Determination of pBr. For increased accuracy and convenience of measurement, i t would be advantageous t o employ the p H scale of t h e Beckman Model G p H meter. The sensitivity of t h e meter is increased by a factor of 100 to 59 a n d compensation for slight variations i n t h e individual indicator electrodes can be accomplished with the zero adjust control. The temperature control on the meter compensates for temperature variations. The pBr as defined in these experiments is given by the equation
pBr
= (Eesll -
E’)/(2.303 R T / F ) = - log[Br-]
where Eoe1lis the observed e.m.f. of the cell and E’ is the e.m.f. of a cell 1.44 in potassium bromide and 1 M in potassium nitrate. A sca!e reading of 11 was chosen as a convenient point for zero pBr. I n order t o obtain pBr, the scale reading is subtracted from 11. The results of a series of measurements
on potassium bromide and tetraethyIammonium bromide solutions using the p H scale of the p H meter are presented in Table IV. Determination of the Solubility Product of Lead Bromide. T h e solubility product constant of slightly soluble bromide salts, such as lead bromide, can be calculated from t h e values obtained by direct potentiometry. The concentration of bromide ion in a saturated solution of lead bromide a t 25’ C. was determined from potential measurements. The solubility product constant was calculated from the following equation K(PbBr2) = (Pb*z)(Br-)2 = (Br-)3/2 The potential of a saturated solution of lead bromide was found to be -76 my. A value of 2.75 X 10+M bromide ion concentration was calculated from the A equation for the cell potential. solubility product constant of 1.05 X 10-6 was calculated from the above equation. This value can be expressed as pK(PbBr2) and is 4.97.
T‘alues of 4.56, 5.04, and 4.41 have been reported (7). LITERATURE CITED
( I ) Brown, A. S., J. Am. Chem. SOC.56, 646 (1934). (2) Chanin, M., Science 119, 323 (1954). ( 3 ) Helmkamp, G. K., Gunther, F. A., Wolf, J. P., Leonard, J. E., J. Agr. Food Chem. 2 , 836 (1954). (4)Ives, D. +; G., Janz, G. J., “Reference Electrodes, p. 190, Academic Press, New York, 1961. ( 5 ) Latimer, W. M., “Oxidation States of the Elements and Their Potentials in Aqueous Solutions,” p. 234, Prentice Hall, New York, 1952. (6) Lingane, J. J., “Electroanalytical Chemistry,” 2nd ed., p. 27, Interscience, New York, 1958. (7) Schwarzenbach, G., Bjerrum, Sillen, L. G., “Stability Constants,J;: The Chemical Society, London, 1958. ( 8 ) Stern, M., Schwachman, H., Licht, T. deBethune, A., ANAL. CHEM.30, 1506 (1958). RECEIVEDfor review March 2, 1962. Accepted October 17, 1962. Presented before the Division of Analytical Chemistry at the 139th National Meeting of the American Chemical Society, St. Louis, Mo., March 1961.
Characterization of Aromatics from Light Catalytic Cycle Stocks by Spectrometric Techniques Compound Types of the General Formula K. W. BARTZ, THOMAS ACZEL, H. E. LUMPKIN, and
F.
C3H2n-16
and
CnH2,,-,8
C. STEHLING
Research and Development, Humble Oil & Refining Co., Baytown, Tex.
b The aromatic components of a narrow distillation fraction (622’ to 6 2 5 ’ F.) of a light catalytic cycle stock were separated by elution chromatography and identified b y integrated interpretation of mass spectrometric, nuclear magnetic resonance, ultraviolet, and infrared data. Alkyl fluorenes were found to comprise the major compound type in the C,Hnn-la series, although minor concentrations of alkyl-9,lO-dihydroanthraceneswere also detected. Significantly, acenaphthylenes were not found in any of these fractions. Both methylphenanthrenes and -anthracenes were identified in the C,,HZ,-le series.
