An investigation of the vanadyl porphyrin complexes of the athabasca oil sands

~mleaetCosmochlmlcr.Actr.1WW,Vol.80,pp.207to221. PergamonPrcrrLM. PrintedIn NorthernIreland

An investigation of the vanadyl porphyrin complexes of the Athabasca oil aanda M. F. NE,LSON,*D. S. MONT~OMERY~

and (in part) S. R. BROWN:

(Receivedt3October 1964; in revbedform 28 June 1966) AbrtrrceThe Athabsece oil sends contain, beeidea the vanadium porphyrin pigmenta of normal epectroecopic type common to petroleum deposits, 8 emall amount of an abnormal typ% This miuor component hae been partly separated and concentrated, and ita structure hae been inveetigatad by decomposition and reformation. It appear13 to be the vanadyl complex of 8 porphyrin containing a oarbonyl group conjugated with the main chromophore; B similar complex haa been prepared from a porphyrin derived from chlorophyll. The oxygenated complexinthe oil ecmd irrprobably 13secondary product formed f3om the more common petroporphyrins during an oxidative stage in the history of the deposit.

INTRODUCTION IN TEE thirtyyears since their discovery the petroleum porphyrins have been ex-

tensively investigated, both because of their importance as a source of volatile vanadium compounds that are troublesome in catalytic cracking operations and because they form a distinctive class of compounds whose origin is intimately related to that of petroleum as a whole. This latter aspect has recently been reviewed (HODGSON, PEAKEand BAKER, 1963). For some years the Mines Branch of the Department of Mines and Technical Surveys, Ottawa, has investigated the separation, utilization and constitution of the bitumen from the Athabasca oil sands of northern Alberta; as part of this programme a study of the vanadyl porphyrin complexes in the bitumen was undertaken. Our early investigations revealed the presence of a minor component. The major part of the vanadyl porphyrin pigments had an absorption spectrum with maxima at about 670, 634 and 410 rnp; the minor component was responsible for a shoulder or weak absorption maximum at about 690 rnp (Fig. 1). This minor absorption band has since been noted by Hodgson et al. (1963) and, in investigations of other crude oils, by COSTAN-ES and ABICH(1963), but no suggestion has yet appeared concerning the nature of the minor component. In a further investigation of vanadyl porphyrin pigments we studied the formation and decomposition of vanadyl derivatives of porphyrin bases that had been prepared from a commercially available chlorophyll product and crudely fractionated according to basicity. The fractions could be grouped into three classes according to the order of intensity of the bands in their absorption spectra (Fig. 2); these l Senior Scientiflo OflFicer. t Senior Soientist, Fuels aud Mining Practice Division, Minea Branch, Department of Bfinea and Teohnical Surveya, Ottawe, Canada. 1 Formerly Technical Oflicer (Seasonal 1968), Fuels Divieion, Minea Brauch, Ottawa. Preeent addma: Department of Biology, Queen’s Univereity, King&on, Ontario. Work done at Fuele and Mining Practice Division. Crown Copyright Reserved.

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M. F. MILLBON,

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,

D. S. MONTGOMERY

BHOWN

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500 550 600 Wavelength, rnp Fig. 1. Absorption spectrum of a fraction of Athabasca bitumen obtained by extraction with ethanol and chromatography on fuller’s earth (Dioxane solution).

Wavelength,

and S. R.

mp

Fig. 3. Absorption spectra of vanadyl complexes prepared from various types of porphyrin basee (benzene solutions). from et.io - - - from rhodo type; or phyllo type

Wavelength,

rnp

Fig. 2. Absorpt.ion spectra of porphyrin bases prepared from commercial chlorophyll (benzene solutions). - ..- rhodo; --ct.io; - - - phyllo

Wavelength,

rnp

Fig. 4. Absorption spectra of vanadyl porphyrin aggregate from Athabasca oil sand, at identical conaentration in two solvents -- cyclohexane solution; - - - benzene solution

An invwtigation of the vanadyl porphyrin complexes of the Athabaaca oil sands

209

to the phyllo, etio and rhodo types of spectra noted by FINHER and ORTH(1937). From those fractions that had specfra of the phyllo or etio type, vanadylation by the method of EEDMAN,RAMSEY, KALENDA and HANSON(1950) produced vanadyl derivatives possessing absorption spectra with maxima at about 670 and 534 rnp (Fig. 3). Vanadylation of porphyrin fractions that had rhodo-type spectra was more difficult,and required more vigorous conditions ; from the reaction products was separated a vanadyl derivative with an absorption spectrum showing maxima at 587,542 and 414 rnp (Fig. 3). These results made it seem likely that the minor peak at 690 rnp in the absorption spectra of vanadyl porphyrin concentrates from the Athabasca oil sands was due to a vanadyl derivative of a porphyrin carrying substituents similar to those in the rhodoporphyrins, and this possibility has been further investigated. classes correspond

