Reactions of benzazole-2-thiones with 3,5-di-tert-butyl-4-hydroxybenzyl acetate

Article abstract of DOI:10.1134/S1070363217010054

The benzylation of benzothiazole(oxazole, imidazole)-2-thiones with 3,5-di-tert-butyl-4-hydroxybenzyl acetate involves either the sulfur or nitrogen atom depending on the reaction conditions. The S- and N-benzylation products of benzazole-2-thiones are kinetically and thermodynamically controlled products, respectively. The use of 3,5-di-tert-butyl-4-hydroxy-benzyl acetate allows sterically hindered hydroxybenzyl derivatives of benzаzole-2-thiones to be generally synthesized under milder conditions than in known methods of their synthesis.

Full text of DOI:10.1134/S1070363217010054

ISSN 1070-3632, Russian Journal of General Chemistry, 2017, Vol. 87, No. 1, pp. 22–28. © Pleiades Publishing, Ltd., 2017.
Original Russian Text © R.G. Tagasheva, D.R. Gataullina, I.F. Zaripova, S.V. Bukharov, G.N. Nugumanova, T.R. Deberdeev, Yu.K. Voronina, 2017,
published in Zhurnal Obshchei Khimii, 2017, Vol. 87, No. 1, pp. 26–32.
Reactions of Benzazole-2-thiones
with 3,5-Di-tert-butyl-4-hydroxybenzyl Acetate
R. G. Tagashevaa*, D. R. Gataullinaa, I. F. Zaripovaa, S. V. Bukharova,
G. N. Nugumanovaa, T. R. Deberdeeva, and Yu. K. Voroninab
a Kazan National Research Technological University, ul. K. Marksa 68, Kazan, Tatarstan, 420015 Russia
*e-mail: tagashevar@mail.ru
bArbuzov Institute of Organic Chemistry, Kazan Research Center, Russian Academy of Sciences, Kazan, Tatarstan, Russia
Received May 26, 2016
Abstract—The benzylation of benzothiazole(oxazole, imidazole)-2-thiones with 3,5-di-tert-butyl-4-hydroxy-
benzyl acetate involves either the sulfur or nitrogen atom depending on the reaction conditions. The S- and
N-benzylation products of benzazole-2-thiones are kinetically and thermodynamically controlled products,
respectively. The use of 3,5-di-tert-butyl-4-hydroxy-benzyl acetate allows sterically hindered hydroxybenzyl
derivatives of benzаzole-2-thiones to be generally synthesized under milder conditions than in known methods
of their synthesis.
Keywords: sterically hindered phenols, benzothiazole-2-thione, oxazole-2-thione, imidazole-2-thione, benzylation
DOI: 10.1134/S1070363217010054
Benzazole-2-thione derivatives are widely used as
polymer additives (stabilizers, rubber accelerators,
corrosion inhibitors) [1–4]. Furthermore, they are bio-
logically active compounds which exhibit anti-inflam-
matory, analgesic, antibacterial, and fungicide pro-
perties [5–9]. This fact generates interest in the synt-
hesis and properties on sterically hindered phenol
derivatives of benzаzole-2-thiones [10].
zoles [4, 13]. The same confusion takes place with
some of their derivatives. Thus, in the patents [1, 2],
the pilot commercial antioxidant stabilizer Agidol-70
was assigned the name S-(3,5-di-tert-butyl-4-hydroxy-
benzyl)-2-mercaptobenzothiazole. At the same time, in
the patent [14], the same stabilizer is named N-(3,5-di-
tert-butyl-4-hydroxybenzyl)benzothiazole-2-thione.
There are two known synthetic approaches to ste-
rically hindered hydroxybenzyl derivatives of
benzothiazole-2-thione: the Mannich reaction of com-
pound 1, formaldehyde, and 2,6-di-tert-butylphenol 2
and the reaction of compound 1 with benzylating
agents 3a–3d.
