[CONTRIBUTION FROM
THE
DEPARTMENT OF CHEMISTRY OF THEUNIVERSITY OF TEXAS]
THE IDENTIFICATION OF SULFONIC ACIDS ELIZABETH CHAMBERS AND GEORGE W. WATT Received November 8, 1940
Of the numerous methods which have been suggested for use in the identification of sulfonic acids, none has proved to be generally applicable. Undoubtedly, the method most commonly employed is that involving formation of the sulfonyl chloride followed, where necessary, by conversion to the corresponding amide or anilide (1-4). Aside from the fact that this procedure is somewhat time-consuming, the only serious objection to it is the fact that the formation of the sulfonyl chloride is frequently complicated by the presence of substituent groups which react with phosphorus pentachloride. Another method to which one finds frequent reference, but which apparently has not been used extensively, involves the formation of aliphatic (5) or aromatic (5-22) amine salts. The success attendant upon the use of this method seems to depend largely upon the purity of the sulfonic acid to be identified. With impure acids, and in some cases with mixtures, oils which are difficult if not impossible to crystallize are commonly encountered. The microscopic examination of crystalline derivatives has been suggested as a means of identifying certain sulfonic acids. Such properties as index of refraction, crystal habit, etc. have been examined using metal salts (10) as well as amine salts (10, 23), and benzoyl (24) and thiuronium (25) derivatives. Other possible procedures include the hydrolysis of the acids to the corresponding hydrocarbons or substituted hydrocarbons (1, 2, 26, 27) ; the replacement of the sulfonic acid group by halogen when the familiar bromine water test is used with phenolsulfonic or aminosulfonic acids (26); and the ebullioscopic method (28). In 1935 one of us had occasion to make use of the so-called “S-benzylthiuronium chloride” in the formation of solid derivatives of certain xanthates (29), dithio acids (29, 30), and mercaptans (31). At that time, the need for a more satisfactory method for use in the characterization of sulfonic acids was recognized and, since the earlier work of R. F. Chambers and Scherer (32) indicated that the thiuronium chloride might prove to be a reagent of general applicability, a number of derivatives of sulfonic 376
IDENTIFICATION OF SULFONIC ACIDS
377
acids mere prepared, purified, and analyzed. While this work was in progress, however, there appeared a paper by Donleavy (33) in which the thiuronium derivatives of thirty-six carboxylic acids and three sulfonic acids were described. Since Donleavy had established priority (34) and had indicated that further work designed to extend the use of this method was planned, the preliminary studies referred to above were discontinued. In view of the fact that no further reports have been published by Donleavy, and since there have appeared recently from other laboratories a number of publications (35, 36, 37) bearing on the subject, it seemed permissible to resume the study of the original problem. This seemed worth while also in consideration of the fact that published data indicate a lack of agreement in the melting points of a number of these derivatives. The desirability of so doing is further indicated by recent evidence of interest in the use of the thiuronium chloride reagent (38, 39, 40). An examination of the data published by earlier workers shows that the analytical data frequently fail to agree with calculated values unless it is assumed that the thiuronium derivatives are hydrated. Since the same situation was encountered in the present work, an effort was made to determine whether the presence of water of crystallization could be demonstrated by dehydration. There was also made a preliminary study of the possibility of separating, on the basis of differences in the solubility of their thiuronium derivatives, sulfonic acids (isomeric and otherwise) which appear as products of various sulfonation processes. EXPERIMENTAL
Preparation of 8-benzylthiuronium chloride. The chloride was prepared in substantially quantitative yield by a modification of the method described by Donleavy (33). . One-half mole each of benzyl chloride (63.3 g.) and thiourea (38.0 g.) in 75 cc. of 95% alcohol were warmed under reflux on a steam-bath. An exothermic reaction resulted in complete solution of the thiourea. The pale yellow solution was refluxed for one-half hour, after which the reaction-mixture was cooled in ice-water. The white crystalline solid product was washed onto a Buchner funnel with three 25-cc. portions of cold ethyl acetate, filtered by suction, and dried. Additional crops were obtained from the mother liquor by concentration followed by cooling. In the course of a number of preparations, both the low-melting (140-145') and high-melting (172-174') forms (41) were obtained. The former was converted t o the high-melting variety upon recrystallization from water, and melted sharply at 174O.1 In reaction with samples of a particular sulfonic acid, the two forms of the thiuronium chloride lead to derivatives which are identical. 1 All melting points recorded for purified substances are corrected. Mixed melting point determinations were made in all case8 in which the melting point of a sulfonic acid derivative approximated that of either of the two forms of S-benzylthiuronium chloride.
