Oxidation of Unsaturated Ethers with the System Aluminum Tri-tert-butylate-tert-Butyl Hydroperoxide

Article abstract of DOI:10.1023/A:1013967113770

The system aluminum tri-tert-butylate-tert-butyl hydroperoxide oxidizes alkyl allyl and aryl allyl ethers by the radical mechanism at room temperature. In the process, either the substrate skeleton is preserved and the carbonyl and hydroperoxy groups are introduced, or the carbon-carbon and carbon-oxygen bonds in the allyl moiety are cleaved. In allyl benzyl ether the reaction centers are the methylene groups of the benzyl and allyl fragments.

Full text of DOI:10.1023/A:1013967113770

Russian Journal of General Chemistry, Vol. 71, No. 11, 2001, pp. 1802 1806. Translated from Zhurnal Obshchei Khimii, Vol. 71, No. 11, 2001,
pp. 1905 1910.
Original Russian Text Copyright
2001 by Stepovik, Martynova, Dodonov.
Oxidation of Unsaturated Ethers with the System
Aluminum Tri-tert-butylate tert-Butyl Hydroperoxide
L. P. Stepovik, I. M. Martynova, and V. A. Dodonov
Lobachevskii State University, Nizhni Novgorod, Russia
Received August 3, 2000
Abstract The system aluminum tri-tert-butylate tert-butyl hydroperoxide oxidizes alkyl allyl and aryl allyl
ethers by the radical mechanism at room temperature. In the process, either the substrate skeleton is preserved
and the carbonyl and hydroperoxy groups are introduced, or the carbon carbon and carbon oxygen bonds in
the allyl moiety are cleaved. In allyl benzyl ether the reaction centers are the methylene groups of the benzyl
and allyl fragments.
It is known that oxidation of ethers with atmo-
spheric oxygen involves formation of -hydroperox-
ides in the first stage [1]. In most cases these com-
pounds were not isolated, because they either readily
decompose homolytically or undergo various hetero-
lytic transformations to give a complex mixture of
products. Data on low-temperature oxidation of ethers
with organometallic peroxides and systems based on
organometallic compounds and metal alcoholates in
combination with hydroperoxides are scarce [2 4].
For example, the reaction of diethyl ether with the
system triphenylbismuth tert-butyl hydroperoxide is
unusual: only the methyl C H bonds are oxidized, and
the major oxidation product is ethoxyacetaldehyde [3].
The system aluminum tri-tert-butylate (I) tert-butyl
hydroperoxide (II) oxidizes ethers by the radical
mechanism at -methylene and -methine C H bonds,
as demonstrated by the examples of dialkyl, phenyl
alkyl, benzyl alkyl, and benzhydryl alkyl ethers [4].
It is known [4 11] that the system I II generates
oxygen, which efficiently oxidized the methylene and
methine C H bonds in hydrocarbons and their oxy-
gen-containing derivatives [5 7]. Reaction of I and
II is accompanied by evolution of oxygen according
to the equation suggested in [6 9].
active oxygen generated by the system is directed
exclusively at the methylene C H bonds in the benzyl
moiety, whereas the arene and vinyl C H bonds are
not involved. An unusual cleavage of the C C bond
in the allyl moiety was found. It should be noted that
oxidation of saturated hydrocarbons (pentane, hexane)
[9] and 1,2-diphenylethane [10] occurred similarly,
with deep degradation of the carbon skeleton. As
convincingly shown in [10], the reaction involves
intermediate formation of -dicarbonyl compounds.
These species react with hydroperoxide II or with
intermediae di-tert-butoxy-tert-butylperoxyaluminum
to give organometallic peroxides, which, in turn, are
responsible for cleavage of the C C bond.
In contrast to alkanes and alkylarenes, in 3-phenyl-
-propene the C C bond is cleaved directly in the re-
1
action with the primary radicals (carbon-centered and
hydroperoxy) generated by attack of active oxygen at
the CH group of the allyl moiety.
2
In this connection, we have prepared a series of
ethers containing an allyl group and fragments differ-
ing in the reactivity toward the released oxygen: allyl
methyl (III), allyl ethyl (IV), allyl benzyl (V), allyl
phenyl (VI), and diallyl (VII) ethers. Of particular
interest are ethers VI and VII, in which we expected
the attack of the released oxygen exclusively at the
allylic methylene group. Ethers IV and V contain,
along with the allylic methylene group, also methyl-
ene groups of the ethyl and benzyl moieties, which
can also affect the pathways of homolytic oxidation.
