Copper-catalysed oxidative alkoxylation of acyl- and carbomethoxy-hydroquinones

Article abstract of DOI:10.1016/S0040-4020(00)00947-9

Oxidation of title hydroquinones by an [O²/Cu^ICl] system in the presence of alcohols yields (71-88%) corresponding regioselectively 3-alkoxylated compounds. Compared with the classical procedure (silver oxide oxidation) in which alcohols have to be added to intermediate quinones in a second step, leading to a 1:1 mixture of starting material and final quinones, this new selective one-pot system does not oxidize alcohols and regenerates intermediate quinones from starting hydroquinones. Moreover, in situ trapping of the unstable formyl-quinone now allows the preparation of its 3-alkoxy derivative.

Full text of DOI:10.1016/S0040-4020(00)00947-9

TETRAHEDRON
Pergamon
Tetrahedron 57 (2001) 379±384
Copper-catalysed oxidative alkoxylation of acyl- and
carbomethoxy-hydroquinones
*
Patrice Capdevielle and Michel Maumy
Â
Laboratoire de Recherches Organiques de l'ESPCI, associe au CNRS, 10 rue Vauquelin, F-75231 Paris Cedex 05, France
Received 24 April 2000; revised 1 June 2000; accepted 11 July 2000
AbstractÐOxidation of title hydroquinones by an [O2/CuICl] system in the presence of alcohols yields (71±88%) corresponding regio-
selectively 3-alkoxylated compounds. Compared with the classical procedure (silver oxide oxidation) in which alcohols have to be added to
intermediate quinones in a second step, leading to a 1:1 mixture of starting material and ®nal quinones, this new selective one-pot system
does not oxidize alcohols and regenerates intermediate quinones from starting hydroquinones. Moreover, in situ trapping of the unstable
formyl-quinone now allows the preparation of its 3-alkoxy derivative. q 2000 Elsevier Science Ltd. All rights reserved.
1. Introduction
More recent studies2 have shown that, in the absence of
Lewis acid catalyst, moderate yields of mono-alkoxylated
quinones (mixture of isomers) could be obtained through
prolonged heating (48 h) of methyl-benzoquinone with
ethanol.
Despite the large occurrence of alkoxy-substituted quinonic
compounds and their derivatives amongst natural products,
studies about their synthesis through addition of alcohols
onto quinones are somewhat rare.
On the other hand, 1,2-benzoquinones (e.g. 8) are more
sensitive towards nucleophilic addition. As a typical
example, in situ oxidation of pyrocatechol 7 in the presence
of CH3OH leads to 4,5-dimethoxy-1,2-benzoquinone 9,
using lead tetraacetate3 or a [CuII complex/O2] system4 as
oxidant (Scheme 2).
Alkoxylation of 1,4-benzoquinones is well known to require
the presence of a Lewis acid catalyst since Knúvenagel's
studies (Scheme 1).1
Indeed, addition of methanol or ethanol to 1,4-benzo-
quinone 2 proceeds in the presence of the Lewis acid
catalyst ZnCl2 (or CaCl2, MgCl2), and affords the corre-
sponding 2,5-dialkoxy-benzoquinones 6, together with two
equivalents of hydroquinone 1, the latter resulting from the
redox reactions between intermediate alkoxy hydro-
quinones 3 and 5 and the starting benzoquinone 2.
We have previously shown that a [O2/CuI/Cu8] system was
able to successively ortho-hydroxylate phenols and
dehydrogenate the resulting pyrocatechols into 1,2-benzo-
quinones which can then react with the starting phenol to
afford aryloxy-quinones after further dehydrogenation.5±9
Scheme 1.
Keywords: hydroquinones; alkoxylation; oxidation.
* Corresponding author. Fax: 133-1-40-79-46-60; e-mail: patrice.capdevielle@espci.fr
0040±4020/01/$ - see front matter q 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(00)00947-9

380
P. Capdevielle, M. Maumy / Tetrahedron 57 (2001) 379±384
Scheme 2.
Scheme 3.
