silazaned and unsilazaned surfaces. Furthermore, the u values are for disubstituted molecules while the gas chromatographic data are for monosubstituted systems. For the practical separation of hydrocarbons and their halogenated derivatives, salt-coated Porasil C offers the best compromise in terms of speed of analysis, separation effi. ciency, and column temperature. Separations of aliphatic cornpounds are most effective with either Na2S04 or N a r P 0 4 as the coating salt. For substituted benzenes Cos04 is
superior to all other salts studied in terms of separation eficiency. A number of other salts are useful coating materials for the separation of specific complex mixtures; this can be established from the data in Table VI. RECEIVED for review April 4, 1969. Accepted June 13, 1969. Work supported by the U. S. Atomic Energy Commission under Contract No. AT-(11-1)-34, Project No. 45, and by an NSF Graduate Traineeship to A.F.I.
Quantitative Determination of Arylsulfonic Acids and Salts by Alkali Fusion Sidney Siggia, Lee R. Whitlock, and Jane C. Taol Unicersitj-of’Massuchiaetts, Anillerst, Mass.
A method to determine arylsulfonic acids and salts based on alkali fusion and measurement of either the resultant sulfite or phenol is described. Sulfite was measured volumetrically. Phenols were measured by gas chromatography. The sulfonates were fused with potassium hydroxide at 380-400 “C under nitrogen or helium atmosphere. The sulfite-measuring approach gives an analysis for total sulfonate; a standard deviation of better than 3%; a high degree of selectivity since sulfite can come only from the sulfonate; and a fairly wide range of application. The phenol-measuring approach gives an analysis of micro-sized samples; a standard deviation of 1 to 3%; high selectivity; and a fairly rapid method of analysis. The phenol method is also extremely valuable for analyzing complex mixtures of homologs and isomers. With this method the fusion reaction is carried out in a small heated chamber connected directly to a gas chromatograph. The neutralized fusion products are swept into the gas chromatog raph. THE QUANTITATIVE ANALYSIS of sulfonic acids and their salts has always represented a formidable problem for the analytical chemist. Not only must he meet requirements of precision and accuracy in his analysis and d o this with increased speed, but he often must be able to identify each component sulfonate in the sample. The dificulties commonly encountered in such analyses hare been described ( I ) . The clasical methods for determining su!fonate involve precipitation of the sulfonate with either barium, silver, or mercury salts ( 2 ) or with benzidine (3). A somewhat better method involves complexation of the sulfonate with p toluidine, extraction with carbon tetrachloride, and determination of the sulfonate by titration after addition of isopropanol to the carbon tetrachloride ( 4 ) . Many methods for the analysis of sulfonic acids are accomplished using ultraviolet spectrometry (5-9). T o obtain high precision in the analysis of multicomponent systems, the absorbances of the mixture and the pure components must be determined at a large number of wavelengths (1, 8). For an evaluation of the unknown concentrations, a least squares treatment is applied. The applicability of the method depends on the position of the absorption peaks of the components. The procedures generally arequite tedious and time consuming. Also, any nonsulfonated aromatic materials which might be present would interfere with the ultraviolet methods. 1
Present address, Allied Chemical Corp., Petersburg, Va. 23803
Infrared spectrometric procedures have been described (10, II), but these lack selectivity and accuracy.
