Convenient synthesis of 2,2-and 4,4-methylenebisphenols with bulky alkyl substituents and evaluation of their antioxidant activity

Article abstract of DOI:10.1080/00397911.2011.589564

The work is devoted to a convenient procedure of the synthesis of 2,2-and 4,4-methylenebisphenols with alkyl substituents in heterogeneous catalysis. This compounds were obtained with yields up to 87% by reflux of 2,4-or 2,6-dialkylphenols with HCHO in n-octane in the presence of KSF clay. We found that the antioxidant activity on DPPH test for two novel methylenebisphenols having isobornyl fragments was comparable with control drugs.

Full text of DOI:10.1080/00397911.2011.589564

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Convenient Synthesis of 2,2′- and 4,4′-
Methylenebisphenols with Bulky Alkyl
Substituents and Evaluation of Their
Antioxidant Activity
Evgeny V. Buravlev a , Irina Yu. Chukicheva a , Mikhail F. Borisenkov b
& Aleksandr V. Kutchin a
a Institute of Chemistry, Komi Scientific Center, Ural Branch of the
Russian Academy of Sciences, Syktyvkar, Komi Republic, Russia
b Institute of Physiology, Komi Scientific Center, Ural Branch of the
Russian Academy of Sciences, Syktyvkar, Komi Republic, Russia
Accepted author version posted online: 20 Jan 2012.Version of
record first published: 20 Aug 2012.
To cite this article: Evgeny V. Buravlev , Irina Yu. Chukicheva , Mikhail F. Borisenkov & Aleksandr
V. Kutchin (2012): Convenient Synthesis of 2,2′- and 4,4′-Methylenebisphenols with Bulky Alkyl
Substituents and Evaluation of Their Antioxidant Activity, Synthetic Communications: An International
Journal for Rapid Communication of Synthetic Organic Chemistry, 42:24, 3670-3676
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Synthetic Communications1, 42: 3670–3676, 2012
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2011.589564
CONVENIENT SYNTHESIS OF 2,2’- AND
4,4’-METHYLENEBISPHENOLS WITH BULKY ALKYL
SUBSTITUENTS AND EVALUATION OF THEIR
ANTIOXIDANT ACTIVITY
Evgeny V. Buravlev,1 Irina Yu. Chukicheva,1
Mikhail F. Borisenkov,2 and Aleksandr V. Kutchin1
1Institute of Chemistry, Komi Scientific Center, Ural Branch of the Russian
Academy of Sciences, Syktyvkar, Komi Republic, Russia
2Institute of Physiology, Komi Scientific Center, Ural Branch of the Russian
Academy of Sciences, Syktyvkar, Komi Republic, Russia
GRAPHICAL ABSTRACT
Abstract The work is devoted to a convenient procedure of the synthesis of 2,20- and
4,40-methylenebisphenols with alkyl substituents in heterogeneous catalysis. This com-
pounds were obtained with yields up to 87% by reflux of 2,4- or 2,6-dialkylphenols with
HCHO in n-octane in the presence of KSF clay. We found that the antioxidant activity
on DPPH test for two novel methylenebisphenols having isobornyl fragments was compa-
rable with control drugs.
Keywords Antioxidant activity; heterogeneous catalysis; methylenebisphenols
INTRODUCTION
Heterogeneous catalysis attracts attention because of ecological compatibility
of the process and simplification of processing of the reaction mixture, which also
makes it possible to reduce the time and resources on the synthesis. In addition, it
is possible to reuse the catalyst in some cases. Heterogeneous catalysis is particularly
attractive for the synthesis of practically important molecules. Modified and unmo-
dified montmorillonite clays are used as catalysts in numerous reactions with phe-
nolic compounds such as chlorination,[1a] nitration,[1b] alkylation,[1c] acylation,[1d]
allyl phenyl ether rearrangements,[1e] and condensation with prenyl bromide.[1f]
Received April 14, 2011.
Address correspondence to Evgeny V. Buravlev, Institute of Chemistry, Komi Scientific Centre,
Ural Branch of the Russian Academy of Sciences, 48, Pervomayskaya St., 167982 Syktyvkar, Komi
Republic, Russia. E-mail: eugeneburavlev@gmail.com
3670

