Abstract
The aim of our study was the conclusion of the simple kinetic equations to describe ab initio the initiated non-branched-chain processes of saturated free radical addition to C=C, C=O, and O=O bonds of molecules in the binary systems of saturated and unsaturated components. In the processes of this kind the formation rate of the molecular addition products (1:1 adducts) as a function of concentration of the unsaturated component has a maximum. Five reaction schemes are suggested for addition processes of free radicals to the multiple bonds of molecules. The schemes include reactions competing with chain propagation through a reactive free radical. The chain evolution stage in these schemes involves three or four types of free radicals, of which one is relatively low-reactive and inhibits the chain process by shortening of the kinetic chain length. Based on the suggested schemes, nine rate equations containing one to three parameters to be determined directly are set up using quasi-steady-state treatment. These equations provide good fits for the non-monotonic (peaking) dependences of the formation rates of the molecular 1:1 adducts on the concentration of the unsaturated component in liquid homogeneous binary systems consisting of a saturated component (hydrocarbon, alcohol, etc.) and an unsaturated component (olefin, allyl alcohol, formaldehyde, or dioxygen). The unsaturated compound in these systems is both a reactant and an autoinhibitor generating low-reactive free radicals such as СН2=С(СН3)ĊН2, СН2=СНĊНОН, НĊ=O, o-СН3С6Н4СН2
Highlights
In a binary system consisting of a saturated component and an unsaturated one, the abstraction of the most labile atom from a saturated molecule by some initiator converts this molecule into a saturated free radical capable of adding to the double bond of an unsaturated molecule to yield a saturated 1:1 adduct radical
The 1:1 adduct radical (which is the heaviest and the largest among the free radicals that result from the addition of one addend radical to the double bond of Physical Chemistry 2012, 2(3): 18-37 the molecule) may have an increased energy owing to the energy liberated in the transformation of a C=O, C=C, or O=O double bond into an ordinary bond (30–130 kJ mol–1 for the gas phase under standard conditions [1,2,3,4])
In the processes of this kind, in which an addend radical and a low-reactivity, inhibiting radical are involved in three types of quadratic-law chain termination reactions, the formation rate of the 1:1 adduct as a function of the concentration of the unsaturated component has a maximum
Summary
In a binary system consisting of a saturated component and an unsaturated one, the abstraction of the most labile atom from a saturated molecule by some initiator converts this molecule into a saturated free radical (addend) capable of adding to the double bond of an unsaturated molecule to yield a saturated 1:1 adduct radical. Earlier [5, 6], there were attempts to describe such peaking dependences fragmentarily, assuming that the saturated or unsaturated component is in excess, in terms of the direct and inverse proportionalities, respectively, that result from the simplification of a particular case of the kinetic equation set up by the quasi-steady-state treatment of binary copolymerization involving fairly long chains [5] This specific equation is based on an irrational function, whose plot is a monotonic curve representing the dependence of the product formation rate on the concentration of the unsaturated component.
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