Oxidation of 2-naphthol in the presence of catalysts based on modified β-cyclodextrins

Article abstract of DOI:10.1134/S0965544107060047

The oxidation of 2-naphthol to 1,1'-bi-2-naphthol in a biphasic system in the presence of β-cyclodextrins was studied. It was found that the use of macrocyclic receptors leads to substantial enhancement of the activity of catalytic systems. It was shown that the product yield and the reaction rate substantially increase when ligands obtained via molecular imprinting in the presence of 1,1'-bi-2-naphthol as a template are added.

Full text of DOI:10.1134/S0965544107060047

ISSN 0965-5441, Petroleum Chemistry, 2007, Vol. 47, No. 6, pp. 402–408. © Pleiades Publishing, Ltd., 2007.
Original Russian Text © E.A. Karakhanov, Yu.S. Kardahseva, A.L. Maksimov, S.V. Egazar’yants, L.M. Karapetyan, O.A. Zatolochnaya, 2007, published in Neftekhimiya, 2007,
Vol. 47, No. 6, pp. 435–441.
Oxidation of 2-Naphthol in the Presence of Catalysts Based
on Modified b-Cyclodextrins
E. A. Karakhanov, Yu. S. Kardahseva, A. L. Maksimov, S. V. Egazar’yants,
L. M. Karapetyan, and O. A. Zatolochnaya
Faculty of Chemistry, Moscow State University, Leninskie gory, Moscow, 119992 Russia
e-mail: kar@petrol.chem.msu.ru
Received April 15, 2007
Abstract—The oxidation of 2-naphthol to 1,1'-bi-2-naphthol in a biphasic system in the presence of β-cyclo-
dextrins was studied. It was found that the use of macrocyclic receptors leads to substantial enhancement of the
activity of catalytic systems. It was shown that the product yield and the reaction rate substantially increase
when ligands obtained via molecular imprinting in the presence of 1,1'-bi-2-naphthol as a template are added.
DOI: 10.1134/S0965544107060047
The use of molecular receptors (cyclodextrins,
At the first step, the preorganization of cyclodextrin
calixarenes, urea-based macrocycles) opens up a wide and the template molecule takes place; as result, a host–
range of opportunities for designing new high-perfor- guest inclusion complex is formed. The structure
mance metal complex catalysts. Owing to the ability in formed can be fixed with the use of agents containing
molecular recognition, their use as components of cat- two or more functional groups capable of reacting with
alyst systems makes it possible to substantially enhance the cyclodextrin hydroxyl groups.
the substrate-binding selectivity and to attain a
uniquely high selectivity of processes [1, 2].
The molecular imprinting technique has found
application in catalysis as well; e.g., in the oxidation of
ethylbenzene, cobalt complexes anchored to polymers
in the presence of the substrate showed two to three
times higher activity than the macrocomplexes pre-
pared in the absence of the substrate [6]. We have found
that the use of unsaturated macroligand compounds
produced via the reaction of cyclodextrins with tolu-
ene-2,4-diisocyanate or N,N'-methylenebisacrylamide
in the presence of some templates (dodecene-1, hexa-
decene-1, and p-tert-butylstyrene) as components of
catalyst systems in Wacker oxidation substantially
alters the substrate selectivity of the process. The activ-
ity of catalytic systems that contain β-cyclodextrins
modified in the presence of templates turned out to be
substantially higher than that of the same systems con-
taining a macroligand produced without a template [7].
In this work, we studied the efficiency of cyclodex-
trin-containing catalysts in the reaction of 2-naphthol
oxidation into 1,1'-bi-2-naphthol in a two-phase sys-
tem. Note that 1,1'-bi-2-naphthol (BINOL) and its
derivatives are optically active ligands used in various
organic reactions catalyzed by transition metal (Cu(I),
VO(2+), etc.) complexes, e.g., in the synthesis of opti-
cally active crown ethers [5, 6].
The activity and selectivity of such catalysts can be
controlled in two ways. The first is targeted selective
modification of the macromolecular receptor itself with
complexing groups, whose arrangement predetermines
the coordination of a substrate to the metal atom in the
macromolecular catalyst formed. In this manner, a
number of effective oxidation, hydrogenation, hydro-
formylation, etc. catalysts were synthesized [1].
