1-Aryl-3,3-dialkyltriazenes: A convenient synthesis from dry arenediazonium o-benzenedisulfonimides - A high yield break down to the starting dry salts and efficient conversions to aryl iodides, bromides and chlorides

Article abstract of DOI:10.1055/s-2001-18072

This research comprises three parts. The first part regards the synthesis of 1-aryl-3,3-dialkyltriazenes 3 by reaction of dry arenediazonium o-benzenedisulfonimides 1, also coming from weakly basic aromatic amines with dimethylamine or diethylamine in aqueous solution at 0-5 °C. Yields were usually greater than 90% and there was the possibility of recovering the o-benzenedisulfonimide (5), which could be reused to prepare the salts 1. In the second part it was demonstrated that there is the possibility of reconverting the triazenes 3 into the starting stable dry salts 1 by using 5 as acid. The reactions were carried out in glacial acetic acid at 50-55 °C and normally afforded salts 1 in yields of around 90-99%. The third part concerns the setting up of two procedures for the conversion of 3 to aryl iodides 9, bromides 10 and chlorides 11. Procedure A used the corresponding aqueous hydrogen halides in acetonitrile at r.t. or 60 °C, sometimes in the presence of aqueous HBF₄, sometimes Cu powder (25 examples, yields 65%-88%). Procedure B usually used anhydrous methanesulfonic acid and tetraalkylammonium halides in anhydrous acetonitrile at temperatures varying from r.t. to 80 °C, sometimes in the presence of Cu (16 examples, yields 65-88%).

Full text of DOI:10.1055/s-2001-18072

2180
PAPER
1-Aryl-3,3-dialkyltriazenes: A Convenient Synthesis from Dry
Arenediazonium o-Benzenedisulfonimides – A High Yield Break Down to the
Starting Dry Salts and Efficient Conversions to Aryl Iodides, Bromides and
Chlorides
1
-Aryl-3,3-dialkyltriaz
a
enes: ACo
r
nvenient
g
S
ynthesis fr
h
om
D
ryAre
n
e
ediazonium
r
o
-
Benz
i
enedisu
t
lfonim
a
ides Barbero, Iacopo Degani,* Nicola Diulgheroff, Stefano Dughera, Rita Fochi*
Dip.to di Chimica Generale ed Organica Applicata dell’Università, C.so M. D’Azeglio 48, 10125 Torino, Italy
E-mail: fochi@ch.unito.it
Received 10 August 2001; revised 31 August 2001
It was within a wider investigation aimed at evaluating the
Abstract: This research comprises three parts. The first part re-
gards the synthesis of 1-aryl-3,3-dialkyltriazenes 3 by reaction of
dry arenediazonium o-benzenedisulfonimides 1, also coming from
weakly basic aromatic amines with dimethylamine or diethylamine
synthetic potential of the dry arenediazonium o-
benzenedisulfonimides2 1 that the present research was
undertaken, it consists of three parts: i) the setting up,
in aqueous solution at 0–5 °C. Yields were usually greater than 90% based on the use of dry arenediazonium o-benzenedisul-
and there was the possibility of recovering the o-benzenedisulfon-
fonimides 1, of a simple synthetic procedure for 1-aryl-
imide (5), which could be reused to prepare the salts 1. In the second
3,3-dialkyltriazenes 3, also valid for the preparation of un-
part it was demonstrated that there is the possibility of reconverting
known or difficult to obtain compounds; ii) break down of
the triazenes 3 into the starting stable dry salts 1 by using 5 as acid.
the triazenes 3 to the starting dry salts 1; iii) realisation of
The reactions were carried out in glacial acetic acid at 50–55 °C and
efficient procedures for converting, in aqueous or anhy-
drous organic solvents, the 1-aryl-3,3-dialkyltriazenes 3
into aryl iodides, bromides and chlorides, via the corre-
sponding arenediazonium salt intermediates.
normally afforded salts 1 in yields of around 90–99%. The third part
concerns the setting up of two procedures for the conversion of 3 to
aryl iodides 9, bromides 10 and chlorides 11. Procedure A used the
corresponding aqueous hydrogen halides in acetonitrile at r.t. or
60 °C, sometimes in the presence of aqueous HBF4, sometimes Cu
powder (25 examples, yields 65%-88%). Procedure B usually used
anhydrous methanesulfonic acid and tetraalkylammonium halides
With regard to 1-aryl-3,3-dialkyltriazenes synthesis, it
must first be said that numerous derivatives are known
in anhydrous acetonitrile at temperatures varying from r.t. to 80 °C, and in most cases, there is no great difficulty in obtaining
sometimes in the presence of Cu (16 examples, yields 65–88%).
them through the reaction of arenediazonium salts with
secondary aliphatic amines or cyclic amines like pyrroli-
dine or piperidine. Nevertheless there are several cases
where the synthesis of the 1-aryl-3,3-dialkyltriazenes is
quite troublesome. This is especially so when the diazoni-
um salts used come from weakly basic aromatic amines,
particularly nitroanilines or polyhalogenoanilines, that
can be diazotised only in very harsh conditions, which has
been optimised to obtain specific salts.3 This said, we be-
lieve it useful to develop a general method for the synthe-
sis of 1-aryl-3,3-dialkyltriazenes 3, the method being
based on the preliminary preparation of dry arenediazoni-
um o-benzenedisulfonimides 1 and a subsequent reaction
with aliphatic dialkylamines. The dry arenediazonium
salts 1a–l were easily prepared following a general meth-
od we had already developed and used to obtain many
salts.4 This method is extremely simple and fast and in-
volves the diazotization of primary aromatic amines with
i-pentyl nitrite in the presence of o-benzenedisulfonimide
(5) in glacial acetic acid (or formic acid) at 0–5 °C and the
isolation, by filtration, of the virtually pure salts that pre-
cipitate from the reaction medium. Like all the previously
prepared arenediazonium o-benzenedisulfonimides, also
the new dry salts 1f,h–l are obtained pure and in excellent
yields. They are extremely stable and can be safely stored,
ready for use, for unlimited times.
Key words: stable dry arenediazonium salts, triazenes, retro reac-
tions, radical reactions, aryl halides
Triazenes are a class of compounds of great interest.1
Their biological activity has been and still is, the subject
of numerous studies; several triazenes are chemothera-
peutic agents active against bacterial and especially, pro-
tozoal infections, while the 1-aryl-3,3-dimethyltriazenes
possess significant in vivo anti-tumor activity. For exam-
ple, wide therapeutic use is made of dacarbazine, i.e. 5-
(3,3-dimethyltriazeno)imidazole-4-carboxamide, as an
active principle against human malignant melanoma. Still
in the medical field, triazenes are used in the preparation
of radiolabeled materials, used as tracers in diagnostic
procedures. In technological applications, the ability of
triazenes to break down to yield, in situ, diazonium ions
with coupling properties is widely used to produce insol-
uble azo dyes directly on natural and synthetic fibres. Fi-
nally, the triazene group plays a significant role in organic
synthesis, being a protected form for both the diazonium
group and hence for all the functional groups deriving
from it and for the aromatic and aliphatic amines from
which it arose.
