both practical and desirable. Use of molten salt stationary phases makes possible separations of high boiling compounds limited only by their thermal stability. LITERATURE CITED
(1) Adlard, E. R., Whitman, B. T., “Gas Chromatography,” D. H. Desty, ed., p. 351, Butterworths, London, 1958. ( 2 ) Cropper, F. R., Heywqpd, A., “Vapor Phase Chromatography, D. H. Desty,
ed., p. 316, Butteraorths, London, 1957. (3) Davies, A. J., Johnson, J. K., Ibid., p. 185. (4) Felton, H. R., “Gas Chromatography,” V. J. Coates, I. S. Fagerson, and H. J. Noebels, eds., p. 131, Academic Press, Sew York, 1958. (5) Guild, L., Bingham, S., Aul, F., “Gas Chromatography,” D. H. Desty, ed., p. 226, Butterworths, London, 1958. (6) Hawkes, J. C., “Vapor Phase Chromatography,” D. H. Desty, ed., p. 266, Butterworths, London, 1957.
( 7 ) Juvet, R. S., Wachi, F. M., ANAL. CHEM.32.290 11960).
Xoebels, eds., p, 51, y4cademic Press, New York, 1958. RECEIVEDfor review March 17, 1960. Accepted June 13, 1960. Division of Analytical Chemistry, 137th Meeting, ACS, Cleveland, Ohio, April 1960. Work conducted in part under Atomic Energy Commission Contract .4T(11-1)-174.
Analysis of Sulfonic Acids and Salts by Gas Chromatography of Volatile Derivatives J. J. KIRKLAND Industrial and Biochemicals Department, Experimental Station, E. I. du font de Nemours 8, Co., lnc., Wilmingfon, Del.
b Gas chromatography has proved to b e extremely valuable for analyzing a wide range of nonvolatile sulfonic acids and salts. Following quantitative conversion to volatile derivatives, complex mixtures of difficultly analyzed homologs and isomers can b e separated by conventional techniques. Aliphatic, aromatic, and alkyl aryl sulfonic acids and their salts are conveniently converted to corresponding sulfonyl chlorides by reaction with thionyl chloride or phosgene in the presence of a catalyst. Free sulfonic acids, including hydrates, may also b e similarly analyzed as methyl ester derivatives after esterification with diazomethane. Procedures are given for carrying out the conversion reactions, and illustrations of the analysis of typical mixtures are shown.
G
because O f its exceptional selectivity, has been used for the analysis of a wide range of volatile rnaterials containing close-boiling homologs and isomers. Nonvolatile, or lowvolatility compound., have also been analyzed, following conversion to more volatile derivatives (1, 5, 7 ) . Kew methods are herein proposed for analyzing complex mixtures of nonvolatile sulfonic acids and salts by gas chromatography of volatile derivatives. The suggested techniques are faster, more convenient, and more precise than liquid and paper chromatography approaches, and have the advantages of higher selectivity and accuracy over possiblt infrared spectrophotometric procedures. Aliphatic, aromatic, and alkyl aryl sulfonic acids and salts may be conAS CHROMATOGRAPHY,
1388
ANALYTICAL CHEMISTRY
verted in very high yields to corresponding sulfonyl chlorides by reaction with thionyl chloride or phosgene in the presence of certain formamide derivatives (g-4). This procedure has been found convenient for the quantitative preparation of sulfonyl chloride derivatives which can be analyzed by conventional gas chromatography techniques. Esterification reactions have previously been employed for the gas chromatographic separation of carboxylic acids; however, sulfonic acids have not been handled in this manner. I n this study, methods have been developed for analyzing sulfonic acids using this principle. I t was found that diazomethane is a convenient reagent for the esterification, but that chromatographic separations must be carried out a t reduced pressure to prevent sample decomposition. The esterification approach is preferred for the analysis of free sulfonic acids containing other functional groups which react with thionyl chloride or phosgene, or with compounds which isomerize or decompose during the vigorous reaction with these reagents.