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ELIZABETH CHAMBERS AND GEORGE W. WATT
TABLE I TEIURONIUM DERIVATIWS OF SULFONIC ACIDS TEIURONIUM DERIVATIVEI
Nitrogen
ACID
M.P., "C. Calc'd (%)4
Ethylsulfonic .........................
114.7 212.4 . . . . . . . . . . . . . . . . . . . 209.7 133.7 147.5-148.5 181-182 o-Xylenesulfonic ...................... 207.6-208.1 m-Xylenesulfonic ..................... 145.6-146.1 183.7 146.1 184.5-185.0 182.4 168.7 174.9-175.4 214.3 171.O 211.1 136.8 190.5-190.8 205 (decomp.) 195.1 (decomp.) 179.4 1-Naphthylamine-8-sulfonic d. 300 (decomp.) 182-189 (decomp.: 312 (decomp.) l-Amino-8-naphthol-3,6-disul 2-Naphthylamine-6-sulfonic. . . . . . . . . . . 330 (decomp.) 209-211 (decomp.: 2-Naphthylamine-4,8-disulfonic 2-Naphthylamine-6,8-disulfonic. . . . . . . 276 (decomp.) 1-Naphthol-2-sulfonic. . . . . . . . . . . . . . . . . 169.4 1-Naphthol-4-sulfonic . . . . . . . . . . . . . . . . . 103.4 l-Naphthol-4,8-disulfonic. ..... 205.2 2-Kaphthol-6-sulf onic . . . . . . . . . . . . . . . . . 206.7 2-Naphthol-3,6-disulfonic. . . . 233.2 Benzothiazole-2-sulfonic0 . . . . . . . . . . . . . 170.5-171.0
8.97 6.76 (1 Hz0) 6.72 (1 HzO) 5.88 8.64 8.28 7.92 7.92 7.92 10.84 (1 HzO) 12.35 10.69 7.82 (1 H10) 7.45 (1 HzO) 9.51 (1 H2O) 7.25 (7 HzO) 5.94 (1 HzO) 7.14 (1 HzO) 7.00 (2 H2O) 8.53 (2 H2O) 5.62 (20 HzO) 10.79 5.62 (20 Ht0) 7.70 (8 H20) 8.08 (2 H20) 7.38 (10 HzO) 10.71 (1 HzO) 8.98 (8 HzO) 7.18 8.23 (7 HzO)' 8.80
7.18 8.80 11.02
Found (%)
8.80
6.57 6.67 5.84 8.57 8.15 7.98 7.83 7.76 10.83 12.16 10.67 7.76 7.57 9.51 7.25 5.81 7.23 7.01 8.51 5.52 10.93 5.43 7.58 8.00
7.27 10.62 8.89 7.21 8.25 8.70 7.31 8.69 11.01
4 Unless otherwise indicated the values listed in this column relate to the products to be anticipated as the result of elimination of alkali halide between one or more molecules of S-benzylthiuronium chloride and the alkali salts of acids containing one or more sulfonic acid groups. Sulfur: Calc'd for CI~HI~NZOSSZ, 19.75. Found, 19.87. 0 Sulfur: Calc'd for CI~HISNZOSS~, 18.93. Found, 18.60. d The high melting point, low yield obtained, and the analytical value for nitrogen
IDENTIFICATION OF SULFONIC ACIDS
379
Preparation of derivatives. In general, the procedure for the preparation of derivatives consisted in dissolving the sulfonic acid in 2 N sodium hydroxide solution and neutralizing any excess base with dilute hydrochloric acid. In case the sodium or potassium salt of the acid was available, the salt was dissolved directly in water. In some few cases it was necessary to apply heat in order to effect complete solution. Where the solubility of the alkali salt permitted, the solution was cooled in an icebath before addition of the thiuronium chloride. A quantity of S-benzylthiuronium chloride sufficient to react with the sodium salts formed by all acidic groups present in the molecule of the sulfonic acid was dissolved in water and the resulting solution was cooled in an ice-bath. In the majority of cases, the cold solution of the alkali salt of the acid was added, with stirring, to the thiuronium chloride solution. When, however, no solid product was obtained in this manner, a reversal of the order of addition sometimes resulted in the appearance of a crystalline derivative. The solid derivatives so prepared were filtered, washed with water, recrystallized (from 50% alcohol) to constant melting point, and analyzed for nitrogen by the Kjeldahl method. Several derivatives were analyzed for sulfur by the Carius method. The data relevant t o the derivatives prepared are given in Table I. In addition to the acids listed in Table I, the following were also used in attempts to