Di(4,5,6,7-tetrafluorobenzothiazol-2-yl) disulfide: Synthesis and reactions with amines

Article abstract of DOI:10.1007/s11172-007-0193-y

Di(4,5,6,7-tetrafluorobenzothiazol-2-yl) disulfide, obtained by oxidation of 2-mercapto-4,5,6,7-tetrafluorobenzothiazole, readily reacts with aliphatic and alicyclic amines to form the corresponding sulfenyl amides.

Full text of DOI:10.1007/s11172-007-0193-y

Russian Chemical Bulletin, International Edition, Vol. 56, No. 6, pp. 1271—1272, June, 2007
1271
Di(4,5,6,7ꢀtetraf luorobenzothiazolꢀ2ꢀyl) disulfide:
synthesis and reactions with amines*
N. А. Orlova,ꢀ Е. F. Kolchina, and V. V. Shelkovnikov
N. N. Vorozhtsov Novosibirsk Institute of Organic Chemistry,
Siberian Branch of the Russian Academy of Sciences,
9 prosp. Akad. Lavrent´eva, 630090 Novosibirsk, Russian Federation.
Fax: +7 (383) 330 9752. Eꢀmail: vsh@nioch.nsc.ru
Di(4,5,6,7ꢀtetrafluorobenzothiazolꢀ2ꢀyl) disulfide, obtained by oxidation of 2ꢀmercaptoꢀ
4,5,6,7ꢀtetrafluorobenzothiazole, readily reacts with aliphatic and alicyclic amines to form the
corresponding sulfenyl amides.
Key words: 2ꢀmercaptoꢀ4,5,6,7ꢀtetrafluorobenzothiazole, di(4,5,6,7ꢀtetrafluorobenzoꢀ
thiazolꢀ2ꢀyl) disulfide, (4,5,6,7ꢀtetrafluorobenzothiazolꢀ2ꢀyl)sulfenyl amides.
2ꢀMercaptobenzothiazole (captax) and its derivatives
(disulfide, sulfenyl amides) are widely used in industry as
initiators of polymerization.1 The quest of new initiators
of photopolymeric holographic compositions prompted us
to synthesize derivatives of fluorinated analogs of captax,
i.e. 2ꢀmercaptoꢀ4,5,6,7ꢀtetrafluorobenzothiazole (1).
Tetrafluoroꢀsubstituted benzothiazoles are known for quite
a while,2 however, 2ꢀmercapto derivative 1 was obtained
only in 2004.3
In order to broaden the scope of fluoroꢀsubstituted
initiators of polymerization, we studied the possibility of
substitution of the fluorine atoms in benzothiazole 1 by
reaction with Nꢀnucleophiles, such as morpholine and
piperidine. However, starting benzothiazole 1 was only
isolated from the reaction mixtures, obtained by reflux of
compound 1 with these amines in ethanol or DMF. In
order to avoid the effect of tautomeric equilibrium
40% aq. H2O2 in ethanol at room temperature, giving
disulfide 2 in high yield.
We have shown that disulfide 2 reacted with primary
and secondary aliphatic and alicyclic amines in ethanol at
20 °С (Scheme 2); the reaction with benzylamine, taking
place under reflux, was the only exception. The substituꢀ
tion of fluorine atoms does not occur in this case, rather
(4,5,6,7ꢀtetrafluorobenzothiazolꢀ2ꢀyl)sulfenyl amides
3а—е are formed, the structures of which were ascerꢀ
1
tained based on H and 19F NMR spectroscopy, mass
spectrometry, and elemental analysis data.
Scheme 2
thione
thiol on the reactivity of compound 1, it was
oxidized to di(4,5,6,7ꢀtetrafluorobenzothiazolꢀ2ꢀyl) diꢀ
sulfide (2) (Scheme 1). The reaction proceeded with
R1R2N = BuNH (a), Bu2N (b), PhCH2NH (c),
(d),
(e)
Scheme 1
The 19F NMR spectra of compounds 3а—е each conꢀ
tain four signals of equal intensity, which differ in chemiꢀ
cal shifts from those of starting disulfide 2. In the 1H NMR
spectra, there are signals of protons, corresponding to the
amine residues. The highꢀresolution mass spectrum of
compound 3е also confirms its structure.
The nonꢀfluorinated benzothiazolylsulfenyl amides are
normally obtained by reaction of 2ꢀmercaptobenzoꢀ
thiazole, its salts or the corresponding disulfide with
amines in the presence of strong oxidants, vis. Cl2,4 I2,5
NaClO.6 An example of electrochemical transformation
of a disulfide to a sulfenyl morpholide is also described.7
* Dedicated to the memory of Academician N. N. Vorozhtsov
on the 100th anniversary of his birth.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1225—1226, June, 2007.
1066ꢀ5285/07/5606ꢀ1271 © 2007 Springer Science+Business Media, Inc.