The second way (molecular imprinting) is based on
the targeted design of macroreceptors by means of tem-
plate synthesis [3]. As a template, various organic mol-
ecules that determine the structure of the material to be
synthesized are used. The macroligands prepared in
this manner turn out to be able to selectively bind mol-
ecules similar to those used as templates. The imprint-
ing process involving cyclodextrin molecules occurs as
shown in Scheme 1 [4, 5].
Structure
fixation
Preorgani-
zation
+
A
A
A
B
B
B
Template
removal
Some BINOLs form structural units in many alka-
loids and natural biologically active compounds. As
components of catalyst systems, we used both conven-
tional modified cyclodextrins (Scheme 1) and cyclo-
dextrin-based materials prepared by means of molecu-
lar imprinting with the use of 1,1'-binaphthol as a tem-
Scheme 1. Imprinting process involving
host (cyclodextrin) and guest (template)
molecules.
4
02

OXIDATION OF 2-NAPHTHOL
Table 1. Macroligands synthesized by means of molecular imprinting
403
Template
Cyclodextrin/template ratio
Binding agent
Epichlorohydrin
Ligand
Bi-2-naphthol
Bi-2-naphthol
Bi-2-naphthol
Bi-2-naphthol
Bi-2-naphthol
Without template
Without template
Without template
2 : 1
1 : 5
2 : 1
1 : 5
2 : 1
β-CD1
β-CD2
β-CD3
β-CD4
β-CD5
β-CD6
β-CD 7
β-CD 8
Epichlorohydrin
Diepoxybutane
Diepoxybutane
Diglycidyl ether of glycerol
Epichlorohydrin
Diepoxybutane
Diglycidyl ether of glycerol
plate. In the latter case, as a linker for fixing the
The procedure for the modification of β-cyclodex-
structure of the supramolecular ligand, we chose a trin with epichlorohydrin in the presence of the tem-
number of bifunctional compounds capable of reacting plate was as follows. To a β-cyclodextrin (0.44 mmol,
with β-cyclodextrin hydroxyl groups: epichlorohydrin, 500 mg) solution in H O (5 ml) and NaOH (2.2 mmol,
2
diepoxybutane, diepoxyoctane, and diglycidyl ether of 88 mg), 0.5-,1-, 2-, 5-, and 10-fold excess of template
glycerol.
was added and the mixture was stirred for 10 min.
Then, 2.2 mmol of epichlorohydrin (176 µl) was intro-
duced and stirring continued for 6 h at room tempera-
ture. The reaction was stopped by the addition of HCl
EXPERIMENTAL
(
2.3 mmol). The product was precipitated with acetone
β-Cyclodextrin from SigmaAldrich, 1,1'-bi-2-naph-
thol (BINOL), epichlorohydrin (Epy), diepoxybutane
and washed with the same solvent to remove template
molecules. The precipitate was decanted and the prod-
uct was dried in vacuum. Obtained in this manner were
(
DEB), diepoxyoctane, and glycerol diglycidyl ether
GDG) (SigmaAlrdich) were used without additional
(
samples β CD1-β-CD5.
purification. As a reaction medium, distilled water was
used.
In the synthesis of the macroligand in the absence of
Nuclear magnetic resonance measurements were the template (β CD6-β-CD8), 2.2 mmol of epichlorohy-
carried out on an Avance Bruker instrument with an drin (176 µl) added to a solution of β-cyclodextrin
operating frequency of 400 MHz. To determine the (0.44 mmol, 500 mg) and NaOH (2.2 mmol, 88 mg) in
fractional composition of the cyclodextrins obtained, H O (5 ml). The other operations were the same as for
2
we used matrix-activated laser desorption/ionization the template synthesis.
mass spectrometry with a time-of-flight analyzer
The samples were characterized by means of NMR
spectroscopy and MALDI–TOF and ESI mass spec-
trometry.
(
MALDI-TOF) and liquid chromatography–mass spec-
trometry with electrospray ionization (LC–MS–ESI).
The analysis by the former method was carried out on
a MALDI-TOF-MS Bruker (Germany) instrument
operating in the reflecto-mol mode. Ionization was pro-
duced with a UV laser at an incident wavelength of 336
nm. The substrate was a nickel plate, and 2,5-dihydrox-
ybenzoic and sinapic (4-hydroxy-3,5-dimethoxycin-
namic) acids were used as references.