Finally, ether III contains, along with the allylic reac-
tion center, also the methyl group whose reactivity
with respect to oxidation of the C H bonds is strongly
influenced by the nature of adjacent atoms and groups
Experiments on oxidation of -methyl(phenyl)-
substituted alkenes with the system I II showed that
the released oxygen reacts with the methyl group of
the substrate to form intermediate allyl radicals. Sub-
sequent transformations involved migration of the
double bond in the allyl moiety and formation of
tertiary hydroperoxides, which underwent further
transformations [8]. Experiments on oxidation of
monophenyl-substituted alkenes (3-phenyl-1-propene
and 4-phenyl-1-butene) showed that the attack of [4, 5, 8].
1
070-3632/01/7111-1802$25.00 2001 MAIK Nauka/Interperiodica

OXIDATION OF UNSATURATED ETHERS
1803
Products formed by oxidation of ethers CH =CHCH OR with the system Al(OBu-t) t-BuOOH in benzene (molar
2
2
3
a
ratio 1 : 1 : 2, 20 C, 1 day)
Product
R = Meb
R = Etb
R = Phb
R = Allyl
R = Bzb
Volatile compounds
t-BuOH
t-BuOOH
2.74
0.13
0.05
0.06
0.07
0.07
2.59
0.06
0.06
0.18
0.02
0.09
2.51
0.19
2.58
0.11
2.19
0.11
CH =CHCOOR
2
c
d
Tracesd
Traces
0.05
d
CH =CHCHO
0.17
Traces
0.13
2
HC(O)OOBu-t
Traces
0.06
e
CO2
PhCHO
0.08
Hydrolysis products of nonvolatile residuef
t-BuOH
t-BuOOH
ROH
1.85
0.19
0.20
0.05
0.09
0.16
0.11
1.38
0.28
0.24
0.07
1.80
0.05
0.26
0.07
2.27
0.19
0.03
0.06
2.02
0.13
0.08
0.04
[
CH =CHOH]g
2
HCOOH
CH COOH
0.27
0.05
0.14
0.28
0.03
0.30
0.12
0.04
3
CH =CHCOOH
2
CH =CHC(O)OR
0.02
0.16
2
CH =CHC(O)OOBu-t
0.17
2
a
b
c
Per mole of CH =CHCH OR (averaged data). Conversion of ethers, %: III, 60; IV and V, 70; VI, 49. Formaldehyde was also
2
2
d
e
detected (TLC). Acetaldehyde and condensation products of carbonyl compounds were also detected (TLC). Total amount of
CO , including hydrolysis product. 1 mol of Al in all runs; hydroxyethanal was detected qualitatively. For ether V, the following
f
2
compounds were also detected in hydrolysis products (mole per mole of ether): CH =CHCH OH 0.02, PhCOOAllyl 0.06, PhCOOH
2
2
g
0.13, PhC(O)OOBu-t 0.10.
Determined in the form of vinyl acetate.
All reactions were performed in benzene at room
temperature; the reactant ratio ether III VII : alcoho-
late I : hydroperoxide II = 1 : 1 : 2. The reactivity of
the ethers depends on their structure. The highest con-
version (up to 70%) is observed with IV and V. The
major products are carbonyl compounds, alkyl acry-
lates, tert-butyl peroxocarboxylates, and also alcohols
and carboxylic acids (see table). As seen from these
data, esters undergo deep oxidation with cleavage of
the C C bond. Relatively low yield of some reaction
products containing a double bond may be due to their
polymerization and condensation.
ROCH CH=CH2
2
.
.
Al(OBu-t)3 + 2t-BuOOH
Al(OBu-t)3
[
ROCHCH=CH2 OOH]
a
b
(1)
ROCH(OOH)CH=CH2
CH =CHC(O)OR + H O
2 2
A
R = Me, Et, Ph, Allyl, Bz.
The composition of the isolated reaction products
alcohols, aldehydes, carboxylic acids) shows that the
(
Oxygen released by the system I II apparently
reacts with the C H bond of the allylic methylene
group in III VII, because the radical formed in this
case is the most stable. In the first stage, two radicals,
carbon-centered and hydroperoxy, are formed. The
following oxidation pathways are realized: recombi-
nation of radicals with formation of hydroperoxides
ethers undergo deep oxidation with cleavage of the
carbon skeleton.