I
in the composition of light cycle stocks from catalytic cracking stems from the possibility of using this relatively low-cost material as a source of higher valued products. Because the nature of the products obtained depends on the feedstock composition, it is highly desirable t o have an accurate analysis of the latter. NTEREST
1814
ANALYTICAL CHEMISTRY
Alkyl acenaphthene and acenaphthylene types have been reported in the mass spectrometric analysis of virgin gas oil (6). However, when this procedure is applied t o samples in the light catalytic cycle stocks range, spurious results are obtained. This has led t o the question of whether the compounds in the C,H2,-14 and CnH2n--16series are truly acenaphthenes and acenaphthylenes, respectively, in not only the light crcle stock range but also in gas oils. Thus, although the over-all characterization of light cycle stocks is desirable, the first step, which is the focal point of the present study, has been the identification of the compound types in the so-called acenaphthylene series. Simultaneously with the partial resolution of this problem, additional information on the phenanthrene series is also discussed in this paper. Early in the investigation, some chemical reactions were carried out in attempts t o prove or disprove the presence of acenaphthylenes in light catalytic cycle stocks. Attempts at selective hydrogenation of the CnHZn--16 com-
pounds in a catalytic oil fraction, indicated by low voltage mass spectrometry t o contain 17% of these materials, were unsuccessful. A suspension of palladium black in cyclohexene %as used as a catalyst (3). The failure was apparently not due to inactive catalyst or catalyst poisons, as pure acenaphthylene, when added t o the cycle stock fraction, was smoothly reduced t o acenaphthene. I n addition, although hexachlorocyclopentadiene readily reacts with acenaphthylene (12) t o yield a crystalline adduct, no adduct was formed in a similar reaction with an acenaphthylene concentrate from the pertinent cycle stock fractions. With the chemical and preliminary analytical data indicating doubt concerning the structure of some of the condensed aromatics in this particular fraction of petroleum, it was decided that only by detailed spectrometric examination of highly separated material could the identity of these compound types be ascertained. A preliminary survey of narrow boiling distillate
trated by plotting successive percolation fractions against low voltage (LV) parent peak intensities of the individual series (Figure 1). A similar plot of the high voltage (HV) fragmentation peak intensities, summed according to series, is illustrated in Figure 2.
'4
3
1
'C
11
Figure 1 .
12
1
I
I
15
13 i4 CUT NYMBER
I
16
I
17
I
I8
1'9 $0 '212
A i
Initial percolation
tow voltage parent peaks summed by series
fractions of a light catalytic cycle stock had indicated that the C,,Hz,-,6 compound types attained a maximum concentration a t about 625' F. Therefore a 622' to 625' F. fraction of this oil was selected for detailed examination. After removal of the saturates by silica gel percolation and the olefins by alumina, the aromatic portion was rechromatographed over alumina, employing the elutriation technique (5, 79, 2 1 ) . The resulting fractions have been examined primarily by mass spectrometry, hut nuclear magnetic resonance, ultraviolet, and infrared spectrometry data have also been utilized on selected fractions in which compounds either were unidentified or their identities \yere uncertain by mass spectrometry. The maw spectrometer is the best survey tool for investigations of this nature. I t is the most sensitive for detecting changes in concentration and for recognizing the advent of neiv compound types when spectral features are plotted against weight per cent of sample off the chromatographic column. Therefore, the compounds are described and referred to in usual mass spectrometric terminology. This paper, then, describes in con4derahle detail the spectrometric examination of highly separated aromatics from a light catalytic cycle stock fraction, an examination which, though not nearly completed, has already revealed that the composition of this fraction of petroleum is much more complex than has been previously supposed.
Hydrogen N M R spectra were obtained with a modified 60-mc. Varian HR-60 N M R spectrometer equipped with proton control of the magnetic field. All samples were dissolved in CC1,. Tetramethylsilane was added as an internal standard and chemical shifts are reported in r units (IS). N M R nomenclature used is that of Chamberlain (4). Infrared and ultraviolet spectra were obtained with Perkin-Elmer Model 21 infrared and Cary Model 14 recording spectrophotometers, respectively. Initial Separation. h light catalytic cycle stock fraction (b.p. 622' t o 625' F.), from which the saturates mere chromatographically removed, was adsorbed upon alumina gel and the aromatics were differentially displaced by a series of graded solvents beginning with iso-octane and ending with a 50 volume % mixture of isooctane in benzene. Mass spectra were obtained on selected fractions and the peak heights recorded in various combinations to aid in spectral interpretation. The compound type separation effected by this procedure is clearly illus-
It is readily apparent from these figures that the various aromatic types have been partially separated. The separation of the -6, -8, and -10 series is as expected (IO). The first two maxima in the -6 series have been identified (by mass spectrometry) as alkyl benzenes and benzothiophenes, respectively, but no attempt has been made to assign the structure of the compounds in the third maximum of this series. The initial maxima in the -8 and -10 series are reported as indanes and indenes. The identifications were based solely on mass spectrometric data, as the concentrations of these particular aromatics in the distillation-separation fractions were insufficient to permit corroborating evidence from nuclear magnetic resonance, infrared, or ultraviolet. DISCUSSION
From an examination of Figures 1 and 2 it is evident that the maxima of the LV parent and the HV fragmentation peak intensities coincide for each series. I n both the CnH2n--12 and the C,H2,-le a bimodal distribution of peak intensities is observed. The first maximum in the -12 series has been identified as being due to naphthalenes, 11-hile the second is attributed to dibenzothiophenes. These identifications n-ere based on exact isotopic ratios and the presence of characteristic fragment peaks in the M S spectrum. However, the assignment of structural types to each of the two maxima in the -16 series (acenaphthylenes) has not been completely resolved.
i
, /
EXPERIMENTAL
The mass spectrometer used was. a modified Consolidated Electrodynamics Corp. Model 21-103C instrument with a heated inlet system. Peak heights were recorded both by recording oscillograph and the CEC peak digitizer (Mascot).
