Oxidation and reductive bromination of Bis(4-tert-butylphenyl)aminoxyl

Article abstract of DOI:10.1134/S1070428013080083

One-electron oxidation of bis(4-tert-butylphenyl)aminoxyl with antimony pentachloride and bromine leads to the formation of oxoammonium salts with anions SbCl ₆ ^- and Br ₃ ^- respectively. The salt with the Br ₃ ^- anion converted at heating into a mixture of bromodiphenylamines which formed also from the aminoxyl as a result of previously unknown reaction of three-electron reductive bromination. The mechanisms of these reactions were assumed.

Full text of DOI:10.1134/S1070428013080083

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2013, Vol. 49, No. 8, pp. 1143−1149. © Pleiades Publishing, Ltd., 2013.
Original English Text © V.A. Golubev, V.D. Sen’, 2013, published in Zhurnal Organicheskoi Khimii, 2013, Vol. 49, No. 8, pp. 1161−1167.
Oxidation and Reductive Bromination
of Bis(4-tert-butylphenyl)aminoxyl
V. A. Golubev and V. D. Sen’
Institute of Problems of Chemical Physics, Russian Academy of Sciences,
Chernogolovka, Moscow oblast,142432 Russia
e-mail: vgolubev@icp.ac.ru
Received February 9, 2013
Abstract—One-electron oxidation of bis(4-tert-butylphenyl)aminoxyl with antimony pentachloride and bromine
leads to the formation of oxoammonium salts with anions SbCl6– and Br3– respectively. The salt with the Br3– anion
converted at heating into a mixture of bromodiphenylamines which formed also from the aminoxyl as a result of
previously unknown reaction of three-electron reductive bromination. The mechanisms of these reactions were
assumed.
DOI: 10.1134/S1070428013080083
Oxoammonium salts are used as selective stoichio- group the signals of ortho- and meta-benzene protons and
metric oxidants and as catalysts of alcohols oxidation of the tert-butyl groups are shifted downfield by 1.1, 0.4,
[1–5]. These catalysts found an industrial application and 0.13 ppm as compared with the corresponding signals
in the synthesis of pharmaceuticals [6]. The essential in the spectrum of the respective amine.
drawback of the oxoammonium salts is their low stabil-
ity that restricts their practical application. Aiming at the
search for stable oxoammonium salts we investigated the
oxidation of bis-(4-tert-butylphenyl)aminoxyl (I) with
antimony pentachloride and bromine.
Bromine readily oxidizes aminoxyl I into oxoammo-
nium salt III (Scheme 2).
Primarily formed bromide A adds a molecule Br2
converting into more stable tribromide III. When the
bromination of aminoxyl I is carried out in CCl4 at –20°C
the dark brown crystalline modification of salt III formed
in 92% yield. When aminoxyl I is brominated at ~20°C,
The antimony pentachloride quantitatively oxidized
aminoxyl I to oxoammonium salt II (Scheme 1).
The dark brown crystals of salt II are well soluble in a 41% yield copper-red crystalline modification of
in MeCN and CHCl3 forming dark red solutions whose salt III is obtained. Both modifications have no precise
color is due to the strong absorption band of the oxoam- melting point and decompose in the range 110–130°C.
monium cation, λmax 505 nm (ε 16900 l mol−1 cm−1). At IR spectra of the crystalline modifications of salt III es-
room temperature this salt is sufficiently stable both in the sentially differ by the band intensity, and the UV spectra
crystalline state and in solution, yet it fast decomposes at of both modifications are identical and qualitatively
heating and has no precise melting point. In the 1H NMR coincide with the UV spectrum of hexachloroantimonate
spectrum of salt II under the effect of the oxoammonium II. The IR spectrum of the latter is similar to the spec-
Scheme 1.
2
+ 3 SbCl5
2
+ SbCl3
N+
N
SbCl6_
.
O
O
I
II
1143

GOLUBEV, SEN’
1144
Scheme 2.
