Table 111. Transformations to Quadratic Fits Gaussian function: Equation 9 Given parameters: a = 100.0; 0 = 1.00; y = 2.00 Twenty points
Transformed weights Untransformed weights
a 100.01 96.03
B
R,
1 7
x x
10-4 10-4
1.0000 0.9998
R@
1 1
x x
10-4 10-4
R,
Y
2.0000 2.0072
7 7
x
7 1
x
x
10-6 10-5
U
0 457 1.833 I
Cauchy function: Equation 13 Given parameters: a = 100.0; B = 1.00; y = 2.00 Twenty points
Transformed weights Untransformed weights
a 100.01 100.92
R, 7 1
x x
10-6 10-2
B 0.9999 0.9940
Curve envelopes can be fit by functions which are combinations of Gaussian and Cauchy functions such as their sum
Reports of fitting this function to an infrared band envelope indicate that good fits are obtained with 6 = 0.1 CY (the Gaussian has a smaller amplitude than the Cauchy function) and y = kE where 0.4 < k < 0.8 (the Gaussian is wider than the Cauchy function) (13). The iterative fitting of this function to an infrared band envelope is aided by supplying the best possible parameters from which to start. A set of starting parameters can be derived as follows. Fit a Cauchy function to the band envelope. The three Cauchy parameters can then be used to obtain starting iterative parameters consistent with the findings mentioned above. Use the found Cauchy centroid for p ; use nine tenths of the Cauchy amplitude for a and one tenth for 6; use the Cauchy width for y and twice its value for E . Thus one has obtained
9 4
Rfi 10-6
x
x
10-3
R,
7
2.0000 1 9788 I
x
10-0 10-2
U
0.509 0.646
values for the five parameters of Equation 18. It has been found that fitting a Cauchy function to such an envelope gives very good values for p, the centroid, and good values for CY and y. For example, an envelope was developed from Equation 18 with the parameters a = 90.0, p = 0.0, y = 2.50, 6 = 10.0, and E = 3.90. The resulting Cauchy parameters from the fit were a = 102.2,p = 0.00, y = 2.28, and the overall standard deviation of the fit was 0.81, which shows that the fit was good. These Cauchy parameters could be used as described to start an iterative routine to fit Equaton 18 to the envelope. Curve fitting using transformations of data to different functional forms can be used empirically. The original data points to be fit ( x t , yf) can be transformed into a different functional form ( x f , y f ’ ) and they can be fit empirically in that form. The weights associated with the points must always be transformed using Equation 6. Use of this method may result in the fitting of the original data with an acceptably good curve using fewer parameters than an expansion might require.
RECEIVED for review January 9,1970.
Accepted April 6,1970.
Identification of Polycyclic Aromatic and Heterocyclic Crude Oil Carboxylic Acids Wolfgang K. Seifert
Chevron Oil Field Research Co., P. 0. Box 1627, Richmond, Calif. 94802 Richard M. Teeter
Chevron Research Co., Richmond, CaliJ 94802 Compound classes of polycyclic aromatic and heterocyclic carboxylic acids, hitherto unknown in petroleum, were found in a California crude oil after conversion of the acids to their corresponding hydrocarbons followed by chromatographic separation on alumina and molecular spectrometry by various methods, including high resolution mass spectrometry. New classes of carboxylic acids found are mainly derivatives of benzfluorene-, acridine-, tetrahydrobenzacridine-, benzcarbazole-, tetrahydrobenzcarbazole-, cyclopentanophenanthrene-, di benzfuran-, and benzologs and of partly hydrogenated benzologs of the latter and of benzthiophene. The present study confirms and extends a preceding investigation of the polycyclic naphthenic, mono-, and diaromatic crude oil carboxylic acids. The conventional view of “Naphthenic Acids” in petroleum as primarily mononaphthenic and alkanoic acids is expanded by about 40 classes of carboxylic acids. Quantitative estimates are presented. 750
ANALYTICAL CHEMISTRY, VOL. 42, NO. 7, JUNE 1970
PRIOR TO THE WORK recently published from this laboratory (I) structural information on crude oil carboxylic acids was limited to alkanoic, 1-ring naphthenic, and simple aromatic types. The literature on the large amount of previous work has been summarized in one of our recent papers (2) which deals with the conversion of these California crude oil carboxylic acids to hydrocarbons for easier identification. High resolution molecular spectrometry of the derived hydrocarbons of low polarity ( I ) led to the discovery of some 15-20 compound classes of carboxylic acids of predominantly terpenoid polynuclear naphthenic, and mono- and diaromatic structure whose presence in petroleum was hitherto unknown. (1) W. K. Seifert and R. M. Teeter, ANAL.CHEM., 42, 180 (1970). (2) W. K. Seifert, R. M. Teeter, W. G . Howells, and M. J. R. Cantow, ibid., 41, 1638 (1969).
