PreparatiVe Oxidation of Organic Compounds
J. Am. Chem. Soc., Vol. 119, No. 23, 1997 5287
1
Table 1. Formulations of Microemulsions on a Weight Basis
(microemulsion) is suitable for the chemical formation of O2
and the oxidation of highly hydrophobic substrates on the
preparative scale with a minimum loss of O2.
τ∆ (µs)a
exp hom het
micro- molybdate water SDS butanol CH2Cl2
1
emulsion (mmol/kg) (%) (%)
(%)
(%)
A
B
C
D
E
F
G
H
I
48
5
6.0 9.5
5.0 7.7
2.2 6.5
8.3 7.3
13.9 8.6
21.0 9.6
30.0 9.9
39.9 9.9
49.9 9.6
9.5
15.3
12.9
14.6
17.3
19.3
19.8
20.0
19.4
75.0 40.2
72.0 42.4
Experimental Section
78.4 45.0 34.7 42.2
69.8 37.7 22.0 34.4
60.2 30.1 16.5 28.4
50.1 23.9 12.9 23.7
40.3 20.1 10.3 19.8
30.2 16.2 8.6 16.5
21.1 13.2 7.4 13.9
(A) Chemicals. Sodium molybdate dihydrate (99%), 5,6,11,12-
tetraphenylnaphthacene (rubrene, Rub, 1, 98%), 9,10-diphenylan-
thracene (DPA, 2, 98%), 1,3-diphenylisobenzofuran (DPBF, 3, 97%),
tetraphenylcyclopentadienone (tetracyclone, TCP, 4, 98%), R-terpinene
(Terp, 5, 98%), â-citronellol (Citro, 7, 95%), dibenzyl sulfide (DBS,
9, 98%), diphenyl sulfide (DPS, 10, 98%), 5,10,15,20-tetraphenyl-21H,-
23H-porphine (TPP, 98%), and 5,10,15,20-tetraphenyl-21H,23H-por-
phine-p,p′,p′′,p′′-tetrasulfonic acid, tetrasodium salt dodecahydrate
(TPPS, 98%), were purchased from Aldrich Chemie and used as
received. 2-Methyl-5-tert-butylthiophenol (8, 99%) was a generous
gift of Hoechst France. Adamantylideneadamantane12 (Ada, 6) was
prepared according to known procedures. Methylene chloride (Nor-
mapur), butanol (Normapur), methanol (HPLC Grade), sodium dode-
cylsulfate (SDS, 98%), and hydrogen peroxide (50%, Rectapur) were
obtained from Prolabo. Deuteriated chloroform and deuterium oxide
(99.9%) were acquired from CEA (Commissariat a` l’Energie Atomique,
Saclay, France).
a Lifetimes of 1O2 (τ∆) measured (exp) or calculated by considering
the mixture as a homogeneous medium (hom) or a microheterogeneous
system (het).
Oxidation of 9,10-Diphenylanthracene (2). A solution of 1.0 g
(3.0 mmol) of 2 in the microemulsion B (50 g) was treated with 60 µL
(1.0 mmol) of 50% H2O2. The red-brown solution was stirred at room
temperature for 13 min until the color faded to gold-yellow. Nineteen
other fractions of 60 µL of H2O2 were allowed to react in the same
way, and the reaction was monitored by HPLC. Thus, after 4 h, 2
was completely oxidized. The solvents (methylene chloride, butanol,
and water) were rotary evaporated at 40 °C in vacuum. The semisolid
residue was stirred vigorously with 100 mL of methylene chloride for
30 min. The suspension was filtered by suction through a sintered-
glass funnel to recover the solid sodium molybdate and sodium
dodecylsulfate. The filtrate was rotary evaporated at 20 °C in vacuum,
and the yellowish residue was washed successively with water (2 ×
20 mL), methanol (2 × 20 mL), and ether (2 × 20 mL) giving 0.97 g
(89%) of pure endoperoxide as crystalline colorless solid.
(B) Instrumentation. HPLC. High-performance liquid chroma-
tography analyses was carried out with a Gilson pump model 303 by
using a 25 cm column packed with Spherisorb RP18-5 ODS. A mixture
of H2O and CH3OH was used as eluent, and UV detection was
performed with a variable-wavelength monitor (Gilson Holochrom
H/MD).
Flash Photolysis. (Laboratoire de Biophysique, Museum National
d’Histoire Naturelle, Paris.) The photosensitized production of 1O2 was
carried out by energy transfer from a photosensitizer (TPP or TPPS)
to 3O2. A 2 mL sample of an air-saturated microemulsion was irradiated
with a short (6 ns) flash of light at 532 nm, emitted by a Nd-Yag laser.
Infrared phosphorescence of singlet oxygen at 1270 nm was detected
perpendicularly with a Ge photodiode (Judson J16), and the signal was
recorded with an oscilloscope (Tektronix 556) and analyzed according
to a first-order decay. The flash photolysis apparatus13 and the detection
system14 have been previously described in detail.