2,20- AND 4,40-METHYLENEBISPHENOLS
3671
Montmorillonite KSF used as a catalyst in the reaction of phenols with
paraform has been previously described. As a result, the heating of phenols with
montmorillonite KSF=HCHO=Et3N in toluene in an autoclave led to salicylic
aldehydes.[2] We showed for the ortho-isobornylphenols that the formylation reaction
could lead to salicylic aldehydes with the terpene fragment (with yields up to 70%) by
reflux of the reagents without using of high pressure.[3] Carrying out this reaction
without the addition of Et3N, as reported in Ref. 2, led to methylenebisphenols
and cyclic acetals.
Methylenebisphenols are usually prepared using mineral acids[4] or bases[5] as
catalysts. It is well known that 2,20- and 4,40-methylenebisphenols are used as antiox-
idants and stabilizers of polymeric materials.[6] Thus, the development of a selective
procedure for obtaining methylenebisphenols in heterogeneous catalysis is important.
In this work we carried out the synthesis of methylenebisphenols with bulky
alkyl substituents in heterogeneous catalysis using montmorillonite KSF clay. We
obtained 2,20-methylenebisphenol 2a (59%) in a mixture with the cyclic acetal 3
(8%) by reflux of 2,4-di-tert-butyl phenol 1a with montmorillonite KSF=HCHO (in
the absence of Et3N and without high pressure) in toluene and isolated the product
of condensation of phenol with toluene 4 (21%) (Scheme 1). Interestingly, 2,4-di-
tert-butyl-6-(40-substituted benzyl) phenols 4 were previously synthesized via the coup-
ling of substituted benzyl chlorides with 2,4-dialkyl phenols in the presence of ZnCl2.
In addition, such compounds possess chemosterilant activity against house flies.[7]
Then, we replaced an aromatic solvent by high-boiling n-alkane (the synthesis
was predominantly carried out in n-octane). In this case, the reaction pathway varied
in the formation of the desired products of condensation 2. Indeed, as a result
2,20-methylenebisphenols 2a–c (Table 1, entries 1–3) were obtained from phenols
1a–c with yields up to 87%. The proposed conditions were also suitable for the syn-
thesis of 4,40-methylenebisphenols 2d–f, which were obtained with moderate yields
up to 61% (Table 1, entries 4–6).
Methylenebisphenols with terpene substituents were synthesized using the
racemic isobornylphenols 1c and 1e; therefore the products 2c and 2e corresponded
to a mixture of meso-=rac-diastereomers in a 1:1 ratio (Fig. 1).
Rapid precipitation of mixtures of the meso-=rac-diastereomeric compounds
2c and 2e from hexane led to samples with a predominant content of one of the
diastereomers. The composition of obtained samples had been analyzed by high-
performance liquid chromatography (HPLC) on a Chiralcel OD-H column, and
then we assigned the correlation of signals each of the diastereomers on the NMR
1H and 13C spectra. The protons of the benzylic CH2-group in meso-2c on
1H NMR spectra are diastereotopic and give two signals, whereas these protons
in rac-2c are equivalent and give one signal. In contrast to the compound 2c, the
Scheme 1. Condensation of 2,4-di-tert-butylphenol with HCHO using montmorillonite KSF in toluene.

3672
E. V. BURAVLEV ET AL.
Table 1. Montmorillonite KSF–catalyzed synthesis of 2,20- and 4,40-methylenebisphenols
Entry
Reaction
Substituents
Time (h)
Yield (%)a
1
2
3
4
5
6
1a ! 2a
1b ! 2b
1c ! 2cc
1d ! 2d
1e ! 2ed
1f ! 2fd
R1 ¼ R2 ¼ t-Bu, R3 ¼ H
2
2
2
4
3
6
85 (77)b
79
87
R1 ¼ t-Bu, R2 ¼ Me, R3 ¼ H
R1 ¼ isobornyl, R2 ¼ Me, R3 ¼ H
R1 ¼ R3 ¼ t-Bu, R2 ¼ H
50
61
31e
R1 ¼ isobornyl, R2 ¼ H, R3 ¼ Me
R1 ¼ R3 ¼ isobornyl, R2 ¼ H
aIsolated yield after column chromatography on SiO2 (without conversion).
bYield of compound 2b after synthesis in n-heptane is shown in brackets.
cProduct of reaction is a mixture of two diastereomers.
dProduct of reaction is a single meso-diastereomer.
eParaformaldehyde was also added portionwise every 1.5 h (1.47 mmol per serving).
protons of the benzyl CH2-group for both diastereomers derived from 2e give
individual signals, which differ only in chemical shift values.
The individual compound meso-2f was obtained from the compound meso-1f
1
(Table 1, entry 6), as evidenced by the presence of one set of signals in the H and
13C NMR spectra of the start and final materials.
Antioxidant activity (AOA) of the novel methylenebisphenols 2c and 2e was
determined by their ability to react in vitro with the stable radical 2,2-diphenyl-1-
picrylhydrazyl (DPPH)[8] in comparison with the known methylenebisphenols 2a,
b, d and phenolic antioxidants [2,6-di-tert-butyl-y-methylphenol (BHT) and (þ)-6-
hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid (Trolox)]. The DPPH
method advantages for determination of AOA are simplicity of reaction and possi-
bility of performing mass analysis of various compounds. Antioxidant activity of
samples is expressed in the concentration units, which corresponds to a 50% disco-
loration of the DPPH radical occurred over a certain time period.
Figure 1. Diastereomers of compound 2c.