Gas chromatography has proved to be valuable for analyzing a wide range of low and nonvolatile compounds follohing conversion to volatile derivatives. Kirkland (1-3) ha> converted mixtures of alkyl- and arylsulfonic acids and their salts to the corresponding sulfonyl chloride and methyl ester derivations with subsequent analysis by gas chromatography. Reporting only a qualitative study, Parsons (13) prepared the sulfonyl fluoride derivatives which he showed to possess greater volatility and thermal stability than the corresponding chloride derivatives. Experience of these inveatigatnrs has shown, however, that the methql esters and higher molecular weight sulfonyl chlorides give thermal decomposition during gas chromatography (12, 13). Also, compounds containing substituents such as amino groups and h l d r o q l pro~iparcact with the thionyl chloride used to prepare the sulfonji chloride and so cannot be handled by this approach. The basis of this method for thc determinaiion of arylaulfonates is alkali fusion of the sulfonic acid giLiny quantitative conversion to sulfite and phenol. ArS03M
+ M’OH
-
ArOH 4- hlh4’SO,
where M and M’ can be the same or different cation5 and M can be a hydrogen atom. The alkali fusion of benzenesul~
~~~~~~~~
(1) H. Cerfontain, L. Vollbracht, and H. G. .J. Duin, ANAL.CHEW, 35, 1005 (1963). (2) S . Siggia, “Quantitative Organic Anal! sis Via Functional Groups,” 3rd ed, John Wiley and Sons, Inc., New York, N. Y . , 1967, p 631. (3) D. A. Shiraeff, Amer. DyestufReptr., 36, 513 (1947). (4) T. U. Marron and J. Schefferli, TND. ENG. CHEW,ANAL.ED., 18,49 (1946). (5) M. W. Scoggins and J. W. Miller, ANAL. CHEM., 40,115.5 (1968). (6) W. J. Weber, Jr., J. C . Morris, and W. Stumm, ibid., 34, 1844 (1962). (7) J. C. Sternberg, H. S. Stillo, and R. H. Schwendeman, ihid., 32, 84 (1960). (8) J. M. Arends, H. Cerfontain, I. S. Herschberg, A. .I. Prinsen, and A. C. M.Wanders, ibid., 36, 1802 (1964). (9) I. S. Herschberg and F. L. J. Sixma, Koninkl. h’ed. Airad. Wetenscliap. Proc. Ser. B 65, 244, 256 (1962). (10) S . D. Kullbom, W. K. Pollard, and H. F. Smith, ANAL, CHEM., 37, 1031 (1965). (11) S . D. Kullbom and H. F. Smith, ibid., 35,912 (1963). (12) J. J. Kirkland, ibid., 32, 1388 (1960). (13) J. S . Parsons, J . Gas Chromarogr.,5, 254 (1967). VOL. 41, NO. 11, SEPTEMBER 1969
1387
n
r-
A
I1 r'ltFB I
I
I
G Figure 1. Apparatus for alkali fusion used in the sulfite-measuring method A nitrogen inlet; H nitrogen outlet; C closed boro-
silicate glass chamber; D stainless steel crucible; E sand bath
VIEW
-
A storage area for samples awaiting analysis; B side-arm with rubber septum; C furnace inlet; D storage area for sample boats after analysis; E platinum sample boat; F pusher; G carrier gas inlet; H retriever; I variable temperature furnace; J boat stop; K heated connector; L gaschromatograph; M recorder
EXPERIMENTAL
Apparatus. SULFITEMETHOD. The equipment used for the fusion reaction for the sulfite-measuring method is shown in Figure 1. The sample and caustic were held in a stainless steel crucible, D (Scientific Glass Company, catalog no. 2610). The crucible, enclosed in a glass chamber, C, was placed in a sand bath, E, and heated by an open flame. Oxygen-free nitrogen was passed into the chamber through A over the fusion mixture and vented out through B. Hot copper mesh (temperature 450-600 "C) was used to remove traces of oxygen from the nitrogen. PHENOLMETHOD. To measure the phenol, the fusion and gas chromatography were done in essentially one piece of apparatus which is shown in Figure 2 . The fusion unit was a modified version of a pyrolysis apparatus described by Ettre and Varadi (16) and now commercially available from the Perkin-Elmer Corp., Norwalk, Conn. (Pyrolysis Accessary 154-0825). The fusion unit was connected to a PerkinElmer Model 881 gas chromatograph equipped with programmed temperature and a thermal conductivity detector. The fusion unit consisted of a borosilicate glass and quartz (14) C. Wurtz, A H ~ L144, , 121 (1897). (15) S . Oal, N. Furukawa, and M. Kise, BUN.Chem. SOC.Jnp., 39, 1212 (1966). (16) K. Ettre and P. F. Varadi, ANAL.CHEM., 35, 69 (1963). ANALYTICAL CHEMISTRY
rrm
Figure 2. Apparatus for alkali fusion and measurement of phenol used in the phenol-measuring method
fonic acid was first effected by Wurtz (14) more than a hundred years ago and has long been used for the manufacture of phenol and related hydroxy compounds. The reaction mechanism has been recently classified conclusively as a simple S,v-2 type nucleophilic aromatic substitution (15). This has clarified some conflicting literature which previously has suggested other mechanisms that could lead to the production of various phenol isomers and rearranged products in the fusion reaction. With this mechanism, the phenol produced resembles the starting sulfonate and identification of the phenol also identifies the sulfonate. For quantitative measurement of the sulfonate using alkali fusion, two approaches are possible; either the sulfite or the phenol produced in the fusion reaction can be measured. If the sulfite is measured, then a total sulfonate analysis is ob-, tained. If the phenol is measured, it is possible to obtain both a total sulfonate analysis and an analysis for each sulfonate present in the sample. This paper describes both approaches.