0.5 Br2
Br2
I
N+
O
N+
Br _
Br3_
O
A
III
trum of the dark brown modification of tribromide III.
1H NMR spectrum of tribromide III contains broadened
signals of all protons. The broadening is apparently due
to the equilibrium between the oxoammonium cation
and aminoxyl I.
bromoamines V–VIII we synthesized these compounds
by an independent method, the bromination of amine
IV. The composition and structure of bromoamines were
confirmed by elemental analysis, NMR, UV, IR, and mass
spectra (see EXPERIMENTAL). The location of the
bromine atoms in bromoamines V–VIII was established
using NMR spectra H – H NOE based on the effect
of intensification of the signals belonging to tert-butyl
groups and benzene protons.
At the bromination of aminoxyl I alongside with
oxoammonium salt III products of three-electron reduc-
tion of aminoxyl I, amine IV and its bromoderivatives
V–VIII, were obtained (Scheme 3).
1
1
The bromination of benzene, its derivatives and
other arenes is known to proceed by the mechanism of
electrophilic substitution [7]. Evidently this mechanism
operates in the formation of bromoamines V – VIII at
the bromination of amine IV (Scheme 4).
The ratio between the products of oxidation and
reduction of aminoxyl I depend on the bromination tem-
perature. At –20°C the fraction of the reduction products
equals 8%. The main among them, dibromoamine VI,
tribromoamine VII, and amine IV, formed in the yields
6.4, 1.0, and 0.5 mol% respectively.At ~20°C the fraction
of the products of aminoxyl I reduction grew to ~50%.
The main among them, dibromoamine VI, tribromoamine
VII, and amine IV, formed in the yields 20, 19, and 3
mol% respectively. Bromoamines VI, VII were isolated
in the pure state, and bromoamines V, VIII and amine
IV were identified by chromatography by the retention
volumes and also by UV spectra. To prove the structure of
Bromine adds to amine IV with the formation of
carbocation B that reacts with the anion Br– giving bro-
moamine V and HBr. The latter with excess amine IV
affords ammonium salt IV·HBr. However this mechanism
of electrophilic substitution does not explain the reduc-
tion of the nitroxyl into amino group at the bromination
of aminoxyl I.
The main product of the reductive bromination of
Scheme 3.
N
H
N
N
H
V
H
Br
Br
Br
IV
VI
Br
Br
Br
N
H
N
H
Br
Br
Br
Br
VII
BrH
VIII
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OXIDATION AND REDUCTIVE BROMINATION
1145
Scheme 4.
Br2
+
V
IV
_HBr
N
H
Br _
Br
H
B
.
IV HBr
IV + HBr
aminoxyl I, tribromoamine VII, forms along the simple
stoichiometric equation
three bromine atoms leads to the three-electron reduction
of aminoxyl I to tribromoamine VII. The sum of these
successive reaction is the stoichiometric equation (1).
The second product of the reductive bromination of
aminoxyl I, dibromoamine VI, formed apparently by the
reaction of the intermediate bromohydroxylamine D with
hydrogen bromide (Scheme 6).
Bromohydroxylamine D like the other N,N-diaryl-
hydroxylmines [8] by reaction with HBr converts into
salt H, which through imine I isomerizes into the final
dibromoamine VI. The conversion of aminoxyl I into di-
bromoamine VI is described by a stoichiometric equation
I + 1.5 Br2 → VII + H2O.
(1)
In keeping with this stoichiometry the nitroxyl group
is reduced to amino group by three hydrogen atoms of
benzene rings that are substituted by bromine.Apparently
the reductive bromination occurs as a result of successive
addition of bromine atoms to aminoxyl I (Scheme 5).
Bromine atoms add to benzene ring of aminoxyl I with
the formation of nitrone C that isomerizes into hydrox-
ylamine D. As a result the nitroxyl group of aminoxyl I
undergoes the one-electron reduction into the hydroxy-
amino group. The addition of the second bromine atom to
the benzene ring of hydroxylamine D provides adduct E
that via water elimination converts into aminyl radical F.