Synthesis 2001, No. 14, 26 10 2001. Article Identifier:
1437-210X,E;2001,0,14,2180,2190,ftx,en;Z09301SS.pdf.
© Georg Thieme Verlag Stuttgart · New York
ISSN 0039-7881
The 1-aryl-3,3-dialkyltriazenes 3a–l (R = Me, Et) were
prepared by reacting, at 0–5 °C, the salts 1a–l with dime-
thylamine or diethylamine 2 in aqueous solution, in the

PAPER
1-Aryl-3,3-dialkyltriazenes: A Convenient Synthesis from Dry Arenediazonium o-Benzenedisulfonimides
2181
presence of sodium hydroxide (molar ratio reaction. Nevertheless, to the best of our knowledge, in all
1:2:NaOH = 1:1.1:1) or absence (molar ratio 1:2 = 1:2.2) the cases reported in the literature, with only two excep-
(Scheme 1). The reactions went rapidly to completion and tions (i.e., 4-toluenediazonium trifluoroacetate and triflu-
the yields of the triazenes, virtually pure at the moment of oromethanesulfonate),7 the diazonium salts obtained from
isolation or easily purified by column chromatography, the triazenes were not isolated, but were left to react di-
were always very high, usually greater than 90% rectly in situ. Such methodology limits the synthetic po-
(Table 1). A relevant advantage of the procedure is the tential of diazonium salts obtained from triazenes, in that
possibility of recovering the o-benzenedisulfonimide (5) deprotection is normally carried out with acids and the re-
that can be reused to prepare the salts 1, the recovery sultant reaction medium can thus become incompatible
yields being between 88 and 99%.
for subsequent in situ reactions. On the contrary, after car-
rying out the desired reactions on substrates containing
the triazene moiety, the modified triazenes are converted
to the stable dry diazonium salts, they are able to fully ex-
press their synthetic potential. The present work achieved
this goal. In fact, the triazenes 3 were easily reconverted
to the corresponding dry arenediazonium o-benzenedisul-
fonimides 1, simply by adding them to a solution of the o-
benzenedisulfonimide (5) (molar ratio 1:5 = 1:2.2) in gla-
cial acetic acid or acetic acid–formic acid (9.7:0.3), main-
tained at 50–55 °C for 15–30 min. On cooling the reaction
mixture to 20–25 °C, the arenediazonium o-benzenedisul-
fonimides 1 precipitated spontaneously and could be col-
lected by filtration, normally in yields of around 90% to
99% (Experimental Section). High yields of the o-ben-
zenedisulfonimide (5) were easily recovered from the ace-
tic solution containing the dialkylammonium salts. The
only negative result concerned the triazene 3g.
With regard to the conversion of triazenes to aryl halides,
it must be noted that most of the work reported in the lit-
erature has been principally aimed at the preparation of
aryl iodides;8 little attention has been paid to aryl
bromides6,8b,9,10 and aryl chlorides are dealt with only ex-
ceptionally.6 The most significant procedures for the con-
version of the 1-aryl-3,3-dialkyltriazenes to aryl iodides
takes the following routes: i) break down of 3 with aque-
ous hydrochloric acid or trifluoroacetic acid in the pres-
ence of potassium iodide (5 examples, isolated product
yields: 51–66%);8a ii) conversion by the action of iodotri-
methylsilane in acetonitrile (4 examples, isolated product
yields: 65–92%);8b iii) treatment with sodium iodide and
a sulfonic acid cation-exchange resin in anhydrous aceto-
nitrile (10 examples, isolated product yields 72–95%);8c
iv) treatment with methyl iodide in a sealed tube at 100–
120 °C (9 examples, G.C. or isolated product yields >
94%);8d v) iodine-promoted decomposition in a sealed
tube at 80–100 °C in different solvents (6 examples, G.C.
yields: 85–98%).8e Considering the various procedures
developed in the past we have, to some extent, been sur-
prised by the fact that there is no mention in the literature
of the possibility of converting 1-aryl-3,3-dialkyltriazenes
to aryl iodides simply by aqueous hydroiodic acid treat-
ment. Available to us was the series of the 1-aryl-3,3-di-
alkyltriazenes 3a–l where, in most cases, the presence of
electron withdrawing groups on the aryl makes conver-
sion to aryl iodides via diazonium cations difficult; this
prompted us to attempt the conversion of such triazenes
by treating them with aqueous hydroiodic acid. This was
not so simple and in reality, we had to carry out many
Scheme 1
Relative to the break down of 1-aryl-3,3-dialkyltriazenes
3 to the starting dry salts 1, it was our intent to demon-
strate the possibility of reconverting the triazenes to dry
stable diazonium salts. As emphasised above, the triaz-
enes constitute a protected form of the diazonium group.1
In fact the triazene moiety combines extreme resistance to
basic hydrolysis with resistance to oxidants (PDC, H2O2,
peracids), metal hydrides (LiAlH4, NaBH4), hydrogena-
tion (Pd/C in MeOH), alkylating agents (MeI at r.t.), alkyl
lithium and lithium amide bases (s-BuLi, t-BuLi, LDA)
and Lewis acids (Ti(Oi-Pr)4).5,6 Consequently, numerous
reactions can be carried out on substrates containing the
triazene group, without any effect whatever on the func-
tional group itself. When necessary the triazene can be re-
converted to the diazonium salts, allowing further
Synthesis 2001, No. 14, 2180–2190 ISSN 0039-7881 © Thieme Stuttgart · New York