,
I
I
I
78
3
IO
11
Figure 2.
I 12
1 13 CUT NUMBER
I 14
I
15
I 16
I
1
17
10
I
1
19 20
I l l /
22 26
Initial percolation
High voltage fragment peaks summed by series
VOL. 34, NO. 13, DECEMBER 1962
1815
~
- -8
~ ~ ~ ~ ~ _ __ __~ __ ___~ ,/
18001-
_1
j
\
It
?
,
w
%
a
1
:
i
\\
,
\
2208 = ( M e208 +e22 t 2361
1!
I.
a 1400:
I
I
,
I
',
z
detailed discussion of the -14 series, as well as the -12 series, is presented in another paper ( I ) . The complexity of each percolation cut made it impracticable to attempt a detailed structural examination of the compounds contained therein. Another chromatographic separation simplified Ohese mixtures so that the -16 and the -18 series could be characterized. For this purpose, fractions 14, 16, 17, and 18 (fraction 15 was inadvertently lost) were rechromatographed, forming fractions of Percolation B. The results of this separation sequence are illustrated in Figures 4 and 5 and, as an aid in the subsequent discussion, the -12 and -14 series are included. The volume per cents by carbon number calculated from LVMS data are given in Table J. These concentration data cannot be considered as highly accurate, because of the uncertainties of compound type identification. I n fact, revision of the low voltage sensitivity coefficients is one of the aims of this study. These calculated concentrations, which appear as the ordinate in Some of the figures discussed beloTv were, hornever, of value in comparing mass spectrometric data with data arising from infrared, ultraviolet, and nuclear magnetic resonance. K i t h occasional references to Table I and the figures, the -16 and the -18 series are discussed in detail below. C,Hz,-16. 11s data indicate the presence of a t least two compound typesin the C,Hz,-16 series which are maximized, respectively, in cuts 15 and 29 of the initial percolation (see Figure 1). After repercolation of fractions 14, 16, 17, and 18 of the initial percolation the -16 series was concentrated in Percolation B, as shown in
7
\\
I
,
-
L \-
1 3
1
-
m/e
_ _ _ - -1.. .-.---,
-X-?0%
m - -
0
10
1
I
11
9
78
30
20
1
70
50 60 WEIGHT I PER I CENT I I 12 13 14 15
40 I
10
11
194
- - 4- - - - - -
,'
/
.----- - - - - - J
-_._____, 90 100
80
I
I
I
16
17
18
I
I
I
19 20
l
I
,
l
22 2j
CUT NUMBER
Figure 3.
Initial percolation, CnHzn-16 series
Selected parent and fragment peaks
A plot of selected LV parent and HV fragment peak intensities for this series is presented in Figure 3. From the diagram it is obvious that the fragmentation peak intensity at m/e 179 also has a bimodal distribution which is coincident with the two LV parent maxima a t m/e 194. This suggests that the -16 series consists of two different compound types, each contributing strongly to the fragment mass 179. The maximum in the HV peak a t m/e 165 is not bimodal and does not coincide with the occurrence of either the LV peak at m/e 194 or the other parent peaks in the -16 series, 208, 222, and 236, but it does overlap the LV parent peaks of the latter to some extent. Therefore, although the aromatics in the -16 series do contribute to the m/e 165 ion, it is apparent that
other compounds also give rise to this fragmentation peak. The L v Parent Peaks of the -18 series coincide with the high voltage fragment peaks characteristic of phenanthrenes and anthracenes. The bimodal distribution pattern of both parent and fragmentation ions is barely perceptible in the CnHz,-14 (acenaphthene) series. Since the intensity of the second maximum occurring a t about percolation cut 29 is low, no attempt was made to investigate the compounds responsible for this maximum. The HV fragmentation pattern for the first maximum in the -14 series is consistent with its LIr parent peak summations, and hence no irregularity was detected by mass spectrometry on these fractions of the initial alumina gel percolation. -4
,
500 Percolat
on B
?
1
\
-
400
~
_
iL
c %
P e r c o l o t 0'
B
7mc-
-
_
X165 xi91
Y
X197
a 300 -
-
-
Acenaphthylener Phenanthrenes Dibenzothiophenes
z
P -
2
-
2191
5000 -
z
100
'-. h
I
1
I
5
I
YrEIGHT PER CENT
1 0
15
20
I
25
30
I
1
35 36
WEIGHT OER CENT
111
40 44
42
1
5
IC
Figure 4.
Percolation B
l o w voltage parent peaks summed by series
1816
ANALYTICAL CHEMISTRY
20
CdT NUMBERS
CUT NUMBERS
Figure 5.
25
30
Percolation B
High voltage fragment peaks summed by series
35
4dS4 42
Table I.
