1979
V O L U M E 28, NO. 12, D E C E M B E R 1 9 5 6 ACKNOWLEDGXIENT
Low Concentrations. The salicylaldehyde procedure has been slightly modified for the determination of low concentrations of ethylamine in diethylamine and presumably is adaptable to other amine combinations.
The authors gratefully acknowledge the work of R. L. Anderson and 0. R. Trimble, who obtained some of the data presented in this paper.
For this determination pipet 25 ml. of 0.1A- salicylaldehyde in pyridine into a suitable glass-stoppered flask. Add 75 ml. of pyridine and introduce a 10-ml. sample of known specific gravity. Allo~vto react 15 minutes a t room temperature and titrate with standard 0.1-V sodium methylate reagent to a phenolphthalein end point which should last 15 seconds. The use of a blanket of nitrogen above the liquid helps to prevent fading of the end point thereby increasing the precision. Diethylamine and salicylaldehyde produce an orange color in this determination, which obscures the thymolphthalein end point.
LITERATURE CITED
(1) Critchfield, F. E., Johnson, J. B., A N ~ LCHEM. . 2 8 , 430 (1956). (2) I b i d . , p. 436. (3) Fritz, J. S.,Keen, R. T.,Zbid.;25, l i 9 (1953). ( 4 ) Moss, 11. L., Elliott, J. H., Hall, R. T., I b i d , 20, i 8 4 (1948). (5) Riddick, J. A , Fritz, J. S.,Davis, XI. AI., Hillenbrand, E. F., Jr., Markunas, P. C., Ibid., 24, 310 (1952). (6) Kagner, C. D., Brown, R. H., Peters, E. D., J . Am. C h e m . SOC. 69, 2609 (1947). (T) Wilson, H. S . ,Heron, A. E., Analyst 7 0 , 38 (1945).
9 sample of refined diethylamine was carefully fractionated, and samples of known ethylamine content were prepared and analyzed. Table I11 shows the results obtained.
R E C L I V Efor D review Janua:.y 11, l % G .
. i c c e p t c d . i u g u s t 7 , 1956.
Detection of Surface-Active Alkylaryl Sulfonates by Alkaline Fusion and Formation of an Azo Dye MILTON J. ROSEN and GERALD C. GOLDFINGER D e p a r t m e n t o f Chemistry, Brooklyn College, Brooklyn, N. Surface-active agents containing the alkylaryl sulfonate group may be detected by the purple, red, or orange color produced when the phenol obtained from their fusion with potassium hydroxide reacts with diazotized dianisidine. Compounds containing nitro or halo substituents on the benzene ring give false negatives.
Y.
The phenol produced is then detected by reaction with diazotized dianisidine to form an azo dye.
A
LTHOlTGH the alkylar! 1 sulfonate group is the functional group most commonly found in surface-active agents (I), the literature contains no simple, convenient, and definitive test for the qualitative detection of this grouping. Published tests for this group are based on formation of a precipitate with 10% cupric sulfate solution ( 5 ) ; nitration of the aromatic nucleus, reduction of the product, and detection of the resulting aromatic amine ( 4 ) ; or alkaline fusion of the aromatic sulfonate and detection of the resulting phenol (6, 7 ) . The first type of test (cupric sulfate precipitation) is unsatisfactory, as a number of types of surfactants which do not contain this functional group are also precipitated by cupric sulfate (S), n hile certain alkylaryl sulfonates are unaffected by the reagent. The second IL-pe also suffers from lack of specificity, because it is given by all aromatic nuclei, sulfonated or unsulfonated. For example, it gives positive results with all alkylphenol-ethylene oxide condensates. The third test seems to have the greatest potential spwificity; the fact that it is given by all phenols, sulfonated or not, is not considered a serious disadvantage, as unsulfonated phenols are not ordinarily used as surface-active agents and phenol--ethylene oxide condensates n-ould give negative results. Honever, the published procedures (6, 7 ) for performing the alkaline fusion type of test are inconvenient, require a good deal of experience, or are not specific to aryl sulfonates. The test as outlined by Muller (6) suffers from a lack of specificity, as it gives false positive results n i t h many easily oxidized compounds, 1% hile the fusion devised by Kurzschmitt ( 7 ) must be done under carefully controlled conditions and, according to the author, needs experience to be performed correctl?. The procedure outlined below has been devised to remedy these deficiencies. The aryl sulfonate first reacts with molten potassium hydroxide in the usual fashion to give a phenol, according to thp equation
I
L
1-c3-o
i
-I
Diazotized dianisidine was chosen for this purpose because, under the conditions of the test, it forms azo dyes that are more intensely colored than those of any other amine tested. Because diazotized amines produce colors not only with the phenols produced by the fusion with molten alkali, but also with the by-products formed during the fusion, it was necessary to remove these by-products by solvent extraction before the coupling reaction. For this purpose, the reaction mixture was first extracted with benzene, while still alkaline, to remove benzene-soluble by-products and unreacted sulfonate and then, after acidification, extracted with petroleum ether to remove the phenol from the remaining by-products. Ethyl ether, which is used to extract the phenol in other tests of a similar nature (6), was found to dissolve by-products of the fusion reaction as well as the phenol and thereby give false positive results in a number of cases. PROCEDURE
Preparation of Diazonium Salt Solution. Dissolve 20 mg. of dianisidine in 10 ml. of 1 to 4 (by volume) hydrochloric acid.