2,20- AND 4,40-METHYLENEBISPHENOLS
3673
Table 2. Antioxidant activity of compounds
spectrophotometry
2 determined by
Entry
Compoundsa
DPPH binding activity (%)
1
2
3
4
5
6
7
BHT
Trolox
2a
0.045
0.014
0.272
0.006
0.007
0.030
0.032
2b
2cb
2d
2eb
aCompound 2f was not used in AOA test because of a low solubility
of sample in EtOH.
bUsed as mixtures of diastereomers meso-=rac-, 1:1.
The compound 2c is almost equal to AOA with the known methylenebisphenol
2b and shows better results on AOA than BHT and Trolox (Table 2). The
4,40-bisphenol 2e in this test is comparable on AOA with the compound 2d and is
not inferior to BHT.
Thus, we proposed a convenient method for the synthesis of 2,20- and
4,40-methylenebisphenols with alkyl fragments.
Antioxidant activity of the novel compounds 2c, e having an isobornyl fragments
is comparable with tert-butyl containing phenol (BHT) and methylenebisphenols. The
presence of a chiral terpene fragment in the phenol molecules 2c, e suggests the emerg-
ence of pharmacological activity what will be further investigated with in vivo models.
EXPERIMENTAL
The infrared (IR) spectra were recorded on a Shimadzu IR Prestige 21
1
Fourier-transform (FT) spectrometer in KBr pellets. The H and 13C NMR spectra
were measured on Bruker Avance II 300 instrument (300 MHz and 75 MHz) in
CDCl3. The melting points were measured on a Kofler hot-stage apparatus. The
course of the reactions was monitored by thin-layer chromatography (TLC) on
Sorbfil plates using light petroleum ether (PE)=Et2O solvent systems. To detect the
compounds, the plates were treated with a KMnO4 solution (15 g of KMnO4,
300 mL of H2O, and 0.5 mL of concentrated H2SO4). Toluene and n-octane were
freshly distilled. Paraformaldehyde was of reagent-grade quality. Column chromato-
graphy used silica gel 60 (70=230 m, wet packed). Commercially available phenols 1a,
b, d, BHT, Trolox, montmorillonite KSF, and DPPH (Alfa Aesar, Sigma-Aldrich)
were employed without purification. The racemic phenols 1c, e, f have been pre-
viously prepared by alkylation of p-cresol, o-cresol, and phenol by camphene with
corresponding (4-Me-PhO)3Al, (2-Me-PhO)3Al, and (PhO)3Al as a catalysts.[9]
General Procedure for 2
A solution of the phenol 1 (1.23 mmol), paraformaldehyde (1.47 mmol),
and montmorillonite KSF (0.4 g) in n-octane (7 mL) was heated at reflux under
efficient stirring. After 2–6 h (see Table 1), the reaction mixture was cooled to room