stirred air bath was maintained constant ( h 0 . l o C.), with a Thermotrol proportional controller (Model 1050, Hallikainen Instruments, Berkeley, Calif.). T o permit independent heating, the vaporizer block of the instrument was equipped with a small metal contact heater powered by a Variac. Programmed temperature separations were carried out on a Model 202-B gas chromatograph (F & 11 Scientific Corp., 1202 Arnold Ave., S e w Castle County Air Base, h’ew Castle, Del.). This unit was equipped with a 1-mv. Minneapolis-Honeywell Brown recorder. Reduced-pressure separations of sulfonic esters were made on an F Br: M Scientific Corp. Model 17-A gas chromatograph. The column outlet was connected in succession to a cold trap, 5-liter surge tank, Cartesian manostat, and vacuum pump. The manostat regulated the outlet pressure, which was measured with a mercury manometer. Carrier gas was delivered into the column a t the desired flon- rate by means of a fine control needle valve placed between the regulator and the column inlet. Only a very slight positive pressure on the inlet of the needle valve was needed to attain the desired flow rate, I n front of the valve, a rotameter was inserted to estimate the carrier gas flow through EXPERIMENTAL the column. A mercury manometer was connected in parallel n i t h the Apparatus and Reagents. G a s IXSTRUMENTS. A4 column input t o measure the input CHROMATOGRAPHIC pressure. The detector bridge output Perkin-Elmer Model 154-A Vapor was monitored with a 1-niv. 1IinneFractometer, equipped with a 1-mv. apolis-Honeyr-iell Brown recorder. Leeds & Korthrup Speedomax Type Dry helium was used as the carrier G recorder, was used for isothermal gas in all operations. Helium floiv rates separations of sulfonyl chlorides. T h e were measured with a soap film meter, instrument was modified t o permit except in the reduced pressure separaoperation up t o 225’ C. by t h e additions. tion of sufficient insulation a n d heatCOLUMN^. For the isothermal sepaing capacity. Thermistors of 8000rations of sulfonyl chloride derivatives, ohm resistance mere installed to provide a 2-foot silicon grease column was adequate sensitivity a t the higher temprepared b y coating 40- to 50-mesh peratures. The temperature of the
acid-washed Chromosorb (Jolins-AIanville Corp., Manville, N. J.) with 20% b y weight of Doiv Corning high-vacuum silicone grease (Dow Corning Corp., Midland, Mich.). The grease was dissolved in ethyl acetate which was slowly evaporated in the presence of the Chromosorb as the mixture \vas gently stirred on a steam bath. Tliis material was then placed in a vacuum oven held at 100" C. for 2 hours, and 3.10 grams of the resulting dry mixture was packed into a 2-foot, 6-mm. outside diameter glass U-tube, using vibration. The programmed temperature column was a 4-foot unit containing silicone rubber gum suspended on Celite 545. It was prepared similarly to that described above, except that 20% by weight of the silicone rubber gum (Type SE-76, General Electric Co., Silicone Products Dept., Waterford, S . Y . ) \vas dissolved in boiling chloroform and evaporated onto 80- to lOO-mesh Celite 545 (Johns-llanville Corp., Nanville, N. J.). This column contained 5.00 grams of packing material. The column used for the reducedpressure analysis of sulfonic esters was a 2-foot, 6-mm. outside diameter, glass U-t,rtbe filled with 5.60 grams of packing composed of 20y0 .Ipiezon L grease (James G. Biddle Co., Philadelphia, Pa.) suspended on 40- to 50-mesh Chroniosorb. The grease n-as placed on the support by evaporating a carbon tetrachloride solution in the manner described above. OTHEREQUIPMEST. Liquid samples were injected n-ith a Hamilton microsyringe, 10-111. or 50-pl. capacity (Model Xos. 7OlN and 705K, respectively, The Hamilton Co., 1134 Khitley