Nitrogen and Oxygen Compound Types in Petroleum Total Analysis of a 400-700
O F
Distillate from a California Crude Oil
L. R. Snyder Union Oil Company of California, Research Dcpartment, P.O. Box 76,Brea, Gal$ 92621 The oxygen and nitrogen compound types present in the 400-700 O F fraction of a California crude oil were analyzed by means of a standard separation scheme, high resolution mass spectrometry, and other techniques. All compound types present in other than trace amounts were accounted for; their molecular structures were determined and their concentrations were measured. Major compound types (>0.05% w) included the indoles, carbazoles, pyridines, quinolines, pyridones, quinolones, dibenzofuranes, dihydrobenzofuranes (coumarans), phenols, aliphatic esters and ketones, sulfoxides, and carboxylic acids. Lesser amounts of other compound types were also found. A new technique for removing sulfides from heterocompound concentrates was developed: chromatography on mercuric-ion impregnated ion exchange resin. The present study confirms and extends a preceding analysis of the 700-850 O F fraction from this same crude oil.
A PRECEDING paper ( I ) has described the development of a general separation scheme for the analysis of the nitrogen and oxygen compound types (heterocompounds) in petroleum. Application of this procedure to a 700-850 O F fraction from a California crude oil resulted in a complete, detailed analysis of the heterocompound types in that sample (2). A similar analysis of the heterocompound types in the 400700 O F fraction from this same California crude oil is reported here. The original separation scheme has been further improved, mainly by development of a procedure to remove sulfides from heterocompound concentrates. Minor changes were also made in the way separated fractions were analyzed. The present study largely confirms the accuracy of the preceding analysis of the 700-850 O F distillate, although some small changes in interpretation of the data of (2) are suggested. Further details on the molecular structure of individual heterocompound types in these samples (400-850 OF distillates) have been uncovered. EXPERIMENTAL
Separation Scheme. 250 grams of the 400-700 OF crude distillate were separated into major heterocompound fractions as shown in Figure 1, The various silica, alumina, and ion exchange chromatography separations have been described in detail ( I ) . The SOfraction of Figure l, which includes essentially all of the hydrocarbon and aromatic sulfur compound types in the original crude distillate, was further separated into individual compound types by means of a previously described standard procedure (3). The latter separation, which represents a change from the original scheme ( I ) , gives improved determination of individual oxygen compound types in the SOfraction; it also facilitates the determination of individual hydrocarbon and sulfur compound types at the same time heterocompound types are being analyzed. Following the major separation of Figure 1, the Ao-2 fractions [for further explanation of these frac(1) L. R. Snyder and B. E. Buell, ANAL.CHEM., 40, 1295 (1968). (2) L. R. Snyder, B. E. Buell, and H. E. Howard, ibid., p 1303. (3) L. R. Snyder, ibid., 37, 713 (1965). 314
ANALYTICAL CHEMISTRY
tion labels, see (I)] were separated on mercuric-ion-impregnated ion exchange resin (see below) to remove sulfides from these fractions. The resulting sulfide-free fractions are distinguished here by an M label (e.g., A. SI4M is the sulfides-free fraction resulting from the separation of A s l a ) . The AO-2M , A 3 and S2-4fractions were separated on charcoal into Coand C1 fractions (see below), and the CE2 fraction was separated on alumina into C& Ao3and CE2 A 4 5fractions. Sulfide Removal. Amberlyst XN-1005 cation exchange resin is prepared in the mercuric ion form as follows. The acid form of the resin is washed in aliquots with 10 mmoles of saturated aqueous mercuric acetate per gram of resin. The resulting resin is washed in sequence with 10 ml/gram of water, methanol, benzene, and pentane. An Ao, A I , or A2 fraction from the standard separation scheme is charged to a column of the latter resin (10 mg of sulfides per gram of resin), The column is washed in turn with each of the following solvents (2.5 ml/gram of resin): pentane (A), benzene (B), methanol (C). The individual fractions (A-C) are stripped of solvent and analyzed for sulfide sulfur (see 2). Fractions which are predominantly free of sulfides (usually A-C) are combined into a sulfide-free M fraction. Charcoal Chromatography. These separations were carried out as determined previously ( I ) , with the exception of the solvents used for elution. The new solvent sequence is as follows: 12 ml per gram of adsorbent of 2 % vol, 10% vol and 50 vol benzene-(10 vol ethanol-pentane), followed by 50 ml/gram of hot (100 "C) toluene. Chemical Determinations. These have been described previously ( 2 ) , with the exception of the determination of nitrogen as pyrroles plus indoles by a modification of the colorimetric procedure of Thompson et al. (4). Instrumental Techniques. These were carried out as described previously (2), with one exception. The mass spectrometer parent peak sensitivities of carbazoles and phenols (in fractions where they occur together) were not assumed constant. Carbazoles were found to have a higher sensitivity (peak height per unit weight) than phenols, in the ratio of 3.2:l. SEPARATION ON MERCURIC-ION-IMPREGNATED CATION EXCHANGE RESIN In the separation scheme of Figure 1, aliphatic oxygen compounds (ketones, esters, etc.) are grouped together with sulfides in fractions Ao-s These two compound types can be separated from aromatic compound types (which occur in these same fractions) by means of charcoal chromatography (dliphatics in the Co fraction). In the preceding study of the 700-850 OF crude distillate, the aliphatic oxygen compounds COwere analyzed by difference (concenin fractions AO--3 trations and elemental analysis), after mathematically subtracting the sulfides (and minor amounts of sulfoxides) in these fractions. Because the concentrations of sulfides in these fractions can be much larger than the concentrations of aliphatic oxygen compounds, this procedure is relatively inaccurate. A better approach to the problem is the selective removal of sulfides from these fractions, leaving only the aliphatic oxygen compounds as major components. (4) R. B. Thompson, T. Symon, and C. Wankat, ibid., 24, 1465 (1952).
