Does H4SO5 exist?

The possible existence of H4SO5 in aqueous sulfuric acid is analyzed in detail. For bare H4SO5, the computed free energy barrier for the exergonic transformation of H4SO5 into the H2SO4H2O complex is only 3.8 kcal mol-1. The presence of water or sulfuric acid catalyzes the dehydration to such an extent that it becomes almost a barrierless process. In the gas phase, dehydration of H4SO5 is an autocatalytic reaction as the water molecule produced by the decomposition of one H4SO5 molecule induces further dissociation. Thus, in solution, the surrounding water molecules make the para-sulfuric acid a very vulnerable species to exist. The simulated Raman spectra also corroborate the absence of H4SO5 in solution.

H-Bond interactions between silicates and water during zeolite pre-nucleation.

The relative strength of water-water, water-silicate and silicate-silicate interactions are studied, in order to explain the low solubility of the monomer (Si(OH)(4)), and determine the degree of dispersion of silicate clusters in solution during the hydrothermal synthesis of zeolites. We will show how the hydrogen bond interactions between water and monomeric silicate species are similar to that in pure water, whilst monomer-monomer interactions are stronger. However, when larger silicate species are also considered we find the relative hydrogen-bonding strength to follow: water-water < silicate-water < silicate-silicate. The effects of pH are also considered. The implications of the relative strength of these interactions on the formation of larger silicate species, leading to zeolite pre-nucleation, are discussed.