The results of experiments on oxidation of mono-
phenyl-substituted alkenes with the system I II sug-
gest that one more pathway of the reaction of carbon-
centered and hydroperoxy radicals is possible, with
formation of 1,2-dioxetane.
[
scheme (1), a] or direct radical oxidation of the ether
methylene group with formation of acrylic acid esters
scheme (1), b]:
Decomposition of 1,2-dioxetane to alkyl formate
and acetaldehyde is the major pathway responsible for
[
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 11 2001

1804
STEPOVIK et al.
the cleavage of the C C bond in the allyl group of the
ether [scheme (2)]:
The presence of the vinyloxy group bound to alu-
minum was proved by formation of vinyl acetate on
treatment of the solid residues with acetic anhydride
[12]. Also, the vinyloxy group is displaced with ex-
cess t-BuOH [13] with subsequent isomerization into
acetaldehyde; it can also transform into the epoxide
by the reaction with the system I II. In hydrolysis
products of the nonvolatile residues, we idenfified
qualitatively hydroxyethanal in the form of 2,4-dini-
trophenylhydrazone.
H
H
.
.
[
ROCHCH=CH OOH]
ROC CCH3
2
O
O
CH CHO + HC(O)OR.
(2)
3
R = Me, Et, Ph, Allyl, Bz.
The presence of vinyl alcohol and hydroxyethanal
in the hydrolysis products of the nonvolatile residue
is an unambiguous evidence of another degradation
pathway: via organometallic peroxide formed by reac-
tion of alcoholate I with hydroperoxides A. These hy-
droperoxides can be formed, according to scheme (1),
a, by reaction with the released active oxygen [7 10]
and by radical oxidation initiated by alkoxy radicals
that are generated by the system I II [8, 11]. Alumi-
num-containing peroxide B is unstable and can under-
go transformations described by schemes (3) and (4):
The competition of pathways c and d in scheme (4)
is governed by the structure of the alkyl moiety in
ethers. Pathway c is not realized with VI; pathway d
is the most characteristic for benzyl allyl and phenyl
allyl ethers. As for pathway e, it is realized with all
the ethers IV VII.
The decomposition products undergo further trans-
formations. Aldehydes are oxidized to aluminum acyl-
oxy derivatives which are hydrolyzed to the corre-
sponding acids (see table). The IR spectra of nonvola-
tile residues from all the reactions contain strong
O
absorption bands at 1570 1590 cm 1 characteristic of
A + I
H C=HC HC
2
CHR + t-BuOH (3)
stretching vibrations of the carboxylate ion.
O
H
Esters (alkyl acrylates, alkyl formates) enter into
ester interchange with hydroperoxide II to give per-
oxocarboxylic acid esters and alkoxy-tert-butoxy de-
rivatives of Al [7]. tert-Butyl peroxoformate was
detected in the products of reaction of the system I II
with methyl formate.
OAl(OBu-t)2
B
c
d
e
2
CH =CH CHO + R CHO + HOAl(OBu-t)2
B
CH =CHCOOCH R + HOAl(OBu-t)
2
(4)
2
2
CH =CHOAl(OBu-t) + HC(O)OCH R
In the reaction products we also detected CO2.
We believe that it originates from alkoxyaluminum
alkyl carbonates formed by reaction of alkyl formates
with the system I II. These salts decompose with CO2
evolution spontaneously or as a result of hydrolysis
2
2
2
R = R CH = Me, Et, Bz, Allyl; R = H, Me, Ph, CH=CH .
2
2
Aldehydes are formed by migration of the hydro-
gen atom from the alkyl group to the oxygen atom
bound to metal [scheme (4), c]. In all cases we de-
tected acrolein and also formaldehyde (for III), acet-
aldehyde (for III and V), and benzaldehyde (for V).
Migration of the hydrogen atom from the allyl radical
[14, 15] [schemes (5), (6)]:
R CH OC(O)H + Al(OBu-t)3 + t-BuOOH
2
[
R CH OCH(OOBu-t)OAl(OBu-t) ]
2 2
to the oxygen atom of the OAl(OBu-t) group results
2
t-BuOH + R CH OC(O)OAl(OBu-t)
(5)
(6)
2
2
in formation of esters [scheme (4), d]. It should be
noted that such transformations were observed previ-
ously in oxidation of alkyl benzyl and alkyl benzhy-
dryl ethers [4].
