Polyaromatic Hydrocarbons (PAH) are readily formed in combustion processes and circumstellar envelopes of carbon stars. Coronene 4 (C24H12) and corannulene 9 (C20H10) are cyclic polyaromatic hydrocarbons, which act as precursors for carbon nanotubes, buckminsterfullerenes, and graphene. Protocol to grow PAH from simple benzene or indene to pyrene, benzindene, coronene and/or corannulene require as precursors halogenated arenes and various PAH as calibration compounds. For example, a phenyl radical in reaction with vinyl acetylene or indene radical with methyl radical can produce naphthalene. Likewise, 1-halotriphenylene is required as a precursor for the gas phase synthesis of coronene 4 with acetylene (C2H2). We developed a regioselective synthesis of 1-bromo(or iodo)triphenylene from triphenylene 1. Thus, treatment of 1 with HNO3 in Ac2O at 60 oC provided 1-nitrotriphenylene in addition to 2-nitrotriphenylene. Subsequent reduction of 1-nitrotriphenylene with Fe/NH4Cl in EtOH/H2O at 80 oC followed by diazotization-halogenation (Br and I) of the resulting 1-aminotriphenylene gave 1-bromotriphenylene 2 or 1-iodotriphenylene 3. Moreover, 7-bromofluoranthene 5 serves as a precursor for a gas phase synthesis of corannulene 9 with acetylene. A calibration compound 7-ethylenefluoranthene 8 has been prepared from 7-nitrofluoranthene 6. Thus, reduction of 6 with Fe/NH4Cl and subsequent diazotization-iodination of the resulting 7-aminofluoranthene with t-BuONO/CH2I2/I2/CuI afforded 7-iodofluoranthene 7. Sonogashira coupling of 7 with TMS-acetylene followed by desilylation with K2CO3 provided 7-ethynylfluoranthene 8. In addition, synthesis of other three or four-arene ring systems and various arene enyne derivatives which serve as precursors and calibration compounds for the PAHs growth will be discussed.

Synthesis and application of polyaromatic hydrocarbons toward gas phase synthesis of coronene and corannulene

ACS Spring Meeting 2021

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