ISOLATION OF THE VANADYL PORPHYRIN PIGMENTS FROM THE ATHABASCA BITUMEN

Most investigations of petroporphyrins have involved, at an early stage, fhe decomposition of the metal complexes with a solution of hydrogen bromide in acetic acid. This vigorous reagent may produce artifacts, as has been especially pointed out, by BLUMER (1961), and its use was postponed in the present,investigation until fractionation of the vanadyl complexes had been carried out ; in this way it was hoped to correlate some of the fractions of the metal complexes with different types of free porphyrin bases. Separation of the vanudyl porphyrin aggregak from. the bitumen Bitumen from the Athabasca deposit, (Abaaand quarry) was available as a solution in kerosine (about 60% bitumen content) from the cold-water separation plant of the Canadian Mines Branch (DJINGEEUUX and WARREN, 1961). On the scale of operation (several kilograms of bitumen) that was necessary to provide a reasonable quantity (500-1000 mg) of porphyrin pigments, the most convenient laboratory technique for the primaiy separation of the vanadyl complexes from the available mixture was liquid-liquid extraction. Earlier work in the Mines Branch laboratories with aniline-hydrocarbon mixtures had shown a favourable distribution of the vanadyl pigments toward the aniline layer, and aniline proved to be a satisfactory extraction medium for removing the vanadyl porphyrin compounds from the bitumen-kerosine mixture. Much of the non-porphyrin material was removed from the aniline extracts by washing with kerosine, methylcyclohexane and n-heptane successively. The progress of the extraction and washing procedures was easily followed with the aid of a small hand-spectroscope. From the washed solutions, most of the aniline was removed by distillation under diminished pressure and the remainder, after addition of benzene, was washed out with acid. The crude porphyrin concentrate from the aniline treatment was taken up in methylcyclohexane and the solution was extracted with aqueous pyridine (water 20% v/v) according to the procedure of BEACH and SHEWBUKER (1957) until no more vanadyl porphyrin pigment was being removed. The aqueous extracts were washed with methylcyclohexane, and Cnally the vanadyl complexes were collected in methylcyclohexane and freed from pyridine by washing with water. During the

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and 8. R. BROWN

dashing of the aqueous pyridine extracts with methylcyclohexane, it could be seen that nickel porphyrin complexes were removed from the aqueous layer much more readily than were the vanadyl derivatives. 3, 3’-Oxydipropionitrile (ODPN) was found to be an excellent medium for extraction of vanadyl porphyrin pigments from solutions in saturated hydrocarbons, the non-porphyrin components being largely retained in the hydrocarbon layer. The dinitrile did not extract nickel porphyrin complexes from a methylcyclohexane solution of a nickel porphyrin concentrate that had been obtained from a heavy crude oil by adsorption chromatography. Accordingly, the vanadyl porphyrin complexes from the aqueous pyridine treatment were further purified by distribution between ODPN and methylcyclohexane or n-heptane. The increasing purity of the pigment extracts was followed by means of their absorption spectra. As a working rule, the ratio of the absorbance at the maximum near 570 m,q to that at the minimum near 350 m,u, was taken as a measure of the relative purity. This ratio, the relative purity ratio R. P. R., takes no account of impurities that do not absorb appreciably in the visible or nea.r ultra.violet regions, but is convenient because it is rapidly and easily determined. The vanadyl porphyriu solutions from the extraction procedures were further freed from non-porphyrin material by partition chromatography in saturated hydrocarbon solvents on columns of ODPN supported on diatomaceous silica, and by adsorption chromatography on columns of magnesium silicate (“Florisil”) and of alumina, until no improvement in their absorption spectra was being brought about. The absorption spectra of the eluates from these columns showed that in the course of this chromatography there was little separation of the material with absorption maximum near Ii90 rnp, from that with maximum near 670 rnp, but the purity improved from R. P. R. values of less than O-6to values greater than 2.6. At this stage. some of the better fractions had absorptivities* at their maxima near 670 m,uof about 37 ems/g in cyclohexane solution (669 mp), or about 33 cm*/g in benzene solution (671 rnp) (see Fig. 4). The corresponding absorptivity value for a synthetic vanadyl mesoporphyrin-IX preparation (Fig. 5) was 466 cm2/g in benzene:ethylacetate (10: l), corresponding to a molar extinction coefficient of 2.77 v IO*; this preparation also had an R. P. R. of 2.6. The natural product from the Athabasca bitumen is a mixture of many components which do not all show maximum absorption at the same wavelength, and hence it would be expected to show a lower maximum absorptivity than the synthetic complex on an equimolar basis ; nevertheless, similar values of the integrated absorption in the whole absorption band might be expected for the and ARICH(1963) have shown that natural and synthetic products. COSTANTZNIDES for solutions of vanadyl etioporphyrin-I in different solvents the absorptivities of the 570 rnp maxima vary considerably with the nature of the solvent; however, the integrated absorption values of the 570 m,u band measured by the conventional baseline technique were much less dependent on the nature of the solvent, and were about 663 and 680 cm2/ g x rnp in o-xylene and decalin solutions respectively. It is also probable that instrumental factors such as slit-width and resolution, which may l The absorptivity of a substance is the absorbance (or optical density) due to that subetance in a 1 cm light-path through a solution containing 1 g/l., or absorbance Absorptivity = concentration in g/l. x cell thickness in cm

