Studies on the mechanism of decomposition of 1-methyl-1-(1-naphthyl)ethyl hydroperoxides to 2-(1-naphthyloxy)propenes

Article abstract of DOI:10.1007/s00706-009-0206-7

Thermal decomposition of 1-methyl-1-(4-methyl-1-naphthyl)ethyl hydroperoxide under gas chromatography-mass spectroscopy (GC-MS) conditions gives 2-((4-methyl-1-naphthyl)oxy)propene as the main product (50.5%), without any detectable traces of the isomeric

Full text of DOI:10.1007/s00706-009-0206-7

Monatsh Chem (2009) 140:1459–1463
DOI 10.1007/s00706-009-0206-7
ORIGINAL PAPER
Studies on the mechanism of decomposition of 1-methyl-1-
(1-naphthyl)ethyl hydroperoxides to 2-(1-naphthyloxy)propenes
•
Beata Orlinska Jan Zawadiak
•
´
•
•
Roman Mazurkiewicz Zbigniew Stec
Henryk Koroniak
Received: 22 April 2009 / Accepted: 12 October 2009 / Published online: 11 November 2009
Ó Springer-Verlag 2009
Abstract Thermal decomposition of 1-methyl-1-(4-
methyl-1-naphthyl)ethyl hydroperoxide under gas chroma-
tography-mass spectroscopy (GC–MS) conditions gives
2-((4-methyl-1-naphthyl)oxy)propene as the main product
(50.5%), without any detectable traces of the isomeric
2-((5-methyl-1-naphthyl)oxy)propene. This finding excludes
the rearrangement pathway of 1-methyl-1-(1-naphthyl)ethyl
hydroperoxides to the corresponding 2-(1-naphthyloxy)
propenes, which involves formation of a naphthofuran
derivative as an intermediate and transfer of the isoprope-
nyloxy group to the 8 position. This result, as well as our
previous density functional theory (DFT) calculations, points
to the rearrangement pathway involving an oxirane-type
intermediate as the most plausible pathway to 2-(1-naph-
thyloxy)propenes. This rearrangement is responsible for the
unusual inhibition effects of 1-methyl-1-(1-naphthyl)ethyl
hydroperoxide on the liquid-phase oxidation of isopropyl-
arenes with oxygen.
Introduction
Free-radical chain oxidation of isopropylarenes with oxy-
gen is well known to be affected by the resulting
hydroperoxides, which are primary oxidation products.
Usually, as a result of thermal decomposition of hydro-
peroxides into free radicals, the process becomes
autocatalytic in nature [1]. Recently, we have demonstrated
that 1-methyl-1-(1-naphthyl)ethyl hydroperoxide (1)
inhibits free-radical oxidation of isopropylarenes, e.g.
oxidation of 1-isopropylnaphthalene, 2-isopropylnaphtha-
lene or cumene, whereas 1-methyl-1-(2-naphthyl)ethyl
hydroperoxide (2) actually acts as an initiator of these
reactions [2]. The inhibition activity of hydroperoxide 1
creates a serious technical problem, since 2-isopropyl-
naphthalene, used in 2-naphthol production by means of a
method analogous to phenol production, is contaminated
by a small amount (5–10%) of 1-isopropylnaphthalene,
which is difficult to remove. The 1-isopropylnaphthalene
present in the raw material reduces the oxidation rate
and results in lower yield and poorer selectivity in the
production of hydroperoxide 2 [3–10].