Therewith hydroxylamine D undergoes the one-electron
reduction into aminyl F. The addition of the third bro-
mine atom to aminyl F gives imine G that isomerizes
into bromoamine VII. Thus the successive addition of
I + 0.5Br2 + HBr → VI + H2O.
(2)
Hydrogen bromide can form in the reaction of inter-
mediate nitrone C or hydroxylamine D with bromine
(Scheme 7).
Amine IV evidently forms at the disproportionation
of aminoxyl I under the action of HBr:
4I + 3HBr → IV + 3A + H2O
(3)
Scheme 5.
Br2
I
.
D
Г
I
+ Br
N+
N
_
Br
H
O
OH
D
Br
C
Br
H
.
Br
Br2
VII
.
CH
Br
_H2O
N
N
N
.
Br
H
OH
Br
Br
Br
Br
F
G
E
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 49 No. 8 2013

GOLUBEV, SEN’
1146
Scheme 6.
HBr
_H2O
D
VI
+
N
N
Br _
Br
H
Br
Br
H
I
Scheme 7.
.
(C
D) + Br
_HBr
N
O
.
Br
This disproportionation is characteristic of all diaryl-
nitroxyls [8]. Bromoamine V and tetrabromoamine VIII
form in small amounts apparently by the bromination of
amine IV and tribromoamine VII respectively.
proceeds along Schemes 5 and 6 respectively.
Therefore during the reaction of aminoxyl I with bro-
mine two processes occur simultaneously: One-electron
oxidation of aminoxyl I to oxoammonium salt III and
three-electron reductive bromination of aminoxyl I with
the formation of bromoamines VI, VII. The first process
is typical for all nitroxyl radicals, yet the reductive bro-
mination was observed for the first time. Presumably the
reductive bromination is a reaction characteristic of all
diarylnitroxyls. The thermal decomposition of oxoam-
monium salt III proceeds as the reaction between the
We also studied the stability of oxoammonium salt
–
III with Br3 anion. In an acetonitrile solution this salt
decomposes completely within ~8 h at room temperature
and within ~5 min in the boiling solution. The main de-
composition products are tribromoamine VII and dibro-
moamine VI which form in the yields 61 and 37 mol%
respectively.
–
oxoammonium cation and Br3 anion. As a result the
The following stoichiometric equation corresponds to
the conversion of salt III into tribromoamine VII:
four-electron reductive bromination of this cation occurs
affording as the products bromoamines VI, VII.
III → VII + H2O.
(4)
EXPERIMENTAL
The result of this transformation is the four-electron re-
duction of oxoammonium group of the cation into amino
group. Nominally the oxoammonium group is reduced
Bis(4-tert-butylphenyl)aminoxyl (I) was obtained by
procedure [9] and crystallized from methanol, mp 137°C.
Bis(4-tert-butylphenyl)amine (IV) was obtained by pro-
cedure [10] and crystallized from methanol, mp 108°C.
The chromatographic analysis was performed on a chro-
matograph Milikhrom equipped with an UV detector
(column 2 × 64 mm, Separon C18, 5 μm). The preparative
TLC was carried out on plates 200 × 200 mm with a layer
of silica gel G 1.5 mm thick, with fluorescent indicator.
IR reflection spectra were registered on a spectrometer
Spectrum 100, absorption spectra were recorded on a
spectrophotometer Specord 75IR. NMR spectra were
taken on a spectrometer Bruker AIII, 500 MHz, UV
spectra were measured on a spectrophotometer Specord
UV-VIS. Electron impact mass spectra (70 eV) were re-
–
by Br3 anion and three benzene hydrogen atoms which
are replaced by three bromine atoms.Apparently the first
stage of the decomposition of salt III consists in adding
Br3– anion to one of the benzene rings of salt III cation
with the formation of the intermediate nitrone C that
undergoes the isomerization into bromohydroxylamine D.