Benzothiazole(oxazole and imidazole)-2-thiones
undergo thione‒thiol tautomerization, which allows
preparation of both the N- and S-derivatives of these
compounds [11]. According to published data, benzo-
thiazole-2-thione [12] and 1,3-dihydrobenzimidazole-
2-thione [9] exist in the thione form in both solution
and melt. The same is true of benzoxazole-2-thione,
whose 13С NMR spectrum contain a signal of the C=S
group (181 ppm) and does not contain a signal of the
=C–S group (167 ppm [12]).
The synthesis of compound 4 by the Mannich reac-
tion in an isopropanol or a DMF solution in the
presence of a base (dibutylamine) was reported in [12,
15]. An analogous reaction of benzothiazole-2-thione
with 2-tert-butyl-4-methylphenol in the presence of an
acid catalyst (conc. HCl) gives rise to an S-benzyl
derivative [16]. The same effect of the acid‒base
catalysis on the reaction route is observed in reactions
of benzothiazole-2-thione 1 with benzylating agents.
The reaction of compound 1 with benzyl alcohol 3а in
the presence of H2SO4 forms an S-benzyl derivative 5
[17]. At the same time, benzyl bromide 3b and quar-
ternary ammonium salt 3d reacts with benzo-thiazole-2-
N
N H
SH
S
Х
Х
Х = O, S, NH.
At the same time, it should be noted that these
compounds are frequently named mercaptobenzothia-
zoles, mercaptobenzoxazoles, and mercaptobenzimida-
22

REACTIONS OF BENZAZOLE-2-THIONES
23
Scheme 1.
NH
S
S
1
OH
OH
t-Bu
t-Bu
t-Bu
t-Bu
_
_
HX
H2O
2
X
HC(O)H
t-Bu
OH
t-Bu
3a−3d
N
S
S
4
N H
S
t-Bu
S
OH
t-Bu
5
X = OH (a), Br (b), N(CH3)2 (c), N(CH3)2 (d).
COCH3
thione 1 in the presence of trimethylamine react to
form an N-benzyl derivative 4 [18]. Controversial data
are available for the reaction of benzothiazole-2-thione
of acetone with formic acid (1 : 1) at 40–50°С, or in a
mixture of isopropanol and acetone (3 : 2) in the
presence of KОН at ambient temperature. With DMF
and acetone‒formic acid solvents, equimolar reagent
amounts were used. In the presence of KOH, a double
excess of benzothiazole-2-thione was used to prevent
side reactions of benzyl acetate 6 in the alkaline
medium [22]. The reaction progress was monitored by
TLC. It was found that the reaction of benzyl acetate 6
with benzothiazole-2-thione always gave two isomers,
specifically, the N- and S-benzylation products.
with
3,5-di-tert-butyl-4-hydroxybenzylamine
3c.
According to [12, 15, 19], this reaction in DMF and
absolute ethanol yields compound 4. At the same time,
according to the patent [20], this reaction in toluene
provides compound 5 (Scheme 1).
It should be noted that the synthesis of compound 5
is complicated by the isomerization of the latter to
thione 4. The isomerization occurs under heating in a
solvent or without it and is accelerated in polar
solvents or in the presence of base catalysts [15].
t-Bu
O
O
In the present work we have studied the reaction of
3,5-di-tert-butyl-4-hydroxybenzyl acetate 6 with benzo-
thiazole-2-thione 1. As known, acid, base, and dipolar
aprotic solvent activate benzyl acetate 6 in reactions
with weak nucleophiles [21].
4 + 5
HO
t-Bu
+ 1
6
When formic acid was used, the product mixture
always contained benzyl formate 7 formed from
unreacted benzyl acetate 6 [23].
The reaction of benzyl acetate 6 with benzothiazole-
2-thione was performed for 2–3 h in DMF or a mixture
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 87 No. 1 2017

24
TAGASHEVA et al.
Compositions of the benzylation products of benzothiazole-
2-thione
The resulting data allow us to consider compounds
5 and 4 a kinetically and a thermodynamically con-
trolled products, respectively. These products easier
interconvert in a basic compared to an acid medium.