To modify β-cyclodextrin with the binding agents
diepoxybutane and glycerol diglycidyl ether, we fol-
lowed that same procedure with reference to the
absence or presence of the template. The amounts of
the linking agents and the template were 2.2 and
0
.22 mmol, respectively.
1
b-CD-1, b-CD-2 (template). H NMR (DMSO-d ,
6
The analysis of oligomers by means of electrospray-
ionization mass spectrometry in conjunction with liq-
uid chromatography was carried out on a Agilent 1100
LC–MSD Trap SL instrument in the negative ion mode.
Samples were prepared in DMSO (HPLC grade, Ald-
rich) at a concentration of ~ 1mg/ml. A 1 : 9 (by vol-
ume) methanol–water blend was used as an eluent.
1
ppm) 5.75 (OH-2), 5.65 (éç-3), 4.9 (C ç); 3.6–3.64
3
5
6
‡,b
(
C ç, C ç, C ç , -é-ëç -ëçéç-ëç éç);, 3.4
2 2
4 2
(
C ç), 3.39 (-é-ëç -ëçéç-ëç éç), 3.2 (C ç);
2 2
1 4
1
3
C NMR (DMSO-d , ppm): 101.76 (ë ). 81.5 (ë ),
6
3
2
7
7
4.5 (-é-ëç -ëçéç-ëç éç), 72.9 (ë ), 72.3 (ë ),
2 2
5
2.1 (-é-ëç -ëçéç-ëç éç), 71.9 (ë ), 66.7 (-é-
2
2
6
ëç -ëçéç-ëç éç), 59.86 (ë ). MALDI–TOF
2
2
A series of macroligands was synthesized by means (m/z): 1157, 1231, 1305, 1379, 1453, 1527, 2347, 2421,
of molecular imprinting in the presence and absence of 2495, 2569, 2643, 2717; LC–MS–ESI (target mass at
the template via modification with epichlorohydrin, m/z 1500): 1157, 1253, 1327, 1401, 1475, 1549, 2369,
diepoxybutane, and diglycidyl ether (Table 1).
2443, 2517, 2592, 2739.
PETROLEUM CHEMISTRY Vol. 47 No. 6 2007

4
04
KARAKHANOV et al.
1
b-CD-6. H NMR (DMSO-d , ppm) 5.75 (OH-2), perature. The solvent was distilled off to dryness on a
6
1
3
5
6
‡,b
5
.65 (éç-3), 4.9 (C ç), 3.6–3.64 (C ç, C ç, C ç , rotary evaporator, and the resulting viscous white mate-
4
-
é-ëç -ëçéç-ëç éç), 3.4 (C ç), 3.39 (-é-ëç - rial was dissolved in acetone and precipitated with
2 2 2
2 13
ëçéç-ëç éç), 3.2 (C ç); C NMR (DMSO-d , water. The product was filtered off.
2
6
1
4
ppm): 101.76 (ë ). 81.5 (ë ), 74.5 (-é-ëç -ëçéç-
1
2
From the H NMR spectrum, it follows that the
3
2
ëç éç), 72.9 (ë ), 72.3 (ë ), 72.1 (-é-ëç -ëçéç-
2
2
degree of substitution of hydroxyl groups is close to
5
ëç éç), 71.9 (ë ), 66.7 (-é-ëç -ëçéç-ëç éç),
1
2
2
2
50%. The yield was 91.5%. H NMR (DMSO-d , ppm)
6
6
5
1
9.86 (ë ). MALDI–TOF (m/z): 1157, 1231, 1305,
6
4
.06, 5.6, 5.3 (-CH=CH ); 5.76 (OH-2); 5.61 (éç-3);
2
1 3 5
379, 1453, 1527, 2347, 2421; LC–MS–ESI (target
.92 (C ç); 4.12 (-CH -CH=CH ) 3.7–3.6 (C ç, C ç,
2 2
6 ‡,· 4 2
mass at m/z 1500): 1157, 1253, 1327, 1401, 1475,
C ç ); 3.4–3.2 (C ç, C ç). MALDI–TOF (m/z):
1
549, 2369, 2443.
1
375.5, 1415.5, 1455.5, 1495.5. 11535.5, 1575.5,
1
b-CD-3, b-CD-4 (template). H NMR (DMSO-d , 116115.5, 1655.5.