Compound Types b y Series and Carbon Number Distribution
Percolation B Low voltage MS analysis, volume per cent
CnHzn-1s
1
5
10
15
20
25
30
35
36
40
41
42
43
44
1.5
11.8
23.9
35.9
46.7
63.2
75.0
98.5 0.5
99.0 0.7
99.2 0.1
99.8
0.5 1.2
0.5 0.5
0.3
0.1
0.1 0.5 0.1 1.1 1.7 3.8 2.1 0.3 39.9 37.3 5.9 0.6 1.1 2.6 2.0 0.7
0.4 1.7 0.3
88.6 0.2 0.1
97.7 0.4
0.1 0.9 0.6 0.1 0.5 6.4 1.4 0.8 0.5 32.7 24.6 15.8 0.4 3.0 5.8 5.2 0.3
85.4 0.1 0.1
18.2 1.2 2.8 0.2 5.6 25.2 4.7
31.4 1.0 2.9
29.5 1.0 1.6
21.2 0.5 1.3
11.2 0.3 0.6
8.4 0.3 0.3
1.6 0.2 0.2
1.5 0.3 0.3
1.3 0.3 0.3
0.4 0.3 0.2
0.2 0.3 0.3
1.7 15.2 2.1
0.8 8.4 0.8
0.8
7.0 0.5
0.6 6.4 0.3
0.5 6.9
0.5 5.9 0.1
0.6 3.5 0.3
0.3 1.1
0.5 0.2
0.3 0.3
13.8 22.9 2.8
16.3 13.2 0.7
10.4 6.8 0.3
10.9 5.7 0.1
12.0 4.2 0.3
13.9 4.3
23.6 5.9 0.1
33.3 7.4 0.1
57.4 7.7
64.6 2.8 0.1
0.5 0.2 0.2
14.5
0.5 39.6
1.0 50.9
1.4 62.5
1.3 63.8
0.7 60.8
0.1 0.1
0.3 0.2 0.3 0.1
0.6 51.4 0.1 0.1
1.0 29.3 0.3 0.3
0.5 25.2 4.8 0.2 0.1
54.8 1.2 0.4 0.2 0.6 38.9 1.1 0.7 0.4 0.3
0.3 3.3 0.9 1.2 0.5 16.5 29.4 9.8 0.3 4.2 25.0 5.1 0.2
...
c 1 4
CIS c 1 6
C,i
cis
0.3 0.3 0.3
c 1 9
Figures 4 and 5. Maxima which can
the second maximum appearing in B-42 and in B-43 is due to the same compound types responsible for the second maximum in the -16 series of the initial sepalation (Figure 1). This deduction has been verified. Throughout the percolation the major fragment peaks in the series are m/e 179 and 193 (see Figure 7), pointing to a nuclear molecular weight of 166 or 180. As
be attributed to a first compound type appear in B-5 to B-10 for Ci7, B-10 for CI6,and B-20 for C15(see Figure 6). The Cls and C16 compounds each present a second maximum in B-43 and B-42, respectively. Thus the positions of the maxima are as would be expected by the alumina gel separation of two compound types. Also, from techniques employed in the separation procedure, it is very likely that
3000
both compound types give rise to the same fragment peaks (179, 193), this behavior suggests that the compound types are themselves similar. The 165 fragmentation peak intensity, usually attributed to the -16 series, decreases rapidly from B-l t o B-20, and thereafter reaches a plateau. The lack of correlation between the peak intensity of m/e 165 and the concentra-
i
r
2530
a
I
1
5
,
IO
1 15
1
20 CUT
Figure 6.
I
I
25
33
l
l
35 36
I1 4044 42
1
I
I
1
10
5
NUMBER
Percolation B, Low voltage analysis
I
I 20
15 CUT
series
Figure 7.