1388
I
tube, a section of which was surrounded by a variable temperature furnace, I . Section A of the tube was used to store samples awaiting analysis; section B is a side arm capped with a rubber septum through which acid was added to the fusion mixture, liberating the phenol from the phenolate; section C is the furnace inlet; and section D was used for storage of sample boats after analysis. To convert the standard Perkin-Elmer Pyrolysis accessory to a fusion unit suitable for this application, several modifications were ma.de. The gas sampling valve located between the fusion unit and the gas chromatograph was removed to eliminate a potential source of cold spots where high boiling phenols could condense. The heated connector tube supplied with the pyrolysis unit proved unsuitable for carrying high boiling phenols from the furnace to the injection port of the gas chromatograph. This was replaced by a n 18-inch section of IB-inch stainless steel tubing encased in 1/4-inch copper tubing which was wrapped with a heating element controlled by a V a r i x and covered with asbestos insulation. A thermocouple was embedded in the asbestos in order to monitor the connector temperature. This temperature was adjusted depending on the sample being analyzed. The side arm capped with a rubber septum (B, Figure 2) was added t o the fusion tube assembly to eliminate the need for removing each fusion sample for acidification. The samples were contained in micro-size platinum bcats (Fisher Scientific Co.) and were propelled in and out of the furnace and along the tube assembly by small steel cylinders manipulated externally with a magnet. To ensure good contact between >ainp!s and caustic, the length of the platinum boats was shortened to 5 mm, about half their original length. This was done by cutting away the end of the boat with a sharp knife and folding up a section of bottom forming a new end. The boats were cleaned after each analysis by ignition in an open flame for a few seconds. N o evidence of attack on the boats by the caustic was found. Porcelain boats were tried, but they were attacked by the caustic, and longer fusion times were needed for the reaction to be complete. Rcagents. All sulfonates were obtained from Eastman Organic Chemicals in the purest grade available. White label reagents were generally used as received, while other grades were further purified by recrystallization of the sodium salt from alcohol-water. All sulfonates were checked by elemental analysis for purity. Analytical reagent grade potassium hydroxide (85 %) was obtained from Mallinckrodt Chemical Works. Sodium sulfite, sodium sulfate, and sodium acetate were anhydrous Fisher Certified reagent grade.
