Synthesis of unsymmetrical hydroxybenzylphenols from 2-isobornyl-4-methylphenol

Article abstract of DOI:10.1134/S1070428015050061

2-Hydroxymethyl-6-isobornyl-4-methylphenol was synthesized from 2-isobornyl-4-methylphenol. Reactions of this hydroxymethyl derivative with 2,4- and 2,4-di-tert-butylphenols gave new unsymmetrical hydroxybenzylphenols.

Full text of DOI:10.1134/S1070428015050061

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2015, Vol. 51, No. 5, pp. 623–628. © Pleiades Publishing, Ltd., 2015.
Original Russian Text © E.V. Buravlev, I.Yu. Chukicheva, М.А. Elfimova, K.Yu. Suponitskii, А.V. Kutchin, 2015, published in Zhurnal Organicheskoi
Khimii, 2015, Vol. 51, No. 5, pp. 645–649.
Synthesis of Unsymmetrical Hydroxybenzylphenols
from 2-Isobornyl-4-methylphenol
E. V. Buravleva, I. Yu. Chukichevaa, М. А. Elfimovab,
K. Yu. Suponitskiic, and А. V. Kutchina
a Institute of Chemistry, Komi Research Center, Ural Branch, Russian Academy of Sciences,
ul. Pervomaiskaya 48, Syktyvkar, 167982 Russia
e-mail: buravlev-ev@chemi.komisc.ru
b Pitirim Sorokin Syktyvkar State University, Syktyvkar, Russia
c Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Moscow, Russia
Received February 17, 2015
Abstract―2-Hydroxymethyl-6-isobornyl-4-methylphenol was synthesized from 2-isobornyl-4-methylphenol.
Reactions of this hydroxymethyl derivative with 2,4- and 2,4-di-tert-butylphenols gave new unsymmetrical
hydroxybenzylphenols.
DOI: 10.1134/S1070428015050061
Previously we reported on the synthesis of un-
symmetrical hydroxybenzylphenols basing on 4-(hyd-
roxymethyl)- and 4-(bromomethyl)-2,6-diisobornyl-
phenol under catalysis with formic acid. As a result
hydroxybenzylphenols with various positions of alkyl
and phenol ОН groups were obtained [1]. These
compounds along with symmetrical 2,2'- and 4,4'-
methylenebisphenols with alkyl substituents may be
interesting for the investigation of their antioxidant
properties.
In the present study we describe the synthesis
of new unsymmetrical hydroxybenzylphenols pro-
ceeding from 2-isobornyl-4-methylphenol 1. By the
method [2] from compound 1 and paraformaldehy-
de in the presence of H3BO3 2-(hydroxymethyl)-6-
isobornyl-4-methylphenol
2
was synthesized in
92% yield. Its interaction with 2,4- and 2,6-di-tert-
butylphenols at reflux in chloroform in the presence of
formic acid leads to the formation of hydroxybenzyl-
phenols 3 and 4 (Scheme 1) (numeration of atoms is
Scheme 1.
OH
OH
OH
OH
OH
OH
18
18
18
20
20
19
21
22
19
OH
21
22
24
HCOOH
HCOOH
24
H
H
H
OH
23
23
3
2
4
OH
HCHO H3BO3
OH
8
9
7
10
12
11
Br
13
14
6
2
1
.
HCOOH, AcONa 3H2O
4
H
3
5
16
15
17
1
623

BURAVLEV et al.
624
Scheme 2.
OH
HO
OH
H+
2
HCHO
_1
H+
5
resin
introduced for convenient interpretation of NMR
spectra).
Yield of hydroxybenzylphenol 4 was 59% at 70%
conversion of compound 2. In mother liquor after
precipitation of the main amount of phenol 4 4,4'-
methylenebis(2,6-di-tert-butylphenol) 5 was found,
which was identified by 1H and 13C NMR spectra.
Compound 3 is isolated in 53% yield by precipita-
tion from pentane. Compound 4 was purified by
column chromatography with further precipitation.
Its generation may be due to a side reaction of
formaldehyde elimination followed by condensation of
the latter with 2,6-di-tert-butylphenol (Scheme 2).
However in the reaction mixture cresol 1 has not been
found although it is the second product of the
formaldehyde elimination from alcohol 2. Its absence
may be caused by resinification.