St., Whittier, Calif.). Areas were measured with a n A. Ott compensating polar planimeter (Burrell Corp., Pittsburgh, Pa.). I'REPARATIOS OF DIAZOMETHAXE. Ethereal-alcoholic solutions of diazomethane may be convenimtly prepared from Diazald (Aldrich Chemical Co., Inc., Milwaukee, Kis.), in the following manner: Ethyl alcohol (05FG>25 nil.) is added t'o a solution of potassium hydroxide (5 grams) in water (8 ml.) in a 100-ml. distilling flask fitted with a dropping funnel and an efficient condenser set downward for distillation. This condeiisw is connected t o two receiving flasks in series, the second of which contains 20 to 30 nil. of ether. The inlet tube of the second receiver dips below the sur,facc of the ethei, and both recrivcrs are cooled to 0" C. The flask csontaining the alkali solution is heatcd in a water bath to 65' C., after n-hicli a solution of 21.5 grams (0.1 molts) of Diazald in about 130 nil. of ethcsi, is slow1~- adtlpd tlii~ougli the dropping f u n n t ~ l . 'lhc rat(. of atldition s h ~ u l t lalmut eclual thc rat(, of tlistillation. iilien the ciroppiiig funnel is empty, another 20 nil. of ether is added slonly. and the tlistillatioii is continued until the distilling cthw is colorless. The combined ethrwal distillate contains about 3 grams (0.07 mole) of diazomethane. which is sufficient to up to about 2 p a m s of aromatic c~stci~ify
sulfonic acids with a molecular weight, gram sample of the sulfonic acid or of about 150. (The preparatioii of salt is placed in a small rounddiazomethane and reactions with this bottomed flask fitted with a magnetic compound should be carried out in a stirring bar and a hemispherical shielded, well-vent'ilated hood.) If heating mantle. T h e flask is atmaintained a t wet ice temperature, tached t o a condenser and then 0.50 diazomethane solutions can be used for ml. of dimethylformamide and 20 ml. 2 to 3 days with only a moderate of thionyl rhloride are addcd, redecrease in diazomethane concent'ration. spectively. T h e resulting solution is STAXDARDS.Unless indicated otherrefluxed until no off-gas is detected jvith wise, all materials were used in this a bubbler tube attached t o the constudy without further treatment. denser and containing chlorobenzene. p-Toluenesulfonic acid, monohyThe time required for complete reaction drate, Eastman Kodak Co. KO.984, varies from several minutes to as long as White Label. 2 hours, depending on the sample. If 2,,5-Dimethylbenzenesulfonic acid, dithe reactant is a salt of a sulfonic acid, hydrate, Eastman Kodak Co., KO 1869, it is necessary to remove the insoluble White Label. chloride reaction product before prepar2-Naphthalenesulfonic acid, monoing the solution for gas chromatographic hydrate, Eastman Kodak Co., S o . 897, analysis. This is accomplished b y K h i t e Label. diluting the reaction with a n equal Benzenesulfonic acid, sodium salt, volume of dichloromethane and caremonohydrate, Eastman Kodak Co., Xo. fully passing the yellow solution through 324, recrystallized twice from 90% a fine-porosity sintered-glass filter. Exmethanol. cess thionyl chloride and solvent are p-Toluenesulfonic acid sodium salt, then removed by careful low-pressure Eastman Kodak Co., Xo. 524, K h i t e distillation or by evaporation in a Label. rotating vacuum evaporator. (If fairly 2,5-Dimethylbenzenesulfonic acid, volatile sulfonyl chlorides are present, sodium salt, monohydrate, Eastman elimination of these excess materials Kodak Co., S o . 469, White Label. must be carried out carefully to prevent 2-Naphthalenesulfonic acid, sodium loss of the sample.) The final residue salt. 2-Saphthalenesulfonic acid, Eastis dis,solved in a suitable solvent such as man Kodak Co.. S o . 