reference electrode were introduced, and to the mixture was added, dropwise, 6 N sulfuric acid until the p H of the system was 9-10. Then 0.1N sulfuric acid was added uiu a buret until the pH was reached at which the excess potassium hydroxide was just neutralized. This pH, designated as PI in Figure 3, was approximately S but varied slightly with each sulfonate being measured. The exact p H should be predetermined for accurate work. At this point 1 ml of formaldehyde (36% aqueous) was added; the pH of the system was observed to rise as hydroxide was liberated by the bisulfite addition reaction (see Reaction 2). A safe practice is to run a blank on the formaldehyde used for it may contain some formic acid. However, this blank is generally negligible. The liberated base was then titrated potentiometrically with standard 0.1N sulfuric acid to the inflection point, designated P?in Figure 3. This titration was not carried to a definite pH value but was carried past the endpoint, and the inflection point was determined from the plot of pH cs. milliliters. The milliliters of standard sulfuric acid used to titrate the liberated base was the basis of the calculation for sulfonate content: V X N X M X 100 % sulfonate = s x 1000
Volume of H,SO,
Added
Figure 3. Typical titration curve SULFITEMETHOD. Certified ACS formaldehyde solution (36.8%) was used as received from Fisher Scientific Co. PHENOLMETHOD. Phenol and the related hydroxy compounds were obtained from Eastman (white label) and Baker (Baker grade) and checked for purity by gas chromatography. The potassium salts of phenol and 2-naphthol were prepared by dissolving 0.21 moles of phenol in 1 5 4 methanol and adding 0.20 moles of potassium hydroxide dissolved in 85% aqueous methanol. Solvent was evaporated under vacuum at 60 "C. The white crystals were washed with petroleum ether and dried under vacuum. A saturated aqueous solution (solubility 78 g/100 ml) of maleic acid (Matheson, Coleman, and Bell white label) was prepared in the usual manner. The column packing materials were all obtained from Analabs, Hamden, Conn. Procedure. SULFITE METHOD. Samples were prepared for fusion by placing approximately 3 millimoles of sulfonate along with 5 grams of potassium hydroxide pellets in a stainless steel crucible. The crucible was placed in the glass chamber and oxygen-free nitrogen was flushed through the system for at least 5 minutes to displace the air. The temperature was brought up to 400 "C and maintained for 1/2 to 1 hour. The temperature can be measured with a thermometer in the sand directly adjacent to the glass chamber or a thermocouple can be inserted through the gas outlet tube and placed under the crucible. The latter procedure was a better temperature indicator but was not needed because the optimum temperature range is rather broad. The key observation at this stage is the fusion of the reaction mixture; if fusion does not occur, conversion of the sulfonate will generally be low. After fusion, the system was allowed to cool to room temperature by removing the sand bath. During the cooling period, the flow of nitrogen was maintained. The crucible was removed from the glass chamber, and 30- to 50-ml of distilled water was added. The mixture was gently stirred with a magnetic stirring paddle until dissolution was complete. The solution was then quantitativeiy transferred to a 250-ml beaker. A glass indicating electrode and calomel
where V is volume of standard H2S04 used to titrate the liberated base; N is the normality of H2s0.1; M is the molecular weight of sulfonate; S is weight of the sample. PHENOLMETHOD. Samples for the phenol measuring approach were prepared for fusion by first weighing into the platinum boat between 10 and 50 microequivalents of sulfonate. Approximately 8 mg of powdered potassium hydroxide was added and mixed with the sample. Potassium hydroxide pellets were pulverized in a dry box and the powder stored in a vacuum desiccator. If standard size combustion boats (11 mm long) are used, s e x r a l milligrams of sodium acetate should be added to the fusion mixture at this point. The caustic and sample alone lacked sufficient volume to give a homogeneous melt. Sodium acctate was not necessary when the smaller (5 mm) boats were used. A study of fusion conditions using a platinum boat was made and the best results were obtained with a fusion temperature of 380 "C. Often conversions were low when this temperature was increased or decreased more than 20 "C. For most sulfonates, a fusion time of 20 minutes was sufficient for the fusion reaction to be complete. As many as six samples may be prepared and loaded into the fusion unit at one time. After the sample boats were placed in the storage area ( A , Figure 2), the system was closed and flushed with carrier gas for 4-5 minutes before moving the first sample into the furnace. The furnace temperature should not exceed 100 "C when a new sample is moved into it. The temperature was then increased to 350 "C for fusion. After the fusion reaction was complete, the boat was moved out of the furnace and directly under the acidification assembly. To the cooled fusion mixture was added several microliters of a saturated aqueous solution of maleic acid which liberated the phenol. The acid was added using a 10-pl Hamilton syringe injected through the rubber septum of the acidification assembly. The furnace temperature was adjusted to 320 "C and the sample boat was moved back into the furnace to vaporize the phenols. From the furnace the volatile products were swept into the gas chromatograph. RESULTS AND DISCUSSION
Sulfite Method. The first system tried was /;-toluenesulfonic acid fused with sodium hydroxide. This waq wed because quantitative synthesis yields of p-crcsoi have been reported (17). The sulfite resulting from the fusion was mea(17) M. C. Boswell and J. V. Dickson, J. Amer. Chem. SOC.,40, 1786 (1918).
