(33) St. C. Flett, M:,
“Characteristic Frequencies of Chemical Groups in the Infra-Red,” p. 33, Elsevier, New York,
1963. (34) Stevenson, D. P., McConnell, H. M., Spectrochim. Acta 12, 262 (1958). (35) van Krevelen, D. W., Chermin, H. A. G., Fuel 33, 338 (1954). (36) Wagner, R. H. in “Physical Methods
of Organic Chemistry,” A. Weissberger, ed., p. 547, Vol. I, Part 1, Interscience, New York, 1949. (37) Waterman, H. I., ‘Correlation be-
tween Physical Constants and Chemical Structure,” pp. 3-26, Elsevier, New York, 1958. (38) Williams, R. B., Spectrochim. Acta 14, 24 (1959). (39) Williams, R. B., Chamberlain, N. F., World Petrol. Congr., 6th PTOC.,Frankfurt, West Germany 5 , 217 (1963). (40) Winniford, R. S., Bersohn, M., Di-
vision of Fuel Chemistry, Am. Chem. Soc., Preprints, Vol. 1, p. 21, Atlantic City, 1962.
(41) Yen, T. F., Erdman, J. G., Division
of Petroleum Chemistry, Am. Chem. SOC.,Pre rints, Vol. 7, No. 3, p. 99, Atlantic &y, 1962. (42) Young, C. W., DuVall, R. B., Wright, N., ANAL.CHEM.23, 709 (1951). RECEIVEDfor review June 28, 1965. Accepted November 22, 1965. Work supported by a Petroleum Research Fund Grant (No. 591-AI) to R. N.
Traxler.
Isolation and Identification of to C,, AI kylna phthalenes, AI kylbiphenyls, and Alkyldibenzofurans from the 275” to 305” C. DinucIear Aromatic Fraction of Petroleum c 1 3
FOCH FU-HSIE YEW and BEVERIDGE J. MAlR Petroleum Research laboratory, Carnegie Institute of Technology, Pittsburgh 7 3, Pa. A substantially complete analysis in terms of the amounts of the individual components in the dinuclear aromatic portion of petroleum boiling in the range from 275’ to 305’ C. was achieved. Twenty-nine compounds were isolated or identified. These include eight C13 alkylnaphthalenes, seven CI4 alkylnaphthalenes, five C14 alkylbiphenyls, four C,a alkylbiphenyls, four dibenzofurans, and fluorene. Methods were developed for identifying individual alkylnaphthalenes from their NMR spectra in those cases where synthetic samples and reference spectra were not available.
P
-
E 0 m
(5 0
In (u
169-
c 0
.-0
0.
e
c
0
z“
-
X
0 ‘0
5 al
.-> c
- 1.59:
0
0)
D
the API Research Project 6 has concentrated its efforts on investigating the composition of the aromatic portion in the gas oil range of its reference petroleum. Preceding investigations have covered the trinuclear aromatic fractions of the heavy gas oil and light lubricating distillate, 305’ to 405’ c. (12) ; the mononuclear aromatic material in the light gas oil range, low refractive index portion, 230’ to 305’ C. (10) ; and the dinuclear aromatics in the light gas oil r~+nge,230’ to 275’ C. (11). The present research continues the program on the dinuclear aromatics in the light gas oil range, 275’ to 305’ C. Analysis in terms of the amounts of the individual compounds was substantially complete. Some compounds within this range have not yet been synthesized; therefore, their physical and spectrometric propURING THE PAST FEW YEARS,
Volume in l i t e r s Figure 1.