2182
M. Barbero et al.
PAPER
Table 1 1-Aryl-3,3-dialkyltriazenes 3a –l
Compd.a Ar
R
Chromato-
graphic
Yieldb Mpc (°C) or
MS m/z Yield(%) 1H NMR (CDCl3)
(%)
bp (°C)/mbar
(M+)
of 5
d (ppm), J (Hz)
solventd
recovered
f
f
f
3a
3b
3c
3d
4-MeOC6H4
Me
Me
Me
Et
PE–Et2O (9:1) 91
PE–Et2O (9:1) 90
141–142/1.5e
55.6–56.8e
179
183
194
245
92
98
96
97
4-ClC6H4
4-O2NC6H4
2,6-Cl2C6H3
CHCl3
86
142.6–143.7e
155/4.7¥10–3
g
90h
1.31 (t, 6 H, J = 7.1), 3.79 (q, 4 H,
J = 7.1), 6.97 (t, 1 H, J = 7.9), 7.29
(d, 2 H, J = 7.9)
g
3e
3f
2,6-Br2C6H3
Et
Et
95h
91
35.9–36.5
59.0–59.4
333
256
94
89
1.35 (t, 6 H, J = 7.1), 3.80 (q, 4 H,
J = 7.1), 6.82 (t, 1 H, J = 7.9), 7.52
(d, 2 H, J = 7.9)
2-Cl-4-
O2NC6H3
C–Et2O
(9.6:0.4)
1.35 (t, 6 H, J = 7.1), 3.88 (q, 4 H,
J = 7.1), 7.52 (d, 1 H, J = 8.0), 8.10
(dd, 1 H, J = 8.0, 2.0) 8.30 (d, 1 H,
J = 2.0)
g
3g
2,4-
(O2N)2C6H3
Me
94h
131.0–132.2
239
88
3.30 (s, 3 H), 3.75 (s, 3 H), 7.92 (d,
1 H, J = 8.0), 8.53 (dd, 1 H, J = 8.0,
2.0), 8.75 (d, 1 H, J = 2.0)
3h
3i
2,4,6-Cl3C6H2 Et
2,4,6-Br3C6H2 Et
PE–Et2O
(9.8:0.2)
93
92h
95
92
159/2.0¥10–3
191/2.0¥10–3
49.5–50.0
279
411
351
290
98
98
99
98
1.29 (t, 6 H, J = 7.1), 3.76 (q, 4 H,
J = 7.1),7.31 (s, 2H)
g
1.31 (t, 6H, J = 7.1), 3.77 (q, 4H, J
= 7.1),7.67 (s, 2 H)
3j
2,6-Br2-4-
FC6H2
Et
Et
PE–Et2O
(9.8:0.2)
1.32 (t, 6 H, J = 7.1), 3.82 (q, 4 H,
J = 7.1), 7.38 (d, 2 H, J = 8.0)
3k
2,6-Cl2-4-
O2NC6H2
PE–EtOAc
68.8–69.4
1.30 (t, 3 H, J = 7.1), 1.37 (t, 3 H,
J = 7.1), 3.81 (q, 4 H, J = 7.1), 8.19
(s, 2 H)
(9.8:0.2)i
3l
2,6-Br2-4-
O2NC6H2
Et
C–Et2O
(9.6:0.4)
94
82.4–83.3
378
97
1.25 (t, 3 H, J = 7.1), 1.31 (t, 3 H,
J = 7.1), 3.65 (q, 4 H, J = 7.1), 8,00
(s, 2 H)
a Satisfactory elemental analyses were obtained for all new triazenes 3d–l.
b Unless otherwise noted, yields refer to pure products isolated by column chromatography.
c Crystallization solvent: EtOH.
d PE = petroleum ether; C = cyclohexane.
e Lit.17: bp 59 °C/0.75mbar for 3a, mp 55–56 °C for 3b and mp 143–144 °C for 3c.
f 1H NMR data were identical to those reported.17
g The crude isolated product was virtually pure (TLC, 1H NMR).
h Yield of virtually pure product (TLC, 1H NMR).
i By flash chromatography.
tests, often with negative or misleading results, before In some cases almost all the triazene had already disap-
reaching a general procedure that was completely reliable peared by the end of the addition; extending the reaction
with regard to reproducibility and satisfactory yields. The time for a further 15 min brought the reactions to certain
difficulties we encountered could be why other authors completion (entries 1, 4, 7). The triazenes 3f, 3k and 3l
had given up on the use of aqueous hydroiodic acid. The (entries 18, 32 and 35) had significantly longer reaction
new procedure consists simply in adding, over a period of times, while the triazene 3g reaction was still incomplete
30 min, the triazenes 3 dissolved in acetonitrile to a solu- even after 24 hours (entry 21). In this last case the reaction
tion of aqueous hydroiodic acid in the same solvent, main- could be brought to completion by adding aqueous tetra-
tained at r.t. or heated at 60 °C and kept under vigorous fluoroboric acid that made the formation of the intermedi-
stirring (Scheme 2, Procedure A). The results are reported ate 2,4-dinitrobenzenediazonium cation easier and the
in Table 2.
overall reaction time was drastically reduced (entry 22).
Synthesis 2001, No. 14, 2180–2190 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
1-Aryl-3,3-dialkyltriazenes: A Convenient Synthesis from Dry Arenediazonium o-Benzenedisulfonimides
2183
Scheme 2
The addition of tetrafluoroboric acid was also useful in ac- the behaviour of the triazenes 3d, 3e, 3h and 3i. In fact in
celerating the reactions of 3f, 3k and 3l (entries 19, 33 and these cases the iododediazoniation process did not reach
36). With regard to these particular results it must be not- completion, not even on extending the reaction times to 24
ed, as is commonly admitted, that the conversion of 1- h at 60 °C, after the disappearance of the triazenes (test of
aryl-3,3-dialkyltriazenes in aryl iodides takes place azo coupling with 2-naphthol always positive; footnote h
through a two step process: first a heterolytic dissociative of entries 10, 14, 25 and 28). When the reactions were car-
process that gives rise to arenediazonium cations, the sec- ried out in the presence of aqueous tetrafluoroboric acid,
ond a homolytic iododediazoniation process.10 It is quite still at 60 °C, the process of iodedediazoniation was mark-
evident that the presence of electron withdrawing groups edly slower than the dissociative one; nevertheless the re-
(particularly nitro groups) on the aryl slows the first pro- actions reach completion after 24 h (entries 11, 15, 26 and
cess, that gives rise to the cationic species and instead, 29). The reaction times could be shortened, though the
favours the second process in that one-electron transfer in- yields were lowered slightly, by first carrying out the dis-
volved in the iododediazoniation is facilitated. The elec- sociation of the triazenes to the corresponding diazonium
tron donors on the aryl act in the opposite way. On the cations with aqueous tetrafluoroboric acid in acetonitrile
other hand it is well known that the iododediazoniation re- and then adding aqueous hydroiodic acid (entries 12, 16,
actions have a positive outcome regardless of the nature of 27 and 30). Despite the difficulties encountered, the con-
the substituents present on the aryl, even in the absence of ditions found for the conversion of the triazenes 3a–l into
a catalyst, in that the iodide ion itself is a good electron do- the corresponding aryl iodides 9 are simple and efficient.
nor.11 Therefore it was expected that the dissociative pro- The yields are certainly very good when compared with
cess would be the most difficult in the conversion of the those obtained by the other known methods, considering
1-aryl-3,3-dialkyltriazenes 3 containing strong electron the difficulties inherent in most of the chosen examples.