Keywords Reaction mechanism Á Oxidations Á
Peroxides Á Thermal decomposition
Our comparative studies of the thermal decomposition of
hydroperoxides 1 and 2 under GC–MS conditions revealed a
considerable dissimilarity in the decomposition route of these
two isomeric hydroperoxides [11]. The hydroperoxide 2
decomposition product was typical for decomposition of this
kind of compound and contained 2-(2-naphthyl)-2-propanol
(39%), 2-(2-naphthyl)propene (21%) and 2-acetylnaphtha-
lene (40%), whereas the hydroperoxide 1 decomposition
products contained 2-(1-naphthyl)-2-propanol (23.5%), 2-(1-
naphthyl)propene (9.2%) and 1-acetylnaphthalene (19.7%),
and, unexpectedly, 2-(1-naphthyloxy)propene (45.6%) as the
main product [11]. Similar results were obtained when
we compared the thermal decomposition under GC–MS
´
B. Orlinska (&) Á J. Zawadiak Á Z. Stec
Department of Chemical Organic Technology
and Petrochemistry, Silesian University of Technology,
Gliwice, Poland
e-mail: beata.orlinska@polsl.pl
R. Mazurkiewicz
Department of Organic Chemistry, Biochemistry
and Biotechnology, Silesian University of Technology,
Gliwice, Poland
H. Koroniak
Faculty of Chemistry, Adam Mickiewicz University,
Poznan, Poland
123

´
B. Orlinska et al.
1460
conditions of 1-(2-anthryl)-1-methylethyl hydroperoxide and
1-(1-anthryl)-1-methylethyl hydroperoxide. In this case, the
main product of decomposition of the latter compound was
2-(1-anthryloxy)propene (81.2%) [11]. To the best of our
knowledge, 2-aryloxypropenes have thus far not been
described as thermal decomposition products of 1-aryl-1-
methylethyl hydroperoxides.
Results and discussion
As should be expected, the results of the thermal
decomposition of 1-methyl-1-(4-methyl-1-naphthyl)ethyl
hydroperoxide 3 under GC–MS conditions were similar to
those obtained for hydroperoxide 1. The main decompo-
sition product of hydroperoxide 3 was the corresponding
2-(naphthyloxy)propene (50.5%) with molecular mass
of 198, which could have the structure of 2-((4-methyl-1-
naphthyl)oxy)propene 4 or the isomeric structure of
2-((5-methyl-1-naphthyl)oxy)propene (Table 1).
Assuming that the inhibition effect of hydroperoxide 1
is connected with its atypical thermal decomposition to
2-(1-naphthyloxy)propene, we considered three plausible
pathways of the transformation of 1 to 2-(1-naphthyl-
oxy)propene (Scheme 1, X = H) [2, 11, 12].
In order to determine the structure of the 2-(naphthyl-
oxy)propene, we carried out the thermal decomposition of
hydroperoxide 3 on a preparative scale in cumene at
120–140 °C (Table 1). As we expected because of the
instability of 2-aryloxypropenes [11], the decomposition
products contained much less 2-(naphthyloxy)propene
(6.9%);nevertheless, we were able to isolate a pure sample of
2-(naphthyloxy)propene using preparative thin-layer chro-
matography (TLC). Its MS spectrum was identical to the MS
spectrum of 2-(naphthyloxy)propene obtained by decom-
Pathways A and B start from the abstraction of a
hydrogen from the peri position of the neighbouring ring.
Pathway C consists of the intramolecular attack of the
oxygen radical on the carbon atom at position 1 with for-
mation of an epoxy-like product. In all of the considered
reaction paths, intermolecular hydrogen abstraction by
1-methyl-1-(1-naphthyl)ethoxy radical or other radicals is
necessary for the formation of 2-(1-naphthyloxy)propene
(Scheme 1). We assume that this very reaction step is
responsible for the inhibition effect of hydroperoxide 1 in
the oxidation of isopropylarenes, as it terminates the free-
radical chain [11].
