Activated zeolites and heteropolyacids: An efficient catalysts for the synthesis of triacetoxyaromatic precursors of hydroxyquinones

Article abstract of DOI:10.14233/ajchem.2013.14276

The Thiele-Winter reaction is of interest for synthesis of triacetoxyaromatic precursors of hydroquinones. Liquid acid such as, chlorosulfonic acid and solid acids like heteropolyacids have an efficient catalyst can effectively replace sulfuric acid in acetoxylation reaction of quinones without use of organic solvent at room temperature.

Full text of DOI:10.14233/ajchem.2013.14276

Asian Journal of Chemistry; Vol. 25, No. 11 (2013), 6112-6116
http://dx.doi.org/10.14233/ajchem.2013.14276
Activated Zeolites and Heteropolyacids: An Efficient Catalysts for the
Synthesis of Triacetoxyaromatic Precursors of Hydroxyquinones
*
DOKARI HADJILA and HAMMADI MOHAMED
Faculty of Sciences, University of Boumerdes, 35000 Boumerdes, Algeria
*Corresponding author: Fax: +213 24816284; Tel: +213 792037937; E-mail: hadjila_2@yahoo.fr
(Received: 7 July 2012; Accepted: 29 April 2013)
AJC-13414
The Thiele-Winter reaction is of interest for synthesis of triacetoxyaromatic precursors of hydroquinones. Liquid acid such as, chlorosulfonic
acid and solid acids like heteropolyacids have an efficient catalyst can effectively replace sulfuric acid in acetoxylation reaction of
quinones without use of organic solvent at room temperature.
Key Words: Heteropolyacids, Actived zeolites without solvent, Hydroxynaphthoquinones.
synthesis of 2,5-dihydroxy-1,4-naphthoquinone (3b). This
synthesis involves first the oxidation of 1,5-dihydroxy-
naphthalene in product (3) and its transformation into
tetracetoxy (3a) by Thiele-winter reaction. The saponification
of (3a) followed by catalytic oxidation in situ of naphthotriols.
(Scheme-I).
INTRODUCTION
The hydroxynaphthoquinones1 are well known substances
for their chemical and biological properties2. The hydroxynaph-
thoquinones like phthiocol3, lawsone4, juglone5, menadione
and atovaquone6, have gained large interest due to their pres-
ence in natural products and their pharmacological properties
as antitumoral, antiprotozoal, antiinflammatory, antiviral and
antifungal7.
O
OAc
O
OAc
OH
KOH-CH3OH
Acid Catalyst
20°C, 20h
1°)
Ac2O
+
We have used this methodology to prepare the
acetoxylation reactions of quinones and naphthoquinones
acid-catalyzed by ClSO3H (Ho = -13.80) and heteropolyacids
H3PW12O40 (Ho = - 13.6), in the absence of solvent at room
temperature.
2°)
O
Pc [Co]/K10,
2
O
OAc OAc
OH
OH
O
3
(3a)
(3b)
Scheme-I: Synthesis of 2,5-dihydroxy-1,4-naphthoquinone (3b) from juglone
Our attention has focused on the use of metallic phthalo-
cyanines supported in the oxidative reactions of naphthotriols
prepared from the Thiele-Winter reaction in order to synthesize
hydroxynaphthoquinones natural products having antibiotic
properties. The acetoxylation reaction of juglone, menadione
and lawsone with acetic anhydride catalyzed by sulfuric acid8,9,
(Ho = -11.94), at room temperature is slow with low yields
especially in the presence of substituents on the naphthoquinone
as electron donors. Sulfuric acid was replaced by chlorozincique
acid10 and tetrafluoroboric acid1 with low yields.
EXPERIMENTAL
Melting points (m.p.) were determined with a Kofler hot
apparatus and are uncorrected. Proton NMR spectra (PMR)
were determined on Brucker AC 250 (250 MHz, CDCl3,
Me4Si). The IR spectra were recorded as KBr pellets on Perkin
Elmer 16 PC FT-IR spectrometer UV-visible spectra [λmax
log(ε)] were obtained with spectrophotometer Perkin-Elmer
Lamda-15.
Microwave irradiation were carried out with a commercial
microwave oven (Toschiba ER 7620) at 2450 MHz. and with
resonance cavity TEo13, joined to a generator MES 73-800
of microwaves. Masse spectra were carried out on a Nermag
Riber R10; TLC analyses were performed by using Kieselgel
Schleicher and Shull F 1500 Ls 254 and Merck 60 F 254. The
grinding of products were carried out on a analytical grinder
A 10 of Janke and Kenkel-IKA Labortechnik. The mont-
morillonite K10 was obtained from the firm of Sûd Chemie.