An investigationof the vanadylporphyrincomplexesof the Athabaacaoil eands

211

greatly affect recorded values of extinction coefficients, are much lees obtrusive in determination of the integrated absorption. With the conventional baseline technique, determinations of the integrated absorption in the “670 m$’ band of the vanadyl complexes from the Athabasca bitumen gave values of 430 and 448 cme/g x rnp in benzene and cyclohexane solutions respectively. On the same basis, the synthetic vanadyl mesoporphyrin-IX(benene-ethyl acetate) gave a value of 667 cma/g x rnp, or 3.37 x 10” cmg/mole x m,u, which is close to the value of 3.6 x 10” given by COSTANTIXIDES and ARICHfor their etioporphyrin derivative measured in o-xylene solution. CORWINand BAKER (1964) have suggested that petroporphyrins may carry large substituent groups which hardly affect either the form of the absorption spectrum in the visible range, or the molar absorptivity of the complex, but which greatly decrease the absorptivities per unit weight of the natural complexes compared with those of the simple synthetic products. A phenomenon of this sort might be the reason why the natural complexes from the Athabasca bitumen could not be obtained with higher absorptivity in the 670 rnp band than the figures given above, although the further purification described below gave solutions with R. P. R. values greater than 3. A preliminary investigation had shown that chromatography on columns of activated silica gel was extremely effective in removing non-porphyrin impurities from the vanadyl porphyrin complexes isolated from the Athabasca bitumen, and a vanadyl porphyrin solution with R. P. R. value greater than 4.6 was obtained using this adsorbent. However, at this level of purity, only a part-usually less than half-of the porphyrin pigments introduced into the column was recovered in the eluates, and that part which was recovered could not be preserved overnight in a stoppered vessel in the dark--only a brown to green solution remained by morning. The decomposition is presumably due to oxidation after some natural antioxidant has been removed from the porphyrin solution or some catalytic agent has been generated in the silica gel column. In order to avoid, as far as possible, any similar but less easily detectable chemical transformations, the use of activated silica gel was avoided in the main course of the investigation, although it was found that chromatography on a silica gel column did not adversely affect a solution of the vanadyl mesoporphyrin-IX complex. F9u.&ondion of the vanadyl complexes No success was achieved in an attempt to apply the method of BLUMEE(1966) for separation of vanadyl porphyrin pigments (paper chromatography in isooctrtnecarbon tetrachloride) to the vanadyl complexes from the Athabasca bitumen. However, as a development from this attempt it was found that chromatography of the complexes on columns of powdered cellulose in hydrocarbon solvents effected the removal of some non-porphyrin impurities and also brought about a noticeable separation of the minor constituent with absorption maximum at 690 rnp from the major part with absorption maximum near 670 rnp. The vanadyl porphyrin complexes that had been purified by chromatography on columns of alumina were therefore repeatedly subjected to chromatography on columns of powdered cellulose until little further separation of the constituents was detectable in the absorption

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31. F. MILLSON,D. S. MONTGOMERY

end S. H. BROWS

spectra of the eluates. It was possible by this mean8 to obtain a solution of the major component almost completely free from the minor components; the absorption spectrum of one of these fractions, shown in Fig. 6, has an R.P.R. value of 3.1. It had been noticed, at an early stage of these investigations, that if a hot solution of the vanadyl porphyrin pigments in hydrocarbon solvents deposited a precipitate on cooling, then the precipitate was enriched in t.he minor constituent with absorption maximum near 590 mp. Advantage wa8 taken of this phenomenon for the final stages of the separation of the minor components by repeated fractional precipitation of the pigments from solutions in benzene/n-heptane or benzene/methylcyclohexane. This fractionation wa8 continued until it seemed likely that further subdivision would give fractions too small for further investigations. Absorption spectra of some of the fractions obtained are shown in Fig. 7 ; to the eye those solutions with absorption minima near 565 rnp and maxima near 575 and 59O m/L appeared a weak bluish-ptiple quite different from the full red or magenta of t.he normal vanadyl porphyrin solution. THE NATURE OF THE

