Identification of Certain Solvents by the Xanthate Reaction Application to Alcohols WILLETF. WHITMORE AND EUGENE LIEBER Polytechnic Institute of Brooklyn, Brooklyn, N. Y.
W
ITHIN the past decade the application of chemical research to industrial problems has made available in quantity organic solvents which previously had been considered only as museum specimens or laboratory curiosities (18, 25). This development has been due chiefly to the investigation and utilization of products obtainable from petroleum and natural gas, although new synthetic and fermentation processes have played an important part. The glycol ethers (cellosolves and carbitols) are comparatively recent additions to the increasing list of organic compounds which are of considerable technical importance. The identification and characterization of these forms is very difficult indeed if the conventional methods of qualitative organic procedure are followed. This paper presents the results of an investigation which has led to the development of a satisfactory procedure for the identification of certain types of solvents.
Hallet and Ryder (12) determined the xanthate by converting to the copper derivative, igniting, taking up the ash in nitric acid, and determining the copper electrolytically. Nickels (g3) weighed the cuprous xanthate directly and was first to weigh the potassium xanthate as such. ignited the cuprous xanthate and weighed as cupric oxide. Macagno (19) and Hehner and Carpenter (14) titrated the cold aqueous solution of the xanthate, slightly acidified with acetic acid, with 0.1 N copper sulfate solution, determining the end point with potassium ferrocyanide. Selivounof (27) titrated the neutral solution of the xanthate with very dilute copper sulfate solution using guaiacol as indicator, extreme accuracy being claimed. Harding and Doran (13) precipitated the cuprous xanthate with an excess of copper acetate and determined the excess, after filtration, iodometrically. Calcott, English, and Downing (4) precipitated the cuprous xanthate, filtered, decomposed the residue with nitric acid, and determined the copper iodometrically. Matuszak (21) decomposed the cu rous xanthate with bromine water and estimated the copper iodbmetrically. Holmberg (16) and Hirschkind (16) added excess of standard acid to the aqueous solution of the xanthate, allowed it t o stand for 10 minutes, and back-titrated with standard alkali (barium hydroxide) using either phenolphthalein or methyl red as indicators. Stavorinus (98)and Weiss ($3) oxidized the xanthate solution with hydrogen peroxide and determined the resulting sulfate either gravimetrically or volumetricall in the usual manner. Tarugi and Sorbini (29) added the unznown xanthate solution to a standard solution of arsenic trioxide, extracted the arsenic xanthate with an organic solvent, and titrated the aqueous layer containing excess of arsenic with iodine. The direct titration of xanthate solutions with iodine is based upon the following reaction: 19 2CzHs0. CS. S- = 21(CzH60. CS. S)z and seems to have been first proposed by Delachanal and Mermet ( 7 ) ,although the action of iodine on xanthates was studied as early as 1845 by Zeise (34). The reaction is of quantitative accuracy and has the important advantage of being very easily and quickly carried out. In this respect it stands in marked contrast to the methods enumerated above as the operations of precipitation, filtering, washing, etc., are eliminated. The quantitative aspects of the reaction have been studied and reported by Gastine ( I I ) , Rupp and Krauss (26), Andre (I), Cundal (6),and Matuszak (20),the latter critically discussing the previous work on the subject.
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PREVIOUS WORK Although the monoalkyl ethers of ethylene and diethylene glycol have been available commercially during the past decade, no fundamental data exist in the literature for their qualitative identification by the usual scheme of organic analysis. However, Palomoa (24) and Conn, Collett, and Laxxell (6) prepared a series of aromatic esters of the monoalkyl ethers of ethylene glycol and diethylene glycol-the benzoyl and p-nitrobenxoyl derivatives-and found these esters to be liquids of high boiling point. Zeise (36) was the first to report the formation of xanthic acid and its salts. Although Zeise reported many of the characteristic reactions of that substance of which we now have knowledge, it did not seem to have occurred to him that it could be extended to alcohols other than ethyl alcohol and it is only within comparatively recent times that it has been shown how extensive and characteristic xanthate formation is for the hydroxyl function. As a reaction leading to the formation of identifying derivatives, the xanthate reaction with but few exceptions has received but little attention. Bamberger (2, 3) studied and characterized the tetrahydronaphthols by this reaction. Tschugaeff (31) applied the xanthogenic reaction for the preparation of both characteristic derivatives of the terpene series and unsaturated hydrocarbons (Tschugaeff reaction), and further suggested its use for the differentiation of primary, secondary, and tertiary alcohols based on the stability of the xanthogenic acid esters on distillation (10, $1). Probably the greatest single analytical application of the xanthogenic reaction is in the detection and quantitative estimation of carbon bisulfide. This is detected by absorption in alcoholic potassium hydroxide, which is then decomposed by making acid and adding copper sulfate. A golden yellow precipitate or coloration of cuprous xanthate forms, the test being sensitive to 1 part in 90,000 (9, 32). For the quantitative determination of carbon bisulfide absorption in alcoholic potassium hydroxide, as before, is the &st step. Variations from this point are based upon the manner in which the resulting potassium ethyl xanthate is estimated. Zeise (36)made ultimate analyses for the separate constituents.