III → (C → D) + Br2.
(5)
As a result of this reaction the oxoammonium group of
salt III suffers a two-electron reduction into a hydroxy-
amine group. Further transformation of bromohydroxyl-
amine D into tribromoamine VII and dibromoamine VI
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OXIDATION AND REDUCTIVE BROMINATION
1147
corded on an GC-MS instrument Finnigan. Melting points
were determined on a heating block PNMК.
bromine in 3 ml of CCl4 was added to a solution of 387 mg
(1.31 mmol) of aminoxyl I in 5 ml of CCl4 cooled to
–20°C (bath filled with ice with salt). Immediately a fine
crystalline precipitate of tribromide III separated that was
filtered off, washed with CCl4, and dried in a vacuum.
Yield 641 mg (92%), dark brown crystals, t.decomp.
110–130°C.
Bis(4-tert-butylphenyl)oxoammonium hexachlo-
roantimonate (II). A solution of 168 mg (0.56 mmol)
of SbCl5 in 2 ml of CCl4 was added to a solution of
107 mg (0.36 mmol) of aminoxyl I in 2 ml of CCl4
cooled to –15°C in a bath filled with ice mixed with salt.
The separated precipitate was filtered off, washed with
CCl4, dried, and purified by reprecipitation from CHCl3
with hexane. Yield 220 mg (96%), dark brown crystals,
t.decomp. 115–120°C. UV spectrum (MeCN), λmax, nm
(ε, l mol–1·cm–1): 505 (16900), 370 (6270), 320 (6040),
308 (6170), 269 (12900). IR spectrum (reflection), cm–1:
3099 (CHaryl); 2970, 2908, 2873 (CH3); 1580 (aryl), 1476,
1440, 1424, 1366, 1347, 1327, 1312, 1256, 1173, 1104,
1026, 851, 815, 714, 679. 1H NMR spectrum (CDCl3 +
SbCl5), δ, ppm: 1.43 s[18H, C(CH3)3], 7.89 br.d (4H,
H3,5, J 8.7 Hz), 8.09 br.d (4H, H2,6, J 8.8 Hz). Found,
%: C 38.21; 3.78; Cl 33.24; N 2.22. C20H26Cl6NOSb.
Calculated, %: C 38.08; H 4.15; Cl 33.72; N 2.22.
The solution was evaporated in a vacuum to obtain a
residue of 50 mg of a compounds mixture whose HPLC
showed the following result (MeCN, λ 210 nm), Vsp, μL
(Irel, %): 240 (13) (IV), 300 (7.6) (VII), 400 (100) (VI),
705 (1.3). The data of the quantitative HPLC analysis
revealed that the mixture consisted of 36.4 mg (6.4%) of
dibromoamine VI, 6.7 mg (1%) of tribromoamine VII,
and 1.9 mg (0.5%) of amine IV.
Bis(4-tert-butylphenyl)oxoammonium tribromide
(III). a. Copper-red crystalline modification forms in
the reaction of aminoxyl I with Br2 in CCl4 at ~20°C.
Copper-red plate crystals, t.decomp. 120–125°C (CCl4).
UV spectrum (MeCN), λmax, nm (ε, l mol–1cm–1): 506
(23000), 370 (8700), 316 sh (8800), 269 (54000). IR
spectrum (reflection), cm–1: 3071 (CHaryl); 2963, 2904,
2869 (CH3); 1585, 1520 (aryl); 1478, 1446, 1425, 1406,
1366, 1333, 1255, 1181, 1109, 1026, 851, 829, 753, 714,
679. 1H NMR spectrum (CD3CN), δ, ppm: 1.33 br.s (18H,
CH3), 7.31 br.s (4H, H3,5), 7.74 br.s (4H, H2,6). Found,
%: C 45.06; H 4.95; Br 44.12; N 2.73. C20H26Br3NO.