C’OYPONENTSISOLATED

The apparent position of the maximum absorption due to the minor component is about 588 rnp when the amount present is only sufficient to produce a shoulder on the main absorption band, and about 590 rnp when this component constitutes a major part of the fraction. On the other hand, the apparent position of the “major” component appear8 to be shifted gradually from 570 rnp to 575 rnp as the proportion of this constituent decreases. It is well known that in the spectra of two-component systems, if the absorption band8 overlap, then by simple mathematical addition of the absorptions the positions of the maxima may vary in wavelength with the However, it is not possible that the relative concentrations of the components. absorption maxima near 575 m,u in the spectra in Fig. 7 are derived in that way from an absorption band, such as that in Fig. 6, with maximum near 570 rnp, because the rate of decrease of absorption with increasing wavelength is very great on the high wavelength side of the 570 m,u band. The slightness of the shift8 produced in the positions of the absorption maxima when two vanadyl porphyrins are mixed can be seen in Fig. 8 ; this graph shows the a.bsorption spectra of mixture8 of vanadyl mesoporphyrin-IX (maxima 57 1, 534, 407; Fig. 5) and t.hc vanadyl complex of a rhodo-type porphyrin (maxima 587, 542, 414 nip; curve 2, Fig. 3). The Beckman DK-2 spectrophotometer used in this investigation allowed a direct approach to the problem of “subtracting” one absorption spectrum from another by utilizing the double beam feature. In this way the differential spectrum between a porphyrin fraction rich in the 590 rnp material and vanadyl mesoporphyrin-IX was plotted (Fig. 9). It is obvious that a substance with absorption maximum at 571 rnp cannot entirely account for the peak which accompanies that. at 590 rnp, and that there is a component of the natural fraction with an absorption maximum between 571 and 580 m,u. It aeemed likely that a plot of the absorption spectrum of the sub8tance responsible for the 690 rnp peak could be obtained by taking differential spectra between two similar vanadyl porphyrin fract.ions from the Athabasca bitumen which differed in the relative intensities of their absorption maxima near 575 and 590 mp. Figure 10 shows a series of traces obtained in this

An investigation of the vanadyl porphyrin complexes of the Athabaeca oil sands

f-

I

I’

1

I

I

‘.I

I

550 600 Wavelength, mp

boo

Fig. 5. Abeorption epectrum of vanadyl mesoporphyrin-IX (benzene/ethyl acetate solution).

500 550 Wavelength,

Wavelength,

mp

600 rnp

Fig. 6. Absorption epectrum of a vanadyl porphyrin fraotion from Athabaeca bitumen; low absorption at 690 rnp (n-heptane solution).

I

Fig. 7. Absorption spectra of vanadyl porphyrin fractions from Athabasca bitumen; high absorption at 690 rnp (benzene solutions).

I

I

Wavelength,

I

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rnp

Fig. 8. Absorption spectra of mixtures of vanadyl mesoporphyrin-IX and the vanadyl complex of a rhodo-type porphyrin (benzene solutions).

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F. MILLSON, D. S. MONTGOMERY and 8. It. &OWN

way as the concentration of the “low 590 m$’ fraction in the “reference” cell was increased. The moat reasonable explanation of these results is that in the Athabasca bitumen there are a number of different vanadyl porphyrin compounds and that they comprise at least three groups. The most abundant group have absorption spectra similar to that in Fig. 6 with maxima near 570 and 534 rnp, the second group have absorption maxima near 575 and 540 m,u, and the third group have maxima near 590 and 645 m,u. Referring again to Fig. 10, it seems that in the fractions used for the spectra determinations the relative amounts of components of the second (575, 540 rnp) and third (596, 545 mp) groups do not greatly differ, and that the main difference between the fractions is in the relative amounts of complexes of the first (570,534 rnp) group. Similar results to those shown in Fig. 10 were obtained with other vanadyl porphyrin fractions, and it appears that the complexes with absorption maximum near 575 rnp closely followed those with a maximum near 590 rnp through all the separation processes detailed above. It remains possible, of course, that the substance responsible for the absorption maximum at 590 rnp is also responsible for that near 575 m,u, although the preparation of a vanadyl complex with absorption maxima a.t 587, 542 m,a (Fig. 3), described earlier, makes that possibility unlikely. As has been stated above, experiments with porphyrins derived from chlorophyll had given reason to believe that the various pigments in the fractions separated from the Athabasca bitumen were all vanadyl derivatives, despite their considerable spectral differences. It seemed that a simple way to check this was to remove the vanadyl groups and separate the porphyrin bases, and then to reconstitute the vanadyl derivatives and compare absorption spectra of the original and reconstituted pigments. Devanadylation of porphyrin complexes has been reported by many workers ; the usual reagent is a concentrated solution of hydrogen bromide in acetic acid. In this investigation, use of this reagent was found to give very satisfactory results with crude oils, but attempts to devanadylate purified fractions of the porphyrin pigments resulted in almost complete destruction of the porphin ring system. However, if a small amount of 4, 4’-methylenebis(2, 6ditertiarybutylphenol) was added to the reaction mixture, a good yield of porphyrin bases was obtained; the use of phenol as a bromine scavenger has since been reported by HOWE (1961). The metal-free porphyrins were fractionated with dilute acid. From those fractions of the vanadyl complexes that contained only components with absorption peaks near 570 rnp, were obtained porphyrin bases that had spectra of either the phyllo or etio types (Fig. 11). Vanadylation of these bases by the method of ERDMANet&. (1956) produced complexes possessing typical vanadyl porphyrin absorption spectra similar to those of the fractions from which they were derived, with maxima near 570 rnp. Demetalation with hydrogen bromide of concentrates of the minor vanadyl porphyrin components with absorption maxima near 575 and 590 mp, followed by fractionation with hydrochloric acid, yielded, in addition to va.rious bases with etioor phyllo-type absorption spectra, very weakly basic porphyrin fractions which had typical rhodo-type absorption spectra (Fig. 12, curve 1). The fractions with etio- or phyllo-type spectra were readily converted to vanadyl derivatives that possessed “normal” absorption spectra similar to those in Fig. 6. The preparation of vanadyl