897, !vas dissolved carbon tetrachloride, transferred quantiin methanol and neutralized to pH 7 tat,ively to a 5-ml. volumetric flask with methanolic sodium hydroxide. using solvent n.aPhes, and diluted to The resulting sodium salt precipitate volume. was filtered off and recrystallized twice Sulfonic acids and salts ma!. also be from 90%) methanol. converted to sulfonyl chlorides with 1-Butanesulfonic acid, sodium salt, phosgene instead of thionyl chloride, Eastman Kodak Co., S o . 5035, White using a similar procedure. The sample Label. to be converted is refluxed n.ith an inert 3-~Iethyl-l-butanesulfonicacid, sosolvent such as carbon tetrachloride dium salt, Eastman Kodak Co., Xo. containing dim~thylformamidecatalyst. 4987, recrystallized tu-ice from 90% Phosgene is passed into the solution methanol. until a yellow color develops. The p-n-Butylbenzenesulfonic acid, soreaction is continued for a n additional dium salt, Procter & Gamble Co., 10 to 15 minutes to ensure completion, Cincinnati, Ohio. and the resulting solution xorked up as n-Dodecylsulfonic acid, sodium salt, described above. Procter & Gamble Co., Cincinnati, PREPaRATIOS OF LIETHYL SULOhio. FOSATES. A O.j-gram sample of free Benzenesulfonyl chloride, Eastman sulfonic acid is dissolved in a minimum Kodak Co., S o . 32, K h i t e Label. quantity of diethJ.1 ether. (X small p-Toluenesulfonyl chloride, Eastman amount of methanol may be added to Kodak Co., KO. 532, White Label. put hydrates in solution.) Ethereal 2,5-Dimethylbenzenesulfonylchloride, diazomethane solution is introduced Eastman Kodak Co., No. 5077, White slowly while agitating, until a yellow Label. color persists. i i n additional 15 to 2-5aphthalenesulfonyl chloride, East207, e x c w volume of diazomethane man Kodak Co., S o . 778, twice resolution is added and the mixture is crystallized from equal volumes of benallowed to stand for about 10 minutes. zene and petroleum ether. The solvent is then carefully evaporated Methyl-p-tolcenesulfonate, Eastman on a steam bath or with a Ftreani of dry Kodak Co., KO. 165, K h i t e Label nitrogen, and the residue is transferred material was distilled undcr reduced to a volumetric flask with a suitable pressure t o obtain a fraction which solvent such as carbon tetrachloride or boiled a t 186" c'. a t 26 mni. of mercurl.. benzme. ~liethyl-2.5-dimeth~~lbenzenesulfo1iate. Eastman Kodak Co., Xo. 50'77, 2.5dimcth!~llienzcneiulfonyl chloride was DISCUSSION AND RESULTS refluxed in methanol with an excess of sodium methoside until the reaction was Analysis of Sulfonic Acids and completc. The solvent was stripped Salts a s Sulfonyl Chloride Derivaoff of the resulting mixture, and the tives. OPERSTIXG \7.kRI.kBL€.S. Free residual oil distilled under reduced sulfonic acids or salts may be quantitapressure to obtain a fraction which tively converted t o corresponding boiled a t 179" C. a t 20 mm. of mercury. sulfonyl chlorides b y reaction rvith Procedure. PREPARATION O F SULFOXPI. CHLORIDE DERIVATIVES. A 0.5thionyl chloride or phosgene in the VOL. 32, NO. 1 1 , OCTOBER 1960
1389
4
W fn
2
0
a
fn
w
a
A4
a W
a a 0 0 W K
-
63
COLUMN T E M R , T .
2
TIME, MINUTES
76
88
100
112
4
6
8
IO
Figure 1 . Gas chromatogram of acids as acid chlorides
butanesulfonic
1. Solvent 2. Dimethylformamide 3. 1 -Butanesulfonic acid, sodium salt 4. 3-Methyl-1 -butanesulfonic acid, sodium salt Column, silicone gum rubber on 80- to 1 00-mesh Chromosorb; length, 4 feet; initial column temperature, 50' C.; femperature program, 6.4' C. per minute; flow rate, 4 4 cc. of helium per minute
presence of formamide derivatives having two substituents attached to the nitrogen atom (5, 7). The reactions with thionyl chloride are : R-SO3H
+ SOClz
+
+ SO? + HC1
R-SOZCl R-SOJa
+ SOClz+. R-SO,CI
+ SO?+ SaCl
Similar reactions take place 151th phosgene, except that carbon dioxide 15 the gaseous by-product instead of sulfur dioxide. While compounds of the general formula: H-C--S
I/
0
R1 / \
K?