6
1
ppm) 5.75 (OH-2), 5.65 (éç-3), 4.9 (C ç), 3.6–3.64
Per(bromopropyl)-β-cyclodextrin was prepared as
follows. Gaseous HBr was passed through a solution of
perallyl-β-cyclodextrin persulfonic acid in CH Cl at
3
5
6
‡,b
(
C ç, C ç, C ç , -é-ëç -ëçéç-ëçéH-
2
4
CH OH), 3.4 (C ç), 3.38 (-é-ëç -ëçéç-ëçéH-
2
2
2
2
2
13
CH OH), 3.2 (C ç); C NMR (DMSO-d , ppm):
2
6
room temperature for 1.5 h. The solvent was distilled
off and the products was purified by reprecipitation
from acetone. The yield was 90%. According to
1
4
1
01.76 (ë ), 81.5 (ë ), 75.0 (-é-ëç -ëçéç-ëçéH-
2
3
CH OH), 72.9 (ë ), 72.5 (-é-ëç -ëçéç-ëçéH-
2
2
2
5
CH OH), 72.3 (ë ), 71.9 (ë ), 64.2 (-é-ëç -ëçéç-
1
2
2
H NMR data, the addition involved a half of allyl
6
ëçéH-CH OH), 59.86 (ë ). MALDI–TOF (m/z):
2
groups. The relative amount of the bromide produced
via the addition to the terminal allyl atom was 80%.
1
157, 1261, 1365, 1469, 1573, 2377, 2481, 2585, 2689;
LC–MS–ESI (target mass at m/z 1500): 1157, 1283,
1
H NMR (DMSO-d , ppm) 6.06, 5.6, 5.3 (-CH=CH );
6
2
1
387, 1595, 2399, 2503, 2607, 2711.
1
5
.76 (OH-2); 5.61 (éç-3); 4.92 (C ç); 4.12 (-CH -
2
3 5 6 ‡,·
1
b-CD-7. H NMR (DMSO-d , ppm) 5.75 (OH-2), CH=CH
) 3.9–3.5 (-CH
-CHBr-CH
-CH -CH Br); 1.85 (CH
-CHBr-CH ). MALDI–TOF (m/z):
, C ç, C ç, C ç );
6
2
2
3
1
3
5
6
‡,b
4
5
-
-
.65 (éç-3), 4.9 (C ç), 3.6–3.64 (C ç, C ç, C ç , 3.5–3.2 (C ç, -CH
2
2
2
2
-CH
-
2
4
é-ëç -ëçéç-ëçéH-CH -OH), 3.4 (C ç), 3.38 CH
Br), 1.72 (-CH
2
2
2
2
3
2
13
é-ëç -ëçéç-ëçéH-CH -OH); 3.2 (C ç);
C
1657.5, 1739.4, 1819.3, 1901.2, 1981.2.
2
2
1
4
NMR (DMSO-d , ppm): 101.76 (ë ), 81.5 (ë ), 75.0
6
Compound βCD-9 was prepared according to the
3
(
(
(
(
1
1
-é-ëç -ëçéç-ëçéH-CH -OH); 72.9 (ë ); 72.5
2 2
2
following procedure. A 9% Na SO aqueous solution
2
3
-é-ëç -ëçéç-ëçéH-CH -OH); 72.3 (ë ); 71.9
2
2
(10 ml) was slowly added with vigorous stirring to a
solution of per(bromopropyl)-β-cyclodextrin (0.80 g)
in ethanol (10 ml). The resulting mixture was refluxed
for 3 days. After the reaction, the solvent was distilled
off to dryness. The product was dissolved in 10 ml of
water, and inorganic salts were precipitated with 50 ml
of acetone. The filtrate solvent was distilled off on a
rotary evaporator. The precipitate was washed with eth-
5
ë ); 64.2 (-é-ëç -ëçéç-ëçéH-CH -OH); 59.86
2
2
6
ë ). MALDI–TOF (m/z): 1157, 1261, 1365, 1469,
573, 2377, 2481; LC–MS–ESI (target mass at m/z
500): 1157, 1283, 1387, 1595, 2399, 2503.