Results of the azeotropic distillation of Portion 5A
Numbers near the bottom of the figure indicate parts which were investigated additionally
erties are not available. For this reason, it became necessary to develop spectrometric methods of identification from basic principles and a knowledge of the spectra of model compounds; these methods are applicable to other similar problems. PROCEDURE
The method used to separate the dinuclear aromatic material from the light gas oil fraction of petroleum and the results of the subsequent distillation have been described previously (11). Portions 5 and 6 of the distillate, illus-
trated in Figures 1 and 2 of Reference (11) constituted the starting material for this investigation. Some of the distillate fractions near the middle of Portion 5 contained crystalline material which was subsequently identified as 2,3,&trimethylnaphthalene. After the removal of most of this compound by crystallization, the mother liquors, designated Portion 5 4 were azeotropi d l y distilled with dimethoxytetraethylene glycol. Portion 6 was azeotropically distilled with triethylene glycol. Results are given in Figures 1 and 2. The numbers at the bottom of each figure indicate the portions of the distillate which were investigated in detail. VOL. 38, NO. 2, FEBRUARY 1966
231
The steps in the investigation were as follows: 1. Examination of a number of fractions across the whole distillate range by analytical gas-liquid chromatography (GLC) and low voltage mass spectrometry. 2. Separation of selected distillate fractions, as completely as possible, by preparative scale gas-liquid chromatography into smaller fractions containing one or more individual compounds. 3. Separation of solid GLC fractions from Operation 2 by crystallization a t different temperatures and in various solvents, where this was feasible, to give individual compounds or pairs of compounds. 4. Fractionation of the noncrystalline material from Operations 2 and 3 by crystallization of the molecular complexes formed with 1,3,5-trinitrobenzene or 2,4,7-trinitrofluorenone. Hydrocarbons were recovered by decomposing the complexes on basic alumina. 5. Products from Operation 4 were reprocessed with Operation 3. 6. Examination of products from Operations 2, 3, 4,and 5 by mass, infrared, ultraviolet, and nuclear magnetic resonance spectrometry to identify and determine the amounts of the individual compounds. The equipment and procedures used for the gas-liquid chromatographic separations and analyses and for the spectrometric examinations were essentially those described previously (11). A few differences may be noted. For the preparative scale separations with a Beckman Alegachrom, silicone nitrile was used as the partitioning liquid a t 275' C. for fractions from Portion 5.4, and m - bis [m - (m - phenoxyphenoxy) phenoxylbenzene as the partitioning liquid a t 290'-300' C. for fractions from Portion 6. The same two liquids were used in 500-foot capillary columns, 0.02 inch in diameter, a t 190' C. for the analytical experiments. FORMATION OF MOLECULAR COMPLEXES
The formation and crystallization of the molecular complexes which aromatic hydrocarbons form with certain aromatic nitro compounds proved to be an effective separation technique. The relative abilities of the three nitro compounds used in this investigation to enter into complex formation are in the
Table 1.
Type a,2p
2 4
232
E E 0 (0
180.0;
.-0d 170.0: 0
al
N
5 160.02 .0
a 150.0 CI,
.-C 0
l
.
0
5
0.I
Figure 2.
9
0.2 0.3 Volume in l i t e r s
I
IDENTIFICATION OF ALKYLNAPHTHALENES
Some of the aromatic hydrocarbons isolated from this portion have not been synthesized. Their identification therefore depends largely on an interpretation of NMR spectra. Two features of the NMR spectrum may be used to establish the identity of an unknown polymethylnaphthalene. These are (a) the chemical shifts of the methyl protons, and (b) the structure of the aromatic proton portion of the spectrum. The chemical shifts of the methyl protons may be calculated with the aid of an empirical equation
847)
6i3( 7 )
Position Measured Calculated Position Measured Calculated 1
7.40
7.42
1,3,7-
1
7.42
7.42
1,2,6-
1
7.49
7.47
1 5
ANALYTICAL CHEMISTRY
7.48 7.39
0.5
m -140.0
Results of the azeotropic distillation of Portion 6
order : 2,4,7-trinitrofluorenone > 1,3,5trinitrobenzene > picric acid. Usually 2,4,7-trinitrofluorenone and 1,3,5trinitrobenzene form crystalline complexes with the C13to C14alkylnaphthalenes but not with the biphenyls. This provides a method for separating these two classes. 2,4,7-Trinitrofluorenone was used for this operation since its complexing power is sufficiently strong to make it possible t o strip out nearly all the alkylnaphthalenes from the biphenyls. On the other hand, its complexing ability is so great that alkylnaphthalene isomers can scarcely be differentiated and, for this purpose, 1,3,5-trinitrobenzene is preferred.
1,3,6-
1,2,5-
0.4
A
Numbers have the same signitlcance as for Figure 1
Measured and Calculated Values for Chemical Shifts of Methyl Protons for Four Trimethylnaphthalenes
Compound
~
7.47 7.38
3 6 3 7 2 0
7.59 7.50 7.59 -.
2
7.58
- .54 I
.