I 25
I 30
I 35
11, 40 44 42
NUM8ER
Percolation B, C,,HB~--~ series Selected fragment peaks
VOL. 34, NO. 13, DECEMBER 1962
1817
tion of the -16 compounds, as computed by LV parent peaks, n-as also observed in the initial percolation. Therefore, any calculation of the -16 conipound type concentration based (in part) on the total peak intensity of the 165 ion would be in error. TYPE 1. Unfortunately, for those samples in which the first compound type in the C,,H2,- 16 is concentrated, the CnH2n--14series is also found in large concentrations (see Figure 4). Furthermore, the concentrations of these two typcs in many of the fractions are about the same, so it is not possible to correlate changes in either the S h I R or the ultraviolet spectra with the appearance or disappearance of a part)icular compound type as seen by TIS. However, the accumulated analytical data obtained for the -16 series in these fractions are consistent with those expected for either 9,10dihydroanthracene or its angular isomers. Of the two possibilities, the anthracene derivatives are preferred t'o those of 9,lO-dihydrophenanthrenes. These tentative conclusions are based on the following experimental data: Both 9,lO-dihydroanthracenes and -phenant,hrenes belong to the CnHln--lS series and both have nuclear niolecular weights, 180, which is consistent with AIS low and high voltage data. The high voltage spectra of these fractioiispresent strong fragments a t m / e 179 and 193, corresponding to a nucleus - 1 and nucleus +13 peak, respectively, for a nucleus of mass 180. The high voltage mass spectra of both 9,lO-dihydroanthracene and -phenanthrene present strong parent - 1 fragment peaks. It is logical to assume that the alkyl homologs of these dihydroaromatics will form both nucleus - 1 and nucleus 13 fragment,s ( m i e 179 and 193) under siinilar conditions. Since in the fractions under consideration the -16 compound types are maximized a t C15 and CIS, which would correspond to methyland dimethyl- or ethyldihydroanthracenes or -phenanthrenes, the strong 179 and 193 fragmentation peaks areassigned to tlie proposed aromatic structures. iliis aromatic type issues from the chroniatographic column in the relative order eqiected for 9,lO-dihydroanthracenes or -phenanthrenes. The X:\IR spectra of these fractions contain bands a t about 6.5 T, which is characteristic of CH2 groups c y 2 to aromatic rings (.$). Of the two isomers in question only 9,10-dihydroanthracene has a CH, group cyz to aromatic rings. Fluorenes, which belong to the -16 series, also have a CH? group c y 2 t o aromatic rings, but as fluorenes were identified in the latter percolation fractions (see below), they were not considered to be present as major constituents in these particular fractions. Fractions B-11, -13, -15, and -17
+
r
7
181 8 -*
ANALYTICAL CHEMISTRY
form adducts with p-benzoquinone. The hydrogen transfer reaction, described by Braude, Jackman, and Linstead ( 2 ) for 9,10-dihydroanthraceneJ consists in the aromatization of this compound with p-benzoquinone as the hydrogen acceptor. Part of the anthracene formed reacts with the excess dienophilic p-benzoquinone present, forming an adduct, as illustrated in Equations 1 and 2. 0
M W : I80
0 MU': 108
can be excluded, because this would not give a resonance in the 6.4- to 6.7-7 range, and because no resonance is observed a t about 6.9 T , nhere the methylenes in this structure TF-ould absorb. Furthermore, acenaphthylenes in major concentrations can be excluded because of the absence of the sharp absorption band a t 3.2 T , which is characteristic of the olefinic hydrogens in acenaphthylene. Acenaphthylenes would also not 0 FI
OH MW: 110
0
H
m++0
MW: 286
Experiments carried out in our laboratories confirmed that this type of reaction is possible with 9,lO-dihydroanthracene and not with 9,lO-dihydrophenanthrene. The reactions carried out on fractions B-11, -13, -15, and -17 resulted in the formation of adduct products of molecular weight 302, 314, and 316 and of hydroquinone (this latter in practically theoretical yield). Furthermore, the compound types in the -16 series decreased by 32.1%. The adduct of molecular weight 314 is that eupected for the c16 dihydroanthracenes present in our fractions, but those of molecular weight 302 and 316 could derive from Cli and c16 dihydroanthracenes only by further hydrogenation. While this latter point is still under investigation, it is believed that the forination of adducts and hydroquinone by themselves furnish evidence that 9,lO-dihj-droanthracenes are present a t least in the amounts indicated by the decrease in concentration observed for the compound t j pes in the -16 series. TI PE 2. The second compound type in the CnH2,1--1Bseries occurring in appreciable concentrations in fractions B-36 to -44 is shown by AIS to be a hydrocarbon. Its nucleus must have a CH, group cyz to aromatic rings to account for an absorption between 6.4 and 6.7 T in the YAIR spectra of these fractions. The diacenaphthene type
account for the observed bands in the 6.4- to 6.7-T region. Two structural types in the C,,Hn,-16 series may be proposed which have a CH, group cyz to aromatic rings-namely,
Fluorene
1d
9,lO-Dihgdroanthracene From the AIS analysis (see Table I) the intensities of the bands in the X N R spectrum niay be calculated, assuming that the C,,H2,-lc series is a fluorene type or a dihydroanthracene type. These calculations n-we made for fraction K-42, aswniing 110 substitution on the niethylene groups, and t'hat the bands between 8.3 and 9.2 T are given by CH, groups substituted on the methylene group of tlie nucleus. The results of these calculations are given in Table 11. The error limits of the intensity nieasureinents quoted above are the standard deyiations from five consecutive rune. The agreement of the calculated intensities n-ith the experimental intensities is niuch better for fluorenes than for dihydroanthracenes. This confirms the conclusions obtained by ultraviolet (see below) that fluorene is the second coinpound type in the CnH2n--16 series. I n Figure 8 the ultraviolet absorption spectrum of E-42 is compared with
Table
II.
