508 J. CHEM. RESEARCH (S), 1999
J. Chem. Research (S),
1999, 508^509y
Solid State Photolysis of Triazene 1-Oxides with
Naphthols. Synthesis of Azo Dyesy
Shaaban K. Mohamed* and A. M. Nour El-Din
Chemistry Department, Faculty of Science, El-Minia University, El-Minia, Egypt
Sunlight irradiation of solid mixed crystals of the photolabile triazene 1-oxides and a- or b-naphthol afford azo
dyes.
Almost all the energy received by the earth comes from the
sun which is not only a cheap and continuous energy source
but also has no waste product problems. As a result, solar
energy applications have acquired great importance. It is
well known that sunlight can be used directly in many
chemical reactions and syntheses.1
The aryldiazenyl radical has been postulated as an
intermediate. Therefore it seemed that it was interesting
to examine the possibility of the use of sunlight directly
to irradiate the photolabile 1,3-diaryltriazene 1-oxides 1a^d
in the presence of a- and b-naphthols in the solid state
hoping that azo dyes may be formed via coupling between
the probable formed diazonium radical species and a- or
b-naphthol.
Thus, on exposure of equimolecular mixtures of the oxide
and of 1-a-naphthol and 2-b-naphthol (see experimental) to
sunlight, the mixtures gradually changed to deep red.
The photoreactions were monitored by thin layer chroma-
tography. After 7^10 h, the reaction mixture was dissolved
in acetone and separated on a preparative thin layer
chromatoplate using a 1 : 10 mixture of ethyl acetate:
toluene as eluent to a¡ord the azo dyes as the sole products.
The structures of the azo dyes 3a^d (83^93%) and 4a^c
(69^81%) were established from comparison of their melting
points and their IR spectra with those of authentic samples.
The formation of the products 3a^d and 4a^c may arise
from an initial hydrogen shift to give the tautomeric
hydroxy form, which undergoes N^N bond ¢ssion forming
the N-phenylhydroxylaminyl radical 5 and the correspond-
ing aryldiazenyl radical 6. The latter could attack the more
active phenolic ring at the ortho position to give the adducts
7 and 8 which in turn may lose a hydrogen radical to a¡ord
the corresponding azo dyes 3a^d and 4a^c.
Recently,2 the solid state photoreactions, photoaddition,
hydrogen abstraction and condensation between two di¡er-
ent organic compounds, have been reported. Here we report
our results of the solid state photolysis of mixtures of
1,3-diaryltriazene 1-oxides or a- and b-naphthols with direct
sunlight.
In previous works3;4 we have shown that the treatment of
1,3-diaryltriazene 1-oxides with oxalyl chloride in dry tolu-
ene at room temperature gave only solid arenediazonium
chlorides, while their photolysis in aromatic and
non-aromatic solvents, led to the formation of
2-hydroxyazobenzene, mono- and di-substituted biaryls.
N
N
N+
O–
Ph
N
Ar
Ph
N
N
Ar
H
O H
1a–d
1a Ar = Ph
b Ar = p-MeC6H4
Sunlight hν
c Ar = p-MeOC6H4
d Ar = p-ClC6H4
Ar
N•
+
Ph N• OH
Experimental
N
6
5
The triazene 1-oxides were prepared according to literature
methods.5 All melting points were recorded on a Galenkamp melting
point apparatus and are uncorrected. Preparative TLC were carried
out on air-dried 1 mm layers of silica gel Merck PF254 on plates 20 cm
by 48 cm.
OH
OH
Preparative Photolysis.öMixing of 1 mmol of triazene 1-oxide 1
with 1 mmol of a- or b-naphthol in acetone followed by evaporation
gave the mixed crystals. These were ¢nely ground in a morter, spread
on petri dishes and directly exposured to sunlight. TLC examination
showed that the reactions were ¢nished within 7^10 h. The tempera-
Ar
OH
H
N
N
OH
H
N
N
Ar
Table 1 Melting point and yields of 3a^d and 4a^c
8
7
–H•
–H•
Compound
Yield(%)
91
Colour
Mp/ 8C
OH
3a
scarlet red
132
Ar
(132^133)a
133
N
N
3b
3c
3d
4a
4b
4c
93
83
87
73
69
81
deep red
red
(133^134)a
140
OH
(139^140)b
156
N
N
bright red
brown
Ar
(155^157)b
183
4a–c
3a–d
(182^184)c
193
Scheme 1
deep brown
brown
(193^194)c
171
* To receive any correspondence.
(170^172)c
y This is a Short Paper as de¢ned in the Instructions for Authors,
Section 5.0 [see J. Chem. Research (S), 1999, Issue 1]; there is
therefore no corresponding material in J. Chem. Research (M).
aRef. 6. bRef. 7. cRef. 8.
Mohamed, Shaaban K.
