 1079
1080
MERLE D. RIGTERINK AXD WESLEY G. F'RAKCE
while the others possess the nucleus
EXPERIiMENTAL
Potassium sulfate way selected for this investigation, since preliminary experiments showed that it adsorbed a number of the dyes of these series, Qualitative experiments were made to determine which of the dyes were adsorbed, and therefore which should be chosen for further quantitative experiments. In 50 cc. of a saturated potassium sulfate solution was dissolved 0.005 rt 0.0005 g. of each dye. These solutions were then set aside in 50-cc. beakers, and slow evaporation allowed to take place a t room temperature. The resultant crystals were examined for adsorption and habit modification. For the quantitative experiments equal molar concentrations of dye rather than equal weight concentrations were used. A concentration of 2 X moles of dye per 100 cc. of solution was chosen for this purpose, since for the majority of the dyes this is approximately equal to the 0.01 per cent concentration by weight used in all of the qualitative experiments. 1 x lop4mole of each dye was dissolved in 500 cc. of a saturated potassium sulfate solution. The resulting solution was filtered and set away in eight 100-cc. beakers t o crystallize by slow evaporation at 30°C. z!= 0.1" a t constant humidity for 96 hr. I n those cases in which the dyes were slightly soluble the solutions were prepared by dissolving the dye in a hot saturated potassium sulfate solution and then allowing the mixture to stand a t 30°C. for two days to allow the excess dye to precipitate out. The crystals were removed after their growth, rinsed twice with distilled water, dried above an electric oven a t a temperature of 5O-6O0C., and allowed to cool in a desiccator containing Drierite (anhydrous calcium sulfate). A portion of the crystals was then weighed, dissolved in water, and diluted t o 100 cc. A standard solution with an approximately equal dye concentration was also prepared. The two solutions were then compared in a Leitz colorimeter with an average of ten readings taken as the colorimeter reading used in the calculation. From these data the number of moles of dye adsorbed, per mole of potassium sulfate that crystallized, was calculated RESULTS
The results obtained are summarized in tables 1, 2, 3, and 4. I n the second determinations appearing in the tables a new crop of crystals was
ADSORPTION OF DYES BY POTASSIUM SULFATE
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used for th? analysis, and an equal concentration of the salt was used in the standard solutions. In table 5 are given the results of quantitaave measurements made of the amount of adsorption of P-P-OH-6 at a number of different concentramoles of dye per tions. The results above concentrations of 3 X 100 cc. of solution are not quite as accurate as the results at lower concenBummary oft
TABLE 1 ct of soluble acid dyes on potassiumsulfate MOLES O F DYE ADSORBED (PER MOLE OF Ka804) 105
x
DYE
PER CENT
PURITY
P-@-OH*. . . . . . . . . . . . . . . . . . M-@-OH-6*,. . . . . . . . . . . . . . .
84.63 71.25 74.15 P-@-OH-6*,. . . . . . . . . . . . . . . 66.40
0-8-OH-7* . . . . . . . . . . . . . . . . 0-D-OH-6* . . . . . . . . . . . . P-,%OH-7*. . . . . . . . . . . . MU-OH-3. . . . . . . . . . . . . . . . . Ma-OH-4, . . . . . . . . . . . . . . . . 0-8-OH-3 :6*. . . . . . . . . . . . . . M-a-OH-3 :8. . ..... 0a-0H -5 . . . . . . . . . . . . . . . . .
A-@-OH-6:8*,. . . . . . . . . . . . . Pa-OH-3 . . . . . . . . . . . . . . . . Pa-OH-4, ..... Pa-OH-5. ..... Pa-OH-3 :8. . . . . . . . . . . . . . . Ma-OH-5. . . . . . . . . . . . . . . . . M-8-OH-6 :8*. . . . . . . . . . . . . . Oa-OH-4 . . . . . . . . . . . . . . . . .
98.87 93.05 61.25 Li4.61 77.87 46.01 68.28 82.39 55.10 90.25 62.75 89.99 62.52 62.20 63.00 96.66 73.99 43.41 93.86
First determination
Second determination
91 87 79 49 24 14 8.9 4.3 3.7 1.9 0.8