The average sulfides content of the combined A-C fractions is only 1% wt, cs. 13-88% wt sulfides in the starting fractions. For the fractions, the per cent of the original fraction which is held on the resin is within a few per cent of the calculated per cent sulfides in the starting fraction. This means that sulfides are the only compounds in these fractions which are held on the resin. However, for the A 3 fractions, the per cent of the fraction held on the resin is much greater than the calculated concentration of sulfides in the original fraction. This means that compound types other than sulfides are held on the resin in the case of the A 3 (and presumably fractions. Fortunately the bulk of the sulfides in a crude distillate are found in fractions A k z , and their removal from these fractions is of greatest importance. It is not recommended that the present procedure be used for fractions other than Ao-2.
We have so far been unable to recover the sulfides from the resin. Because our present interest is in the oxygen and nitrogen compound types in crude distillates, this is not important. However we must consider the possible presence of compounds which contain both a sulfide group and a nitrogen or oxygen group within the same molecule, since such heterocompounds would be lost during separation on mercuric ion impregnated resin. We can calculate the fraction (Ao, Ai, etc.) in which compounds of this type will be found if they were present in the starting crude distillate (see I , 6). Thiaethers of the structure R-S-R’-0-R” (R is an aliphatic hydrocarbon group) are calculated to possess €1 values of 0.16-0.20 on alumina, and they should therefore be found in the Ai-2 fractions [see ( I ) ] . Thia-ketones (R-CO-R’S-R”) and thia-esters (R-0-CO-R’-S-R‘ ’) have calculated el values of 0.23-0.41 and should be found in the A3-4 fractions. Other heterocompounds of this general type should be found in the A3--5or CE1--ofractions. Thus only the thia-ethers are likely to be lost during separation of the Ao--2 fractions on mercuric-ion-impregnated resin. The aliphatic ethers are minor components of the 400-850 O F distillate from the present crude (see Table VII), and on this basis we believe that thia-ethers are not significant components of the present crude oil. Their possible loss during separation is therefore relatively unimportant.
SILICA
I
-
L
I
Figure 1. Initial sample separation scheme The procedure for removing sulfides which is described in the Experimental section is based on the selective complexation of sulfides by mercuric ion (e.g. Ref 5). This procedure was first applied to the total crude distillate, but it was found that compounds other than sulfides are also held on the mercuric-ion-impregnated resin--i.e., selective separation of sulfides from other compound types does not occur. The same separation was then applied to individual fractions from the 400-700 O F and 850-1000 O F distillates from the present crude oil. The results of these separations, summarized in Table I, show the relative distribution of eluted material in fractions A-C and the relative per cent sulfides in each of these fractions. Table I also compares the per cent sulfides (original fraction basis) removed by the resin with the calculated sulfides content of the original fraction. In most cases we see that the eluted fractions (A€) are largely free of sulfides.
(6) L. R. Snyder and B. E. Buell, J . Chem. Eng. Data, 11, 545 (1966).
(5) W. L. Orr, ANAL.CHEM., 38,1558 (1966).
Table I. Sulfides Removal on Mercuric-Ion Impregnated Cation Exchange Resin“ Total each eluted fraction Wt sulfides in each fraction Held on A B C A B C resinc
zWt of total nonsulfides in
Starting fraction 400-700 “F distillate Ao Ai A2 As 850-1000
81 95 93 60
10 5 2 35
9 0 5 5
0 0
26 2 1 1
88 88 55 57
4 0 36 16
8 12 9 26
0 0 0 0
6 6 1 0
3
1
20
zwt sulfidesh In original fractiond
...
87 64 25 27
88 60 22 13
14 0 6 0
52 50 21 68
53 48 18 5
... 6
OF
distillate Ao AI A2 Aa a
Procedure of Experimental section.
* In starting fraction.
Calculated from amount of fraction held on resin, corrected for small amount of sulfides eluted in fractions A-C. Calculated from sulfide sulfur content of starting fraction and average boiling point of original crude distillate.
VOL. 41, NO. 2, FEBRUARY 1969
315
DETERMINATION OF INDIVIDUAL HETEROCOMPOUND TYPES
Table I1 summarizes the chemical analyses of the standard fractions of Figure 1. These fractions were further characterized by their mass, infrared (IR),and ultraviolet (UV) spectra. The interpretation of these data in terms of the molecular composition of each fraction proceeded in essentially the same fashion as previously (2), and the types of compounds found were in most cases those expected on the basis of the preceding study (keeping in mind the lower boiling range of the present crude distillate). The following discussion of the analysis of these standard fractions will therefore concentrate on those points which involve new information or new interpretations of previous data.