in n-hich RI and R2 represent alkyl, aryl, or aryl alkyl radicals, are utilizable as catalysts, dimethylformamide was employed in the present work because of its high rcactivity and availability. Although the amount needed varies with the reaction to be carried out, sufficient material must be added to prevent t8he formation of sulfonic anhydrides and produce the drsired reaction rate. In most cases, an amount 1 to 3 mole 7cwith respect to the acid appears to be minimum ( 3 ) ; 1390
ANALYTICAL CHEMISTRY
however, in the reactions carried out in this study: a large excess vias employed. Conversion of sulfonic acids or their salts has been found to be quantitative \r-ithin the limitations presented b!- the methods of the analyses used and t.he purity of the standards employed. Recoveries of 96 to 100yo werc obtained for all reactions carried out by the recommended procedures, nhct'her using thionyl chloride or phosgene. While either compound may be employed for the conversion, the former is generally preferred because it is easier to handle and presents less of a safety problem. -1lthough the amount of thionyl chloride nwds only to be slightly in excess of theoretical, it is convenient to use this material as the solvent, since the reaction of sulfonic acids proceeds quite rapidly in the refluxing material. If desired, t'he conversion may be carried out in inert solvent-for example, chloroform, carlion tetrachloride, chlorobcnzrne. toluene, xylene, or dioxane. Both thionyl chloride and phosgene are suitable for the preparation of mono- and polysulfonic acid chlorides. as well as carboxylic and sulfocarboxylic acid chlorides. Compounds containing substit,uents which watt with these
I
0
1
1
1
1
1
1
1
2 3 4 5 6 TIME-MINUTES
Figure 2. Gas chromatogram of mixture of aromatic SUIfonic acids as sulfonyl chlorides 1. Solvent ond dimethylformamide 2. Ethyl benzoate (internal standard) 3. Benzenerulfonic acid, sodium salt 4. p-Toluenesulfonic acid, sodium solt 5. 2,5-Dimethyl b e n z e n e r u l f o n i c acid, sodium solt Column, silicone high-vacuum grease on 40- to 50-mesh Chromosorb; length, 2 feet; column temperature, 165' C.; flow rate, 6 5 cc. of helium per minute
reagents, as. for example, free amino groups and hydroxyl groups, generally cannot be handled with this procedure. The gas chromatography of the sulfonyl chlorides studied required no special techniques or handling. The compounds are apparently thermally stable during the vaporization and separation prociisses, and h>-drolyze only very slowly in contact nith moist air. Good separations were obtained e n i s invcstigated using silic or silicone rubber gum columni;. .Uthough .ipiezon L grrast. was also found to be a t;uitablc stationary phase. silicone packing was preferred for the present work. since the formpr is more retentive and requires highcr operatirig temperatures :ind,'or longw :inalysis times. Chromosorb, Celite, and firebrick were successfully employed as column support F.
benzoate internal standard peak height ratios with those of standard sulfonyl chloride calibration mixtures. The results of the study are summarized in Table 11. Similar determinations were carried out on several synthetic samples of 2naphthalenesulfonic acid, sodium salt, containing minor amounts of benzeneand toluenesulfonic acid, sodium salts. Quantitative measurements for this system were made using peak height calibrations prepared from standard sulfonyl chlorides. A gas chromatogram of one of these converted mixtures is shown in Figure 3 and results of the analyses of the synthetic samples are given in Table 111. Alkyl aryl sulfonic acids may also be analyzed by the sulfonyl chloride derivative technique. A n-dodecylsulfonic acid, sodium salt sample containing about 30% of a lower molecular weight component, \Tas spiked m-ith a known amount of purified p-n-butylbenzenesulfonic acid. sodium salt, and analyzed: added, 10.1%; found, 9.9%. The chromatogram of this mixture is shown in Figure 4. Table IV lists the relative retention volumes of several of the aromatic sulfonyl chlorides. These data were obtained on the 2-foot column of
I
2
I
I
2
4
I
1
I
6 8 IO TIME -MINUTES
I
I
I
I2
14
16
Figure 3. Gas chromatogram of 2-naphthalenesulfonic acid mixture as sulfonyl chlorides 1.
Solvent and dimethylfarmamide Benzenesulfonic acid, sodium salt 3. p-Taluenesulfonic acid, sodium salt 4. 2-Naphthalenesulfonic acid, sodium salt Column, silicone high-vacuum grease on 40- to 50-mesh Chromosorb; length, 2 feet; column temperature, 165’ C.; flow rate, 80 cc. of helium per minute 2.
SALY LYSIS OF MIXTURES. T o illustrate the versatility and accuracy of the technique of analyzing sulfonic acids as sulfonyl chlorides, seyeral test systems were devised. Mixtures of the aliphatic compounds, 1-butanesulfonic acid, sodium salt, and 3-methyl-1-butanesulfonic acid, sodium salt, were prepared and converted, using either the thionyl chloride or phosgene reaction procedures. The resulting solutions were analyzed by programmed temperature chromatography using a 4-foot silicone gum rubber column. A typical separation of a converted sulfonic acid sample is shown in Figure 1. The concentrations of the two components were determined by peak area normalization calculations, and the results of the analyses are given in Tahlc I. Analyses of aromatic sulfonic acids n ere demonstrated by preparing and converting mixtures of the sodium d t s of benzene, p-toluene. and 2,5dimethylbenzenesulfonic acids. Gas chromatographic separations of the resulting sulfonyl chlorides \\ere carried out on a 2-foot silicone grease column operated at a. temperature of 165’ C. -1 chromatogram of one of these mixtures is shown in Figure 2. Quantitative determinations were made by comparing the component to ethyl
Table I.
