Analysis of crude oil carboxylic acids after conversion to their

Analysis of Crude Oil Carboxylic Acids after Conversion to Their Corresponding Hydrocarbons Wolfgang K. Seifert Chevron Oil Field Research Company, P . 0. Box 1627, Richmond, Gal$ 94802 Richard M. Teeter, W. Glenn Howells,’ and Manfred J. R. Cantow2 Chevron Research Company, Richmond, Calif. 94802

A new and comprehensive approach has been developed for the identification of carboxylic acids in virgin crude oil. Knowledge of the structures of these acids is relevant to questions concerning the origin of petroleum and the origin of life. The identification involves initial conversion of acids, via the corresponding alcohols and their p-toluene sulfonate esters, to hydrocarbons. The hydrocarbons are separated by a combination of silica gel and gel permeation chromatography and identified by ultraviolet, infrared, and high resolution mass spectrometry. For the acidhydrocarbon conversion, proof was obtained for the maintenance, on an average statistical basis, of most of the carbon skeletal structures of the original acids. The structure determination of the hydrocarbons and the retention of carbon skeleton during conversion permits identification of many classes of carboxylic acids not previously discovered in virgin crude oil. These classes include polycyclic naphthenic, mono-, di-, and polynuclear aromatic, mono- and dibenzthiophenic, carbazolic, and phenolic types. This identification procedure affords the first semiquantitative assessment of carboxylic acid classes in a crude oil relative to all of the acids present.

DURING THE PAST 100 years an enormous amount of effort has been devoted to the elucidation of petroleum carboxylic acid structures. The work to 1955 has been summarized (1, 2), and with the exception of fatty acids, the Cl0 limit had not been exceeded. Many fatty acids of various carbon number and different geochemical origin have since been reported, and this work has recently been summarized (3). Also, some branched chain aliphatic carboxylic acids up to Clz were found in an Austrian crude oil (4). The extensive and profound recent work by J. Cason and coworkers on “Naphthenic Acids” of California origin resulted in identification of Cll (5) to Czo(6) acyclic isoprenoid acids and a C11 (7) monocyclic isoprenoid acid as well as a CIOnonisoprenoid cyclic acid (8). Paraffinic acids (9) and isoprenoid paraffinic acids were also found in Green River shale (10-14) and recent

(1) H. L. Lochte and E. R. Littman, “Petroleum Acids and Bases,” Chemical Publishing Company, Inc., New York, 1955. (2) Ibid., p 233. (3) K. A. Kvenvolden.J. Amer. Oil Chem. SOC..44.628 (1967). R. Bock and K. Be’hrends,2.Anal. Chem., 208 (5), 338 (1965). (5) J. Cason and A. I. A. Khodair, J. Org. Chem., 32, 3430 (1967). (6) J. Cason and D. W. Graham, Tetrahedron, 21,471 (1965). (7) J. Cason and K-L. Liauw, J . Org. Chem., 30,1763 (1965). (8) J. Cason and A. I. A. Khodair, ibid., 31,3618 (1966). (9) R. L. Leo and P. L. Parker, Science, 152,649 (1966). (10) G. Eglinton, A. G. Douglas, J. R. Maxwell, J. N. Ramsay, and S. Stallberg-Stenhagen,ibid., 153,1133 (1966). (11) P. Haug, H. K. Schnoes, and A. L. Burlingame, ibid., 158, 772 (1967). (12) A. L. Burlingame and B. R. Simoneit, ibid., 160, 531 (1968). (13) A. L. Burlingame and B. R. Simoneit, Narure, 218,252 (1968). (14) T. Maclean, G. Eglinton, K. Douraghi-Zadeh, R. G. Ackman, and S . N. Hooper, ibid., 218, 1019 (1968).

(4

1638

ANALYTICAL CHEMISTRY

sediments (15). Also reported in Green River shale were dicarboxylic ( I I ) , ketocarboxylic (16),and aromatic carboxylic acids (17) of the phenylalkanoic, indanoic, and naphthoic types. The recent increase in activity in structural elucidation of carboxylic acids in petroleum has resulted from the availability of more powerful tools of separation and instrumental analysis-e.g., mass spectrometry combined with gas-liquid chromatography whose application to the structural elucidation of complex hydrocarbon mixtures had been shown earlier (18, 19). Carboxylic acid analysis has geochemical significance since these acids are generally regarded as the precursors of petroleum hydrocarbons (3, 20). Consequently, the knowledge of their structure is intimately connected with the question of the origin of petroleum (14, 21-23) and the origin of life on earth (24,25). The above summary of the known structures of carboxylic acids in petroleum shows that the information is still very fragmentary. Furthermore, some of the samples on which the above investigations were carried out were not virgin crude oils-e.g., the “California Petroleum” investigated (5-8)was a refinery-treated sample of commercial naphthenic acids-and much of the work carried out on Green River shale (9-17) suffers from uncertainties of possible structural rearrangement during the isolation procedures-e.g., HCl/HF and Zn/HCl and oxidation treatments. The existence of fatty (3) and isoprenoid (5-17) carboxylic acid structures in samples of different geological origin and the presence of analogous hydrocarbon structures in crude oils (26) eliminates doubt about these particular compounds being present in 1 Present address, Forest Chemicals Division, MacMillan Bloedel Research Ltd., Vancouver 12, British Columbia, Canada. Present address, Airco Central Research Laboratories, Murray Hill, N. J. 07971

(15) M. Blumer and W. J. Cooper, Science, 158,1463 (1967). (16) P. Haug, H. K. Schnoes, and A. L. Burlingame, Chem. Commun., 1967, 1130. (17) P. Haug, H. K. Schnoes, and A. L. Burlingame, Geochim. Cosmochim. Acta, 32,358 (1968). (18) W. K. Seifert, Tenside, 2, pp 150, 181 (1965). (19) W. K. Seifert, “Fourth International Congress on SurfaceActive Substances,” Gordon and Breach Sci. Pub., New York, 1967, Vol. 1, p 471. (20) J. E. Cooper and E. E. Bray, Geochim. Cosmochim. Acta, 27, 1113 (1963). (21) H. M. Smith, J. Amer. Oil Chem. SOC.,44,680 (1967). (22) E. D. McCarthy and M. Calvin, Nature, 216,642 (1967). (23) W. Henderson, G. Eglinton, P. Simmonds, and J. E. Lovelock, ibid., 219, 1012 (1968). (24) R. Robinson, ibid., 212, 1291 (1966). (25) G . Eglinton and M. Calvin, Sci. Am., 216, 32 (1967). (26) I. R. Hills, G. W. Smith, and E. V. Whitehead, presentation at the 156th National Meeting of the American Chemical Society, Atlantic City, N. J., September 1968, Symposium on Hydrocarbons from Living Organisms and Recent Sediments.