ANALYTICAL CHEMISTRY
1980 Table I.
Reactions of Commercial Surfactants to Alkaline Fusion and Coupling with Diazotized Dianisidine
Alkanol B-, Aerosol Ob
Color Produced
Structurea
Source
Product
Purple Purple
Du Pont Am. Cyanamid
Result
++
Aresket 300
Monsanto
Red
++ ++ ++ +
Daxad 2 1
Dewey 8: Almy
Amber
-
Daxad 23
Dewey 8: Almy
Red
I
Daxad 1 1
Dewey & Almy
Purple
+
Aerosol 18d
Du Pont Procter & Gamble Carbide & Carbon Stepan Am. Cyanamid
Red Red Red Red Orange, then red Orange
Carbide & Carbon Am. Cyanamid Antara Igepon T Sulfonate O A 5 d
Antara Tenn. Corp.
Cd3asOSOsSa CnHz~OSOaNa CnHaaOSOsNa ROSOaXa CH2COOKa
Amber
C H (SOsNa) COKHClsHs: CaHGH=C(CzHs)CHzSO&a ROOCCHzCH(S0aNa)COOR Sulfated castor oil 0 RfiX(CHs)CHzCHzSOsSa RVH(CHz)nCOOH
Yellow-amber Amber
I
h'atl. Aniline Antara ilntara Onyx
SOsNa CizHzsOOCCH%SOaSa RCOOCHzCHzSOsNa (coconut f.a. deriv.) RCOOCH*CH&OsNa (oleic acid deriv.) RRH(OS0sNa) (CHdnCOOR
Alrosene 31
Geigy
Colorless
Triton X-2OOb
Rohm & Haas
Amber
Triton 770b
Rohm & Haas
Red e
Alipal CO-436a
Antara
Amber
Petronate H Hyponate L5Ob
Sonneborn Sonneborn
Albatex P O
Ciba
Nekal NSb
Antara
Petroleum sulfonate Petroleum sulfonate (oil-free)
Amber Yellow-amber
Amber
ROOCCHz ROOCCHSOaNa ROOCAHt R
=
alkyl or alkenyl group.
b Dried and suspended in methanol. c
d
Made into paste with water and sodium sulfate, dried, and crushed. Dried and crushed with sodium sulfate. Product gives same color with diazotized anisidine before fusion.
Amber
V O L U M E 28, NO. 1 2 , D E C E M B E R 1 9 5 6 Cool to 0’ to 5” C. in an ice bath, add 100 mg. of sodium nitrite, and agitate well. The red color that forms a t first turns yellon after 5 to 10 minutes. About 10 minutes after the yellow color appears, add about 0.1 gram of urea to the test tube to remove excess nitrous acid. Fusion Reaction. Fuse 2 to 2.5 grams of potassium hydroxide in a nickel crucible. Add 200 mg. of finely divided, anhydrous surfactant (obtained by solvent extraction or other suitable procedure from a surfactant-containing composition) to the melt. (Compounds that are not in the form of a finely divided powder are made into a paste with n-ater and an equal weight of sodium sulfate, dried, and ground. Compounds that form pastes upon drying are dissolved or suspended in methanol and added to the crucible by means of a long medicine dropper.) Stir the molten mixture well for 3 to 4 minutes while heating with a flame that barely touches the bottom of the crucible. Cool, add 5 ml. of water, stir well to dissolve all water-soluble material, and centrifuge (or filter) the suspension. Extract the clear centrifugate (or filtrate) once with an equal volume of benzene, acidify the extracted aqueous layer t o Congo red paper with concentrated hydrochloric acid, cool, and extract the phenol twice with 5-ml. portions of petroleum ether. (It may be necessary to centrifuge in order t o break any emulsions that form.) Evaporate the petroleum ether extracts to dryness, add 3 ml. of 10% sodium hydroxide to the residue, and stir well t o dissolve all alkali-soluble material. Test the mixture nith litmus paper, and add more 10% sodium hydroxide solution if it is not strongly alkaline. Transfer the alkaline solution t o a test tube and add about 1 ml. of the diazonium salt solution. Xote the color.