Sample
Conversion Reagent snci, --*
S O .
--
1
soc1, coc1,
2 3
Table II.
Analysis of Aliphatic Sulfonic Acids
I-Butanesulfonic Acid, Na Salt, Wt. % Theory Found 49 9 5 4 1 81
3-Methyl-1-butanesulfonic
Acid, Na Salt, Wt. % Theory F o u r
50 9
50 1 94 6 98 2
5_ 2-
1.77
49 1 94 8 98 2
Analysis of Aromatic Sulfonic Acids
Benzenesulfonic rlcid, p-Toluenesulfonic ’ sulfonic-Acid, sample conversion Na Salt H20, Wt. % Acid, Xa Salt, Wt. % Na Salt H20, Wt. % No Reagent Theory Found Theory Found Theory Found 1 SOCI, 100.0 98.7 ... ... ... 2 SOCl? ... ... loo.0 97.2 3 SOC1, ... ... ... ... 1oo:o 1oi:o
coc1,
4
SOCl?
5 6
SOC1,
...
...
, . .
1.74 0.99 24.4 15.0
1:92 0.91 21.9 15.6
...
100 0. 98 3 99.0 52 3 11 9
SOC1, SOC1, SOC1, Added as free p-toluenesulfonic acid H20.
c
; 9
Table 111.
98.0 97.7 99.2 51.2 15 4
100.0
104.0
. .
...
. . . . .
... 23.3 70.1
23 1 69 1
. , ,
Analysis of 2-Naphthalenesulfonic Acid, Sodium Salt Mixtures
Benzenesulfonic -4cid. ?;a Salt. Hg0. - ,
p-Toluene~ulfonic 2-T\’aphthalenesulfonic Acid. Na Salt. Acid. Ka Salt. Wt. % ’ wt. % ’ Theory Found Theory Found
Sample Conversion wt. 7 0 No. Reagent Theory Found 1 COCI? . . , . . ... ,.. 100.0 96.8 2 SOClZ 5.1 3.9a 6.1 5.7 88.8 90.6 3 SOClZ 5.0 4.0n 5.1 4.8 89.9 86 4 a Some benzenesulfonyl chloride believed to have been lost during solvent evaporation step.
VOL. 32, NO. 1 1 , OCTOBER 1960
e
1391
m W
z
0 v)
K
z
K W
2
0
K 0
t
0 W -I LL W
W K
0
a
\I I
21
W 0
a
3
0
0
2
0
w
a
c
0
I
I
I
2
4
6
1
TI ME
-
8 IO MINUTES
12
-
Figure 4. Gas chromatogram of alkyl aryl sulfonic acid mixture as sulfonyl chlorides 1. 2. 3. 4.
Solvent and dimethylformamide Unknown p-n-Butylbenzenesulfonic acid, sodium salt n-Dodecylsulfonic acid, sodium salt Column, silicone high-vacuum grease on 40- to 50-mesh Chromosorb; length, 2 feet; column temperature, 180' C.; Row rate, 8 3 cc. o f helium Der minute
silicone high-vacuum grease previously drscribed. Analysis of Free Sulfonic Acids a s Methyl Esters. The reaction of diazoIiwtlianc with sulfonic acids is :inalogow to the r,stcrific*ation of ca:irl)os>-lic.acids :
+ CHPS2 + R-POjCH1 + S,
It-SO,>H
However, when diazonicthanc is placed in contact with highly acidic sulfonic acids, there are competing reactions, one of which is:
Table IV. Relative Retention Volumes of Sulfonyl Chlorides (Column temperature, 165" C.)