General. Melting points were determined using a FisherJohns apparatus and are uncorrected. Infrared spectra were obtained in 0.05-mm microcells using a Perkin-Elmer Model 337 spectrometer fitted with a beam condenser. Ultraviolet spectra were obtained on a Cary Recording Spectrophotometer. Interpretation of UV spectra was made with the assist-

ance of a catalog (30) of model compounds. The gel permeation instrument, Waters, Inc., was equipped with a MiltonRoy Minipump for solvent circulation, a degasser, and a Waters differential refractometer. The charge was injected through a special four-port valve which allows injection of an exactly determined volume of solution. The volume of eluate was measured by a 5-ml siphon which, upon emptying, activates a signal. The mass spectrometer was an Associated Electrical Industries MS-9 equipped with a quartz direct insertion probe and a total ion current recorder as described previously (29). Reduction of Fraction D (27). The separation scheme leading to the isolation of 4 0 z of the crude oil carboxylic acids as Fraction D is repeated in Figure 1, and the transformation scheme is shown in Figure 2. A solution of Frac-360, 1.99 g, 5.5 mmol) in ether was heated tion D under reflux for 21 hours with lithium aluminum hydride (1.46 g, 38 mmol). The reaction mixture was quenched with dilute aqueous hydrochloric acid and extracted with ether (6 X 50 ml). The ether solution was washed to neutrality with water and evaporated to yield 1.83 g of Fraction D alcohol in approximately 9 6 x yield. The product exhibited no carbonyl absorption in the infrared. Hydroxyl absorption was shown at v,,,(CC14) 3620 and at vmar(CSz) 3610 and 10351050 cm-l. Tosylation of Fraction D Alcohol. The alcohol (1.80 g, -5.2 mmol) and p-toluene sulfonyl chloride (8.59 g, 15 mmol) were allowed to react for 17 hours in anhydrous pyridine (15 ml) at 5 "C. The reaction mixture was pipetted into a mixture of 100 ml of water and 50 g of ice and stirred for 30 min, during which time a dark brown gum separated. Ether (100 ml) was added and the mixture stirred for an additional 1 hr. The mixture was extracted with portions (400 ml, 150 ml, 75 ml, 75 ml, 150 ml) of a 3:l ether-benzene mixture and finally with five 50-ml portions of benzene. The combined extracts were washed with 1 N aqueous hydrochloric acid (4 X 100 ml), then to neutrality with water; and finally, the solvent was evaporated yielding 2.28 g (88 of Fraction D alcohol tosylate: IR vmax(CS2)1187, 1176, 1096, 963, 660, and 550 cm-'. Absence of absorbance at 1080, 695, 650, 570, and 528 cm-l that is exhibited by a mixture of p-toluene sulfonyl chloride and Fraction D alcohol indicated no contamination by excess p-toluene sulfonyl chloride nor could unconverted alcohols be detected. Fraction D Hydrocarbon. Fraction D alcohol tosylate (MW -500, 1.83 g, 3.65 mmol) was stirred with lithium aluminum hydride (715 mg, 18.8 mmol) in refluxing ether (25 ml) for 19 hr. After stirring for an additional 6 hr at room temperature, the reaction mixture was pipetted into 150 ml of 1 N aqueous hydrochloric acid. Extraction with ether (5 X 50 ml), washing of the combined ether extract first with 1 % aqueous sodium hydroxide (4 X 200 ml) to remove p-thiocresol and then with water to neutrality, gave, after removal of solvent, 1.10 g of Fraction D hydrocarbon in 91 % yield. Low infrared absorption at 1176 cm-l indicated about 95 Z removal of the tosylate groups. Reactions of Model Compounds. 5P-Cholanic acid (Mann Research Laboratories) was reduced by the same technique and on the same scale as Fraction D to give a 97% yield of crude 24-cholanol which showed no carbonyl absorption in the infrared but showed hydroxyl absorption at v,,,(CC14) 3620 and vmax(CSZ) 3610, 1050 cm-1. Recrystallization from ether/pet. ether (30-60 "C) gave 75 % of 24-cholanol melting at 132" [lit. (31)mp 129.5-130.5"]. The 24-cholanol was tosylated as above in 84% yield after recrystallization from aqueous acetone seeded with authentic 24-tosyloxycholane. The product melted at 99-100' [lit. (31) mp 99-100.5"]. Reduc-

(27) W. K. Seifert and W. G. Howells, ANAL.CHEM.,41, 554 (1969). (28) W. K. Seifert, ibid., p 562. (29) W. K. Seifert and R. M. Teeter, ibid., p 786.

(30) R. A. Friedel and M. Orchin, "Ultraviolet Spectra of Aromatic Compounds," John Wiley and Sons, New York, 1951. (31) R. T. Blickenstaff and F. C. Chang, J. Amer. Chem. SOC.,80, 2726 (1 958).

Extract' Carboxylic Acids

Ion Exchange -W,eakiy

-

B a s k Resin

6

ion Exchange Sljongly Basic Resin

Ion Exchange - +akly Basic Resin

Fraction'

'Thls extract represents 3.54% of the total crude 011; 2.5% based o n Crude Oil Is RCOOH, see Tables I, I I, and I II of reference 21.

'Percentages are based on total crude oil.

Figure 1. Separation scheme virgin petroleum. However, claims of evidence for other types of carboxylic acids mentioned above (11, 16, 13,apart from saturated structures in petroleum should be regarded as speculative until confirmed from other sources or until such acids are shown to be stable under the conditions of isolation. In addition, quantitative data on the occurrence of any carboxylic acid types relative to the total carboxylic acids in a given petroleum are entirely unexplored-e.g., individual compounds identified in many instances were only minor or trace constituents. Our previous papers (27-29) dealt with the quantitative isolation of carboxylic acids (27) from a virgin California crude oil, interfacial activity studies at alkaline pH (27, 28), identification of phenols ( 2 3 , carbazoles (28), and indoles (28) as integral parts of the carboxylic acids, and high resolution mass spectrometry of the acids (29). The last study was carried out on 5 x of the carboxylic acids present in this California crude oil and resulted in reducing the enormous complexity of mixtures to about 1500 compounds. Many terpenoid polynuclear alicyclic, mono-, and polynuclear aromatic and naphtheno-aromatic carboxylic acid structures not discovered previously in petroleum were postulated on the basis of mass spectrometry alone. This paper is part of a broader study involving the conversion of 4 0 x of the total acids of this crude oil to the corresponding hydrocarbons which were subsequently subjected to separation and molecular spectroscopy. Also the extent of structural change occurring in the acid molecules during this conversion to hydrocarbons has been established. The objective of our work is identification of the major classes of carboxylic acids naturally occurring in one crude oil. The study represents a new method and the first semiquantitative assessment of carboxylic acid structure relative to all acids in one crude oil. Many classes of carboxylic acids which we postulated on the basis of high resolution mass spectrometry (29) were confirmed and many new ones were discovered. EXPERIMENTAL

(m

x)

VOL. 41, NO. 12, OCTOBER 1969

1639

LIAIH, RCOOHO-

I

-

CISOl QCH, RCHzOH

rRCHzOSOOCH,

t

RCH,

1

SWI

I

-

PEAK COUMS

, UV, IR, hlS

UV, IR

GTMS,UV, IR

-

0

UV Ullraviolel IR - I n f r a r e d AIS .Mass Spectrometry HR -High Resolution GT GroupType

Figure 3. Gel permeation chromatogram of polycyclic naphthenic hydrocarbons derived from carboxylic acids Fraction 1 of elution silica gel chromatography

-

HRMS GTMS

GTMS

'Fraction D, representing M. of all Carboxylic Adds present In crude oil. for delalii of Iso1ation, see figure 1.