VOL. 41, NO. 11, SEPTEMBER 1969
0
1389
Table I. Analysis of Sulfonic Acids and Salts by Alkali Fusion and Measurement of Sulfite Standard deviaCompound Analysis, wt tion p-Toluenesulfonic acid 99.4 (30) 1.6 p-Toluenesulfonic acid 100.0 (5) 1.o (recrystallized) 97.4 (6) 0.4 Benzenesulfonic acid sodium salt 97.9 (5) 6.3b Benzenesulfonic acid monohydrate 97.9 (3) 2.5 p-Acetylbenzenesulfonicacid sodium salt 100.8 (3) 0.7 p-Acetylbenzenesulfonicacid sodium salt (recrystallized) (4) 3.3 2-Naphthalenesulfonic acid 100.1 sodium salt 100.0 (3) 2.3 2-Naphthalenesulfonic acid sodium salt (recrystallized) 98.6 (3) 3.8 2-Naphthalenesulfonic acid monohydrate 93.3 ( 2 ) C 4.0 2-Anthroquinonesulfonic acid Figure in parentheses is number of trials. b Compound is very hydroscopic which may account for poor endpoints. c Compound gave poor endpoints, probably due to reaction of quinone with sulfite.
Table 11. Analysis of Sulfonic Acids and Salts by Alkali Fusion and Measurement of Phenol by Gas Chromatography Standard deviaCompound Analysis, wt tion p-Toluenesulfonic acid 97.4 (10) 1.3 Benzenesulfonic acid 96.7 (4) 1.4 sodium salt 2,5-Dimet hylbenzenesulfonic 98.1 (4) 1.2 acid sodium salt p-Sulfobenzoic acid 95.5 (5) 2.5 monopotassium salt p-Phenolsulfonic acid 97.3 (5) 2.8 sodium salt Benzenesulfonamide 95.7 (3) 1.5 2-Naphthalenesulfonic acid 97.6 (5) 2.1 sodium salt a Figure in parentheses is number of trials.
xu
sured iodometrically (18). Erratic, low results were obtained even after a large number of attempts with varied fusion conditions. T o determine if the sulfite measurement might have been part of the problem, pure sodium sulfite was analyzed iodometrically. Many results would agree fairly well, but a significant number of analyses would yield low, erratic results. An alternate method to determine the sulfite was tried (19). Formaldehyde was added to the sulfite solution, and the resultant base was titrated with standard acid. Na2S03 CH2O H20-.CH20H NaOH
+
+
I
+
S03Na (18) I. M. Kolthoff and R. Belcher, "Volumetric Analysis," Vol. 3, Interscience Publishers, New York, N. Y., 1957, p 293. (19) E. Przybylowicz, Eastman Kodak, personal communication, 1967. 1390
ANALYTICAL CHEMISTRY
This approach worked quite well. Standard sodium sulfite samples were put through the fusion procedure and complete recovery was attained. Fusion reactions are not the easiest to handle and, even though there was considerable improvement in accuracy after the adoption of the formaldehyde method for the sulfite, the results were often erratic. An attempt was made to avoid fusion by using 50 sodium hydroxide solutions and refluxing. This was unsuccessful, giving essentially no reaction. Refluxing a 5N solution of NaOH in ethylene glycol with the sulfonate yielded n o reaction, even though the reflux temperature was in the order of 200 "C. It was felt that there was no alternative to the fusion. Observation had shown that the fusion reaction with sodium hydroxide was two-phased; the sulfonate apparently did not dissolve in the melt. Thus it was felt that a flux was needed which did not reduce the temperature too significantly. Sodium oleate (mp 232 "C) was tried but this foamed badly on dissolution of the sample and had to be abandoned. Sodium acetate (mp 324 "C) was tried and appeared to work. However, this buffered the system to such a degree that it interfered with the titration of the base formed on reaction between the sulfite and the formaldehyde. Finally, it was determined that potassium hydroxide gave a better fusion than did sodium hydroxide with no flux needed. All fusions were subsequently run with potassium hydroxide. A study of fusion conditions showed that fusion temperature is an important variable. Fusion had to occur for the reaction to even approach completion. Thus, the minimum temperature is the melting point of potassium hydroxide, 360 "C. Temperatures as high as 450 "Ccould be tolerated without decomposition of the sample in most cases. Fusion times ranged from 30 minutes to 36 hours; however, one hour was found to be sufficient in most cases. The fusion apparatus was so arranged that oxygen-free nitrogen was passed over the