In the particular case of 4-methoxyphenol, the resulting
4-methoxy-5-(4-methoxyphenoxy)-1,2-quinone is amenable
to selective substitutions of the aryloxy leaving group by a
variety of alcohol5±9 and amine10 nucleophiles to give access
to the synthesis of numerous additional quinonoid
compounds. In particular, alkylation of the nucleus through
Claisen±Cope reactions can be obtained after addition of
allylic alcohols5,9 and amines11±14 onto this 1,2-quinone.
gel's pioneering results.1 Here also, since silver oxide is
used as an oxidant, alcohols are added to quinone 11c in a
second step, and two equivalents of 11c give rise to one
equivalent of 3-alkoxy-quinone 13c (effective yieldˆ40±
45%) along with one mole of starting material hydroquinone
10c, as shown in Scheme 4.
The regioselective addition of various nucleophiles on the 3-
carbon position of quinones 11a±c was clearly ascribed by
all the authors15,21±23 to the electron-withdrawing character
of the formyl, acetyl or carbomethoxy substituents on the 2-
carbon position, which renders the 2,3 double bond more
reactive than the 5,6 one. Additional conformational studies,
based on redox potentials and spectroscopic data, showed
that the preferred conformation of 11a was planar, with the
formyl carbonyl group anti to the 1-carbonyl, whereas ace-
tyl group in 11b and other more bulky acyl groups were
approximately perpendicular to the quinonoid ring.24 The
effect of the most powerful electron-withdrawing formyl
group is then enhanced by a favorable geometry, whereas
the less withdrawing carbomethoxy is totally inef®cient,
presenting a non-planar conformation. Complexation of a
bidentate chelating metal ion like Mg11 with the C(1)- and
carbomethoxy-carbonyl groups23 has therefore a double
advantage; it establishes a more planar conformation and
activates the system by acid catalysis.
The reactivity of para-quinones is greatly enhanced when
they are substituted by an electron-withdrawing group, as in
formyl and acetyl compounds 11a,b. Selective mono-
addition of alcohols R0 ±OH on the activated carbon-3 posi-
tion have thus been obtained in benzene, without addition of
any Lewis acid catalyst, in the case of 2-acetyl-1,4-benzo-
quinone (11b) (Scheme 3).15
Quinone 11b was prepared by silver oxide-mediated oxida-
tion of 2-acetylhydroquinone 10b in the presence of a
desiccating agent (MgSO4, Na2SO4) in 90±95% yield;16±19
Quinone 11b was then separated from the excess of Ag2O to
avoid oxidation of alcohol R0 ±OH, which is consequently
added in a second step. The transient 3-alkoxy-hydro-
quinone 12b is rapidly oxidised by the higher-potential
unreacted quinone 11b, and the alkoxylated quinone 13b
is ®nally obtained together with one equivalent of starting
material 10b, in a theoretical yield at the best equal to 50%
(37±50% effective yield from quinone 11b).
2. Results
2-Formyl-1,4-benzoquinone (11a) is quite more reactive
than 11b; it can be obtained with dif®culty through Ag2O
oxidation of 10a in a very moderate yield of 32%,20 and only
thio21 and azido22 nucleophiles have yet been successfully
added onto it, but not alkoxy ones.
Having previously studied in our laboratory the oxidizing
properties of the CuII complexes resulting from the reaction
of CuICl and molecular oxygen with simple phenol, pyro-
catechol and hydroquinone substrates,25,26 we were logically
prompted to apply these conditions to the oxidative alkox-
ylation of the formyl-, acetyl- and carbomethoxy-hydroqui-
nones 10a±c.
2-Carbomethoxy-1,4-benzoquinone (11c) is quite less reac-
tive than 11b thanks to its weaker electron-withdrawing 2-
substituent. Hormi et al.23 recently reported that the addition
of alcohols to 11c leads to 3-alkoxy-hydroquinones 12c only
in the presence of MgCl2 as a Lewis acid catalyst in toluene
solvent. One can here note the agreement with Knúvena-
Basically, O2 oxidises CuICl in acetonitrile solution into a
m-oxo binuclear CuII complex A, which constitutes a simple
chemical model of copper-enzymes laccases.27 Electron-

P. Capdevielle, M. Maumy / Tetrahedron 57 (2001) 379±384
381
Scheme 4.
enriched phenols 14 (Rˆalkyl, alkoxy or N-acetamido
groups) are hydroxylated by excess complex A into hydro-
quinones 16 by the intermediary of phenoxy radicals 15
through a succession of one-electron oxidations (`SET'),
and the resulting hydroquinones are dehydrogenated into
para-quinones 17 in a 80±85% global yield. Minor amounts
of ortho-quinones possibly formed through ortho-hydroxyl-
ation of starting phenols have not been detected, since they
are readily subject to nucleophilic additions (water,
phenolic compounds) and further oxidations in these con-
ditions. This sequence, in which CuICl clearly plays a
catalytical role with regard to the oxidant O2, is described
in Scheme 5.