3674
E. V. BURAVLEV ET AL.
temperature, and the catalyst was filtered and washed with CHCl3. The excess of
solvent was removed at reduced pressure. The reaction mixture was separated
over a column (silica gel, light PE=Et2O as eluent) to afford the corresponding
methylenebisphenol 2, which was crystallized from light PE.
6,6’-Methylenebis(2,4-di-tert-butylphenol) 2a
Yield 85%; mp 137–139 ꢀC (lit.[4a] mp 141–142 ꢀC).
6,6’-Methylenebis(2-tert-butyl-4-methylphenol) 2b
Yield 79%; mp 125–127 ꢀC (lit.[4a] mp 128–129 ꢀC).
6,6’-Methylenebis(4-methyl-2-(1,7,7-trimethylbicyclo[2.2.1]hept-
exo-2-yl)phenol) 2c
Yield 87%. Mixture of two diastereomers (1:1). Yellow solid; mp 191–194 ꢀC.
IR (KBr, cmꢁ1): 3595, 3437, 3250 (OH), 1190 (CꢁO), 2949, 2874, 1464 (Me,
CH2). Found (%): C, 83.60; H, 9.42. Calc. for C35H48O2 (%): C, 83.95; H, 9.66.
Diastereomeric composition of rac-2c and meso-2c was determined by HPLC
with a Chiralcel OD-H column (hexane=i-PrOH 99=1, 0.6 mL=min, k ¼ 230 nm;
t(rac-2c) ¼ 11.58 and 18.00 min, t(meso-2c) ¼ 10.37 min).
Diastereomer rac-2c. 1H NMR (300 MHz, CDCl3): d ¼ 0.77 (s, 6H), 0.85 (s,
6H), 0.89 (s, 6H), 1.27–1.47 (m, 4H), 1.53–1.70 (m, 4H), 1.79–1.93 (m, 4H), 2.13–2.34
(m, 2H), 2.26 (s, 6H), 3.02 (br.t, 2H), 3.88 (s, 2H), 5.74 (s, 2H), 6.92 (s, 2H), 6.98 (s,
2H). 13C NMR (75 MHz, CDCl3): d ¼ 150.09, 129.83, 129.09, 128.23, 127.31, 125.57,
49.67, 48.14, 45.89, 45.54, 40.20, 34.29, 32.04, 27.55, 21.38, 20.98, 20.39, 12.48.
Diastereomer meso-2c. 1H NMR (300 MHz, CDCl3): d ¼ 0.75 (s, 6H), 0.84
(s, 6H), 0.88 (s, 6H), 1.27–1.47 (m, 4H), 1.53–1.70 (m, 4H), 1.79–1.93 (m, 4H),
2.13–2.34 (m, 2H), 2.26 (s, 6H), 3.02 (br.t, 2H), 3.83 (d, 1H, J ¼ 14.5 Hz), 3.91 (d,
1H, J ¼ 14.6 Hz), 5.97 (s, 2H), 6.94 (s, 2H), 6.96 (s, 2H). 13C NMR (75 MHz, CDCl3):
d ¼ 149.80, 129.41, 129.17, 128.42, 127.16, 126.06, 49.70, 48.14, 45.97, 45.50, 40.05,
34.04, 31.68, 27.55, 21.43, 20.98, 20.19, 12.36.
4,4’-Methylenebis(2,6-di-tert-butylphenol) 2d
Yield 50%; mp 149–151 ꢀC (lit.[4b] mp 153–155 ꢀC).
4,4’-Methylenebis(2-methyl-6-(1,7,7-trimethylbicyclo[2.2.1]hept-exo-
2-yl)phenol) 2e
Yield 61%. Mixture of two diastereomers (1:1). Yellow solid; mp 155–157 ꢀC.
IR (KBr, cmꢁ1): 3563 (OH), 1188 (CꢁO), 2949, 2876, 1476 (Me, CH2). Found
(%): C, 83.78; H, 9.88. Calc. for C35H48O2 (%): C, 83.95; H, 9.66. Diastereomeric
composition of rac-2e and meso-2e was determined by HPLC with a Chiralcel