Figure 2. Scheme of transformations of carboxylic acids and separations of derived hydrocarbons

tion of 24-tosyloxycholane yielded crude cholane (91 %). Recrystallization from ethanol gave cholane melting at 91.592.5" [lit. (31) mp 90'1. Capillary Silica Gel Chromatography (Figure 2). A solution of 22.4 mg of hydrocarbons from Fraction D dissolved in a mixture of 22.3 mg of distilled benzene and 36.1 mg of distilled cyclohexane was charged to a standard ASTM (32) column packed with 100-200 mesh Davison silica gel. The syringe and walls of the column were washed with 0.12 ml of a mixture of benzene and cyclohexane. As soon as the hydrocarbon solution had been absorbed by the gel, ethanol was added and 4-6 psi nitrogen pressure was applied for development. The colorless saturate fraction was visible by column wetting and the well-defined benzene-soluble aromatic and heterocyclic fractions were visible by their own color and their fluorescence under UV light. The data are summarized in Table I. A blank run to isolate impurities was carried out with 0.1 g of benzene and 0.07 g of cyclohexane. A total of 0.7 mg of impurities was isolated (Table I). The mass spectrum of the contaminant of Fraction 1 (Table I) showed no interference with the spectra of paraffins and naphthenes. In all experiments described above, fractions were worked up by evaporation of solvents at 5Oo/l torr. The total net recovery was 85 % after correction for contaminants. Elution Silica Gel Chromatography (Figure 2). Silica gel (Grace-Davison Chemical, 100-200 mesh activated Grade 923 desiccant) was washed with distilled methanol (4 X 100 ml), filtered on a Biichner funnel, washed once with distilled methanol (300 ml), and finally dried at 165 "C under nitrogen. Solvents used were first distilled through a 60-cm by 2.5-cm i.d. glass column containing Penn State Packing. Fraction D hydrocarbon (96.6 mg) dissolved in benzene (1 ml) and cyclohexane (1 ml) was added to 240 g of the silica gel wetted with cyclohexane and contained in a 70-cm by 2.4cm i.d. column. Elution was carried out with cyclohexane (500 ml, 400 ml, and 300 ml) to give Fractions 1, 2, and 3 shown in Table 11. Further elution with cyclohexane (2.2 1.) gave Fraction 4 and displaced UV-fluorescent material to the bottom of the column. Subsequent elution with a 1 :2 mixture of ether and benzene (150 ml), ether (3.7 l.), and methanol (3 1.) gave Fractions 5, 6, and 7, respectively. Fraction 7, contaminated by inorganic material originating in the silica gel, was transferred to a separatory funnel using ethanol (20 ml), benzene (20 ml), methanol ( 5 ml), and water ( 5 ml), (32) American Society for Testing and Materials, Petroleum Products-Fuels, Solvents, Lubricating Oils, Cutting Oils, Grease, Part 17, Philadelphia, Pa., January 1969, p 481. 1640


washed with water (4 X 20 ml) and then worked up to give Fraction 7 as shown in Table 11. A blank run for determination of contaminant from silica gel and solvent was made by eluting an identical column with the same type and volume of solvents as before to give the data shown in Table 11, Column 4. Gel Permeation Chromatography (Figure 2). Three columns, each 122 cm long and 0.9 cm in diameter, were used in series. They were packed with Waters gel (polystyrene, crosslinked with divinylbenzene) of 45 A nominal pore size. The experiments were carried out at room temperature using redistilled toluene as eluting solvent at a flow rate of about 0.75 ml/min. Charges of about 10 mg of product were made in each run. Approximately two thirds of the material entered the column. Most of the difference was recovered from the overflow and the dead volume of the injection valve. The fractions were worked up by stripping the solvent at 50°/1 torr and transferring them to accurately weighed microflasks using distilled benzene. Deviation of recovery of material from 100% was due to losses in the injection procedure and the recovery operations, and to impurities eluted from the columns. The column impurity amounted to 0.8 mg/100 ml and is deducted in the recovery data of Figures 3-5. Mass Spectrometry. Three types of analyses were performed by mass spectrometry. Using a quartz direct insertion probe (33) samples from capillary silica gel chromatography were examined at low resolution (-1 :1100) for prominent homologous series and outstanding fragment ions. The general technique has already been described for the case of fluoroalcohol esters of precursor acids (29). In this case, with the more volatile hydrocarbons, it was necessary to start each series of spectra at a low probe and source temperature (about 60-75 "C) to avoid premature volatilization of thelower MW portions of the samples. Four or five scans were recorded as the probe temperature was increased to about 300 "C. The data are reported in Table 111. Samples for both high resolution mass measurement (Tables IV and V) and intermediate resolution type analysis (34) (Tables 11, IV, and VI) were vaporized in an all-glass expansion bulb system (35) designed to eliminate any contact of sample vapor with potentially catalytic metal surfaces. (33) E. J. Gallegos, I.P. 30, Seventh World Petroleum Congress, Mexico City, D.F., Mexico, April 2-8, 1967. (34) E. J. Gallegos, J. W. Green, L. P. Lindeman, R. L. LeTourneau, and R. M. Teeter, ANAL.CHEM.,39, 1833 (1967). (35) R. M. Teeter and W. R. Doty, Rev. Sci. Instrum., 37, 792

(1966).

Fraction 1

Table I. Capillary Silica Gel Chromatography of Hydrocarbons Derived from Carboxylic Acids MS group type analysis, MonoIR analysisc*' ConbenzUV X 1Wa cm-' tamiand 3610 Yield,a nant,b Satu- Aroma- dibenzl./mole cm at mp Fluores- 3483 wt. % wt. % ratesc tics thiophenes 230 260 294 cence" -NH-OH Assignment 13 1.3 96 4 Trace 0 0.04 0 0 0 0 Polycyclic naphthenes ... ... ... 1.o 1.0 0.3 xxx X 0 Mono- and diaromatics 23) 0.5 17 ... *.. ... 4.1 0.02 0 X X 0 Pyrroles, thiophenes 31 1.3 ... ... ... 0.80 0 0.3 x xx xx Phenols, carbazoles

3 4 Per cent of Fraction D, representing 40% of all carboxylic acids in Midway Sunset 31E Crude Oil. b Obtained from blank run; per cent based on Fraction D. 3.7% Paraffins, 5.6% 1-ring-, 13.3% king-, 30.7% 3-ring-, 35.3% Cring-, 6.4% king-, 1.2% &ring-naphthenes. d Solvent: Mixtures of cyclohexane and ethanol. x-Small, xx-considerable, xxx-strong. In carbon tetrachloride. 0

0

Table 11. Elution Silica Gel Chromatography of Hydrocarbons Derived from Carboxylic Acids

MS group type analysis, % Mono.

ConFraction

Eluent

yield,^ wt. %

22

1

3

@}

4

@J+

12.6

taminant,b wt.

