Nitrenium ions. ? reactions of N,N-dimethyl-p-benzoyloxyaniline-iminium chloride with indoles and indolizines. X-ray structure of unexpected [2-chloro-4-(4-dimethylaminophenyl-ONN-azoxy)-phenyl]dimethylamine (azoxy derivative)

Article abstract of DOI:10.1039/b308088a

N,N-Dimethyl-p-nitrosoaniline reacts with benzoyl chloride affording a complex salt containing a cation, a hybrid between a nitrenium ion and an iminium ion. The salt reacts with nucleophiles (indoles, indolizines) yielding compounds characterized by a new carbon-nitrogen bond, derived from the nitrenium ion form. According to the type of nucleophile, the reaction, to differing extents, is in competition with an electron transfer process which leads to the formation of the dimer of the nucleophile and of the azoxy corresponding to the N,N-dimethyl-p-nitrosoaniline. In one of the reactions studied, a chlorinated azoxy derivative was also isolated, and its structure was elucidated by X-ray analysis.

Full text of DOI:10.1039/b308088a

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Nitrenium ions.† Reactions of N,N-dimethyl-p-benzoyloxyaniline-
iminium chloride with indoles and indolizines. X-ray structure of
unexpected [2-chloro-4-(4-dimethylaminophenyl-ONN-azoxy)-
phenyl]dimethylamine (azoxy derivative)
Lucedio Greci,*a Riccardo Castagna,a Patricia Carloni,a Pierluigi Stipa,a Corrado Rizzoli,b
Lara Righib and Paolo Sgarabottob
a Dipartimento di Scienze dei Materiali e della Terra, Università Politecnica delle Marche,
Via Brecce Bianche, I-60131 Ancona, Italy. E-mail: greci@univpm.it
b Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica,
Università di Parma, Viale delle Scienze, I-43100 Parma, Italy
Received 17th July 2003, Accepted 8th September 2003
First published as an Advance Article on the web 1st October 2003
N,N-Dimethyl-p-nitrosoaniline reacts with benzoyl chloride affording a complex salt containing a cation,
a hybrid between a nitrenium ion and an iminium ion. The salt reacts with nucleophiles (indoles, indolizines)
yielding compounds characterized by a new carbon–nitrogen bond, derived from the nitrenium ion form.
According to the type of nucleophile, the reaction, to differing extents, is in competition with an electron
transfer process which leads to the formation of the dimer of the nucleophile and of the azoxy corresponding
to the N,N-dimethyl-p-nitrosoaniline. In one of the reactions studied, a chlorinated azoxy derivative was also
isolated, and its structure was elucidated by X-ray analysis.
Introduction
Results
Nitrosoarenes react with benzoyl chloride affording a benzo-
yloxy iminium cation which can also be represented as a
nitrenium ion (eqn. (1)).