1
b-CD-5 (template). H NMR (DMSO-d , ppm)
6
1
DGD-
5
.75 (OH-2), 5.65 (éç-3), 4.9 (C ç), 3.87 (-C
3 5 6 ‡,b DGD
HOH-), 3.6–3.64 (C ç, C ç, C ç , -C H -), 3.4
2
4
2
13
anol and purified by means of dialysis. Yield 0.4 g.
(
C ç), 3.2 (C ç); C NMR (DMSO-d , ppm): 101.76
6
1 4 DGD 3 2
1
H NMR (DMSO-d , ppm) 6.06, 5.6, 5.3 (-CH=CH );
(
ë ), 81.5 (ë ), 74.8 (-C H -), 72.9 (ë ), 72.3 (ë ),
6
2
2
1
5
DGD
6
5
.76 (OH-2); 5.61 (éç–3); 4.92 (C ç); 4.12 (-CH -
2
3 5
7
1.9 (ë ), 69.9 (-C HOH-), 59.86 (ë ). MALDI–
CH=CH ) 3.9–3.5 (-CH -CHSO Na-CH , C ç, C ç,
TOF (m/z): 1157, 1379, 1469, 1601, 1823; LC–MS–
ESI (target mass at m/z 1500): 1157, 1401, 1623.
2
2
3
3
6
‡,·
4
C ç ); 3.5–3.2 (C ç, -CH -CH -CH SO Na); 2.18
2
2
2
3
1
(CH
2
-CH
2
-CH
2
SO
3
Na), 1.79 (-CH
2
-CHSO Na-CH )1.
3 3
b-CD-8. H NMR (DMSO-d , ppm) 5.75 (OH-2),
6
1
DGD
MALDI–TOF (m/z): 1870.4, 1766.5, 1661.5.
5
.65 (éç-3), 4.9 (C ç), 3.87 (-C HOH-), 3.6–3.64
3 5 6 ‡,b DGD 4 2
In catalytic experiments, iron(III) chloride and
vanadyl sulfate were used as components.
(
C ç, C ç, C ç , -C H -), 3.4 (C ç), 3.2 (C ç);
2
1 4
1
3
C NMR (DMSO-d , ppm): 101.76 (ë ), 81.5 (ë ),
6
DGD
3
2
5
7
4.8 (-C H -), 72.9 (ë ), 72.3 (ë ), 71.9 (ë ), 69.9
The coupling reaction of 2-naphthol was carried out
2
DGD
6
(
-C HOH-), 59.86 (ë ). MALDI–TOF (m/z): 1157, in the 1 : 1 (vol.) water–dichloroethane biphasic system
1
379, 1469, 1601, 1823; LC–MS–ESI (target mass at with intense stirring at atmospheric pressure, a temper-
m/z 1500): 1157, 1401, 1623.
ature of 60°ë, and ratios between the catalyst compo-
,6-Perallyl-β-cyclodextrin was prepared as fol-
lows. β-Cyclodextrin (2g, 1.76 mmol) and dry DMF
100 ml) were placed in a three-necked flask (250 ml)
nents of 2-naphthol : FeCl : β-CD = 20 : 40 : 1 and of
2
3
2
-naphthol : VOSO : β-CD = 5 : 1 : 1.
4
(
The catalyst system was prepared according to the
equipped with a reflux condenser, a dropping funnel, following general procedure. A 10-ml flat-bottomed
and an argon supply system. Sodium hydride (0.963 g glass flask was charged with the components of the cat-
in oil mull) was added. To the mixture stirred with a alytic system in calculated amounts: 50 mg of 2-naph-
magnetic stirrer, allyl bromide (2.6 ml, 30 mmol) was thol and distilled water and dichloroethane, 1 ml each;
added and the reaction continued for 24 h at room tem- the reaction mixture was stirred upon heating. At cer-
PETROLEUM CHEMISTRY Vol. 47 No. 6 2007

OXIDATION OF 2-NAPHTHOL
405
Table 2. Characterization of materials based on epichlorohydrin-modified cyclodextrins
Ratio of peak areas on mass
chromatogram
Average number of glycerol units
per cyclodextrin unit
Sample
Linking agent
S
2
000–3500
for compounds contain- for compounds contain-
-
---------------------
S
1
000–1700
ing 2 CD molecules
ing a CD molecule
β-CD-7
β-CD-6
β-CD-3
β-CD-1
β-CD-4
β-CD-2
Diepoxybutane
Epichlorohydrin
Diepoxybutane
Epichlorohydrin
Diepoxybutane
Epichlorohydrin
0.11
0.17
0.25
0.32
0.51
0.81
3
4
3–4
3–4
3–4
5–6
5–6
4
5–6
5–6
6–7
7–8
tain intervals, the organic layer was sampled and the mass spectrometry (MALDI–TOF and LC–MS) tech-
small samples were dissolved in 1 ml of acetonitrile. niques. The mass spectra of modified cyclodextrins
The products of oxidative coupling of 2-naphthol with turned out to display peaks of molecular ions corre-
air as an oxidizing agent was studied by means of sponding to compounds containing one and two cyclo-
HPLC on an Agilent SL 1100 chromatograph using a dextrin units. The number of added oligoglycidol units
Zorbax Eclipse XDB-C18 column of 2.1 × 150 mm varied from 2 to 8 in these compounds.