7.54 7.63
developed by Yew, Kurland, and &lair (16). A comparison of the observed chemical shifts with those calculated can frequently serve to identify the unknown compound. However, there are cases where the chemical shifts for two or more isomers do not differ sufficiently to permit positive identification. This is illustrated in Table I ; the calculated shifts for 1,3,6- and l13,7-trimethylnaphthalene are identical. In such cases it is necessary to consider the aromatic proton portion of the spectrum. Pople, Schneider, and Bernstein (14) analyzed the NMR spectrum of naphthalene as two superimposed .4*B2 spin systems, by neglecting the spin coupling between protons in different rings. The coupling constants measured in a 40 mc./second magnetic field are J1.2 = 8.6 c./second, J1,3 = 1.4 c./second, J ~= J 6.0 c./second, and J I , = ~, 0.0 c./ second. The chemical shift difference between LY and p protons is 14.3 c./ second. MacLean and Mackor analyzed NMR soectra of svmmetrical dimethvlnaDhthalenes (8)." They found that chemical shifts of aromatic protons are increased by methyl substitution and decreased by steric hindrance (as with the 5,8protons in 1,4-dimethylnaphthalene). These authors also found t h a t the coupling constants for ring protons do not change appreciably with substitution. Because of their importance in interpreting the spectra of other alkylnaphthalenes, the aromatic proton spectra of the symmetrical dimethylnaphthalenes are discussed. Four of these are shown in Figure 3. For 2,6and 2,7-dimethylnnphthalene the spectra consist of AB spin quadruplet lines and a single X absorption peak. The small spin coupling between protons I3 and X broadens the signals of I3 and X. The chemical shift of the A protons in 2,6dimethylnaphthalene is found to be 7.5 c./second higher than
a
,7:d im et h $1 n (1pht hblen e
6-’dim et hyl-n o ph t hbl en e ‘
b
Table II. Chemical Shifts of Methyl Protons of Alkylbiphenyls Posi- Chemical
Compound tion 3-Methyl 3 2-Methyl 2 2.2’.4.4’-Tetramethvla 2.2’
shift (tau) 7.61 7.76 7.97 7.62
414’
2 I
l
I
.
C
5-dimeth;lnaphthalene
I
I
0
From Reference ( 6 ) .
d
3 l d i m e t hylnaphihalene
C(X) cli3
I
I
I
I
2 Chemical s h i f t (T)
2
spectra contributed by the protons on each ring separately. If substituents are present in any of the 2,2’,6,6’ positions the rings are no longer coplanar, and the chemical shift differences between the A, B, and C protons are reduced giving rise to relatively narrow aromatic absorption bands. This is one method for recognizing substitution in these positions. This type of substitution may also be recognized from the high chemical shift of methyl protons in these positions (Table 11). The UV and I R spectra of methylbiphenyls have been systematically studied by Beaven and Johnson ( 2 ) . For an unknoivn compound, the UV spectrum is effective in differentiating ortho(2,2’,6,6’)-substituted biphenyls and nonorthosubstituted ones, and I R spectrum gives decisive structural information. I n the present investigation, combined information from UV, IR, and NMR spectra was used for identification of the individual compounds.
3
3
Figure 3. Aromatic absorption band of the nuclear magnetic resonance spectra of a. b.
2,7-Dirnethylnaphthalene 2,6-Dirnethylnaphthalene
C.
