The Identification of Cyclopenta-Fused and Ethynyl-Substituted Polycyclic Aromatic Hydrocarbons in Benzene Droplet Combustion Products

Abstract

In order to investigate new aspects of polycyclic aromatic hydrocarbon (PAH) growth and soot formation, we have synthesized special reference standards of cyclopenta-fused PAH (CP-PAH) and ethynyl-substituted PAH. We have identified several of these CP-PAH and ethynyl-PAH in benzene droplet combustion products, using high pressure liquid chromatography (HPLC) and ultraviolet-visible (UV) absorption spectroscopy. Although one CP-PAH identified in these products-acenaphthylene-has previously been identified as a product of a variety of combustion systems, we have identified six additional CP-PAH and two ethynyl-PAH which have never before been unequivocally identified as the products of benzene pyrolysis or combustion: spectra we have obtained from specially synthesized reference standards. We also present the UV absorption spectra of two additional ethynyl-PAH reference standards -3-ethynylfluoranthene and 1 -ethynylpyrene ~ which we have synthesized.

C16H10Ethynyl-substituted Polycyclic Aromatic Hydrocarbons from the Pyrolysis of Coal, Coal Volatiles, and Anthracene

“…The above observations on the ethynylanthracenes are exactly parallel to those we have made on the ethynylnaphthalenes from the same fuels [16-18,341 and from benzene [14]: (1) Just as the absence of 1 -ethynylnaphthalene and presence of acenaphthylene (in our product mixtures) [14,16--18,34] are consistent with potential energy surface calculations [3,36] showing that formation of the cyclization product acenaphthylene is energetically preferred over formation of 1 -ethynylanthracene -so are the apparent absence of 1 -ethynylanthracene and presence of aceanthrylene consistent with calculations [36] showing that aceanthrylene is the energetically preferred product over 1 -ethynylanthracene. (2) Just as acetylene addition to the 2-naphthyl radical cannot lead to a cylization product, neither can acetylene addition to the 2-anthryl radical.…”

“…The relatively recent syntheses of ethynylnaphthalene and ethynylacenaphthylene standards [13 -151, however, have led to the identification of specific isomers of these species in pyrolysis and/or combustion products of: coal [ 16 -181, anthracene [6], naphthalene [ 191, and benzene [ 14,201. Ethynylacenaphthylenes, not specified by isomer, have also been identified among the products of naphthalene [ 191, ethylene [21,22], and ethylene-naphthalene mixtures [23].…”

Origin of Kinetic Instability of Fullerenes That Violate the Isolated Pentagon Rule

“…Acenaphthylene (17), acephenanthrylene (18), and cyclopenta[cd]pyrene (19) in Figure 4 are among the benzene droplet combustion products. 31 Five-membered rings in these cyclopenta-fused polycyclic aromatic hydrocarbons are slightly aromatic with small positive BREs. However, TREs for 17, 18, and 19 have a bit smaller than those for their respective parent PAHs 20, 21, and 22 (Table 1).…”

Newly Identified Products of Benzene Droplet Combustion: Polycyclic Aromatic Hydrocarbons of Three to Ten Rings

“…Reverse-phase HPLC chromatogram of a liquid-phase benzene droplet combustion sample (taken at 60-70 ms residence time) that has been concentrated. Structures of newly identified product components are indicated, from left to right, in the two segments of the chromatogram, a (5-30 min) and b (30- (24,25) product components, which are better resolved in unconcentrated droplet samples (24). The rise in baseline at 43 minutes corresponds to a change in HPLC mobile phase composition to UV-absorbing dichloromethane.…”

“…Employing high pressure liquid chromatography (HPLC) with diode-array ultraviolet-visible (UV) absorption detection, our previous work (24,25) reports the identification and quantification of 36 PAH and related compounds that are found in the liquid-phase droplet in increasing concentrations over the New Products of Benzene Droplet Combustion 229 droplet lifetime. The presence of these heavy secondary components in the droplet can explain (2,26) the observed multicomponent droplet phenomenon of disruptive burning even though the droplet is initially pure benzene.…”