1
position of hydroperoxide 3 under GC–MS conditions. H
and 13C nuclear magnetic resonance (NMR) spectra of the
2-(naphthyloxy)propene revealed that we obtained 2-((4-
methyl-1-naphthyl)oxy)propene 4, without any detectable
traces of the isomeric 2-((5-methyl-1-naphthyl)oxy)pro-
pene. Crucial for this conclusion was the detailed analysis of
the 1H NMR spectrum of naphthyloxypropene 4 in the range
of the naphthyl group (8.1–7.0 ppm). Apart from two mul-
tiplets at 8.04–7.97 ppm (2H) and 7.57–7.48 (2H), which
were assigned to protons at positions 5, 6, 7 and 8, there were
two doublets at 7.27 ppm (1H, J = 7.2 Hz) and 7.05 ppm
(1H, J = 7.5 Hz), which clearly indicated protons at posi-
tions 2 and 3 in an AX spin system. Such a spin system of two
coupled protons, isolated from coupling with other protons
The aim of our investigations described in this paper
was to establish if the isopropenyloxy group in 2-(naph-
thyloxy)propenes remains at position 1, as would be
expected for pathways B or C, or whether it migrates to
position 8 of the naphthalene ring, according to pathway
A (Scheme 1). This differentiation would allow us to
exclude one or two of the three considered pathways of
formation of 2-(1-naphthyloxy)propene. We tried to
achieve this goal by marking the 4 position of 1-methyl-
1-(1-naphthyl)ethyl hydroperoxide with a methyl group
(Scheme 1, X = Me).
Scheme 1
HOO
.
O
O
O
.
X = H for 1
X = Me for
R = 1-(1-naphthyl)-1-methylethyl
ROH
RO
ROH
3
.
RO
.
RO
ROH
X
X
X
X
∆
A
B
.
O
.
.
O
=
.
HO
OH
H
OH
H
H
.
O
.
.
RO
ROH
.
X
X
X
X
X
X
C
.
.
=
O
O
X
O
O
.
.
RO
ROH
X
X
X
123

Decomposition mechanism of 1-methyl-1-(1-naphthyl)ethyl hydroperoxides
1461
Table 1 Products of thermal decomposition of hydroperoxide 3 under GC–MS conditions and in cumene
OOH
3
∆
OH
O
OH
O
4
5
6
7
8
Yield of decomposition products (%)
Aryloxypropene 4
Alcohol 5
Ketone 6
Alkene 7
Phenol 8
GC–MSa
Cumeneb
a
50.5
6.9
15.4
41.1
18.3
6.4
13.5
35.5
0.0
6.4
Solution of 3 was introduced directly into the GC–MS apparatus
b
Solution of 3 in cumene was decomposed and the obtained product was determined by GC–MS
of the naphthalene ring, is possible only in the case of
naphthyloxypropene 4.
by decomposition of hydroperoxide 1 [12]. The higher
steric hindrance of the alkoxy radical derived from
hydroperoxide 1 results in a higher energy for this radical
and lowers the rearrangement barrier for this radical
(DG = 40.2 kJ/mol) if compared with the energy barrier
for the radical derived from hydroperoxide 2 (56.1 kJ/mol)
[12]. The results and conclusions of the DFT calcula-
tions are consistent with the results of experiments
described in this paper and point to pathway C as the
most plausible rearrangement of hydroperoxide 1 to 2-(1-
naphthyloxy)propene.
Identification of naphthyloxypropene 4 as the main
product of thermal decomposition of hydroperoxide 3
under GC–MS conditions means that decomposition path-
way A (Scheme 1), involving formation of a naphthofuran
derivative as an intermediate, can no longer be considered.
To determine the reasons for the differences in the
chemical behaviour of hydroperoxides 1 and 2, we carried
out calculations of the possible rearrangement pathways of
alkoxy radicals derived from 1 and 2 using first a simple
semiempirical AM-1 method with MOPAC-7 (RHF for
open shell system) [11, 13], and later, more advanced DFT
computations with GAUSSIAN-98 using the unrestricted
B3LYP hybrid functional with the 6-31G* base [12]. The
AM-1 method pointed to paths A or B as more favourable
ways of rearrangement of the alkoxy radical derived from
hydroperoxide 1, which eventually proved to be misleading
[12]. On the other hand, DFT-level calculations showed
that the rearrangement via the oxirane-type triangle inter-
mediate (path C) was more favourable if compared with
the abstraction of a hydrogen atom from the peri position
and explained why 2-(naphthyloxy)propene is formed only
Experimental
A GC–MS apparatus equipped with a Varian 3300 gas
chromatograph (DB5 capillary column, 30 m, u =
0.25 lm, helium 30 cm3/min) conjugated with a SSQ 700
Mat Finnigan mass spectrometer with EI ionisation (70 eV)
was used. High-resolution mass spectra (HRMS) were
recorded on an AMD 604 spectrometer with EI ionisation.