sample during fusion. This was needed to perserve both the sodium sulfite and the phenols from oxidation. The oxidation of the phenols, particularly the polyhydric phenols, was more of a problem than the oxidation of the sulfite. The polyhydric phenols oxidize very rapidly t o yield quinoid-type compounds which react weakly with sulfite, resulting in poor titration endpoints. With monohydric phenols, purified grade tank nitrogen was sufficient. However, with the polyhydric phenols a hot (temperature 450-600 "C) copper mesh was used to scavenge traces of oxygen from the nitrogen. The inflection points in the potentiometric titration curves in the cases of monosulfonates were quite sharp as shown in Figure 3. However, in the cases of disulfonated, or hydroxysulfonated compounds when polyhydric phenols resulted, somewhat buffered titration curves resulted due to the reaction by-products. To circumvent this, excess acid was added to react with the base liberated from the reaction of the sulfite with the formaldehyde. The excess was back-titrated with standard base. This procedure yielded somewhat better titration inflection points probably because the formaldehyde reaction with sulfite is an equilibrium, and the excess acid pulls it to completion (20). An attempt to determine p-hydroxybenzenesulfonate, however, was unsuccessful. No inflection point was obtained in the titration curve after formaldehyde addition. This was probably due t o some oxidation of hydroquinone to the quinhydrone as evidenced by the appearance of a colored solution. The quinhydrone produced will react with the sodium sulfite. (20) S. Siggia and W. Maxcy, IND. ENG. CHEM.,ANAL.ED., 19, 1023 (1947).
1 2
J
5 0
c
1
F I
I
I
2
3
4
J 2
i
I
5
I
I
6 7
I
8
9
1011 1213
TIME -minutes
Figure 4. Gas chromatogram of phydroxybenzenesulfonic acid sodium salt after alkali fusion and acidification
I
3
I 4
I
5
I
I
6 7 TIME -minutes
I
8
1
9
I
1
10
11
Figure 5. Gas chromatogram of sodium salts of benzenesulfonic acid, ptoluenesulfonic acid, and 2,5-dimethylbenzenesulfonic acid after alkali fusion and acidiRcation Peak l-gaseous decomposition product of maleic acid, 2-water, 4-pcresol,5-2,5-xylenol
Peak l-gaseous decomposition product of maleic acid, +water, +hydroquinone
The data in Table I show the results of analyses of some sulfonic acids and salts by the sulfite method. The method has been applied successfully to both benzenesulfonates and naphthalenesulfonates. Attempts to determine sulfonilamide and p-diphenylaminesulfonic acid sodium salt were unsuccessful due to decomposition of the sulfonate during fusion. Phenol Method. The results of the analysis of some sulfonic acids and salts using the phenol method are given in Table 11. A typical chromatogram of a sulfonate after fusion and acidification is shown in Figure 4. The chromatogram of a single sulfonate will generally show only two peaks. The first peak which is quite large and shows considerable tailing results from the water used as a solvent in the acidification procedure. This peak will usually mask any small peaks arising from low boiling impurities and excess maleic acid. The second peak is the phenol. To obtain the best results the phenol peak must be sharp and well resolved. T o avoid possible interference, the size and tailing of the water peak must be minimized. The volume of water can be kept low by using maleic acid for acidification for it is a strong, diprotic organic acid with very high water solubility. Inorganic acids cannot be used as they will corrode the detector and may damage the column materials. The gas chromatography of the fusion mixture required no special techniques. Good separations were obtained for the compounds investigated using a 12-foot by 0.25-inch stainless steel column containing 1 2 x SE-30 supported on AnakromABS of 110-120 mesh size. For analysis of certain mixtures where isomers or similar boiling phenols must be resolved, other column materials can be used (21, 22). Programmed (21) S. T. Preston, Jr., "A Guide to the Analysis of Phenols by
Gas Chromatography," Polyscience Corp., Evanston, Ill., 1966. (22) T. S. Ma and D. Spiegel, Microchem. J., 10,61 (1966).