To overcome this problem where the acidity of the
medium thus protonation of the quinone is the decisive step,
we opted for the use of liquid hyperacid more acidic than
sulfuric acid in homogeneous conditions such as chlorosulfonic
acid: ClSO3H11 (Ho = -13.80) and solid superacid as hetero-
geneous conditions in the heteropolyacid: H3PW12O40 (Ho =
-13.6). In our work we are particularly interested in the

Vol. 25, No. 11 (2013)
Synthesis of Triacetoxyaromatic Precursors of Hydroxyquinones 6113
Zeolites (ZSM-5, DAY) as ammonium form wer calcinatd at
500 ºC under dry flow before use. (firm BDH). Heteropolyacids
were commercially avaible from Fluka.
of authentic samples. The UV spectral of quinones was carried
out in water-dioxane mixture.
Acetoxylation reaction under homogeneous conditions
(liquid acids): In a typical experiment, 10 mmol of juglone
was dissolved in acetic anhydride (0.2 mol). 5 mmol of catalyst
was added and the mixture was stirred at room temperature.
After 20 h the mixture was stirred at room temperature. The
solution was poured on ice and after the ice melted the mixture
was filtered and the solid 1, 2, 4, 5-tetracetoxynaphthalene,
produce (3a) was crystallized in ethanol.
Phthalocyanine (Co) Supported on K10
Preparation of montmorillonite K10 exchanged by
Co2+: In a 250 mL flask, the montmorillonite K10 (20 g) was
added to a solution of CoCl2 (0.2 mol) dissolved in 100 mL of
distilled water. The reaction al mixture was stirred for 24 h at
room temperature. The suspension was washed twice with
distilled water then centrifuged. The montmorillonite
exchanged by Co2+ was washed with methanol and re-centri-
fuged. The solid was dried for 24 h in vacuum then finely
ground. The final product was a clear beige colour.
Acetoxylation reaction under heterogeneous conditions
(solid acids): In a typical experiment, 10 mmol of juglone
was dissolved in acetic anhydride (0.2 mol; 21.64 g).
1 g of catalyst was added and the mixture was stirred at
room temperature. After 48 h, the products were separated by
chromatography on a silica column eluted successfully with
ethyl acetate/cyclohexane (10/90). The different fractions gave
respectively a yellow solid (unreacted quinone) and a beige
solid (1, 2, 4, 5-tetracetoxynaphthalene) (3a). It must be noted
that traces of products of diacetylation could be detected by
thin layer chromatography.
Phthalocyanine intercalated in the montmorillonite
K10: A solution of phthalonitrile (20 mmol; 2.56 g) dissolved
in 20 mL of dichloromethane was added the solid montmori-
llonite K10 (5 g) exchanged with some metallic cations (Co2+).
After contact for 2 h, the remaining liquid was evaporated
under reduced pressure. The activation of the solid under
microwaves irradiation: p = power, t = time of irradiation)
was carried out in a resonance cavity. After cooling, the solid
was successively washed with water, acetone (20 mL) and then
with dichloromethane (20 mL). The solid was dried under
reduced pressure and the extracted with acetonitrile as a solvent
using a Soxhlet for 8 h. Catalysts were characterized by FT-
IR, electronic spectra of metalated phthalocyanine intercalated
into montmorillonite was very close to those observed with
pure metalated phthalocyanine, but the bands were shifted.
Preparation of zeolites exchanged H+: 10 g of zeolite
(ZSM5 or DAY) are placed in a 50 mL flask and then treated
with a solution of NH4Cl (0.1 M) previously prepared with deion-
ized water. The stoppered flask is allowed to stand overnight at
room temperature. The solid residue was recovered by filtration
and then activated in a muffle furnace at 500 ºC for 24 h. The
zeolite in H+ (H+ -ZSM5 or H+ -DAY) is stored in a dry container.
Preparation of hydroquinones: In a typical experiment,
the phenol (100 mmL) was dissolved in 200 mL of 10 % solu-
tion of sodium hydroxide under stirring at room temperature.
A saturated aqueous solution of sodium persulfate (100 mL);
23.8 g) was slowly and carefully added for 3 h. At the end of
the addition, stirring was maintained at room temperature. The
mixture was stand over-night. The solution acidified with
Congo red and was extracted twice with ether. The aqueous
layer was treated with an excess of hydrochloric acid and
warmed in a steam bath for 0.5 h. After cooling, it was once,
dried on magnesium sulphate and finally distilled to afford
the corresponding hydroquinone.