prepare satisfactory solid derivatives: o-aminophenol-p-sulfonic; phenylhydrazine-p-sulfonic; 2-amino-8-naphthol-6-sulfonic; 2-naphthylamine-5,7-disulfonic;1naphthylamine-3,6,8-trisulfonic; 2-naphthol-8-sulfonic; l-naphthol-3,8-disulfonic; 2-naphthol-6,8-disulfonic;and 1,8-dihydroxynaphthalene-3,6-disulfonic.In these cases, the products were oils, resinous materials, or substances which decomposed so rapidly that purification of the derivatives was impossible. Dehydration studies. Small samples of derivatives believed to contain water of crystallization were dried i n vacuo over sulfuric acid, transferred to small glassstoppered weighing bottles which had been dried i n vacuo t o constant weight, and subsequently heated in a vacuum oven a t 125” and 28-30 mm. Derivatives, the analysis of which indicated no hydration, were heated concurrently as controls. Representative data are given in Table 11. Solubility measurements. The solubilities of a number of derivatives were estimated by determining the quantities of the thiuronium derivatives dissolved by all suggest that the unchanged sodium salt of the acid might have been recovered. However, qualitative and fusion tests demonstrated the absence of sodium. e For reasons similar to those given in the preceding footnote, together with the fact that some excess hydrochloric acid was present, there is suggested the possibility that the product obtained might be the hydrochloride of the original aminosulfonic acid. That such is not the case was shown by failure to secure a positive qualitative test for halogen and by the analytical data for sulfur. Sulfur: Calc’d for Cl&sIY\.’a07S8.2H20,18.84. Found, 18.91. Both the analyses for nitrogen and sulfur correspond to the dihydrate of the product which would result from reaction involving only one of the two sulfonic acid groups. f This calculated value assumes the heptahydrate of the product obtained if reaction occurred at both the - 0 N a and -S08Na groups. The analytical data for sulfur, however, do not check with this formulation and the analyses for sulfur and nitrogen do not correspond to any other product which might reasonably be expected. Sulfur: Found, 17.37. Found, 25.72. 0 Sulfur: Calc’d for C & I ~ N @ ~ S25.20. ~,
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ELIZABETH CHAMBERS AND GEORGE W. WATT
measured volumes of various solvents. Such measurements were made both a t room temperature and a t temperatures near the boiling points of the solvents. Among the solvents employed were: water, methyl alcohol, ethyl alcohol, diethyl ether, chloroform, carbon tetrachloride, carbon disulfide, dioxane, benzene, toluene, and xylene. The experimental data are too extensive and not sufficiently conclusive to warrant inclusion in this paper. DISCUSSION
Of the forty-three sulfonic acids used in this study, thirty-four formed crystalline derivatives with .S-benzylthiuronium chloride. The physical characteristics of these derivatives are such as to render them useful for purposes of identification. A careful examination of the data of Table I points to considerable uncertainty as to the composition of certain of these products. For both TABLE I1 RESULTSOF ATTEMPTSTO DEHYDRATE THE THIURONIUM DERIVATIVES OF CERTAIN SULFONICACIDS PARENT ACID
m-Xylenesulfonic
...........................
DURATION OF HEATINQ (HRS.
l-Naphthol-4,8-disulfonic. ..................
m-Benzenedisulfonic ........................ ~aphthalene-2,7-disulfonic ................. Diphenyl-p, p'-disulfonic .................... l-?u'aphthol-4-sulfonic . . . . . . . . . . . . . . . . . . . . . . . 2-Naphthylamine-6-sulfonic . . . . . . . . . . . . . . . . .