All the reactions were carried out in acetonitrile or in chloro-
form by adding a solution of the appropriate nucleophile 3–7
to the suspension of the salt formed from N,N-dimethyl-p-
nitrosoaniline and benzoyl chloride at ca. 5 ЊC under magnetic
stirring. In the case of compounds 3, 4 and 5 the reaction
mixture was poured into water, extracted and the products were
separated by silica gel chromatography (see Experimental). In
the case of nucleophiles 6 and 7, the reaction mixture was
treated with NaClO4 in order to isolate products 13 and 15
as cation perchlorates. All products listed in Table 1 were
identified by their analytical and spectroscopic data (see
Experimental) or compared with authentic samples. Com-
pound 11 was investigated by X-ray analysis in order to
establish that the chlorine atom is bonded in the ortho position
with respect to the dimethylamino group on the phenyl ring
in the opposite site to the N-oxide aryl moiety (Fig. 1). Further-
more, X-ray analysis showed that the compound consists of two
symmetry-independent molecules (called molecules A and B)
showing a trans conformation of the aromatic rings with
Ar–N᎐O ϩ PhCOCl
Ar–Nϩ–O–COPh ClϪ ↔ ϩAr᎐N–O–
᎐
᎐
COPh ClϪ
(1)
In fact, in a previous study, in the reaction between 1-methyl-
2-phenyl-3-nitrosoindole and benzoyl chloride, this cation was
isolated and characterized by X-ray spectroscopy.1 In this
study it was shown, supported by AM1 calculations,1 that the
interaction of nitroso indoles or N,N-dimethyl-p-nitrosoaniline
with benzoyl chloride produces an intermediate which can
be likely represented by both the structures of an iminium ion
and of a nitrenium ion. For a long time nitrenium ions were
an object of discussion and many doubts arose as to their
existence.2–4 In fact, when a double bonded nitrogen atom
bearing a positive charge (nitrenium ion)5–7 is linked to a
benzene ring, the positive charge is better localized on the
conjugated aromatic system. However, we have already demon-
strated that such nitrogen atoms may attack a carbon atom of
an appropriate nucleophile.8,9
In the present paper we report the reactions between N,N-
dimethyl-p-nitrosoaniline, benzoyl chloride (Scheme 1) and
different indoles and indolizines; the isolated products show
that the ionic path involving a nitrenium ion is in competition
with an electron transfer process (see discussion).
Scheme 1
Fig. 1 An ORTEP view (50% probability ellipsoids) of (a) molecule A
and (b) molecule B in compound 11.
† Part 5. For Part 4 see ref. 1
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 3 7 6 8 – 3 7 7 1
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
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Table 1 Isolated products and yields from the reactions of salt 2 with
nucleophiles 3–7
Table 2 Experimental data for the X-ray diffraction study on crystal-
line compound 11
Nucleophile
Products
Compound
11
Formula
a/Å
b/Å
c/Å
C16H19ClN4O
25.207(4)
7.631(2)
17.000(3)
90
α/Њ
β/Њ
95.50(10)
90
3255.0(13)
8
γ/Њ
V/Å3
Z
Formula weight
Space group
T/ЊC
318.8
P21/n
23
1.54178
1.301
λ/Å
ρcalc/g cmϪ3
µ/cmϪ1
21.35
Transmission coefficient
