Quenching rate constants for the removal of SO₂ (³B₁) by various aromatics

Abstract

A competitive technique employing the SO₂ (³B₁) photosensitized isomerization of cis‐C₂F₂H₂ to trans‐C₂F₂H₂ in the presence of various aromatics has been used at 3660Å and 22°C to determine the rate constants of the quenching reaction SO₂ (³B₁) + M^k4?removal. Using P_SO2 = 25.1 Torr and P_cis‐C2F2H2 = 0.230 Torr the results from Stern‐Volmer plots gave k₄ estimates (units of l mole^‐1 sec^‐1 × 10¹¹) of 0.883 ± 0.085, 1.43 ± 0.13, 2.04 ± 0.19, 2.17 ± 0.26, 2.29 ± 0.20, and 2.15 ± 0.19 for M = benzene, toluene, ethyl benzene, o‐xylene, m‐xylene, and p‐xylene, respectively. These results indicate that increasing the e^‐ density in the aromatic nucleus due to e^‐ releasing alkyl substituents results in an increase in the magnitude of k₄. However, the o, m, and p‐xylene results indicate that the value of k₄ is not sensitive to the position of the alkyl substituent on the aromatic ring.

Key words:

• sulfur dioxide
• aromatics
• reaction rates