Fraction of the reaction product, %
Reaction conditions
4
5
6
4
–
–
7
–
9
–
Thus, the reaction of 3,5-di-tert-butyl-4-hydroxy-
benzyl acetate with 2-mercaptobenzothiazole can
provide either N- or S-benzylation products, depending
on conditions.
DMF
72.5
42.0
23.5
49.0
24.0
Acetone–formic acid
In the presence of KOH 76.0
According to published data, the alkylation and
acylation of benzoxazole-2-thione, too, can take the
way of N- and S-substitution [4]. We found that ben-
zoxazole-2-thione reacts with benzyl acetate 6 in DMF
or a mixture of acetone with formic acid under heating,
or in a mixture of acetone with formic acid in the
presence of KОН at ambient temperature gives rise to
N-benzyl derivative 8.
t-Bu
HCOOH
6
HO
t-Bu
_CH3COOH
O
CH
O
7
The product ratio was measured by 1Н NMR
spectroscopy as the intensity ratio of the proton signals
of the СН2N (5.21 ppm), CH2S (4.60 ppm), and CH2О
(5.14 ppm) groups. The compositions of the reaction
mixtures are listed in the table.
NH
+ 6
S
O
_
CH3COOH
The reaction of benzothiazole-2-thione 1 with
benzyl acetate 6 in DMF for 7 h at 50°С forms,
according the Н NMR data, N-benzyl derivative 4.
t-Bu
OH
t-Bu
1
The reaction in acetone‒formic acid (1 : 1) at ambient
temperature for 1 day gave 53% of compound 5.
N
O
1
According to the Н NMR data, the filtrate contained
S
59% of compound 5, 20% of compound 4, 11% of
benzyl acetate 6, and 10% of benzyl formate 7. When
heated in DMF at 50°С for 5 h, S-benzyl derivative 5
completely isomerizes to N-(3,5-di-tert-butyl-4-hyd-
roxybenzyl)benzothiazole-2-thione 4. The isomeriza-
tion of compound 5 in an acetone–formic acid
medium, other conditions are the same, gives a mixture
of compounds 4, 5, and 7 (71.5 : 20 : 8.5, respectively).
The appearance of compound 7 among the iso-
merization products is indicative of the elimination of
the 3,5-di-tert-butyl-4-hydroxybenzyl fragment in the
course of isomerization of S-benzyl derivative 5 to
N-benzyl derivative 4.
8
The structure of compound 8 was established by X-
ray diffraction analysis. The molecules of compound 8
in crystal represent two nearly planar fragment linked
together by a methylene bridge (Fig. 1), as a result of
which the angle between these fragment is determined
of the conformation of sp3 carbon and equals 112.98(3)°.
The bond lengths and the bond and torsion angles span
ranges typical of each bond type [24]. The crystal
packing of compound 8 (Fig. 2) is primarily
determined by O14–H14···S2 hydrogen bonds [the O···S
distance is 3.616(7) Å and the OHS angle is 141.4(6)°]
which bind the molecules into infinite chains. In their
turn, the latter form a 3D network due to С–Н···π
interactions (the Н···Сg distances are 2.85–2.96 Å and
the С–Н···Cg angles are 121°–126°, where Cg is the
centroid of the aromatic ring).
t-Bu
N
+CH2
OH
t-Bu
5
+
4
S
S
HC(O)OH
The conversion of benzyl acetate 6 after a 24 h
reaction in DMF at ambient temperature was 26%.
1
+ 7
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 87 No. 1 2017

REACTIONS OF BENZAZOLE-2-THIONES
25
Fig. 2. Packing of and noncovalent interactions in the
crystal of compound 8 (projection on the a0c plane).
the presence of alkali. Amery et al. [25] described in
their patent the synthesis of 2-thioimidazoles and
imidazoline-2-thiones containing one and more
sterically hindered para-hydroxyphenyl groups, which
found application as antioxidants in mineral and
vegetable oils, fats, rubber resins and vulcanized
rubber, and polyurethanes and polyolefins. Thus, di-N-
benzyl derivative 10 was prepared by hours-long
heating at 120–130°С of benzimidazole-2-thione with
either Mannich base 3d or phenol 2 and paraform in
the presence of dimethylamine. It should be noted that,
according to the same patent, the reaction of 2-tert-
butyl-4-(dimethylamino)methyl-5-methylphenol with
1,3-dihydrobenzimidazole-2-thionein a 1 : 2 ratio gives
rise to 2-[(5-tert-butyl-4-hydroxy-2-methylbenzyl)sul-
fanyl]-3-[(5-tert-butyl-4-hydroxy-2-methylbenzyl)]benz-
imidazole 11.
