Ultraviolet Photolysis of CH₂I₂in Methanol:  O−H Insertion and HI Elimination Reactions To Form a Dimethoxymethane Product

Abstract

Ultraviolet photolysis of low concentrations of CH2I2 in methanol solution found that CH2I2 is converted into dimethoxymethane and some H+ and I- products. Picosecond time-resolved resonance Raman (ps-TR3) experiments observed that the isodiiodomethane (CH2I-I) photoproduct decayed faster as the concentration of methanol increases, suggesting that isodiiodomethane is reacting with methanol. Ab initio calculations indicate isodiiodomethane is able to react with methanol via an O-H insertion/HI elimination to form an iodoether (ICH2-O-CH3) and HI products. The iodoether can then further react via another O-H insertion/HI elimination reaction to form the dimethoxymethane (CH3-O-CH2-O-CH3) observed in the photochemistry experiments. A reaction mechanism consistent with these experimental and theoretical observations is proposed.

Photochemistry of Iodoform in Methanol: Formation and Fate of the Iso‐CHI2‐I Photoproduct

“…The observed decay is analogous to the behavior of the iso-CH 2 I-I isomer of a structurally related CH 2 I 2 molecule. The lifetime of iso-CH 2 I-I in CH 3 CN and C 6 H 14 solutions is at least 70 times longer (0.25 and 8 ms, respectively [7,14] ) than that in CH 3 OH (3.7-5 ns [7,22] ). UV photolysis of CH 2 I 2 in CH 3 OH indicated that CH 2 I 2 is converted into CH 3 -O-CH 2 -O-CH 3 and some H + and I À products.…”

“…UV photolysis of CH 2 I 2 in CH 3 OH indicated that CH 2 I 2 is converted into CH 3 -O-CH 2 -O-CH 3 and some H + and I À products. [22] Ps-TR 3 experiments showed that the iso-CH 2 I-I photoproduct decays faster as the relative concentration of methanol increases, which suggests that iso-CH 2 I-I reacts with CH 3 OH. [23] Ab initio calculations provide further support by showing that iso-CH 2 I-I reacts with CH 3 OH via an O-H insertion/HI elimination to form an iodoether (ICH 2 -O-CH 3 ) product and an HI leaving group.…”

“…[23] Ab initio calculations provide further support by showing that iso-CH 2 I-I reacts with CH 3 OH via an O-H insertion/HI elimination to form an iodoether (ICH 2 -O-CH 3 ) product and an HI leaving group. [22] The iso-CH 2 I-I and iso-CHI 2 -I isomers undergo similar cyclopropanation reactions with alkenes. [14,24,25] This similarity of the carbenoid behavior of iso-CH 2 I-I and iso-CHI 2 -I suggests that they both undergo O-H insertion/HI elimination reactions with methanol.…”

Spectroscopic and computational studies of matrix-isolated iso-CHBr3: Structure, properties, and photochemistry of iso-bromoform

“…Here, photolysis is known to lead to facile production of the iso-halomethanes following geminate recombination of the initially formed radical pair in the solvent cage, and the isomers have been shown to play a pivotal role in the reactivity of halomethanes in solution. [40][41][42][43][44][45][46][47][48][49][50][51][52][53] For example, iso-CH 2 I 2 is the primary species responsible for the FIG. 1.…”

Matrix isolation and computational study of isodifluorodibromomethane (F2CBr–Br): A route to Br2 formation in CF2Br2 photolysis

“…33,34 Many experimental and theoretical studies of these species have since been carried out, which illustrate novel chemistry for the isopolyhalomethanes. [35][36][37][38][39][40][41][42][43][44][45][46] For example, iso-CH 2 I 2 is the primary species responsible for the cyclopropanation of olefins when CH 2 I 2 is photolyzed in the presence of olefins. 37 In Maier's work, a number of possible resonance structures for the iso-CH 2 XY halons were considered.…”