These findings bear on the question of the origin of petroleum (3)and because petroleum is derived from living organisms (4) and carboxylic acids are generally considered to be precursors of petroleum hydrocarbons (3, the knowledge of the structure of the acids is expected to stimulate geochemical speculations. The quantitative isolation of carboxylic acids from a California crude oil by exhaustive extraction with sodium hydroxide has been described previously (6). The presence of nitrogen-containing species of the carbazole and/or indole type (7) as well as of the polynuclear aromatic types (8) has been made likely although not proved. This paper deals with the investigation of carboxylic acids containing 2-5 aromatic rings with and without 0, S, and N atoms and often fused with naphthenic rings via spectrometric identification of derived hydrocarbons. Preliminary conclusions (first paragraph p 1466, Reference 9) which were based mainly on low resolution mass spectrometry are overruled by the conclusions of this paper, which is mainly based on high resolution mass spectrometry.
Extract a Carboxylic Acids
-
Ion Exchange Weakly Basic Resin
6
lor) DclIInge - St[ongly.Basic
i o n Exchange - yeakly Basic Resin
Resin
L
RCH,
I
*
Yield
RCH,OSO,QCH,
91%
Naphthenes, Monoaromatics
24%
.
CISO,
LIAIH,
1
Dia%t&
15%
Triaromatics
IC%
0
CH,
96701LIAiH,
RCH,OH
88%
dsz:C! 18%
Very Polar Fractions 32%
EXPERIMENTAL Starting Materials. After sodium hydroxide extraction of all carboxylic acids from Midway Sunset 31E California crude oil and separation from phenols by ion exchange chromatography (6), Fraction D, representing 4 0 z of all carboxylic acids, was reduced to “hydrocarbons” (2). The scheme leading to this point is repeated in Figure 1. Chromatography was accomplished on neutral alumina of activity grade I1 packed in a 12.5-mm i.d. by 150-cm column. A continuous change in solvent character was accomplished with an apparatus in which solvent of higher polarity was added at a constant low rate to a mixing chamber filled with solvent of lower polarity. The slowly changing mixed solvent then passed to the top of the column. Two-hundred eighteen milligrams of “hydrocarbon” Fraction D ( 2 , 6) (Figure 1) were chromatographed, and the combined diaromatic fraction (Fractions 3-6 of the first separation, 32 mg, 1 5 z ) was then rechromatographed on acidic alumina. The scheme of both separations is depicted in Figure 1 ; and types and amounts of solvent, yields, and material balances are listed in Tables I and 11. Low Resolution Mass Spectrometry. Each fraction was examined in the mass spectrometer by two methods. A portion of each fraction was vaporized directly into the ion source from a direct insertion probe (IO),and a series of scans was recorded at low resolution (about 1100). Because of the introduction technique, fractionation of the sample led to shifts in relative importance of compound types and a gradual increase in molecular weight. Table I11 records the data collected. Molecular weight range figures reflect the estimated starting point of the first scan and the estimated end point of the last scan. The average molecular weights were estimated from the ranges of the several scans, taking into account their relative contributions based on the total ion current which was recorded continuously. The mole percent of nitrogen and sulfur compounds was then calculated from the measured weight percent of the elements and the estimated average molecular weight (Table 111). (3) E. D. McCarthy and M. Calvin, Nature, 216,642 (1967). (4) R. Robinson, ibid., 212, 1291 (1966). (5) J. E. Cooper and E. E. Bray, Geochim. Cosmochim. Acta., 27, 1113 (1963). (6) W. K. Seifertand W. G. Howells, ANAL.CHEM., 41,554 (1969). (7) W. K. Seifert, ibid., p 562. (8) W. K. Seifert and R. M. Teeter, ibid., p 786. (9) W. K. Seifert and R. M. Teeter, Chem. Znd. (London), 1969,1464. (10) E. J. Gallegos, I.P. 30, Seventh World Petroleum Congress, Mexico City, D. F., April 2-8, 1967.
Monoarornatics, Yield
Naphthenes 8%
Diarornatics
52%
Phenanthrenes Tri~~o~~ics 10%
Polycyclicr
15%
mo
High Resolution Mass Spectrometry. Spectra were scanned at a resolving power of about 10,000 at a rate of 160 seconds per decade and recorded on analog magnetic tape (Honeywell 7600 tape recorder). The data were converted to digital form and further processed on a digital computer (Electronic Associates, Inc., Princeton, N. J.) to yield a table of empirical formulas and relative peak intensities for each scan. Instrumentation. Spectra were obtained as follows : Ultraviolet (UV) spectra on a Cary recording spectrophotometer, Model 10-11; infrared (IR) spectra in 0.05-mm microcells using a Perkin-Elmer Model 337 infrared spectrophotometer fitted with a beam condenser; fluorescence emission (FL) and excitation spectra on an Aminco-Bowman spectrophotofluorometer Model 4-8202, American Instrument Co. ; nuclear magnetic resonance (NMR) spectra on a Varian HA-100 spectrometer, mass (MS) spectra on an Associated Electrical Industries MS-9, as described previously (8). RESULTS AND DISCUSSION
Following reduction of the carboxylic acids to their corresponding hydrocarbons ( 2 ) many naphthenic, monoaromatic (Fraction 2 isolated on neutral alumina, Figure 1) and diaromatic structural types (Fraction 4, isolated on acidic alumina, Figure 1) were identified ( I ) . This paper deals with the investigation of the more polar types of carboxylic acids. Two hundred fractions were isolated on neutral alumina, and on the basis of their UV spectra they were combined into the 22 fractions listed in Table I. An analogous procedure on acidic alumina lead to the 12 fractions listed in Table 11. Fractions 7 and 13, isolated on neutral alumina (Figure 1 and Table I), and Fractions 8 and 10, isolated on acidic alumina ANALYTICAL CHEMISTRY, VOL. 42, NO. 7, JUNE 1970
751
TABLE I U L T R A V I O L E T A N D I N F R A R E D D A T A OF A L L H Y D R O C A R B O N S a D E R I V E D FROM CAR.BOXYLIC A C I D S AFTER S E P A R A T I O N ON N E U T R A L A L U M I N A
‘rac:ion
-
Eiue
Ct
Eb
!00
0
-
--2
3-6 I00
0
-I nb
ml
2M
g- 270 280 290 x
x
0 100 24.1
x
- 7 w ?ox 740 x”c -
300 310 320 3% 340 ?&
0
x
x
x
x
-
3483
0
X
610
0 Naphthenes and
x
x
X
xx
0
x
Diaromatics: Acenaphthenes, Naphthalenes, Benzthiophenes.