%

0.8

2.4

benz-

and dibenzSatu- Aro- thiorates matics phenes 91

11

.. ....

8

80

1

9

...... ... ... ...

5 EtOH CoH6 19.7 2.4 6 EtOEt 26.4 5.7 7 MeOH 14.5 3.7 a Per cent of Fraction D, representing 4 0z of all carboxylic acids. b Obtained from blank run; percent based on Fraction D. c Solvent: 50% Cyclohexane/50% ethanol. d In carbon tetrachloride. e xx = Considerable amount.

UV analysis: e X 10-8 ]./mole cm at mp 230 260 294

0.01

IR analysis,d,e cm-l 3483 3610

-NH- -OH

0,2

0

0

12.1

0.6

0

0

13.8

0.5

0

19.4

2,3

0 0 0

0.9 0

0.7 0.04 0.03

Assignment

0

PoIycyclic naphthenes

0

0

Fused diaromatics

0

0

O I 0

1.7

xx

xx Phenols, carbazoles

t} S,N,O-Compounds

Table 111. Low Resolution Mass Spectral Data of Hydrocarbons Derived from Carboxylic Acids and Separated by Capillary Si02 Chromatography

Fraction 1 2 3 Approximate MW, range 340-600 260-600 250-700 Estimated average MW 380-420 380-430 380-450 Parent peak region ,1- ( decreasing importance 1-6, -8 >> -4, -2,O[ 1-2,O > -4, -61 1-3,b -5, -1, -9 > -7 Outstanding peaks 414, 428 418,432 411 Fragment peak region 2-category, decreasing importance -5, -7, -3 -7, -5 -4 Outstanding peaks 191,263 273,287, 301 246 Predominating structure (MS, UV, Steranes, pentacyclio Mono- and diAcridines, pyridines, carbIR, polarity) terpanes aromatics azoIes a For a description of Z-category, see text. b An odd Z for a parent peak implies an odd number of nitrogen atoms in the molecuIe.

4 200-650 400-450

I

1-3, -6, -8 > -41 386, 319 -7, -5

Carbazoles, phenols

VOL. 41,NO. 12, OCTOBER 1969

0

1641

t IMPURITIES, DEDUCTED

[

FLUORESCENCE X L - X X X d X X

X SLIGHT X X MEDIUM

n

Figure 4. Gel permeation chromatogram of polynuclear aromatic hydrocarbons derived from carboxylic acids Combined fractions 2, 3,4 of elution silica gel chromatography Exact masses were measured by the peak-matching technique at a resolving power of about 15,000 using perfluorotributylamine as the mass reference.

RESULTS AND DISCUSSION The isolation from a Midway Sunset (California) petroleum of the carboxylic acid fraction which was chosen for this study has been described previously (27) and is repeated in Figure 1. The choice of Fraction D was made on the basis of highest acidity (neutralization equivalent 362) and lowest phenol content (6 mole %) of the major fractions isolated. Figure 2

d v,

APPEARANCE 1-YELL0 RECOVERY

W

XX/-X

4

40

COLORLESS

Figure 5. Gel permeation chromatogram of heterocyclic hydrocarbons derived from carboxylic acids Fraction 5 of elution silica gel chromatography summarizes our general approach. Hydrocarbons were obtained from the acids in a three-step conversion via alcohols and p-toluene sulfonates. The most convenient method of gross characterization of these hydrocarbons is by capillary silica gel separation into saturates, aromatics, and heterocyclics coupled with ultraviolet and infrared spectrophotometry and low resolution mass spectrometry. More efficient separation leading to more detailed characterization was achieved by column (elution) silica gel chromatography followed by gel permeation chromatography in conjunction with ultraviolet and infrared spectrophotometry and high resolution mass spectrometry of selected gel permeation fractions.

Table IV. High Resolution and Type Analysis by Mass Spectrometry of Saturated Hydrocarbons Derived from Carboxylic Acids and Separated by Elution Si02 and Gel Permeation Chromatography (GPC) Type analysis, f GPC fraction 18 High resolution, GPC fraction 17 of SiOzelution fraction 1 of Si02 elution fraction 1 Observedb m/e Mole %Q Calculated m/e Formula ZC Intensity Type ** 5-Ring 8 . 2 314.2963 -8d 314.2973 *** 4-Ring 17.3 316.3127 - 6d 316.3130 **** 3-Ring 25.8 -4 318.3279 318.3286 **** 2-Ring 21.5 -2 320.3436 320.3443 * Acenaphthenes 0.0 - 14 322.2655 322.2660 * I-Ring 15.0 0 322.3594 322.3599 * Naphthalenes 0.3 - 12 324.2810 324.2817 * &Ring 1.8 - 10 326.2971 326.2973 Paraffins P . A detecte0.0 +2 Fluorenes 0.0 Not detected - 16 Phenanthrenes 0.6 Not detected - 18 Pyrenes 0.7 Not detected -22 Chrysenes 0.1 Not detected - 24 Sulfur compounds 0.0 Not detected +2, -4, -6 Benzdinaphthenes 1.8 ... - 10 Benzenes 6.4 ... -6 Indanes-tetralins 2.3 ... -8 Based on parent peaks only. * Maximum experimental error is =!= 5 ppm. c See footnote h of Table VI. d Assigned to saturated alternative on the basis of correspondence with the type analysis and on the basis of the separation scheme. Formulas of esters identified by high resolution measurements. The closest observed higher and lower homologs of the hydrocarbon precursor acid (plus C7H2Fi2) are listed. f Based on fragments only. Q See footnote b of Table VI. 0

~~

0

1642


Reduction of Carboxylic Acids. Carboxyl groups were converted to methyl groups to facilitate separation and identification. Different methods for this conversion involving rather harsh conditions have been described in the past (36-43). To minimize structural rearrangements while obtaining nearly quantitative conversions, the three-step transformation (44, 45) outlined in Figure 2 was developed for a mixture of crude oil carboxylic acids. 50-Cholanic acid was used as a model compound to study optimum conversion conditions ana to obtain infrared analytical data. The reduction of Fraction D acids with lithium aluminum hydride gave alcohols in nearly quantitative yield and provided additional information regarding the nature of the sulfur incorporated in these acids. Lithium aluminum hydride is reported (46) to produce hydrogen sulfide and/or thiols from disulfides, episulfides, polysulfides, sulfinic acids, and sulfinic acid esters. Upon lithium aluminum hydride treatment of the major carboxylic acid fractions, no hydrogen sulfide was detected; and the thiol contents, as determined by microcoulometric titrations (47), were only marginally increased (Table VII). Therefore, the incorporation in the carboxylic acid molecules of those sulfur-containing structures listed above may be ruled out. The absence of sulfonic acid groups, which could possibly be present on the basis of the isolation procedure with NaOH (27), was proved by the absence of infrared absorption at 1135 cm-1. Such absorption was detectable in a solution of 0 . 2 x synthetic primary paraffin sulfonic acid (MW 334) dissolved in the major acidic extract. p-Toluene sulfonyl chloride esterification of the alcohols was carried out with excess reagent to ensure that all groups potentially susceptible to tosylation would undergo this reaction. conversion was nearly quantitative, and the absence of p-toluene sulfonyl chloride in the ester product was proved by infrared examination. Analyses of the hydrocarbon product, obtained by nearly quantitative reduction of the p-toluene sulfonate esters with lithium aluminum hydride, and comparison with the analyses of the starting acids are summarized in Table VIII. An examination of these analytical data allows conclusions to be drawn regarding gross chemical changes which may have occurred during the conversion and the presence of other functional groups in the starting acids and the derived hydrocarbons : 1. Small amounts of phenols (27), carbazoles (28), and indoles (28) assumed to be part of the acid structures, survive the reduction procedure (Table VIII). 2. Agreement of the saponification and neutralization equivalents prior to reduction indicates the absence of significant amounts of esters (48) in the original carboxylic acid sample.