R
0.928–1.000
0.050
a
wR2
GOF
N-observed
N-independent
0.073
0.870
2468
6196
b
c
d
N-refinement
5243
Variables
397
a Calculated on the observed reflections having I > 2σ(I ). b N-observed
is the total number of independent reflections having I > 2σ(I ).
c N-independent is the number of independent reflections. d N-refine-
ment is the number of reflections used in the refinement having I > 0.
Table 3 Selected bond distances (Å) and angles (Њ) for compound 11
Molecule A
Molecule B
Cl(1)–C(2)
O(1)–N(3)
N(1)–C(1)
N(1)–C(13)
N(1)–C(14)
N(2)–N(3)
N(2)–C(4)
N(3)–C(7)
N(4)–C(10)
N(4)–C(15)
N(4)–C(16)
1.730(3)
1.253(5)
1.402(5)
1.466(5)
1.445(4)
1.273(4)
1.422(5)
1.456(5)
1.367(5)
1.426(5)
1.447(4)
1.726(3)
1.250(4)
1.401(5)
1.470(5)
1.447(4)
1.283(5)
1.406(5)
1.446(4)
1.363(4)
1.436(4)
1.458(5)
C(1)–N(1)–C(13)
C(1)–N(1)–C(14)
C(13)–N(1)–C(14)
N(3)–N(2)–C(4)
O(1)–N(3)–N(2)
O(1)–N(3)–C(7)
N(2)–N(3)–C(7)
C(10)–N(4)–C(15)
C(10)–N(4)–C(16)
C(15)–N(4)–C(16)
N(2)–C(4)–C(3)
N(2)–C(4)–C(5)
C(3)–C(4)–C(5)
115.9(3)
114.8(3)
111.0(3)
119.3(3)
126.9(3)
116.5(3)
116.6(3)
121.9(3)
120.7(3)
117.4(3)
112.0(3)
130.1(3)
117.8(3)
116.6(3)
115.1(3)
110.4(3)
119.9(3)
125.9(3)
117.8(3)
116.3(3)
121.5(3)
119.2(3)
116.3(3)
129.4(3)
112.6(3)
117.9(3)
respect to the azoxy group (Fig. 1). The two molecules however
differ in the mutual orientation of the dimethylaminoazoxy-
benzene and dimethylaminochlorobenzene moieties, as
indicated by the value of the C(1) ؒ ؒ ؒ C(4) ؒ ؒ ؒ C(7) ؒ ؒ ؒ C(10)
pseudo torsion angle (158.1(10) and Ϫ173.6(9)Њ for molecules A
and B, respectively). Bond distances and angles within the
azoxy group are in agreement with those reported in the
literature (Table 3). In particular, the N(2)᎐N(3) (1.273(4) and
Molecule A: C(5) ؒ ؒ ؒ O(1), 2.715(4) Å; H(5) ؒ ؒ ؒ O(1), 2.15 Å;
C(5)–H(5) ؒ ؒ ؒ O(1), 117.8Њ; C(12) ؒ ؒ ؒ O(1), 2.670(5) Å;
H(12) ؒ ؒ ؒ O(1), 2.34 Å; C(12)–H(12) ؒ ؒ ؒ O(1), 100.4Њ;
C(8) ؒ ؒ ؒ N(2), 2.757(5) Å; H(8) ؒ ؒ ؒ N(2), 2.47 Å; C(8)–
H(8) ؒ ؒ ؒ N(2), 97.9Њ. Molecule B: C(3) ؒ ؒ ؒ O(1), 2.705(4) Å;
᎐
1.283(5) Å), C(7)–N(3) (1.456(5) and 1.446(4) Å), C(4)–N(2)
(1.422(5) and 1.406(5) Å) and N(3)–O(1) (1.253(5) and 1.250(4)
Å) bond lengths are consistent with the presence of electron
delocalization Nϩ
OϪ in the N-oxide group. In order to avoid
excessively short distances between ortho hydrogen atoms of
the aromatic rings and the azoxy group, the aromatic rings in
both independent molecules are not strictly coplanar, the
dihedral angle formed by the mean planes through the
Cl(1),C(1) ؒ ؒ ؒ C(6) chlorobenzene ring and the C(7) ؒ ؒ ؒ C(12)
benzene ring being 5.7(1) and 11.9(1)Њ for molecules A and B,
respectively. In this conformation the interatomic distances
involving the ortho hydrogen atoms and the azoxy group are:
H(3) ؒ ؒ ؒ O(1),
C(12) ؒ ؒ ؒ O(1), 2.696(4) Å; H(12) ؒ ؒ ؒ O(1), 2.39 Å; C(12)–
H(12) ؒ ؒ ؒ O(1), 99.2Њ; C(8) ؒ ؒ ؒ N(2), 2.748(5) Å;
H(8) ؒ ؒ ؒ N(2), 2.45 Å; C(8)–H(12) ؒ ؒ ؒ N(2), 98.6Њ.
The deviation from coplanarity is reflected also in a sig-
nificant deviation from the ideal values of the bond angles
involving the C(4) carbon atom of the chlorobenzene ring
(Table 3).