The acid solids e.g., zeolites and hetero-polyacids have
been tested in this study and the results are reported in Table-2.
Saponification and oxidation in situ: In a typical
experiment, a current of air was passed through à U tube fitted
with a filter flask. The tube contains the [Pc (Mn)/K10 (0.1
g)] in suspension in a solution of product (4) (0.6 g) dissolved
in CH3OH (20 mL) and KOH (2 g) for 6 h at room tempe-
rature. After filtration and evaporation of the methanol, the
product (5) was crystallized.
(Pc [CO] supported on K10): Purple solid, m.p. > 300 ºC
MO; microwaves irradiation resonance cavity. (P = 630 W, t =
10 min); C32H16CoN8; Yields: 85 % UV-visible λmax log(ε)/
(1-chloronaphthalene) nm : 669.5 (4.42); 642.1 (3.88); 604.2
(3.78); 580.1 (3.22); IR (KBr, νmax, cm-1): 1636, 1522, 1400,
1044, 870, 796, 756, 532, 525, 466.
2-Methyl-1,4-benzoquinone (2a): Brown solid, yields:
95 %, m.p: 72-73º (lit. 73 ºC)12; C7H6O2, calcd. H 4.95 % C
68.85 %, Found: H 4.87 % C 68.73 %; UV-visible λmax log (ε)
(dioxane/H2O) nm: 278.2 (4.15), 312.3 (2.75), 422.6 (1.31);
NMR 1H (CDCl3) δ: 2.01 (s, 1H, CH3); 6.23 (s, 1H); 6.52 (m,
1H), 6.85 (d, 2H); IR (KBr, νmax, cm-1): 1689 ( γ C=O).
2,6-Dimethyl-1,4-benzoquinone (2b): Brown solid,
yield: 90 %, m.p.: 73-74 ºC (lit. 71-73 ºC)13; C8H8O2, calcd. H
5.92 % C 70.58 %, Found: H 6.01 % C 70.50 %; UV-visible
λ
max log (ε) (dioxane/H2O) nm: 270.6 (4.29), 318.1 (2.52), 414,
3 (1.25); IR (KBr, νmax, cm-1): 1685 (γ C=O).
2,6-Dimethoxy-1,4-benzoquinone (2c): Brown solid,
yield: 89 %, m.p.: 253 ºC; C8H8O4, calcd. H 4.80 % C 57.14 %,
Found: H 4.87 % C 57.12 %; UV-visible λmax log (ε) (dioxane/
H2O) nm: 279.5 (4.25), 379 (2.69), 465.5 (0.45); IR (KBr,
Oxidation to quinones: In a typical experiment, a current
of air was passed through à U tube fitted with a filter flask.
The tube contains the supported phthalocyanine (0.1 g) in
suspension in a solution of hydroquinone (5 mmol) dissolved
in 10 mL of a mixture of dioxane/water (60: 40) for 6 h at
room temperature. The oxidation of hydroquinone was
followed by TLC. After disappearance of hydroquinone, the
solution was filtered and evaporated under vacuum. The quinones
were purified by chromatography on silicagel or by subli-
mation.All products are known compounds and were identified
by comparaison of their physical and spectral data with those
ν
max, cm-1) : 1678 (γ C=O).
5-Hydroxy-1,4-naphthoquinone: (Juglone) (3): Red
solid, Yield: 87 %, m.p.: 159-160 ºC (lit. 161 ºC)13; C10H6O3,
calcd. H 3.47 % C 68.97 %, Found: H 3.58 % C 68.92 %; UV-
visible λmax log (ε) (dioxane/H2O) nm: 249.3 (4.21), 331.1
(3.18), 422.1 (2.98); NMR 1H (CDCl3) δ : 6.76 (s, 2H, CH=);
7.25-7.45 (m, 3H, H arom.); 7.77 (s, 1H, OH ); IR (KBr, νmax
cm-1) : 3241 (γ OH), 1683 (γ C=O), 1587, 1170, 884, 536.
,

6114 Hadjila et al.
Asian J. Chem.
