Radicals From The Gas-phase Pyrolysis Of Hydroquinone: 2. Identification Of Alkyl Peroxy Radicals

摘要

The formation of radicals from the gas-phase pyrolysis of hydroquinone (HQ) from 400 to 825 ℃ was studied using the technique of low-temperature matrix isolation-electron paramagnetic resonance (LTMI-EPR). Cooling the reactor effluent in a CO_2 carrier gas to 77 K produced a cryogenic matrix that exhibited complex EPR spectra. The observed EPR spectra were very sensitive to the delivery rate of HQ, presence/absence of carrier gas, and traces of O_2 in the reaction gas that required careful manipulation of the experimental conditions to separate labile and persistent radicals. Conclusive identification of peroxy] radical formed during the pyrolysis of HQ in the presence of oxygen was based on the anisotropy of EPR spectra, high g value, hyperfine splitting constant, and spectral width that matched very well with literature data. The presence of peroxyl radicals during gas-phase, oxidative pyrolysis of HQ suggests the formation of alkyl radicals as precursors of light hydrocarbons: methane, ethane, and olefins previously observed from the pyrolysis of HQ.