withdrawing groups, like the nitro group, to the corre-
sponding aryl iodides. What we did find surprising was
Table 2 Aryl Iodides 9, Aryl Bromides 10 and Aryl Chlorides 11 from Triazenes 3: Procedure A
Ta
(°C)
Timeb
(min)
Yield (%)c,d
Chromatog-
Entry
Compd. Ar
R
6
Acid
Cata-
lyst
raphic solvente
Ar–I
Ar–Br Ar–Cl
9
10
11
76f
68
1
2
3
4
5
6
7
3a
3b
3c
4-MeOC6H4 Me
HI
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
60
15
15
15
15
15
15
15
PE–Et2O (9:1)
PE–Et2O (9:1)
PE–Et2O (9:1)
PE
84
71f
88
HBr
HCl
HI
Cu
Cu
81f
4-ClC6H4
Me
HBr
HCl
HI
Cu
Cu
PE
79f
PE
4-O2NC6H4 Me
PE–Et2O (9:1)
Synthesis 2001, No. 14, 2180–2190 ISSN 0039-7881 © Thieme Stuttgart · New York

2184
M. Barbero et al.
PAPER
Table 2 Aryl Iodides 9, Aryl Bromides 10 and Aryl Chlorides 11 from Triazenes 3: Procedure A (continued)
Ta
(°C)
Timeb
(min)
Yield (%)c,d
Chromatog-
Entry
Compd. Ar
R
6
Acid
Cata-
lyst
raphic solvente
Ar–I
Ar–Br Ar–Cl
9
10
11
8
9
HBr
HClg
HI
60
60
60
60
15
PE–Et2O (9:1)
PE–Et2O (9:1)
PE
83f
Cu
Cu
Cu
15
85f
10
11
3d
2,6-Cl2C6H3 Et
30h,i
24 hi,k
59j (2)
83 (tr)l
HI
HBF4
aq.
12
HIm
HBF4
aq.
60
15
72 (tr)l
13
14
15
HBr
HI
r.t.
60
60
15
PE
PE
70 (15)
3e
2,6-Br2C6H3 Et
30h,i
24 hi,k
71j (tr)l
79 (11)
HI
HBF4
aq.
16
HIm
HBF4
aq.
60
15
73 (3)
17
18
HCl
HI
r.t.
60
15
PE
79 (12)
3f
2-Cl-4-
Et
7 h
PE–Et2O
(9.8:0.2)
74 (2)
74 (2)
O2NC6H3
19
20
21
22
HI
HBF4
aq.
60
60
60
60
30
HBr
HI
30
PE–Et2O
(9.8:0.2)
74 (9)
3g
2,4-
Me
24 h
4 h
PE–Et2O (4:1)
46n (1)
82 (tr)l
(O2N)2C6H3
HI
HBF4
aq.
23
24
HBr
60
60
4 h
PE–Et2O (4:1)
PE–Et2O (4:1)
82 (tr)l
HClo
HBF4
aq.
Cu
120
77 (5)
25
26
27
28
29
30
3h
2,4,6-
Cl3C6H2
Et
Et
HI
60
60
60
60
60
60
120h,i
24 hi,k
15
PE
54p (4)
86 (3)
75 (6)
60 (9)
84 (2)
74 (13)
HI
HBF4
aq.
HIm
HI
HBF4
aq.
3i
2,4,6-
Br3C6H2
120h,i
24 hi,k
15
PE
HI
HBF4
aq.
HIm
HBF4
aq.
31
3j
2,6-Br2-4-
FC6H2
Et
HI
60
90
PE–Et2O
(9.8:0.2)
71 (tr)l
Synthesis 2001, No. 14, 2180–2190 ISSN 0039-7881 © Thieme Stuttgart · New York

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1-Aryl-3,3-dialkyltriazenes: A Convenient Synthesis from Dry Arenediazonium o-Benzenedisulfonimides
2185
Table 2 Aryl Iodides 9, Aryl Bromides 10 and Aryl Chlorides 11 from Triazenes 3: Procedure A (continued)
Ta
(°C)
Timeb
(min)
Yield (%)c,d
Chromatog-
Entry
Compd. Ar
R
6
Acid
Cata-
lyst
raphic solvente
Ar–I
Ar–Br Ar–Cl
9
10
11
32
33
34
35
36
37
38
39
3k
2,6-Cl2-4-
O2NC6H2
Et
HI
60
60
r.t.
60
60
60
60
60
13 h
60
PE–Et2O
(9.8:0.2)
65 (9)
HI
HBF4
aq.
63 (2)
HBr
HI
3 dq
13 h
60
PE–Et2O
(9.8:0.2)
83 (tr)l
3l
2,6-Br2-4-
O2NC6H2
Et
PE–Et2O
(9.5:0.5)
79 (7)
74 (4)
HI
HBF4
aq.
HBr
HCl
HCl
120
7 h
PE–Et2O
(9.5:0.5)
94 (tr)l
Cu
Cu
PE–Et2O
(9.8:0.2)
74 (9)
82 (3)
HBF4
aq.
60
a r.t. = 20–25 °C.
b After the addition of triazenes 3.
c Yields refer to the pure (GC, GC-MS, TLC, 1H NMR) halides 9–11 isolated by column chromatography.
d Hydrodediazoniation products, that were present in all the reactions, were always isolated and in many cases also quantified; yields are re-
ported in parentheses. In entries 1–3, 4–6 and 7–9, anisole, chlorobenzene and nitrobenzene respectively were isolated but not quantified be-
cause no particular device was adopted to avoid their loss during the workup and the following chromatography.
e PE = petroleum ether.
f Arylation products of the obtained halides were sometimes identified by GC and GC-MS analyses of the crude reaction mixtures: entries 4,
5, 8 and 9 (MS: m/z = 348 (M+), 300 (M+), 322 (M+) and 278 (M+), respectively). Biaryls corresponding to the intermediate diazonium salts
were identified in entries 2, 3 and 5 (MS: m/z = 214 (M+), 214 (M+) and 222 (M+), respectively).
g As collateral proof the reaction was carried out in the absence of Cu. After 24 h at 60 °C, 1-chloro-4-nitrobenzene was obtained in only 51%
yield. By-products were nitrobenzene and 1,4-dichlorobenzene (4%).
h After this time a test of azo coupling with 2-naphthol was positive. It remained positive when the reaction mixture was heated at 60 °C for
24 h.
i The second step of iododediazoniation of the intermediate diazonium salts, i.e. 2,6-dichloro-, 2,6-dibromo-, 2,4,6-trichloro- and 2,4,6-tribro-
mobenzenediazonium salt, formed from the corresponding triazenes 3d, 3e, 3h and 3i in the first dissociative step, was very slow in these
reaction conditions. As collateral proof 2,4,6-tribromobenzenediazonium tetrafluoroborate18 reacted at once with aq HI in acetonitrile and the
corresponding iodide was obtained in 85% yield.
j Yield remained unvaried when the reaction was carried out at 60 °C for 24 h.
k A test of azo coupling with 2-naphthol was negative only after this time.
l tr = traces.
m Procedure A was modified as reported in the Experimental Section.
n The reaction was incomplete and 3g was recovered in 22% yield.
o As collateral proof the reaction was carried out in the absence of Cu. After 24 h at 60 °C, 1-chloro-2,4-dinitrobenzene and 2,4-dinitrobenzene
were obtained in 40% and 13% yield, respectively.
p When the reaction was carried out at 60 °C for 24 h, yield increased to 71%.
q At r.t. the dissociative step was very slow and after 3 days 3k was recovered in 8% yield. The reaction was also tried at 60 °C. It was com-
pleted after 150 min. However, GC and GC-MS analyses showed the presence of the expected bromide and of a chlorosubstitution product,
MS: m/z = 313 (M+), in a GC ratio of 3:1.