Calculated, %: C 44.81; H 4.89; Br 44.71; N 2.61.
Bromination of bis(4-tert-butylphenyl)aminoxyl (I).
a. At ~20°C.Asolution of 287 mg (1.8 mmol) of bromine
in 3.6 ml of CCl4 was added to a solution of 347 mg
(1.17 mmol) of aminoxyl I in 5 ml of CCl4. Immediately
a precipitate of bis(4-tert-butylphenyl)oxoammonium
tribromide (III) separated that was filtered off, washed
with CCl4, and dried in a vacuum. Yield 259 mg (41%),
copper-red flake crystals, t.decomp. 120–125°C.
b. Dark brown crystalline modification forms in the
reaction of aminoxyl I with Br2 in CCl4 at –20°C. Dark
brown crystals, t.decomp. 110–130°C (CCl4). UV spec-
trum (MeCN), λmax, nm (ε, l mol–1cm–1): 506 (23000),
370 (8700), 316 sh (8800), 269 (54000). IR spectrum
(reflection), cm–1: 3092 (CHaryl); 2966, 2904, 2869 (CH3);
1576 (aryl); 1487, 1436, 1422, 1399, 1365, 1334, 1311,
1249, 1167, 1102, 1024, 852, 813, 712. 1H NMR spectrum
(CD3CN), δ, ppm: 1.33 br.s (18H, CH3), 7.31 br.s (4H,
H3,5), 7.74 br.s (4H, H2,6). Found, %: C 44.78; H 4.81;
Br 44.37; N 2.49. C20H26Br3NO. Calculated, %: C 44.81;
H 4.89; Br 44.71; N 2.61.
The solution was evaporated in a vacuum to obtain as
a residue 316 mg of resinous solid whose HPLC showed
the following result (80% aqueous MeCN, λ 210 nm),
Vsp, μL (Irel, %): 470 (2.5), 950 (6.2) (IV), 1360 (2) (V),
2170 (100) (VII), 3200 (90) (VI), 3600 (1.5) (VIII). The
data of the quantitative HPLC analysis revealed that the
mixture consisted of 117 mg (19%) of tribromoamine
VII, 104 mg (20%) of dibromoamine VI, 10 mg (3%)
of amine IV, 6 mg (1%) of tetrabromoamine VIII, and
4 mg (1%) of bromoamine V.
The resinous product was washed with MeOH (3
×
5 ml), thereafter remained 219 mg of solid colorless sub-
stance that was separated on four chromatographic plates
with silica gel eluting with hexane. From the first chro-
matographic zone we isolated 95 mg of dibromoamine
VI, colorless crystals, mp 163°C (i-PrOH). From the
second zone 90 mg of tribromoamine VII was obtained,
colorless crystals, mp 182°C (heptane).
N-(2-Bromo-4-tert-butylphenyl)-N-(4’-tert-butyl-
phenyl)amine (V). A solution of 329 mg (2.06 mmol)
of bromine in 4 ml of CCl4 was added within 10 min to
a solution of 1.16 g (4.12 mmol) of amine IV in 4 ml
of CCl4 cooled to –20°C (bath filled with ice with salt).
