Naphthalene oxidation by peracetic acid catalysed by Mn3+ porphinoid complexes

Article abstract of DOI:10.1070/MC2001v011n03ABEH001429

A comparison of the oxidation of naphthalene and its d⁸-derivative by peracetic acid catalysed by Mn³⁺ tetranitrotetra-tert-butyltetraazaporphine allowed us to refine both the mechanisms of 1,4-naphthoquinone and 1-naphthol formation and the structures of the final products of 1-naphthol oxidation.

Full text of DOI:10.1070/MC2001v011n03ABEH001429

, 2001, 11(3), 116–118
Naphthalene oxidation by peracetic acid catalysed by Mn3+ porphinoid complexes
Svetlana V. Barkanova,* Oleg L. Kaliya and Eugene A. Luk’yanets
Institute of Organic Intermediates and Dyes, 103787 Moscow, Russian Federation. Fax: +7 095 254 1200; e-mail: rmeluk@cityline.ru
10.1070/MC2001v011n03ABEH001429
A comparison of the oxidation of naphthalene and its d8-derivative by peracetic acid catalysed by Mn3+ tetranitrotetra-tert-
butyltetraazaporphine allowed us to refine both the mechanisms of 1,4-naphthoquinone and 1-naphthol formation and the structures
of the final products of 1-naphthol oxidation.
The oxidation of aromatic compounds in nuclei is a subject of
continual interest; in the last decade, certain success has been
achieved in the resolution of this problem. It was reported on
2-methylnaphthalene conversion to 2-methyl-1,4-naphthoquinone
(menadione) in 45–65% yield by means of different oxidants
[H2O2,1 (Me3SiO)2,2 KHSO5,3 AcOOH4–6] and catalysts of both
non-porphinoid (Re7+ oxo complexes1,2) and porphinoid struc-
ture (Mn and Fe complexes of substituted porphyrin3 and aza-
porphines4–6). Previously, we found the effectiveness of Mn3+
azaporphines in naphthalene (Nph) oxidation by peracetic acid
to the corresponding para-quinones and oligomeric products in
acetonitrile–acetic acid solutions. Of studied complexes {3,5-octa-
nitrophthalocyanine (ONPcMnCl),4,5 tetra-R-tetra-tert-butyltetra-
azaporphine [RTAPMnCl; R = NO2 (1), Br]6}, tetraazaporphine
1 was the most active in the formation of para-quinones. We
hypothesised that under the reaction conditions naphthalene oxi-
dation proceeds via two parallel paths with the participation
of oxene and peroxide Mn complexes with the formation of
1-naphthol (as a primary product, NOH) and 1,4-naphthoquinone
(Q), respectively. Here, we describe the results of the compara-
tive oxidation of naphthalene and its deuterated analogue (C10D8)
in 1 + AcOOH catalytic system.
Previously, we found that the kinetics of 1-naphthol forma-
tion was almost the same in the naphthalene oxidation in the
catalytic systems AcOOH + Mn3+-porphinoids (PMnX) [P = meso-
tetra(2,6-dichloro-6-R-phenyl)porphyrins (RTDCPPMnCl, R =
= MeO, H, Br, Cl, NO2),7 tetraazaporphines (RTAPMnCl, R = H,
PhSO2, 1),8 phthalocyanine (ONPcMnCl)5]. The epoxidation of
cis-olefins in the same catalytic systems was found to be highly
stereospecific,7,8 which is commonly accepted as a proof of the
formation of highly-reactive Mn5+-oxene {[PMn5+(O)(L)](X)}.
Nevertheless, comparative and competitive oxidation of naph-
thalene and olefins7,8 revealed that naphthalene hydroxylation is
fulfilled by another catalytic intermediate, presumably by the
600
500
400
300
200
100
0
0.00
0.01
0.02
0.03
[Naphthalene]0/mol dm–3
in
NOH
Figure 1 Partial rate (W
/ [1]) of 1-naphthol formation as a function
of naphthalene concentration. [1] = (0.5–2)×10–8 mol dm–3, [AcOOH] =
= 0.05 mol dm–3. MeCN + AcOH (0.5 M).