2.0-3.0 6.4-6.7 7.2-8.0 5.3-9.2
T
Calculated and Experimentally Determined NMR Band Intensities for Second Compound Type in C,,Hz,-la
Band (aromatic H )
T
(CH2 a* t o Ar) (CH3 a to Ar)
7
(CHIp * to Ar)
T
Calculated intensities for fluorenes Assuming no substituAssuming subtion on 9 stitution on C atom 9 C atom 4.5 53.6 10.2 6.4
Calculated intensities for dihydroanthracenes Assuming no Assuming substitution on substitution 9 and 10 on 9 and 10 C atoms C atoms 54.4 55.3 18.5 15.0
Series
Experimental intensities, areas 45.3 & 2.870 7.5 zt 2 . 3 7 0
I
141.0
26.7
s j ntlietic mixtures of methylfluorenes
and methylphenanthrenes. One of these mixtures consists of 2-methylfluorene and 1-methylphenanthrene, while the other consists of trimethylfluorenes and methj lphenanthrenes isolated from a n analogow petroleum fraction. The close agreement between the above spectra at the shorter wavelengths substantiates the structural assignment of fluorene to the second compound type in the -16 series. The lack of similarity a t the longer wavelengths is due t o anthracenes in Our Percolation frattions. The synthetic mixtures are devoid of anthracenes. An examination of the ultraviolet spectra of the synthetic mixtures of Figure 8 re1 eals that the alkylfluorene absorption band at ea. 303 mp is cornpletely resolved from the absorption band of methylphenanthrenes at ea. 298 mp. Accordingly, aromatic nuclei belonging to the CnHPn--iG series, havinga NLIR band characteristic of CH2groups a2 to aromatic rings, and having a n ultraviolet absorption maximum a t ea. 303 mp are identified as fluorenes. MS and CV data on some fractions containing compound types satisfying these criteria and ultraviolet data on the sjnthetic mixtures are given in Table 111. Qualitatively, the agreement between percolation fractions is excellent, for those mivtures containing the largest __
Table 111.
MS Compositional and Ultraviolet Absorption Data on Percolation Fractions and Two Synthetic Mixtures
Fraction B-41 B-42 B-43 B-44 Mixture A b Mixture Bd
MS composition, vol. Yoa C,Hz,C,H2,Others 40 52 8 65 30 5 67 31 2 56 41 3 60 6c 39 4 ... 62 7c 37 3
K303
K 3 0 4
K805
15.3
20 1 21 1 15 8
31.4
44.5
I* * See Synthetic mixture
of API trimethylfluorenes and methylphenanthrenes. Keither mixture anal zed by pvIS, Synthetic mixture 0!2-methylfluorene and 1-methylphenanthrene.
concentrations of fluorenes (C,Hz,-16) also have the highest absorption maxima at ea. 303 mp. The lack of quantitative agreement between the absorbance in the 303- to 305-mp region and the alkyl fluorene concentrations as determined by LIS in the synthetic mixtures and the percolation fractions can be attributed to MS concentration errors due t o the assumptions in sensitivity values and/or differences in the methyl substituent positions between the fluorenes in the mixtures and those contained in the percolation fractions. Probably both effects contribute to the discrepancy. MS data indicate that the majority of the alkyl fluorenes in B-42 and B-43 contain two methyl groups per molecule
-
~~~~
-B 42 _____ MIXTURE A
-9
P P I SAMPLES ( 3 9 4 % Melhylphenanthrenes, 60 6 % TrimetnylfluarenesT MIXTURE B (37 3 % 1 Methylphenanthrene, 62 7 % 2 Methylfluorenej7
--_
-
- 5 -5 -
&
s
I
x
-3
23
WAVELENGTH IVILLIMICRGNS)
Figure 8.
Maximum UV absorption
Ultraviolet spectra of cut 8-42 and synthetic mixtures A and
B
and combined data from both NMR and infrared suggest that substantial concentrations of the fluorenes contain one methyl group per aromatic ring. However, some methyl on the 9 carbon atom is proposed to account for an NMR absorption band above 8.3 r. Intensity of the aromatic CHI absorption to that of the 8.3- t o 9.2-7 band in B-42 indicates that the ratio of aromatic methyls t o nonaromatic methyls is of the order of 3 to 1. Three peaks observed at 6.4, 6.55, and 6.7 r in B-41 and in some of the other fractions are believed to be caused by the effect of substitution in the 1 and 8 positions. Because of the magnetic anisotropy of the C-C bond, an upfield shift of the 9hydrogens would be expected if a 1- or 8-hydrogen were replaced by a methyl group. We suggest that the band a t 6.4 7 is given by a CH2 group with no substituents a t the 1 and 8 positions, the 6.55-7 band is git en by a CH2 group with a substituent at either the 1 or 8 positions but not both, and the 6.7-r band is given by a CH2 group with substituents a t both the 1 and 8 positions. The proposals, although partly substantiated by infrared, are admittedly speculative. C,Hz,-18. A major compound type, phenanthrenes, predominates in this series from fractions B-20 t o B-41. Essentially only one carbon number, C15,is present (methylphenanthrenes) . The proof of this structure is evident both from the lor? voltage and high voltage mass spectral data (see Figure 9). As expected, the main fragment VOL. 34, NO. 13, DECEMBER 1962
1819
Table IV.
