Reginald H. Mitchell

PAHs in the Fraser River basin: a critical appraisal of PAH ratios as indicators of PAH source and composition

Abstract Parent and alkyl PAHs (51 compounds and alkyl homologues) have been quantified in suspended particulates and sediments (345 samples) from the Fraser River system, British Columbia, Canada. The best potential to distinguish natural and anthropogenic sources is exhibited by ratios of the principal mass 178, 202, 228 and 276 parent PAHs, 1,7/2,6+1,7-DMP (dimethylphenanthrene), the phenanthrene/anthracene and fluoranthene/pyrene alkyl PAH series and several less commonly applied PAHs (e.g. acephenanthrylene and pentaphene). Using these ratios we infer sources of PAH to the Fraser basin and evaluate the consistency of these source assignments and the suitability of various commonly applied PAH ratios as indicators. PAH ratios and total concentration data reveal a basin lightly impacted by a variety of sources in its remote regions, especially near roads, but heavily impacted in urban areas, particularly near Vancouver. Contamination sources shift from biomass (e.g. wood and grass) burning to vehicle emissions between remote and urban locations. Stormwater and wastewater discharges appear to collect PAH from urban areas and release them as point sources. In contaminated areas ratios are specific for combustion vs. petroleum sources, and some ratios (202 and 276) distinguish biomass or coal from liquid fossil fuel combustion. At lower concentrations multiple sources at times make interpretations based on a single ratio misleading and the higher mass ratios (228 and 276) may be most applicable to urban areas. In all cases the examination of a variety of PAH indicator ratios that encompass a range of masses is necessary for a robust interpretation.

Benzannelated annulenes. 8. Toward the understanding of benzannelated annulenes: synthesis and properties of [a,h]- and [a,i]-ring dibenzannelated dihydropyrenes

The benzannelated dihydropyrenes 3 and 4 were synthesized from 1,3-bis(bromomethyl)naphthalene (16) and 1,3-bis(bromomethyl)-2-methylnaphthalene (22) (the latter obtained in 18% yield in seven steps from 2,3-dimethylnaphthalene) in 7.4% and 4.8% overall yields, respectively, using Stevens or Wittig rearrangement-Hofmann elimination sequences on the dithiacyclophanes 13 and 14, followed by valence tautomerization of the resulting cyclophanedienes 11 and 12. The dihydrobenzopyrene 3 rapidly dehydrogenates to benzo[a]pyrene (21), whereas the dimethyl derivative 4 is relatively stable. The internal protons of 3 and 4 show only about 50% of the shielding of the corresponding protons in the parent hydrocarbons 8 and 1, respectively, and this effect is ascribed to bond localization caused by the benzannelating ring. The residual diatropicity of 3 or 4 is larger than that for the related less rigid 40 or 41. Unlike the parent 1, no evidence was found for a reversible valence isomerization of 4 to 12. Coupling constants of the external protons of 4 were used to compare bond orders to calculated ones, and it was shown that both rings of 4 considerably perturb the delocalization of the other, in accordance with Giinther’s calculations. A comparison of the IH NMR spectra of 4 and benzo[a]pyrene (21) was made. While many annulenes are now known,3 few are as well suited for the study of effects associated with aromaticity as Boekelheide’s4 trans1 5 1 6-dimethyldihydr~pyrene~ (1). This annulene is stable and has a planar6 14a-electron periphery, but most important it has its internal bridges and substituents close to the “center of the ring current”, which make them extremely sensitive’ probes for changes in ring current and hence aromaticity.* Thus study of a phenomenon which changes the aromaticity of an annulene should have a much more pronounced magnetic resonance effect on internal groups, e.g., the internal methyl protons of 1, which normally appear a t 6 -4.25, than for external groups, e.g., the external ring protons of 1, or indeed any other annulene.

Measuring aromaticity with the dimethyldihydropyrene ring current probe. experimental and computational studies of the fulvenes and the strongly antiaromatic cyclopentadienone reveal large mills-nixon-type Bond localization effects. synthesis of fulvene-fused dihydropyrenes

The synthesis of the methylfulvene- and phenylfulvene-annelated dihydropyrenes 10 and 22 from the cyclopentadiene-fused dihydropyrene 7 in 68% and 80% yields, respectively, are reported. However, the attempted formation of the parent fulvene-fused dihydropyrene 18 failed, both from the cyclopentadiene 7 with formaldehyde and from the cyclopentadienone 5 in Wittig-type reactions. Chemical shift data for the methylfulvene (35) and phenylfulvene (36)-fused dihydropyrenes 10 and 22 were used to estimate the reduction in the dihydropyrene nucleus aromaticity (DHPN) (relative to benzene fusion) in 10 and 22 (12-16% and 22-25% respectively). Calculations revealed that this reduction in diatropicity, contrary to the situation with benzene fusion, is not due to any aromaticity of the annelating fulvenes but instead is caused by Mills-Nixon-type effects. We conclude that methyl- and phenylfulvene are nonaromatic. An improved synthetic route to the cyclopentadienone 5 was found in an unprecedented cyclization of the trans-cinnamic acid analogue 29 in 80% yield. This enabled an X-ray structure of 5 to be obtained, for comparison to that of the saturated ketone 4. Even though crystals of 5 and 4 show diastereomeric disorder, when the average bond length data of cyclopentadienone 5 is compared with those of cyclopentenone 4 and the parent and benzo dihydropyrenes 6 and 33, it is clearly evident that 5 has the opposite bond-alternation pattern, consistent with a [4n] fused annulene. From the bond length data, cyclopentadienone has approximately 87% of the effect of a benzene ring on bond alternation, which is in reasonable agreement with the previously found NMR value (78%). Structure and nucleus-independent chemical shift calculations support these results.