Aromatic Nitrogen Compounds: C,H,,+,N. Table I11 provides a summary of the aromatic nitrogen compound types in the standard fractions of Figure 1, apart from N-0, N-N, and N-S compounds. These latter compound types are discussed separately. INDOLES AND CARBAZOLE^ CEI-,). The UV and IR spectra of these fractions support the identification of these nitrogen compounds as indoles and carbazoles. The mass spectral analyses of Table I11 confirm this assignment, showing compound types beginning with C, H2,-9N (indoles) or C, H Q ~ - - (carbazoles). ~~N Figure 2 shows a plot of the absorptivity (cmz/gram) of the characteristic N-H band at 2.87 S1-4 and CEI from N of fractions p us. the average elemental and mass spectral analysis. The plot of Figure 2
Table 11. Preliminary Analysis of Standard Fractions from 400-700
Fraction
so
AO 1 s4 AIS14
Ad14
A3SLZ AS34 A4PS.1 A4S2
A4S3 A464 Ais23
CE1 CEz
cE3
Yield, wt 95.9 1.134 0.361 0.484 0,025 0.089 0.056 0.055 0.065 0.085 0.042 0.335 0.282 0.592
%S
Totale 0.0002 0.0
0.2 0.4 1.6 1 .o
Z N N-Hb 0.0 0.0 0.0
Indolesc
0.2 1.3 0.7
0.0
1.o 0.6
1.3 0.0 0.0 4.0
0.0
3.2 3.5 5.4
0.7
Total6 13.1 8.9 3.3 0.9 1.9 0.2
15.3 8.0 2.1 0.8 1.6
0.5
0.002 0.006 0.004
1.9 7.3 3 .O 8.1 0.5
0.002 0.004 0.036 0.51
0.0
7.0 6.1 9.4 8.8 3.6 3.8 0.3
0.2 2.0
0.6 0.5 4.3 0.5
Crude Distillate
z
wt SulAiiwt Very weak foxidesb phaticso sulfidesh bases (meq/gram) 0.001 0.0 87 64 0.0 0.06 29 0.2 0.283 0.005 0.4 0.064 22 0.000 0.2 0.000i 0.0 0.000i 0.0 0.008 0.3 0.023 0.5 0.000 0.0 0.43 0.m 0.0 3.01 0,069 3.8 0.4 (3.5); 0.0 O.Oo0" __
Sulfides'
0.042
0.0 0.0
0.0
Od
O F
x
400-700 O F crude distillate 0.013 (0.021); Orig. spl. 0.25 0.062 0.013 (0.021)i 0.23k Composite 0.058 Coulometric (see 2); IR; 0 colorimetric; d by gas chromatography (see 2); e X-ray fluorescence (see 2 ) ; iodine complex; charcoal chromatography plus UV analysis (yo w of original distillate); * absorbed on mercuric ion resin (yow at fraction); i estimated; j weak bases (titrable in glacial acetic acid); k includes 0.11 0 from carboxylic acids lost on alumina.
Fraction
Table 111. Aromatic Nitrogen Compounds in Standard Fractions from 400-700 O F Crude Distillate; Determination by High Resolution Mass Spectrometry. % wt of 400-700 "F distillate as indicated compound type C,,HZ~+~N - 5z - 72 - 92 -112 -13~ -152 -172 -192 -212
0.0002
0.003 0.010 0.016
0.085
0.113
0.0003
0.007 0.030 0.002 0,122
Composite analysis Sa, (N-alkyl carbazoles) 0.013 0.039 Indoles Carbazoles Pyridines and higher benzologs 0.016 0.085 0.113 0,122 a Parent peak analysis (see Experimental section and ( 2 ) . From N in fraction. Estimated.
316
ANALYTICAL CHEMISTRY
0.0002
0.003 0.010 0.004 0.123
0.017
0.123
0.0001 0.0083 0.0160 0.0154 0.0016 0.161 0.004 0.030 0.074
0.0010 0.0016 0.0003 0.0002 0.005 0.002 0.003 0.024
0.006 0.230
0.003 0.010
0.003
0.074
0.024
0.023
0.0002 0.0002 0.0002 0.001 0.001 0.023
0.012
Av Total % Wt mol wt 0.003 0.012b (230)c 0 .032b (230)" 260 0.001 258 0.010 244 0.018 223 0.016 216 0.002 0.181 209 0.057 243 0.040 243 263 0.592
0.04 0.08 0.24 0.012
0.59
(230)"
300 -
400 -
250
300 -
-
200 150-
too I o/o
50 1
2 3 4 N-H ( A V G )
I-
IO0
Figure 2. Correlation of N-H absorbance at 2.87 p (A2.81) us. N as aromatic compounds (average of mass spectral data and elemental analysis) in Fractions A3-& and CEI implies a molar absorptivity E of 135 liters/mole-cm, us. a corresponding value of 82 for the 700-850 O F distillate (a value of 75 was reported in (2), since corrected to 82 because of the difference in mass spectral sensitivities for phenols us. carbazoles [Experimental section]). These E values are plotted in Figure 3 (open circles-dashed line) us. fraction molecular weights (average), along with corresponding e values for the pure compounds carbazole and benzcarbazole (benzene solvent, fractions run in cyclohexane solvent). In addition, an average value of e from corresponding fractions of the 8501000 O F distillate (unpublished studies) is included in Figure 3. The fractions from which the e values were derived (Aw, CE,) contain only small amounts of indoles, so that the correlation of Figure 3 appears reasonable. The molar absorptivity of the N-H group in the carbazoles and benzcarbazoles declines sharply with increasing molecular weight of the sample. The colorimetric procedure of Thompson et al. ( 4 ) for pyrroles plus indoles was applied to several of the standard fractions (see Table 11). This test confirmed the presence of major amounts of indoles in CEZand minor amounts in CE1 (cf. Table 111). Other fractions had only traces of indoles (however A3 S ~ was Z not analyzed for pyrroles plus indoles). The procedure of Thompson et al. reports only half as much indole nitrogen as shown by mass spectral analysis, but this can be attributed to the presence of alkyl substituents on both the 2- and 3- positions of some of these indoles (which blocks condensation with the p-N,N, dimethylamino benzaldehyde reagent). Several of the fractions of Table I1 were analyzed colorimetrically for carbazoles by the procedures of Hartung and Jewell (7) and Gilbert et al. (8). These results were in complete disagreement with preceding spectral analyses of these fractions, and they also failed to correlate with each other (see Table IV). It appears to us that these latter colorimetric procedures are generally unreliable for the determination of carbazoles in high boiling petroleum distillates, although they may be useful in specific situations. Minor amounts of nitrogen compounds (4% of the total nitrogen compounds in the original crude distillate) occur in (7) G. K. Hartung and D. M. Jewell, Anal. Chim. Acta., 26, 514 (1962). (8) G. Gilbert, R. M. Stickel, and H. H. Morgan, Jr., ANAL. CHEM.,31, 1981 (1959).
O
200
300
400
MOLECljLAR WT.