Methylanthracene Concentration of Fractions
(Determined by UV absorption measurements at 377 mp) K377, 1 , ~ ~Methylanthracene, . 70 Fraction cm. UV MS B-36 B-41 B-42 B-43 B-44
,
I
5
'0
I
I5
O
20
Figure 9.
I
25
I
I
1
3 0 35 CUT NUVEER
Percolation B,
I
I '
I
4 0 4142 4 4 43
CnH2,-l*
series
Low voltage parent and high voltage fragment peaks
peak coinciding with the low voltage parent region is m/e 191. I n Figure 10 comparisons are made of the ultraviolet spectra of fractions B-36, B-44, and a mixture of isomeric methylphenanthrenes obtained from the API. Even though sample B-36 contains only ca. 59% of methyl phenanthrenes, the agreement between its spectrum and that of the API sample is excellent. The differences in the spectra, not discussed in detail in this paper, are almost certainly due t o concentration effects and to the presence of other compound types in B-36 (see Table I). The appearance of absorption bands in the XMR spectra of fractions B-20 to -44 between 1.4 and 2.00 r confirms that the first compound type in the C,H2,-1~ series consists of phenanthrenes, This absorption arises from the angular hydrogens-i.e., the 4 and 5 hydrogens in the structure
-4second compound type appears in the last cuts, as is evident from an increase in slope of both the parent and fragment peak curves a t B-43 in Figure 9. A gradual increase in the concentration of this second compound type, identified as anthracenes by ultraviolet, is noted as the phenanthrene concentration decreases in cuts proceeding from B-41 t o B-44. The fragmentation ion intensity a t m / e 177 increases in these same fractions. As shown in the spectrum of B-44 Figure 10, the ultraviolet identification of anthracenes is based on the appearance of two maxima and a minimum appearing a t 357,377, and 365 mp, respectively, which are characteristic of the anthracene nucleus. As the main constituents of B-44, phenanthrenes and fluorenes, are essentially nonabsorbing a t 377 mp, the absorption maximum in this
-
Y
1820
0
ANALYTICAL CHEMISTRY
13.6
region was used to calculate the anthracene concentration. For this purpose a sensitivity of Kaii = 43.5 liters per gram cm. was used. The value was arrived at by applying a molecular Feight correction to the gram absorptivity value of anthracene, K3i7 = 47 liters per gramem. This assumption was made on the premise that only two of the three possible isomeric methylanthracenes are present in B-44, as 9-methylanthracene was excluded because of the absence of its characteristic absorption band at ea. 386 mp. The calculated concentrations are listed in Table IT, together with one AIS value based on a semiquantitative extrapolation from Figure 9. Qualitatively these results are in agreement with the AIS data and confirm the presence of anthracenes as a minor constituent of the CnH2n-18 series. CONCLUSIONS
The investigation discussed has led t o a radical change in our ideas of the nature of certain compound types in light catalytic cycle stocks. iilthough the preliminary conclusions are ob'5
__ 8-36 .......
6-44
' I I
10
Five possible isomeric methylphenanthrenes exist; the substituent positions are 1, 2, 3, 4, and 9. The relative intensity of the 1.4- to 2.0-7 band indicates that there is little, if any, substitution in the 4 position and comparison of the infrared spectrum n7ith that of 9-methylphenanthrene eliminates this isomer as a constituent. The presence of a narrow, relatively intense NMR band a t 1.8 r in the characteristic angular hydrogen region suggests that some of the phenanthrenes are substituted in the 3 position. Qualitative infrared data indicate that the fractions also contain substantial concentrations of I- and/or 2-methylphenanthrenes.
1.0 3.7 5.0 7.3 12.7
1
@@ 8
0.44 1.60 2.16 3.20 5.55
MIXTURE OF PPI METhYLPHEP-lANTHREhES
--13
-
-.----_ 1 .A1 210 230 250 270 290 310 330 350 370 390 WAVELENGTH IMILLIMICRONSI ~
Figure 10.
Ultraviolet spectra of cuts 6-36, 6-44, and API methylphenanthrenes in iso-octane
viously restricted t o the narrow boiling distillate under examination, at least an insight into the complexity of this petroleum product has been gained. The work already done is only the first step toward the characterization of light catalytic cycle stocks. The data obtained on this narrow fraction have to be extended, and fractions containing other interesting compound types, such as indanes and Tetralins, indenes and dihydronaphthalenes, etc., must also be investigated. Since mass spectrometry is the only conceivable tool for the routine detailed analysis of the complex gamut of compounds present in light catalytic cycle stocks, the high voltage and low voltage calibration data at present available must be improved and extended, so that definitive procedures for analysis may be developed.
(4) Chamberlain, N. F., ASAL. CHEM.