2.15
Å;
C(3)–H(3) ؒ ؒ ؒ O(1),
117.2Њ;
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 3 7 6 8 – 3 7 7 1
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Discussion
Reaction of indoles 3–6 and indolizine 7 with salt 2. General
procedure
The reactions here described demonstrate once again that
activated nitrosoarenes having an electron donating group in a
conjugated position, such as nitrosoindoles or N,N-dimethyl-p-
nitrosoaniline 1, react with nucleophiles in the nitrenium form
giving rise to a new nitrogen–carbon bond. This mechanism
was observed in almost all the reactions studied, affording
compounds 8, 10, 13 and 15, and already described elsewhere.1,8
These results are also in agreement with AM1 calculations,1
which showed that the most positive position for a non-
hindered nucleophilic attack is represented by the nitrogen
of the nitroso group. The formation of 4,4Ј-bis(dimethylamino)-
azoxybenzene 9, isolated almost in all cases, and of compounds
11, 12 and 14, could be likely explained by an electron transfer
process, which could be in competition with the ionic pathway
mentioned above.11 Moreover, on the basis of the obtained
products, the electron transfer process seems to be the only
possible mechanism in the case of 2-methylindole 5.13 The
reduction potential of N,N-dimethyl-p-nitrosoaniline 1 (0.392
V vs. SCE at pH 2.3)14 and the oxidation potentials of nucleo-
philes 3, 4, 5, 6 and 7 (0.73,15 0.57 (see Experimental), 0.46,16
0.64,17 0.21517 V vs. Ag/Agϩ in MeCN, respectively) are in
agreement with an outer-sphere electron transfer process,
except for indoles 3 and 6.18 However, there is no linear corre-
lation between the redox potentials of the reagents and the
extent of the electron transfer process (in the case of indolizine
7, which has the lowest oxidation potential, the electron trans-
fer process should be the most favourable),18 probably because
the two mechanisms (ionic and radical) depend strongly on
kinetic factors. In the case of nucleophiles 3 and 6 an inner-
sphere electron transfer could also be possible as discussed
previously.19
In order to gain more insight into the unexpected formation
of the chlorinated azoxybenzene 11, its probable precursor 9
was reacted with chloride anion (which is formed in the reaction
medium): compound 11 was however not obtained. Azoxy
derivative 9 was then reacted with a donor of positive chlorine
such as N-chlorobenzotriazole (NCBT)20 in 1 : 1 ratio, and this
time compound 11 was isolated in quantitative yield. In the
main reactions the chlorinating agent could be molecular
chlorine formed in the reaction medium by oxidation of the
chloride ion promoted by the protonated salt 2.21 To verify this
hypothesis, the azoxy derivative 9 was then reacted with
molecular chlorine, generated from hydrochloric acid and
potassium permanganate, and the chlorinated-azoxy 11 was
isolated together with compound 16, probably because of the
chlorine excess used. All these results confirm that compound
11 was formed by chlorination of compound 9.
Benzoyl chloride (0.5 mmol in 10 ml of MeCN) was added
dropwise and under magnetic stirring to a solution of N,N-
dimethyl-p-nitrosoaniline (0.5 mmol in 20 ml of MeCN) cooled
at ca. 5 ЊC with an ice/water bath. The green colour of the
nitroso compound became lighter and a yellow precipitate of
salt 2 formed. A solution of the nucleophile (0.5 mmol in 15 ml
of MeCN) was then added dropwise to this mixture under
stirring. After 3 h the reaction was worked up.
In the case of indoles 3, 4 and 5 the reaction mixture was
poured into 10% NaOH (50 ml) and extracted with toluene
(2 × 50 ml). The organic layer was washed with water
(2 × 30 ml), dried with Na2SO4 and evaporated to dryness;
the residue was then chromatographed on a silica gel column
eluting with cyclohexane–ethyl acetate 9 : 1.
In the case of nucleophiles 6 and 7 the reaction mixture was
treated with an excess of 10% NaClO4 under stirring and the
solution was kept overnight. The sodium chloride formed was
then filtered off and the solution reduced to a small volume.
By addition of dry diethyl ether the perchlorate salt 13 or 15
(respectively) was precipitated, filtered off and crystallized
from chloroform–diethyl ether. The filtrate was evaporated to
dryness and chromatographed on a silica gel column eluting
with cyclohexane–ethyl acetate 9 : 1.
The reaction with indoles 3, 4 and 5 was also carried out in
chloroform under the same conditions and the results were
almost the same.