The reaction mixture was stirred for 5 min at cooling and
10 min at ~20°C. The separated precipitate of amine IV
hydrobromide (720 mg) was filtered off, and the solution
b. At –20°C. A solution of 315 mg (1.97 mmol) of
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GOLUBEV, SEN’
1148
was evaporated in a vacuum. The residue was dispersed in
4 ml of MeOH, filtered off, washed with MeOH, and dried
in a vacuum. Yield 531 mg of a mixture of bromoamine
V and dibromoamine VI. The mixture was separated by
column chromatography (30 × 200 mm, silica gel KSK,
40–50 μm, elution with heptane). The composition of elu-
ate was monitored by TLC. The evaporation of the eluate
of the second zone afforded 320 mg (22%) of bromoamine
V. Colorless crystals, mp 90°C (MeCN). UV spectrum
(EtOH), λmax, nm (ε, l mol–1cm–1): 286 (21800), 238 sh
(7530), 202 (40140). IR spectrum (reflection), cm–1: 3415
(NH), 3049 (CHaryl); 2960, 2902, 2864 (CH3); 1604,
1518 (aryl); 1478, 1463, 1390, 1362, 1320, 1264, 1117,
1037, 879, 842, 710. 1H NMR spectrum (CDCl3), δ, ppm:
1.28 s [9H, 4-C(CH3)3], 1.32 s [9H, 4'-C(CH3)3], 5.93 s
(1H, NH), 7.07 d.m (2H, H2',6', J 8.6 Hz), 7.17 m (2H,
H5,6), 7.32 d.m (2H, H3',5', J 8.6 Hz), 7.51 br.d.d (1H, H3,
J 0.9, 1.5 Hz). 1H–1H NOE NMR spectrum (CDCl3): the
intensification of NMR signals indicated the interaction
between protons 4-C(CH3)3 (δ 1.28) s H3 (δ 7.51) and
H5 (δ 7.17); 4'-C(CH3)3 (δ 1.32) s H3' and H5' (δ 7.32).
Mass spectrum, m/z (Irel, %): 363 (2.7), 362 (17.8), 361
(97.7), 360 (17.5), 359 (100) [M]+; 347 (15.5), 346 (58.8),
345 (16.6), 344 (54.3) [M – CH3]+. Found, %: C 54.92;
H 5.75; Br 36.69; N 3.19. C20H26BrN. Calculated, %:
C 54.69; H 5.74; Br 36.38; N 3.19. [M]+ 363.13 (2.2),
362.13 (21.5), 361.12 (99.5), 360.13 (21.9), 359.12 (100).
1H–1H NOE NMR spectrum (CDCl3): the intensification
of NMR signals indicated the interaction between protons
4-C(CH3)3 (δ 1.30) with H3 (δ 7.56) and H5 (δ 7.21). Mass
spectrum, m/z (Irel, %): 442 (12.0), 441 (49.4), 440 (22.8),
439 (100), 438 (15.2), 437 (49.1) [M]+; 427 (13.5), 426
(53.9), 425 (19.5), 424 (98.7), 423 (11.9), 422 (51.4) [M
– CH3]+. Found, %: C 54.92; H 5.75; Br 36.69; N 3.19.
C20H25Br2N. Calculated, %: C 54.69; H 5.74; Br 36.38;
N 3.13. [M]+ 443.04 (1.1), 442.03 (10.7), 441.03 (51.0),
440.04 (21.9), 439.03 (100), 438.04 (11.3), 437.04 (51.4).
N-(2,6-Dibromo-4-tert-butylphenyl)-N-(2'-bromo-
4'-tert-butylphenyl)amine (VII). A solution of 2.15 g
(13.5 mmol) of bromine in 2 ml CCl4 was added within
7 min at stirring to a solution of 1.28 g (4.55 mmol) of
amine IV in 8 ml of CCl4. The reaction mixture was boiled
for 70 min. The solvent was evaporated in a vacuum,
the residue was dispersed in 10 ml of hot MeOH. The
insoluble precipitate was filtered off, washed with MeOH,
and after drying it was twice recrystallized from heptane.
