New reaction of aluminum phenoxide with terpene alcohols

Full text of DOI:10.1134/S0012500810100058

ISSN 0012ꢀ5008, Doklady Chemistry, 2010, Vol. 434, Part 2, pp. 266–268. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © A.V. Kuchin, I.V. Fedorova, A.A. Koroleva, I.Yu. Chukicheva, 2010, published in Doklady Akademii Nauk, 2010, Vol. 434, No. 6, pp. 768–770.
CHEMISTRY
New Reaction of Aluminum Phenoxide with Terpene Alcohols
Corresponding Member of the RAS A. V. Kuchin, I. V. Fedorova, A. A. Koroleva, and I. Yu. Chukicheva
Received June 4, 2010
DOI: 10.1134/S0012500810100058
Alkylation is one of the main methods for building
The structure of alcohol affects the possibility of its
the carbon skeleton of a molecule and, therefore, this hydroxy group to be coordinated to an organoalumiꢀ
reaction is of large importance for the organic syntheꢀ num compound and the subsequent reaction with the
sis of new materials and compounds. Lewis acids, aromatic nucleus. Furthermore, the alcohol structure
mineral acids, zeolites, and transition metal comꢀ has an effect on the formation of the carbocation
plexes are known to be used as catalysts in the alkylaꢀ whose presence also affects the formation of alkylation
tion of phenols with alcohols. The reaction is carried products.
out in gas and liquid phases under pressure at 80–
The condensation of aluminum phenoxide (
isoborneol (II) results mainly in Cꢀalkylated phenol
IV) with a terpene substituent of isobornyl structure
in the ortho position to the OH group (58%) at 160°C
and short reaction time (2 h), indicating the high reacꢀ
tivity of the exo hydroxy group (Scheme 1).The reacꢀ
tion of aluminum phenoxide with borneol (III), a
stereoisomer of isoborneol, requires heating of the
reaction mixture up to 170–180°C for 7 h; the yield
I) with
400°C [1–4]. It is impossible to suggest a single mechꢀ
anism covering all variations of alkylation reaction
because the electrophilic agent can be involved into a
polarized complex or react as a carbocation [5–7].
(
The synthesis of novel terpenophenols with potenꢀ
tial physiological activity that behave as highly effiꢀ
cient stabilizers and antioxidants is the actual task of
practical importance.
of
оꢀisobornylphenol (IV) was 48% (Scheme 1).
In the present work, we suggest a new reaction of
aluminum phenoxide, (PhO)3Al, with terpene alcoꢀ
The reaction of alcohols with phenoxide (PhO)3Al
hols. The reaction proceeds within the coordination or a mixture of phenol with aluminum isopropoxide
sphere of aluminum, and the structure of the alkylatꢀ ꢀPrO)3Al is supposed to occur within the aluminum
(i
ing agent plays a leading role [8–11]. The composition coordination sphere. Each of these aluminum comꢀ
of alkylation products was found to be also dependent pounds has a different effect on the reaction of phenol
on reaction temperature.
with terpene alcohols and, hence, on the composition
H
O
OH
+
(PhO)2Al
O
T
(°C)
H
(PhO)3Al + ROH
I
IV
OH
H
ROH =
;
OH
H
II
III
Scheme 1.
Institute of Chemistry, Komi Research Center, Ural Division
of the Russian Academy of Sciences, ul. Pervomaiskaya 48, Syktyvkar, 167982 Russia
266

NEW REACTION OF ALUMINUM PHENOXIDE WITH TERPENE ALCOHOLS
267
OPh
O Al OPh
OPh
HO
T(°C)
+
PhO Al O
O H
+
V
OH
OH
O
V
VI
VII
VIII
Scheme 2.
of alkylation products. According to the literature
data, aluminum phenoxide is strongly associated and
exists as dimer even at high temperatures [12, 13]. The
hydroxy group of an alcohol (for example, geraniol) is
coordinated to the aluminum atom, a partial positive
charge appears at the alcohol carbon atom that interꢀ
acts with the nucleophilic nucleus of the phenoxy
group. A supposed reaction route is depicted in
Scheme 2.
The alkylation of phenol in the presence of
iꢀPrO)3Al is accompanied by the formation of mixed
aluminum phenoxide–alkoxide (Scheme 3). Since
phenol is a stronger acid than alcohol, it displaces the
isopropoxy group at the aluminum atom in the alumiꢀ
num isopropoxide molecule, and then the reaction
proceeds through the formation of coordination bond.
(
The formation of aluminum phenoxide from (iꢀ
PrO)3Al at 80°C occurs slowly: the phenoxy group
poorly displaces the isopropyl groups at the aluminum
atom in the aluminum isopropoxide molecule. When
temperature increased, the reaction proceeds selecꢀ
The reaction of aluminum phenoxide with geraniol
, GerOH) at 80°C proceeds unexpectedly with high
(
V
regioselectivity without allyl isomerization to give
оꢀ
tively through the formation of
It should be noted that the alkylation of phenol with
geraniol with the use of ꢀPrO)3Al results in the prodꢀ
oꢀgeranylphenol (VI).
geranylphenol (VI, 41%), which converts at 120°C
into a chromanꢀtype ether (VII, 58%). Increasing
temperature of the reaction mixture to 140°C leads to
(i
formation of 2,6ꢀdigeranylphenol (VIII, 57%) (table). ucts of Cꢀalkylation (up to 80%, table). Small
Reaction conditions and products of alkylation reaction of aluminum phenoxides with geraniol
Reaction product, %
Reagents (ratio)
Reaction conditions
VI
VII
VIII
IX
PP*
(PhO)3Al/GerOH
(1 : 1)
140
120
80
°
°
°
C, 4 h
–
–
57
25
–
6
–
22
16
24
C, 4 h
58
17
C, 3 h, benzene
41
12
(
i
ꢀPrO)3Al + PhOH/GerOH 140
°
°
°
C, 4 h
10
67
–
2
63
2
6
5
20
15
(1 : 1 : 1)
120
80
C, 4 h
C, 3 h, benzene
No reaction
* Inseparable mixture of polymerization products (PP).
DOKLADY CHEMISTRY Vol. 434
Part 2
2010

268
KUCHIN et al.
O Prꢀi H
iꢀPrO Al
O Prꢀi
O Prꢀi
iꢀPrO Al
T
(°C)
GerOH (V)
O
O
–iꢀPrOH
O Prꢀi
OH
O Al O Prꢀi
O H
+
VI
Scheme 3.
Chemical Synthesis of Biologically Active Substances),
Moscow: GEOTARꢀMED, 2002.
amounts of 4ꢀgeranylphenol (IX) were isolated from a
mixture of reaction products.
6. Kheifits, L.A. and Aul’chenko, I.S., in Khimiya i tekhꢀ
nologiya dushistykh veshchestv i masel (Chemistry and
Technology of Fragrances and Aromatic Oils), Mosꢀ
cow: Pishchevaya promꢀst', 1968, issue 8, pp. 142–190.
Thus, we have shown in this work the high reactivꢀ
ity of aluminum phenoxide toward activated terpene
alcohols.
7. Chukicheva I.Yu., Spirikhin, L.V., and Kuchin, A.V.,
Zh. Org. Khim., 2008, vol. 44, no. 1, pp. 69–73.
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DOKLADY CHEMISTRY Vol. 434
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2010