An investigation of the venadyl porphyrin complexes of the Athabasc aoil sands

6 ._

z

$

a

Wavelength, “yc Fig. 9. Absorption spectrum of e vanadyl porphyrin fraction from Athabasca bitumen,and differential spectra with vanaciyl m-porphyrin-IX (benzene solutione) . - - - fraction ex bitumen; - . . - differential epectra

550

Wovelengfh,

600

mp

W

550 600 Wavelength, ml”

Fig. 10. Differential absorption spectra of two vanadyl porphyrin fraction (benzene solutions).

e

, Wavelength,

Figs. 11 and 12. Absorption spectra of metal-free porphyrins bitumen fractions (benzene solutions). Fig. 11. etio type; - . . - phyllo type Fig. 12. rhodo type

600 nyc

prepared

from

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M. F. MILLSON, D. S.

MONTGOXERY

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BROWS

derivatives from those fractions that had rhodo-type absorption spectra was more difficult, as had been expected in view of similar problems encountered in the treatment of the same class of compound derived from chlorophyll. This difference in reactivity was of some use in purification of the rhodo-type porphyrins, since by following the vanadylation procedure at a reduced tempertlture (103°C instead of 118°C) some non-rhodo-type porphyrin could be preferentially removed from the fractions with rhodo-type spectra. The absorption spectrum of a fraction purified in this way is shown in Fig. 12, curve 2. Eventually it was found that t.he vanadylation reaction could be successfully brought about with the rhodo-type porphyrins under more vigorous conditions than were required by the other fractions, provided that a small amount of antioxidant was present. Before this discovery, however, another approach to the vanadyl derivative had been tried, since treatment with vanadyl sulphate in acetic acid had produced vanadyl derivatives directly from nickel complexes of porphyrin bases prepared from a commercial “chlorophyll”. Although nickel or copper complexes were very readily formed by the rhodo-type porphyrin fractions prepared from the Athabaaca bitumen, attempts to convert these derivatives to the vanadyl complexes were unsuccessful. However, it was noted that the wavelengths of maximum absorption in the absorption spectra of these nickel (Fig. 13) and copper (Fig. 14) compounds were far displaced (about 15 mp) from those of similar derivatives of the more common types of petroporphyrins ; this provided, by analogy, some confirmation of the belief that vanadyl porphyrins might have absorption maxima at wavelengths as great as 590 mp. After a successful technique had been discovered, various fractions of the rhodotype porphyrins from the bitumen were converted to vanadyl complexes. The vanadyl derivatives so formed had absorption spectra (Fig. 15) very similar to those of the fractions isolated from the bitumen, despite the fact that after devanadylation with hydrogen bromide the porphyrin bases had been fractionated with acid and separated into the various spectral classes, etio-, phyllo-, and rhodoporphyrins. This suggests that in either the devanadylation or vanadylation procedures used in this investigation, a pa.rt of the porphyrins with rhodo-type spectra may be converted to etio- or phyllo-type; the nature of the reagents used leads to the belief that decomposition or conversion is much more likely to occur in the devanadylat,ion than in the vanadylation step. In the course of isolating the reconstituted vanadyl complexes of the rhodo-type porphyrins from the reaction mixtures in which they were formed, the crude products were chromatographed on columns of magnesium sulphate. Figure 16 shows the absorption spectra of some of the fractions thus obtained. It appears that one of the spectra is due to a mixture of two components having absorption maxima near 570 and 575 rnp, and the other to a mixture of three components having maxima near 570, 576 and 690 rnp. This provides some additional evidence that in the spectra of vanadyl derivatives with absorption maxima near 675 and 590 rnp, these two peaks are due to separate entities and not t.o a component with a doublet peak. However, a note of warning may appropriately be sounded at this point : the amounts of material available in the experiments directed toward reconstituting the vanadyl derivatives of the rhodo-type porphyrins were extremely limited, and, in particular,