s
s
X
X
0
X
Fluorenes, Phenanthrenes, Naphthobenz thiophenes.
(51
7-10 95 1-5 99
0 1400
1-12 90 7. 93 10 13 75 25 4-18 0 40. 60 100
01oOO
xx
4.2
3.5 0 2600 14.8
99
1 300 20.3
0-22
0
0
00/1300(11 5
xyx
x
x
x
xyxxx
s
x
s
x
X
X
X
X
X W M
S
S
S
S
X
X
xx
c
X
X
iydrosen onding
X
X
iydrogel onding
X
0
iflrosen onding
0 Phenanthrenes
td I
-
0500
0
--
x t s ) Is) x
-
19
’otal
x xxx xx
6.1
Assignments IFriedel-0 r c h i n
Monoaromatics: Benzenes, lndane Tetralins, Octahydrophenanthrenes.
-
xx xx xx
0 193 15.4 xxxx xx
I
Infrared Absorptions, cm-1
Ultraviolet Bands and Shoulders, nm
Yield.1 Wt. 70
70
Carbazoles
MXXX
Similar to Cut 13
xxx
Nondescript
0
I
-
Nondescript
__ 99.9
-
E CFraction D representing 40% of all carboxylic acids present In Midway Sunset 31E Crude O i l =Cyclohexane; E Diethyl Ether; M = M e t h a n o l *
x = Weak; xx -Medium; xxx = Strong; xxxx I n carbon tetrachloride solvent.
=
Very Strong; I s I = Shoulder; I d ) = Doublet
TABLE i i ULTRAVIOLET AND INFRARED DATA OF D i A R O M A T i C H Y D R O C A R B O N S a DERIVED FROM C A R B O X Y L i C A C I D S AFTER SEPARATION ON A C i D l C A L U M I N A ~
~~
Uitraviolel Bandreand Shoulders,
Fraclion
Eluent, %
Yield, vt. 70
7.8
nm ~~
228 232 255 273 285 290 Mo 35 328 Inactive
I
xxxx
32.7
18.8
xxx
10-11
14.6
Total
21.8 xxx 96 0
xxx
-xx
xx
Like Fraction 4
-
(st
(st
is)
1-
Is1 Is1 Broad Nondescript
IS1
Assignments
3610
Ixx -
islist
(St
-
10.3 xxxd
I :TI
0
t x
xx
I 1
Naphthenes, Carbonyl :ompounds Trisubstituted Naphlhaienes, Acenaphthenes, Perinaphlhenes, BenzIhiophenes.
X
Diaromalics like Fractions 4-7, Phenanthrenes. Benzthiophenes.
0
Phenanthrenes
x
a Rechromatography of Fractions 3-6 isolated on neutral alumina, see Table i and Figure 2. b~ * Cyclohexane; E = Ether; M Methanol
n-Hexane d A m nm
-* 1 . 5
A255 nm e x = Weak; xx =Medium; x u = Strong; xxxx * Very Strong; ( s i * Shoulder
(Figure 1 and Table 11), were selected for extensive analysis because they occurred in predominant amounts and possessed U V spectra which were different from each other and similar to fractions eluted directly after them, The selected fractions were, therefore, roughly representative of the percentages of occurrence listed in Figure 1. It should be remembered that 752
ANALYTICAL CHEMISTRY, VOL. 42, NO. 7, JUNE 1970
the starting carboxylic acid material of the separation sequence depicted in Figure 1 represents 40% of all crude oil carboxylic acids which in turn amounts to 2.5 % of the crude oil itself. The apparent structures with which UV and I R spectra are consistent are summarized in Tables I and 11. The apparent structures with which fluorescence spectra are consistent are
(a,
TABLE I I i LOW R E S O L U T I O N M A S S S P E C T R A L D A T A 1 7 0 V ) O F SELECTED H Y D R O C A R B O N F R A C T I O N S D E R i V E D F R O M C A R B O X Y L I C A C I D S AND SEPARATED B Y AI203 CHROMATOGRAPHY
*h?
