17 TH ISPAC CONFERENCE NEWS!.doc

A couple of things concerning ISPAC and the newsletter First in the last newsletter I forgot to list Stephen Nesnow of the U S Environmental Protection Agency as one of the newly elected ISPAC Board members My apologies for leaving him off the list Second a membership application is once again enclosed If you plan to attend the Bordeaux meeting you must be a member of ISPAC when you register in order to receive the discount Third once again a solicitation for items for the newsletter Its timing is totally dependent on content In this issue Leo Jennekens and Steve Wise contributed articles and so this issue is now in your hands Any articles or news items or even small bits of useful information for others working with PACs would be welcomed Send them to me at jcfe or John Fetzer Chevron Research and Technology Company P O Box 1627 Richmond CA 94802 USA 17TH ISPAC CONFERENCE NEWS The 17th International Symposium on Polycyclic Aromatic Compounds will be held on October 25th through 29th at the Palais des Congres in Bordeaux France The symposium will include parallel technical sessions on the chemistry and biology of polycyclic aromatic compounds PACs Topics will include Metabolism and metabolic activation DNA and protein adducts Bioassays Mutagenicity Carcinogenicity Toxicity Detoxification Immunochemistry Biomarkers Epidemiology Biomonitoring Risk assessment and regulation Biodegradation Bioremediation Analytical methods Photochemistry Spectroscopy Synthesis Theoretical and physiochemical properties Molecular modeling SAR and QSAR Environmental studies Organic geochemistry soil sediment atmosphere PAHs in extraterrestrial systems PACs in food Exposure models Reference materials Specimen banking There will be several social functions including a welcoming wine and cheese reception the conference banquet in a famous chateau tour of a vineyard in the Saint Emillion area and an evening organ recital in the St Andre s Cathedral In addition short courses on PAC topics will be offered on the 25th prior to the conference Topics will include extraction techniques reference materials physiochemical properties biomarkers exposure to and effect of PACs and new analytical techniques For those interested in submitting a proposed paper an abstract in English should be printed on plain white paper 15 cm width x 20 cm height The title should be entirely in capital characters followed by the authors listed as surname initials and affiliation The character size should be in standard 12 point and not exceeding 15 characters per inch Proposed papers are to be sent by May 31st to ISPAC 17 Dr Philippe Garrigues LPTC Universite de Bordeaux I 351 cours de la Liberation F 33405 Talence Cedex France or Ispac17 lptc u bordeaux fr Website for further information http www lptc u bordeaux fr or http ispac tor ec gc ca IUPAC CHANGES NOMENCLATURE RULES Dr G P Moss sent an e mail that the IUPAC nomenclature rules have changed Two of note are that tetracene is now the accepted name for the four ring linear PAH rather than naphthacene and that a four ring bent structure has been added to make the core structures consistent There had been phenanthrene pentaphene hexaphene etc Now tetraphene has been added This is the same structure as benz a anthracene and the IUPAC preferred name for benzo a pyrene becomes benzo pqr tetraphene Also acenaphthene and cholanthrene are no longer acceptable trivial names There are probably other names that are affected by these rule changes www chem qmw ac uk iupac or www chem qmw ac uk iubmb AIR PARTICULATE SRM FOR PAHS MEASUREMENTS REISSUED In 1982 the National Institute of Standards and Technology NIST issued Standard Reference Material SRM 1649 Urban Dust Organics which was one of the first natural matrix SRMs for the determination of polycyclic aromatic hydrocarbons PAHs SRM 1649 was issued with certified concentration values for five PAHs fluoranthene benz a anthracene benzo a pyrene benzo ghi perylene and indeno 1 2 3 cd pyrene and noncertified concentrations for nine additional PAHs The certified values for these five PAHs were based on the combined results of analyses by two analytical techniques gas chromatography with flame ionization detection GC FID and reversed phase liquid chromatography with fluorescence detection LC FL The values reported for the remaining nine PAHs were based on results from only one analytical technique i e either GC FID or LC FL The relative uncertainties associated