Involvement of phenoxy radical intermediates 15 has been
inferred from the formation of dimers or polymers of the
starting phenols, instead of quinones 17, at low values of the
ratio A/phenol; the coupling rate of these radicals is then
superior to the rate of the oxidative ±OH ligand transfer
15!16.25,26 Such a behaviour is representative of one-
electron oxidants such as FeCl3, K3Fe(CN)6, Ag2CO3 and
some CuII salts.28
Scheme 5.
Scheme 6.

382
P. Capdevielle, M. Maumy / Tetrahedron 57 (2001) 379±384
Scheme 7.
As shown in Scheme 6, complex A reacts with water and
alcohols to afford mononuclear species such as the methoxy
complex B when A reacts with methanol;25,26 this divalent
copper complex B is also able to dehydrogenate hydro-
quinones into para-quinones.
Oxidation of 2-formyl-1,4-hydroquinone (10a) with MeOH
in MeCN at room temperature leads to poor yields of addi-
tion product 12a, besides tarry materials; the reaction is
preferably performed at 08C, where the high reactivity of
quinone 11a towards nucleophilic reagents allows to reach
completion in 2 h.
It thus appeared that complexes of type B could be valuable
candidates for the oxidative alkoxylation of hydroquinones
10a±c, in the presence of an ef®cient desiccating agent in
order to limit troublesome competition between H2O and
the alcohol R0 ±OH in the nucleophilic addition step 11a±
c!12a±c (Scheme 7).
The oxidant CuII complex B takes part in a catalytic process,
being regenerated from CuICl by oxidation (O2) and
alcoholysis (R0 ±OH) of intermediate A. H2O is trapped by
®nely ground anhydrous CaSO4 (Drieritew), which affords
better results than Na2SO4 or MgSO4. Once the oxidation
completed, copper complexes are reduced down to metallic
CuO by excess aqueous Na2S2O4 and the products are
recovered as stable alkoxy-hydroquinones 12a±c since
quinones 13a±c are readily reduced under these conditions.
It is important to ensure that the reduction of copper is
complete, since traces of CuI/CuII may contaminate ®nal
product and cause its decomposition upon air exposure.
High-melting acetyl-hydroquinone (10b) requires ®rst to be
re¯uxed in a 1:1 mixture of MeCN-EtOAc for complete
dissolution; the oxidation addition reaction is then
performed at 208C for 3 h (MeOH) to 5 h (BnOH). Ester
10c, giving the less activated 2-carbomethoxy-1,4-quinone
11c, needed to be reacted for 5 h at room temperature with
n-hexanol in pure MeCN.
Increasing yields of the desired 3-alkoxy-hydroquinones
12a±c (Scheme 8) are apparently obtained when decreasing
the reactivity of the 2-acyl-quinones. This is plausibly due
to the relative ease of H2O addition onto the quinones 11a±c
and 13a±c, since water is present as traces in the course of
the oxidation, and even in much greater quantity during the
®nal reduction step 13a±c!12a±c with aqueous Na2S2O4.
It was also noted that, carbomethoxy-quinone 13c is stable
under silica gel TLC conditions;23 this is not the case for
acetyl-quinone 13b and especially not for the formyl-
quinone 13a.
Hence, 2-formyl-hydroquinone (10a) reacted with methanol
under these conditions to afford the 3-methoxy substituted
compound 12a, 2-acetyl-hydroquinone (10b) reacted with
methanol, ethanol and benzyl alcohol to give 3-methoxy-
acetylhydroquinone 12b1, 3-ethoxy-acetylhydroquinone
12b2 and 3-benzyloxy-acetylhydroquinone 12b3, respec-
tively (Scheme 8). At last, 2-carbomethoxy-hydroquinone
10c and n-hexanol directly gave 3-hexyloxy-carbomethoxy-
hydroquinone 12c, without any addition of a Lewis acid like
MgCl2.
