Abstract
A mechanism of the initiated nonbranched-chain process of forming 1,2-alkanediols and carbonyl compounds in alcohol–formaldehyde systems is suggested. The quasi-steady-state treatment is used to obtain kinetic equations that can describe the nonmonotonic (with a maximum) dependences of the formation rates of the products on the concentration of free unsolvated formaldehyde. The experimental concentrations of the free unsolvated form of formaldehyde are given at the different temperatures, solvent permittivity, and total concentrations of formaldehyde in water and alcohols. An empirical equation for calculating the free formaldehyde concentration in alcohol–formaldehyde (including water/ethanediol–formaldehyde) systems at various temperatures and total formaldehyde concentrations and an equation for evaluating solvent concentrations in these systems were derived. The experimental dependence of the ethanediol radiation-chemical yields on formaldehyde concentration in γ-radiolysis of methanol–formaldehyde system at 373–473 K is shown.
Highlights
Free radicals add to the carbon atom at the double bond of the carbonyl group of dissolved free formaldehyde
The concentration of free formaldehyde in the solution at room temperature is a fraction of a percent of the total formaldehyde concentration, which includes formaldehyde chemically bound to the solvent [1]
Free 1-hydroxyalkyl radicals add at the double bond of free formaldehyde dissolved in the alcohol, forming 1,2-alkanediols [7,8,9,10, 12,13,14,15,16,17,18], carbonyl compounds, and methanol [14, 15] via the chaining mechanism. (The yields of the latter two products in the temperature range of 303 to 448 K are one order of magnitude lower)
Summary
Free radicals add to the carbon atom at the double bond of the carbonyl group of dissolved free (unsolvated, monomer) formaldehyde. The concentration of free formaldehyde in the solution at room temperature is a fraction of a percent of the total formaldehyde concentration, which includes formaldehyde chemically bound to the solvent [1]. The energy released as a result of this addition, when the C=O bond is converted into an ordinary bond, is 30 to 60 kJ mol–1 The resulting free 1:1 adduct radicals can both abstract hydrogen atoms from the nearestneighbor molecules of the solvent or unsolvated formaldehyde and, due to its structure, decompose by a monomolecular mechanism including isomerization [7, 8]. The quasi-steady-state treatment is used to obtain kinetic equations
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