Thermodynamics and Kinetics of Imidazole Formation from Glyoxal, Methylamine, and Formaldehyde: A Computational Study

Abstract

Density functional theory calculations, including Poisson-Boltzmann implicit solvent and free energy corrections, are applied to study the mechanism of experimentally observed imidazole formation from the reaction of glyoxal and methylamine in solution. Our calculations suggest that a diimine species is an important intermediate in the reaction. Under acidic conditions, we find that the diimine acts as a nucleophile in attacking the carbonyl group of either formaldehyde or glyoxal to first generate an acyclic enol intermediate, which then goes on to close the ring and form imidazoles. Our results confirm that formaldehyde and, by extension, other small aldehydes are likely to be incorporated into imidazole ions in the presence of glyoxal and primary amines in clouds and aqueous aerosol. This is a new mechanism of aerosol formation by formaldehyde, the most abundant aldehyde in the atmosphere. The amount of aerosol formed will depend on the amounts of glyoxal and amines present.

Secondary organic aerosol formation in cloud droplets and aqueous particles (aqSOA): a review of laboratory, field and model studies

“…While neither aldehyde reactions with water nor the selfreaction (including aldol condensation) are predicted to efficiently form aqSOA, interactions of aldehydes with inorganic compounds such as ammonium leading to imidazoles have been suggested to be thermodynamically and kinetically favored (Kua et al, 2011). Several laboratory experiments confirm the reaction of glyoxal and methylglyoxal with ammonium (Noziere et al, 2009;Shapiro et al, 2009) and with monomethylamine and amino acids in the absence of photochemical oxidants (De Haan et al, 2009a.…”

Hydrogen bonding and orientation effects on the accommodation of methylamine at the air-water interface

“…For example, MA seems to promote the growth of secondary organic aerosols, 11,12 SOAs, especially by interacting with glyoxal and methylglyoxal. 6,13 Current chemical transport models for atmospheric modeling underestimate the formation of SOAs, a process which has an important impact on our atmosphere since SOAs can be converted to brown carbon particulates, i.e., aerosols capable of strongly absorbing sunlight in the near-UV and visible range. 6,14 The reliability of weather, climate, and air-quality predictions is still generally affected by the lack of kinetic and thermodynamic data for heterogeneous mixtures and chemistry of atmospheric amines (MA especially).…”

Fundamental Heterogeneous Reaction Chemistry Related to Secondary Organic Aerosols (SOA) in the Atmosphere

“…Yu et al (2011) have proposed reaction pathways for glyoxal and ammonium sulfate. Kua et al (2011) studied the thermodynamics and kinetics of imidazole formation from glyoxal and methylamine in the presence and absence of formaldehyde based on quantum chemical computations. Solution phase Gibbs energy of related species relative to the neutral reactants glyoxal, water, methylamine, and formaldehyde ( r G in kcal mol −1 ), and activation energy barriers for optimized transition states were calculated.…”

“…Solution phase Gibbs energy of related species relative to the neutral reactants glyoxal, water, methylamine, and formaldehyde ( r G in kcal mol −1 ), and activation energy barriers for optimized transition states were calculated. Based on a theoretical study (Kua et al, 2011), a scheme of the main reactions between glyoxal dihydrate and methylamine in the aqueous phase has been proposed as shown in Fig. 26.…”