3-phenol,
column temperature was used in all analyses, normally starting at 70 "C and programmed at a rate of 32 "C/min up to 200 "C and as high as 300 "C for the higher boiling phenols. This generally produced a chromatogram with the phenol peak(s) 3-5 minutes after the water peak. However, water gives severe tailing, and it is not possible to completely resolve the phenol and water peaks as shown in Figures 4 and 5. Instead, the long, nearly flat tail of the water peak serves as a pseudo base line for the phenol peak area measurements. Quantitative determinations were obtained by measuring the area of the phenol peak and comparing it to phenol standards run under the same analytical conditions. Area measurement was done by the cut and weigh method. Some samples were fused containing varying amounts of sodium sulfate mixed with the sulfonate. No effect on the results was seen even when the amount of sodium sulfate was three times greater than the sulfonate. Thermal Stability. A study of the thermal stability of some of the sulfonates and phenol salts was made, both in air and helium atmospheres. The thermal decomposition was followed by thermal gravimetric analysis to determine the upper temperature limits of their stability. Some of the variable results occasionally found with some compounds was believed due to partial decomposition of either the sulfonate or its phenolate derivative during the alkali fusion reaction. The results in Table I11 show that most sulfonates are stable to temperatures well above that used for the fusion reaction. Potassium phenolate and potassium 2-naphtholate partially decomposed in air at the fusion temperature, but these salts were found to be stable when heated under helium. This supports the observation that for consistent quantitative results, the fusion reaction should be carried out under inert atmosphere. The analysis of sulfonilamide and p-diphenylaminesulfonate by the sulfite method was unsuccessful probably because of decomposition of the sulfonate. Erratic, low results were obtained for p-sulfobenzoic acid monopotassium salt when the fusion temperature used was similar to that used for sodium VOL. 41,NO. 11, SEPTEMBER 1969
1391
Table 111. Decomposition Temperature of Some Sulfonic Acid Salts and Phenol Salts in Air and Helium Decomposition temperature, "C Air Helium Compound Potassium phenolate 215 420 Potassium 2-naphtholate 250 480 Benzenesulfonic acid 550 ... sodium salt 2-Naphthalenesulfonic acid ... 510 sodium salt m-Benzenedisulfonic acid 530 575 sodium salt 390 405 p-Sulfobenzoic acid monopotassium salt p-Diphenylaminesulfonic acid ... 400 sodium salt
benzenesulfonate. Thermal analysis showed that the compound decomposes near this temperature. When the fusion temperature was lowered to 360 "C, the fusions were quantitative. The analysis of sulfonic acids containing substituents which react with alkali, as, for example, free halogen, can be analyzed by the sulfite method without interference. However, the phenol method would not necessarily yield unambiguous results, because each halogen group would be replaced by a hydroxyl substituent. Analysis of Mixtures. To illustrate the versatility and selectivity of the phenol method using gas chromatography, several test mixtures were devised. Mixtures of the sodium salts of benzenesulfonic acid, p-toluenesulfonic acid, and 2,5-dimethylbenzenesulfonicacid were prepared, fused, and analyzed by programmed temperature gas chromatography. A typical chromatogram of the phenol
Table IV. Analysis of Sulfonic Acid Sodium Salt Mixtures by the Phenol Method Benzenesulfonic p-Toluenesul2,5-Dimethylacid sodium fonic acid benzenesulfonic salt, sodium salt, acid sodium wt K O , Wt 72 salt, wt Blend Actual Found Actual Found Actual Found