(a)
O2
O1
С10
С17
С6
С7
С13
С14
С1
С12
С11
С9
At boiling the 2,6-di-tert-butylphenol in a system
HCOOH–CHCl3 in the absence of alcohol 2 the
generation of compound 5 was not observed. By the
С2
С5
С8
С16
1
gas chromatography and H NMR spectroscopy in the
С3
С15
С4
reaction mixture after processing only initial phenol
and its dealkylation product, 2-tert-butyl-phenol, was
detected. This may be regarded as a proof of the
participation of alcohol 2 in the generation of 4,4'-
methylenebisphenol 5.
С18
(b)
Compound 4 was obtained by authentic synthesis
C17
C32
from cresol
1
and synthetically available 4-
C15
C16
(bromomethyl)-2,6-di-tert-butylphenol (Scheme 1) in
78% yield at a full conversion of initial phenols. 4,4'-
Methylenbisphenol 5 was not present in the reaction
mixture.
C14
C31
C29
C24
C18
C19
C20
C11
C2
C13
O1
C3
C8
C7
C30
C12
C23
C4
For compounds 2 and 4 single crystals were
obtained for X-ray diffraction (XRD) analysis. The
general appearance of molecules of these compounds
is shown in Fig. 1. In symmetrically independent part
of crystal cell of compound 4 there is one molecule,
while compound 2 crystallizes with the location in the
unit cell of two independent molecules A and A' (main
component of disordered molecule). Relative orient-
tation of the terpene and the phenyl fragment in
compounds 2 and 4 and in previously studied deri-
vatives of о-isobornylphenols [1, 3–5] is practically the
same [torsion angle C16C11C2C3 –19.5(2), 22.9(4),
C21
O2
C22
C5
C1
C10
C25
C27
C6
C9
C28
C26
Fig. 1. Molecular structures of 2-(hydroxymethyl)-4-
methyl-6-(1,7,7-trimethylbicyclo[2.2.1]hept-exo-2-yl)phe-
nol 2 (а) and 2,6-di-tert-butyl-4-{2-hydroxy-5-methyl-3-
(1,7,7-trimethylbicyclo-[2.2.1]hept-exo-2-yl)benzyl}phenol
4 (b) according to the X-ray diffraction data. Thermal ellip-
soids are shown with 50% probability. For compound 2 the
appearance of the first independent molecule is presented.
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SYNTHESIS OF UNSYMMETRICAL HYDROXYBENZYLPHENOLS
625
O2A
O1'
O2'A
O1A
O1
O2'
O1'A
O2
Fig. 2. Н-bonded tetramer in crystal structure of compound 2.
–15.0(6)° in compounds 4, 2A and 2A' respectively]
and, according to calculated data [6], is mostly
determined by intramolecular forces. In the minor
component (30%) of the disordered molecule of
compound 2 the terpene substituent is turned by an
angle C16C11C2C3 of 109(2)°. In crystal packing of
both compounds the associates are formed connected
by hydrogen bonds. In compound 4 the bond O2H2O1
[O···O 3.051(4), H···O 2.29 Å, angle CHO 149°] is
fairly weak, while the other acid proton (H1) does not
take part in Н-bonding that is caused by steric
hindrances created by bulky tert-butyl and isobornyl
groups. In previously studied of 4,4'-methylenebis-
phenol [5] and hydroxybenzylphenol [1] the hydroxy
groups located between two tert-butyl or isobornyl
substituents did not form hydrogen bonds in the
crystal.
H2···O2' [O···O 2.675(8), H···O 1.83 Å, angle CHO
179°] binds symmetrically independent molecules
A···A', resulting in generation of tetrameric H-bond
associates (Fig. 2), and, evidently, is responsible for
generation of two symmetrically independent
molecules in the unit cell. Sufficiently strong
intermolecular interactions between symmetrically
independent molecules we have already observed
before [7–10].
The structure and composition of compounds 2–4
are confirmed by spectral data and elemental analysis.
Compounds 2–4 are racemates because the racemic 2-
isobornyl-4-methylphenol 1 was used to obtain them.