TABLE-1
OXIDATION OF HYDROQUINONES INTO QUINONE WITH SUPPORTED METALATED PHTHALOCYANINES
Phenols
Hydroquinones
OH
Oxidation catalysts
Pc [Co]/K10
Quinones
O
m.p. (ºC)
72
Yield (%)
95
2-Methylphenol
CH3
CH3
O
OH
(1a)
(2a)
O
OH
2,6-Dimethylphenol
2,6-Dimethoxyphenol
Pc [Co]/K10
Pc [Co]/K10
73
90
89
CH3
CH3
CH3
CH3
OH
O
O
OH
253
OMe
OMe
OMe
OMe
O
OH
(1c)
(2c)
2-Hydroxy-1,4-naphthoquinone: Lawsone (4): Orange
solid, yields: 79 %, m.p.: 194 ºC (lit.; 191-194 ºC)13; C10H6O3,
calcd. H 3.47 % C 68.97 %; Found: H 3.53 % C 68.92 %; UV-
visible λmax log (ε) (dioxane/H2O) nm: 276.3 (4.48), 334.3
(3.28); 1H NMR (CDCl3): δ : 6.37 (s, 1H, OH); 7.26 (s, 1H, H
arom.); 7.25-8.14 (m, 4H, H arom); IR (KBr, νmax, cm-1): 3166
(γ OH), 1676 (γ C=O), 1592, 1170, 874, 668, 536.
2-Hydroxy-3-methyl-1,4-naphthoquinone (5b):Yellow
solid,Yields: 92 %, m.p.: 173-174 ºC (ether + hexane), C11H8O3
calcd. H 4.29 % C 70.21; Found: H 4.35 % C 70.08 %, UV-
visible λmax log (ε) (dioxane/H2O) nm: 271.3 (4.44), 346.6 (3.
21); 1H NMR (CDCl3): δ: 2.08 (s, 1H, CH3); 6.42 (s, 1H, OH);
7.29 (s, 1H, OH); 7.5-8.1 (m, 4H, H arom.); IR (KBr, νmax, cm-1):
3330 (γ OH), 1655 (γ C=O), 1589, 1174, 878, 536.
2-Methyl-1,4-naphthoquinone : Menadione (5):Yellow
solid, Yield: 80 %, m.p.: 104-105 ºC (lit. 105-107 ºC)13;
C11H8O2, calcd. H 3.38 % C 78.25 %, Found: H 4.42 % C
78.18 %; UV-Visible λmax log (ε) (dioxane/H2O) nm: 264, 1
(4.18), 332.5 (3.36); 1H NMR (CDCl3): δ : 2.21 (s, 1H, CH3);
6.85 (s, 1H, H); 7.75-8.14 (m, 4H, H arom); IR (KBr, νmax, cm-1):
1732, 1668, (γ C=O), 1593, 1082, 940, 884, 720, 650.
1,2,4,5-Tetracetoxynaphthalene (3a): Marron solid,
Yield: 63 %, m.p.: 137-138 ºC; NMR 1H (CDCl3): δ : 2.33 (s,
3H, OCOCH3); 2.35 (s, 3H, OCOCH3); 2.40 (s, 3H, OCOCH3);
2.42 (s, 3H, OCOCH3); 7.68-8.07 (m, 4H, H arom); IR (KBr,
RESULTS AND DISCUSSION
Oxidation of phenols and hydroquinones into quinones:
The phenol oxidation products are used for the synthesis of
natural products such as vitamins and their intermediates.
Concerning the oxidation of phenols or hydroquinones into
quinones numerous oxidants were described in the literature
such as silver oxide14, ceric ammonium nitrate15.
In a preliminary study, we were inspired by the reaction
of Elbs16 to access to hydroquinones by oxidation of phenols
by sodium persulfate (Na2S2O8). We have tested the oxidation
of hydroquinones into quinones by air catalyzed a metalated
phthalocyanine17 on the sheet of a montmorillonite K10.
hydroquinones and substituted hydroquinones was easily
oxidized at room temperature in quinones by using (Pc[Co]/
K10) and air (1 atm), as indicated in (Scheme-II). Results
obtained from different phenols were reported in Table-1.
ν
max, cm-1) : 3009 (γ CH arom.), 1774 (γ OCOCH3), 1762, 1719.
1,2,3,4-Tetracetoxynaphthalene (4a): Beige solid,Yield
1
66 %, m.p: -140-143 ºC; H NMR (CDCl3) δ : 2.39 (s, 6H,
OCOCH3); 2.44 (s, 6H, OCOCH3); 7.46-8.14 (m, 4H, H arom);
IR (KBr, νmax, cm-1): 3012 (γ CH arom), 1760 (γ OCOCH3),
1718; MS m/z (%); 360 (M+; 24.46), 318 (3.41), 276 (16.38),
192 (100), 146 (11.95), 105 (23.55).