The procedure developed for the conversion of the 1-aryl- the conversion of the triazenes 3c,f,g,k,l into the corre-
3,3-dialkyltriazenes 3a–l in aryl iodides 9 was, after ap- sponding bromides (entries 8, 20, 23, 34 and 37). These
propriate adaptation, extended to the conversion of the last conversions could have a positive outcome in the ab-
same triazenes into the corresponding aryl bromides 10 sence of any catalyst as the presence of nitro groups on the
and/or chlorides 11. Aqueous hydroiodic acid was re- aryl of the triazenes 3c,f,g,k,l allowed electron transfer to
placed by aqueous hydrobromic or hydrochloric acid and the arenediazonium cations from the bromide anion, that
copper powder was added as catalyst (Table 2), except for has, as is known,11 a redox potential comparable to that of
Synthesis 2001, No. 14, 2180–2190 ISSN 0039-7881 © Thieme Stuttgart · New York

2186
M. Barbero et al.
PAPER
iodide and chloride anions. Also the conversions of the tri- procedure is based on the use of the dry arenediazonium
azenes 3a–l into the corresponding aryl bromides 10 and/ o-benzenedisulfonimides 1. Secondly, very high yields
or chlorides 11 resulted in very good yields.
were achieved in the break down of the triazenes 3, that
constitute a protected form of the diazonium group, to the
starting dry stable arenediazonium salts 1. Finally, two
new procedures have been developed for the conversion,
in high yield, of 1-aryl-3,3-dialkyltriazenes 3 into aryl io-
dides 9, bromides 10 and chlorides 11: one is based on the
use of aqueous hydrogen halides in acetonitrile, the other
realised in anhydrous acetonitrile with tetraalkylammoni-
um halides 7, in the presence of methanesulfonic acid or,
sometimes, tetrafluoroboric acid - diethyl ether complex.
Various by-products were produced alongside the aryl ha-
lides 9–11 in the studied conversions. The main ones were
the arenes (Ar-H) from the reductive dediazoniations;
these were always isolated and, in many cases, also quan-
tified. Some arylation products of the obtained halides, bi-
aryls corresponding to the intermediate diazonium salts
and various substitution products, were also present in
traces and were identified by GC and GC-MS analyses of
the reaction mixtures. There was never the presence of the
acetanilides corresponding to the salts 1 and this testifies
to the homolytic pathway of the halodediazoniation reac-
tion.12 No particular difficulties arose in separating the
aryl halides 9–11 from the by-products.
Column chromatography and TLC were performed on Merck silica
gel 60 (70–230 mesh ASTM) and GF 254, respectively, using the
eluents reported in the Tables. Petroleum ether (PE) refers to the
fraction boiling in the range 40–70 °C. Room temperature
(r.t.) = 20–25 °C. 1H NMR spectra were recorded on a Bruker
WP80SY spectrometer. All the reagents, anhyd MeCN and the ref-
erence compounds were purchased from the Aldrich Chemical Co.
Copper powder and Dowex 50X8 ion-exchange resin (H+) were
purchased from Carlo Erba and Fluka, respectively.
Still on the theme of triazene conversion of aryl iodides, it
can be observed that in one of the routes reported in the lit-
erature and cited above, the treatment with sodium iodide
and a sulfonic acid cation-exchange resin in anhydrous ac-
etonitrile was particularly efficient.8c Nevertheless, as the
procedure requires a very expensive resin, Bio-Rad AG
50W-X12, we modified it, replacing the resin with anhy-
drous methanesulfonic acid (Scheme 2, Procedure B).
Thus a new, convenient procedure was developed for the
conversion of several of the triazenes 3a–l, into the corre-
sponding aryl iodides 9. This procedure, adapted appro-
priately, was also successfully applied to the conversion
of some triazenes into the corresponding aryl bromides 10
and chlorides 11. The conversions were realised by react-
ing the triazenes 3 with methanesulfonic acid and tetra-
alkylammonium halides, i.e. tetrabutylammonium iodide
(7a), tetrabutylammonium bromide (7b) and benzyltrieth-
ylammonium chloride (7c), in anhydrous acetonitrile,
with or without copper as catalyst, at temperatures vary-
ing from r.t. to 80 °C (Table 3). In the case of 3g the con-
version to the corresponding iodide was incomplete, even
after 24 h at 60 °C (entry 11) while that to the bromide and
chloride, although requiring relatively long times, went to
completion (entries 13 and 15). By replacing methane-
sulfonic acid with a tetrafluoroboric acid - diethyl ether
complex the conversion of 3g to 9g and 10g proceeded ad-
vantageously, the complex being more efficient in catal-
ysing the dissociative process (entries 12 and 14). It
should be noted however, that in the conversion of 3g to
11g the catalytic action of the copper was annulled by the
tetrafluoroboric acid (Table 3, footnote h). Also in Proce-
dure B, the yields of the pure aryl halides 9–11 were al-
ways good, ranging from 65% to 88%. The physical
properties of all the aryl iodides, bromides and chlorides
obtained according to both Procedures A and B are listed
in Table 4.
o-Benzenedisulfonimide (5) was prepared according to the litera-
ture procedure,13 starting from o-benzenedisulfonyl chloride14 and
NH3 gas, via ammonium o-benzenedisulfonimide and its conver-
sion using Dowex 50X8 resin.15
Dry Arenediazonium o-Benzenedisulfonimides 1
Dry 2,6-Dibromo-4-nitrobenzenediazonium o-Benzene-
disulfonimide (1l); Typical Procedure
According to the procedure previously described by us for the prep-
aration of 1a–d4 and 1e,g,16 diazotization of 2,6-dibromo-4-nitroa-
niline (2.96 g, 10 mmol) was carried out with i-pentyl nitrite (1.29
g, 11 mmol) in the presence of o-benzenedisulfonimide (5; 2.63 g,
12 mmol) in glacial HOAc (60 mL) at 0–5 °C. A white precipitate
of 1l began to separate at once. Precipitation was completed by ad-
dition of anhyd Et2O (100 mL). The diazonium salt was gathered by
filtration on a Buchner funnel and washed several times on the fun-
nel with anhyd Et2O (6 ¥ 5–6 mL) to complete the elimination of
HOAc. After drying under reduced pressure, the dry titled com-
pound 1l was obtained in 97% yield (5.10 g). It was virtually pure
(NMR, dp = decomposition point) and could be used in the next
step, without further purification. For analytical purposes, a sample
was purified by dissolution in hot HCOOH and precipitation with
anhyd Et2O after cooling: dp 165 °C.
1H NMR (CF3COOD): d = 7.82 and 8.63 (2 m, 1:2).