An investigation of the vanadyl porphyrin complexea of the Athabams

, 500

550

Wavelength,

I

I

600

rnp

Fig. 13. Absorption spectra of nickel porphyrin complexes (benzene solutions). from etio type; - - - - from rhodo type

e

oil tam&

500

550

WOVelGngth,

600 mp

Fig. 14. Absorption spectra of copper porphyrin complexes (benzone eolutions). -from phyllo type: - - - - from rhodo type

I

Wavelength

600 m+~

Fig. 15. Absorption spectra of a vanadyl porphyrin fraction from Athabasca bitumen and the vanadyl complex of a rhodo type porphyrin (benzene solutions). 1. fraction from the bitumen 2. vanadyl derivative of a rhodo-type porphyrin obtained by demetalation of a bitumen fraction

500 550 Wovelength,

600 rnp

Fig. 10. Absorption spectra of minor products from a vanadylation reaction (benzene solutions).

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F. MILLWN,D. S. MOXTQOYERY and 8. H. BROWN

the spectra in Fig. 16 represent very small quantities of material only just sufficient for spectra determination. On occasion, throughout the work here reported, a new absorption band would make an appearance at a wavelength where previously no band had been found, especially in the range 605-650 mp, and from time to time it complete vanadyl porphyrin fraction would be found to have changed from a bright red solution to a dirty green-brown material mostly forming a film on the flask walls, even though that fraction had been stored along with, and under apparently identical conditions to, many other fractions which remained apparently unchanged over a period of several years. For these rea.sons,great reliance must not. be placed on the evidence of the occasional occurrence of weak absorption bands. The porphyrin bases from the Athabasca bitumen that had rhodo-type spectra were not extracted from benzene solution by 1% sodium hydroxide solution, and, even after treatment under saponification conditions with 30?/0 potassium hydroxide solution (HODQSON et al., 1963), no porphyrin was detectable in the aqueous layer. It seems likely, therefore, that these rhodo-type porphyrins contain neither carboxylic acid nor ester groups, and are not true rhodoporphyrins. Nevertheless, it may reasonably be expected that the substituents on the porphin ring systems in these fractions resemble those of the true rhodoporphyrins in their effect.s on the electronic structure of the system as reflected in the absorption spectra. For similar reasons, absorption spectra of the rhodo-type are possessed by certain porphyrin compounds of known structure other than the true rhodoporphyrins, in particular by some acetylpyrroporphyrins, in which the ketonic ca.rbonyl group is conjugated with the main aromatic system. THE ORIGINOF THE MINORCOMPONENT The presence, in crude oils, of metal complexes of compounds possessing rhodoporphyrin-like absorption spectra was suggested by HOWE (1961), although the possibility that his rhodo-type products were artifacts of the hydrogen bromide reaction has been raised (BLUMER, 1961). The present study lends credence to the original suggestion that HOWE’Sproducts were present in the crude oils as complexes although absorption spectra of the metal complexes in those crude oils have not been published. Despite the uncertainty concerning the nature of the substituents on the porphin ring system, it seems certain that the minor peak at about 690 rnp in the absorption spectra of porphyrin pigment extracts from the Athabasca oil sands is due to vanadyl complexes. It may be pointed out that the corresponding nickel complex with absorption maximum near 669 rnp (Fig. 13) seems not yet to have been detected in this or any other deposit. If the vanadyl porphyrin compound with absorption maximum at 690 rnp in the Athabasca bitumen does in fact carry a carbonyl group in a position adjacent to the porphyrin nucleus, as seems most probable, and if the band at 690 rnp found by COSTANTINI~E~ and ARICH (1963) in many crude oils is due to the same type of vanadyl complex, as also seems likely, then an apparent contradiction is established with the statement of BLUMERand OXENN(1961) that carbonyl pigmente have never been found in sediments of appreciable age. From this stem various possibilities: either the conditions in the sediments in which the Athabasca bitumen and other