Compounds 88 (N,N-dimethyl-NЈ-(2-phenylindol-3-ylidene)-
benzene-1,4-diamine), 910 {[4-(4-dimethylaminophenyl-ONN-
azoxy)phenyl]dimethylamine}, 1211 (2,2Ј-dimethyl-1H,1ЈH-
[3,3Ј]biindolyl) and 1412 (1,1Ј-dimethyl-2,2Ј-diphenyl-1H,1ЈH-
[3,3Ј]biindolyl) were identified by comparison with authentic
samples. Analysis and spectroscopic data of isolated products
are reported below.
N,N-Dimethyl-NЈ-(2-phenylindol-3-ylidene)benzene-1,4-
diamine 8:8 mp 214–215 ЊC (from benzene–petroleum ether);
νmax/cmϪ1 1600 (C᎐N); δ (200 MHz; CDCl ; Me Si) 3.08 (6H, s,
᎐
H
3
4
NMe2), 6.84 (2H, A2B2, J 9.0, Ph), 7.01 (1H, dt, J 7.6 and 1.2,
Ph), 7.20 (2H, A2B2, J 9.0, Ph), 7.46 (6H, m, Ph), 8.41 (2H, m,
Ph); m/z (EI) 325 (Mϩ, 5), 311 (3), 283 (12), 205 (4), 69 (100).
N-(2-tert-Butylindol-3-ylidene)-NЈ,NЈ-dimethylbenzene-1,4-
diamine 10: mp 137–138 ЊC (from benzene–petroleum ether);
(Found: C, 78.58; H, 7.62; N, 13.73. Calc. for C20H23N3: C,
78.651; H, 7.5905; N, 13.7583%); νmax/cmϪ1 1588 (C᎐N), 1547,
᎐
1513; δH (200 MHz; CDCl3; Me4Si) 1.54 (9H, s, But), 3.03 (6H,
s, NMe2), 6.78 (2H, A2B2, J 9.0, Ph), 7.05 (2H, A2B2, J 9.0, Ph),
6.65–7.45 (4H, m, Ph); m/z (EI) 305 (Mϩ, 100%), 290 (33), 275
(18), 262 (21), 248 (27), 185 (4), 171 (9).
[2-Chloro-4-(4-dimethylaminophenyl-ONN-azoxy)phenyl]-
dimethylamine 11: mp 97–98 ЊC (from ligroin 60–80 ЊC);
(Found: C, 60.31; H, 6.12; N, 17.53. Calc. for C16H19ClN4O: C,
60.279; H, 6.0071; N, 17.5743%); νmax/cmϪ1 1592 (N(O)᎐N),
᎐
1177 (N O); δH (200 MHz; CDCl3; Me4Si) 2.90 (6H, s, NMe2),
3.07 (6H, s, NMe2), 6.67 (2H, A2B2, J 9.3 and 1.7, Ph), 7.08 (1H,
d, J 9.8, Ph), 8.10 (1H, dd, J 9.8 and 2.0, Ph), 8.17 (2H, A2B2,
J 9.3 and 1.7, Ph), 8.33 (1H, d, J 2.0, Ph); m/z (EI) 320 (Mϩ,
19%), 318 (Mϩ, 54), 168 (50), 135 (32), 133 (100), 120 (69).
3-(4-Dimethylaminophenylimino)-1-methyl-2-phenyl-3H-
indolium perchlorate 13: mp 174–176 ЊC (from chloroform–
diethyl ether); (Found: C, 62.83; H, 5.08; N, 9.50. Calc. for
C23H22N3ClO4: C, 62.799; H, 5.0409; N, 9.5524%); νmax/cmϪ1
Experimental
Melting points are not corrected and were measured by an
electrothermal apparatus. IR spectra were recorded in Nujol on
a Perkin Elmer Spectrum MGX1 spectrophotometer equipped
with a Spectra Tech. “Collector” for DRIFT measurements. 1H
NMR spectra were recorded at room temperature in CDCl3 or
DMSO-d6 on a Varian Gemini 200 spectrometer (δ in ppm
referred to tetramethylsilane). Mass spectra were recorded on a
Carlo Erba QMD 1000 spectrometer in EIϩ mode. Elemental
analyses of the new compounds were performed with a Carlo
Erba CHNSO E.A. 1108 elemental analyser.