Figure 3. Molar absorptivity of sulfoxides and carbazole derivatives as a function of sample molecular weight Pure sulfoxides Sulfoxides in crude distillates Carbazole and benzcarbazole 0 Carbazoles and benzcarbazoles in crude distillates 0 0
fractions AI.+ These could not be determined by mass spectrometry because of their small concentrations and the difficulty in resolving nitrogen compounds from hydrocarbons. On the basis of arguments summarized in (2), we believe that these nitrogen compounds are largely M-alkyl carbazoles. Indoles and N-alkyl indoles are not present in significant amounts in the fractions, on the basis of colorimetric analysis. PYRIDINES,QUINOLINES, AND BENZQUINOLINES (CE,). This fraction was separated by charcoal chromatography as previously (2), giving a composite (UV) analysis of 60% pyridines, 35 quinolines, and 5% benzquinolines. This analysis is consistent with the data of Tables I1 and 111. Aromatic Nitrogen-Oxygen Compounds: C,H2n+zN0. Table V summarizes the N-0 compounds found in the standard fractions of Figure 1. The IR spectra of these fractions exhibit the characteristic amide bands in the 5.9-6.1 N region, supporting the prior identification (2) of these compound types as pyridones and 2-quinolones. The N-0 compounds of the Adv5 fractions may be a minor exception to this characterization, however. The UV spectrum of the S4 Cl fraction, which is largely composed of N-0 compounds, is shown in Figure 4a. While this spectrum resembles that
Table IV. Comparison of Spectral and Colorimetric Analyses for Indoles Plus Carbazoles in Fractions of Table I1 N as indoles plus carbazoles Present study Fraction MS IRG Ref. 7 Ref. 8 AlSl4 A& AaSsa A nSs A d i CEi CEa a
N-H
0.2b 0.4b 1.2 1.5 0.1 3.6 2.0
0.0 0.0 0.7 1.3 0.0 4.0 0.7
0.14 1.24 0.36 0.58 0.26 0.18 0.90
0.06 0.09 0.78 0.07 0.05 0.35 1.30
indoles and carbazoles only.
* Total nitrogen (elemental); not analyzed by MS. ~-
VOL. 41,
NO. 2, FEBRUARY 1969
317
\
\
\ I
I
250
m/u
Figure 4. Ultraviolet spectra of fractions Ad5S4C1 (a) and AlS14MCo(6)
of the 2-quinolones over the region 250-350 mp, it lacks a major absorption band in the 220-230 mp region. The essential absence of -112 and -132 N-0 compounds in this fraction suggests the presence of some new compounds type beginning with the series C, N 0. Fraction Ad5 S4 possesses a major amide band at 6.00 p [see previous discussion (Z)]. The same series of N-0 compounds (C, H2,--15 N 0, C , H?,-I; N 0, etc.) is also observed to concentrate in Sa fraction of the 700-850 O F distillate (see 2). This the suggests that this new N-0 compound type is less basic than the quinolones. These -15z N-0 compounds were first observed in another crude oil by J. R. Fox of our laboratory, and a more detailed characterization of their molecular structure is under way by Dr. Fox. In the course of titrating the CE1-2fractions for very weak bases (perchloric acid in acetic anhydride), it was noticed that characteristic color changes normally occur as the end point is approached. This suggested that UV spectral shifts in acid media might be useful for the further characterization of the CE1-2fractions, in particular the N-0 compounds in these fractions. We therefore obtained the UV spectra of fractions CE1,CE2AO3and CE2Aq5in acetic anhydride and acetic anhydride plus an excess of perchloric acid, over the range 310-500 mp. In the case of the CE2fractions, the UV spectra in acid and neutral solution were quite similar, showing generally enhanced absorption in acid solution but no new absorption bands. The CE1fraction developed a broad band at ~
Fraction AaS3Ki AaSaCi AasS4Ci CEzAoa CEzAas
~
~~
~~
Table V. Aromatic Nitrogen-Oxygen Compounds in Standard Fractions from 400-700 OF Crude Distillate; Determination by High Resolution Mass Spectrometrya % wt of 400-700 OF distillate as indicated compound type C,Hz,+,N 0 - 5Z -72 -92 -1lz - 132 - 152 -172 Total wt o.ooo1 0.0009 0.0001 0.001 0.0001 0.0001 0.000 0.0010 0.0012 0.0175 0.0001 0.020 0.001 0.005 0.005 0.004 0.001 0.016 0.020 0.013 0.013 0,029 0,030 0.010 0.001 0.118
z
Composite analysis 0.020 0.014 0.018 0.035 a Parent peak analysis [see Experimental section and (2)].
0.035
0.030
0.002
Table VI. Aromatic Oxygen Compounds in Standard Fractions from 400-700 Crude Distillate; Determination by High Resolution Mass Spectrometry"
Fraction So(diarom) So(polyarom) So(hetero) AiSiaMCo AiSi4MCi AzSi4MCi A 3S12Co
% wt of 400-700 O F distillate as indicated compound type C,Hz,+,O -62 -82 -102 - 1 2 ~ -142 -162 -182 -202 -222 0.024 0.029 0.202 0.241 0.020 0.013 0.004 0.017 0.032 0.008 0.001 0.003 0.0008 0.0005 0.0006 0.0004 0.0010 0.0005 0.0001 0.0028 0.0025 0.0019 0.0007 0.0011 0.0008
A as2 AiSaCo AIsS~CO AaaSiCi ASS23 CEi
0.0091 0.0061 0.0055 0.0006
0.180
0.0136 0.0122 0.0009 0.0082 0.0102 0.018 0.052
0.149 0.0114 0.0103 0.0012 0.0047 0.032
0.0049 0.0037 0.0034 0.0005
0.0010 0.014
0.0052 0.0035 0.0031 0.0003 0.0126 0.008
Composite analysis Furane benzologs 0.025 0.030 Dihydrobenzofuranes 0.017 0.032 0.008 0.003 Phenols 0.051 0.110 0.078 0.029 0.034 a Parent peak analysis [see Experimental section and (211.