C
CO2 + R CH OAl(OBu-t)
2
2
C
+
H O, H
2
CO2 + R CH OH
2
We assume that there is one more reaction path-
way: decomposition of peroxides B to form aluminum
vinyloxy derivatives. Vinyl alcohol can form only
by migration of the vinyl group to the oxygen atom
bound to aluminum, similarly to rearrangements of
aluminum-containing peroxides with the participation
of the phenyl group [4, 5]. We found no published
data on such transformations.
R = H, Me, Ph, CH=CH2.
To confirm this assumption, we performed the
reaction of the system I II with methyl formate;
0.16 mol of CO evolved in the course of the reaction,
2
and 0.19 0.26 mol (per mole of methyl formate), as
a result of hydrolysis of the nonvolatile residue.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 11 2001

OXIDATION OF UNSATURATED ETHERS
1805
EXPERIMENTAL
ethyl ether, bp 66 67 C, n20 1.3876 [21]. Allyl ben-
D
zyl ether was prepared similarly by treatment of sodi-
um allylate with benzyl chloride, bp 204 205 C [21],
The IR spectra were taken on a Specord IR-75
spectrometer.
2
0
n
1.5074. Diallyl ether was prepared by dehydration
D
1
9
of allyl alcohol [22], bp 94 C, n 1.4158 [20]. The
D
Chromatographic analysis of reaction products in
the liquid phase was performed with a Tsvet 2-65
chromatograph (flame-ionization detector, carrier gas
argon). Low-boiling components (acrolein, methyl
acetate, vinyl acetate, ethyl acetate, allyl acetate, ethyl
acrylate) were determined with a 2400 3-mm col-
umn, stationary phase 10% polyethylene glycol adi-
pate on crushed TZKM brick, 55 70 C. In all the
other cases Chromaton N-AW-DMCS was used as
the support. Phenol, phenyl acrylate, methyl benzoate,
allyl phenyl ether, allyl benzyl ether, benzaldehyde,
benzyl alcohol, allyl benzoate, and benzyl acrylate
were determined with a 2400 3-mm column, station-
ary phase 15% Apiezon L, 100 170 C. tert-Butyl
hydroperoxide, tert-butyl alcohol, hydroxymethyloxi-
rane, methyl acrylate, allyl methyl ether, allyl ethyl
ether, and tert-butyl peroxoformate were determined
with an LKhM-80 chromatograph, 3000 3-mm col-
umn, carrier gas helium, stationary phase 15% dinonyl
phthalate on Chromaton N-AW-DMCS, 40 80 C.
The chromatograms were calculated using external
reference samples.
product purity was monitored chromatographically;
the products were stored at 0 C in the dark.
Aluminum tri-tert-butylate was prepared by reac-
tion of tert-butyl alcohol with aluminum [23] with
subsequent sublimation at 160 170 C (1 mm Hg).
Found Al, %: 11.12. C H AlO . Calculated Al, %:
12 27
3
1
0.96.
Reference samples of acrylic acid esters (ethyl,
phenyl, benzyl, isopropyl) were prepared from acrylo-
yl chloride and appropriate alcohols in the presence
of diethylamine. Their constants were consistent with
reference data. tert-Butyl peroxoformate was prepared
from formic acid and tert-butyl hydroperoxide [24].
tert-Butyl hydroperoxide was of no less than 99.5
99.8% purity.
Oxidation of allyl methyl ether III with the sys-
tem I II. A mixture of 2.01 g of alcoholate I, 0.59 g
of ether III, and 1.48 g of hydroperoxide II in 30 ml
of benzene was kept at room temperature for 1 day.
Within 30 min gas evolution was observed; CO was
2
qualitatively detected in this gas. The colorless trans-
parent solution transformed into a slightly yellowish
gelatinous mass within 20 h. The solvent and volatiles
were distilled into a trap cooled with liquid nitrogen.
In the condensate, unchanged ether III, tert-butyl alco-
hol, hydroperoxide II, tert-butyl peroxoformate, acro-
lein, and methyl acrylate were determined chromato-
graphically. The positive reaction with fuchsin sul-
furous acid reveals the presence of aldehydes. After
treatment of the condensate with 2,4-dinitrophenylhy-
drazine, a precipitate of 2,4-dinitrophenylhydrazones
was obtained. Its TLC examination revealed the pres-
ence of the formaldehyde and acrolein derivatives.