ACKNOWLEDGMENT
The authors thank D. J. Krisher, J. L. Taylor, G. R.Taylor, R. K. Saunders, T. J. Denson, The0 Hines, and H. W. Kinsey for their valuable contributions to experimental phases of this work and N.F. Chamberlain for discussion of the SAIR interpretations. They thank B. J. AIair, XPI Research Project 6, for donating synthetic mixtures of methylfluorenes and methylphenanthrenes. LITERATURE CITED
(1) Aczel, Thomas, Bartz, K. W,, Lumpkin, H. E., Stehling, F. C., ASAL. CHEU. 34, 1821 (1962). ( 2 ) Braude, E. 8., Jackman, L. M.,Linstead, R. P., J . Chern. SOC.1954, 3568. Linstead, R. P., Ibid., (3) Braude, E. 8., 1954,3544.
31,56 (1959). ( 5 ) Claesson, S., d r k i v Kemi, Xineral, Geol. 23A. S o . 1119461. (6) Hastings, S. H., Johnson, B. H., Lumpkin, H. E., ASAL. CHEM.28, 1243 (1956). ( 7 ) Hibbard, R. R., Ind. Eng. Chem. 41,197 (1949). ( 8 ) Hirschler, A. E., Amon, S., Ibid., 39,1585 (194i). ( 9 ) Lipkin, 11. R., Hoffecker, W. A., Martin, C. C., Ledley, R. E., ANAL. CHEM.20, 130 (1948). ( I O ) Lumpkin, H. E., Johnson, B. H., Ibzd.. 26. 1719 11954). (11) &iair,'B. J.,'Forziati, A. F., J . Res. .\-atl. Bur. Std., 32, 165 (1944). (12) Morrison, D. C., J . Org. Chem. 25, 1665 (1960). (13) Tiers. G. V.. J . Phus. Chem. 62.
RECEIVEDfor review July 23, 1962. Accepted October 8, 1962. Division of Petroleum Chemistry, 141st Meeting ACS, Washington, D. C., March 1962.
Characterization of Aromatics in Light Catalytic Cycle Stock by Spectrometric Techniques Compound Types of the General Formula THOMAS ACZEL,
K. W.
BARTZ, H.
E. LUMPKIN,
Research and Development, Humble Oil & Refining
,This paper describes the identification of aromatic compound types in a narrow fraction of a light catalytic cycle stock. Particular emphasis is given to the part of the investigation concerned with the analysis of compounds in the CnH2n--14series. The data obtained indicate that these compounds are naphthenonaphthalenes, such as tetrahydroanthracenes, tetrahydrophenanthrenes, and benzindanes, and the corresponding ketones. Analytical evidence in support of the conclusions reported is discussed in detail. The investigation was carried out on sharp chromatographic fractions obtained b y alumina gel percolation of the aromatic portion of a narrow distillate (622' to 625' F.). Individual fractions were examined mainly by mass spectrometry, but ultraviolet, nuclear magnetic resonance, infrared, and catalytic microdehydrogenation techniques were also employed.
x EXTEXSIVE program has been recently carried out in our laboratories for the characterization of the major aromatic components in light
CnH2,,--12
and
CnH2,,--14
and F. C. STEHLING
Co., Baytown,
Tex.
catalytic cycle stocks. The experimental details on the separation and analytical techniques used in this lvork, as well as our findings concerning the nature of the compound types in the C,HZn- 16 and C,H?,-18 series, have been described in detail (1). I n brief, the former consisted of an initial separation on alumina gel and repercolation of the cuts which appeared to be of interest on the same medium. Feed for the repercolation, heretofore referred t o as Percolation A, consisted of cuts 10, 11, 12, and 13 obtained in the first step. Feed for Percolation B consisted of cuts 14, 16, 17, and 18. The two percolations can be considered therefore as contiguous. I n fact, they are slightly overlapping, as noticeable in Figure 1. This paper deals with the identification of the other major compound types present in the narrow distillate fraction analyzed. For convenience, these are referred to as belonging t o the C,H2,-12 and C,H2,-14 series, although some of them, of identical molecular weights, contain heteroatoms such as sulfur and oxygen.
DISCUSSION
C,H2,-1?Series. As expected, this series consists of two compound types, naphthalenes a n d dibenzothiophenes (6). The bimodal distribution of the parent peak intensities, plotted against cumulative weight per cent of the chromatographic fractions, in the - 12 series is shown in both Figures 1 and 2. The separation between the Cl5 naphthalenes and the c13 dibenzothiophenes of the same molecular weight is particularly evident in Figure 2, as well as the carbon number separation, in order of decreasing molecular weight, achieved for the naphthalenes in Percolation A. These identifications are substantiated by the data shown in Figure 3, in which the characteristic fragment peaks are plotted. Fragment peaks characteristic of alkylnaphthalenes are predominant in Percolation A, coinciding with the first maximum in the parent peak plot, while the intense peak a t m/e 1 9 i , attributed t o dibenzothiophenes, coincides with the maximum in Percolation B. The presence of a compound of molecular formula CI3HlaSis proved also by VOL. 34, NO. 13, DECEMBER 1962
1821