Table V. High Resolution Mass Measurements on Hydrocarbons of Fraction D and Correlation with Acids and Esters

2 4

0

-2

-4

-6 -8

-10

-12

-14

-16

-18 (36) A. Aschan, Chem. Ber., 25,3664(1892). (37) N. Zelinsky, ibid., 57,43 (1924). (38) G. Komppa, ibid., 62, 1562 (1929). (39) J. Mueller and S . Pilat, Brennstof-Chem., 17, 461 (1936). (40) T. Kuwata, C.A., 23,1390 (1929). (41) G. E. Goheen, Znd. Eng. Chem.,32,503 (1950). (42) J. H. Caro. Erdbl Zeitschrift -~ d r Bohr und Foerdertechnik. 78, 435 (1962): (43) J. Knotnerus. J. Inst. Petrol.. 43. 307 (1957). (44) K. Biemann,’“MassSpectrometry, Organic Chemical Applications,’’ McGraw-Hill, New York, 1962, p 179. (45) V. Wollrab, M. Streibl, and F. gorm, Chem. Znd., 1962,1762. (46) N. G. Gaylord, J. Chem. Educ., 34,367 (1957). 37,644(1965). (47) R. L. Martin and J. A. Grant, ANAL.CHEM., (48) G. I. Jenkins, J . Inst. Petrol., 51, 313 (1965). ’

-24 -28

Observed mass 224.2503 238.2661 252.2818 266.2970 222.2345 236.2502 250.2662 264.2815 278.2966 234.2347 248.2502 262.2653 276.2813 246.2351 260.2502 274.2662 244.2197 258.2347 272.2499 246.1988 274.2301 242.2034 256.2189 270.2346 244.1832 258.1982 272.2137 246.1441 260.1589 274.1746 240.1881 254.2035 268.2193 242.1669 256.1824 270.1987 224.1568 238.1720 252.1878 266.2038 240.1516 254.1666 268.1821 222.1412 236.1569 250.1736 264.1880 278.2047 224.1193 238.1358 252.1518 266.1674 268.1277 234.1411 248.1573 262.1732 276.1883 222.1040 250.1362 256.1268 270.1417 266.1104

Formula

CorreMass lation meawith sureacids ment and Calculated error, esters mass ppm

CisHaz Ci7H34 CisHsa CisHas c i a 3 0

Ci7H32 CisHsa CiQH36 CzoHss Ci7H30 CiSH32 CiQH34 CZOH~P, CisH30 Ci~H3z CzoHa4 CisHu CisHso CzoHsz Ci7H260 CisH300 cisHz6 C19H28 CzoHao C17H24O CI&IZ,O CiQHuO CieH2zS Ci7Hz4S CisHz6S CisHir C~QHZB C20H2s Ci?HzzO CisHz40 Ci9H260 Ci&o CisHzz CisHz4 CZOHZB Ci7Hzoo Ci8Hzz0 CisHz40 Ci7His CisHzo CigHzZ czoHz4 cziH26

CleH16O ci?Hiso CisHz00 CigHzz0 CisHzoS ‘%His

C~QHZO CzoHZz CziH24 C16H140 CisHisO CzoHis C,iHis CziHi4

xb XXc

x XX XX XX

x XX X XX XX XX X

xx XX

x xx XX X

. .. ... XX XX

xx X

x X

... ...

... XX XX XX

... ... ...

x xx x xx XX

x X

x xx x XX

x x XX X

x

... XX

x x x X X X

x

. ..

224.2504 238.2660 252.2817 266.2973 222.2347 236.2504 250.2660 264.2817 278.2973 234.2347 248.2504 262.2661 276.2817 246.2347 260.2504 274.2660 244.2191 258,2348 272.2504 246.1984 274.2297 242.2034 256.2191 270.2347 244.1827 258.1984 272.2140 246.1442 260.1599 274.1755 240.1878 254.2035 268.2191 242.1671 256.1827 270.1984 224.1565 238.1721 252.1878 266.2034 240.1514 254.1671 268.1827 222.1408 236.1565 250.1722 264.1878 278.2034 224.1201 238.1357 252.1514 266.1671 268.1286 234.1408 248.1565 262.1721 276.1878 222.1045 250.1358 256.1252 270.1408 266.1096

0 0 0 -1 -1 -1 $1 -1 -3 0 -1 -3 -1 $2 -1 +1 +2 0 -2 $2 $1 0 -1 0 +2 -1 -1 0 -4 -3 $1 0 +1

-1 -1 $1 +1 0 0

$2

0

-2 -2 +2 $2 $6 $1

+6 -4 0

+2 +1 -3 +1 +3 $4 $2 -2 $2 $6 $3 +3

2 is from the expression CnHQn+,OS. “x” indicates that a homolog of the corresponding acid or fluoroalcohol ester was reported previously (reference 29). “xx” indicates that an exactly corresponding acid or fluoroalcohol ester was reported previously (reference 29). (1


1643

Compound type Paraffins 1-Ring 2-Rings 3-Rings 4-Rings 5-Rings 6-Rings Total saturates Benzenes Indanes, tetralins Benzdinaphthenes Naphthalenes Acenaphthenes Fluorenes Phenanthrenes Pyrenes Chrysenes Total aromatics Benzthiophenes Dibenzthiophenes Naphthobenzthiophenes

+ + 4, mole %*

z= +2 0

2 3 2.2 4.0 2.7

-4 -6 -8

0.0 2.0 0.0 0.0

-2

-10

10.9

11.5 13.3 16.3

-6 -8 10 12

--

6.6 9.6 11.4 6.4 0.0

-22 -24

--1610 -22

80.3

4.2 4.6 0.0

SH-Content, reduction, PPmC Before After 72 62 139 70

15.9

*.. 216 153 99

0 Contains all carboxylic acids present in crude oil plus about 30% other components. b Represents the major portion of carboxylic acids. 0 An SH-content of 100 ppm for a compound with the molecular weight of 330 corresponds to 0.1 RSH.

mole Z 2.7 6.5 3.8

F9 0.3

17.9 3.0

29.5

5.5

0.4 3.9

@ 11.7

5.6 0.0

4.6 1.5 0.0

(Rules out: RSSR, RS02H, RSOzR’)

Crude oil Major acidic extract5 Ion exchange fraction Bb Ion exchange fraction Db