Neutral Alumina, Fraction Acidic Alumlna, F r x t i o n Yield, %b
24.1
Approximate Mole.
I. Range ,
Estlmatd AverilgcMole.
0.007 Trace
I RT
o
S u l f u r Compoundsd, Mole % , , ;p PeJ: Z-Cdwrye
0.03 0.6
3.5 &l -%l O
5.2
340 0.32 7. a 8.6
3M
0.12 2.5 7.1
234268
236
222.236
293,291
-3
-7, -5, -3 193,219,167
-2, -4-6
0.24
5,6
8.2
El
,Decreasing lmportanci
Oulstanding Peaks
302,322
-11,-3
Z-Catqptye, Decreasing importance Outstanding Peaks
0.27 6.2
m a El a
I
Fragment Pedr Region
13
3 200-Mo
Wt.
Wt. % Nitrogen Compounds, Mole % Nltrcg8nc,
-
7
'19,227,165
I
180,165, 221,153
248,m
222,236
-
a Combined dlaromdic portion, rechromatographed. Based on Fraction 0. representing @%of all lnlerfaclaily active carboxylic acids present in Midway Sunset 31E Crude Oil, Determined by the M i c r m u l o m e t r i c Dohrmann method. d Based on M S group type analysis. e 'Z-Category"is the '2"In CnH,n+z of the most saturated hydrocarbon homologous series whose nominal molecular weights coincide with the homologous series in question, Le.. paraffins ( 2 = +Z), naphthalenes I2 = -12). and dibenzothiophenes 12 -16) are all in 2-Category + 2. A n odd '2"Indicates I h e presence of an odd number of nitrogen atoms in the molecule.
-
A n even 'Z"a1so may be equivalent to an even number of nitrogen atoms.
TABLE
TABLE V
IV
F L U O R E S C E N C E E M I S S I O N A N D E X C i T A T l O N W A V E L E N G T H S OF M O D E L C O M P O U N D S A N D SELECTED H Y D R O C A R B O N F R A C T I O N S D E R I V E D FROM C A R B O X Y L I C A C I D S Excitationa nm
Sample
312
Acidic A l u m i n a Fraction 8
)i
q*
Arslgnment
342'. %*,
Acidic AI,O,
-
Fraction-
1 3 1 4 ~ 5 t 6aI
7
4
~
E
372"
j
10
'Subst. Naphthalenes
\
**Subs!. I , 2-Naphthobenzothiophener Subst. I , 2 - B e n m l l u o r e n e r
320. 34. 329'. 346'.
Neutral Alumina Fraction 7
Neutral AI,O, Fraction
EmirsionD,c
nm
3%'.
H Y D R O G E N N M R D A T A OF SELECTED H Y D R O C A R B O N F R A C T I O N S DERIVED FROM C A R B O X Y L I C A C I D S
9 m
E'.. E**
Z*.. 312..
MI. 3.
9' 347.
398 --Trace
Pyrener
J62
_____
346***, 355"'
Neutral Alumina Fraction 13
**'
331.
"'Subst.
Carbaoles
346
Type of Hydrogen
0.7-1. 1
Aiiphatic C H ,
1. 1-2.0 2.0-2.4
Aliphatic ICH2 Plus {HI
2.4-3.4
Aromatic ICH2 Plus -$HI
3.446
Aromatic -CH,- Aromatic
Aromatic-CH,
1
,i ~
Atom 70 H
I I
!
1
1
, Predominance , ,
17. Olxxl 43.4ixxxi
xx
xx
8.4~~1
14. llxxl 3. 91x1
aCombined. rechromatographed. bcomputer averaged spectrum. 'Not obtainable without computer a v e r q i n g
ail'avelength 01 excitation f o r emission spectrum. bUnderlmed: Strangesf peaks. CAr!erirks correlate navelengths w i t h assignmenis.