1981 nucleus Rill not produce a phenol (2). Slthough no surfaceactive agents n i t h this type of grouping could be obtained, the test a as tried on sodium p-chlorobenzene sulfonate and m-nitrobenzenesulfonic acid. Negative results were obtained with both compounds. Daxad 21, a calcium salt of a sulfonated alkylphenylmethylene polymer, was the only alkylaryl sulfonate tested which gave a negative result. This was probably due to the insolubility of the calcium salt in the molten alkali, as both Daxad 23, a sodium salt of similar structure, and Daxad 11, a sodium salt of an alkylnaphthalene homolog of similar structure, gave positive results. The only compound that gave a false positive was Triton 770, a sodium alkylphenyl polyoxgethylene sulfate. Hop-ever, when this compound was tested with diazotized dianisidine before the fusion reaction, it gave the same red color, indicating that the original compound contained some free phenol. An ammonium salt of similar structure from a different source gave the expected negative result. All other alcohol sulfates gave negative results, as did many types of alkyl sulfonates, sulfated oils, and petroleum sulfonates. Compounds containing double bonds, which are subject to oxidation during the fusion reaction, gave positive results when the by-products formed in the fusion reaction were not removed by extraction, and gave amber colors after these extractions.
DISCUSSION OF RESULTS
LITERATURE CITED
Table I describes the results obtained with various tjpes of surface-active agents. All of the alkylaryl sulfonates tested, n-ith the one exception noted below (Daxad 21), gave colors ranging from orange or red to purple. Saphthalene derivatives gave purple colors, while benzene derivatives gave red dyes. These are considered positive results. Yellow or amber colors are considered negative. A4sulfonated benzimidazole (Albatex PO), gave negative results. It has been reported that the alkaline fusion of alkylaryl sulfonates containing nitro or halo substituents in the aromatic
Chem. Eng. Yews 34, 558 (1956).
Fieser, L. F., and Fieser, ll., “Organic Chemistry,” 2nd ed., p. 631, Heath, Boston, 1950. Gilby, J. A., Hodgson, H. W., M f g . Chemist 21, 371 (1950). Guerbet, hl., Compt. rend. 171, 40 (1920). Linsenmeyer. K., Melliand Teztilber. 21, 371 (1950). hluller, E., “Methoden der organischer Chemie,” Vol. 11, 4th ed., p. 609, George Thieme, Stuttgart, 1954. Wurzschmitt. B., 2. anal. Cheni. 130, 105 (1950). RECEIVED for review May 7, 1956. -4ccepted .Sugust 14, 1956.
Determination of Specific Surface Area of Colloidal Silica by Titration with Sodium Hydroxide GEORGE W. SEARS, Jr. Grasselli Chemicals Department, Experimental Station,
A rapid method determining the specific surface area of silica particles of colloidal size involves a titration of the silica surface with sodium hydroxide, in a medium of 20% aqueous sodium chloride between pH 4 and 9. At pH 9, 1.26 hydroxyl ions are adsorbed per square millimicron of surface. The titer, therefore, is a measure of the total surface present and can be related by an empirical equation to the specific surface area of the colloidal particles as determined by nitrogen adsorption. Advantages of the method are rapidity, accuracy for particles of very high specific surface area, and applicability to particles in colloidal solution as well as to powders.
T
H E specific surface area of amorphous silica has been commonly determined either by calculation from particle size observed in electron micrographs, or by adsorption techniques involving nitrogen (6, 8) or methyl red (8, 16). Methods for determining the size and shape of particles of colloidal silica and the relation between particle diameter and specific surface area have been reviewed by Iler (9).
E. 1. du Pont
d e Nemours
& Co.,
lnc., Wilmington, Del.
In the study of polymerization and depolymerization of colloidal silica, a simple, rapid method for determining the specific surface area of silica in the form of a colloidal solution, especially in the range of extremely small particles (below 10 mp in diameter) has been needed. Although particle size in this range can be measured with the aid of the electron microscope, the process is slow, and equipment is often unavailable. Specific surface areas cannot be measured by conventional adsorption methods without first drying the silica requiring special techniques to avoid coalescence of particles and reduction of surface area (1, 14). The ion exchange capacity of silica and silicate minerals has been the subject of frequent investigation (7, I S ) . Bryant (6) has shown that for a given SiOz: NazO ratio, the p H of a silica sol increases with increasing particle size and decreases with increasing electrolyte concentration of the medium. These studies indicate the possibility of developing a quantitative method of determining the specific surface area of colloidal silica or silica powders by titration nith a base. EXPERIMENTAL
In the work reported here, the amounts of alkali reacting under closely controlled conditions with various samples of