3. Conclusion
The use of the inexpensive copper/O2 system as oxidant of
hydroquinones 10a±c instead of silver oxide brings another
advantage in the fact that the alcohols R0 ±OH are not
oxidized by CuII complexes A and B. A `one-pot' proce-
dure, in which quinones 11a±c are thoroughly alkoxylated,
Scheme 8.

P. Capdevielle, M. Maumy / Tetrahedron 57 (2001) 379±384
383
is thus permitted and avoids the wastage of half the starting
hydroquinones 10a±c.
Procedure B. 2-Formyl-hydroquinone 10a, 1.38 g
(0.01 mol), is dissolved in dry MeCN (40 ml) with 3 ml
(0.075 mol) MeOH, then stirred with anhydrous powdered
CaSO4 (20 g) under a dioxygen atmosphere at 08C, and 3.2 g
(0.032 mol) Cu(I)Cl are added. Conditions are maintained
for 2 h, then an aqueous solution (100 ml) of 10 g Na2S2O4
and 2 g NaHCO3 is added to the reaction mixture. After
overnight stirring, the resultant slurry is extracted with
4£150 ml EtOAc, and the organic phase rinsed with 15 ml
saturated brine. After drying over MgSO4, the solvents are
evaporated under reduced pressure to afford 1.2 g 12a
(0.0071 mol, 71% yield).
Quinones 11a±c are produced in the presence of alcohols
R0 ±OH, and no longer in a preliminary step. The more
reactive 2-formyl-hydroquinone 11a is rapidly trapped and
gives rise to the desired alkoxylated quinone 13a, then to
hydroquinone 12a, so far inaccessible by this type of
reaction.
The CuII ion in the complexes of this oxidant system
behaves as a Lewis acid, and, like MgCl2 in Hormi's
work,23 catalyses the addition of R0 ±OH onto the poorly
reactive carbomethoxy-quinone 11c, allowing the direct
and ef®cient one-pot transformation of hydroquinone 10c
into 3-alkoxylated quinone 13c.
4.1.2. 2-Acetyl-3-methoxy-hydroquinone (12b1). 2-Acetyl-
hydroquinone 10b, 1.52 g (0.01 mol), is totally dissolved
through re¯uxing in dry MeCN (40 ml) and co-solvent
EtOAc (40 ml) with 3 ml (0.075 mol) MeOH, then stirred
with anhydrous powdered CaSO4 (20 g) under a dioxygen
atmosphere at 208C, and 3.2 g (0.032 mol) Cu(I)Cl are
added. Conditions are maintained for 3 h, then an aqueous
solution (100 ml) of 10 g Na2S2O4 and 2 g NaHCO3 is added
to the reaction mixture. After overnight stirring, the resulting
slurry is extracted with 3£150 ml EtOAc, and the organic
phase rinsed with 15 ml saturated brine. After drying over
MgSO4, the solvents are evaporated under reduced pressure
to afford 1.55 g 12b1 (0.0085 mol, 85% yield). As yellow
crystals, mp 90±918C mp lit.15,30±32 908C. 1H NMR
(CDCl3): d(ppm) 2.75 (s, 3H), 3.88 (s, 3H), 5.40 (s, 1H),
6.70 (d, 1H, Jˆ9 Hz), 7.20 (d, 1H, Jˆ9 Hz), 12.10 (s, 1H).
4. Experimental
4.1. General
Melting points were determined on a Ko¯er (Reichert)
apparatus; H NMR spectra were obtained with internal
1
standard SiMe4 on a Bruker AC 300 spectrometer
(300 Mhz).
Oxidations are carried out under an oxygen atmosphere in a
250 ml round-bottomed ¯ask, ®tted with a magnetic stirrer
and a water or ice/water bath. Acyl-hydroquinones 10a,b
and cuprous chloride are of 98±99% pure commercial
quality. MeCN, 99.5% pure commercial quality,
H2O,0.1%, is used without further puri®cation. Anhydrous
CaSO4, Drieritew, is purchased from W. A. Hammond
Drierite Co.