kN[Naphthalene]0
WNOH
~
~
at kd > kN[Naphthalene]0
(1)
(2)
kd + kN[Naphthalene]0
k
WNOH
N [Naphthalene]0
kd
These data allow us to reject the radical, oxygen-rebound and
concerted non-synchronous mechanisms (the last is characterised
by a high KIE value of the first intermediate transformation to
the final product10). The proposed11 intermediate formation of
1,2-arene oxides last time is considered rather questioned both
for mimicking3 and enzyme-depending systems12 and does not
occur under the reported conditions because of the absence of
isomeric 2-naphthol in the RTAPMnCl-catalysed reactions.† This
4+
+
4+
·
Mn -oxene of a porphinoid π-cation radical {[ PMn (O)(L)](X),
2; L = AcOH}. The intimate mechanism of oxygen atom transfer
from oxene 2 to the naphthalene molecule, though, was not
established. As reported, hydrocarbon hydroxylation in both
actual enzymes and model systems can occur via either H-atom
abstraction9 or the insertion of an oxygen atom of metallo-oxene
into the C–H bond with the intermediate formation of a penta-
coordinated carbon atom.10 To discriminate some of the pro-
posed possibilities, we compared the rates of 1-naphthol forma-
tion in the course of C10H8 and C10D8 oxidation by AcOOH + 1.
Actually, if an oxygenated product is formed with H-atom
abstraction from a substrate molecule, its formation should be
4
1
3
2
2
characterised by a significant kinetic isotope effect (KIE).
in
NOH
The initial rate of 1-naphthol formation (W
) exhibits the
1
Michaelis–Menten kinetics [Figure 1; equation (1)], indicating
the participation of a hydroxylating moiety in both 1-naphthol
formation and catalyst destruction [rate constants kN and kd,
respectively; unimolecular catalyst degradation is considered for
simplicity].
0
50
100
2500
5000
If 1-naphthol formation had been fulfilled with H-atom ab-
t/s
straction from a molecule of naphthalene, then at its low con-
Figure 2 Kinetic curves of 1-naphthol formation in the reaction of C10H8
(open squares and circles) and C10D8 (solid squares and circles) oxidation
by AcOOH catalysed by 1. (1) [1] = 1×10–8 mol dm–3, [C10H8] = [C10D8] =
= 0.025 mol dm–3, [AcOOH] = 0.05 mol dm–3, [AcOH] = 0.5 mol dm–3; (2)
[1] = 2×10–8 mol dm–3, [C10H8] = [C10D8] = 0.004 mol dm–3, [AcOOH] =
= 0.025 mol dm–3, [AcOH] = 0.25 mol dm–3.
in
centrations [equation (2)] the W
value should have been
NOH
much lower for C10D8 than for C10H8 (kNdeut << kNnondeut). This
contradicts the experiment: as shown in Figure 2, the kinetic
curves of 1-naphthol formation are identical for both substrates.
– 116 –

, 2001, 11(3), 116–118
last also contradicts with the mechanism of one-electron naph-
thalene oxidation followed by proton abstraction. We suggest
that the discussed reaction occurs by a ‘concerted’ mechanism
of oxygen insertion into the Carom–H bond or via the intermediate
formation of the σ-adduct PMn–O–Carom, which has been pro-
posed3 for Mn(Fe) porphyrin-catalysed oxidation of 2-methyl-
naphthalene by KHSO5 (Figure 3).
naphthoxy radical, oxidation to 3, its acetylation and hydroxyla-
tion. In terms of this hypothesis, the oxidation of C10D8 instead
of C10H8 under the same conditions should yield a lower number
of oligomers. Really, MALDI analysis‡ of the spent reaction solu-
tion of C10D8 oxidation revealed only dimer 4 and its 4,4'-di-
hydroxy derivative (m/z 191.9 and 192.9, z = 2; Figure 4).
O
OAc
OH
MnIII
OH
OH
+ H
H
O δ
IV
O
IV
Mn
Mn
+
L
L
L
O
(a) Concerted mechanism
4-d9
O
O
O
H
O
H
O
+ O
δ
+
MnIV
MnIV
O
H
L
L
O
O
O
5
5a
Figure 4 The proposed structures of the oligomeric products of naphthalene
oxidation.
OH
OH
MnIII
When 0.1 M naphthalene or 1-naphthol was oxidised by drop-
wise addition of AcOOH to a mixture of the catalyst and the
substrate, the single product was a violet precipitate unstable both
in solution and in the solid state. Based on the data of elemental
analyses (13–16% oxygen content per naphthalene unit), MALDI§
spectra (m/z 426.3, 286), 1H NMR (only broadened peaks at 7.0–
8.0 ppm) and IR spectra (peaks corresponding to the C–OH and
C=O bands), we suppose this compound to be a mixture of
1,1'-dinaphthoquinone-4,4' complexes with the naphthyloxy radi-
cal and its oxygenated form (5, C30H19O3, M = 427; 5a; Figure 4).