Yield 1.05 g (45%), colorless plate crystals, mp 182°C,
sublimed at temperature >140°C. UV spectrum (EtOH),
λ
max, nm (ε, l mol–1cm–1): 286 (9380), 234 sh (18400),
208 (69300). IR spectrum (reflection), cm–1: 3355 (NH),
3039 (CHaryl); 2962, 2902, 2865 (CH3); 1610, 1541,
1506 (aryl); 1476, 1383, 1313, 1263, 1037, 868, 815,
1
736, 712. H NMR spectrum (CDCl3), δ, ppm: 1.27 s
[9H, 4'-C(CH3)3], 1.32 s [9H, 4-C(CH3)3], 5.96 s (1H,
NH), 6.29 d (1H, H6', J 8.5 Hz), 7.10 d.d (1H, H5’, J 2.2,
8.5 Hz), 7.52 d (1H, H3', J 2.2 Hz), 7.60 s (2H, H3,5).
1H–1H NOE NMR spectrum (CDCl3): the intensification
of NMR signals indicated the interaction between pro-
tons 4-C(CH3)3 ( 1.32) s H3 and H5 (δ 7.60); 4'-C(CH3)3
(δ 1.27) s H3' (δ 7.52) and H5' (δ 7.10). Mass spectrum,
m/z (Irel, %): 522 (7.1), 521 (34.2), 520 (20.1), 519 (96.1),
518 (20.3), 517 (100), 516 (9.9) and 515 (40.9) [M]+; 506
(19.8), 505 (13.8), 504 (56.2), 503 (12.3), 502 (53.6),
501 (1.1), 500 (12.5) [M – CH3]+. Found, %: C 46.30;
H 4.44; Br 46.27; N 2.69. C20H24Br3N. Calculated, %:
C 46.36; H 4.67; Br 46.26; N 2.70. [M]+ 521.94 (6.9),
520.94 (33.8), 519.95 (21.5), 518.94 (99.7), 517.95 (21.9),
516.94 (100), 515.95 (7.5), 514.95 (34.3).
Bis(2-bromo-4-tert-butylphenyl)amine (VI). A so-
lution of 1.6 g (10 mmol) of bromine in 2 ml of CCl4 was
added within 12 min while stirring and cooling to –20°C
(bath of ice with salt) to a solution of 2.81 g (10 mmol)
of amine IV in 10 ml of CCl4. The reaction mixture was
stirred for 15 min at cooling, the separated precipitate
of amine IV hydrobromide was filtered off, the reaction
solution was evaporated in a vacuum. The residue was
dispersed in 10 ml of MeOH, the precipitate was filtered
off and washed with hot MeOH (3 × 5 ml), and after
drying it was twice recrystallized from i-PrOH. Yield
1.3 g (30%), colorless crystals, mp 163°C, sublimed at
temperature >150°C. UV spectrum (EtOH), λmax, nm (ε,
l mol–1cm–1): 287 (22700), 236 sh (9300), 208 (39900).
IR spectrum (reflection), cm–1: 3389 (NH), 3038 (CHa-
ryl); 2961, 2900, 2866 (CH3); 1601, 1519 (aryl); 1331,
1262, 1116, 1036, 882, 814, 712; (c CCl4): 3380 (NH),
3030 (CHaryl); 2956, 2898, 2862 (CH3); 1605, 1510
(aryl); 1315, 1265, 1115, 1040, 880. 1H NMR spectrum
(CDCl3), δ, ppm: 1.30 s [18H, C(CH3)3], 6.26 s (1H, NH),
7.21 m (4H, H5,6), 7.56 br.d.d (2H, H3, J 0.7, 1.8 Hz).
Bis(2,6-dibromo-4-tert-butylphenyl)amine (VIII).
A solution of 1.3 g (8 mmol) of bromine in 1 ml of CCl4
was added within 5 min at stirring to a solution of 1.13 g
(4 mmol) of amine IV in 4 ml of CCl4. The reaction mix-
ture was boiled for 2 h, then 0.64 g (4 mmol) of bromine
was added, and the mixture was boiled for 0.5 h more.
On cooling the solvent was evaporated, the residue was
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OXIDATION AND REDUCTIVE BROMINATION
1149
oxoammonium tribromide (III). A solution of 0.1 g
(0.19 mmol) of tribromide III in 0.25 ml of MeCN was
heated to boiling. The brown-red color of the solution
turned light brown, and colorless crystals precipitated.