Fig. 1. Molecular structure of compound 8 in crystal.
Along with the starting reagents, the reaction mixture
contained 21% of S-(3,5-di-tert-butyl-4-hydroxybenzyl)-
2-mercaptobenzoxazole 9 (4.56 ppm, CH2S) and 5% of
N-(3,5-di-tert-butyl-4-hydroxybenzyl)benzoxazole-2-
thione 8 (5.34 ppm, СН2N). Thus, the isomerization of
the S-benzyl to N-benzyl derivative in benzoxazole-2-
thione occurs faster than in benzothiazole-2-thione.
Bespalov et al. [9] found that 1,3-dihydro-
benzimidazole-2-thione is alkylated by the sulfur atom
and aminomethylated by the nitrogen atoms to give
mono- and bisaminomethylation products. It should be
noted alkylation with alkyl halides was performed in
OH
t-Bu
N
N
S
OH
t-Bu
11
We found that the reaction of 1,3-dihydrobenz-
products no longer contains the СН2S proton signal
(4.82 ppm); instead, СН2N proton signals (5.51 and
5.45 ppm) from di-N-benzyl derivative 10 and,
apparently, to the mono-N-benzyl derivative appear
(Scheme 2).
imidazole-2-thione with benzyl acetate 6 in DMF at a
1 : 2 reagent ratio yields di-N-benzyl derivative 10
both under heating and at ambient temperature. The
same reaction in an acetone‒formic acid medium
provides S-benzyl derivative 11.
Thus, in the present work we determined conditions
for the synthesis of S- and N-benzylation products of
benzothiazole(oxazole, imidazole)-2-thiones in the reac-
tions of the corresponding benzаzole-2-thiones with
Like S-benzyl derivative 5, compound 12, when
heated in DMF for 50°С for 5 h, isomerizes to N-benzyl
1
deruvatives. The Н NMR spectrum of the reaction
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 87 No. 1 2017

26
TAGASHEVA et al.
Scheme 2.
t-Bu
OH
t-Bu
.
2 mol 6,
N
N
DMF
S
_
CH3COOH
t-Bu
N H
N H
OH
S
t-Bu
10
.
1 mol 6,
N H
HCOOH
t-Bu
S
_
CH3COOH
N
OH
t-Bu
12
3,5-di-tert-butyl-4-hydroxybenzyl acetate. The use of
benzyl acetate 6 generally allows more facile synthesis
of sterically hindered hydroxybenzyl derivatives of
benzаzole-2-thiones than known methods of their
synthesis.
All calculations were performed using WinGX [27]
and APEX2 [28]. Molecular visualization was
accomplished with PLATON [29] and MERCURY
[30]. The crystal data were deposited at the Cambridge
Crystallographic Data Center (CCDC 1472194).
N-(3,5-Di-tert-butyl-4-hydroxybenzyl)benzothia-
zole-2-thione (4). A solution of 1.39 g (0.005 mol) of
benzyl acetate 6 and 0.835 g (0.005 mol) of
benzothiazole-2-thione 1 in 12 mL of DMF was heated
for 7 h at 50°С and then cooled down to ambient
temperature and poured into aqueous NaCl. The
precipitate that formed was filtered off, washed with
water, and dried in air. Yield 1.87 g (97%), mp 155–
157°С (ethanol) (mp 152–153°C [12]). 1Н NMR
spectrum (CDCl3), δ, ppm: 1.42 s (18Н, CMe3), 5.21 s
(1Н, ОН), 5.62 s (2Н, СН2N), 7.25–7.32 m (4Н, Н5,6,
ArH), 7.33–7.40 m (1Н, Н4), 7.46–7.52 m (1Н, Н7).