with the certified values ranged from a low of 7 fluoranthene to a high of 24 benzo ghi perylene with the remaining three PAHs at 12 to 17 Even though SRM 1649 had only a limited number of certified values it has been used extensively during the past 17 years for validation of new analytical methods and as a quality control material Since SRM 1649 was first issued NIST have developed and implemented improved analytical methods for the measurement and certification of a significantly greater number of PAHs in environmental matrix SRMs Because there was still a considerable supply of SRM 1649 available recertification of SRM 1649 was undertaken with the following goals 1 to provide an increased number of certified concentrations for PAHs and other analytes and 2 to reduce the uncertainties associated with the certified concentrations The recertified air particulate material has been reissued recently as SRM 1649a Urban Dust The analytical approach for the recertification consisted of solvent extraction with different solvents using both Soxhlet extraction and pressurized fluid extraction PFE followed by measurement of the PAHs in the extract using the following analytical techniques 1 reversed phase liquid chromatography with fluorescence detection LC FL for analysis of the total PAH fraction 2 reversed phase LC FL analysis of isomeric PAH fractions isolated by normal phase LC i e multidimensional LC and 3 gas chromatography mass spectrometric GC MS analysis of the PAH fraction using three different stationary phases each with different selectivity for PAH separations The results from these techniques were combined to provide certified concentrations for 22 PAHs and reference concentrations for an additional 22 PAHs The relative uncertainties associated with the certified concentrations in SRM 1649a ranged from a low of 2 to a high of 24 with the relative uncertainties for most of the PAHs in the 5 to 10 range In addition to PAHs certified and reference concentrations were determined for other organic contaminants including polychlorinated biphenyls PCB congeners chlorinated pesticides and dibenzo p dioxin and dibenzofuran congeners Reference values are also reported for trace elements total extractable material total organic carbon mutagenic activity carbon composition and particle size characteristics Increasing the number of certified and reference concentrations for the PAHs reducing the uncertainties of the certified values and providing values for an expanded number of organic contaminants will significantly increase the usefulness of SRM 1649a For SRM ordering information phone 301 975 6776 or visit the SRM website at http ts nist gov srm HIGH TEMPERATURE CHEMISTRY OF NON ALTERNANT POLYCYCLIC AROMATIC HYDROCARBONS THE FLASH VACUUM THERMOLYSIS APPROACH Leonardus W Jenneskens Edward J Vlietstra Martin Sarobe and Stefano N R Ponzano Debye Institute Department of Physical Organic Chemistry Utrecht University Padualaan 8 NL 3584 CH Utrecht The Netherlands email jennesk chem uu nl Abstract The utility of Flash Vacuum Thermolysis for the study of the high temperature chemistry of non alternant Polycyclic Aromatic Hydrocarbons PAH between 500 1200 C is demonstrated The results are of relevance for detailed understanding of processes operational during combustion viz PAH build up rearrangements and interconversions Introduction It is well established that Polycyclic Aromatic Hydrocarbons PAH are invariably generated during incomplete combustion of fossil fuels viz the most important energy source in our society 1 Hence as a consequence of anthropogenic activities PAH are continuously introduced into our terrestrial environment Natural combustion processes such as forest fires and volcanic activity further contribute Unfortunately many PAH have to be classified as environmental pollutants due to their genotoxic properties i e PAH are also of significant biological interest 2 Besides the terrestrial abundance of PAH diverse studies have indicated that up to 20 of all carbon in the galaxy is confined into ionized PAH If this is the case ionized PAH represent the most prevalent class of organic molecules in the universe 3 These considerations already indicate that PAH represent a class of organic molecules of particular interest for the natural sciences i e chemistry physics biology medicine geology and materials science 1 Without the intervention of bureaucrats PAH research from its infancy onwards represents genuine interdisciplinary