The precipitate was filtered off, washed with MeCN,
and dried in a vacuum. Yield of the precipitate 85 mg.
HPLC of the precipitate (MeCN, λ 210 nm), Vsp, μL (Irel,
%): 240 (1.7) (IV), 300 (100) (VII), 400 (39) (VI), 700
(0.2). The data of the quantitative HPLC analysis revealed
that the precipitate contained 61.5, 37.5, 0.4 mol% of
tribromoamine VII, dibromoamine VI, and amine IV
respectively.
dispersed in 10 ml of MeOH. The precipitate of bro-
moamines was filtered off, washed with MeOH, and dried
in a vacuum. To the obtained mixture of bromoamines
4 ml of CCl4 and 0.64 g (4 mmol) of bromine were added,
and the mixture was boiled for 1 h. The solvent was
evaporated, the residue was dispersed in 5 ml of MeOH.
The precipitate was filtered off, washed with MeOH, and
after drying it was twice recrystallized from i-PrOH. Yield
1.65 g (69%), colorless crystals, mp 208–209°C, sublimed
at temperature > 170°C. UV spectrum (EtOH), λmax, nm
(ε, l·mol–1cm–1): 294 (13600), 257 (9030), 216 (45960).
IR spectrum (reflection), cm–1: 3383 (NH), 3039 (CHaryl);
2963, 2902, 2867 (CH3); 1589, 1549, 1535, 1501, 1489
(aryl); 1460, 1383, 1313, 1262, 871, 736, 701. 1H NMR
spectrum (CDCl3), δ, ppm: 1.29 s [18H, C(CH3)3], 5.76 s
(1H, NH), 7.48 s (4H, H3,5). 1H–1H NOE NMR spectrum
(CDCl3): the intensification of NMR signals indicated
the interaction between protons 4-C(CH3)3 (δ 1.29) s H3
and H5 (δ 7.48). Mass spectrum, m/z (Irel, %): 601 (17.6),
600 (10.5), 599 (54.1), 598 (19.3), 597 (100), 596 (10.2),
595 (54.8), 594 (3.9), 593 (18.1) [M]+; 586 (10.3), 585
(1.7), 584 (33.1), 583 (15.0), 582 (75.6), 581 (8.9), 580
(32.8), 578 (9.7) [M – CH3]. Found, %: C 40.17; H 3.66;
Br 53.13; N 2.38. C20H23Br4N. Calculated, %: C 40.24;
H 3.88; Br 53.53; N 2.35. [M] 601.85 (3.5), 600.85 (17.3),
599.85 (14.3), 598.85 (67.2), 597.86 (22.0), 596.85 (100),
595.86 (15.0), 594.85 (68.5), 593.86 (3.9), 592.86 (17.6).
ACKNOWLEDGMENTS
The authors express their gratitude to A.B. Chernyak
for registering the NMR spectra.
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Bis(4-tert-butylphenyl)amine hydrobromide
(IV)·HBr formed as a precipitate at the bromination of
amine IV in CCl4 (see above). Colorless needle crystals,
t.decomp. 185–200°C. IR spectrum (reflection), cm–1:
3064 (CHaryl); 2963, 2902, 2868 (CH3); 2701, 2632, 2577,
2468 (NH2); 1608, 1551, 1511 (aryl); 1477, 1408, 1271,
1203, 1178, 1111, 1017, 865, 838, 795. 1H NMR spectrum
(CDCl3), δ, ppm: 1.28 s [18H, C(CH3)3], 7.41 d.m (4H, Hm,
J 8.8 Hz), 7.60 d.m (4H, HO, J 8.8 Hz), 12.8 br.s (2H, NH2).
Found,%:C66.15;H7.45;Br22.12;N4.05.C20H27N·HBr.
Calculated, %: C 66.29; H 7.79; Br 22.05; N 3.87.
Themal decomposition of bis(4-tert-butyl-phenyl)
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 49 No. 8 2013