1610 (C᎐N); δ (200 MHz; DMSO-d6; Me4Si) 3.03 (6H, s,
᎐
H
NMe2), 3.97 (3H, s, NMe), 6.96 (2H, m, Ph), 7.3–7.7 (9H, m,
Ph), 7.90 (1H, d, J 7.7, Ph), 8.02 (1H, d, J 7.8, Ph); m/z (EI) 341
(Mϩ Ϫ ClO4ϩ1, 100%), 327 (33), 221 (9), 207 (26).
Compounds 1, 3, 5 and 6 were purchased from Aldrich.
Compounds 419 and 722 were prepared according to the liter-
ature reports.
1-(4-Dimethylaminophenylimino)-3-methyl-2-phenyl-1H-
indolizinylium perchlorate 15: mp 200–201 ЊC (from chloro-
form–diethyl ether); (Found: C, 62.78; H, 5.05; N, 9.59. Calc.
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 3 7 6 8 – 3 7 7 1
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for C23H22N3ClO4: C, 62.799; H, 5.0409; N, 9.5524%); νmax/cmϪ1
0.32 × 0.35 × 0.47 mm. The structure was solved by direct
1610 (C᎐N); δH (200 MHz; DMSO-d6; Me4Si) 2.58 (3H, s, Me),
methods (SIR9723) and anisotropically refined for all the non-H
atoms. The hydrogen atoms were located from a difference
Fourier map and thereafter allowed to ride on their attached
atoms with isotropic displacement parameter 1.2 greater than
the Ueq of the attached atom. The structure was refined on F 2
values (SHELXL9324) by using the weighting scheme w = 1/σ2-
᎐
3.10 (6H, s, NMe2), 6.65 (2H, br s, Ph), 7.08 (2H, br s, Ph), 7.32
(2H, br s, Ph), 7.43 (3H, br s, Ph), 8.01 (1H, td, J 6.4 and 1.6,
Ph), 8.31 (1H, br d, J 7.2, Ph), 8.39 (1H, t, J 7.4, Ph), 9.10 (1H,
d, J 6.2, Ph); m/z (EI) 341 (Mϩ Ϫ ClO4ϩ1, 34%), 326 (11), 221
(8), 206 (13).
2
(Fo ). For 5243 unique reflections having I > 0 collected
at T = 296(2) K on an Enraf-Nonius CAD4 diffractometer
(3 < 2θ < 140Њ) and corrected for absorption the final R is
0.050 (wR2 = 0.073; S = 0.870). Further details concerning the
X-ray diffraction study on crystalline compound 11 are given in
Table 2.
Reaction of compound 9 with N-chlorobenzotriazole
Compound 9 (71 mg, 0.25 mmoles, in 5 ml of CHCl3) and
N-chlorobenzotriazole (39 mg, 0.25 mmoles, in 5 ml of CHCl3)
were mixed at room temperature. After 30 min the reaction
solution was evaporated to dryness and the residue was
chromatographed on silica gel TLC plates eluting with cyclo-
hexane–ethyl acetate 9 : 1. Compound 11 and benzotriazole
were isolated almost quantitatively.
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(10%).
[2-Chloro-4-(3-chloro-4-dimethylaminophenyl-ONN-azoxy)-
phenyl]dimethylamine 16: mp 106–108 ЊC (from ligroin 60–
80 ЊC); (Found: C, 54.42; H, 5.10; N, 15.85. Calc. for C16H18-
Cl2N4O: C, 54.402; H, 5.1361; N, 15.8606%); νmax/cmϪ1 1585
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J. Chem. Soc., Perkin Trans. 2, 1984, 1281–1284.