2-Methyl-1,3,4-triacetoxynaphthalene (5a): Beige
1
solid, Yield: 59 %, m.p.: 148-150 ºC; NMR H (CDCl3): δ:
O
OH
OH
Na S O
R
1)
2)
R'
R
R
2
2
8
R'
R'
O2
HCl
2.16 (s, 3H, CH3); 2.37 (s, 3H, OCOCH3); 2.45 (s, 3H,
OCOCH3)7, 2.49 (s, 3H, OCOCH3) 7.48-7.76 (m, 4H, H arom);
IR (KBr, νmax, cm-1): 3000 (γ CH arom.), 1774 (γ OCOCH3),
1760; MS m/z (%); 316 (M+; 39.13), 274 (12.50), 233 (17.38),
174 (6.63), 115 (2.88).
Pc[Co]/K
T= 22 °C
24h
10
O
OH
Phenol
R = H , R' = CH3
R = R' = CH3
Quinone
Hydroquinone
R = R' = OMe
2,5-Dihydroxy-1,4-naphthoquinone (3b):Yellow solid,
Yields: 89 %, m.p.: 210 ºC; UV-visible λmax log (ε) (dioxane/
H2O) nm: 279, 3 (4, 68), 331, 3 (3, 08); 1H NMR (CDCl3): δ:
6.39 (s, 1H, OH); 6.40 (s, 1H, OH); 7.18-8.01 (m, 5H, H arom);
IR (KBr, νmax, cm-1) : 3168 (γ OH), 1679 (γ C=O), 1591, 1176,
881, 544.
Scheme-II: Oxidation of hydroquinones into quinones
The direct oxidation of phenols with oxygen in presence
of supported metalled phthalocyanines as oxidant generally
gave quinone at room temperature but the reaction is very slow
and not selective.
2,3-Dihydroxy-1,4-naphthoquinone (4b): Beige clear
solid, yields: 91 %, m.p.: 201 ºC; UV-visible λmax log (ε) (di-
oxane/H2O) nm: 289.3 (4.77), 339.3 (3.27); 1H NMR (CDCl3)
δ: 6.41 (s, 1H, OH); 6.42 (s, 1H, OH); 7.31-8.11 (d, 4H, H
arom); IR (KBr, νmax, cm-1) : 3172 (γ OH), 1678 (γ C=O), 1589,
1174, 878, 536.
We have also tested this type of reaction in naphtho-
quinone series. Many of naphthoquinone are natural products
with interesting biological properties. The catalytic system
[Pc(Co)/K10] in presence of pure oxygen oxidises easily the
1,5-dihydroxynaphthalene in Juglone (yield 87 %). (This latter

Vol. 25, No. 11 (2013)
Synthesis of Triacetoxyaromatic Precursors of Hydroxyquinones 6115
TABLE-2
OXIDATION OF HYDROXYNAPHTHALENE
Hydroxynaphthalene
Oxidation catalysts Naphthoquinone
O
Pc [Co]/K10
m.p. (ºC)
159
Yield (%)
87
UV-Visible λmax nm
331,1
1,5-Dihydroxynaphthalene
OH
O
Juglone 3
O
1,3-Dihydroxynaphthalene
Pc [Co]/K10
Pc [Co]/K10
194
103
334,3
332,5
79
80
OH
O
Lawsone 4
O
2-Methyl-1,4-Dihydroxy naphthalene
CH3
O
Menadione 5
TABLE-3
ACETOXYLATION OF JUGLONE AT 20 ºC
Catalyst
ClSO3H
Aspect
Liquid
Solid
Solid
Solid
Solid
Solid
Hammet: Ho
Experimental
20 ºC, 20 h
20 ºC, 48 h
20 ºC, 48 h
20 ºC, 48 h
20 ºC, 48 h
20 ºC, 48 h
m.p. (ºC)
IR vester (cm-1)
Yield
55%
56%
54%
61%
-
-13,80
148
149
148
149
-
1773
1772
1776
1773
-
H+-DAY
-
H+-ZSM5
H3PW12O40
H3PMo12O40
H4SiW12O40
-
-13,6
-
-
152
1774
63%
from green to deep blue, roving the reduction of PMO. The
result with (PMO) is not surprising owing to its high redox
potential resulting from the presence of molybdenum atom.
Results of acetoxylation of Juglone by acetic anhydride obtained
from different acids catalysts were reported in Table-3.