+
+
PRINCIPLE OB ANALYTICAL SCHEME From an examination of the literature of the xanthate reaction it is evident that numerous methods exist for the quantitative estimation of the alkali xanthates. In spite of the large amount of work which has been done upon that problem with respect to the determination of carbon bisulfide, no one has ever suggested its systematic extension to the identification of alcohols. The general formula of an alkali xanthate is:
RO where
‘cs
MS/
R = an alkyl residue M = an alkali metal
If we apply one of the methods used for the quantitative estimation of a xanthate, it is evident that the amount of
127
INDUSTRIAL AND ENGINEERING CHEMISTRY
128
standardized reagent, whether it be copper solution, acid, or iodine solution, will depend upon the molecular weight of R. Hence i t is possible to assign to each alcohol an “alkali xanthate reagent number” which will sharply characterize the alcohol. A review of the quantitative methods cited for the estimation of the xanthate used indicated that the direct titration with iodine was the simplest, quickest, and quite accurate. MATERIALS AND REAQENTS
PURIFICATION OF ALCOHOLS.All of the alcohols and monoalkyl ethers of ethylene and diethylene glycol studied in this paper were purified by careful fractionation with forced reflux and only the purest fraction of each substance was taken. Table I presents the physical data obtained for the monoalkyl ethers of ethylene and diethylene glycol obtained by purification of commercial samples of the cellosolves and carbitols obtained through the courtesy of the Carbide and Carbon Chemicals Corporation.
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should be permanent for a t least 5 to 10 minutes. The addition of iodine was accompanied by vigorous agitation. As the iodine is added a whitish emulsion appears, consisting of the resulting “dixanthogen.” The iodine equivalent of the xanthate was calculated from the experimental data as follows:
I,
=
C X I G
where I, = iodine equivalent of the xanthate expressed in milligrams of iodine per gram of xanthate C = volume in cc. of iodine solution required I = value of iodine solution expressed in mg. of iodine per cc. G = weight of alkali xanthate taken expressed in grams CALCULATION OF THEORETICAL IODINE EQUIVALENT VALUES. The theoretical iodine equivalent values for the alkali xanthates are based upon the reaction equation:
TABLEI. PHYBICAL PROPERTIES SPECIFIC GRAVITY REFRACTIVE i. 20 INDEX
+
2KX f 1 2 2KI Xz where X = (R0.CS.S-)
e., two moles of xanthate are equivalent to one mole of E T H Y L E N E GLYCOL 0.9305 1,4077 134.7-135 Monoethyl ether iodine. 124.4 0,9605 1.4017 Monomethyl ether Figure 1 sum169.3-169.5 0.9027 1.4190 Monobutvl ether D I E T H Y L E N E GLYCOL marizes in graphical 5 194-195 1.0397 1.4300 Monoethyl ether form, with typical $700 0.9650 1.4321 Monobutyl ether 228.5-230.0 examples cited, the d theoretical xanthate i REAGENTS.The potassium hydroxide and carbon bisulfide were of c. P. reagent grade. The ethyl alcohol and acetone used iodine equivalents r: for purifications were c. P. absolute. The diethyl ether used was of the alcohols stud- d 5600 of ordinary grade. This was allowed to stand over calcium ied in this report. z chloride for several days, and then stored over sodium, and was 5 The practical use of filtered before use. STANDARD IODINBI SOLUTION.This was prepared as outlined t h i s c u r v e i s d i s - s 1 by Treadwell and Hall (50) and standardized by methods indi- cussed below. W cated in that text. One cubic centimeter of the standard iodine 3 DETERMINATION8 5 0 0 solution employed contained 0.00952 gram of iodine. POINTS. STARCH SOLUTION.This was prepared fresh before use by OF MELT~NG dissolving 0.5 gram of soluble starch in 100 cc. of boiling water. Melting points were determined with the MOLECULAR %CHT oc ALCOWPO apparatus and proEXPERIMENTAL PROCEDURE FIGURE 1 cedure described by PREPARATION AND PURIFICATION OF ALKALIXANTHATES. Mulliken (22). T o 1.2 molar proportion of the purified alcohol was added 1.0 molar proportion of pulverized potassium hydroxide, and EXPERIMENTAL RESULTS the mixture heated with stirring until the alkali dissolved. The experimental data obtained in the manner outlined To this an equal volume of dry ether was added after cooling, and then a 1.5 molar proportion of carbon disulfide was above are summarized in Table 11. Melting point determinations are similarly summarized in gradually added in small portions with vigorous stirring. The yellow precipitate of the xanthate formed immediately. Table 11. I n general the majority of the melting points lie After the addition of carbon disulfide, two additional volumes above 200’ C. and for many of the alcohols are quite close of ether were added, and the product mas filtered off on a together, Attention is, however, directed to the characterBuchner funnel, pressed, and washed with dry ether. The istic