(N(O)᎐N), 1130 (N O); δH (200 MHz; CDCl3; Me4Si) 2.93
᎐
(12H, s, NMe2), 7.07 (1H, d, J 9.0, Ph), 7.09 (1H, d, J 8.8, Ph),
8.12 (1H, dd, J 8.9 and 2.9, Ph), 8.13 (1H, dd, J 9.0 and 2.2, Ph),
8.31 (1H, d, J 2.8, Ph), 8.38 (1H, d, J 2.2, Ph); m/z (EI) 356
(Mϩ, 3%), 354 (Mϩ, 7), 352 (Mϩ, 24), 254 (3), 184 (6), 168 (60),
133 (100), 118 (12).
Electrochemical measurements
14 D. W. Leedy and R. N. Adams, J. Electroanal. Chem., 1967, 14,
The oxidation potential of compound 4 was measured at room
temperature under nitrogen in a three-electrode cell, using
5 × 10Ϫ3 M acetonitrile solutions containing 0.1 M tetraethyl-
ammonium perchlorate (TEAP). Cyclic voltammetric experi-
ments were performed at sweep rate 0.5 V sϪ1 using a stationary
platinum disk (AMEL 492) of about 1 mm diameter as working
electrode, a platinum wire as auxiliary electrode and a Ag/0.1 M
AgClO4 electrode as reference. The experiments were performed
using a multipolarograph AMEL 472/WR coupled with a
digital x/y recorder AMEL 863.
119–122.
15 C. Berti, L. Greci, R. Andruzzi and A. Trazza, J. Org. Chem., 1982,
47, 4895–4899.
16 R. J. Waltmann, A. F. Diaz and J. Bargon, J. Phys. Chem., 1984, 88,
4343–4346.
17 M. Colonna, L. Greci, M. Poloni, G. Marrosu, A. Trazza,
F. P. Colonna and G. Distefano, J. Chem. Soc., Perkin Trans. 2, 1986,
1229–1231.
18 L. Eberson, in Electron Transfer Reactions in Organic Chemistry,
Springer Verlag, Berlin, 1987, p. 22.
19 P. Carloni, L. Greci, M. Iacussi, M. Rossetti, P. Cozzini and
P. Sgarabotto, J. Chem. Res. (S), 1998, 232–233; (M), 1998,
1121–1152.
20 C. W. Rees and R. Storr, J. Chem. Soc. (C), 1969, 1474–1477.
21 The hydrochloric acid formed during the reaction may promote the
protonation of salt 2, increasing its oxidation power; the protonated
salt 2 reacting with chlorine ion could simulate the reaction carried
out with KMnO4 and HCl.
Crystal structure of [2-chloro-4-(4-dimethylaminophenyl-ONN-
azoxy)phenyl]dimethylamine 11‡
C16H19ClN4O, Mr = 318.8, monoclinic, space group P21/n, a =
25.207(4), b = 7.631(2), c = 17.000(3) Å, β = 95.50(10)Њ, V =
3255.0(13) Å3, Z = 8, ρ = 1.301 g cmϪ3; λ(Cu-Kα) = 1.54178 Å,
µ(Cu-Kα) = 21.35 cmϪ1: pale yellow prism, crystal dimensions
22 M. Colonna, P. Bruni and A. Monti, Gazz. Chim. Ital., 1964, 94,
509–520.
23 A. Altomare, M. C. Burla, M. Camalli, G. Cascarano,
C. Giacovazzo, A. Guagliardi, A. G. G. Moliterni, G. Polidori and
R. Spagna, J. Appl. Crystallogr., 1999, 32, 115–119.
24 G. M. Sheldrick, SHELXL93. Program for crystal structure
refinement, University of Göttingen, Germany, 1993.
‡ CCDC reference number 213658. See http://www.rsc.org/suppdata/
ob/b3/b308088a/ for crystallographic data in .cif or other electronic
format.
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 3 7 6 8 – 3 7 7 1
3771