PYROLYTIC STUDIES OF CARBONACEOUS MATTERIN ANTARCTIC CARBONACEOUS CHONDRITES
Tatsushi MURAE, Akimasa MASUDAand Takeyoshi TAKAHASHI
Department of Chemistry, Faculty of Science, The Uuiversity of Tokyo,
Hongo 7-chome, Bunkyo-ku, Tokyo 113
Abstract: Pyrolysis products of the major carbonaceous matter in six Antarctic
carbonaceous chondrites, Y-74662 (C2), Y-791198 (C2), Y-793321 (C2), B-7904(C2), Y-791717 (C3), and ALH-77307 (C3), have been examined by GC-FID andGC-MS. There is apparently a similarity in the structure of all samples. Manysulfur-containing compounds have been detected as major products in pyrolysis of
the residues which were obtained by partial mineral dissolution of Y-791717 andALH-77307 with concentrated hydrochloric acid.

1. Introduction
The major carbonaceous matter in carbonaceous chondrite is not extractable inany solvent (MuELLER, 1953). Various methods have been applied to the characterization of solvent-unextractable carbonaceous matter (SCHULZ and ELOFSON, 1965;
HAYES and BIEMANN, 1968; SIMMONDS et al., 1969; GREEN II et al., 1971; BREGER etal., 1972; LEVY et al., 1973; BANDURSKI and NAGY, 1976; HAYATSU et al., 1977, l980;
HOLZER and ORo, 1979; WHITTAKER et al., 1980; SMITH and BUSECK, 1981). A polyaromatic structure has been proposed for this material in Murchison and other several
carbonaceous chondrites (HAYATSU et al., 1977). Although carbines have been claimed
to be the material in Murchison (WHITTAKER et al., 1980) and Allende (WHITTAKERet al., 1980; HAYATSU et al., 1980), it has been suggested that the major carbonaceous
mater in Allende occurs possibly as a noncrystalline graphite like compound (SMITHand BUSECK, 1981). Although analysis of the pyrolysis products is one of the mostuseful methods for the 'investigation of organic polymer in meteorites (HAYES andBIEMANN, 1968; SIMMONDS et al., 1969; LEVY et al., 1973; BANDURSKI and NAGY, l976;
HOLZER and OR6, 1979; MURAE et al., 1984a), the effect of coexisting minerals (whosecontents are much higher than that of carbon) on pyrolysis is not clear. Analysisof acid-resistant residues obtained by mineral dissolution (treatment with hydrochloricand hydrofluoric acids) gives direct information on residual carbonaceous matter(SMITH and BusECK, 1981), but the possibility of alteration of the polymeric structureduring acid treatment remains.
The authors have investigated the major carbonaceous matter in six Antarctic
carbonaceous chondrites by examination of pyrolysis products with gas chromatographyequipped with a flame ionization detector (GC-FID) or a mass spectrometer (GC-MS).
These chondrites are Y-74662 (C2), Y-791 198 (C2), Y-793321 (C2), B-7904 (C2), ALH-77307 (C3), and Y-791717 (C3) (Y for Yamato, B for Be1gica, and ALH for Allan Hills).
Carbonaceous matter in the HCl-resistant residues from Y-791717 and ALH77307
was also examined by the same method. The results are reported in this paper.
2. Sample Preparation and Experimental Apparatus
Samples used in the present work were taken from small chips delivered from themeteorite curator of National Institute of Polar Research. After washing with nhexane, the chips were powdered (grain size: 10-20 pm) and the powder was used for
pyrolytic studies. A part of the powdered sample of Y-74662 was extracted withbenzene-methanol (2: 1) for 12 hrs using a Soxhlet extractor. Partial mineral dissolution of ALH-77307 (144 mg) and Y-791717 (l52 mg) was carried out by treatment
with cone. hydrochloric acid (12N: 2.5 ml) at room temperature for 3 days, followed
by washing with distilled water, treatment again with cone. hydrochrolic acid (12N:2.5 ml) at room temperature for one day, filtration using a glass filter, washing theresidue with distilled water, and then drying under air stream. In the acid treatments
52 and 587o weight tosses were observed for AuI-77307 and Y-791717, respectively.
The same instruments and conditions as those described previously (MURAE etal,, 1984a) were used for the present work (pyrolysis followed by analysis by GC-FIDor GC-MS), although the GC column and oven temperature were different. An open
tubular fused silica capillary column (25 m x0.25 mm i.d.) coated with silicon OV-101
as stationary phase (film thickness: 0.40 μm) was used for GC-FlD analysis. The
rate of temperature increase was programed to be 4℃/min from 60 to 260℃ after
keeping the initial temperature for 16 min. An open tubular fused silica capillarycolumn (25 m x 0.25 mm i.d.) chemically bonded with silicon OV-1 as stationary
phase (film thickness: 1.5 μm) was used for GC-MS analysis, because it was confirmedthat this column had the applicability to the same type of compounds with much better
resolution (sharp peaks with high intensity) compared with that of the wall coatedov-lOl column used for GC-FID analysis. Incremental increae in oven temperature
at a rate of 4oC/min from 60 to 230oC was started immediately after pyrolysis. Theoperation of an exhaust valve after pyrolysis, required in the previous study (MURAEet al., 1984a) was not necessary when these capillary columns were used.
3. Results and Discussion
Extraction with organic solvents has been carried out for several carbonaceouschondrites to show the presence of organic monomers (reviewed by ANDERS et al., 1973).
No change in the components produced in pyrolysis of Y-74662 before and after solvent
extraction showed that those components were yielded by thermal degradation of
unextractable major carbonaceous matter. It was difficult to detect extractable organic
monomers from the sample amount used for pyrolysis, because concentration of eachmonomer is known to be very low (PERING and PONNAMPERUMA, 1971).
Chromatograms of the components yielded in pyrolysis at 740oC of Y-791198,Y-74662, Y-79332l, Y-791717, B-7904, and ALH-77307 are shown in Fig. 1. The
major products shown in Fig. 1 were identified by the comparison of the mass spectrum