z
A B C
28.6 69.0 25.7
x
27.8 67.8 26.3
20.4 10.8 35.2
20.5 10.5 34.0
51.0
20.2 39.1
48.7 19.3 38.0
derivatives is shown in Figure 5. The small unidentified peaks on the chromatogram are from impurities in the aqueous maleic acid solution used for acidification of the fusion mixture. The concentrations of the three components were determined from peak area comparisons to phenol standards run separately. The results of the study are given in Table IV. In addition to the capability for analyzing mixtures, another advantage of the phenol method over the sulfite method, and in general over most sulfonate analysis techniques, is its great sensitivity for the analysis of small samples. Using gas chromatography, a complete analysis can be made using only a few milligrams of sample. ACKNOWLEDGMENT Acknowledgment is made t o the early efforts of J. Gordon Hanna who studied the caustic fusion. Those efforts led to the current study. RECEIVED for review May 5 , 1969. Accepted June 16, 1969. The authors also acknowledge the support of the National Science Foundation under grant GP-7360.
Detection and Identification of Oxocarboxylic and Dicarboxylic Acids in Complex Mixtures by Reductive Silylation and ComputerAided Analysis of High Resolution Mass Spectral Data W. J. Richter, B. R. Simoneit, D. H. Smith, and A. L. Burlingame Space Sciences Laboratory, Uniaersity of California, Berkeley, Calg. 94720 The complex nature of the acidic fractions of Green River Formation oil shale solvent extracts makes it necessary to carry out chemical transformations to study the various classes of compounds. One such class, the oxoacids, was substantiated by borohydride reduction, followed by silylation of the hydroxy derivatives thus formed. This procedure allows a differentiation by means of mass spectrometry between the oxoacids and other oxygen containing components present in the fractions, ;.e., dicarboxylic and aromatic acids. High resolution mass spectra of the treated mixtures, followed by computer sorting and heteroatomic plotting of the silicon containing peaks, separates the derivatized oxoacids from other classes of compounds. It also allows assignment of the location of the keto functionality along the hydrocarbon chains of the oxoacid homologs in the extract. This method i s applicable to mixture samples ranging from 0.5 to 3 mg. As an example, a sample obtained from oxidation of Green River Formation kerogen was analyzed and a homologous series of (w-1)-oxoacids ranging from C4to Clzwas thus established. 1392
ANALYTICAL CHEMISTRY
SUCCESSIVE SOLVENT extractions of a n oil shale from the Green River Formation yield complex mixtures of similar classes of compounds (a) prior to chemical, (b) after demineralization with HF/HCl, and (c) after chromic acid oxidations of varying duration. The sample of oil shale was collected by one of us (BRS)from a cliff outcrop at Parachute Creek, 8 miles NW of Grand Valley, Colo. (lat. N 39" 37'; long. W 108" 7'; elev. 7300 ft.) The acidic fractions of these mixtures were found to consist mainly of aliphatic monocarboxylic and dicarboxylic acids, with aliphatic oxoacids and aromatic carboxylic acids being present in lesser amounts (1-4). ~~
~
(1) P. Haug, H. K. Schnoes, and A. L. Burlingame, Chem. Commun., 1967, 1130. (2) A. L. Burlingame and B. R. Sirnoneit, Nature, 218, 252 (1968). (3) A. L. Burlingame and B. R. Simoneit, Nature, 222, 741 (1969). (4) A. L. Burlingame, P. Haug, H. K. Schnoes, and B. R. Simoneit,
in "Advances in Organic Geochemistry 1968," I. Havenaar and P. A. Schenck, Eds., Vieweg, Braunschweig, Germany, 1969.