318
ANALYTICAL CHEMISTRY
0.15
O F
Av
-242
0.0010
0.0001
A~Sizci
Total wt 0.25 0.26 0.02 0.06 0.003 0.002 0.009
z
0.000
0.0028 0.0017 0.0015
0.055 0.040
0.036 0.004 0.042 0.131
0.0005
0.0038 0.005
0.0004
0,458
0.021
0.0010
0.0002
0.001 0.005
0.001
0.017
Av mol wt 253 225 239 236 235
0.001
0.001
0.001
0.54 0.06 0.32
mol wt 212 211 196 216 248 228 295 252 250 235 234 246 237 206
about 405 mk in acid solution, whereas in neutral solution the CE1 fraction showed no strong absorption past 380 mp. Since the characterization of the CEI fraction (Le., as phenols plus carbazoles) is reasonably free from ambiguity, we conclude that these acid-induced spectral shifts are of little value in characterizing these very weak base fractions (CEI--2). Other Nitrogen Compound Types. Traces (0.003% wt of starting distillate) of compounds with the formulas Cn H2,-11 NO2 and C, Hzn-lsr NOe were found in fraction CEZ A03. These same compounds were also observed in corresponding fractions from the 700-850 O F distillate (2). Traces of dinitrogen containing compounds (CnH2,-sN2, C,Hz,-loNz, etc.) were observed in the CE3 fraction from the 700-850 OF distillate (2), but no aromatic compounds containing two nitrogens per molecule were found in the 400-700 O F distillate. No aromatic compounds containing both nitrogen and sulfur were observed in the present fractions. The elemental analysis data of Table I1 suggest that only minor amounts of sulfur compounds (other than sulfoxides and sulfides) occur in fractions which contain large concentrations of nitrogen compounds ( A 3SI2,A 3 S34, A 4 S I CE1-,). Aliphatic nitrogen compounds are not present in the 400-700 O F distillate in significant amounts (the same is true of the 700-850 OF distillate). This is shown by the correlation of Figure 5. For each of the standard fractions of Figure 1, per cent nitrogen by mass spectral analysis (z'.e., aromatic compounds) is plotted VS. elemental nitrogen. None of the points fall significantly below the theoretical curve, as would be the case if significant amounts of aliphatic nitrogen compounds were present in any fraction. Aromatic Oxygen Compounds: CnH2n+z0. Table VI summarizes the aromatic oxygen compound types found in the standard fractions of Figure 1. No compounds containing both 0 and S were found, but minor amounts (0.02x wt) of compound beginning with C, Hz,-s 0 2 were found in CE1. These compound types were not found in the 700850 O F distillate. They may be aromatic carboxylic acids or phenolic ketones, held on the cation exchange resin in the same way as phenols (see below). Because the 700-850 O F distillate was separated on alumina before ion exchange separation, any aromatic carboxylic acids in that sample would have been irreversibly held on the alumina and would not have appeared in CEl. BENZOFURANES, DIBENZOFURANES, AND NAPHTHOBENZOFURANES (SO). The distribution of compound types by z number in the various fractions from So (Table V) supports the identification of these as benzofuranes (C, H2,+-10 O), dibenzofuranes (C, H2n-16 0) and naphthobenzofuranes (C, H2n--12 0),along with cycloalkyl derivatives. Only these compound types are expected in SO(see 2). The alkyl furanes, if present, should be concentrated into the monoaromatic fraction from SO. A detailed mass spectral analysis of the monoaromatic fraction from SOshowed no aromatic oxygen compounds, and it is believed that alkyl substituted furanes (as distinguished from benzofuranes and dibenzofuranes) are absent altogether from the 400-700 and 700-850 "F distillates. The separation of the Sofraction into saturates, monoaromatics, etc. as in Figure 1 eliminates a major part of the difficulty in the mass analysis of the oxygen compounds in these fractions [cy. discussion of (2)]. It is observed that the calculated oxygen content of the So fraction, 0.042% based on the mass data of Table VI, is exactly equal to that found by elemental analysis (Table 11). DIHYDROBENZOFURANES (A1 S14 CO). This fraction (Table VI) shows a series of compounds beginning with C, Hz,-sO. The I R spectrum of AI S14shows negligible carbonyl absorp-
N (elem.) Figure 5. Correlation of % N as aromatic compounds (% N from mass analysis) us. % N by elemental analysis. Standard fractions of Figure 1
tion, and the UV spectrum of AI S I 4 M COis shown in Figure 46. The fact that these oxygen compounds concentrate into the A1 fraction suggests that they are aromatic ethers (see I , 6). The dashed curve of Figure 46 is that of an alkyl dihydrobenzofurane (coumaran) taken from the literature [complete curve, ethanol solvent, from (9), corrected for solvent shift by using data of (IO)]. This series of compounds begins with C, Hz,-~O), and there seems to be little doubt that the aromatic oxygen compounds in AI S14 Coare indeed dihydrobenzofuranes. From the molar absorptivity of the dihydrobenzofuranes (IO), it can be calculated that 50% of A1 S I 4 M COare dihydrobenzofuranes, leaving 50% of this fraction as aliphatic compounds. In the preceding study ( 2 ) of the 700-850 OF distillate, a similar series of oxygen compounds (beginning with C, H2+,0) was observed in the various Az fractions and tentatively identified as phenyl ketones. The latter identification was made uncertain by the large concentration of sulfides in these fractions, and we now feel that these compounds in the 700-850 OF distillate are probably also dihydrobenzofuranes (because of the presence of this compound type in the 400700 O F fraction). PHENOLS AND HYDROXYBIPHENYLS CE1). The aromatic oxygen compounds in these fractions are clearly phenol derivatives, as shown by their UV and IR spectra, as well as by the distribution of empirical formulas in Table VI-Le., beginning with the alkyl phenols, C, Hz,-8O). The presence of hydroxybiphenyls, in addition to phenols, is apparent from the comparison in Figure 6 of the IR and mass data for fractions A 5 S 2 3 and CE1 [cf discussion of (31. Fraction A&3 shows major IR bands at 2.76 and 2.82 p , corresponding to free 0-H (phenols) and hydrogen bonded 0-H (e.g., 2hydroxybiphenyls). Fraction CE1 shows only the single 0-H band at 2.76 I.(. The distribution of compound types in A 5 Snaus. z number (Figure 6) shows a sharp jump from - 122 to - 142, indicating an absence of naphthols but a large concentration of hydroxybiphenyls and/or isomeric compounds. Fraction CE1 shows only minor amounts of these - 142 compound types. Other fractions containing phenols ~~~