1H and 13C NMR spectra were recorded in CDCl3 on a
Varian Unity Inova-300 spectrometer using TMS as an
123

´
B. Orlinska et al.
1462
After evaporation of the solvent, the pure hydroperoxide
(2.7 g, 12.5 mmol, oil) was isolated by column chroma-
tography using benzene/acetone 20:1 (v/v) as the eluent
internal standard. Elemental analyses were performed
using a Perkin Elmer 2400 series II instrument, and the
results agreed with calculated values. Melting points of
synthesised compounds were determined in capillary tubes
on an SMP 3 (Stuart Scientific) apparatus. Kieselgel 60
(Merck 0.063–0.200 mm) was used for column chroma-
tography. TLC analyses were performed using Merck’s
plastic plates coated with silica gel 60 F254. Preparative
TLC was performed using Merck’s glass plates coated with
silica gel 60 F254 (20 cm 9 20 cm 9 2 mm).
1
(77% yield); H NMR (300 MHz, CDCl3): d = 8.71–8.68
(m, 1H, Ar), 7.91–7.87 (m, 1H, Ar), 7.37–7.34 (m, 2H, Ar,
–OOH), 7.24 (d, J = 7.5 Hz, 1H, Ar), 7.09 (d, J = 7.4 Hz,
1H, Ar), 2.52 (s, 3H, –CH3), 1.67 (s, 6H, C(CH3)2) ppm;
13C NMR (75.5 MHz, CDCl3): d = 137.1, 134.8, 133.6,
130.9, 126.1, 125.8, 125.7, 125.2, 125.0, 124.9 (Ar), 86.0
(C(CH3)2), 26.9 (C(CH3)2), 19.6 (–CH3) ppm. Elemental
analysis was performed after additional purification by
column chromatography (benzene/acetone 20:1 v/v).
2-(4-Methyl-1-naphthyl)-2-propanol
To a stirred suspension of 1.76 g magnesium turnings
(72.6 mmol) in 60 cm3 dry THF was added a solution of
15 g 1-bromo-4-methylnaphthalene (67.9 mmol) in 21 cm3
dry THF dropwise. An iodine crystal and methyl iodide
were added to start the reaction. The reaction mixture was
boiled under nitrogen for 3 h. After cooling to 0 °C, a
solution of 5 cm3 dry acetone (97.9 mmol) in 24 cm3 THF
was added. The stirring was continued for 1.5 h at 0–5 °C,
and the reaction mixture was poured into 33 g ice with
57 cm3 sulphuric acid (5%). The precipitated crystalline
substance was filtered off, the organic and water layers
were separated, and both were extracted with toluene. The
combined toluene extracts were washed with an aqueous
solution of Na2CO3 (10%) and then with water, and dried
over MgSO4, and the solvent was evaporated. A quantity of
10.4 g crude product was obtained and then crystallised
from 50 cm3 hexane to obtain 5.6 g pure product
(28 mmol, 41% yield). m.p.: 83–84 °C (85–86 °C [14],
Thermal decomposition of 3 in GC–MS
A solution of hydroperoxide 3 in CHCl3 at a concentration
of 0.001 mg/cm3 was introduced into the GC injector at
60 °C, and the injector temperature was gradually
increased at a rate of 25 °C/min up to 270 °C. Decompo-
sition products were separated on a DB5 capillary column
(30 m, u = 0.25 lm, helium 30 cm3/min).
Thermal decomposition of 3 in cumene
The hydroperoxide 3 was decomposed in a closed glass test
tube. Each test tube was filled with about 1.5 cm3 3 (1.7 g,
7.8 mmol) dissolved in 16 cm3 cumene (0.5 mol/dm3),
flushed with argon, closed, and immersed in an oil bath at
120 °C for 3 h and then at 140 °C for 4 h. The hydroper-
oxide was completely decomposed. Composition of the
obtained products was determined by GC–MS analysis.
The naphthyloxypropene 4 was isolated from the obtained
product.