research Additional impetus was given in 1985 by the imaginative proposal that during laser evaporization of graphite under appropriate conditions stable closed carbon surfaces i e the fullerenes C60 and C70 are formed 4 It is noteworthy that these experiments were originally aimed at understanding the mechanisms which give rise to long chain carbon molecules in interstellar space Although the fullerene proposal was received with skepticism in 1990 C60 as well as C70 were isolated from mundane soot obtained by either resistive or arc heating of graphite 5 Moreover also the carbon nanotubes buckytubes were subsequently identified and isolated from graphite soots 6 Again many of these experiments originally served different objectives i e to establish the role of carbon particles as carriers of the interstellar 217 nm UV feature of the diffuse interstellar bands DIBs With regard to the fact that PAH are invariably generated during incomplete combustion the identification of C60 and C70 in certain flame exhausts besides the common ubiquitous PAH effluents has had major impact and firmly linked fullerene and PAH science 7 This connection was further substantiated by the proposal that fullerene formation is of possible relevance for the formation and morphology of soot 8 This issue led to considerable debate 9 The Flash Vacuum Thermolysis Approach The awareness that the genotoxicity of combustion exhausts can be accounted for by the presence of distinct PAH of which the externally cyclopenta fused derivatives CP PAH such as cyclopenta cd pyrene 1 pose an extraordinary biohazard has made the elucidation of CP PAH build up under high temperature conditions in the gas phase a topical issue 10 Here we report an account of our research activities in the area of non alternant PAH in which Flash Vacuum Thermolysis FVT 11 plays a central role FVT is a powerful tool to study the build up rearrangements and interconversions of non alternant PAH under controlled conditions temperature and or pressure dependence presence of gaseous additives etc Moreover FVT is also of interest from a preparative point of view Convenient syntheses of pure non alternant PAH 321 C2 C2H2 which require lengthy and or tedious classical wet chemical synthetic routes have been disclosed 1 Method In an FVT experiment a precursor is sublimed rate ca 0 1 1 0 gh 1 into the hot zone of a furnace quartz tube length 40 cm diameter 2 cm which is heated between 500 1200 C the pressure is usually maintained at ca 10 2 Torr Whereas the volatile pyrolysate products are collected in a cold trap N2 l the low volatility products either condense or even crystallize behind the hot zone outside the furnace The isolated pyrolysates are subjected to analysis 1H 13C NMR capillary GC GC MS GC cryotrapped FT IR HPLC Results and Discussion The C18H10 CP PAH Cyclopenta cd pyrene 1 and Benzo ghi fluoranthene 6 Our attention was initially focussed on the elucidation of an efficient gas phase synthesis of the ubiquitous non alternant CP PAH combustion effluent cyclopenta cd pyrene 1 C18H10 10 It is noteworthy that 1 ethynylpyrene 2 is frequently proposed as the primary intermediate for 1 Scheme 1 10 During combustion 2 is suggested to be Scheme 1 derived from pyrene 3 by the addition of either C2 or C2H2 It should be emphasized that 3 next to phenanthrene and fluoranthene represents one of the three most prevalent PAH combustion effluents If this pathway is indeed operational non toxic 3 will be converted into the genotoxic 1 under high temperature conditions in the gas phase This will have a marked effect on the genotoxic properties of PAH combustion exhausts 10 Recently we have shown that FVT 1000oC 10 2 Torr of 1 chloroethenyl pyrene 4 a volatile masked ethynyl precursor gave 1 in near quantitative yield mass recovery 90 Scheme 2 12 The unequivocal identification of 1 ethynylpyrene 2 in pyrolysates obtained at T 800oC corroborated that 2 is indeed the precursor of 1 Compound 2 is presumably converted into 1 by an ethynyl ethylidene carbene equilibration 2 5 followed by carbene C H insertion 5 1 under FVT conditions It is noteworthy that 1 is conveniently accessible on a gram scale by FVT of readily available 4 Scheme 2 Incidentally above 1000 C besides 1 its isomer benzo ghi fluoranthene 6 was unambiguously identified as a novel minor product Scheme 3 13 Independent FVT 1000 C T 1200 C of 1 showed that 1 indeed rearranges into 6 Semi empirical AM1 PM3 as well as ab initio quantum