depicted in Table IV. Qualitative NMR data are given in Table V relative to atom percent hydrogen calculated as previously ( I ) for the mono- plus diaromatics. The procedures used to arrive at actual structural assignments of these complex mixtures were as follows: A set of low resolution mass spectra was obtained as described in the experimental section. These spectra, generally, were similar to each other for any one sample, differing primarily in molecular weight. The most prominent homologous series were selected and assigned to Z-Categories (see footnote e, Table 111) on the basis of nominal molecular weights. Such assignment leads to a list of possible empirical formulas for each homologous series. In a separate experiment on a new portion of sample, high resolution mass spectra were recorded on magnetic tape and processed by computer. The occurrence of multiplets at high resolution increased the number of peaks
observed in each spectrum from about 300 (low resolution) up to about 1700 (high resolution). The magnitude of the interpretive task required that attention be limited to one scan for each sample and only one block of 13 mass units in each scan. Selection of the scan and the region of the scan to be examined in detail was on the basis of the closest correspondence in the maximum of the envelope of the parent peak region with the average molecular weight of the sample as estimated from the low resolution spectra. Because of the complex nature of the samples, it was necessary to allow the computer considerable latitude in its calculation of empirical formulas; and, consequently, most peaks yielded several possible formulas from which the most probable was selected using. the following criteria: minimum mass error, smallest number of heteroatoms, structures known to be present in petroleum, and agreement with other spectrometric and chromatographic information. Some peaks, usually small, were eliminated from consideration because no empirical formula could be found ANALYTICAL CHEMISTRY, VOL. 42, NO. 7, JUNE 1970
753
TABLE V I H I G H R E S O L U T I O N M A S S S P E C T R O S C O P Y OF POLYNUCLEAR A R O M A T I C AND HETEROCYCLIC HYDROCARBONS ( F r a c t i o n 8, A c i d i c AloO,l
1
,;:kcJ
Possible Structural Tvpes
356.2160 356.2140
Observed mlc :alculated ml Formula
:Mass i:
361.28~ 361.2769
+2.a
Relative Importance
Possible Structural Types
-17
C26H35N
356.2za 356. 2538
I I I I ** I I
362.2018 362.2034 CZ8Ht6
363.29U 363.2926
356.25w Fluorescence
*
I(I
03-
UH33
W C l 4 ' 2 9
C26H31N
H
364.2145
364.2191
358.1755 364.2896 364.2878
I
C25H36N2
I
1
358.2661 3 E 3
I
t8.9
**
-m
e+ C10H2
1
t
I
366.2393 366.2380 C25H34S
368.2142 368.2140 Cz1HzaO
360.1911 368.2485 368.2503 C2&2
t4.9
)t**
-24
\'
0
uv
369.2498 369.24% C21H31N
which seemed reasonable on application of the foregoing criteria. The results for the samples discussed in this paper are given in Tables VI, VII, and VIII. If meaningful confirmation by another method was obtained from Tables I-V, the method is listed under the structure. Table VI, Fraction 8 on Acidic Alumina. This fraction was isolated after rechromatography of the aromatics (last horizontal row, Figure 1); it represents at least 0.6% of all carboxylic acids present in this crude oil. The block from m/e 356 through 369 was selected. High resolution measurements are arranged in order of increasing molecular weight. Because the relative sensitivities for the various species are not known, a scale of peak intensities ranging from * for the weakest to **** for the strongest was used to arrive at a semiquantitative evaluation. The 18 listed peaks represent 43% of the observed peaks and account for 59% of the total ion current in the range mje 356-369. Possible structural types, not considering the presence of isomers such as variation in saturate ring size and position of alkyl substituents, are given. Some additional points, not apparent from the table, are discussed below. 754
ANALYTICAL CHEMISTRY, VOL. 42, NO. 7, JUNE 1970
Fluoranthene and pyrene, alternate structures for benzfluorene are ruled out by UV. Alkyl chrysenes are consistent with the UV spectrum of this fraction (shoulder at about 330 nm, Table 11). Their presence as a major component was indicated in a previous study on the basis of high resolution mass measurements of fluoroalcohol esters (8). Phenanthrenes with a fused saturated ring are confirmed by a fragment peak at 231.1184 which fits this same structure (ClsHI5= 231.1174, compare also Table HI), as well as by the relative importance of Z-Category - 6 (Table 111). (One can visualize the diagenesis of cyclopentanophenanthrenes as secondary products from sterane structures by aromatization of the three 6-membered rings.) Other noticeable contributors in Table VI are phenanthrenes, which were reported previously ( I ) and which are supported by a fragment peak at m/e 219.1200 (C17Hl5 = 219.1 174), and acridines, with which the amount of nitrogen shown in Table I11 is consistent. A fragment at 165.0716 (Table 111) corresponds to ClaHewhich is probably a fluorene ion, possibly derived from 9-phenylfluorene ( Z = - 24), which
TABLE VI1
H I G H R E S O L U T I O N M A S S S P E C T R O S C O P Y OF POLYNUCLEAR AROMATIC A N D HETEROCYCLIC HYDROCARBONS
( F r a c t i o n 7 , N e u t r a l A120,1
)served mie lculated mif Formu I a
llass rror, ppm
Relative mportancf
300. 1174 300. 1150
+a. 0
**
‘2
lH 16’2
300. 1819 300. 1878
-
__ .19.6
Possible Structural Types
-26
IR
-
***
-22
C2?H24
300.2034 3W. 2034
0
-20
*Y**
C23H26
UV, NMR
__
304. 1830 304. 1827 C22H2,O
il.0
***
-20
.$
IR
,HI1 IR
-
3 M . 2192 3 M . 2191
tO.3
***
- 18 .
C23H28
306.2017 306. 1984 C22H26O
-10.8
~
****
-
306.2280 306.2397
-21 9
.