0.0

3.7 4.6

Table VII. Thiol Content of Carboxylic Acid Fractions before and after Reduction with Lithium Aluminum Hydride

Sample

fia 21.8 6.0 5.5

5.2

-14 --16 18

Fraction 19, mole Z 0.0 6.7

0.0

78.0 3.1 0.0 0.0

67,3

3. The small amount of saponifiable material found in the hydrocarbon sample is partially due to 5 % unchanged p toluene sulfonates. 4. Allowing for 5 % unchanged p-toluene sulfonates and 6% phenols which remain unaltered by the overall hydrocarbon conversion process, there is available for conversion 89% carboxylic acids. Quantitative conversion of these acids to hydrocarbons should result in the loss of 7.86z oxygen, equivalent to 4.23% residual oxygen (12.09-7.86%) in the hydrocarbon sample. The observed oxygen content is, however, 3.15x corresponding to a loss of 8.94% oxygen (12.09-3.15%). This 8.94Z loss in oxygen being larger by 1.08% (8.94-7.86%) than that expected from carboxylic acid or ester conversion alone indicates the presence of other reducible oxygen functions in the acid sample. These calculations are not affected by oxygen increase due to 5 unchanged p-toluene sulfonates in the hydrocarbon sample be-

x

~~~

Table VIII. Analysis“ of Carboxylic Acidsb and Derived Hydrocarbons RCOOH RCHs Found, % Found Calcdd Implications 6 6 6 Phenols in RCHa (0.27 0) PhenolsC Carbazoles: Indoles 7 7 7 ... 5 ... Tosylates in RCHs (0.48 % 0, 0.32 S) TosylatesO 12.09 3.15 4.23 Ketones, lactones, fluorenones, quinoOxygen lones in RCOOH 75.96 83.04 82.03 2.4% 0; 50% 0-compoundsg Carbon 9.23 10.54 10.49 (e.g., furans) Hydrogen 1.39 1.66 1.48 No denitrogenation, 40% N-compoundsg Nitrogen 1.30 1.66 1.58 No desulfurization, 18 S-compounds‘ Sulfur 0 0 No esters in RCOOH Neutralization equiv., 362 5400 ... Tosylates in RCHl Saponification equiv., 363 5 Average of duplicate determinations. b Fraction D representing 40% of all carboxylic acids in Midway Sunset 31E Crude Oil. c Quantitative infrared analysis based on 2-isopropyl phenol (3610 cm-’), carbazole (3483 cm-l), and 24-tosyloxycholane(1176 cm-l). d Including 5 % unchanged tosylates and 6% phenols. e Assuming 1 heteroatom/mole, and an average mole weight = 344.

1644


cause of the similarity in molar values (sulfonates: 9.56% oxygen, carboxylic acids: 8.84 oxygen). The presence of compounds such as ketones (2), lactones (49), fluorenones (50), quinolones (51), dicarboxylic acids (52), and diacid halfesters (29) which have previously been reported in crude oils could explain this result. The measured carbon content, which is 1 higher than the calculated carbon content, leads to the same conclusion. 5 . The amount of oxygen found in the hydrocarbon sample (3.15%) is larger by 2.4%than that calculated for the sum of phenols (0.27 %) and p-toluene sulfonates (0.48%) which indicates the presence of other oxygen compounds stable under the conditions of the reduction, for example, benzfurans which have been reported (53)in crude oil. 6. Agreement of found and calculated nitrogen and sulfur values including 0.32 sulfur due to unreduced p-toluene sulfonates shows that little or no denitrogenation or desulfurization has occurred during the reduction. 7. Assuming one hetero-atom per molecule and a molecular weight averaged from acid-derived hydrocarbons and unreduced p-toluene sulfonates, the hydrocarbons contain 40 % nitrogen compounds including 7 % carbazole and indoletype compounds, 18 % sulfur compounds including 5 % p-toluene sulfonates and 50 oxygen compounds other than phenols (6 %) and p-toluene sulfonates (5 %). In summary the above data show that, with the exception of the loss of some ketonic oxygen functions or lactone structures, the hydrocarbons are representative of the carboxylic acids from which they were derived. Separations and Instrumental Analyses. In order to better correlate this hydrocarbon sample with the previously reported acid and ester samples (29), a detailed picture of the kinds of reduction products present in the low molecular weight region (c16-c21) was obtained by examination at high resolution of a sample of the total hydrocarbon vaporized in the hot inlet of the mass spectrometer. Table V lists the masses observed, the empirical formulas assigned on the basis of mass measurement, the calculated masses, errors, and the Z (from C,H2,+,0S) for each. The symbol “X” in Column 4 marks the formulas in the table for which a homolog of the corresponding acid or fluoroalcohol ester has been reported previously (Table VI1 of Reference 29). The symbol “ X X ” marks the formulas for which the exactly corresponding acid or ester was found. Structural formulas corresponding to many of the Z’s listed in Table V were suggested in the previous paper (29). Several 2 s were represented in the acid and fluoroalcohol ester samples which were not found in the reduced acid but this is because the acid and ester fraction comprised only about 5 % of Fraction D, and relative concentrations are expected to be different. Nevertheless, there is considerable correspondence between the two sets of data which supports the assertion that the reduced product truly reflects the nature of the original acid sample. The four sulfur species in Table V correspond in Z to benz2 = -10) and a dithiophenes (CI~HZZS, C I ~ H ~ClsH& ~S, benzthiophene (C18HzOS, 2 = -16). These two types of (49) D. H. R . Barton, W. Carruthers, and K. H. Overton, J. Chem. Soc., 1956,788. (50) D. R. Lathan, C. R. Ferrin, and J. S. Ball, ANAL.CHEM., 34, 311 (1962). (51) E. C. Copelin, ibid., 36,2274 (1964). (52) K. Hancock and H. L. Lochte, J . Amer. Chem. Soc., 61, 2448 (1939). (53) American Petroleum Institute, Research Project 52, Report No. 22, July 1, 1961, to June 30, 1962, p 28.

compounds were later confirmed by mass spectrometric type analysis (Table VI) of a portion of the Fraction D hydrocarbons after further separation by elution chromatography on silica gel. All of the oxygen-containing compounds of Table V, except the two of 2 = -8, can be accounted for by benz- and dibenzfurans with up to two fused saturated rings in addition to the aromatic portion. An oxygen compound of 2 = -8 is likely to be a phenolic derivative of an indan or tetralin which would be consistent with the quantitative infrared analysis of Fraction D and its reduction product (6xphenols, Table VIII) because aromatic -OH would appear essentially the same on both benzene and on indane or tetralin nuclei. Autoxidation products or small amounts of unreduced ketones could be responsible for some carbonyl absorption at 17101740 cm-’ in this latter material. The results of separation by capillary silica gel chromatography and analyses of the resultant products are summarized in Table I. The contaminants isolated in a blank run did not interfere with the analysis. The colorless nonfluorescing paraffin plus naphthene Fraction 1 which, as expected, shows no nonhydrocarbon functional groups (infrared) and little aromaticity (ultraviolet) consists mainly of 3- and 4-ring naphthenes (Footnote c of Table I). The group-type (34) mass spectrum shows some 4 z paraffins in this fraction. Since paraffins are expected to be entirely eluted in this fraction of lowest polarity and the fraction itself represents about 3 wt (13 of 40%) of all crude oil carboxylic acids, the amount of paraffinic carboxylic acids in fraction D is less than 1 % of all acids. The presence of some paraffinic acids has qualitatively been established by high resolution mass spectrometry of perfluoroalcohol ester derivatives (29). Fraction 2 of this capillary separation appears as a narrow, very strongly fluorescing band and possesses ultraviolet absorption