melting points of the monoalkyl ethers of ethylene glycol product was removed from the funnel, washed again with dry (cellosolves) xanthates. UNSATURATED ALCOHOLS.Furfuryl and allyl alcohols ether by agitation, and refiltered. In order to purify, the product was dissolved in the smallest were chosen as representative of this class. The potassium quantity of hot ethyl alcohol or acetone, filtered, cooled in an xanthates were prepared and purified in the manner described ice bath, and dry ether added to complete precipitation. and titrated with iodine. Allyl potassium xanthate behaved The recrystallized product was filtered off on a Biichner normally and gave experimental values in excellent agreement funnel, pressed, and washed with dry ether. In all cases with theory. Furfuryl potassium xanthate gave high values the above procedure was repeated to give the final purified due to addition of iodine to the double bonds. TERTIARY ALCOHOLS.Experimental data upon the potasproduct used in the subsequent work. The final product was then dried in a vacuum desiccator for several hours or, sium xanthates derived from tertiary alcohols (butyl and amyl) confirmed the previous work of Dubsky (8) on the when convenient, overnight. IODOMETRIC TITRATION OF THE ALKALI XANTHATES.From instability of these products. It was not possible to obtain 0.15 to 0.25 gram of the purified xanthate was dissolved in any definite xanthate iodine equivalent values, data in all 200 cc. of water, After the addition of 4 CC. of freshly pre- experiments being 30 to 40 per cent high and with no perpared starch solution, it was titrated directly with the stand- manent end point. It was found that aqueous solutions of ardized iodine solution to a distinct blue end point which the tertiary xanthates quickly develop an odor of hydrogen SOLVENT
BOILING C.
POINT,
20
200
c.
March 15, 1935
ANALYTICAL EDITION
129
lent also leads to the simultaneous determination of the molecular weight of the unknown alcohol. The usual characterizing derivatives for this group, the 3,bdinitrobenzoates (R)aCO.CS.SK HOH = (R)aC.OH KHS COS and the phenyl urethanes, give no further information than COS HOH = COz HzS a melting point, a physical constant which is extremely sensitive to even traces of impurities. An examination of a table In all probability the decomposition is further catalyzed by the products of decomposition, since hydrogen ions are of melting points of a series of 3,&dinitrobenzoates further produced. Xanthates derived from primary and secondary reveals melting points too low for convenient measurement, alcohols are stable in aqueous solution, but decompose slightly and in some cases the derivatives of alcohols boiling a t subwith evolution of hydrogen sulfide on prolonged boiling. stantially the same temperature have melting points which The tertiary xanthates decompose rapidly in boiling aqueous are so close together that definite characterization by this derivative alone is impossible. solution. Isomeric alcohols yield the same xanthate iodine equivaMONOALKYL ETHERSOF GLYCOLS.The monoalkyl ethers lent. Identification is, however, possible because of differof ethylene glycol (cellosolves) yielded with no difficulty nice crystalline potassium xanthates of definite melting points, ences in physical constants and melting points of the indiwhich gave iodine values agreeing closely with the calculated vidual xanthates. While pure and anhydrous alcohols were used in estabvalues (Table 11). lishing the reliability of the method, in actual practice this need not be the case. The analyst is frequently in possession TABLE11. IDENTIFICATION OF ALCOHOLS.4s XANTHATES of sufficient facts concerning his unknown, so that extensive .UO.CS. SK IODINE EQUIYALENT~MELTING POINT isolation, purification, and determination of physical conTYPE R Expt. Calcd. COR. MR./o. M -d .O- . c. stants are unnecessary. The alcohol need not be anhydrous, Primary Methyl 874 869 Darkens a t 195-215 as the alkali xanthates form in the presence of water. The Ethyl 797 793 215.3 Propyl 726.5 729 205.7 method may be applied directly to a solvent mixture, proButyl 676.5 676 223.9 vided only one alcohol is present. The curve of Figure 1 is Amyl 625 628 226 Tetraparticularly helpful where only a boiling point determination hydrofurfurvl 590 587.5 213.2 is available. Secondary Propyl 721 729 Darkens at 236 A method for the direct identification of the alkoxy group Butyl 671.5 675 244.1 -4myl 633 628 211.7 in esters, based upon the xanthate reaction, has been deHexyl 592 587.5 Darkens a t 199 veloped and will be presented in a separate report. Cyclosulfide, easily confirmable by moist lead acetate paper. probable reaction is
+ +
hexanol Cellosolve Methyl Butyl Carbitols Carbitol Butyl Unsaturated Furfuryl Allyl a M g . of iodine per gram of
Cellosolves
+
+
The
+
589
593
Darkens at 242
620.5 667 544 516 425
622 668 547 6U 460 599 738
186.7 202.5 167.9
740:5 xanthate.
