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PATHWAYS OF LIQUID-PHASE OXIDATION OF CYCLOHEXANOL
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packed with Chromaton N-AW-super + XE-60 sili-
cone at 358 K (internal reference chlorobenzene).
To determine isomeric 2-, 3-, and 4-hydroxycyclo-
hexyl hydroperoxides (cis- and trans-) and 1,2-, 1,3-,
and 1,4-dihydroxycyclohexanes (cis- and trans-), sam-
ples of oxidized alcohol were concentrated under
reduced pressure, the peroxides were reduced with a
50% solution of KI in 0.1 M HCl, and the products
were extracted with 1,2-dichloroethane. The extract
was dried over MgSO4, the solvent was distilled off,
and the diols were converted to diacetates by treat-
ment with a 1 : 1 acetic anhydride pyridine mixture
for 2 h at 373 K [12]. A procedure for identification
and quantitative determination of isomeric cyclo-
hexanediol diacetates by GLC (20% diethylene gly-
col succinate on Chromaton N-AW-HMDS and 5%
1,2,3,4,5,6-hexakis- -cyanoethoxyhexane on Chroma-
ton N-AW-HMDS) is described elsewhere [8].
To accomplish our goals, we studied the kinetics
of accumulation of products characteristic of various
pathways of cyclohexanol oxidation with molecular
oxygen at 403 K: hydrogen peroxide, 1-hydroxycyc-
lohexyl hydroperoxide, cyclohexanone, 2- and 4-hy-
droxycyclohexanones, 2-cyclohexenone, 2-, 3-, and
4-hydroxycyclohexyl hydroperoxides (cis- and trans-),
and 1,2-, 1,3-, and 1,4-dihydroxycyclohexanes (cis-
and trans-) (Fig. 1). The accumulation curves of hy-
drogen peroxide, organic hydroperoxides (of which
the major product is 1-hydroxycyclohexyl hydroper-
oxide), and cyclohexanone shows that H2O2 and cy-
clohexanone are accumulated earlier than 1-hydroxy-
cyclohexyl hydroperoxide, with the relative content of
the latter increasing with conversion. This fact cannot
be attributed to higher rate of hydrogen peroxide de-
composition, because it is known [2] that adducts of
H2O2 or organic hydroperoxides with cyclohexanone
decompose faster than free hydroperoxides.
Fig. 1. Kinetic curves of product accumulation in oxidation
of cyclohexanol at 403 K: (c) product concentration and
( ) time; the same for Fig. 4. (1) 1-Hydroxycyclohexyl
hydroperoxide, (2) hydrogen peroxide, (3) cyclohexanone,
(4) cis-2-hydroxycyclohexyl hydroperoxide and cis-1,2-
dihydroxycyclohexane, (5) trans-2-hydroxycyclohexyl hy-
droperoxide and trans-1,2-dihydroxycyclohexane, (6) cis-
3-hydroxycyclohexyl hydroperoxide and cis-1,3-dihydrox-
ycyclohexane, (7) trans-3-hydroxycyclohexyl hydroper-
oxide and trans-1,3-dihydroxycyclohexane, (8) cis-4-hy-
droxycyclohexyl hydroperoxide and cis-1,4-dihydroxycyc-
lohexane, (9) trans-4-hydroxycyclohexyl hydroperoxide
and trans-1,4-dihydroxycyclohexane, (10) 2-hydroxycyclo-
hexanone, (11) 2-cyclohexenone, and (12) 4-hydroxycyc-
lohexanone.
To refine the sequence of formation of products
originating from cyclohexanol oxidation at the -CH
bond, we compared [1] the accumulation rates of the
reaction products, determined by graphic differentia-
tion of the kinetic curves (Fig. 1). Indeed, the ratios
of the accumulation rates of organic hydroperoxides
and H2O2, and also of organic hydroperoxides and
cyclohexanone (Fig. 2) confirm the assumption that,
under the experimental conditions, 1-hydroxycyclo-
hexyl hydroperoxide is mainly formed by reversible
nucleophilic addition of hydrogen peroxide to cyclo-
hexanone [reaction (1a)], rather than from 1-hydroxy-
cyclohexylperoxy radical [reaction (1b)]:
Fig. 2. Ratio of the rates of product accumulation in oxida-
tion of cyclohexanol at 403 K: (A) cyclohexanone : 1-hy-
droxycyclohexyl hydroperoxide and (B) hydrogen perox-
ide : 1-hydroxycyclohexyl hydroperoxide. ( ) Time.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 75 No. 2 2002