13С NMR spectrum (CDCl3), δС, ppm: 30.2 (СМе3),
34.3 (СМе3), 49.7 (CH2N), 113.2, 121.2, 124.6, 124.7,
125.2, 126.8, 127.8, 136.3, 141.8, 153.7 (Ar), 189.9 (C=S).
EXPERIMENTAL
1
The Н NMR spectra were measured on a Bruker
AVANCE-600 instrument (600.13 МHz) relative to
the residual proton signals of deuterated solvents.
Elemental analysis was performed on a EuroEA-3000
analyzer (EuroVector, Italy).
The unit cell parameters of compound 8 and the
intensities of 15492 reflections were measured on a
Smart Apex II CCD diffractometer (296 K, MoKα
radiation, graphite monochromator, φ- and ω-scanning,
θmax 26.00°). Crystal of compound 8 (C22H27NO2S, М
369.51), monoclinic, space group P21/n, a 9.929(8), b
9.985(8), c 20.904(17) Å, β 101.696(11)°, V 2029(3) Å3,
Z 4, F(000) 792, dcalc 1.209 g/cm3, μ 0.175 mm–1. The
structure was decoded and refined first isotropically
and then anisotropically using SHELXL-97 [26]. The
hydrogen atoms were located geometrically. Final
R factors: R1 0.0852 for 1606 unique reflections with
I > 2σ(I) and wR2 0.2643 for 3992 unique reflections.
2-[(3,5-Di-tert-butyl-4-hydroxybenzyl)sulfanyl]-
benzothiazole (5). A solution of 0.8 g (0.003 mol) of
benzyl acetate 6 and 0.5 g (0.003 mol) of benzo-
thiazole-2-thione 1 in a mixture of 6 mL of acetone
and 6 mL of formic acid was allowed to stand at
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REACTIONS OF BENZAZOLE-2-THIONES
27
ambient temperature for 1 day. The precipitate was
filtered off, washed with water, and dried. Yield 0.59 g
(53%), mp 143–144°С (ethanol) (mp 140.5–141.8°C
[17]). The filtrate was poured into aqueous NaCl. The
precipitate was filtered off and recrystallized from
ethanol to obtain an additional 0.24 g of compound 5.
2.5 mL of acetone, and a solution of 0.15 g
(0.0026 mol) of KОН in 3.5 mL of isopropanol was
allowed to stand at ambient temperature for 3.5 h to
obtain 0.33 g (66%) of compound 8.
1,3-Bis(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3-di-
hydrobenzimidazole-2-thione (10). a. A mixture of
0.92 g (0.0033 mol) of benzyl acetate 6 and 0.25 g
(0.0016 mol) of 1,3-dihydrobenzimidazole-2-thione in
7 mL of DMF was heated at 60°С for 2.5 h, cooled
down to ambient temperature, and poured into aqueous
NaCl. The precipitate that formed was filtered off,
washed with water, and dried in air. Yield 0.93 g
1
The total yield of compound 5 was 73%. Н NMR
spectrum (CDCl3), δ, ppm: 1.45 s (18Н, CMe3), 4.58 s
(2Н, СН2S), 5.24 s (1Н, ОН), 7.29 s (2H, ArH), 7.43–
7.52 m (2Н, Н5,6), 7.78 d (1Н, Н7, 3J = 7.9 Hz), 7.96 d
(1Н, Н4, 3J = 8.2 Hz).
Reaction of benzyl acetate 6 with benzothiazole-
2-thione in the presence of of KОН. To solution of
1
(95%), mp 244–245°С (ethanol) (mp 240°С [24]). Н
benzyl acetate 6, 0.375 g (0.0014 mol)
and
NMR spectrum (CDCl3), δ, ppm: 1.41 s (36Н, CMe3),
5.18 s (2Н, ОН), 5.51 s (4Н, СН2N), 7.14–7.19 m (2H,
Н5,6), 7.20–7.25 m (2Н, Н4,7), 7.39 s (4Н, ArH).
benzothiazole-2-thione 1, 0.5 g (0.003 mol) in 2.5 mL
of acetone was added a solution of 0.15 g (0.003 mol)
of KОН in 3.5 mL of isopropanol. The reaction
mixture was stirred at ambient temperature for 3 h and
then poured into aqueous NaCl. The precipitate that
formed was filtered off, washed with water, and dried
to obtain 0.42 g (80.8%) of a mixture of the reaction
products. The list of the products is shown in the table.
b. A mixture of benzyl acetate 6 and 1,3-di-
hydrobenzimidazole-2-thione in DMF was allowed to
stand at ambient temperature for 1 day to obtain 96%
of compound 10.