Our conclusion on 1-naphthol radical oxidation agrees with
the results on 2,3,5-trimethylphenol (TMP) oxidation under the
same reaction conditions ([AcOOH]:[TMP]:[ONPcMnCl] = 6400:
4000:1). In this case, phenoxy radical coupling is sterically hin-
dered, and exhaustive TMP oxidation leads to the formation of
2,3,5-trimethyl-1,4-benzoquinone in a yield higher than 95%
(based on the oxidant used).
MnIII
L
L
σ
(b) Mechanism with -adduct formation
Figure 3 Possible mechanisms of naphthalene hydroxylation by peracetic
acid in an acetonitrile–acetic acid solution catalysed by MnIII porphinoid
complexes [PMnIII(L)](X), P = substituted porphyrins, porphyrazines, phthalo-
cyanines; L = AcOH; X = Cl–, AcO– (not shown).
Under the specified conditions, firstly formed 1-naphthol under-
goes further oxidation to oligomers;5 the nature of these products
depends on the substrate concentration.
The oxidation of naphthalene or 1-naphthol at low concen-
trations (< 0.01 mol dm–3) leads to a brownish residue, which
was isolated as a main product in the reactions catalysed by
RTDCPPMnCl and Mn3+ tetra-tert-butyltetraazaporphine and
as a by-product in the reactions catalysed by ONPcMnCl and 1.
Capillary electrophoresis, IR spectroscopy and HPLC (4–5 non-
resolved peaks with VR higher that that of naphthalene; Separon
As we found previously,4–6 in the oxidation of naphthalene
and its methyl derivatives in APMnX + AcOOH catalytic sys-
tems, the quinone yield determined at the end of the reaction
(hin) increases significantly (htherm) after heating (40–70 °C) or
continuous storage of neutralised reaction solutions at 20 °C.
HPLC analysis before heating revealed an unidentified peak of
a polar compound, the intensity of which decreases on heating
with a simultaneously increasing peak of para-quinone, thus
indicating the formation of quinone precursor 6.¶ Here, we
report the study of 1,4-naphthoquinone-d6 (Qd) formation in the
reaction C10D8 + AcOOH + 1.
C
18 reverse phase, 10–100% aqueous acetonitrile) and 1H NMR
(8–9 peaks at 1.8–2.4 ppm; ~20 peaks at 7.5–8.0 ppm; Bruker
80 MHz or 300 MHz) indicate that this residue is a mixture
of hydroxylated and acetylated derivatives of naphthoxy radical
coupling products, whose composition depends on AcOOH con-
centration. At a fourfold excess of the oxidant ([AcOOH]:
[Nph]:[ONPcMnCl] = 640:160:1, [Nph]0 = 0.004 M), the isolated
precipitate exhibited m/z 286, 374, 426, 442, 456, 472 and 486
(FAB MS data), which correspond to hydroxy, acetoxy and naph-
thoxy derivatives of 1,1'-dinaphthoquinone-4,4' 3. At [AcOOH]:
[Nph] = 1.5, naphthoxy-3 is not formed: mass ions (m/z 333,
347, 375, 389, 403, 418 and 432) correspond to acetylated and
hydroxylated derivatives of both 3 and 1,1'-dihydro-3. The deter-
mination of the exact composition of such complex mixtures
needs additional research; the reported data, though, fit well with
the hypothesis on the radical mechanism of 1-naphthol oxidation
with H-atom abstraction followed by the coupling of the formed
As in the case of C10H8, the formation of 1,4-naphthoquin-
one-d6 (Qd)†† is preceded by the formation of a 6-type inter-
‡
‘Mass spectrum with matrix assisted laser desorption ionization’ (MALDI);
under the conditions of MALDI analyses (2,5-dihydroxybenzoic acid or
sinapinic acid as a matrix), the authentic samples of 1,4-naphthoquinone
and 2-methyl-1,4-naphthoquinone were determined as the 1,4-dihydroxy
derivatives. We suppose also partial reduction of 4 at MALDI spectrum
registration and attribute a peak m/z 192.9 (z = 2) to its 4,4'-dihydroxy
derivative.
§
2,4,6-Trihydroxyacetophenone was used as a matrix.
Presumably, HPLC analysis detects not intermediate 6, but a product
†
¶
The minor formation of 2-naphthol (10% to 1-naphthol) in RTDCPPMnCl7
and ONPcMnCl5 dependent reactions might be explained by a lower
electrophilicity of the corresponding Mn-oxenes as compared with their
tetraazaporphine analogues.
of its transformation under analytical conditions.