Con1I J 0 I i i I d
Relative Retention T'olumes
I ~ ~ ~ r i z t ~ r i c ~ . i i lctiloridc fr~ii~l I-'-Tolucii~~ulfoiJ?-l chloride
2,5-Iliniet hylbenzenesulfonyl chloride
1 00
1.05 9
''2
p-n-But!-lI)enzenesulfon\.l
chloride 2-Saphthalenesulfonyl chloride n-Dodecylsulfonyl chloride
1392
4 62
8.38 9 33
ANALYTICAL CHEMISTRY
Thus, when converting strong sulfonic acids, it is necessary t o use a large (about 3 to 4 inolc) e s c m of diazoniethanc to &ect :i coniplrte rcaction. The destruction of diazoinethane by the strong acid does not appear to affect tlic course' of tlic, c??tc>iificationreaction or thc .iih.;cqu(~iit c,liromatographic malJ-sis. Variable results n-erc obtained when sulfonic esters were gas chromatographed by the conventional niethod of operating the column n-it11 caarritr gas input pressures above atmospheric and outlet pressure at atmospheric. ,2pparently, under these conditions tlic sulfonic esters decompose and/or react in some manner. However, it was found that by operatiiig the vaporizcr and chromatographic' column :it rctlucrti pressure, the idmired analyses could be carried out nitliout altcration of the component materials. Input pressures of about one half to onc third of atmospheric gave the desired results for the esters studied. Apparently this reduction (from the usual 5 to 15 p.s.i. above
4 TIME-
6 8 MINUTES
12
IO
Figure 5. Gas chromatogram of SUIfonic acids as methyl esters 1. 2. 3.
Solvent p-Toluenesulfonic acid 2,5-Dimethylbenzenesulfonic acid Column, Apiezon L grease on 40- to 50-mesh Chromosorb; length, 2 feet; column temperature, 180' C.; input pressure, 445 mm.; outlet pressure, 150 mm.; flow rote, 48 cc. o f helium p e r minute
atmospheric) permits the sample to vaporize before significant degradation can occur. To demonstrate the applicability of the esterification technique, synthetic mixt'ures of free p-toluene and 2 3 dimrthylbenzeiiesulfonic acids werc prepared and converted by the method described undcr Procedures. Thc estcrs were chroniatogrnphed on a coluniii of Xpiezon L grcase operated at rcduced pressure. A chromatogram Of one of these separativns is shown in Figure 5 . The ronccntrat~ionsof the various cornponeiits were> determinctl by nirxsuring peak heights anti comparing thew with pure ester calibration standards. The data in Tablo 1-show that diazomrtharie esterificatioii is vientially quantitative
Table V.
Analysis of Free Sulfonic Acids as Esters
p-Toluenesam-sulfonic acid ple H20, TT't.____ c;;C S o . Theory Found
2>5-Diniethylhenzcnesulfonic Acid. 2 H,O. IT-t.
Tht.ory
CL;
Found
1 2 :3
100 0 100.0 100 0
95 5
4 5 6
...
100.0
97.8
'3'6 "5 3
4 5 25.3
96.4 74.7
94.8 72 5
(35.0 '35 .-I
,
.
.
,
, .
... ...
The recoveries of 95 to 1007, of theoretical include instrumental variations and the possibility of impurities in the commercial samples used as standards. Because of the unusual difficulties in maintaining constant operating conditions during a series of runs a t reduced prcssurr. frequent calibrations or internal standards (6) should be employed. h routine method devised for the analysis of similar aromatic sulfonic acid mistures gavr results with a two sigma variation of 5% relative for the major component when a peak area method with internal standardization vr-as employed.
ACKNOWLEDGMENT
The author is indebted to IV. A. Gregory for his helpful discussions on the conrcrsion reactions, and t o G. J. Wallace, who assisted in the experimental work. Certain samples of sulfonic acids used in this study were generously supplied by J. E. Callen of the Proctcr & Gamble Co., Cincinnati, Ohio. LITERATURE CITED
(1) Bayer, E., "Gas Chromatography 1958," D. H. Desty, ed., p. 333, Academic Press, New York, 1958. (2) Bosshard, H. H., Mory, R., Schmid,
>I Zollinger, ., H., Helv. Chem. Acta 42,
1658 (1959). (3) Farbwerke Hoechst Aktiensgesellschaft, Belgian Patent 553,871 (Jan. 15) 1957). (4) Gregory, W..L, U. S. Patent 2,888,486 (May 26, 1959). (5) James, A. T , Martin, A. J. P., Brit. hled. Bull. 10, 170 (1954),.( (6) Keulemans, h. I. M., Gas Chromatography," 2nd ed., p. 34, Reinhold, Kew York, 1959. (7) hfcInnes, -4.G., Ball, D. H., Cooper, F. P.. Bishoo. C. T., J. Chromatoq. 1 , 556 (1958)
RECEIVED for review March 31, 1960. Accepted July 15, 1960. Division of Analytical Chemistry, 137th Meeting, ACS, Cleveland, Ohio, April 1960.