LRMS, UV
-
~
18
~
*
-16
C23H3G
-
308.2122 308.2140 C22H28O 310. 1761 310. 1755 c2 , H 2 6 S
310.2527 310.2535 C22H32N 312. 1137 312. 11% C22HI602
-5.8
~
***
-16
**
-26
*
-12
*
-28
e
C
l
G
H
2
1
-
-2.6 -
-2.6
-4.2
-
would be an alternate to chrysene (Table VI), a predominant species. The contribution of all other structures listed in Table VI is very small ; and therefore, supporting evidence from the other methods would not be expected. The NMR spectrum of this fraction strongly resembles that of Fraction 4 of the same separation, indicating a high degree of substitution on aromatic carbon, as discussed previously for Fraction 4 (1). Table VII, Fraction 7 on Neutral Alumina. This fraction represents at least 4 z of all carboxylic acids in this crude oil. High resolution mass measurements on the 10 species listed (33% of all observed peaks) in the block m/e 300 through 313 account for 45% of the total ion current in this mass range.
There is good agreement between low resolution mass spectral data obtained on the whole sample and high resolution data of this selected molecular weight block-e.g., phenanthrenes, which are also supported by a U V maximum at 250-260 nm (Table I), are significant contributors to the doublet at m/e 304 (Table VII) and also belong to the predominate Z-Category -4. A fragment observed by low resolution atmle219 measures219.1159(CliHIS= 219.1174)andappears to be a phenanthrene fragment. Cyclopentanophenanthrenes belong to Z-Category-6, the one of second highest ranking in Table I11 and the exact mass of one of the species of the triplet at molecular weight 300 signals their importance (Table VII). Fluorescence spectra support the presence of substituted 1,2-benzfluorenes (Table IV), which are listed as major contribANALYTICAL CHEMISTRY, VOL. 42, NO. 7, JUNE 1970
755
TABLE V I I I H I G H RESOLUTION M A S S SPECTROSCOPY OF NITROGEN CONTAINING HYDROCARBONS
' O b s e r i e d m'e
LaicJlaled mle
i
I F r a c t l o n 13, N e u t r a l A120,1 hlass Error
Relative Importance
Possible Structural Types
*
Fragment from higher homologs of C2,H, ,N.
3.X5.2378
** 357.24% IR, L R M S
I
358.2576 358.2535 C?bH?2N
t11.5
*
Fragment from higher homologs of CZbH,,N.
~
*** 359.2613
uv
c 12H25 IR
360.2683 360.2691
-2.2
*
ta. 9
****
- 18
Fragment from higher homologs of C,,H,N.
C26H?dN
361.2801 361.2769
e
c
1
3
H
2
7
m
C
l
O
H
2
1
H
C26H?5N
IR, UV, Fluorescence, NMR, LRMS
362.2841 362.2848 Cz6H?6N
-1.9
**
363.2932 363.2926
+ 1.7
***
-7-
Fragment from higher homologs of C,,H,,N
I C26H?7N
n H IR. UV, Fluorescence, NMR
utors and as structural alternates to fluoranthenes and pyrenes ; the latter are also supported by fluorescence. High resolution measurements of the fragments at m/e 193 and 167 (Table 111) indicate fluorenes (Table VII) and acenaphthenes. However, the contribution of the latter must be small (UV). The infrared spectrum shows the presence of small amounts of phenols and carbonyl compounds consistent with structural alternates proposed in Table VII. The nitrogen analysis (Table 111) indicates 8 mole % nitrogen compounds; quinoline, whose fragment is listed in Table VII, can account for some of this result. The UV spectrum (Table I) rules out all MS-derived possibilities of structures containing the naphthalene and benzthiophene chromophores as major contributors because these would require a high absorption near 230 nm and an absorption near 260 nm ( I ) of about one-tenth the intensity of the 230 absorption; however, the opposite is observed for this sample (Table I). Therefore, all structures containing the naphthalene chromophore, and permitted as alternates on the basis of high resolution mass measurement alone, were deleted from Table VII. Table VIII, Fraction 13 on Neutral Alumina. This fraction represents about 7% of all carboxylic acids in this crude oil because the UV spectra of Fractions 14-18 of this separation closely resemble that of Fraction 13. The parent peak region 756
rn
ANALYTICAL CHEMISTRY, VOL. 42, NO. 7, JUNE 1970
uv
of the mass spectrum of the fraction was completely dominated by odd mass peaks implying the presence of nitrogen compounds. The eight listed peaks represent 23% of the observed peaks and account for 68% of the total ion current in the range mje 353-366. The two most important Z-Categories in this sample are - 1 and - 3 suggesting structures of the carbazole and acridine type; these structures, and others with fused aromatic and saturated rings, are confirmed in Table VI11 by exact mass measurements of parent peaks and related fragments. An alternate to substituted carbazole (m/e 363, Table VIII) is a structure containing a quinoline chromophor, which is consistent with the UV spectrum (Table I). Substituted carbazole-type structures are favored by the strong UV absorbance near 260 and 290 nm. Strong additional evidence for the presence of carbazoles is the free-"-absorbance observed at 3483 cm-l in the infrared spectrum. A detailed study of the overtone bands of the -"-type compounds discussed in an earlier report (7) led to the conclusion that the -NH compounds were either substituted carbazoles and/or indoles substituted on the pyrrole ring, but not pyrroles. Elimination of the substituted indole alternate is now possible for this fraction on the basis of high resolution mass spectrometry. Additional evidence for carbazoles is the resemblance of the fluorescence spectrum of this fraction (Table IV) with data pub-