and the retention time in gas chromatography with those of the authentic samples(tentative identification for acephenanthylene). A number of types of compounds
are analyzable (ex. hydrocarbons, Organic halides, organic sulfides, ethers, esters,ketones, alcohols, phenols, nitriles, amines) under the gas chromatographic conditions.
Nevertheless, all of the major pyrolyzates are aromatic hydrocarbons (except benzothiophene). The intensities of the peaks of the pyrolyzates are low in the chromatograms ofALH-77307, B-7904, Y-791717, and Y-793321 (C, D, E, and F in Fig. 1), but
the same compounds are detected as the major products in the chromatograms of allsamples. It has been shown by many examples that chromatographic patterns ofpyrolysis products clearly reflect the structure of the organic polymer originally present(OKUMOTO and TAKEUCBI, 1972; TAKEUCHI and TSUGE, 1977; GLAJCH et al., 1979).
The similarity in the chromatographic patterns (components and their relative in-tensities) of the pyrolysis products suggests the presence of the similar partial structurein the carbonaceous matter of these chondrites. The components indicate that thepartial structure dose not contain hetero atoms (oxgen, nitrogen, etc.) except sulfur.
Although highly nonvolatile compounds such as free carboxylic acids or amino acids
cannot be detected under the analysis condition, the functional groups which yieldsuch compounds are probably not present in the partial structure, because the oxygenor nitrogen-containing compounds were not found in the pyrolysis products. The
carbon contents of these chondrites (Table 1 : determined by combution method using
a CHN analyzer) did not agree with the amounts of pyrolysis products. Those differences are attributed to the differences of the number of the partial structures in the
carbonaceous matter in the meteorites.

