Infrared characterization of formation and resonance stabilization of the Criegee intermediate methyl vinyl ketone oxide

Chen-An Chung,Yuan-Pern Lee

doi:10.1038/s42004-020-00447-1

Abstract

Methyl vinyl ketone oxide (MVKO) is an important Criegee intermediate in the ozonolysis of isoprene. MVKO is resonance stabilized by its allyl moiety, but no spectral characterization of this stabilization was reported to date. In this study, we photolyzed a mixture of 1,3-diiodo-but-2-ene and O2 to produce MVKO and characterized the syn-trans-MVKO, and tentatively syn-cis-MVKO, with transient infrared spectra recorded using a step-scan Fourier-transform spectrometer. The O‒O stretching band at 948 cm−1 of syn-trans-MVKO is much greater than the corresponding bands of syn-CH3CHOO and (CH3)2COO Criegee intermediates at 871 and 887 cm−1, respectively, confirming a stronger O‒O bond due to resonance stabilization. We observed also iodoalkenyl radical C2H3C(CH3)I upon photolysis of the precursor to confirm the fission of the terminal allylic C‒I bond rather than the central vinylic C‒I bond of the precursor upon photolysis. At high pressure, the adduct C2H3C(CH3)IOO was also observed. The reaction mechanism is characterized.

Highlights

Methyl vinyl ketone oxide (MVKO) is an important Criegee intermediate in the ozonolysis of isoprene
With the unique step-scan Fourier-transform infrared (FTIR) absorption technique23, we have successfully detected infrared spectra of several smaller Criegee intermediates CH2OO24,25, CH3CHOO26, (CH3)2COO27, and the associated adduct CH2IOO from the source reaction28; we explored the mechanism and intermediates in reactions of CH2OO with CH2OO29, SO230, and HCOOH31
The stick spectra of two possible photolysis products, (Z)-C2H3C(CH3)I [2] and (Z)-(CH2I)CHC(CH3), according to the scaled harmonic vibrational wavenumbers predicted with the B3LYP method are shown in Fig. 2b and c, respectively

Summary

Introduction

Methyl vinyl ketone oxide (MVKO) is an important Criegee intermediate in the ozonolysis of isoprene. MVKO and MACRO are important Criegee intermediates, because of their critical roles in atmospheric chemistry, and because of their unique structures that are resonance stabilized by the vinyl moiety, which affect their reactivity. Welz et al. reported a novel reaction scheme to generate the simplest Criegee intermediate CH2OO in laboratories from the reaction of CH2I with O2 on photolysis of CH2I2 in O2 with ultraviolet (UV) light; this scheme has promoted active research on Criegee intermediates. Welz et al. reported a novel reaction scheme to generate the simplest Criegee intermediate CH2OO in laboratories from the reaction of CH2I with O2 on photolysis of CH2I2 in O2 with ultraviolet (UV) light; this scheme has promoted active research on Criegee intermediates13–18 Following this concept, to produce MVKO from photolysis of C2H3C(CH3)I2 in O2, is difficult because this precursor is extremely unstable. Four conformers of MVKO, syn-trans, syn-cis, anti-trans, and anti-cis

Methods

Results

Conclusion