An investigation

of the vanadyl porphyrin complexes of the Athabaeca oil aande

219

crude oils originated were not sticiently reducing to remove all the carbonyl groups from the porphyrin pigments, or some of the petroporphyrin pigments can be oxidised without destruction of the porphin nucleus, or the substances responsible for the absorption band at 690 m,u were introduced into the oils at a stage subsequent to the major reduction processes by which the oils were formed. DEAN and WHITEHEAD (1963) have shown that oxidation of a petroleum fraction on standing may cause degradation of vanadyl porphyrins, this degradation being accompanied by an increase in absorption at 690 rnp. This makes it seem probable that the rhodo-type porphyrins in crude oils are derived from the more common petroporphyrins during an oxidative phase of their history. EXPEREUENTLLL DETAILS At all times when porphyrin samples were exposed, only dim illumination of the laboratory was permitted. While hydrogen bromide was in use, light was excluded from the reaction mixtures as much as possible. Chromatographio columns were made up in the wet, by adding the adsorbent as a slurry to a tube partly filled with solvent. Especially with anhydrous magnesium sulphate as adsorbent, it was advantageous for the preparation of evenly packed columns to keep the adsorbent covered with solvent under reduced pressure until air bubbles ceased to be evolved before making up the column. For development and elution of columns of alumina, Florisil, and powdered cellulose, the solvent series n-heptane, methylcyclohexane, benzene, ethyl acetate was used. For magnesium sulphate columns, the series n-hexane or n-heptane, benzene, isopropanoi was usually used. The adsorbent6 used were as follows: Activated alumina, type H, Peter Spence and Sons Ltd., Widnes, England; Florisil, SO/l00 mesh, Floridin Company, Tallahassee, Florida; cellulose powder, Whatman, ashless for chromatography, standard grade. The activated alumina and the Florisil were used as received. The cellulose powder was extracted (Soxhlet) with benzene for several days before use, to remove trace of a resinous material. Absorption spectra were determined on a Beckman DK-2 Ratio Recording spectrophotometer, which was calibrated by means of the emission lines of a hydrogen discharge lamp at wavelengths 666, 681 and 486 rnp. The method of measurement was as follows: the spectrum of the sample wss run in the normal way, using the slowest speed setting of the instrument in the critical regions near absorption peaks; lines corresponding to various wavelengths were then drawn across the recorded spectrum by manipulation of the absorbance”/o transmission selector after the wavelength control had been manually adjusted to give the desired readings on the wavelength scale. It is essential that the manual approach to these various wavelength positions be in the same sense (i.e. from the long wavelength direction) as that of the automatic recording system. The wavelengths of absorption maxima given in this paper are probably correct within f 1 rnp in the range 666-696 mp; for instance, the absorption peak of the spectrum in Fig. 4 (cyclohexane solution) always fell between 668 and 670 rnp and is referred to in the text &B669 mp. Slight changes in experimental procedures were continually being made in the search for improvement ; the procedures which follow are representative composites.

220

M. F. %LISIO?~,D. s. _?~ONMOXEBY

and S. 13. BROWN

Removal of the vanudyl group from van&y1 porphyrin

complexes

A stream of nitrogen was bubbled through glacial acetic acid (60 ml) which was heated on a steam-bath for 1 hour and then allowed to cool. The nitrogen stream was replaced by a st,ream of hydrogen bromide and the acid solution was cooled in ice. When absorption of hydrogen bromide had ceased, a solution of 4, 4’-methylenebis (2, 6ditertiarybutylphenol) (5 mg) in glacial acetic acid (5 ml) was added, the passing of hydrogen bromide was discontinued, and a solution of the porphyrin complex (< 2 mg) in glacial acetic acid (5 ml) was added. The contents of the flask were mixed by swirling, and the flask was placed in a bath at 45’C overnight. The reaction mixture was poured on to cracked ice in a separatory funnel and extracted several times with benzene. From this point the treatment varied according to t,hc nature of the products. (a) If the original vanadyl complexes were of the “normal” 5iO rnp type with little or none of the 590 rnp type, extraction of the benzene extracts with dilute hydrochloric acid (10% HCI) removed any metal-free porphyrins. This acid extract and the aqueous acetic acid layer were combined, neutralised with sodium acetate solution, and extracted with benzene. The benzene layer was freed from acetic acid by washing with water, and then successively extracted with hydrochloric acid solutions of increasing strength. The acid extracts were neutralised with sodium acetate solution and the porphyrin bases were extracted with benzene and freed from acetic acid by washing with water. (b) If the original vanadyl complexes contained much of the “abnormal” 590 rnp type, the initial benzene extract of the diluted rea.ction mixture was extracted fist with 25% hydrochloric acid and then with concentrated hydrochloric acid (sp. gr. 1.18). These acid extracts and the aqueous acetic acid solution were combined, neutralised with sodium acetate solution, and extracted with benzene. The benzene extract was freed from acetic acid by washing with water, and extracted several times with each of a series of hydrochloric acid solutions of increasing strength. The acid extracts were neutralised with sodium acetate solution and the porphyrin bases were extracted with benzene and freed from acetic acid by washing with water. The series of fractions obtained in this way varied in spectra from the types shown in Fig. 11, for those obtained with the weaker acid solutions (leas than 10% HCI), to the type shown in Fig. 12, for those isolated by means of strongly acid solutions (about 20% HCI). Intermediate fractions could be largely separated into the better defined classes by repetition of the acid fractionation procedure. Preparation of a vanadyl derivative of a rho&-type porphyrin from commercially available chlorophyll

which had been prepared

To a solution of vanadyl sulphate dihydrate (12 mg) in aqueous acetic acid (1 ml, 60°/ov/v) were added glacial acetic acid (3 ml), pyridine (1 ml), and a solution of the porphyrin in glacial acetic acid (1 ml). The mixture was sealed in a glass ampoule and heated in an oil bath at about 120% for 60 hours. After cooling, the contents of the ampoule were shaken in a separatory funnel with ether (76 ml) and water (150 ml). The ether layer was separated and washed successively with water, dilute hydrochloric acid, and water. The washed ether solution was evaporated to dryness in a stream of nitrogen, and the residue was chromatographed on a column