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Russ.Chem.Bull., Int.Ed., Vol. 56, No. 6, June, 2007
Orlova et al.
(4,5,6,7ꢀTetrafluorobenzothiazolꢀ2ꢀyl)sulfenyl dibutylamide
(3b). The yield was 57%, m.p. 102—104 °С (from hexane).
Found (%): С, 48.81; Н, 4.74; F, 20.35; N, 7.36; S, 17.36.
C15Н18F4N2S2. Calculated (%): C, 49.16; Н, 4.95; F, 20.74;
N, 7.65; S, 17.50. 1H NMR (CDCl3), δ: 0.87 (t, 6 H, 2 Me, J =
7.5 Hz); 1.36, 1.78, 3.02 (all m, 12 H, 6 CH2). 19F NMR
(CDCl3), δ: –4.01 (t, 1 F, J1 = J2 = 21.0 Hz); 0.01 (t, 1 F, J1 =
J2 = 21.0 Hz); 7.30 (dd, 1 F, J1 = 21.0 Hz, J2 = 13.0 Hz); 22.50
(dd, 1 F, J1 = 21.0 Hz, J2 = 13.0 Hz).
We showed that di(benzothiazolꢀ2ꢀyl) disulfide, containꢀ
ing no fluorine atoms, does not form sulfenyl amides in
the reaction with amines in ethanol neither at 20 °С nor
under reflux.
The readiness of the reaction of disulfide 2 with amines
can be apparently explained by higher electrophilicity of
the sulfur atom and by higher stability of the leaving fragꢀ
ment of the molecule due to the electron withdrawing
effect of the fluorine atoms.
In conclusion, in the present work a simple method
for the synthesis of di(4,5,6,7ꢀtetrafluorobenzothiazolꢀ
2ꢀyl) disulfide (2) is proposed, which reacts with priꢀ
mary and secondary alkyl amines under mild conditions
to form (4,5,6,7ꢀtetrafluorobenzothiazolꢀ2ꢀyl)sulfenyl
amides 3а—е. This enables one to use disulfide 2 for the
introduction of polyfluoroꢀsubstituted benzothiazole fragꢀ
ment into various aminoꢀcontaining molecules.
(4,5,6,7ꢀTetrafluorobenzothiazolꢀ2ꢀyl)sulfenyl benzylamide
(3c). The yield was 87%, m.p. 177—180 °С (from benzene).
Found (%): С, 48.68; Н, 2.37; F, 22.12; N, 7.91; S, 18.83.
C14Н8F4N2S2. Calculated (%): C, 48.83; Н, 2.34; F, 22.07;
1
N, 8.14; S, 18.62. H NMR (CD3CN), δ: 4.31 (s, 2 H, CH2);
4.58 (br.s, 1 H, NH); 7.32—7.46 (m, 5 H, Ph). 19F NMR
(CD3CN), δ: –5.89 (td, 1 F, J1 = J2 = 19.0 Hz, J3 = 3 Hz);
–0.67 (td, 1 F, J1 = J2 = 19.0 Hz, J3 = 1 Hz); 9.70 (ddd, 1 F, J1 =
22.0 Hz, J2 = 13.0 Hz, J3 = 3 Hz); 22.95 (ddd, 1 F, J1 = 22.0 Hz,
J2 = 13.0 Hz, J3 = 1 Hz).
(4,5,6,7ꢀTetrafluorobenzothiazolꢀ2ꢀyl)sulfenyl piperidide
(3d). The yield was 66%, m.p. 121—123 °С (from ethanol).
Found (%): С, 44.82; Н, 3.40; F, 23.28; N, 8.53; S, 19.55.
C12Н10F4N2S2. Calculated (%): C, 44.71; Н, 3.13; F, 23.57;
Experimental
NMR spectra were recorded on a Bruker АСꢀ200 spectroꢀ
meter (200 (1H) and 188.2 MHz (19F)). The H chemical shifts
1
1
N, 8.69; S, 19.89. H NMR (CDCl3), δ: 1.45—1.82 (m, 6 H,
3 CH2 of piperidine); 3.20 (m, 4 H, 2 CH2 of piperidine).
19F NMR (CDC13), δ: –0.06 (t, 1 F, J1 = J2 = 20.5 Hz); 2.88 (t,
1 F, J1 = J2 = 19.5 Hz); 11.97 (dd, 1 F, J1 = 19.5 Hz, J2 =
14.5 Hz); 22.89 (dd, 1 F, J1 = 20.5 Hz, J2 = 14.5 Hz).
(4,5,6,7ꢀTetrafluorobenzothiazolꢀ2ꢀyl)sulfenyl morpholide
(3e). The yield was 88%, m.p. 160—162 °С (from benꢀ
zene—hexane, 1 : 2). Found (%): С, 41.23; H, 2.42; F, 23.15;
N, 8.70; S, 19.73. C11H8F4N2S2O. Calculated (%): C, 40.73;
H, 2.49; F, 23.43; N, 8.64; S, 19.77. 1H NMR (CDCl3), δ: 3.26,
3.84 (both m, 4 H each, H of morpholine). 19F NMR (CDC13),