characteristic of mono- and bicyclic aromatics. A strong ultraviolet absorbance at 230 mp in Fraction 3 is indicative of thiophenes and/or pyrroles. Strong infrared absorbances in the free -OH and -NHregion of the infrared spectrum of Fraction 4 provide proof for the presence of phenols and carbazoles and/or substituted indoles (28). The occurrence of a major contribution of odd masses to the parent peak regions of the mass spectra of Fractions 3 and 4 confirms the presence of nitrogen compounds as observed by infrared. Table I11 summarizes the results of low resolution mass spectrometric examination of all fractions. (Because the members of homologous series differ in mass by multiples of 14 (CHZ),there is overlap in molecular weights between series which differ by a carbon atom and 12 hydrogen atoms. Thus, paraffins (2 = +2) have the same nominal molecular weights as naphthalenes (2 = -12). In this paper these two series are grouped together in “Z-category” +2. An analogous process was followed for the other 2categories. High resolution mass measurements, by establishing empirical formulas, can distinguish between possible t r u e 2 species in a single 2-category; but this distinction cannot be drawn from low resolution spectra solely by knowledge of the nominal masses.) For each fraction are listed several 2-categories in decreasing order of relative peak height as observed in the parent peak region. The significance of 2-category, in terms of possible structures, is given in Table IX. The alternatives listed in the table are possible on the basis ofZ-category, and their presence is supported by other evidence in some cases. The most important ions in the parent peak region of Frac-

x


0

1645

tion 1 are the 2-categories -6 and - 8. Because this fraction is essentially nonaromatic (Table I), the 2-category designation implies the presence of 4 and 5 alicyclic rings, respectively. Fragments of 2-category -7 are derived from parent compounds with 4 rings ( 2 = -6) by alkyl radical loss and from 5-ring compounds (2 = -8) by ring opening accompanying alkyl loss. Fragments of 2-categories - 5 and -3 are products of both 5- and 4-ring fragmentation. Particularly noteworthy is the large peak at m/e 191 which occurs in most of the spectra of Fraction 1 as the largest peak above m/e 123. This ion has been observed previously in petroleum fractions and in pure compounds isolated from petroleum (54). It was also noted (29) in the mass spectra of acids and esters isolated from this same petroleum, and its possible origin was discussed there and related to the probable presence of pentacyclic terpanes. The most important 2-categories in the spectra of Fraction 2 are 0 and - 2 (Table 111). Because this is a predominantly aromatic fraction (Table I), the actual 2 s are probably -14 and - 16. Combining this information with ultraviolet data (Table I) the most likely structural types are diaromatics of the acenaphthene type and naphthalenes with two fused saturated rings; the 2-category -6 in Fraction 2 is most likely representative of a mixture of tetracyclic naphthenes and alkylbenzenes. The 2-categories of the three most intense series of parent peaks in Fraction 3 are - 3, - 5, and - 1 signaling the presence of an odd number of nitrogen atoms in each and probably representing acridines, pyridines, and carbazoles, respectively, the last being confirmed (28) by infrared absorption. The mass spectra of Fraction 4 are too complex to be interpretable without further separations; the assignments of carbazoles and phenols are based on infrared spectra; however, there exists partial confirmation by mass spectrometry since the observed 2-category - 3 may be due to tetrahydrobenzcarbazoles and the 2-category - 4 may be due to phenols. In summary, capillary silica gel chromatography combined with infrared, ultraviolet, and mass spectrometry is a rapid method for semiquantitative determination of general compound class distribution of crude oil carboxylic acid-derived hydrocarbons. For the purpose of further separation of greater quantities of individual fractions, solvent elution chromatography on large columns is preferred. The separation is described in detail in the experimental section, and data are summarized in Table 11. The polycyclic naphthenes (MS) and some monoaromatics (UV; MS) are eluted with the first cyclohexane fraction. Cyclohexane eluates 2, 3, and 4 show extinction coefficients of up to 20,000 l./mole cm at 230 mp and 2300 at 260 mp indicative of naphthalene-type chromophores. The group-type mass spectrum (34) of the three combined diaromatic fractions (Table VI) shows the presence of some 80 total aromatics plus 9 mono- and dibenzthiophenes, thus verifying the ultraviolet and high resolution mass spectrometric assignments. In addition, group-type mass spectrometry also indicates the presence of some 11 phenanthrenes or anthracenes (Table VI). Absorbance of anthracenes near 260 mp (e = 105 l./mole cm) is stronger than that of phenanthrenes (E = 3 X lo4 l./mole cm). For 11 % (Table VI) of three fused aromatic rings to be consistent with an observed extinction coefficient of 2.3 X lo3l./mole cm, the predominant contribution must come from phenanthrenes and not anthracenes. Further support for the assignment of phenanthrenes is observation of low intensity (e = lo2 l./mole

x

x

x

(54) I. R. Hills and E. V. Whithead, Nature, 209, 977 (1966). 1646


cm) absorbances at 350-390 mp in Fractions 2, 3, and 4. Anthracenes show extinction coefficients of about lo4l./mole cm; however, the favored phenanthrenes absorb less than 102 l./mole cm. The presence of pyrenes is indicated by grouptype mass spectrometry and qualitatively confirmed by some absorbance at 320-350 mp. Absence of -NHand -OH functional groups in the first four fractions, amounting to one third of the total, was ensured by IR analysis and only little contamination was found in the blank run. The IR assignment of carbazoles (28) is confirmed by the ultraviolet spectrum of Fraction 5 (Table 11) with strong absorbances at 230 and 294 mH since carbazole itself possesses an extinction coefficient of over IO4 I./mole cm at these wavelengths. Comparing UV and IR extinction coefficients observed in column chromatography-derived fractions with those obtained by silica gel chromatography illustrates the much better separation efficiency of elution chromatography-e.g., naphthalene-type compounds and phenols plus carbazoles are found concentrated in very narrow zones. The major disadvantages of column chromatography are longer time of separation and problems of contamination as observed in Fractions 6 and 7 (Table 11, abundance of carbonyl and alcohol-type absorptions), which, therefore, were not investigated further. However, the preparation of larger quantities of material allowed further separation of the naphthenic Fraction 1, the combined aromatic Fractions 2 plus 3 plus 4, and the heterocyclic Fraction 5 by the technique of gel permeation chromatography (GPC) which has not before been applied to a problem of this nature. GPC is a convenient and rapid method for separating complex mixtures, principally on the basis of their molecular size (55). A solution of the mixture under investigation is passed through a system of columns containing heteroporous gel. According to the increasing amount of accessiblepore volume, the molecules are eluted in the order of decreasing molecular size. The amount of material eluted is measured by a differential refractometer, giving a deflection to the left of the base line (seen in the direction of increasing peak counts) if the eluate contains