size, 5 µl (the column was thermostated at 40°ë). The
The ratio between various isomers of modified
mobile-phase flow rate was 0.5 ml/min, the mobile
cyclodextrins was determined by means of the LC–MS
phase was a methanol/water blend with a gradient of
technique in the electrospray ionization mode. The
8
1
0% water at the beginning to 100% methanol by the
0th min. The detection was performed at a wavelength
ratio of peak areas in the molecular mass ranges 2000–
3
600 and 1000–17000 characterizes the proportion of
of 290 nm with a diode array detector.
dimers in the product.
It was shown that the average degree of polymeriza-
tion of epichlorohydrin and the number of compounds
that include two chemically linked cyclodextrin mole-
cules strongly depends on the presence of the template
and its concentration in the reaction mixture. The
growth in the chain length of the linker on passing from
epichlorohydrin to diepoxybutane leads to a decrease in
the proportion of dimers and the degree of oligomeriza-
tion. Moreover, the dimers were not found at all when
the bulkier reagent diglycidyl ether of glycerol was
used. The characteristics of the materials based on
epichlorohydrin-modified cyclodextrins are given in
Table 2.
RESULTS AND DISCUSSION
In the syntheses of 2,6-dimethyl-β-cyclodextrin,
ethoxylated
β-cyclodextrin,
6-deoxy(ethylenedi-
amine)-β-cyclodextrin, and 2,6-persulfopropyl-β-
cyclodextrin, we employed procedures reported in the
literature [8, 9]. 2,6-Perallyl-β-cyclodextrinsulfonic
acid was synthesized via successive allylation, hydro-
gen bromide addition, and –SO group substitution for
3
bromide. The modification of cyclodextrins with
epichlorohydrin and diepoxybutane was carried out in
an aqueous alkali solution for 6 h. The products was
isolated by reprecipitation from the aqueous solution
with acetone or methanol. The general scheme of
imprinting is described by Schemes 2 and 3.
The materials obtained via modification with
epichlorohydrin and diepoxybutane were also charac-
1
13
terized by means of H and C NMR spectroscopy. The
1
The cyclodextrin molecule contains 21 hydroxyl
H NMR spectra of the samples showed a substantially
groups, whose reactions can lead to various mono-, di-, lower intensity of signals due to hydroxyl groups and
and trisubstituted compounds. Reacting in the presence the appearance of signals at 3.8–4.9 ppm attributed to
of a template are its inclusion complexes with C1–H and C6–H protons of cyclodextrin, the chemical
β-cyclodextrin, in which some hydroxyl groups of the shifts of these protons being changed by modification,
host molecule are inaccessible to the reagents. As a and to free hydroxyls of the oligoglycidyl segments.
result, isomers that form the most stable inclusion com- The most substantial changes were observed in the
plexes with the template prevail in the mixture. As has region of cyclodextrin OH protons.
been shown earlier, owing to the formation of guest–
It should be noted that hydroxyl groups at the third
host complexes composed of two cyclodextrin mole-
carbon atom (éç-3) remained practically intact in the
cules per template molecule, the proportion of the
dimers can increase as well [4, 5, 7].
case of β-cyclodextrins prepared with the use of tem-
plates. This conclusion follows from the intensity ratio
1
The macroligands obtained in the presence and of signals at 5.65 (éç-3) and 4.85 ppm (C ç) in the
absence of templates were studied by the NMR and proton NMR spectrum. This ratio was 0.7–0.8 for the
PETROLEUM CHEMISTRY Vol. 47 No. 6 2007

4
06
KARAKHANOV et al.