A new synthesis of bridge difunctionalised [2,2]metacyclophanes using a low valent titanium coupling procedure. The first synthesis of [O4]-meta-ortho-meta-orthocyclophanes and their possible conversion into biradicaloid dihydropyrenes.

Abstract Titanium (O) coupling of the terphenyl dialdehydes 11a,b gave 75–85% yields of the bridge difunctionalised [2,2]metacyclophanes 12a,b . Oxidation of these 1,2-diols to the 1,2-diketones was achieved with oxalyl chloride-DMSO followed by iPr 2 EtN at −30°C, which then on condensation with o -phenylene diamine provided a route to the first zero bridged meta-ortho-meta orthocyclophanes 15a,b . Irradiation of the latter gave purple compounds which we believe are the biradlcaloid dihydropyrenes 16a,b .

The neutral deoxygenation (reduction) of aryl carbonyl compounds with raney-nickel. an alternative to the clemmenson, wolf-kishner or mozingo (thioketal) reductions.

Abstract W-7 Raney-Nickel reduces mono or diaryl carbonyl compounds in 50% aqueous ethanol in excellent yields to the aryl methanes.

Cyclophanes with large internal substituents. The synthesis and conformational behavior of 2,11-dithia [3,3]metacyclophanes and a [2,2] metacylophane with -butyl substituents. ☆

Abstract The preparation, 1 Hmr spectra and stereochemistry of 1E , 3E , 2F , 3F and 2G are described. The stereochemistry of 3E is supported by an X-ray structure determination.

Photodechlorination of polychlorinated biphenyls in the presence of hydroquinone in aqueous alcoholic media

Abstract On exposure to sunlight or photolysis at λ >300nm, the dechlorination of a polychlorinated biphenyl mixture (Aroclor 1254) in the H donor alcohol 2-propanol under neutral conditions is enhanced by the presence of the photosensitizer hydroquinone. Dechlorination is strongly promoted by an increasingly aqueous solvent (1:1 water:alcohol) and by maintaining neutral conditions (pH 7.0 buffer) both in the presence and absence of sensitizer. Atmospheric oxygen (continuous aeration) retards the hydroquinone induced dechlorination less than the direct photolysis process.

Mechanistic studies on the photochromism of [e]-annelated dimethyldihydropyrenes

The photochemistry of several photochromic arene [e]-annelated dimethyldihydropyrenes (DHPs) was studied. These compounds have much larger photochemical ring opening quantum yields than the simple DHPs, making them potentially more useful as building blocks for photoswitchable materials.

On the relative sizes of hydrogen and fluorine as substituents. Two pathways for the isomerization of syn- to anti-[2.2]metacyclophanes: The synthesis of the first dihydropyrene with internal fluorine substituents

The previously claimed syn-8,1.6-difluoro[2.2]metacyclophane 4 and metacyclophane-1,9-diene 18 were shown to be anti-isomers. The authentic syn-isomers were obtained by complexation of the arene rings of the precursor cyclophanes with a chromium tricarbonyl group, which enables pure syn-isomers to be separated and transformed to products. The isomerization of the syn-difluoro isomer 4 to the anti-isomer 5 occurs at much higher temperatures (300°C) than would be expected on the basis of the analogous methyl 3 (196°C) or hydrogen 1 (0°C) compounds. Analysis of the bridge-SMe substituted examples, clearly indicates that bridge cleavage must occur in the isomerization of 4, while not in the case of 1, and thus two different pathways are operative depending on the internal substituents. The syn-diene 18 on warming valence isomerizes to the bridged [14]annulene, the difluorodlhydropyrene 19, the first example with internal substituents other than alkyl or aryl.

Experimental verification of the homoaromaticity of 1,3,5-cycloheptatriene and evaluation of the aromaticity of tropone and the tropylium cation by use of the dimethyldihydropyrene probe.

By use of a dimethyldihydropyrene experimental probe for aromaticity, 1,3,5-cycloheptatriene (16) is demonstrated to be a neutral homoaromatic hydrocarbon! On the basis of (1)H NMR results, 16 is judged to be ~30%, tropone 18 ~20%, and tropylium 22 ~50% as aromatic as benzene. The latter result may be an underestimation because of charge delocalization. The B3LYP/6-31G* calculated geometries and GIAO-HF/6-31G*//B3LYP/6-31G* calculated NMR chemical shifts and nucleus-independent chemical shifts (NICS) support these conclusions. These estimates were obtained by synthesis of the annelated dihydropyrenes 7 (tropone fused), 9 (1,3,5-cycloheptatriene fused), and 10 (tropylium fused). [4 + 3] Cycloaddition of the isofuran 5 with an oxyallyl cation (prepared from 2,4-dibromopentan-3-one) gave the C7 fused dihydropyrene 6 in 77% yield. Elimination of water gave tropone 7 in 61% yield, which, via LiAlH(4) reduction to alcohol 8 (48% yield) and treatment with HBF(4), gave quantitatively tropylium cation 10. When ketone 7 was reduced with AlH(3) (generated from AlCl(3)/LiAlH(4)) in ether/benzene at 25 °C, the isomeric cycloheptatrienes 11 (70% yield) and 9 (15% yield) were obtained.