The kinetics of the reaction was monitored hourly by
visible spectroscopy ultrat purple. The kinetic of menadione
transformation (bleaching) was monitored at 333 nm, which
is the maximum point of menadione (5) (The vitamin K3
carrier). There is (Scheme-III) changes in the UV/visible
spectrum in the presence of ClSO3H.
is used as alimentary stain for soft drinks). The total oxidation
was about 6 h at room temperature. Results obtained from
different phenols were reported in Table-2.
Thiele-winter reaction: The 5-Hydroxynaphthoquinone
(3) treated with acetic anhydride in the presence of catalyst con-
verts into the1,2,4,5-tetracetoxynaphthalene (3a) (yield 63 %).
We have studied this reaction with strong acids. chloro-
sulfonique acid (Ho = -13.80) and perchloric acid18 (Ho =
-10.31) led to the desired product.
The reaction with solid superacids show a high Brônsted
acidity and it was lower than with homogeny phase.
Heteropolyacids (HPAs also called polyoxometalates)
are catalysts of great interest19. The display has a very high
Brônsted acidity close to superacids. It is decided to test three
heteropolyacids (H3PW12O40 (PW), H4SiW12O40 (SiW) and
H3PMo12O40 (PMO). The (SiW) provide the product with a
yield of 63 % whereas a yield of 61 % was achieved with the
(PW). It has been noticed that the (SiW) appeared a better
catalyst than the (PW). Explanation could be assigned to the
higher ratio of number of protons in (SiW)20.
The kinetic of menadione transformation (bleaching)
depends on acidity of catalyst. It seems that the limiting step of
the Thiele-Winter reaction is the protonation of the quinine.
The 1,2,4,5-tetracetoxynaphthalene (3a) was easily trans-
formed into (3b) by saponification basic and oxidation with
potassium hydroxide (KOH) in methanol (CH3OH) in presence
of air at room temperature. The yield of 2,5-dihydroxy-1,4-
2.0
1.6
1.2
0.8
0.4
0
Zeolites with high Si-Al ration (15-20) are known to
posses strongly acidic sites 10. Two acid zeolites (H+-ZSM5
and H+-DAY) were also tested successfully. Zeolites can be
reused without loss of activity when the reaction is carried out
at room temperature. No poisoning by tar formation was
observed with ZSM5 or DAY. With solid catalysts like zeolite,
the Juglone is too wide to enter the pores of ZSM5 and the
reaction took place on the surface of zeolite.
190.00
272.00
354.00
436.00
We have noticed that no product (3a) was obtained with
the H3PMo12O40 (PMO). The reaction medium colour changed,
1: Ménadione + acetic anhydride [temps : t = 0]

6116 Hadjila et al.
Asian J. Chem.
TABLE-4
SOLID ACID AS CATALYST FOR OXIDATION BY MOLECULAR OXYGEN. SYNTHESIS OF HYDROXYNAPHTHOQUINONES
2º) [Saponification-oxidation] In situ
OH
1º) Thiele-winter : triacetoxyaromatic
O
OAc
O
OAc
OH
OH
OAc OAc
OH
O
OH
OH
OH
O
(3a)
3
(3b)
O
O
OH
OAc
OH
OH
OH
OAc
OH
OH
OAc
O
(4b)
O
OAc
(4a)
OAc
O
OH
OH
4
O
CH3
OH
CH3
CH3
OAc
CH3
OH
O
OAc
O
OH
(5a)
5
(5b)
2.0
1.6
1.2
0.8
0.4
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0
190.00
272.00
354.00
436.00
8. J. Thiele, Ber., 31, 1247 (1898).
2 : Menadione +Acetic anhydride + ClSO3H
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Scheme-III: Evolution of UV/visible spectrum in the presence of ClSO3H
naphthoquinone from (3a) is good (89 %). The results obtained
from the two steps sequence (triacetoxyaromatic and saponi-
fication-oxidation in situ) were reported in Table-4.
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Conclusion
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611 (1996).
In conclusion it appears that chlorosulfonic acid is the
most effective acid catalyst found for the acetoxylation reaction
of juglone under homogeneous conditions. Zeolites (DAY-H+)
heteropolyacids (H3PMo12O40) can easily catalyze the Thiele-
Winter reaction. This work represents the first exemple of
catalysis of this reaction by solid acids. The sequence of the
two steps (acetoxylation, saponification-oxidation) constitutes
a new synthesis of hydroxynaphthoquinones from hydroquinones.
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