EXPERIMENTAL
IR spectra were recorded on Shimadzu IR Prestige
21 instrument from pellets with KBr. 1H and 13C NMR
spectra of the solutions of compounds in CDCl3 were
registered on a spectrometer Bruker Avance II 300
(300.17 and 75.48 MHz respectively). Chemical shifts
were measured from the residual signals of CHCl3 (δH
7.26, δC 77.00 ppm). The assignment of signals was
carried out using the 13С NMR spectra in the mode of
J-modulation and by HSQC method. The purity of the
initial 2,4- and 2,6-di-tert-butylphenols and cresol 1
was monitored by gas chromatography on Shimadzu
GC-2010AF instrument using flame-ionization detec-
tor (carrier gas helium) and capillary column HP-1
The structure of Н-bonding in the crystal packing
of compound 2, where both hydroxy groups
participate, is more complex. The bond O1–H1···O2
[O···O 2.610(5), H···O 1.77 Å, angle CHO 169°] in
molecule
A
is intramolecular. In the second
independent molecule A' this hydroxy group
participates in the formation of a bond between
molecules A'···A' [O1'–H1'···O1', O···O 2.774(7), H···O
1.93 Å, angle CHO 180°] and leads to generation of
dimers additionally stabilized by the O2'–
H2'···O1' [O···O 2.819(9), H···O 1.97 Å, angle CHO
179°] bond. Besides, the hydrogen bond O2–
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 51 No. 5 2015

BURAVLEV et al.
626
(Agilent, 60 m × 0.25 mm × 0.25 µm, oven temperature
programming 100–240°C, heating rate 6 deg/min).
10 mL of toluene were additionally added. By the end
of the reaction the solvent was removed at a reduced
pressure, 30 mL of water was added to the precipitate
and the reaction mixture was left overnight for
hydrolysis of intermediate borosilicate ether. Diethyl
ether was used for extraction (3 × 20 mL), the extract
was washed with water (30 mL), dried with Na2SO4,
the solvent was removed at a reduced pressure. The
residue was subjected to column chromatography
(eluent petroleum ether–Et2O, 100 : 1→35 : 1, then the
polarity was raised by adding CH2Cl2). Yield 2.57 g
(92%). Light-yellow crystals, mp 68–70°C. IR
spectrum, cm–1: 3514, 3368 ν(OH), 2951, 2876 ν(СH3,
CH2), 1609 ν(С=С), 1468, 1383 δ(СH3, CH2),1186
Melting points were determined on
a
Sanyo
Gallenkamp MDP350 device and were not corrected.
The reaction course was monitored by TLC on
Sorbfil plates. Chromatograms were developed treating
with KMnO4 solution (15 g of KMnO4, 300 mL of
H2O, and 0.5 mL of conc. H2SO4). For column chro-
matography silica gel Alfa Aesar 70/230μ was used
(eluent is indicated in each particular case).
Chemically pure chloroform, pure grade formic
acid, diethyl ether, sodium acetate trihydrate, and boric
acid pure for analysis were used without additional pu-
rification. Petroleum ether was distilled, bp 65–70°C.
2-Isobornyl-4-methylphenol 1, 2,4-di-tert-butylphenol,
2,6-di-tert-butylphenol according to GC data contained
more than 97% of the main compound. 4-(Bromo-
methyl)-2,6-di-tert-butyl-phenol was obtained by
method [11]. Values of Rf and spectral characteristics
1
ν(С–О), 771 δ(=С–Н). H NMR spectrum, δ, ppm:
0.83 s (3Н, C10H3), 0.89 s, 0.94 s (3Н each, C8,9H3),
1.37–1.44 m, 1.50–1.69 m, 1.87–1.88 m (6Н, H3, H4,
C5H2, C6H2), 2.24 s (1Н, СН2ОН), 2.20–2.30 m (1Н,
Н3), 2.30 s (3Н, C17H3), 3.30 t (1Н, Н2, J 9.0 Hz), 4.55
s (2Н, C18H2), 6.71 s, 7.12 s (1Н each, Н14,16), 7.28 s
(1Н, ArОН). 13С NMR spectrum, δ, ppm: 12.33 (С10),
20.41, 21.47 (С8,9), 20.86 (C17), 27.54 (С3), 34.04 (С5),
39.80 (С6), 44.94 (С2), 45.75 (С4), 47.99 (С1), 49.84
(С7), 65.08 (С18), 125.61, 128.82, 131.04 (С13,14,16),
123.66, 127.89 (С11,15), 153.12 (С12). Found, %: C
79.02; H 9.36. C18H26O2. Calculated, %: C 78.79; H
9.55.
of 4,4'-methylenebis(2,6-di-tert-butylphenol)
5
coincide with characteristics of the compound sample
that was synthesized previously [12].