Anal. Calcd for C12H6Br2N4O6S2 (526.13): C, 27.39; H, 1.15; Br,
30.37; N, 10.65; S, 12.19. Found: C, 27.40; H, 1.18; Br, 30.46; N,
10.57; S, 12.16.
Yields and physical and spectral data of the new compounds are
given below.
CAUTION! In our laboratory there was no case of sudden decom-
position during the preparation, purification, storage and handling
of salts 1. Nevertheless it must be born in mind that all diazonium
salts in the dry state are potentially explosive. Therefore they must
be manipulated carefully.
In conclusion, the results of this research can be sum-
marised as follows. In the first place we have realised a
simple and efficient synthetic procedure for the prepara-
tion 1-aryl-3,3-dialkyltriazenes 3, many of which are ob-
tained only with difficulty by known methods; the
Dry 2-Chloro-4-Nitrobenzenediazonium o-Benzene-
disulfonimide (1f)
Yield: 98%; dp 163.2–163.9 °C (HCOOH/anhyd Et2O).
1H NMR (CF3COOD): d = 7.52 (m, 4 H), 8.18 and 8.62 (2 d, 2 H,
1:1, J = 9.0 Hz).
Synthesis 2001, No. 14, 2180–2190 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
1-Aryl-3,3-dialkyltriazenes: A Convenient Synthesis from Dry Arenediazonium o-Benzenedisulfonimides
2187
Table 3 Aryl Iodides 9, Aryl Bromides 10 and Aryl Chlorides 11 from Triazenes 3: Procedure B.
Entry Compd. Ar
R
7
8
Cata-
lyst
Ta
(°C)
Timeb Chromatog-
Yield (%)cd
(min) raphic solvente
Ar–I
Ar–Br Ar–Cl
9
10
11
69f
71
84
1
2
3a
3b
3c
4-MeOC6H4
4-ClC6H4
Me
Me
Me
7a
7b
7c
7a
7b
7c
7a
7b
7c
7b
MeSO3H
MeSO3H
MeSO3H
MeSO3H
MeSO3H
MeSO3H
MeSO3H
MeSO3H
MeSO3H
MeSO3H
r.t.
r.t.
r.t.
40
40
40
60
60
60
40
15
15
15
15
15
15
60
60
60
PE–Et2O (9:1)
PE–Et2O (9:1)
PE–Et2O (9:1)
PE
80f
77
85
Cu
Cu
70f
3
4
5
Cu
Cu
PE
82
6
PE
7
4-O2NC6H4
PE–Et2O (9:1)
PE–Et2O (9:1)
PE–Et2O (9:1)
8
81
9
Cu
10
3f
2-Cl-4-
Et
7 h
PE–Et2O
74 (6)
O2NC6H3
(9.8:0.2)
11
12
3g
2,4-
(O2N)2C6H3
Me
7a
7a
MeSO3H
60
60
24 h
60
PE–Et2O (4:1)
35g
HBF4◊Et2O
65
(15)
13
14
15
16
7b
7b
7c
7c
MeSO3H
HBF4◊Et2O
MeSO3Hh
MeSO3H
60
60
80
40
17 h
60
PE–Et2O (4:1)
68
85 (4)
Cu
Cu
16 h
60
PE–Et2O (4:1)
65
3i
3j
3l
2,4,6-Br3C6H2 Et
PE
78
(13)
17
18
2,6-Br2-4-
FC6H2
Et
Et
7a
7b
MeSO3H
MeSO3H
60
60
4 h
PE–Et2O
(9.8:0.2)
67
2,6-Br2-4-
O2NC6H2
13 h
PE–Et2O
(9.5:0.5)
88 (2)
a r.t. = 20–25 °C.
b After the addition of triazenes 3.
c Yields refer to the pure (GC, GC-MS, TLC, 1H NMR) halides 9–11 isolated by column chromatography.
d Hydrodediazoniation products, that were present in all the reactions, were sometimes isolated and quantified; yields are reported in paren-
theses. In entries 1–3, 4–6 and 7–9, anisole, chlorobenzene and nitrobenzene, respectively were isolated but not quantified because no partic-
ular device was adopted to avoid their loss during the workup and the following chromatography.
e PE = petroleum ether.
f Arylation products of the obtained halides were sometimes identified by GC and GC-MS analyses of the crude reaction mixtures: entries 1,
2 and 3 (MS: m/z = 340 (M+), 292 (M+), and 248 (M+), respectively). Biaryls and diazenes corresponding to the intermediate diazonium salts
were identified in entries 1–3 (MS: m/z = 214 (M+) and 242 (M+), respectively).
g The reaction was incomplete and 3g was recovered in 42% yield.
h Using HBF4◊Et2O at 60 °C in the presence of Cu, the reaction was complete after 30 min, but the results were unsatisfactory; in fact 1-chloro-
2,4-dinitrobenzene was isolated in only 37% yield. Besides 2,4-dinitrobenzene, several unidentified by-products were present.
Anal. Calcd for C12H7ClN4O6S2 (402.78): C, 35.78; H, 1.75; Cl,
8.80; N, 13.91; S, 15.92. Found: C, 35.74; H, 1.80; Cl, 8.83; N,
13.84; S, 15.82.
1H NMR (CF3COOD): d = 7.73 and 7.80 (2 m, 1:2).
Anal. Calcd for C12H6Cl3N3O4S2 (426.68): C, 33.78; H, 1.42; Cl,
24.93; N, 9.85; S, 15.03. Found: C, 33.68; H, 1.46; Cl, 24.81; N,
9.82; S, 14.95.
Dry 2,4,6-Trichlorobenzenediazonium o-Benzenedisulfonimide
(1h)
Yield: 98%; dp 173.8–174.9 °C (anhyd MeCN/anhyd Et2O).
Synthesis 2001, No. 14, 2180–2190 ISSN 0039-7881 © Thieme Stuttgart · New York