An investigation of the vanadyl porphyrin complexes of the Athabasca oil sands

221

of maguesium sulphate in n-hexane. From the column, n-hexane eluted a vanadyl porphyrin with absorption maxima at 568, 531 rnp. When the eluent was changed to a mixture of benzene, isopropanol and pyridine (1: 1: l), the vanadyl derivative with the absorption spectrum shown in Fig. 3 (curve 2) was eluted. Preparation of a vanfdyl derivative of a rhodo-type porphyrin obtainedfrom Athubaaca bitumen In a glass ampoule were placed vanadyl acetate solution (1 ml of a solution in dilute acetic acid containing about 1 mg of vanadium per ml ; ca. O-02mmol), pyridine (O-5ml), a solution in glacial acetic acid of 4, 4’-methylenebis (2, Uitertiarybutylphenol) (5 mg), and a solution in glacial acetic acid of the porphyrin (from 4 ml of a benzene solution, absorbance O-6at 541 rnp; ca. O-0002 mmol). The liquid volume was made up to about 8 ml with glacial acetic acid. Air was displaced from the ampoule with nitrogen, and the ampoule was then sealed and heated in an oilbath at 138°C for 12 hours. The ampoule was allowed to cool, opened, and the contents were poured into a mixture of benzene and water. The benzene solution so obtained was washed many times with water and evaporated to dryness in a stream of nitrogen. The residue was taken up in hot n-heptane and chromatographed on a column of anhydrous magnesium sulphate. From the column, n-heptane eluted the antioxidant, benzene eluted vanadyl porphyrin products with spectra similar to that in Fig. 15 (curve 2), and benzene-isopropanol mixtures eluted any uncomplexed porphyrin bases. REFERENOES

SEEWMAKEE J. E. (1957) The nature of vanadium in petroleum. ITZ&W. 49, 1167-1164.

BEACH L. K. and Engng. Chem.

BLUMERM. (1966) Separation of porphyrins by paper chromatography. Analyt. China. a8, 1640-1644. BLUMERM. (1961) Improved chromatographicanalysis of petroleum porphyrin aggregatesand quantitative measurement by integral absorption by W. W. Howe. An&#. Chem. 88, 128& 1289. BLUMER M. and OMEhT G. S. (1961) Fossil porphyrins: uncomplexed chlorins in a Triassic sediment. Geochim. et Coemochim. Acta eS, 81-90. COSTANTINIDES G. and ARICHG. (1963) Research on metal complexes in petroleum r&dues. Paper V-11, Sixth World Petroleum Congress, Frankfurt, Germany. CORWINA. H. and BAIEERE. W. (1964) Structure studies on petroporphyrins. Preprints 9, No. 1, 19-24, Div. of P&r. C&m., Am. Chem. SOL, Philadelphia, Pa., Mar. 1904. DEAN R. A. and WHITEHEADE. V. (1963) The compositionof high boiling petroleum distillates and residues. Paper V-9, Sixth World Petroleum Congress, Frankfurt, Germany. DJIXGHECZIAN L. E. and WARRENT. E. (1961) A study of cold-water separation of bitumen from Alberta bituminous sand on a pilot plant scale. Canad. J. Z’echnol. aS, 170-189. ERDMA.N J. G., RAMSEYV. G., KaLEhma N. W. and HA.NSONW. E. (1956) Synthesis and properties of porphyrin vanadium complexes. J. Amer. Chem. Sot. 78, 5844-6847. FISCHERH. and ORTHH. (1937) Die Chemie de8 Pyrrols, Vol II(l), p. 683. Aksdemische Verlagsgeaellschaft,Leipzig. HODQSONG. W., PEAKE E. and BAKER B. L. (1963) The origin of petroleum porphyrins: the position of the Athabasca oil sands. Contributionto the K. A. Clark Volume of Papers on the Athabasca Oil Sands (Information Series No. 45, Research Council of Alberta, Oct. 1963, price $6.00). pp. 76-100. HONE W. W. (1961) Improved chromatographicsnalysis of petroleumporphyrin aggregates and quantitative measurementby integral absorption. An&. Chem. 33, 256-260. 6