4.1.3. 2-Acetyl-3-ethoxy-hydroquinone (12b2). 2-Acetyl-
hydroquinone 10b, 1.52 g (0.01 mol), is dissolved under
warming in dry MeCN (40 ml) and co-solvent EtOAc
(40 ml) with 3 ml (0.05 mol) EtOH, then stirred with anhy-
drous powdered CaSO4 (20 g) under a dioxygen atmosphere
at 208C, and 3.2 g (0.032 mol) Cu(I)Cl are added. Condi-
tions are maintained for 3 h, then an aqueous solution
(100 ml) of 10 g Na2S2O4 and 2 g NaHCO3 is added to the
reaction mixture. After overnight stirring, the resultant
slurry is extracted with 3£150 ml EtOAc, and the organic
phase rinsed with 15 ml saturated brine. After drying over
MgSO4, the solvents are evaporated under reduced pressure
to afford 1.70 g 12b2 (0.0087 mol, 87% yield). As yellow
Monitoring of the oxidation is performed through reduction
of a little sample (,0.05 ml) by Na2S2O4 in water and
extraction with EtOAc. The organic phase is then analysed
by thin layer chromatography on silica gel (pre-coated silica
gel 60F254 aluminium sheets, Merck). Alkoxy-substituted
hydroquinones 12a±c are all eluted faster than the corre-
sponding starting compounds 10a±c (typically Rfˆ0.5 and
0.4 with an EtOAc:cyclohexaneˆ4:6 eluant mixture).
1
crystals, mp 103±1048C, mp lit.15 102±103.58C. H NMR
(CDCl3): d (ppm) 1.51 (t, 3H, Jˆ7 Hz), 2.75 (s, 3H), 4.10
(q, 2H, Jˆ7 Hz), 5.20 (s, 1H), 6.60 (d, 1H, Jˆ9 Hz), 7.12 (d,
1H, Jˆ9 Hz), 11.90 (s, 1H).
4.1.1. 2-Formyl-3-methoxy-hydroquinone (12a). Procedure
A. To a cooled (08C) solution of 1.38 g (0,01 mol) 2-formyl-
hydroquinone (2,5-dihydroxybenzaldehyde) 10a and 3 ml
(0.075 mol) methanol in dry MeCN (40 ml), stirred with
anhydrous powdered CaSO4 (20 g) under a dioxygen
atmosphere, are added 3.96 g (0.04 mol) Cu(I)Cl; conditions
are maintained for 2 h, then toluene (60 ml) is added and
MeCN distilled off under reduced pressure. The resultant
slurry is diluted with 150 ml EtOAc, the liquid phase sepa-
rated by ®ltration on a Celitew layer and stirred with an
aqueous solution (70 ml) of 6 g Na2S2O4 and 0.6 g NaHCO3
until metallic copper precipitates, then washed again with a
solution of Na2S2O4 (1.5 g). After drying over MgSO4, the
solvents are evaporated under reduced pressure to afford
1.09 g 12a (0.0065 mol, 65% yield). As yellow crystals, mp
80±828C, mp lit.29 85±868C. 1H NMR (CDCl31DMSO d6): d
(ppm) 4.0 (s, 3H), 6,4 (d, 1H, Jˆ9 Hz), 7.2 (d, 1H, Jˆ9 Hz),
7.9±9.1 (broad, 1H), 10.2 (s, 1H), 10.8±11.1 (broad, 1H).
4.1.4.
2-Acetyl-3-benzyloxy-hydroquinone
(12b3).
2-Acetyl-hydroquinone 10b, 1.52 g (0.01 mol), is dissolved
under warming in dry MeCN (40 ml) and co-solvent EtOAc
(40 ml) with 4.32 g (0.04 mol) benzyl alcohol, then stirred
with anhydrous powdered CaSO4 (20 g) under a dioxygen
atmosphere at 208C, and 3.2 g (0.032 mol) Cu(I)Cl are
added. Conditions are maintained for 5 h, then an aqueous
solution (100 ml) of 10 g Na2S2O4 and 2 g NaHCO3 is added
to the reaction mixture. After overnight stirring, the
resultant slurry is extracted with 3£150 ml EtOAc, and
the organic phase rinsed with 15 ml saturated brine. After
drying over MgSO4, the solvents are evaporated under
reduced pressure and the residue crystallized from Et2O/
hexane to separate excess benzyl alcohol and afford 2.05 g
12b3 (0.079 mol, 79% yield). As yellow crystals, mp

384
P. Capdevielle, M. Maumy / Tetrahedron 57 (2001) 379±384
90±918C, mp lit.15 87.5±898C, mp lit.33 948C (from petro-
leum ether). H NMR (CDCl3): d (ppm) 2.70 (s, 3H), 4.95
11. Viallon, L.; Reinaud, O.; Capdevielle, P.; Maumy, M.
Tetrahedron Lett. 1995, 36, 4787±4790.