~
(9) D. Cagniant and P. Cagniant, Bull. SOC.Chim. France, 1957 838. (10) B. Baddely and M. A. Vickars, J. Chern. SOC.,1958,4665. VOL. 41, NO. 2, FEBRUARY 1969
319
%O NO
Figure 6. Partial infrared spectra us. mass analysis of phenols in fractions Asst3and CE1 show the same correlation between the relative intensities of the 2.76 and 2.82 p bands and the relative concentration of - 122 and - 142 compound types. Figure 7 shows a plot of the summed absorptivities at 2.76 and 2.82 p (Aph) cs. % 0 as phenols (mass spectral analysis) for the various fractions of Table VI (circles). Data for corresponding fractions from the 700-850 O F distillate ( 2 ) , open squares, and the 850-1000 O F distillate (unpublished data), open triangles, are also shown. It appears that the molar absorptivity of these petroleum phenols is approximately constant at 165 liters/mole-cm. This provides additional evidence that most of these aromatic oxygen compounds are indeed phenols. The C, H271--14 0 compounds of A5 s 2 3 (hydroxybiphenyls) begin at CI3,rather than Clz,as shown in Figure 8. This distribution suggests that isomeric compounds of type I or I1
OH
I
ANALYTICAL CHEMISTRY
Figure 7. Correlation of 0 - H absorbance at 2.76 and 2.82 f i ( A p h ) us. 0 as phenols (by mass analysis) 0 400-700 "F fractions 0 700-850 "F fractions V 850-1000 O F fractions
Aliphatic Compounds Containing Oxygen. CARBOXYLIC ACIDS. These are assumed to be the sole weak acid constituents of the present crude distillate. The concentration of these compounds in the distillate (0.50z wt) was calculated from the concentration of weak acids (0.028 meq/gram) and an estimate of their molecular weight (179). A similar calculation ( 2 ) for the carboxylic acids in the 700-850 OF distillate (1.09% wt) was in error; the correct figure is 1.74% wt. SULFOXIDES. These compounds can be determined in each fraction from the IR band at 9.8 p if a value of the sulfoxide molar absorptivity is available. In the preceding study of the 700-850 O F distillate (2), a value of E was deduced, equal to 137 litersjmole-cm. This figure is significantly lower than the average value (300) for several pure sulfoxides described by Okuno et 01. (II), and in ( 2 ) this difference was attributed
OH
I1 may be the main components of this compound group, rather than the hydroxybiphenyls. Thus other compound types generally begin at the parent compound (i.e., hydroxybiphenyl), when the parent compound falls within the boiling range of the sample (2-hydroxybiphenyl boils at 547 O F ) . It is seen in Table VI that a large fraction of the phenols in the original crude distillate (41%) are held on the cation exchange resin (CE1). This cannot be explained in terms of the basicity of these compounds. Rather it is believed that the phenol hydroxyl hydrogen bonds to the water or methanol which hydrates sulfonic acid groups on the resin. The aromatic ring of the phenol may also preferentially interact with the polystyrene skeleton of the ion exchange resin at the same time. Similar interactions would be expected for aromatic carboxylic acids, and this may account for the small amounts of C , H2n--8O2compounds jn the CEI fraction (see above discussion). Intramolecular hydrogen bonding, as in the hydroxybiphenyls, would be expected to interfere with the attachment of these compounds to the cation exchange resins by hydrogen bonding (as in Figure 7). 320
A S PHENOLS
NO.
(11) I. Okuno, D. R. Latham, and W. E. Haines, ANAL.CHEM., 39, 1830 (1967).
z-
25 $E E W
I-I
z W Y oa z w
O a V-
n Figure 8. Carbon number distribution of -142 phenols (hydroxybiphenyls) in fraction A S Z 3
I200t
1000I
2c3
800-
\ (u
2 600-
Y
w
0
0
z a m
Y
8 400-
a
U
0
cn
200 -
v,po,20
m
a I
I
I
I
I
I
I
40 60 80 o/e ALIPHATIC OXYGEN COMPOUNDS
Figure 9. Infrared carbonyl absorbance (Aco)of aliphatic oxygen comfractions of Table V I us. pounds in each fraction to our use of a sketched base-line technique in the measurement of the fraction absorbance at 9.8 p. This explanation is now believed to be incomplete. In addition to the base-line effect, it appears that there is a significant decrease in e for the sulfoxides in petroleum fractions as fraction molecular weight is increased. This in turn seems attributable to increased crowding of the sulfoxide group by adjacent alkyl groups within the same molecule as the extent of alkyl substitution is increased. This effect can be recognized in the data of Okuno et af.( I I ) , where e for the uncrowded 3-methylthiacyclopentane-1-oxideis 300, us. a value of only 250 for the slightly crowded 2-methylthiacyclopentane-1-oxide. In the ion exchange fractions of Table 11, it is found that the sulfur contents of fractions CE1and CE, are relatively low (0.5% wt), and their sulfoxide contents (by IR) are essentially zero. In fraction CEz substantial amounts of sulfoxides are present, and the sulfur content of the fraction has jumped to 4.3% wt. It seems reasonable to estimate the sulfoxide sulfur content of CEZat about 3.8% wt (* a few tenths of a per cent). This in turn permits us to estimate e for these sulfoxides: 198 liters/mole-cm. In Figure 3 we have plotted these e values for the 400-700 and 700-850 OF distillates us. the average molecular weights of these samples (open squares). We have also included the average E value for the pure compounds of Okuno et af. (11) (closed square, excludes aromatic sulfoxides and cyclopropane derivatives). A smooth correlation of e cs. sample molecular weight is observed, supporting our postulate that e is a function of the molecular weight of a particular petroleum fraction. The sulfoxide sulfur values of Table I1 were calculated by IR, using an e value of 198. This in turn permits the calculation of sulfoxides in each fraction and in the total crude distillate (assuming an average molecular weight of 174 for the sulfoxides in the 400-700 O F distillate). Another factor which has since been recognized as responsible for the apparent decrease in e with increasing sample molecular weight is the possible presence of additional sulfur atoms in the sulfoxide molecule (e.g., R-SO-R’-S-R”). A following paper dealing with the nitrogen and oxygen compounds in the 850-1000 O F fraction from the present crude oil provides independent confirmation of the regular