†† Thermal transformation of 6d to 1,4-naphthoquinone-d6 was proved by
HPLC and MALDI.
– 117 –

, 2001, 11(3), 116–118
2
1
O
O
OH
OH
2
Cat + O2
(10)
– H2O
50 °C
– 1/2 O2
(9)
20 °C
1
0
O
O
O
O
APMn5+(O)(L)
(8)
O
6
(7)
0.0
0.5
1.0
1.5
2.0
kd'
Catalyst destruction
APMn(O2)(L)
+ Cat
t/h
+ AcOOH
(6)
Figure 5 Time dependence of 1,4-naphthoquinone formation on heating
(50 °C) the neutralised (with solid Na2CO3) reaction solution after exhaus-
tive oxidation of C10H8 (open circles) and C10D8 (solid circles). [C10H8] =
= [C10D8] = 0.004 mol dm–3, [1] = 5×10–6 mol dm–3, [AcOOH] = 0.002 mol dm–3,
[AcOH] = 0.02 mol dm–3.
+ Cat
K1
APMn3+(L) + AcOOH
+ APMn4+(O)(L)
APMn3+(AcOOH)(L)
(1)
k2 (2)
APMn5+(O)(L)
mediate (6d). The rates of C10D8 and C10H8 disappearance were
found to be equal; taking into account the independence of the
‘oxenoid’ pathway on deutero substitution, this evidences the
absence of a significant isotope effect at the stage of 6d forma-
tion. It seems that all H atoms of the substrate are kept in the
molecule of a quinone precursor. On the contrary, the transfor-
mation of 6d to 1,4-naphthoquinone-d6 is significantly hindered
as compared with the non-deuterated analogue: the total time of
heating the neutralised reaction mixture to provide a maximum
quinone yield (50%) is eight times longer for C10D8 than that
for C10H8 (Figure 5).
kd
(3)
(11)
Catalyst destruction
OH
(4)
Cat + AcOOH
O
Moreover, in the case of C10D8 at the beginning of gentle
heating (40–50 °C; HPLC, TLC),‡‡ 1,4-dihydroxynaphthalene,
in addition to a quinone, was detected, thus elucidating two steps
of 6d transformation to the quinone. Presumably, 1,4-dihydroxy-
naphthalene-d8 is the first product of 6d decomposition, and its
further oxidation to 1,4-naphthoquinone-d6 is not accompanied
by an isotope effect due to quick OD–OH exchange. We suppose
that the high isotope effect of para-quinone formation from 6
reflects the breakage of the Carom–H bond in the latter at the
stage of 1,4-dihydroxynaphthalene formation.
brownish and violet
oligomers
(5)
H
L = AcOH, Cat = APMn3+(L), counter ion is not shown
Scheme 1
Based on the data on the comparative and competitive oxida-
tion of aromatic and aliphatic hydrocarbons,4–6 we proposed the
structure of 1,4-peroxo-2,3-epoxy-1,2,3,4-tetrahydronaphthalene
for intermediate 6. The data reported here agree with this attribu-
tion and with the mechanism of 6 formation (Scheme 1, stage 8).
Intermediate 6d is rather stable only in MeCN solutions; we
failed to isolate it in a solid state. Under conditions of MALDI
spectrum measurements, 6d was also decomposed: the spent un-
heated reaction solution shows a peak at m/z 158.9 with z = 2
corresponding to a complex of 1,4-dihydroxynaphthalene-d6 with
naphthol-d7 [(C10D6H2O2)·(C10D7HO), MW 317.4].§§ In terms
of our hypothesis on the structure of 6, these compounds could
be derived from two molecules of 6 by a laser pulse with the
withdrawal of an oxygen atom or an O–O fragment, respectively.
In summary, we specified the stages of formation of 1,4-naph-
thoquinone, 1-naphthol and its oxidative products (Scheme 1,
stages 7–10 and 3–5, respectively) in the proposed mechanism
of aromatics oxidation by peracetic acid catalysed by Mn3+ aza-
porphines.
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This work was supported by the Russian Foundation for Basic
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‡‡ The oxidation of 1,4-dihydroxynaphthalene to 1,4-naphthoquinone by
oxygen in the presence of Mn complexes was demonstrated in independent
experiments. In the case of C10D8, the heating of the neutralised reaction
mixture at 75 °C leads to 1,4-dihydroxynaphthalene without a significant
impurity of para-quinone, supposedly because of the reduced oxygen
content as compared with heating at 50 °C.
§§ 2,5-Dihydroxybenzoic acid was used as a matrix.
Received: 24th January 2001; Com. 01/1755
– 118 –