TABLi I X
C O M P O U N D C L A S S i S O F C A R B O X Y L I C A C I D S :1 hllDWAY S U N S i I 3 l i C A L I F O R N I A C R U D E O I L
IO-IW ppm
R-
R ~ C O O H
COOH
h
R-fXP
O
H
R
e COOH
R
~
C
O
O
H
RO- OH
R
~
R
~
C
O
O
H
li ~
C
O
R-CWH H
O
C
O
O
H
A
gcOoH
R-COOH
R
R-COO3
n - -R
COOH
R
~
C
O
O
H
'OH
HO&
R
Of a l l L l r b O X y I $ c XIdr p r e i e n l l n Ihls crude oil inveiligaled P O I r l b l e l e s i likely ddillonal dleinale rkeleloni bared on m a l i sPeCl'oIcOpy alone diphenyl diphenylmelhane. dirydrophenanlhrene. lluoranlhene. azzpyrene. dihydroarapyrene hexahydroazapyrene phenanlhrene.4 5-inine. Cy~10penldnOphenanlhrol ielralone, atanydrophenanthrone l ~ r a n o n a p h l h o b e n ~ ~ u r a n , al~phdliC~arOmdl~C ilheri b B a i e c on crude 0 8 1 . P$I,lion 01 i u b I l i l u e n l i rings and rina iizei unlnown a 25"
lished for carbazole (11) and the exact masses of two fragments at 236.1484 (C1,H18N = 236.1439)and 222.1295 (CH HIeN = 222.1283). The UV spectrum of this fraction.(TableI) is also consistent with that of acridines (Z-Category -3, Table 111). The NMR spectrum shows the strongest aromatic hydrogen absorption (near 8 ppm) of all of the fractions examined, confirming the above assignments (Table V). The predominant presence of nitrogen compounds is confirmed by abundance of fragments of even masses. In view of the almost complete absence of parent peaks of even masses, the low nitrogen analysis of this fraction by the microcoulometric Dohrmann method is difficult to explain (Table 111). Other Polynuclear Aromatics occur in Fractions 10 and 12 on acidic alumina (Figure 1). They represent about 2% of all carboxylic acids. UV, fluorescence, and NMR spectra are consistent with polynuclear aromatics but provide no detailed information. However, the mass spectra are more informative. Fraction 10 consists mainly of compounds of 2-Category -4 and +2. Z-Category -4 can imply alkylphenanthrenes (remembering that the previous fraction of shorter retention time consisted mainly of triaromatics) and/ or alkylnaphthobenzthiophenes. For the same reason, ZCategory +2 can imply alkyldibenzthiophenes and/or alkylcholanthrenes. Both fractions show evidence for the presence of a single dominant compound, different for the two samples. The earliest spectra from Fraction 10 contained a (11) H. V. Drushel and A. L. Sommers, ANAL.CHEM.,38, 10 (1966).
very prominent parent peak at mje 234 and a major fragment at m/e 219 (loss of CHI.) suggesting the presence of a phenanthrene nucleus with 4 alkyl carbon atoms. It is difficult to assign a structure to this compound because less abundant higher homo!ogs confuse the interpretation, but some inferences can be drawn by analogy with the behavior of the fourcarbon substituted benzenes. The loss of CHI. leads to the formation of the most abundant ion, leading to the elimination of n-butyl, i-butyl, sbutyl, and methyl n-propyl structures from consideration because they would be expected to have their largest peaks at mje 191 or 205. The lack of a prominent peak at mje 205 eliminates a diethyl structure. t-Butylphenanthrene is unlikely because it would probably have a major fragment (about 50z of the height of the 219) at m/e 191;whereas, in the sample, mje 191 is only 22% of the 219 peak. This leaves three possibilities: methylisopropyl-, dimethylethyl-, and tetramethylphenanthrenes of which we prefer the first. Fraction 12 consists mainly of compounds of Z-Category -2 (e.g., hexahydropyrenes, "Z = -16"). The first few mass spectra of Fraction 12 have prominent peaks at m/e's 236, 221, 180,and 165. The Z-Category in this case is -2, and the true Z is probably -16 leading to a C?-substituted hexahydropyrene as a possibility. The mass spectrum of unsubstituted 1,2,3,3a,4,5-hexahydropyrene is known (12) and (12) Catalog of Selected Mass Spectral Data, Serial No. 1980, American Petroleum Institute Research Project 44, Thermodynamics Research Center, Texas A and M University, College Station, Texas. ANALYTICAL CHEMISTRY, VOL. 42, NO. 7, JUNE 1970
757