Single crystals of compound 2 after prolonged
storage at room temperature were taken from the
solution, washed with pentane, and dried; single
crystals of compound 4 were obtained by slow
evaporation of the solution of this compound in
pentane. Experimental intensity of the reflections was
measured on a diffractometer SmartApex II CCD
(graphite monochromator, ω-scanning) using the
MoKα-radiation (λ 0.71073 Å). Processing of the initial
array of the measured intensities was performed
applying programs SAINT and SADABS, included in
APEX2 [13] program package. Structures were solved
by the direct method and refined using full-matrix
least-squares method in anisotropic approximation for
nonhydrogen atoms with respect to Fh2kl. Solving and
refining of the structures was performed with program
SHELXTL [14]. Coordinates of the atoms and
temperature factors for compounds 2 and 4 were
deposited in Cambridge Crystallographic Data Center
(CCDC nos. 1046442 and 1046443).
Crystals of compound 2 (C18H26O2) at 120 K are
triclinic, a 7.3629(9), b 14.419(2), c 15.347(2) Å, α
71.093(2), β 88.245(3), γ 82.340(2)°, V 1527.6(3) Å3,
Z 4, space group P-1, dcalc 1.193 g/сm3, μ 0.075 mm–1,
20404 reflections were measured in the range from
1.51 to 27.00 deg by θ for a single crystal of the size
0.18 × 0.12 × 0.02 mm. The convergence of refi-
nement for all independent reflections wR2 0.2061,
calculated with respect to F2hkl for 6657 independent
reflections (Rint 0.0579) [GOF 1.105, R1 0.0967
calculated with respect to Fhkl for 4931 reflection with
I > 2σ(I)]. The structure contains two symmetrically
independent molecules, one of them is fully disordered
by two positions with the population 0.7 : 0.3. Also the
hydroxy group НO2 of the first independent molecule
is also disordered by two positions with the same
population. The minor component of the disordered
fragments was refined in isotropic approximation. The
hydrogen atom at O1' of both components of disordered
molecule is additionally disordered by two positions.
Hydrogen atoms of the disordered hydroxy groups
were geometrically placed (basing on the H-bonding
system), only the Н atom at O1 was localized from the
2-(Hydroxymethyl)-4-methyl-6-(1,7,7-trimethyl-
bicyclo[2.2.1]hept-exo-2-yl)phenol (2). A mixture of
2.5 g (10 mmol) of 2-isobornyl-4-methylphenol 1, 0.46 g
(15 mmol) of paraformaldehyde, 0.95 g (15 mmol) of
boric acid in 15 mL of toluene was refluxed for 9 h in
a flask equipped with a Dean-Stark trap. Every 4 h
portions of 0.22 g (7.3 mmol) of paraformaldehyde and
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SYNTHESIS OF UNSYMMETRICAL HYDROXYBENZYLPHENOLS
627
differential synthesis of deformation density. All
hydrogen atoms were refined in the rider model.
(18H, 2 t-Bu), 1.17–1.48 m, 1.50–1.67 m, 1.73–1.94 m
(2H each, H3,4, C5H2, C6H2), 2.14–2.32 m (1H, H3),
2.20 s (3H, C17H3), 2.11 t (1H, H2, J 8.9 Hz), 3.89 s
(2H, C18H2), 4.59 s, 5.12 s (by 1H, 2 OH), 6.81 s, 7.02
s (1H, 3H, H14,16,20,24). 13С NMR spectrum, δ, ppm:
12.41 (C10), 20.28, 21.48 (C8,9), 21.02 (C17), 27.52
(C5), 30.27 [2C(CH3)3], 33.93 (C3), 34.32 [2 C(CH3)3],
37.35 (C18), 39.77 (C6), 45.38, 45.63 (C2,4), 48.01,
49.73 (C1,7), 124.98 (C20,24), 127.10, 128.77 (C14,16),
125.93, 128.50, 129.56, 129.79 (C11,13,15,19,21,23),
151.07, 152.60 (C12,22). Found, %: C 83.20; H 9.96.
C32H46O2. Calculated, %: C 83.06; H 10.02.