1
90 °C [15]); H NMR (300 MHz, CDCl3): d = 8.87–8.85
(m, 1H, Ar), 8.05–8.01 (m, 1H, Ar), 7.53–7.44 (m, 3H, Ar),
7.24–7.22 (m, 1H, Ar), 2.67 (s, 3H, –CH3), 1.99 (s, 1H,
–OH), 1.84 (s, 6H, C(CH3)2) ppm; 13C NMR (75.5 MHz,
CDCl3): d = 141.6, 134.4, 133.8, 131.0, 127.8, 125.6,
125.1, 124.9, 122.4 (Ar), 74.0 (C(CH3)2), 31.7 (C(CH3)2),
19.6 (–CH3) ppm.
2-((4-Methyl-1-naphthyl)oxy)propene (4, C14H14O)
The product obtained by decomposition of hydroperoxide 3
in cumene was diluted with 5 cm3 diethyl ether and
extracted with an aqueous solution of NaOH (15 cm3, 8%).
The organic layer was washed with water (3 9 10 cm3)
and dried with MgSO4. The solvents (diethyl ether and
cumene) were evaporated, and 4 was isolated by pre-
parative TLC using first benzene and then hexane as
eluents. A quantity of 0.07 g pure 4 was isolated. Column
chromatography was also used (hexane/acetone 9:1 v/v),
but subsequent reactions occurred (e.g. hydrolysis to
1-naphthol), and 4 was not isolated. HRMS (EI): Found:
198.1048; C14H14O requires: 198.1045; 1H NMR
(300 MHz, CDCl3): d = 8.04–7.97 (m, 2H, Ar), 7.57–
7.48 (m, 2H, Ar), 7.27 (d, J = 7.2 Hz, 1H, Ar), 7.05
(d, J = 7.5 Hz, 1H, Ar), 4.10 (s, 1H, C(CH3)=CH2), 3.81
(s, 1H, C(CH3)=CH2), 2.67 (s, 3H, Ar–CH3), 2.13 (s, 3H,
C(CH3)=CH2) ppm; 13C NMR (75.5 MHz, CDCl3):
1-Methyl-1-(4-methyl-1-naphthyl)ethyl hydroperoxide
(3, C14H16O2)
To an intensively stirred mixture of 5.0 g 2-(4-methyl-1-
naphthyl)-2-propanol (25 mmol) in 56 cm3 toluene was
added a solution of 0.034 cm3 H2SO4 (96%, 0.6 mmol) in
10.9 cm3 H2O2 (65%) at 60 °C. The reaction progress was
monitored by TLC using a benzene/acetone 9:1 (v/v)
mixture as the eluent and a saturated solution of NaI in
acetic acid for developing hydroperoxide spots. After 3 h,
the reaction mixture was cooled to room temperature, and
the organic layer was separated and washed with water
(3 9 15 cm3), an aqueous solution of Na2CO3 (4%,
2 9 12 cm3) and a saturated solution of (NH4)2SO4
(10 cm3), and then dried with MgSO4. The obtained
product (55.6 g) contained 6.3% hydroperoxide 3 (3.5 g,
16.2 mmol, 65% yield) based on iodometric analysis [16].
123

Decomposition mechanism of 1-methyl-1-(1-naphthyl)ethyl hydroperoxides
1463
7. Farberov MI, Bondarenko AW, Shustovskaya GN (1969) Dokl
Akad Nauk SSSR Khimia 187:831
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d = 160.1 (C(CH3)=CH2), 149.6, 133.7, 130.5, 127.2,
126.2, 126.1, 125.5, 124.4, 122.6, 116.2 (Ar), 88.7
(C(CH3)=CH2), 20.0 (Ar–CH3), 19.1 (C(CH3)=CH2)
ppm; MS (EI): m/z = 198 (M?, 63), 158 (100), 157 (42),
155 (37), 128 (52), 127 (23), 115 (21).
´
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´
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Grymel M, Fiedorow P, Koroniak H (2006) Org Process Res Dev
10:289
12. Fiedorow P, Pasikowska M, Koroniak H, Mazurkiewicz R,
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