shows a loss of CzH4to m/e 180 followed by loss of CH3. to m/e 165. The spectrum of Fraction 12 shows a metastable peak at 137.2, consistent with the loss of 56 from the 236 peak to form the 180 fragment and a metastable peak at 151.3 confirming the genesis of the 165 from the 180. A large peak at m/e 221, due to the loss of CH,. from the 236 peak, implies at least one methyl group in the molecule. Taken together, the above information indicates that the structure may be a dimethylhexahydropyrene with the 2 methyls attached to the 2 ring-carbons that are lost in forming the m/e 180 ion. The long chromatographic retention time of this material of relatively low polarity needs to be pointed out. For the present it must be explained as a gel permeation effect, namely, the occurrence of a species of very small molecular size. Summary of This and Previous Work. The classical picture of “Naphthenic Acids” as a mixture of alkanoic and l-ringnaphthenic acids must be greatly expanded for this California crude oil by the discovery of some 40 new compound classes of carboxylic acids. Table IX summarizes the results of this and the previous paper (1). The estimate of the amount of each type listed was obtained via the portion of the ion current for each (MS) and the intensities of other spectrometric absorptions combined with the amount of the subfraction in the parent fraction and of the latter in the crude oil. Because only 25 of all acids present in this oil were investigated and many similar or identical structures are expected to be present in neighboring carboxylic acid fractions of the main separation (6), the estimates are minimum values. The small quantity of each fraction available for investigation and the complexity of the acid mixtures described in this paper prohibit unequivocal identification in many cases. However, most of the structural assignments for the major
components are believed to be correct because of mutually supporting evidence from the various techniques of molecular spectrometry for most types listed in Table IX, previous finding (8) of many structures as fluoroalcohol esters and occurrence of many of the acid structures found here as hydrocarbons in petroleum (11, 13-16). In order to enable future workers in this field to clarify the unavoidable ambiguities, detailed spectral information was listed for each fraction in the Tables of this paper. The findings reported here should, it is hoped, shed light on the puzzling geochemical relationship between carboxylic acids and hydrocarbons. The next paper will deal with deuterium labeling at the site of carboxyl attachment leading to proof of the absence of contamination and identification of individual terpanoid and steranoid polycyclic naphthenic acids. ACKNOWLEDGMENT
The authors thank R. M. Bly for interpretation of fluorescence spectra. RECEIVED for review January 8, 1970. Accepted March 30, 1970. Paper presented in part at the Gordon Research Conference on Organic Geochemistry, Holderness, New Hampshire, August 1968, and in full at thejoint meeting of the American Chemical Society and the Chemical Institute of Canada, Division of Analytical Chemistry, Toronto, May 1970. (13) L. R. Snyder, ANAL.CHEM., 41,314 (1969). (14) C. J. Robinson and G. L. Cook, ibid., p 1548. (15) H. V. Drushel and A. L. Sommers, ibid., 39, 1819 (1967). (16) C. F. Brandenburg and D. R. Latham, J. Chem. Eng. Datu, 13, 391 (1968).
Potentiometric Study of Base Strengths in the Binary Solvent, Acetic Anhydride-Acetic Acid Orland W. Kolling and Wilton L. Cooper Chemistry Department, Southwestern College, Winfield, Kan. 67156 The response of the glass electrode to changes in acetate ion concentration in solutions of bases was examined in the binary solvent, acetic acid-acetic anhydride. In general the potential of the electrode is shifted toward a more positive value with increasing acetic anhydride content of the solvent. The apparent basicities of representative ionic and uncharged bases in the mixed solvent were compared to their pKB values in anhydrous acetic acid. It was found that the relative strengths of the bases are validly expressed by the half-neutralization potentials under conditions of constant concentration for the bases, with HCIO, as the reference acid. Within the separate groups of charged and uncharged bases, the order of decreasing basicity in acetic acid is unchanged by the addition of large amounts of acetic anhydride. The primary effect of acetic anhydride upon the cell potential appears to be the change of the value of Eo in mixed solvents for the mole fraction range of 1.0 to 0.28 in acetic acid. However, the quantitative statement of this effect must be expressed in terms of the mole fraction of dimeric acetic acid. 758
ANALYTICAL CHEMISTRY, VOL. 42, NO. 7, JUNE 1970
A NUMBER of analytical methods involving nonaqueous solvents have employed potentiometric determinations of weak electrolytes in media that are predominantly acetic anhydride. Representative studies have included : the titration of uncharged weak bases ( I ) , basic anions (2), quaternary ammonium salts (3),aromatic N-oxides (4), and phosphine oxides (5); the indirect determination of transition metal cations (6); and the comparative strengths of sulfonic acids (7). The polarographic behavior at the DME for several transition
(1) J. Fritz and M. Fulda, ANAL.CHEM., 25, 1837 (1953). (2) C. A. Streuli, ibid., 30, 997 (1958). (3) M. Puthoff and J. Benedict, ibid., 36, 2205 (1964). (4) C. Muth, R. S. Darlak, W. H. English, and A . T. Hamner, ibid., 34, 1163 (1962). ( 5 ) D. C . Wimer, ibid., p 873. (6) J. S. Fritz, ibid., 26, 1701 (1954). (7) D. J. Pietrzyk, ibid., 39, 1367 (1967).