96 72 72 48 96 96 96
APPARENT WATER CONTENT (MOLES)
WATER REMOVED (MOLES)
0 0 1 2 7 10 20
0.07 0.03 0.30 0.55 0.89
0.20 0.66
metal and amine salts of sulfonic acids, earlier workers have demonstrated (10, 13) the presence of water of crystallization to the extent indicated by analyses for nitrogen, while with but two exceptions (32, 35), those who have reported on the thiuronium derivatives have merely assumed the presence of water. In the present work, the behavior of the derivatives during melting point determinations failed to suggest that these compounds were hydrated. Hydration is indicated, however, by the analytical data, since it seems unlikely that, for a considerable number of these substances, good agreement between the experimental values and those calculated assuming hydration is coincidental. On the other hand, it is indeed difficult to believe that there should be formed hydrates of sufficient stability to resist the rather extreme conditions used in the dehydration experiments. Accordingly, it is felt that where the analytical data suggest an abnormally high degree of hydration, there exists a reasonable doubt as to the nature of the solid derivative obtained. It should be recognized,
IDENTIFICATION OF SULFONIC ACIDS
381
however, that a reproducible solid derivative may be useful for analytical purposes even though its composition and structure may be unknown. 41so questionable is the composition of the derivative of l-naphthol-4sulfonic acid. Analytical data for nitrogen and sulfur are incompatible and there is no ready explanation why in this case alone a reaction should occur between the sodium naphtholate and the thiuronium chloride. Kevertheless, this derivative is reproducible. Several of the derivatives reported in this paper have been prepared by earlier workers and there has been some duplication among previously published data. In order to compare results published thus far, certain sulfonic acids and the reported melting points of their thiuronium derivaTABLE I11 COMPARISON OF MELTING POINTS REPORTED FOR CERTAINTHIURONITJM DERIVATIVES PARENT ACID
M.P.,
"c.
a-Naphthalenesulfonic . . . . . . . . . . . . . . . m-Nitrobenzenesulfonic .............. Benzenesulfonic ..................... p-Toluenesulfonic . . . . . . . . . . . . . . . . . . . p-Arninobenzenesulfonic . . . . . . . . . . . . . p-Naphthalenesulfonic . . . . . . . . . . . . . . . Naphthalene-2,7-disulfonic..........
136-137* (32), 136.8, 138 (25) 140 (33), 146.1 144 (33), 147.5-148.5, 148-149* (35) 170 (33), 181-182, 182-183* (35) 184.5-185, 187-188* (35) 188-189* (32), 190.5-190.8, 193 (25) 199-200* (decornp.) (32), 205 (decornp.), 211212 (decornp.) (25) Naphthalene-1 ,6-disulfonic. .......... 234-235* (decornp.) (32), decornp. above 81 (25) Naphthalene-l,5-disulfonic.. . . . . . . . . 244-245* (32), 251 (25) Saphthalene-2,6-disulfonic . . . . . . . . . . 256 (25), 258* (32)
tives are assembled in Table 111. Where no literature reference is given, the value reported is that found in the present investigation. Melting points marked with an asterisk are uncorrected. While otherwise in fairly good agreement, these data show that the melting points reported by Donleavy (33) are uniformly several degrees low. Veibel and co-workers (35, 36) found the same to be true for melting points recorded by Donleavy for thiuronium derivatives of carboxylic acids. In general, the data recorded in this paper are in good agreement with those of Veibel and Lillelund (35). The advantages peculiar to this method for the identification of sulfonic acids have been outlined elsewhere (33, 35) in a wholly adequate manner and need not be repeated here. Our experience indicates that the method is satisfactory for mono- and di-sulfonic acids if other functional groups are absent. The presence of phenolic or amino groups reduces, but does
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ELIZABETH CHAMBERS AND GEORGE W. WATT