HO3
HO3
HO3
HO3
OH
OH
3
3OH
O–
2
OH
2
–O
O
2
O
2
O
2
O
2
Cl
NaOH
é
H O
2
6
6
6
6
6
6
OH
OH
OH
HO
OH
HO
OH
OH–
HO 3
HO 3
HO 3
O–
2
O
2
O
2
OH
O
Cl
OH–
Cl
O
H O
2
…
O
OH
OH
6
6
6
O
O
O
O
OH
OH
OH
6
6
6
Cl
OH–
O
H2O
2
2
2
O
Cl
O
Cl
O
Cl
3
3
3
O–
HO
OH
HO
HO
O
OH
O–
6
6
O
Cl
OH–
O
H O
2
…
2
2
O
Cl
O
Cl
3
3
HO
O
HO
O
OH
OH
OH
OH
Scheme 2. Cyclodextrin-mediated oligomerization of epichlorohydrin.
samples prepared in the absence of templates and close likely that the hydroxyl groups at C and C carbon
2
6
to unity for the samples prepared in their presence. In atoms (OH-2 and OH-6) predominantly enter the reac-
1
3
tion.
addition, the C NMR spectra of the latter samples did
not display a signal at 73 ppm that would correspond to
When aromatic compounds were oxidized in the
the modified carbon atoms C of β-cyclodextrin. It is water/dichloroethane biphasic medium with different
3
Table 3. Oxidation of 2-naphthol
1
,1'-Bi-2-naphthol
yield, %
Ligand
Metal salt
Metal/2-naphthol ratio
Time, h
Methylated β-CD
FeCl3
FeCl3
FeCl3
FeCl3
FeCl3
VOSO4
Cu2+
2
2
2
39
38
16
32
39
81
24
2
Oxyethylated β-CD
Perallyl β-CD sulfonic acid
Sulfopropyl β-CD
2
2
2
2
2
6
-Ethylenediamino-β-CD
Methylated β-CD
-Ethylenediamino-β-CD
Methylated β-CD
2
2
0.2
0.05
0.05
240
5
6
Cu2+
10
PETROLEUM CHEMISTRY Vol. 47 No. 6 2007

OXIDATION OF 2-NAPHTHOL
407
systems (iron(III) chloride [10, 11], oxygen/vanadyl
ion [12, 13], oxygen in the presence of copper com-
plexes as catalysts [14, 15]), the main product was
Yield, %
80
(a)
6
4
2
0
0
0
1
,1'-bi-2-naphthol with the selectivity for this product
exceeding 95%. In the absence of cyclodextrin, the
reaction proceeds at an extremely slow rate and the
product yield does not exceed 20% for 10 h (in the case
of the iron salt) or 10% for 7 days (in the case of the
vanadium salt). In the presence of copper salts, no for-
mation of binaphthol was observed.
1
2
0
2
4
6
8
10
Yield, %
The use of modified cyclodextrins made it possible
to substantially increase the rate of the process. It is
likely that the rise in the reaction rate is primarily due
to an increase in the concentration of the substrate
1
00
(b)
8
0
60
1
2
-naphthol in the aqueous phase as a result of the for-
4
0
2
mation of guest–host complexes with cyclodextrin. The
yield of the corresponding dimeric products reaches
20
8
1
0% for 8 h of the reaction (with the use of FeCl ) or for
3
0 days in the presence of vanadyl sulfate. It is essential
0
50 100 150 200 250 300 350
Time, h
that the double excess of the metal salt was used in the
former case and a 10 mol % excess in the latter case,
that is, the reaction proceeds in the catalytic mode
involving air oxygen (Table 3). It should specially be
noted that the copper complex of ethylenediamine-
modified cyclodextrin exhibits a relatively high activ-
ity. The use of other cyclodextrins in combination with
copper salts did not lead to the dimerization of the sub-
strate.
Fig. 1. Oxidative coupling of 2-naphthol into 1,1'-bi-2-
naphthol catalyzed by (a) FeCl and (b) VOSO in the
3
4
biphasic system (1) in the presence of 2,6-Me-CD and (2) in
the absence of the macroligand.
