P. Ulanski et C. Von Sonntag, The OH radical-induced chain reactions of methanol with hydrogen peroxide and with peroxodisulfate, J CHEM S P2, (2), 1999, pp. 165-168
Citations number
16
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS 2
Hydroxymethyl radicals, (CH2OH)-C-., were generated radiolytically in the r
eaction of OH radicals with methanol. In the presence of H2O2 they yield fo
rmaldehyde via chain reaction which regenerates an OH radical [reaction (2)
]. G(CH2O) first increases with increasing H2O2 concentration and with the
inverse of the square root of the dose rate, eventually leaching a plateau
near G(CH2O) approximate to 65 x 10(-7) mol J(-1). This indicates that besi
des the bimolecular termination of the CH2OH radicals there must be an addi
tional termination reaction of (pseudo-)first-order kinetics which is attri
buted to an H-abstraction from H2O2 by CH2OH [reaction (12)]. The data have
been fitted using k(2) = 6 x 10(4) dm(3) mol(-1) s(-1) and k(12) = 2.75 x
10(3) dm(3) mol(-1) s(-1). In basic solution the chain length first becomes
longer because the anion of the (CH2OH)-C-. radical, (CH2O-)-C-. [pK(a)((C
H2OH)-C-.) = 10.7] rapidly transfers an electron to H2O2 (k = 4 x 10(5) dm(
3) mol(-1) s(-1)). Upon further increasing the pH, i.e. when the anion of H
2O2 starts to become of importance [pK(a)(H2O2) = 11.6] the chain length dr
ops again. The data can be fitted assuming that (CH2O-)-C-. is not capable
of transferring an electron to HO2- at an appreciable rate and that the H-a
bstraction reaction from HO2- is considerably faster (k = 2.9 x 10(4) dm(3)
mol(-1) s(-1)) than from H2O2.