chemical MRCI CASSCF 6 31G calculations support that the rearrangement of 1 into 6 occurs via a ring contraction ring expansion mechanism consecutive 1 2 H 1 2 C shift or vice versa 14 FVT Cl 21 45 HCl Scheme 3 The Three C20H10 Dicyclopentapyrenes 7a c After the successful preparation of 1 we were prompted to extend our efforts to the three previously unknown dicyclopenta fused pyrenes dicyclopenta cd jk 7a dicyclo penta cd fg 7b and dicyclopenta cd mn pyrene 7c Compounds 7a c were earlier put forward as prevalent C20H10 CP PAH effluents in certain flame exhausts 15 FVT of 1 6 8a 1 8 8b and 1 3 bis 1 chloroethenyl pyrene 8c respectively gave 7a c in good yields 80 100 and reasonable to good mass recoveries 30 80 Scheme 4 16 It is gratifying that Scott and co workers independently prepared 7a c using a similar approach 17 In line with their thermal stability up to 1000 1100 C 7a c were subsequently indeed identified as prevalent C20H10 CP PAH effluents in flame exhausts 18 Analysis of pyrolysates obtained upon FVT of 8a c in the temperature range 700 1100 C revealed that 8a c are converted into 7a c respectively in three steps 1 In situ formation of the related bisethynylpyrenes from 8a c 2 conversion of the bisethynylpyrenes into the appropriate ethynyl substituted cyclopenta cd pyrene derivatives and 3 conversion of these cyclopenta cd pyrene derivatives into 7a c respectively 16 A preliminary investigation of the physicochemical cyclic voltammetry E1 2 0 1 vs SCE and spectroscopic properties 1H NMR UV Vis excitation and emission of 7a c showed Scheme 4 that dicyclopenta fusion topology markedly affects these properties 14 16 17 The C22H10 CP PAH Triscyclopenta cd fg jk pyrene 9 The next target was the unknown congener triscyclopenta cd fg jk pyrene 9 C22H10 Compound 9 was previously predicted to be a high temperature stabilomer on the basis of thermodynamic considerations 19 Recently we have shown that FVT of 1 3 6 tris 1 chloroethenyl pyrene 10 gave 9 via the intermediacy of 1 3 6 trisethynylpyrene 11 C22H10 between 900 950 C Scheme 5 20 However in marked contrast with the above mentioned prediction 19 concerning the stability of 9 and the established thermal stability of its congeners 1 12 and 7a c 16 17 9 as well as 11 were found to be thermally labile compounds They are highly susceptible to undergo C2 extrusions 21 For example FVT of 10 at 800 C gave besides 11 the known CP PAH 7a c 16 17 1 12 and 3 as side products Schemes 2 4 and 5 An analytically pure sample of 9 could be isolated from the 950 C pyrolysate by tedious column chromatography enabling its unambiguous structural assignment 1H NMR HR FAB MS Remarkably at 1000 C neither 9 nor 11 are present instead dicyclopenta cd jk pyrene 7a is the sole product 16 FVT Cl XY Z 7a7c7b FVT 8a 8b 8c Y CCl2CH2 X CCl2CH2 Z CCl2CH2 X Z H Y Z H X Y H Scheme 5 These results suggest that 9 in contrast to 1 and 7a c will only be a fleeting intermediate under high temperature conditions in the gas phase i e 9 and presumably also 11 represent precursors for 1 3 and 7a c 20 The Illusive C24H10 CP PAH Tetracyclopenta cd fg jk mn pyrene 12 So far the last congener of the externally cyclopenta fused pyrene series tetracyclopenta cd fg jk mn pyrene 12 C24H10 has remained illusive Scheme 6 FVT of 1 3 6 8 tetra 1 chloroethenyl pyrene 13 between 800 000 C only gave a still unidentified PAH its structural assignment is under investigation 14 Scheme 6 Formation of Ethynyl Substituted PAH E PAH Under High Temperature Conditions The results discussed above substantiate that ethynyl substituted PAH E PAH play an important role in the build up of externally cyclopenta fused PAH under high temperature conditions in the gas phase However despite the proposal that E PAH are obtained by addition of either C2 or C2H2 to ubiquitous PAH 22 insight in these processes is still scarce To shed light on this issue we have started a systematic study in which the most prevalent combustion effluents pyrene 3 phenanthrene and fluoranthene respectively are subjected to high temperature conditions 1100 1200 C 10 2 Torr in the presence of ethyne 14 C2H2 Pyrolysate product analysis 1H NMR GC MS GC cryotrapped FT IR obtained from the co pyrolysis of pyrene 3 mass recovery 35 or 1 bromopyrene 15 mass recovery 22 with 14 revealed that both pyrolysates possess a well defined and a nearly identical composition pyrene 3 55 cyclopenta cd pyrene 1 27 12 benzo ghi fluoranthene 6 6 13 2 ethynylpyrene 16 6 the bowl shaped CP PAH c