2.8
3.0
5-
5.5
6.0
Figure 10. Infrared spectra of fractions A2SI4MCo and A d 4
trend to lower e values as sample boiling point increases, and a full discussion of this problem will be presented there. Other Aliphatic Oxygen Compounds (AI-6 SI-4). Table VI1 summarizes the total aliphatic compounds in each of the standard fractions of Figure 1 (determined by charcoal chromatography and UV analysis), along with concentrations of the sulfides and sulfoxides (data of Table 11). The difference between total aliphatics and sulfides plus sulfoxides is referred to as “other” aliphatics in Table VII. These should be almost entirely aliphatic oxygen compounds [see discussion of (2)]. The elemental composition of these “other” aliphatics can be determined by difference, as shown in Table VII. On the basis of our preceding study (2), these aliphatic oxygen compounds are believed to be ethers (Aol), simple esters and ketones (A2--4) and difunctional (dicarbonyl) compounds (Ads). These assignments for the fractions of Table VI1 are consistent with their elemental analyses and IR spectra. Thus in Figure 9 we have plotted the integrated carbonyl absorptivities of the various fractions of Table VI1 [A,, values; see (2)] us. the per cent “other” aliphatic compounds in each fraction. The data for the Ao-I fractions (dark circles) show little carbonyl absorption, confirming that these “other” aliphatics are largely ethers. The data for fractions A2-4 (open circles) fall reasonably close to a single straight line (as expected for simple mono ketones and mono esters), and the point for fraction Ad5 S d (dark square) has a carbonyl absorbance about twice that predicted for monofunctional carbonyl derivatives-Le., as in fractions This is quite similar to our observations for the “other” aliphatics of the 700-850 O F distillate (2). If we assume equal molar absorptivity values (per functional group) for both esters and ketones, we can calculate the approximate distribution of these “other” aliphatics ainong simple ethers, ketones, esters, VOL. 41,
NO. 2, FEBRUARY 1969
321
Table VII. Aliphatic Oxygen Compounds in 400-700 "F Distillate Fractions Elemental analysis wt aliphatics of "other" aliphatics Fraction Total Sulfides Sulfoxides Other %O %S A,," AaLM 0.16b 0.01 0.00 0. 15b 3.8 0.0 0 AIS1 4 MCo 0.06 0.00 0.00 0.06 5.6 (7)" 6.1 30 AzSuMCo 0.286 O.Oo0 0.003 0.283 12.3 (12)" 1.5 860 O.Oo0 0.005 5.2 (7)" 0.0 60 AISIZCO 0.006 0.001 A~S~~CO 0.070 0.006 0.001 0.063 11.3 (11)" 0.1 1170 A4S3CO 0.008 O.Oo0 0.001 0.007 15.4 (11)" 0.0 40 AasS4Co 0.023 O.Oo0 0.002 0.021 17.4 ( 1910 5.6 910 a Value for standard fraction (e.g., AoSlr,A&, etc.). This includes both aromatics (mainly hydrocarbons) and aliphatics. Calculated 0, based on aliphatic subtypes; fraction AoSlpMwas not separated on charcoal, and is estimated to be 4%aromatic hydrocarbons on the basis of its 0.
Table VIII. Aliphatic Oxygen Compound Subtypes in 400-700 and 700-850 O F Distillates" %wt
Compound type Monofunctional compounds Ethers Esters Ketones Polyfunctional compounds Dicarbonyls 0-S compounds Total a
400-700
O F
700-850
0.12 0.19 0.12
0.05 0.08 0.17
0.02 0.07 0.52
0.09
O F
0.07 0.46
Other than sulfoxides and carboxylic acids.
and dicarbonyl compounds from the data of Table VI1 and the intensity of the ester carbonyl band (at 5.75 p ) relative to A,, (see discussion of 2). This in turn permits us to calculate the oxygen contents of the "other" aliphatics in each fraction. As seen in Table VII, agreement between experimental and calculated oxygen contents is reasonably close. The better separation of "other" aliphatics from other sample components in the fractions of Table VI1 (compared to the preceding study of the 700-850 "F distillate; see discussion of 2) allows LIS to make a reasonably reliable breakdown of the various oxygen subtypes. These data are summarized in Table VIII, along with less reliable data for the 700-850 OF sample. We see that aliphatic esters are predominant in the 400-700 OF distillate, whereas ketones are the most important subtype in the 700-850 "F distillate. The predominance of esters in the 400-700 "F distillate is illustrated by the partial
~~
~
~~~~
~
Table IX. Summary of Nitrogen and Oxygen Compound Types in 400-700 and 700-850 OF Crude Distillates 700-850 "F AROMATIC COMPOUNDP 400-700 OF
-
CnHZn+*N Indoles (- 92) Carbazoles (- 152) Benzcarbazoles (-212) Pyridines (- 52) Quinolines (- 1lz) Benzquinolinesb (- 172) CnHzn+&" Azaindoles (- 82) Azacarbazoles (- 142) CnBn+zNO Pyridones (-52) Quinolones (- 1lz) CnH2ntsN02 Cn&+cO Benzofuranes (- 102) Dibenzofuranes (- 162) Naphthobenzofuranes (-222) Dihydrobenzofuranes plus phenyl Ketonesc(- 82) Phenols (-62)
0.9% wt 0.07% wt 0.28 0.00 0.35 0.21 0.03
7.1zwt 0.59% wt 3.38 0.48 0.65 1.71 0.26 0.1
0.0
0.03 0.09 0.2
1.1 O.ll+ 1.03-
0.06+ 0.09-
0.02
0.003 0.9 0.05 0.48
2.2 0.09
0.01
0.69 0.34
0.06 0.32
0.07 0.97
ALIPHATIC COMPOUNDS Carboxylic acids 0.50 Sulfoxides 0.07 Other oxygen compoundsd 0.52 Total z numbers in ( ) refer to parent series ( L e . alkyl derivatives). * Phenanthridines in 700-850 "F. Dihydrobenzofuranes in 400-700 OF. See Table VII.