Yield, %
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
(
a)
Note that a nearly quantitative yield of the product
was obtained when the reaction was run for a very long
time.
1
2
3
We compared the activity of catalyst systems con-
taining the macroligands synthesized via the same pro-
cedure in the presence and absence of template mole-
cules. For this purpose, we calculated the reaction-rate
TON
TON
1
enhancement factor ------------ -- , where TON is the number
1
70
(b)
2
6
5
4
3
2
1
0
0
0
0
0
0
of moles of the product per mole of catalyst per hour in
the case when the macroligands was synthesized in the
1
2
presence of the template and TON is the number of
2
moles of the product per mole of catalyst per hour in the
case when the same macroligand was synthesized in the
absence of the template.
0
1
2
3
4
5
The use as catalyst components of cyclodextrins
synthesized in the presence of 1,1'-bi-2-naphthol made
it possible to substantially increase the rate of the reac-
tion as compared with the catalyst system containing
cyclodextrin obtained in the absence of the template, as
well as methylated cyclodextrin. The yield of the dimer
over the reaction time of 5 h was 65% (Fig. 1). It is
important that the reaction rate and the product yield
increase when the macroligand prepared in the pres-
ence of a large excess of the template is used. The reac-
tion-rate enhancement factor was greater than two in
this case.
Time, h
Fig. 2. (a) Catalytic activity of the system using the ligand
prepared via modification with epichlorohydrin in the pres-
ence of (1) excess of epichlorohydrin template or (2) bi-2-
naphthol and (3) in the absence of the template; (b) catalytic
activity of the system using the ligand prepared via modifi-
cation with diepoxybutane (1) in the presence of bi-2-naph-
thol and (2) in the absence of the template.
lower; nonetheless, a similar trend was observed: the
use of binaphthol as a template leads to a dramatic
The activity of the catalysts prepared via modifica- increase in the product yield relative to the catalyst pre-
tion with diepoxybutane turned out to be somewhat pared either in the absence of the template or in the
PETROLEUM CHEMISTRY Vol. 47 No. 6 2007

4
08
KARAKHANOV et al.
presence of 2-naphthol as a template. It should also be
noted that the ligand that had been prepared via modifi-
cation with epichlorohydrin in the presence of the lin-
ear substrate dodecanal and had contained a consider-
able amount of dimers exhibited a considerably lower
activity than the ligand obtained with the use of bi-2-
naphthol as a template. This difference indicates that a
kind of preorientation of cyclodextrin molecules takes
place to fit to the conformation of the product. In this
case, the use of corresponding aromatic compounds as
the bi-2-naphthol template must lead to a growth in the
reaction rate owing to a kind of simulation of the tran-
sition state of the reaction with the use of the template.
REFERENCES
1
2
3
. E. A. Karakhanov, A. L. Maksimov, and E. A. Runova,
Usp. Khim. 74, 104 (2005).
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(
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the naphthyl radical with naphthol has been proposed
for oxidative coupling in the literature [10, 11].
The rate of this process depends on the distance
between interacting molecules; the closer this distance
to the distance in 1,1'-binaphthol itself, the higher the
reaction rate. It is likely that the structure of the dimers
in the case of catalysts obtained in the presence of 1,1'-
binaphthol best satisfies this condition and the reaction
rate turns out to be high.
In summary, studying the coupling of 2-naphthol,
we have shown that the use, as catalyst components, of
cyclodextrins modified under the molecular imprinting
conditions leads to an increase in the reaction rate when
an analog of the reaction transition state is taken as a
template.
6. A. A. Efendiev and V. A. Kabanov, Pure Appl. Chem. 11,
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7
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1
1
1
1
0. K. Ding, Y. Wanf, L. Zhang, and Y. Wu, Tetrahedron 52,
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1. K. Ding, Q. Xu, Y. Wanf, et al., Chem. Commun., 693
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(
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ACKNOWLEDGMENTS
A. C. Jansen, Tetrahedron 41, 3313 (1985).
This work was supported by the Russian Foundation 15. M. Hovorka, J. Gunterova, and J. Zavada, Tetrahedron
for Basic Research, project no. 04-03-32166a.
Lett. 31, 413 (1990).
PETROLEUM CHEMISTRY Vol. 47 No. 6 2007