2,20- AND 4,40-METHYLENEBISPHENOLS
3675
OD-H column (hexane=i-PrOH 9=1, 1.0 mL=min, k ¼ 219 nm; t(rac-2e) ¼ 4.46 and
6.34 min, t(meso-2e) ¼ 5.33 min).
Diastereomer rac-2e. 1H NMR (300 MHz, CDCl3): d ¼ 0.77 (s, 6H),
0.84–0.85 (m, 12H), 1.31–1.47 (m, 4H), 1.54–1.69 (m, 4H), 1.80–1.91 (m, 4H),
2.08–2.17 (m, 2H), 2.20 (s, 6H), 3.05 (t, 2H, J ¼ 8.8 Hz), 3.77 (s, 2H), 4.53 (s, 2H),
6.76 (br.d, 2H), 6.97 (br.d, 2H). 13C NMR (75 MHz, CDCl3): d ¼ 151.06, 132.58,
128.67, 128.25, 126.45, 122.48, 49.62, 48.03, 45.85, 45.56, 41.07, 40.19, 34.32,
27.56, 21.44, 20.33, 16.19, 12.48.
Diastereomer meso-2e. 1H NMR (300 MHz, CDCl3): d ¼ 0.77 (s, 6H), 0.81
(s, 3H), 0.84–0.85 (m, 9H), 1.31–1.47 (m, 4H), 1.54–1.69 (m, 4H), 1.80–1.91 (m, 4H),
2.08–2.17 (m, 2H), 2.20 (s, 6H), 3.05 (t, 2H, J ¼ 8.8 Hz), 3.79 (s, 2H), 4.53 (s, 2H),
6.76 (br.d, 2H), 6.92 (br.d, 2H). 13C NMR (75 MHz, CDCl3): d ¼ 151.06, 132.53,
128.54, 128.33, 126.51, 122.50, 49.62, 48.03, 45.85, 45.54, 40.86, 40.15, 34.25,
27.56, 21.44, 20.25, 16.19, 12.43.
4,4’-Methylenebis(2-((1R,2S,4S)-1,7,7-trimethylbicyclo[2.2.1]hept-
2-yl)-6-((1S,2R,4R)-1,7,7-trimethylbicyclo[2.2.1]hept-2-yl)phenol 2f
1
Yield 31%. Yellowish solid; mp 174–176 ꢀC. H NMR (300 MHz, CDCl3):
d ¼ 0.77 (s, 12H), 0.76 (s, 12H), 0.82 (s, 12H), 1.27–1.43 (m, 8H), 1.49–1.67 (m,
8H), 1.81–1.86 (m, 8H), 2.13–2.19 (m, 4H), 2.96 (t, 4H, J ¼ 8.6 Hz), 3.81 (s, 2H),
4.65 (s, 2H), 6.89 (s, 4H). 13C NMR (75 MHz, CDCl3): d ¼ 152.03, 132.03, 128.15
(2C), 125.88 (2C), 49.84, 48.11, 46.13, 45.46, 41.86, 40.05, 33.99, 27.57, 21.49,
20.22, 12.50. IR (KBr, cmꢁ1): 3607, 3443 (OH), 1184 (C–O), 2949, 2949, 2876, 1458
(Me, CH2). Found (%): C, 85.30; H, 10.31. Calc. for C53H76O2 (%): C, 85.43; H, 10.28.
AOA Evaluation
The reaction was carried out in microplates. Each sample was analyzed three
times. A mixture containing all the components, except the analyzing compound,
served as control. A solution of DPPH (150 mL, 0.6 mM) in EtOH was added to
50 mL of 1, 0.1, 0.01, or 0.001% ethanolic solution of the sample. Simultaneously,
the reaction with ethanolic solutions of Trolox and BHT in the same concentrations
was carried out. Optical density was measured on a PowerWave 200 TM tablet spec-
trophotometer (Bio-Tec Instruments, USA) at k ¼ 517 nm, first immediately after
addition of DPPH and vigorous stirring (t0) and then after 30 min of incubation in
the dark under polyethylene film (t1). The AOA (in %) was calculated by the formula[10]
AOA ¼ ðODblankð0Þ ꢁ ODsampleð1ÞÞ=ODblankð0Þ ꢂ 100;
where ODblank(0) is the optical density of blank, measured immediately after addition
of DPPH, and ODsample(1) is the optical density of the sample, measured after 30 min of
incubation. Then, the AOA was plotted against concentration of the analyzing com-
pound and the concentration of the compound, which corresponded to 50% loss of
color of DPPH.

3676
E. V. BURAVLEV ET AL.
ACKNOWLEDGMENTS
This work was performed with the support of the Russian Academy of Sciences
(fundamental research of the Presidium of the RAS ‘‘Biomedical and Biomolecular
Chemistry’’ (Project No. 09-T-3-1023). The authors are grateful to Elena N.
Zainullina for registration of NMR spectra.
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