166 J. CHEM. RESEARCH (S), 1997
J. Chem. Research (S),
1997, 166–167†
Reaction of Triazene 1-Oxides: Novel Synthesis of Solid
Arenediazonium Chlorides†
Shaaban K. Mohamed,* Mohsen A.-M. Gomaa and Ahmed M. Nour El-Din
Chemistry Department, Faculty of Science, El-Minia University, El-Minia, A. R. Egypt
Treatment of 1,3-diaryltriazene 1-oxides with oxalyl chloride in dry toluene at room temperature gives only solid
arenediazonium chlorides; however, treatment with acetyl and benzoyl chlorides does not afford the corresponding
diazonium chlorides.
In previous reports1,2 we have shown that 1,3-diaryltriazene
1-oxides form stable charge-transfer complexes (1:1) with the
electron-deficient tetracyanoethylene in different solvents.1
The photolysis of these 1,3-dipoles in aromatic and non-
aromatic solvents leads to their decomposition2 giving
2-hydroxyazobenzene and mono- and di-substituted biaryls.
These results prompted us to study the reactivity of these
oxides towards different chemical reagents. Here we report
the results of our investigations of the effect of acid chlorides
on 1,3-diaryltriazene 1-oxides. It has been reported3 that the
analogous 1,3-dipoles, nitrones, rearranged to the isomeric
amides on treatment with acetyl chloride. However the reac-
tion of N-aryl nitrones with oxalyl chloride led to the intro-
duction of the chlorooxalyl group at the ortho position of the
N-aryl group.4
The physical and spectral properties of the diazonium salts
3a–i are summarised in Table 1. The well known instability of
diazonium compounds is one of their outstanding character-
istics, and they usually explode on heating above their melt-
ing points, a property which complicates both their analyses
and mass spectral fragmentation. The IR spectra of 3a–i in
KBr disks showed a sharp absorption characteristic of the
diazonium group sǹNuN at 2250–2280 cmꢀ1. Because of
1
the instability of the diazonium salt, the H NMR spectra
could not be recorded. Chemical evidence for the diazonium
salt structure was provided by coupling the salts 3a,d,g,i with
an ethanolic alkaline solution (NaOH) of 2-naphthol, which
afforded the corresponding azo dyes5,6 4a,d,g,i (Scheme 1).
Chromatographic separation of the mother liquors did not
give any pure compounds.
A rationale for the formation of the arenediazonium salts
3a–i is presented in Scheme 2. It is expected from the dipolar
nature of the triazene 1-oxides that the oxygen of the azoxy
function will behave as a nucleophile and may attack the
electron-deficient carbonyl carbon of the oxalyl chloride to
In the present work, the reaction of the 1,3-dipoles
1,3-diaryltriazene 1-oxides 1a–i with acid chlorides behaved
differently. Addition of oxalyl chloride to the 1,3-dipoles 1a–i
in dry toluene at room temperature gave only the arenediazo-
nium chlorides in good yields (80–95%), Table 1.
Table 1 Physical and spectral data of diazonium chlorides 3a–i
Compound
3
Yield
(%)
Mp
°C
Colour
v
max (KBr)/cmꢀ1
a
b
c
d
e
f
93
80
86
80
87
95
90
80
83
89
White
Pink
59 (decomp.)
3000 (Ar–CH), 2280 (–NǹuN)
71–72
79–80
65
60–61
70–72
74–75
133–135
75–77
87–88
3000 (Ar–CH), 2900 (aliph-CH), 2255 (–NǹuN)
3030 (Ar–CH), 880 (aliph-CH), 2260 (–NǹuN)
3030 (Ar–CH), 2850 (aliph-CH), 2250 (–NǹuN)
3010 (Ar–CH), 2900 (aliph-CH), 2255 (–NǹuN)
3030 (Ar–CH), 2885 (aliph-CH), 2265 (–NǹuN)
3000 (Ar–CH), 2800 (aliph-CH), 2280 (–NǹuN)
3000 (Ar–CH), 2265 (–NǹuN), 775 (C–Cl)
3030 (Ar–CH), 2280 (–NǹuN), 800 (C–Cl)
3030 (Ar–CH), 2260 (–NǹuN), 780 (C–Cl)
Buff
Brown
White
White
Grey
Orange
Brown
White
g
h
i
j
N
form the dipoles 5a–i. Proton shift followed by decomposi-
tion of 6a–i may give rise to the diazonium salts 3a–i, chloro-
oxalic acid 7 and nitrene 8. In previous work7 on the thermal
characterization of triazene 1-oxides, we succeeded in cap-
turing the nitrene species 8 which underwent dimerisation to
form azobenzene in low yield (0.01%; GC–MS analysis). It
was too difficult to separate the dimer by preparative TLC.
However, the chloroxalic acid 7 could not be separated and
although there are plenty of reports8 on this acid, reference to
explain the separation was not found.
In contrast to the oxalyl chloride reaction, treatment of
triazene 1-oxides 1a–i with acetyl chloride and benzoyl
chloride did not give the corresponding arenediazonium salts
but instead gave resins. Chromatographic separation gave
decomposed compounds in small quantities, which could not
be isolated in a pure form.
Cl
Cl
O
O
Ar
N
N
N
Ph
+
H
O
1a–j
solvent R.T.
Ar
N
HO
HO
+
Ar
N
N Cl–
NaOH
3a–j
4a,d,g,j
1,3,4a Ar = Ph
f
Ar = 3-MeOC6H4
Ar = 4-MeOC6H4
Ar = 2-ClC6H4
Ar = 3-ClC6H4
Ar = 4-ClC6H4
b
c
d
e
Ar = 2-MeC6H4
Ar = 3-MeC6H4
Ar = 4-MeC6H4
Ar = 2-MeOC6H4
g
h
i
j
Scheme 1
Experimental
All melting points were recorded on a Galenkamp melting point
apparatus and are uncorrected. Oxalyl chloride, benzoyl chloride
and acetyl chloride were obtained from Aldrich. Toluene was dis-
tilled and dried following the method of Vogel.9 Triazene 1-oxides
1a–i were prepared according to literature methods.10 IR spectra
*To receive any correspondence.
†This is a Short Paper as defined in the Instructions for Authors,
Section 5.0 [see J. Chem. Research (S), 1997, Issue 1]; there is there-
fore no corresponding material in J. Chem. Research (M).