2,4-Di-tert-butyl-6-{2-hydroxy-5-methyl-3-(1,7,7-
trimethylbicyclo[2.2.1]hept-exo-2-yl)-benzyl}phenol
(3). Formic acid was added to a solution of 0.137 g
(0.5 mmol) of compound 2 and 0.103 g (0.5 mmol) of
2,4-di-tert-butylphenol in 2 mL of CHCl3, and the
mixture was heated for 3.5 h under reflux with
vigorous stirring. By the end of the reaction the
mixture was poured in 10 mL of CHCl3, the organic
phase was washed with water (3 × 15 mL) to remove
acid, dried with Na2SO4, solvent was removed at a
reduced pressure. The reaction product was isolated
by precipitating from cold pentane. Yield 0.123 g
(53%). Colorless powder, mp 148–150°C. IR spec-
trum, cm–1: 3595, 3505, 3375 ν(OH), 2953, 2874
ν(CH3, CH2), 1464 δ(CH3, CH2), 1186, 1146 ν(C–O).
1H NMR spectrum, δ, ppm: 0.76 s (3H, C10H3), 0.84 s,
0.86 s (3H each, C8H3, C9H3), 1.32 s, 1.40 s (9H each,
2t-Bu), 1.16–1.49 m, 1.52–1.76 m, 1.78–2.01 m (2H
each, H3,4, C5H2, C6H2), 2.16–2.32 m (1H, H3), 2.26 s
(3H, C17H3), 2.92 t (1H, H2, J 8.6 Hz), 3.92 d, 3.96 d
(1H each, C18H2, J 14.7, 14.7 Hz), 5.40 s, 6.56 s (1H
each, 2 OH), 6.96 br.s, 6.97 br.s, 7.18 d, 7.20 d (1H
each, H14,16,22,24, J 2.2, 2.2 Hz). 13С NMR spectrum, δ,
ppm: 12.36 (C10), 20.17, 21.39 (C8,9), 21.04 (C17),
27.55 (C5), 29.86, 31.66 [2 C(CH3)3], 32.33 (C18),
34.06 (C3), 34.25, 34.83 [2 C(CH3)3], 40.27 (C6),
45.44, 46.26 (C2,4), 48.28, 49.72 (C1,7), 122.70, 125.12,
127.14, 128.57 (C14,16,20,24), 125.82, 126.23, 129.04,
129.80, 135.71, 142.33 (C11,13,15,19,21,23), 149.26, 150.46
(C12,20).Found, %: C 83.31; H 9.87. C32H46O2.
Calculated, %: C 83.06; H 10.02.
b. Formic acid (3 mL) and 0.095 g (0.7 mmol) of
AcONa·3H2O were added to a solution of compound 1
and 0.105 g (0.35 mmol) of 4-(bromomethyl)-2,6-di-
tert-butylphenol in 2 mL of CHCl3. The mixture was
heated for 3.5 h under reflux with vigorous stirring.
Further processing and isolation of the reaction
product was carried out as in the experiment a. Yield
0.127 g (78%). Colourless crystals, mp 130–132°C.
Spectral characteristics are the same as characteristics
of the sample obtained by the a method.
Crystals of compound 4 (C32H26O2) at 120 K are
monoclinic, a 16.9971(11), b 15.2093(10), c 20.8281
(14) Å, β 98.0770(10)°, V 5330.9(6) Å3, Z 8, space
group C2/c, dcalc 1.153 g/cm3, μ 0.069 mm–1. 31516
reflections were measured in the range from 1.80 to
29.00 deg by θ for a single crystal of the size 0.34 ×
0.26 × 0.24 mm. The convergence of refinement for all
independent reflections wR2 0.1450, calculated with
respect to F2hkl for 7093 independent reflections (Rint
0.0320) [GOF 1.157, R1 0.0629 calculated with respect
to Fhkl for 6174 reflections with I > 2σ(I)].
2,6-Di-tert-butyl-4-{2-hydroxy-5-methyl-3-(1,7,7-
trimethylbicyclo[2.2.1]hept-exo-2-yl)benzyl}-phenol
(4). а. The preparation procedure was similar to that of
compound 3 using the 2,6-di-tert-butylphenol. The
fraction containing the main component was isolated
by column chromatography (eluent petroleum ether–
Et2O, 150 : 1). The target product was precipitated
from cold pentane. After removing the solvent from
mother liquor the residue contained additionally about
Authors express their thanks to E. N. Zainullina
(Laboratory of physicochemical research methods) for
registering the NMR spectra.
K. Yu. Suponitskii is grateful to the Russian Foun-
dation for Basic Research for the financial support
(project no. 15-03-06931).
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