Applications of Carbowax 400 in Gas Chromatography for Extreme Aromatic Selectivity LARRY RANDALL DURRETT' Shell Oil
Co.,Houston Refinery
laboratory, Housfon, Tex.
b Carbowax 400 has proved very useful as the stationary liquid in gas chromatography for the selective retention of aromatic hydrocarbons relative to paraffinic hydrocarbons. This selectivity results in benzene, boiling at 80" C., emerging with CIO paraffins boiling a t approximately 170" C. A gas chromatographic method has been developed for the determination of the aromatic content of aviation gasoline 'taking advantage of the selective retention of aromatics by Carbowax 400. All paraffinic hydrocarbons in aviation gasoline are eluted prior to the elution of benzene. This method requires approximately 45 minutes. A further application of gas chromatog ra phy utilizing Ca rbowa x 400 as the stationary liquid has been developed for the determination of hydrocarbon impurities in high-purity petroleum benzene and toluene. This determination also requires approximately 45 minutes.
I
s GAS CHROMATOGRAPHY, aroiiiatic hydrocarbons can be retained selectively relative to paraffinic hydrocarbons to varying degrees, deprnding upon the nature of the material utilized as the stationary liquid. Carbowax 400, a polyethylene glycol \Tith an awrage molrcular weight of approsi1 Present address, Shell Oil Co., Houston Research Laboratory, P.O. Box 2527, Houston, Tex.
niately 400 and available from Union Carbide Chemicals Co., has proved very useful for the sclective retention of aromatics relative to paraffins. ;in evaluation of some polyglycols as stationary liquids in gas rhromatography has been published by Adlard ( I ) . n'hitham (9) has described the use of polyrthylrne glycols as stationary liquids for gas chromatographic solvent nnalyses. Two application:: of gas chromatography of particular inter& to the petroleum industry have been developed which t'ake advantage of the aromatic select,ivity of Carbowas 400. The gas chromatographic mrthod for the determination of the aromatic content, of aviation gasoline: described herein, is superior to thc commonly used methods: silica gel adsorption ( 2 ) and fluorescent indicator adsorption (FId) (6). The f0rmc.r .%ST11 method is sufficiently accurate but is rat'hcr li'ngthy, while the lattcr dS'l3I mrtliod is rclntively short but lws : i ( u r a t ( ' . Thc gas c,lirom:ito~iapliicrnc~thotlrombinrs both *]iced and awurary. Thc gas c,hroin3togl.alihi(' m r t h o d for the detrrmination of 11)-tlrocarbon impurities in high-purity p['trolruni bcnzonc and t o l u ( w i> supcrior to t h r Kattwinke91 rwgcmt t w t (3). n-hicah is uscd (,urr(mtly. -A roii.ac.tivc indes method rcprcwnting an i m p r o w m m t in sensitivity o w r thc .A. has b w n describd by A and Lipkin (10). Fabrizio et al. ( 7 ) recently published a gas chromatographic method for detrrmining trace
impurities in petroleum benzene and toluene which is still more sensitive than the refractive index method. The method described herein is comparable in sensitivity to the method of Fabrizio and coworkers, but has the advantage of determining the amount of hydrocarbon impurities in both petroleum benzene and toluene using a single stationary phase. APPARATUS
G a s Chromatographic Instrument.
.I laboratory-fabricated gas chromatographic unit was used in this work. The unit consisted of a n oil bath with heating element a n d thermoregulator for controlling the bath temperature, regulator valves for carrier gas flom control, a conventional dual-pass thermal conductivity cell with necessary bridge circuitry. attenuator, power supply, and a 0- to 2-mv. Brown recorder. Heliuni was used as thc carrier gas in all caws. Chromatographic Column. The resolving column was a coiled 10-foot length of copper tubing n i t h a n outer diameter of 1 inch and packed with 28.5Yc \wight of Carbowax 400 on 30to 60-mesh firebrick. T h e firebrick was pretreated by washing with aqua wgia and t h r n neutralizing with repcated dilute sodium hydroxide washings. The aqua regia treatment of the firebrick significantly decreased thc prcwure drop across the column with no apparcint effect on resolution. The etatioiiary phase was prepared by dissolving 80 grams of Carbowas 400 in approsiniately 400 ml. of acetone. This misturc was slurried into 200 grams VOL. 32, NO. 1 1 , OCTOBER 1960
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