3.2
1.1 1.74 1 .00
0.46 13.7
3.1
~
322
ANALYTICAL CHEMISTRY
~
~
~~
~~~
IR spectrum of Figure 10 for the A2 S14M COfraction (the A3--4fractions are similar in this respect). The ester carbonyl band at 5.75 p is much more intense than the ketone band at 5.88 p , whereas this situation is reversed in corresponding fractions from the 700-850 O F distillate. Figure 10 also shows the IR spectrum of the A 4 5S4fraction. This is much more complex than that of the AP Slr fraction, as was also observed in the A q 5S4fraction from the 700-850 O F distillate. The most interesting feature of this spectrum is the broad absorption band between 2.9 and 3.1 p, presumably due to internally hydrogen bonded 0-H groups (-0. . H . . O=C, etc.). The molar absorptivity e for the integrated carbonyl absorption (Aco on a liters/mole-cm basis) is 335 for the 400-700 O F aliphatic oxygen compounds, GS. a value of 515 liters/ mole-cm) for the aliphatic oxygen compounds from the 700850 O F distillate. Other data (12) suggest that the absorptivity of aliphatic esters should be greater than aliphatic ketones, which makes the increase in E between the 400-700 O F and 700-850 O F distillates somewhat surprising (since esters are concentrated into the 400-700 O F fraction). Hopefully, our continuing study of these crude distillates will resolve this paradox.
carbazoles, error in the previous calculation of carboxylic acids). No other heterocompound types are believed to be present in these two samples in significant amounts (>0.1% wt). Discussion of the significance of these data will be deferred to the end of the present project, which aims at the complete characterization of the distillable portion of the present crude oil. The present study provides another example of the ability of our general separation procedure to resolve individual nitrogen and oxygen compound types for subsequent analysis by spectral procedures. The recovery of nitrogen, oxygen, and titrable bases in the separated fractions (92-100%, see Table 11) was within the experimental error of the various determinations. The segregation of nitrogen and oxygen compounds from hydrocarbons and sulfur compounds was excellent: 99.8% of the hydrocarbons and sulfur compounds (excluding S-0 compounds) are contained in the So plus sulfides-extract fractions, along with only 0.3% of the total nitrogen compounds and 17% of the oxygen compounds (furane benzologs only). The balance of the nitrogen and oxygen compounds were in the A OS1-4 and CE1-, fractions, the composite analysis of which was 7% hydrocarbons plus sulfur compounds and 93% nitrogen plus oxygen compounds.
DISCUSSION
ACKNOWLEDGMENT
The various oxygen and nitrogen containing heterocompounds present in the 400-700 O F crude distillate are summarized in Table IX. Corresponding data for the 700-850 O F distillate ( 2 ) are included for comparison purposes. The latter data have been modified slightly for reasons given in the text (differing mass spectral sensitivities of phenols and
The author is grateful to the following employees of the Union Research Center for their direct assistance in the present study: F. 0. Wood (separations, UV, titrations), R. J. Kinsella (IR), M. J. Barbee (mass spectra), W'. D. Haley and U. Niwa (colorimetric analyses). In addition the advice and editing of the manuscript by B. E. Buell and J. R Fox were much appreciated.
(12) L. N. Cross and A. C. Rolfe, Trans. Faraday SOC..47, 354 (1951).
RECEIVED for review September 5 , 1968. Accepted November 4, 1968.
An Objective Computer- Oriented Method for Calculation of Stability Constants from the Formation Function Louis P. Varga Department of Chemistry, Oklahoma State University, Stillwater, OkIa. 74074
A computer program written in Fortran I V language to calculate the stability constants of simple mononuclear complexes from formation function data was tested using literature data for the Cu(ll) ammine, the Ni(ll), Cu(lI), and Zn(ll) fluoride, the uranyl monochloroacetate, and the U(IV) bisulfate systems. The program was applied to the calculation of over-all stability constants using, first, ii-ligand concentration data combined from several experimental techniques for measuring the Hf(IV) and Ta(V) fluoride complexes and, second, ;-ligand concentration data for the aquo complexes in 1-butanol of Co(ll) and Ni(ll) obtained by the method of corresponding solutions. New conclusions were reached concerning the nature and stabilities of several of these complex ion systems in both the test series and the final series of calculations. CALCULATION of stability constants for complex ion systems in which the functional form of the model is linear in the coefficients may be considered to be a solved problem. Much of the potentiometric, polarographic, ion exchange, and solvent extraction work done to date on complexes has been interpreted using such a model - i.e.,
+ alX + a 2 X 2+ . . . . a,vX" a minimum of N + 1 measurements of Y
= no
(1)
so that (Xi, Yi) allowed usually a rigorous noniterative calculation of an unambiguous set of the required coefficients, uT1,and their standard deviations. If some measure of experimental error were available to give either over-all or individual weight factors to the data set, methods have been developed to give a measure of the goodness-of-fit of the calculated to the experimental data points. The principal task of the experimeter has been to devise probes and techniques to measure the effect of concentration of free ligand on the concentration of one of the principal species comprising the system. The experimenter has the choice of measuring as a function of free ligand concentration: (1) the uncomplexed kernel ion by several quantitative techniques such as ion specific electrodes and polarography, (2) the positive-charged species by extraction onto a cation exchange resin or solvent extraction of a suitable ion associate adduct, (3) the neutral species by direct transfer across some phase boundary, or (4) the negatively VOL. 41, NO. 2, FEBRUARY 1969
0
323