2188
M. Barbero et al.
PAPER
Table 4 Aryl Iodides 9, Aryl Bromides 10 and Aryl Chlorides 11: Physical Properties
Compd. Ar
Hal MS
Mp (°C) or bp (°C)/
Compd. Ar
Hal MS
Mp (°C)a
m/z
mbara
m/z
(M+)
(M+)
Foundb
Reportedc
51–52
Foundb
Reportedc
9a
4-MeOC6H4
I
234
51.0–51.5
9f
2-Cl-4-
I
283
99.8–100.8 100–10119
O2NC6H3
10a
11a
Br
Cl
186
142
oil
oil
60–61/7 10f
Br
I
235
294
61.0–61.5
86.7–87.9
62
71.5/9
9g
2,4-
87.5–88.5
(O2N)2C6H3
9b
10b
11b
4-ClC6H4
I
238
190
146
53.3–54.1
65.1–65.8
53.9–55.6
57
67
54
10g
11g
9h
Br
Cl
I
246
202
306
71.6–72.9
52.8–53.6
53.3–54.9
75
Br
Cl
51
2,4,6-
53–5420
Cl3C6H2
9c
10c
11c
9d
4-O2NC6H4
I
249
201
157
273
173.1–
174.5
174
9i
11i
9j
2,4,6-
Br3C6H2
I
438
347
378
317
104.–105.0
88.7–89.5
104.0–
104.521
Br
Cl
I
125.7–
127.1
127
83
Cl
I
9122
82.7–83.5
2,6-Br2-4-
FC6H2
128.1–129.1 135.0–
135.621
2,6-Cl2C6H3
2,6-Br2C6H3
65.0–65.8
68
9k
2,6-Cl2-4-
O2NC6H2
I
152.0–153.0 152–15319
10d
9e
Br
I
224
360
64.2–64.9
98.5–99.5
65
10k
9l
Br
I
269
405
87.8–88.9
88
99.0–99.5
2,6-Br2-4-
O2NC6H2
152.7–153.5 153.523
11e
Cl
268
69.8–70.6
71
10l
11l
Br
Cl
357
313
110.5–112.0 112
89.3–90.0
90–9124
a Identical physical and spectral data and retention times, by co-injection, for the resultant halides 9a–c, 9g; 10a–d, 10g and 11a–c,11g and
the corresponding commercially available samples of analytical purity were observed. Structures of the other halides were confirmed by com-
parison of their physical and spectral data with those reported in the literature.
b After crystallization from EtOH.
c Unless otherwise noted, physical data are taken from Ref.25
Dry2,4,6-Tribromobenzenediazonium o-Benzenedisulfonimide
(1i)
Yield: 99%; dp 171.5–172.1 °C (anhyd MeCN/anhyd Et2O).
1H NMR (CF3COOD): d = 7.15 and 7.93 (2 m, 2:1).
1H NMR (CF3COOD): d = 8.42 and 9.12 (2 m, 2:1).
Anal. Calcd for C12H6Cl2N4O6S2 (437.22): C, 32.96; H, 1.38; Cl,
16.22; N, 12.81; S, 14.67. Found: C, 32.93; H, 1.41; Cl, 16.15; N,
12.76; S, 14.62.
Anal. Calcd for C12H6Br3N3O4S2 (560.03): C, 25.74; H, 1.08; Br,
42.80; N, 7.50; S, 11.45. Found: C, 25.69; H, 1.07; Br, 42.89; N,
7.46; S, 11.51.
1-Aryl-3,3-dialkyltriazenes 3; General Procedure
Arenediazonium o-benzenedisulfonimide 1 (5 mmol) was added in
small portions over a period of 5–10 min, to a vigorously stirred
soln of NEt2H (2, R = Et; 0.40 g, 5.5 mmol) or NMe2H (2, R = Me;
40% aq soln, 7.966 M; 0.62 g, 5.5 mmol) and NaOH (0.20 g, 5
mmol) in H2O (20 mL), maintained at 0–5 °C. Stirring was contin-
ued until completion of the reaction (30 min; absence of azo cou-
pling with 2-naphthol). When the triazene was a solid substance, the
precipitate was gathered by filtration on a Buchner funnel and then
dissolved in CH2Cl2 (100 mL). When the triazene was an oily sub-
stance, the reaction mixture was extracted with CH2Cl2 (2 ¥ 50 mL).
In both the cases, the organic soln was then washed with H2O
(2 ¥ 50 mL), dried (Na2SO4) and evaporated under reduced pres-
sure. The crude residue was the title compound 3. Some triazenes
Dry 2,6-Dibromo-4-fluorobenzenediazonium o-Benzene-di-
sulfonimide (1j)
Yield: 98%; dp 171–171.5 °C (anhyd MeCN/anhyd Et2O).
1H NMR (CF3COOD): d = 7.70 (d, 2 H, 3JH–F = 7.4 Hz), 7.85 (m, 4
H).
Anal. Calcd for C12H6Br2FN3O4S2 (499.12): C, 28.88; H, 1.21; Br,
32.02; F, 3.81; N, 8.42; S, 12.85. Found: C, 28.80; H, 1.27; Br,
31.93; N, 8.32; S, 12.77.
Dry 2,6-Dichloro-4-nitrobenzenediazonium o-Benzene-disulfo-
nimide (1k)
Yield: 91%; dp 165.3 °C (anhyd MeCN/anhyd Et2O).
1
(3d,e,g,i) were virtually pure (TLC; H NMR, GC-MS) and were
used in the next step, without further purification. Triazenes 3a–
Synthesis 2001, No. 14, 2180–2190 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
1-Aryl-3,3-dialkyltriazenes: A Convenient Synthesis from Dry Arenediazonium o-Benzenedisulfonimides
2189
c,f,h,j–l were purified by column chromatography. Yields reported
Aryl Halides 9–11; General Procedures
in Table 1 refer to the pure isolated products.
Procedure A
A soln of hydrogen halide (15 mmol), i.e. HI (57 wt.% in H2O; 3.37
g) orHBr (48 wt.% in H2O; 2.53 g) or HCl (35 wt.% in H2O; 1.56
g), in MeCN (10 mL) was prepared at r.t., in the presence or absence
of Cu powder (0.05 g) and maintained at r.t. or warmed at 60 °C by
an oil bath (see Table 2). A soln of 1-aryl-3,3-dialkyltriazene 3 (5
mmol) in the same solvent (10 mL) was added drop wise over a pe-
riod of 25–30 min, under vigorous stirring. During the addition, a
slow evolution of N2 was observed and the presence of the interme-
diate diazonium salt 1 was confirmed by a positive test of azo cou-
pling with 2-naphthol. After completion of the addition, small
portions of the reaction mixture were treated with an aq 5%
NaHCO3 soln, to free the triazene 3 that was then confirmed by TLC
and GC analyses, to verify the progress of the reaction in the time.
After the disappearance of 3, stirring and heating at the indicated
temperatures were maintained for a further 15 min. After this time,
most of the reactions were complete (negative azo coupling test).
On the contrary, the test was positive in entries 10, 14, 25 and 28. It
remained still positive after 24 h at 60 °C. After completion of the
reactions, GC and GC-MS analyses of the mixtures showed the aryl
halides 9–11, always as the major products. The hydrodediazonia-
tion products were present in all the reactions. Among the other by-
products, traces of arylation products of the obtained halides and of
biaryls, corresponding to the intermediate arenediazonium salts 1,
were sometimes identified by GC-MS analysis (see footnote f of
Table 2). Instead, the acetanilides corresponding to 1 were never re-
vealed. The reaction mixtures were extracted with Et2O (3 ¥ 80 mL)
and the combined organic extracts were washed several times with
H2O (3 ¥ 50 mL) to eliminate all the MeCN, dried (Na2SO4) and
evaporated under reduced pressure. The crude residues were col-
umn chromatographed to afford the pure aryl halides 9–11 and the
hydrodediazoniation by-products.