a solute of higher refractive index than toluene solvent and vice versa. Figure 3 shows the GPC recorder trace of the polycyclic naphthenic hydrocarbon fraction. Elution of material begins at Peak Count 14 and ends at Peak Count 19. As observed in blank experiments, Peak Counts 20 to 26 contain low molecular weight impurities from the solvent. These impurities have been deducted graphically in Figures 4 and 5, resulting in the dashed portions of the curves. Because GPC separations described here were carried out on a microscale (10 mg), contamination of the collected fractions was also observed to a minor extent. However, the mass spectrum of the contaminant which had been isolated in a blank experiment was rather nondescript and different from the mass spectra of the samples. For the naphthenic fraction, the change of refractive index with concentration (Figure 3) is entirely negative as expected for paraffins and naphthenes; in addition, the solutions are colorless and display no fluorescence under ultraviolet light. The aromatic and heterocyclic components (Figures 4 and 5) show refractive index profiles larger than toluene as expected. The aromatic Fractions 1623 (Figure 4) are colorless but show strong fluorescence. The heterocyclic components (Figure 5) are deeply colored. ( 5 5 ) J. C. Moore and J. G . Hendrickson, “Analysis and Fractiona-

tion of Polymers,” J. Mitchell, Jr., and F. W. Billmeyer, Jr., Eds., Interscience, New York, 1965, p 233.

~_________

~___________

~

~~_________

Table IX. Possible Structural Types from Low Resolution Mass Spectra of Hydrocarbons Derived from Carboxylic Acids and Separated by Capillary SiOz Chromatography Parent peak region Z-category" Most probable Alternatives Fragment peak region Fraction 1 2,3,4 1 2,3,4 0 Cycloalkanes Acenaphthenes Biphenyls -1 Carbazoles -2 Saturated bicyclics Naphthalene plus two saturated rings -3 Acridines Pyrroles Steranes, terpanes -4 Saturated tricyclics Phenanthrenes, phenols Acridines Pyridines Steranes, terpanes Phenols -5 -6 Steranes Benzenes Benzcarbazoles Steranes, terpanes Benzenes -7 -8 Pentacyclic terpanes Indanes or tetralins Pyrenes Indoles or benzacridines -9 a For a description of 2-category, see text.

In all cases, refractive index profiles, aromaticity, fluorescence, color, and the amounts of material preparatively isolated check well and confirm the data obtained by ultraviolet, infrared, and mass spectrometry (Table 11). Analysis of selected GPC fractions by high resolution mass spectrometry is summarized in Tables IV and VI. The effect of molecular size separation by GPC is best illustrated in Table VI by comparing data of aromatic Fraction 19 with those of aromatic Fractions 23 plus 24 (Figure 4). The 4-ring, 5-ring, and 6-ring naphthenes, whose concentration in the starting material (Table VI, Column 1) was very low and which are smaller in size than other compounds of equal molecular weight have a longer retention time (Fractions 23 plus 24, Table VI); they were not detected in Fraction 19, Table VI, which is larger in molecular size. A similar effect is observed in the aromatic portion of these two fractions as follows: Phenanthrenes and pyrenes, structures of compact molecular size, occur in larger amounts in fractions of longer retention time (23 plus 24, Table VI and Figure 4). However, in this case, the factor of greater polarity of the highly condensed aromatics may contribute to the longer retention time. Indanes and tetralins were found to be concentrated in fractions of larger molecular size (Table VI) for reasons not understood. The group-type analyses presented in Table VI were run at a mass spectrometer resolving power of about 1:5000. The basis for the procedure and its limitations have already been described (34). The species listed in Table VI are the only types considered by the method and undoubtedly are not the only ones present. However, of the 20 types of structures postulated on the basis of high resolution measurements of parent peaks of fluoroalcohol esters of a related acid fraction (29), 15 are covered. One of the other five, a hexahydropyrene nucleus (Table VI1 of Reference 29), is isobaric with fluorenes and is a valid alternative in the present case. For further detailed analysis of the polycyclic naphthenes (Table IV and Figure 3), Fraction 17 was selected for parent peak high resolution mass spectrometry. The neighboring Fraction 18 was subjected to high resolution group-type mass spectrometry which is based on fragment peaks. Both methods indicate predominance of 2-, 3-, and 4-ring naphthenes. One-ring naphthenes occur predominantly in the fraction of smaller average molecular size (Fraction 18). The results of the high resolution measurements on parent peaks that are given in Table IV cannot always distinguish between certain pairs of possibilities which have the same empirical formulas. Thus, 4-ring naphthenes and alkylbenzenes share the empirical formula C,H2,-o. However, the major

portion of CnHao is probably a 4-ring naphthene because Elution Fraction 1 is predominantly saturated, rather than aromatic. (Refractive index is below that of toluene, Figure 3). Cz3H38 and C24Ha have also been considered to be saturated for the same reason. Examination of the list of acid empirical formulas (detected as esters of 1,1,7-trihydroperfluoroheptanol)given previously (29) confirms the presence of homologs of all of the hydrocarbons. In Table IV are listed some of these esters. The first one in the table (C26H3002F12) will be used to illustrate the relationship between the esters and the hydrocarbons of Column 2 of Table IV. An original carboxyl can be reduced to a methyl group (-2 oxygens, +2 hydrogens) or esterified (+7 carbons, +2 hydrogens, +12 fluorines) giving a net difference between a hydrocarbon and its corresponding ester of C702F12. Subtraction of C702F12 from C26H3002F12 yields a hydrocarbon formula of C19H30, for which 2 = -8 and which is a lower homolog of C23H38. Similar treatment of the other ester formulas listed in Table IV demonstrates the presence of acids homologous with all of the hydrocarbons. Most aromatic species were too low in concentration to be detected in this saturate sample. Because these hydrocarbons are derived from carboxylic acids, their structural analogs are expected to be present in the original acid extract. The correspondence between the sets of homologous series of hydrocarbons in Saturate Fraction 17 and those found in the fluoroalcohol ester sample confirms this. Furthermore, agreement between the rough intensity measurements at high resolution on Fraction 17 and the type analysis of Fraction 18 lends credence to identifications in both sets of data. ACKNOWLEDGMENT

A sample of crystalline 24-tosyloxycholane was kindly provided by Professor F. C. Chang of the College of Pharmacy, University of Tennessee. The authors wish to express their appreciation to Professor S. Winstein for stimulating discussions. We thank Messrs. P. E. Monson, L. T. Shoji, and A. D. Alderman for experimental assistance and Dr. E. J. Gallegos for the mass spectrometric type analysis. RECEIVED for review April 16, 1969. Accepted June 6, 1969. Paper presented in part at the Gordon Research Conference on Geochemistry, New Hampshire, August 1968, and at the National Convention of the German Chemical Society, Hamburg, September 1969, and in full at the 158th National Meeting, ACS, Division of Petroleum Chemistry, New York, September 1969. VOL. 41, NO. 12, OCTOBER 1969

1647

Analysis of crude oil carboxylic acids after conversion to their

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