All manipulations with aluminum compounds were
performed in a stream of dry oxygen-free argon.
Carbonyl compounds (formaldehyde, acetaldehyde,
acrolein) were identified in the form of 2,4-dinitro-
phenylhydrazones by the melting point (mixing with
an authentic sample) and TLC (Silufol UV-254 plates,
eluent 5% diethyl ether in benzene). The content of
tert-butoxy groups in the nonvolatile residues was
determined chromatographically and according to
[
16], and the content of carboxylic acids (HCOOH,
CH COOH), according to [17]. All the acids were
3
identified and quantitatively determined in the form
of methyl esters after treatment with diazomethane.
Peroxocarboxylic acid esters (tert-butyl peroxoacrylate
and tert-butyl peroxobenzoate) were identified by
formation of isopropuyl acrylate and benzoate, respec-
tively, after treatment of the reaction solutions with
aluminum isopropylate [18]. The aluminum content
was determined by precipitation in the form of hy-
droxide, followed by calcination to Al O .
A part of the colorless powder remaining after
distillation of the solvent and volatiles was treated
in benzene with excess acetic anhydride, which was
followed by heating at 60 C for 3 h. The solvent and
volatiles were condensed in a trap cooled with liquid
nitrogen; methyl acetate and vinyl acetate were de-
tected in the condensate. Another part of the residue
was hydrolyzed in diethyl ether with 10% H SO . The
aqueous phase was extracted with diethyl ether, and
the combined organic phases were dried over sodium
sulfate. In the extract, tert-butanol and hydroperoxide
II were detected. After treatment of the ether solution
of hydrolysis products with diazomethane, methyl
acrylate was detected. The acidic aqueous phase con-
tained aluminum and tert-butyl alcohol.
2
4
2
3
Allyl phenyl ether was prepared by the Claisen re-
1
8
action [19], bp 193 195 C, n 1.5219 (cf. bp 192 C,
D
2
0
n
1.5200 [20]). Allyl methyl and allyl ethyl ethers
D
were prepared by the Williamson reaction: anhydrous
methylate or ethylate was heated with allyl bromide.
2
0
Allyl methyl ether: bp 46 C, n 1.3780 [20]; allyl
D
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 11 2001

1806
STEPOVIK et al.
To determne the content of saturated carboxylic
acids, we added to a portion of the nonvolatile residue
0 ml of water, 10 ml of concentrated phosphoric
Zaburdaeva, E.A., Zh. Obshch. Khim., 1994, vol. 64,
no. 10, pp. 1715 1721.
10. Dodonov, V.A., Zaburdaeva, E.A., Dolganova, N.V.,
Stepovik, L.P., and Zinov’eva, T.I., Zh. Obshch.
Khim., 1997, vol. 67, no. 6, pp. 988 992.
2
acid, and 100 ml of o-xylene; the mixture was dis-
tilled with a safety trap [17]. The two-phase distillate
was titrated with alkali, after which the xylene phase
was separated, and the aqueous alkaline solution was
concentrated to a volume of 1 ml. The residue was
acidified with sulfuric acid, treated with diethyl ether,
and esterified with diazomethane. Methyl acetate and
methyl formate were detected. For quantitative deter-
11. Zaburdaeva, E.A., Cand. Sci. (Chem.) Dissertation,
Nizhni Novgorod, 1998.
12. Razuvaev, G.A., Stepovik, L.P., and Mitrofano-
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13. Stepovik, L.P., Zaburdaeva, E.A., and Dodonov, V.A.,
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pp. 1173 1178.
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5. Razuvaev, G.A., Dodonov, V.A., and Mitrofano-
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p. 337.
mination of CO , it was absorbed by an aqueous solu-
2
tion of barium hydroxide.
1
Reactions of IV VII with the system I II and anal-
ysis of the resulting products were performed simi-
larly. The ether solution of hydrolysis products of the
nonvolatile residue from oxidation of V was treated
with 10% aqueous alkali. After acidification, benzoic
acid was isolated; its melting point and that of the
mixture with an authentic sample was 121 C.
1
1
1
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RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 11 2001