not preclude, the possibility of securing a satisfactory solid derivative, The presence of the amino group is particularly disadvantageous in the naphthalene sulfonic acids. An advantage not common to the formation of amine salts lies in the fact that satisfactory thiuronium derivatives may be formed using relatively impure sulfonic acids. The frequent production of the decidedly offensive odor of benzylmercaptan resulting from the decomposition of the thiuronium chloride may, to some, constitute a serious objection to the method. Although Veibel and Lillelund (35) claim that the formation of benzylmercaptan can be prevented, we would prefer to state that the technique employed by them tends to, but does not wholly, overcome the difficulty. Finally, it should be pointed out that the studies on the relative solubilities of these derivatives were of an exploratory character. It was found, however, that certain separations may be made. For example, it appears that the isomeric xylenesulfonic acids may be separated by use of appropriate organic solvents. Similar separations seem possible with the a- and @-naphthalenesulfonicacids and with the products obtained upon sulfonation of @-naphthol. SUMMARY
1. The use of S-benxylthiuronium chloride in the identification of sulfonic acids has been investigated, and the melting points of solid derivatives of thirty-four sulfonic acids have been recorded. 2. The results of this study have been compared with those of earlier workers, and certain limitations on the usefulness of the method have been discussed. AUSTIN,TEX. REFERENCES
(1) WHITMORE,“Organic Chemistry,” D. Van Nostrand Co., Inc., New York, N. Y., 1937, pp. 772-6. (2) PORTER, STEWART,AND BRANCH, “The Methods of Organic Chemistry,” Ginn and Company, New York, N. Y., 1927, pp. 235-40. (3) SHRINERAND FUSON, “Systematic Identification of Organic Compounds,” Second Edition, John Wiley and Sons, Inc., New York, N. Y.,1940, pp. 175-6;232-7. (4) KAMM,“Qualitative Organic Analysis,” Second Edition, John Wiley and Sons, Inc., New York, N. Y., 1932,85,281-2. (5) NORTONAND OTTEN,Am. Chem. J., 10, 140 (1888). (6) Reference 3, page 176. (7) ERDMANN AND S ~ ~ V E R Ann., N , 276, 297 (1893). (8) PERKIN AND COPE,J. Chem. Soc., 66, 845 (1894). (9) KLASON,Ber., 63, 706 (1920). (10)AMBLER,J. Ind. Eng. Chem., 12, 1081, 1194 (1920). (11) AMBLERAND WHERRY,J. Ind. Eng. Chem., 12, 1085 (1920).
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VAN DUIN, Rec. trav. chim., 40, 99 (1921). J. Ind. Eng. Chem., 14,964 (1922). LYNCH, PERKIN AND SEWELL,J . Soc. Chem. Ind., 43, 27T (1923). FORSTER AND KEYWORTH, J . SOC.Chem. Ind., 43, 165T (1924); 46, 25T (1927). KEYWORTH, J . SOC.Chem. Ind., 43, 341T (1924); 46,20T, 397T (1927). GARNER, J. SOC.Dyers Colourists, 43, 12 (1927). FORSTER, HANSON, AND WATSON, J . SOC.Chem. Ind., 47, 1f6T (1928). FORSTER AND MOSBY, J . SOC. Chem. I d . , 47,157T (1928). NOLLERAND GORDON, J. Am. Chem. SOC.,66, 1093 (1933). FIESER, Org. Syntheses, 16, 65 (1936). LATIMER AND BOST,J. Am. Chem. SOC., 69, 2500 (1937). GARNER, J . Soc. Dyers Colourists, 62, 302 (1936). WHITMORE AND GEBHART, Ind. Eng. Chem., Anal. Ed., 10, 654 (1938). HANNAND KEENAN,J. Phys. Chem., 31, 1082 (1927). Reference 4, page 85. GATTERMAN AND WIELAND,“Laboratory Methods of Organic Chemistry,” The Macmillan Company, New York, N. Y., 1937, pp. 196-210. (28) MORTON,“Laboratory Technique in Organic Chemistry,” McGraw-Hill Book Co., Inc., New York, N. Y., 1938, p. 61. (29) WATT,British Patent 488,691; Chem. Abstr., 33, 435 (1939). (30) WATT,French Patent, 830,461; Chem. Abstr., 33, 2765 (1939). (31) WATT,United States Patent 2,189,720; Chem. Abstr., 34, 4303 (1940). (32) CHAMBERS AND SCHERER, Ind. Eng. Chem., 16, 1272 (1924). (33) DONLEAVY, J . Am. Chem. Soc., 68, 1004 (1936). (34) DONLEAVY AND JOHNSON, Paper presented at the New Haven Meeting of the A.C.S., April, 1923; Science, 67, 753 (1925). (35) VEIBELAND LILLELUND, Bull. SOC. chim., [5] 6, 1153 (1938). (36) VEIBELAND OTTUNG,Bull. SOC. chim., [5] 6, 1434 (1939). (37) DEWEYAND SPERRY,J. Am. Chem. SOC.,61, 3251 (1939). (38) MASONAND MANNING, J. Am. Chem. SOC., 62,1636 (1940). (39) STILLER,HARRIS,FINKELSTEIN, KERESETESY, AND FOLKERS, J. Am. Chem. SOC.,62, 1789 (1940). (40) EMERSON AND SMITH, J. Am. Chem. SOC.,62, 1871 (1940). (41) WERNER,J. Chem. SOC.,67, 284 (1890). (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22) (23) (24) (25) (26) (27)