N-(3,5-Di-tert-butyl-4-hydroxybenzyl)benzoxazole-
2-thione (8). а. A solution of 0.921 g (0.003 mol) of
benzyl acetate 6 and 0.5 g (0.003 mol) of benzoxazole-
2-thione in 10 mL of DMF was heated at 50°С for
3.5 h. The reaction mixture was cooled down to
ambient temperature and poured into aqueous NaCl.
The precipitate that formed was filtered off, washed
with water, and dried in air. Yield 1.12 g (89.6%), mp
2-[(3,5-Di-tert-butyl-4-hydroxybenzyl)sulfanyl]-
1Н-benzimidazole (12). a. A mixture of 0.46 g
(0.0016 mol) of benzyl acetate 6, 0.25 g (0.0016 mol)
of 1,3-dihydrobenzimidazole-2-thione,
3
mL of
acetone, and 3 mL of formic acid was heated at 40°С
for 6 h. The reaction mixture was cooled down to
ambient temperature and poured into aqueous NaCl.
The precipitate that formed was filtered off, washed
with water, and dried in air. Yield 0.56 g (92%), mp
1
147–148°С. Н NMR spectrum (CDCl3), δ, ppm: 1.43
s (18Н, CMe3), 5.26 s (1Н, ОН), 5.34 s (2Н, СН2N),
7.10–7.15 m (1H, Н4), 7.21–7.29 m (2Н, Н5,6), 7.33–
7.37 m (1Н, Н4), 7.36 s (2Н, ArH). Found, %: С 71.69;
Н 7.21; N 3.92. C22H27NO2S. Calculated, %: С 71.51;
Н 7.36; N 3.79.
1
168–170°С (benzene). Н NMR spectrum (CDCl3), δ,
ppm: 1.34 s (18Н, CMe3), 4.73 s (2Н, СН2N), 5.23 s
(1Н, ОН), 7.17 s (2Н, ArH), 7.23–7.30 m (2H, Н5,6),
7.71–7.78 m (2Н, Н4,7). Found, %: С 71.45; Н 7.83; N
7.27. C22H28N2OS. Calculated, %: С 71.70; Н 7.66; N
7.60.
b. In a similar way, from a mixture of 0.92 g
(0.003 mol) of benzyl acetate 6 and 0.51 g (0.003 mol)
of benzoxazole-2-thione, 6 mL of acetone, and 6 mL
of formic acid under heating at 50°С for 4.5 h we
obtained 1.01 g (81%) of compound 8.
b. A solution of benzyl acetate 6 and 1,3-dihydro-
benzimidazole-2-thione in a 1 : 1 mixture of acetone
and formic acid at ambient temperature for 2 days to
obtain 98% of compound 12.
c. A mixture of 0.92 g (0.003 mol) of benzyl acetate
6, 0.51 g (0.003 mol) of benzoxazole-2-thione, 6.5 mL
of acetone, and 6.5 mL of formic acid was allowed to
stand at ambient temperature for 1 day to obtain 0.97 g
(78%) of compound 8.
ACKNOWLEDGMENTS
The work was financially supported by the Ministry
for Education and Science of the Russian Federation in
the framework of the basic part of the State Contract
for 2014–2016.
d. A mixture of 0.375 g (0.0013 mol) of benzyl
acetate 6, 0.4 g (0.0026 mol) of benzoxazole-2-thione,
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TAGASHEVA et al.
14. Zaikin, A.E, Kharitonov, E.A., Kokorev, G.I.,
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