... ...
154.4 Darkens at 178
Some difficulty was experienced with the carbitols (monoalkyl ethers of diethylene glycol) in a manner which sharply distinguished them from the cellosolves. Preparation of the corresponding potassium xanthates in the usual manner yielded heavy red oils instead of the customary bulky yellow precipitates. The reddish oils are insoluble in ether and soluble in water. On the addition of copper salts to the aqueous solution, heavy precipitates of the brilliant golden yellow cuprous derivatives were thrown down. Like the solid alkali xanthates, the reddish oils were soluble in acetone and benzene, and were reprecipitated by addition of ether. These oils were then drawn off, washed several times with ether by agitation, then placed in wide crystallizing dishes and allowed to dry in a vacuum desiccator for &vera1 days. Carbitol (monoethyl ether of diethylene glycol) yielded an orange-colored pasty solid (melting point, 127’ C.), while butyl carbitol (mono-n-butyl ether) gave a thick reddish jelly-like solid. Both were titrated in the usual manner with iodine. The results are indicated in Table 11. Carbitol shows good agreement with the calculated value, while butyl carbitol, although low, is only 7.6 per cent from the theoretical value. DISCUSSION The method outlined above presents a relatively simple means for the identification of alcohols with reagents which are inexpensive and found in every laboratory. The procedure is relatively simple, rapid, and requires no unusual experience. Further, as may be noted from an examination of Figure 1, the determination of the xanthate iodine equiva-
LITERATURE CITED (1) Andre, Bull. soc. chim., 33, 1679 (1923). (2) Bamberger and Lodter, Ber., 22, 769 (1889). (3) Ibid., 23, 211 (1890). (4) Calcott, English, and Downing, Eng. Mining J . Press, 118, 980 (1924). (5) Conn, Collett, and Lazzell, J . Am. Chem. Soc., 54, 4370 (1932). (6) Cundal, Western Gas, 5 (9), 188 (1929). (7) Delachanal and Mermet, Ann. chim. phys., (5) 12, 108 (1877). (8) Dubsky, J . prakt. Chem., 103, 109 (1921). (9) Feigel and Weiselberg, 2.anal. Chem., 83, 93 (1931). (10) Gandurin, Ber., 41, 4362 (1908). (11) Gastine, Compt. rend., 98, 1588 (1884). (12) Hallet and Ryder, Eng. Mining J. Press, 119, 690 (1925). (13) Harding and Doran, J . Am. Chem. SOC.,29, 1476 (1907). . , Hehner and Carpenter, Analyst, 8, 37 (1883). Hirschkind, Eng. Mining J. Press, 119, 968 (1925). Holmberg, Ber., 46,3853 (1913). Johnson, J. Am. Chem. Soc., 28, 1209 (1906). Jordan, O., “Chemische Technologie der Losungsmittel,” Berlin, J. Springer, 1932. Macagno, Chem. News, 43, 138 (1881). Matuszak, IXD. ENG.CHEY.,Anal. Ed., 4, 98 (1932). Matuszak, J . Am. Chem. SOC.,53, 4451 (1931). Mulliken, “Identification of Pure Organic Compounds,” Vol. 1, p. 218, New York, John Wiley & Sons, 1905. Nickels, Chem. News, 43, 148 (1881). Palonioa, Ber., 42, 3873 (1909). Reid, E. W., IND. EXG.CHEY.,26, 21 (1934). R u p p and Krauss, Ber., 35, 4157 (1920). Selivounof, Analyst, 54, 488 (1929). Stavorinus, J. Gasbeleucht., 49, 8 (1906). Tarugi and Sorbini, Chem. Zentr., 1912, 11, 1399. Treadwell and Hall, “Quantitative -4nalysis,” 7th ed., Vol. 2, p. 554, New York, John Wiley & Sons, 1928. Tschugaeff, Ber., 32, 3332 (1899). Vogel, Ann., 86, 370 (1853). Weiss, J. IND. ENG. CHEM.,1, 605 (1909). Zeise, Ann. Chem. Pharm., 55, 304 (1845). Zeise, Poggendorf’sAnn., 31, 424 (1845). Zeise, Schweigger’s J . Chem. Physilc, 35, 173 (1822). REOEIVED November 21, 1934. Abstracted from a portion of the thesis submitted by Eugene Lieber in partial fulfilment of reauirements for the degree of Master of Science in Chemistry at the Polytechnic Institute of Brooklyn in June, 1934.