The aq soln obtained after filtration or extraction of triazene 3 and
the aq washings were collected and concentrated under reduced
pressure to 4–5 mL and then passed through a column of Dowex 50
× 8 ion exchange resin (about 3 g for 1 g of 5), eluting with H2O
(about 15 mL). After water removal under reduced pressure, virtu-
ally pure (1H NMR) o-benzenedisulfonimide (5) was recovered in
88–99% yield: mp 192–194 °C (toluene) (Lit.4 mp 192–194 °C).
Sometimes, the same dialkylamine 2 was used instead of sodium
hydroxide. In these cases, the molar ratio 1:2 was 1:2.2. Triazenes
3 were obtained in comparable yields.
Chromatographic solvents, yields and physical and spectral data of
triazenes 3 and yields of the recovered o-benzenedisulfonimide (5)
are reported in Table 1.
Break Down of 1-Aryl-3,3-dialkyltriazenes 3 to the Starting Dry
Arenediazonium o-Benzenedisulfonimides 1
Dry 4-Nitrobenzenediazonium o-Benzenedisulfonimide (1c);
Typical Procedure
o-Benzenedisulfonimide (5; 11 mmol, 2.41 g) was dissolved in gla-
cial HOAc (30 mL), by heating at 50–55 °C. 1-(4-Nitrophenyl)-3,3-
dimethyltriazene (3c; 5 mmol, 0.97 g) was then added, in one por-
tion and under stirring. A precipitate of salt 1c began to separate at
once. Heating was maintained for a further 10–15 min, until a TLC
or GC control of a small portion of HOAc soln showed the disap-
pearance of the starting triazene 3c, previously freed from the cor-
responding protonated form by treatment with an aq 5% NaHCO3
soln. After completion of the reaction, the mixture was cooled to
about 20–25 °C, with a water bath, to complete the precipitation of
the diazonium salt that was gathered by filtration on a Buchner fun-
nel and washed several times on the funnel with anhyd Et2O to com-
plete the elimination of HOAc. The dry title compound 1c was
obtained virtually pure in 99% yield (1.82 g).
In some reactions (Table 2: entries 19, 22, 24, 33, 36 and 39), aq
HBF4 (35 wt.% in H2O; 25 mmol, 6.27 g) was added to the starting
MeCN soln containing the hydrogen halide in the presence or ab-
sence of Cu, to make the formation of the intermediate diazonium
salt easier. In particular, in the presence of aq. HBF4 entries 11, 15,
26 and 29 came to completion after 24 h at 60 °C (negative azo cou-
pling test).
dp 143 °C
1H NMR (CF3COOD): d = 7.62 (m, 4 H), 8.32 and 8.58 ppm (2 d, 4
H,1:1, J = 8.5 Hz).
The data were identical to those reported.4
The HOAc soln obtained after filtration of 1c and the Et2O washings
were collected and concentrated under reduced pressure. The resi-
due was virtually pure dimethylammonium o-benzenedisulfonim-
ide.
1H NMR (CF3COOD): d = 2.55 (t, 6 H, J = 4.5 Hz), 7.54 ppm (m,
4 H). Working as described above, the residue was passed through
a column of Dowex 50X8 ion exchange resin (6 g), eluting with
H2O. After water removal under reduced pressure, virtually pure
(1H NMR) o-benzenedisulfonimide (5) was recovered in 99% yield
(1.30 g). When the reaction mixture was cooled down to 18 °C, both
1c and dimethylammonium o-benzenedisulfonimide precipitated.
In entries 12, 16, 27 and 30, Procedure A was modified as follows.
A soln of the triazene 3d or 3e or 3h or 3i (5 mmol) in MeCN (8 mL)
was added, under vigorous stirring, to a soln of aq HBF4 (25 mmol,
6.27 g) in the same solvent (8 mL), previously heated to 60 °C. A
soln of aq HI (15 mmol, 3.37 g) in MeCN (4 mL) was then added
dropwise over a period of 15-20 min. After the addition was com-
plete, a test of azo coupling with 2-naphthol was negative. The re-
action mixtures were worked as described above.
Procedure B
The reactions were performed in oven-dried glassware and anhyd
MeCN was used as solvent. No particular device was however
adopted to exclude moisture or oxygen. A suspension of ammonium
halide (12.5 mmol), i.e. tetrabutylammonium iodide (7a, 4.62 g),
tetrabutylammonium bromide (7b, 4.03 g) or benzyltriethylammo-
nium chloride (7c, 2.85 g), in anhyd MeCN (10 mL) was prepared
at r.t., in the presence (0.05 g) or absence of Cu powder. Anhyd
MeSO3H (25 mmol, 2.40 g) or HBF4◊Et2O (54 wt.% in Et2O; 25
mmol, 4.06 g) was added and the mixture was maintained at r.t. or
warmed at a temperature varying from 40 to 80 °C (see Table 3),
under vigorous stirring. A soln of 1-aryl-3,3-dialkyltriazene 3 (5
mmol) in the same anhyd solvent (10 mL) was added dropwise over
a period of 25–30 min. During the addition, a slow evolution of N2
was observed. As in Procedure A, stirring at the indicated tempera-
ture was maintained until completion of the reaction. The above
work up afforded the pure aryl halides 9–11.
According to the above procedure, also triazenes 3a,b,d–f,h–j gave
the corresponding diazonium salts: 1a (1.41 g, 80%; in this case
NMR spectrum of the HOAc soln obtained after filtration of the salt
showed the presence of both 1a and dimethylammonium o-ben-
zenedisulfonimide, as the major products), 1b (1.62 g, 91%), 1d
(1.76 g, 90%), 1e (2.36 g, 98%), 1f (1.89 g, 94%), 1h (1.92 g, 90%),
1i (2.58 g, 92%) and 1j (2.25 g, 90%). For triazenes 3k,l the reaction
solvent was HOAc/HCOOH (30 mL, 29:1). Working as described
above, 1k and 1l were obtained in 90% (1.97 g) and 91% (2.39 g)
yield, respectively. In all the cases o-benzenedisulfonimide (5) was
recovered in yield varying between 95% and 100%. The reaction
failed in the case of triazene 3g.
Synthesis 2001, No. 14, 2180–2190 ISSN 0039-7881 © Thieme Stuttgart · New York

2190
M. Barbero et al.
PAPER
Reaction conditions and yields of the aryl halides 9–11 obtained ac-
cording to the above Procedures A and B are listed in Tables 2
and 3. Identical physical and spectral data and retention time, by co-
injection, for the resultant pure halides and the corresponding com-
mercially available samples of analytical purity were observed. For
the halides that are not commercially available, structures and puri-
ty were confirmed by comparison of their physical and spectral data
with those reported in the literature (Table 4).
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Acknowledgement
This work was supported by the Ministero dell’Università e della
Ricerca Scientifica e Tecnologica (MURST), National Project
“Dry-state arenediazonium o-benzenedisulfonimides: synthesis, re-
activity and applications”, by the National Research Council of Ita-
ly (CNR), and by University of Torino.
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Synthesis 2001, No. 14, 2180–2190 ISSN 0039-7881 © Thieme Stuttgart · New York