1,5-Dimethylnaphtha!ene
d. 2,3-Dirnethylnaphthalene
that in 2,7-dimethylnaphthalene. For this reason in the spectrum of 2,6dimethylnaphthalene, one of the quadruplet peaks contributed by the A protons is superimposed on the peak of the X protons. This difference may be used to identify 2,6- and 2,7-disubst itu ted alkylnaphthalenes, The spectra of l,5- and lJ8-dimethylnaphthalene have been analyzed by MacLean and Mackor as AI3C and ABX spin systems. Three sharp signals between 2.7 and 3.0 tau characterize this type of compound. The spectra of 2,3-and 1,4-dimethylnaphthalene contain a naphthalene resonance spectrum contributed by the protons on the unsubstituted ring plus a single sharp absorption peak contributed by the two equivalent protons on the substituted ring. I n as much as spin coupling between protons on different rings can be neglected, the spectrum of an unsymmetrical alkylnaphthalene may be interpreted as the superposition of t!vo spectra corresponding to different rings. With 2,3,6-trimethylnaphthalene (Figure 4), the aromatic proton portion of the spectrum consists of a band similar to that of 2,6- or 2,7-dimethylnaphthalene and a strong absorption signal contributed by equivalent 1- and 4-prOtOn5, as in 2,3-dimethylnaphthalene. Following this method of analysis, the aromatic proton pattern for any tri- or tetramethylnaphthalene can be predicted and used for identification. Since coupling constants do not change appreciably with substitution, similar aromatic absorption spectra should be expected from naphthalenes with alkyl substituents other than methyl groups. This fact made the identification of 2-methyl-6-isopropylnaphthalene, 2 -methyl - 6 - n - propylnaphthalene, and 1 - ethyl - 3,7 - dimethylnaphthalene possible by com-
paring their aromatic proton spectra with that of the corresponding 2 , 6 dimethylnaphthalene and 1,3,7 - trimethylnaphthalene. IDENTIFICATION OF ALKYLBIPHENYLS
Biphenyl shows an absorption band typical of an ABpCzspin-spin system a t 2.4 to 3.1 tau. I n biphenyl the coplanar configuration of the benzene rings brings about appreciable chemical shift differences between the A, B, and C protons, that is, those in the C-4, C-3, and C-2 positions. For those alkylbiphenyls without substituents in the 2,2‘,6,6‘ positions the rings are essentially coplanar, and the analysis is, in principle, similar to that of the alkylnaphthalenes, that is, the whole aroniatic proton band can be regarded as a superposition of two aromatic proton
IDENTIFICATION OF DIBENZOFURANS
Dibenzofurans with empirical formula, C,H2,-160, have the same nominal mass numbers as the alkylAs noted by biphenyls, C,H2,-14. previous investigators, methyl substituents have little effect on the ultraviolet absorption spectrum of dibenaofuran ( I S ) . Figure 5 gives the ultraviolet spectrum of a sample of 4,6dimethyldibenzofuran isolated in this investigation. The absorption bands between 240 and 300 mG are characteris-
1
I
2
T
c
I
I
3
4
I
I
I
I
5 6 7 8 C H E M I C A L S H I F T (T)
I
I
9
IO
Figure 4. Nuclear magnetic resonance spectrum of 2,3,6-trimethylnaphthalene from petroleum VOL. 38, NO. 2, FEBRUARY 1966
8
233
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
Part 3
Part 4
0
I.(
0.: Figure 6.
Gas-liquid chromatogram of Portion 5A, Parts 3 and
4
C I
2 0
l
l
t
l
l
l
l
l
l
l
l
2 50 300 Wavelength (my)
Figure 5. Ultraviolet spectrum of 4,6-dimethyldibenzofuran from petroleum
tic of dibenzofurans and easily differentiates them from alkylbiphenyls. Three chemical shift values, 7.51, 7.40, and 7.25 tau, for the methyl protons were found in the four methyldibenzofurans isolated in this investigation. From the geometry of the molecule these are attributable to methyl groups a t the 2- or 3-, 4- and 1- positions, respectively.