IThe similarity of the partial structure and the different number of the partialstructures are explained by the whole structure which has been proposed by the authors
for major carbonaceous matter in carbonaceous chondrites (MURAE et al., 1984,b).
The proposed structure is characterized by a large network of polyaromatic compounds
similar to that of graphite layer. This structure bears edge defects' as shown by
UBBELOHDE (1957) and then ZIMMER and WHITE (1976) (Fig. 2). The pyrolysis products are considered to be produced mainly by degradation of the edge defects which
are constructed with thermal1y weaker bonds compared with those in the condensed
aromatic network (OTANI and SANADA, 1980). Similarity among the chromatographic
patterns of the pyrolysis products suggests that the structure of edge defects is thesame for all carbonaceous chondrites investigated in this work. Difference of thechromatographic intensity of the pyrolysis products among the chondrites shows thatthe number of edge defects is different for the carbonaceous matter in each chondrites.
As shown in Fig. 1 naphthalene gives the most intense peak except very volatilecomponents. The ratios naphthalene yielded in pyrolysis to the amounts of carbon
contained in the chondrites are shown in Table 1. The ratios are considered to reflect
the number of edge defects in the carbonaceous matter. The ratio did not accord
with the chemical and petrographycal classification. This fact suggests that the process of the formation of the carbonaceous matter may be independent of that of theparent body.

Mineral dissolution by treatments with hydrochloric and hydrofluoric acids has
been carried out to recover solvent-unextractable carbonaceous matter in carbonaceouschondrites (ex. BAUMAN et al., 1973; WHITTAKER et al., 1980; HAYATSU et al., 1980;
SMITH and BUSECK, 1981). Some changes in the structure of the carbonaceous matter
may have been caused by the acid treatment. Since the edge defects in the proposed
structure are reactive positions, in the treatment with hydrochloric acid halogenation
and/or oxidation reactions may occur at such positions. When the minerals in themeteorites were dissolved with hydrochloric acid, the reactions may be accelerated
after the formation of FeCl3, AlCl3, etc. as Catalysts.
Pyrolytic studies are considered to give useful information on alteration of thestructure of carbonaceous matter by mineral dissolution of carbonaceous chondrite.
Figure 3 shows pyrograms at 740℃ for the samples of Y-791717 and ALH-77307
before and after treatment with hydrochloric acid. The carbon content of the residues
after the hydrochloric acid treatments was approximately twice that of untreated samples (Table 1). The chromatographic intensities of the components yielded in pyrolysis of the residues after the hydrochloric acid treatment are higher than those of theuntreated samples on the basis of carbon contents. Two explanations are possible forthe increase in chromatographic intensities of the pyrolysis products from acidresistant residue. One is that there is an increase in the number of edge defects inthe carbonaceous matter by the treatment with the acid. A second possibility is
an increase of chemical species by the mineral dissolution. These chemical species
might aid the formation of pyrolysis products in reactions with the radicals produced on thermal fragmentation of the carbonaceous matter.
The pyrolysis products of the acid-treated samples were examined by mass chromatography using all ions from m/I 50 to m/I 250 (ex. Fig. 4). A number of organicsulfur compounds were observed with significant intensities in the pyrolysis products(Fig. 3). These sulfides (except thiophen and benzothiophen) did not give intense
peaks in the pyrograms of acid-untreated samples. This fact indicates two possibilities
which may have occurred during treatment of the carbonaceous chondrite with hydrochloric acid: sulfenylation of the carbonaceous matter and an increase in the amountof reagents (or catalysts) concerned with the formation of sulfur-containing compounds
during pyrolysis. There was no indication of the occurrence of chlorined compounds.
Removal of free sulfur to obtain more exact information by pyrolysis is under way.

4. Summary
Similarity of the pyrolysis products from all of the carbonaceous chondrites shows
the presence of the common partial structures in the carbonaceous matter. This suggests that the carbonaceous matter in all of the chondrites was probably synthesizedby similar processes. Difference of the amount of the pyrolysis products indicatesthe difference of the number of the partial structures (edge defects). Three explanations are possible for the difference : i) the numbers of the edge defects in the same
molecule are different among the chondrites, ii) degrees of incorporation of the samestructure molecules are different among the chondrites, or iii) different molecules
having similar partial structures are incorporated in the same chondrite. A numberof sulfur-containing compounds were found h the pyrolysis products of the acid-resistant residuces. They were probably formed by trapping of the radicals yielded in thethermal degradation of the carbonaceous matter with free sulfur which was given in
the acid treatment. The pyrolytic nature of the carbonaceous matter did not accord
with the chemical and petrographical classification of the chondrites. This probably
suggests that the carbonaceous matter has been synthesized before the incorporation
into the parent body.