are given in δ scale, the signal of the residual protons in CDCl3
(δ 7.24) and CD3CN (δ 1.96) serving as the internal standard.
The 19F chemical shifts are given in ppm relatively to С6F6. The
highꢀresolution mass spectrum was recorded on a Finnigan
MAT 8200 spectrometer (direct injection, temperature of injecꢀ
tor, 314 °С, energy of the ionizing electrons, 70 eV).
Di(4,5,6,7ꢀtetrafluorobenzothiazolꢀ2ꢀyl) disulfide (2). Hydroꢀ
gen peroxide (40% aq., 35 mL) was added dropwise to a suspenꢀ
sion of 2ꢀmercaptoꢀ4,5,6,7ꢀtetrafluorobenzothiazole (1) (5.0 g)
in ethanol (50 mL) with stirring. The reaction mixture was stirred
for 30 min at ~20 °C, the precipitate was filtered off, washed
with water, and dried in air. Disulfide 2 (4.28 g, 85%) was
obtained, m.p. 113—116 °С (from hexane). Found (%): С, 35.79;
F, 31.92; N, 5.76; S, 26.90. C14F8N2S4. Calculated (%): C, 35.30;
F, 31.90; N, 5.88; S, 26.92. 19F NMR (CDCl3), δ: 3.89 (t, 1 F,
J1 = J2 = 20.5 Hz); 5.06 (t, 1 F, J1 = J2 = 19.5 Hz); 14.42 (dd,
1 F, J1 = 19.5 Hz, J2 = 14.5 Hz); 24.90 (dd, 1 F, J1 = 20.5 Hz,
J2 = 14.5 Hz).
δ: 0.77 (t, 1 F, J1 = J2 = 20.5 Hz); 3.51 (t, 1 F, J1 = J2
=
19.5 Hz); 12.50 (dd, 1 F, J1 = 19.5, J2 = 14.0 Hz); 23.22 (dd, 1 F,
J1 = 20.5 Hz, J2 = 14.0 Hz). HRMS, found: m/z 324.0012 [M]+.
Calculated: M = 324.0014.
This work was financially supported by the Siberian
Branch of the Russian Academy of Sciences (Integrational
Grants 15, 17, 33, and 65).
Reaction of disulfide 2 with amines (general procedure). An
amine (40 mmol) was added to a suspension of disulfide 2 (0.48 g,
10 mmol) in EtOH (10 mL), and this was stirred for 30 min at
~20 °C with magnetic stirrer. The reaction mixture was poured
to the iceꢀcold water, the formed precipitate was filtered off,
washed with water, and dried in air to obtain sulfenyl amides 3.
The filtrate was acidified with 3% aq. HCl, the precipitate was
filtered off, washed with water, and dried in air to obtain
mercaptobenzothiazole 1 (0.15—0.20 g).
References
1. Vspomogatel'nye veshchestva dlya polimernykh materialov [Auxꢀ
iliary Substances for Polymeric Materials], Eds К. B. Piotrovsky
and К. Yu. Salnis, Khimiya, Moscow, 1966, 176 pp. (in
Russian).
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3. L. Zhu and M. Zhang, J. Org. Chem., 2004, 69, 7371.
4. US Pat. 2758995; Chem. Abstrs, 1957, 51, 5840.
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2000, 43, 309; Chem. Abstrs, 2001, 134, 131201.
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43, 3223.
(4,5,6,7ꢀTetrafluorobenzothiazolꢀ2ꢀyl)sulfenyl butylamide
(3а). The yield was 63%, m.p. 54—56 °С (from hexane).
Found (%): С, 42.97; Н, 3.27; F, 24.56; N, 8.81; S, 20.42.
C11Н10F4N2S2. Calculated (%): C, 42.57; Н, 3.25; F, 24.49;
1
N, 9.03; S, 20.67. H NMR (CDCl3), δ: 0.93 (t, 3 H, Me, J =
8.0 Hz); 1.41, 1.59, 3.17 (all m, 6 H, 3 CH2); 3.36 (br.t, 1 H,
NH, J = 6.0 Hz). 19F NMR (CDCl3), δ: 0.17 (t, 1 F, J1 = J2 =
20.5 Hz); 3.10 (t, 1 F, J1 = J2 = 19.5 Hz); 12.18 (dd, 1 F, J1 =
19.5 Hz, J2 = 15.0 Hz); 23.12 (dd, 1 F, J1 = 20.5 Hz, J2
15.0 Hz).
=
Received February 26, 2007;
in revised form April 13, 2007