Volume i n l i t e r s
Figure 7. Results of gas-liquid Portion 5A
chromatographic analysis of
letters refer to the GLC peaks described in the text EXAMPLE OF ISOLATION AND IDENTIFICATION
Analytical gas-liquid chromatograms (500-foot capillary column with silicone nitrile) with material from Parts 3 and 4 (Figure 1) of the distillate from Portion 5A are given in Figure 6. The peaks do not necessarily represent individual compounds, for example, Peak B contains 1,3,6- and 1,3,7-trimethylnaphthalene. The manner in which the area of a peak or group of peaks varies throughout the range of distillate is shown in Figure 7. As an example of the procedures involved, the isolation of the components of the Group F material is described. The primary separation of Group F material was performed by preparative scale gas-liquid chromatography with m-bis [m-(m-phenoxyphenoxy)phenoxy 1benzene as the stationary phase. Figure 8 shows a representative chromatogram; letters indicate material collected separately. F-a. This material contained one major compound with empirical formula C17Hm. The NMR spectrum showed that the compound was a pentamethyl234
ANALYTICAL CHEMISTRY
I
l
i
l
l
l
l
l
l
l
A
'Q) v)
Figure 8. Gasliquid chromatogram of the preparative-scale separation of Group F from Portion 5A Letters refer to the products described in the text
C
0
a v)
Q)
a L
Q)
-2 0 u
Q)
E
I I
\
~
I
'I \ i I
~
l
l
~
'
'
~
'
'
biphenyl; absorption peaks a t 8.13 and 8.17 tau indicated methyl groups substituted at 2,2',6 positions, while signals at 7.70 and 7.75 tau were given by two methyl groups a t other positions. F-b. Solid material was obtained by crystallization from absolute alcohol at -20' C. and -80" C. The NhIR spectrum showed that the compound was a dimethylethylnaphthalene : Peaks a t 7.52 and 7.57 tau showed that both methyl groups were attached to @-positions. The presence of an ethyl group was obvious. The aromatic proton absorption band resembled that of I ,3,7-trimethylnaphthalene showing that the compound was 1-ethyl-3,7dimethylnaphthalene. The mother liquor was fractioned by molecular complex formation with 1,3,5-trinitrobenzene. The XhlR spectrum of the material regenerated from the crystalline complex indicated the presence of l-methyl-6(or 7)-isopropylnaphthalene. The NMR spectrum of the material which did not form a crystalline complex with 1,3,5-trinitrobenzene showed that the major component was 3-ethylbiphenyl. F-c. 2 - blethyl - 6 - n - propylnaphthalene was isolated from this portion by crystallization from alcohol a t -80' C. The compound was identified from its NMR spectrum. The presence of methyl and n-propyl substituents was obvious. The aromatic absorption band and that of 2,6-dimethylnaphthalene were identical. This established the positions of the substituent groups. The mother liquor was further processed by molecular complex formation with 1,3,5 - tiinitrobenzene and 2,4,7 - trinitrofluorenone to remove the remaining alkylnaphthalener. The material left was found to be principally 3,3'-dimethylbiphenyl by comparing its X N R spectrum nith that of a synthetic sample, and it5 IR spectrum with that given in the API Catalog for this compound (1).
0
2
nHzn.14
0
1 2
3 4 5
6 7 8 9
10 11
12 13 14 15
16 17 18
in l i t e r s
Figure 9. Results of the mass spectrometric analyses of distillate fractions from Portion 5A Distribution by compound type and carbon number is indicated
F-d. Material was found LO be similar to that of G r o w E (Figure 7 ) . F-e. The major Component was a trimethylnaphthalene. The KA'R 'pectrum showed that the has two a-methyl groups (chemical shifts a t 7.39 and 7.48 tau) and one flmethyl group (chemical shift 7.57 tau) ; the aromatic absorption band showed a n ABC spin-spin split structure similar to that given by 1,j-dimethylnaphthalene (Figure 3 ~ ) . This established the identity as 1,2,5-trimethylnaphthalene. RESULTS
The results of the mass spectrometric analyses of selected distillate fractions from Portions 5=\. and 6, plotted as coni-
Table 111.
No.
Volume
pound type with respect to volume of distillate are shown in Figures 9 and 10, respectively. The distribution with respect to carbon number is also given. Because the dibenzofurans have the same n o m i d mass numbers as the alkYlbiPhenYls the alnount Of this series was determined by activation analysis for oxygen content. The results of the analyses of Portions 5 and 6 are given in Tables I11 and IV. The amounts of the individual cornponents and the incompletely identified mixtures were determined by measuring the areas under each peak from the analytical chromatographic experiments. These are approximately proportional to the volume percentages of
Compounds Isolated from Portion 5"
Est. b.p. at 7,60 mm., C. Name 280 1,3,6-Trimethylnaphthalene 280 1,3,7-Trimethylnaphthalene 283 1,3,5-Trimethylnaphthalene 283 1,4,6-Trimethylnaphthalene 285 2,3,6-Trimethylnaphthalene* 285 lJ6,7-Trimethylnapht halene 286 1,2,6-Trimethylnaphthalene 286 1,2,5-Trimethylnaphthalene 286 2-Met hyl-6-isoprop ylnaphthalene 286 2-Methyl-6-n-prop ylnaphthalene 286 l-Ethyl-3,7-dimethylnaphthalene 286 1-Methyl-6 or 7-isopropylnaphthalene 287 3-Et hylbiphenyl 288 3,3'-Dimethylbiphenyl