1
12. Viallon, L.; Reinaud, O.; Capdevielle, P.; Maumy, M.
Tetrahedron Lett. 1995, 36, 6669±6672.
(s, 2H), 5.25 (s, 1H), 6.70 (d, 1H, Jˆ9 Hz), 7.10 (d, 1H,
Jˆ9 Hz), 7.38 (s, 5H), 11.90 (s, 1H).
13. Viallon, L.; Reinaud, O.; Capdevielle, P.; Maumy, M.
Tetrahedron 1996, 52, 7841±7854.
4.1.5. 2-Carbomethoxy-3-hexyloxy-hydroquinone (12c).
To a cooled (08C) solution of 1.68 g (0.01 mol) methyl
2,5-dihydroxybenzoate 10c34 and 4.08 g (0.04 mol) n-hexa-
nol in dry MeCN (40 ml), stirred with anhydrous powdered
CaSO4 (20 g) under a dioxygen atmosphere, are added
3.96 g (0.04 mol) Cu(I)Cl; conditions are maintained for
1 h, and the mixture warmed-up to 208C for 4 h, always
stirred under O2. 60 ml toluene are then added and MeCN
distilled off under reduced pressure. The resultant slurry is
diluted with 150 ml EtOAc, the liquid phase separated by
®ltration on a Celitew layer and stirred with an aqueous
solution (70 ml) of 6 g Na2S2O4 and 0.6 g NaHCO3 until
metallic copper precipitates, then washed again with a solu-
tion of Na2S2O4 (1.5 g). After drying over MgSO4, the
solvents are evaporated under reduced pressure together
with 100 ml xylene in order to sweep off the excess of
n-hexanol. The crystalline crude product is ®nally dried
under vacuum (0.1 mmHg) to yield 2.37 g 12c (0.088 mol,
14. Viallon, L.; Reinaud, O.; Capdevielle, P.; Maumy, M.
Tetrahedron 1996, 52, 13605±13614.
15. Farina, F.; Valderrama, J. Synthesis 1971, 315±316.
16. Woroshzow, N. N.; Mamaew, V. P. Sb. Statei Obshch. Khim.
1953, 533±535.
17. Kloetzel, M. C.; Dayton, R. P.; Abadir, B. Y. J. Org. Chem.
1955, 20, 38±47.
18. Abdulla, K. A.; Abdul-Rahman, A. L.; Al-Hamdany, R.;
Al-Saigh, Z. Y. J. Prakt. Chem. 1982, 324, 498±504.
19. Mathur, P.; Dismukes, G. C. J. Am. Chem. Soc. 1983, 105,
7093±7098.
20. Bruce, J. M.; Creed, D. J. Chem. Soc. C 1970, 649±653.
21. Ruiz, V. M.; Tapia, R.; Valderrama, J.; Vega, J. C.
J. Heterocycl. Chem. 1981, 18, 1161±1164.
22. Cassis, R.; Fernandez, M.; Tapia, R.; Valderrama, J. A. Synth.
Commun. 1987, 17, 1077±1088.
23. Hormi, E. O. E.; Moilanen, A. M. Tetrahedron 1998, 54,
1943±1952.
1
88%). As colourless crystals, mp 57±58 8C, lit.23 578C. H
NMR (CDCl3): d (ppm) 0.90 (t, 3H), 1.33 (m, 4H), 1.47 (m,
2H), 1.82 (m, 2H), 3.88 (t, 2H), 3.99 (s, 3H), 5.54 (s, 1H),
6.72 (d, Jˆ9.0 Hz), 7.13 (d, Jˆ9.0 Hz), 10.57 (s, 1H).
24. Bruce, M.; Heatley, F.; Ryles, R. G.; Scrivens, J. H. J. Chem.
Soc., Perkin Trans. 2 1980, 860±866.
25. Capdevielle, P.; Maumy, M. Tetrahedron Lett. 1983, 24,
5611±5614.
Â
26. Capdevielle, P.; Maumy, M. L'Actualite Chimique 1986
(Avril), 5±11.
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