STABILIZATION AND MODIFICATION OF CELLULOSE DIACETATE - Photochemical Reactions in Heterochain Polymers - page 58

The value of K 6 = 0,013 kg/mole·sec has been derived from the data on kinetics of dark
destruction of radicals R, having singlet EPR spectrum. The value of other constants K 1 - K 5
should be considered as examples, as their real values may be obtained only from
measurements of the rates of corresponding elementary stages.
Theoretical curves of AcOH, accumulation (solid lines 1 and 3 in Figure 2.1);
dependence of the rate of AcOH formation on light intensity (solid line in Figure 2.2);
hysteresis of the dependence of CA photolysis rate on light intensity (solid lines 1 and 2 in
Figure 2.3); kinetic curves of formation and accumulation of radicals (solid lines 1 and 2 in
Figure 2.4).
Values of the constant, found by selection, are quite possible. Light constants of the rate
according to the value order agree with theoretical values of constants on the basis of
quantum yields (Ф = 0,1 - 1) [167], being characteristic for radicals, and extinction
coefficients (ε - 10 4 l/m·cm). Large value K 4 = 1000 kg/mole for acetyl alkyl radicals may be
caused by acetic acid, taking part in integration of free valency. It is known [168], that small
quantities of low-molecular substance increase the rate of free valency travel by 3-7 orders in
comparison with the rate of usual chemical reaction.
Formation of acetic acid in the darkness is explained by radical-induced deacetylation
according to total reaction
(1)
(2)
Radical=induced deacetylation proceeds in the darkness in several stages according to the
mechanisms S N1 or S E2 in the darkness [169].
Found low value of activation energy of the process of AcOH formation in the darkness
(E T =42-54 kJ/mole) is characteristic for the reaction of radicals decay and agrees with the
given mechanism.
(3)
As it is seen from Scheme 3, central reaction of CA photolysis is photoreaction (3) of
acetoxyalkyl radical R 1 *, presenting chain photoprocess of acetic acid formation. So, it is
necessary to discuss the ideas on mechanism of acetic acid formation, being presented in
literature.