Oxidation of Other Substrates. The moderately soluble substrates
1-4 and 6 were oxidized according to the same procedure in the
microemulsion B, whereas the microemulsion A was preferred for the
highly soluble (5 and 7) and poorly reactive (8-10) substrates. To
achieve a maximum rate for 1O2 generation, H2O2 was added by
fractions, each of them containing about 4 equiv of H2O2 with respect
to MoO42-. The fading of the red-brown to the gold-yellow color was
the signal for an additional fraction of H2O2. The cumulative amounts
of H2O2 consumed, the reaction times, and the yields are reported in
Table 2. The products do not require further purification except
1H and 13C NMR. (Laboratoire d’Applications RMN, Universite´
1
de Lille II.) Spectra were recorded in CDCl3 at 300 MHz for the H
ascaridol that was distilled (bp3 ) 77-78 °C). All the H and 13C
NMR spectra were in agreement with the published spectra or with
those of authentic samples prepared by tetraphenylporphine-sensitized
photooxygenation.15 Control experiments without either H2O2 or
1
and at 75.46 MHz for the 13C by using a Bruker AC 300P FT-
spectrometer. All chemical shifts are relative to the TMS signal (δ )
0 ppm) as reference.
(C) Procedures. Pseudoternary Phase Diagrams. The samples
(12.5 g) were prepared in capped glass vials (50 mL) by introducing
sequentially the surfactant (SDS), the cosurfactant (n-BuOH), and the
organic solvent, (methylene chloride). The slurry obtained was
maintained at a constant (20 ( 0.1 °C) temperature and titrated with
0.2 mL fractions of an aqueous sodium molybdate solution. After each
addition, the samples were vigorously stirred, allowed to settle, and
observed. It is the spontaneous conversion of the turbid emulsion into
a clear, single-phase medium that indicates the beginning of the
microemulsion region. Whereas the appearance of a persistent cloudy
aspect leading to a phase separation after settling delimits the end of
the microemulsion domain.
2-
MoO4 did not lead to any consumption of the substrates. The
unknown sulfonate obtained from the thiophenol 8 exhibits the
following spectral data: 1H NMR (D2O) δ 1.34 (s, 9H, -C(CH3)3), 2.63
(s, 3H, Ar-CH3), 8.05 (d, 1H, -C-(SO3H)dCH), 7.37 (d, 1H, -CHdC-
(CH3)-), 7.6 (dd, 1H, -CHdC-C(CH3)3); 13C NMR (D2O) δ 143.14
(-CdC(SO3H), 152.45 (-CdC(C(CH3)3)-), 136.01 (-CdC(CH3)-),
134.89 (-CdC(CH3)-), 126.55 (-CdC(SO3H)-), 131.45 (-CdC-
C(CH3)3), 36.82 (C(CH3)3), 33.30 (-C(CH3)3), 21.88 (CH3-CdC-).
Results
Pseudoternary Phase Diagrams. The microemulsion region
of the water/SDS/butanol/methylene chloride system delimits
a volume included in a quaternary phase diagram. The
boundaries of this volume were determined from pseudoternary
phase diagrams obtained at 20 °C by maintaining the ratio of
butanol/SDS at a constant value and titration with aqueous
Microemulsions A-J. The microemulsion A was prepared at room
temperature by adding dropwise an aqueous solution of sodium
molybdate (1.15 g in 6 mL of water) to a magnetically stirred slurry of
sodium dodecylsulfate (9.5 g), n-butanol (9.5 g), and methylene chloride
(75 g). The transparent, mobile, isotropic medium obtained after 5
min of mixing can be kept unchanged in a capped flask for several
weeks. Other microemulsions were prepared by applying the same
procedure for the formulations reported in Table 1.
(15) (a) Dufraisse, C. Bull. Soc. Chim. Fr. 1936, 182, 1584-1587. (b)
Rigaudy, J.; Scribe, P.; Breliere, C. Tetrahedron 1981, 37, 2585-2593. (c)
Dufraisse, C.; Ecary, S. Compt. Rend. 1946, 223, 735-773. (d) Bikales,
N. M.; Becker, E. I. J. Org. Chem. 1956, 21, 1405-1407. (e) Schenck, G.
O.; Ziegler, K. Naturwissenschaften 1945, 32, 157. (f) Wieringa, J. H.;
Strating, J.; Wynberg, H.; Adam, W. Tetrahedron Lett. 1972, 169-172.
(g) Ohloff, G.; Lienhard, B. HelV. Chim. Acta 1965, 48, 182-189. (h)
Jongsma, S. J.; Cornelisse, J. Tetrahedron Lett. 1981, 2919-2922. (i) Koch,
E. Tetrahedron 1968, 24, 6295-6318. (j) Liang, J. J.; Gu, M. L.; Kacher,
M. L.; Foote, C. S. J. Am. Chem. Soc. 1983, 105, 4717-4721.
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