New dry arenediazonium salts, stabilized to an exceptionally high degree by the anion of o-benzenedisulfonimide

Article abstract of DOI:10.1055/s-1998-2132

Arenediazonium o-benzenedisulfonimides 3 (20 examples, yield >90%) were prepared in the dry state by diazotization of aromatic amines with (-pentyl nitrite and o-benzenedisulfonimide in glacial acetic acid or formic acid at 0-5°C. Unlike most diazonium salts in the dry state, salts 3 are very highly stable.

Full text of DOI:10.1055/s-1998-2132

SYNTHESIS
August 1998
1171
New Dry Arenediazonium Salts, Stabilized to an Exceptionally High Degree by the
Anion of o-Benzenedisulfonimide
Margherita Barbero,a Marco Crisma,b Iacopo Degani,*a Rita Fochi,*a Paolo Perracinoa
a Dipartimento di Chimica Generale ed Organica Applicata, Università di Torino, C.so M. D’Azeglio 48, I-10125 Torino, Italy
Fax +39(11)6707642; E-mail: fochi@silver.ch.unito.it
b Centro Studi Biopolimeri, CNR, Dipartimento di Chimica Organica, Università di Padova, Via Marzolo 1, I-35131 Padova, Italy
Received 21 October 1997; revised 8 December 1997
Abstract: Arenediazonium o-benzenedisulfonimides 3 (20 exam-
ples, yield >90%) were prepared in the dry state by diazotization
of aromatic amines with i-pentyl nitrite and o-benzenedisulfonim-
ide in glacial acetic acid or formic acid at 0–5°C. Unlike most dia-
zonium salts in the dry state, salts 3 are very highly stable.
Key words: stable dry arenediazonium salts, thermal decomposi-
tion, azo coupling reactions, o-benezenedisulfonimide
It is well known1 that in the dry state most diazonium salts
are quite unstable, being sensitive to physical agents such
as heat, light, shock, static electricity etc. that can lead to
Scheme 1
rapid uncontrollable decomposition and even explosions.
This behaviour is particularly dangerous and has certainly
azo coupling reactions with 2-naphthol to give the corre-
sponding (2-hydroxy-1-naphthyl)aryldiazene 4. In most
cases yields were greater than 90% (Table 1).
had a negative effect on the development of synthetic pro-
cedures on a laboratory scale and, even more, on large-
scale applications. Exceptions to this behaviour are found
in most arenediazonium tetrafluoroborates, in some diaz-
onium salts where complex anions are present, e.g., zinc
double chlorides and hexafluorophosphates, and in certain
arenediazonium sulfonates.
With regard to yields of 3, it is noteworthy that these are
significantly higher (usually about 90%) than the yields
reported for the diazonium salts containing the fluorinated
anions (71–82%).2,3 Samples of analytical purity were
prepared by crystallization from anhydrous MeCN/Et2O.
Satisfactory elemental analyses and NMR spectra con-
firmed the structure of the salts. In one case (3s) the struc-
ture was also supported by an X-ray analysis (Figure,
Table 2). Salts 3 are very soluble in water, unlike diazoni-
um salts containing fluorinated anions;2,3 furthermore,
they are fairly soluble in both polar protic (HCO2H,
MeOH) and aprotic (DMSO, MeCN) solvents. Instead
they are essentially insoluble in apolar or slightly polar
solvents.
Two brief notes recently described some arenediazonium
salts whose counterions are the conjugated bases of
bis(trifluoromethylsulfonyl)amine2,3 (CF3SO2)2NH (three
examples) and the cyclic analog3 SO2(CF2)3SO2NH (one
example). These salts are remarkably stable in the solid
state. Considering that the presence of fluorinated groups
is not indispensable, though favourable for the salts' sta-
bility, we have thought to advantageously substitute the
fluorinated N-anions with the N-anion of o-benzenedi-
sulfonimide (2), to use this as the counterion of arene-
diazonium cations.4 Indeed whereas the synthesis of
bis(trifluoromethylsulfonyl)amineand the cyclic analog is
very laborious and calls for expensive reagents,5 the syn-
thesis of o-benzenedisulfonimide (2) can now be easily re-
alized through simple preparation of o-benzenedisulfonyl
chloride,6,7 the key intermediate to obtain 2.8
One property that makes salts 3 very interesting is their
exceptional stability, a feature that could lead to important
synthetic developments. Samples of 3 stored at 0°C for
The preparation of dry arenediazonium salts 3 was easily
carried out by diazotization of aromatic amines 1 with
i-pentyl nitrite in the presence of o-benzenedisulfonimide
(2) in glacial acetic acid or in formic acid at 0–5°C
(Scheme 1). When using acetic acid as the solvent only a
few minutes are needed for salts 3 to separate out, and the
precipitation can be completed by adding anhydrous
Et2O. When the solvent is formic acid the salts remain in
solution; however, in this case the addition of anhydrous
Et2O also leads to their precipitation. In both solvents salts
3 are obtained dry in high purity and excellent yields (Ta-
ble 1). The crude salt’s structure was always verified by
Figure. X-ray Crystal Structure of Salt 3s

SYNTHESIS
Papers
Table 1. Benzenediazonium o-Benzenedisulfonimides 3a–t and (2-Hydroxy-1-naphthyl)aryldiazenes 4a–t
1172
Ar
Prod-
ucta
Yieldb dpc
1H NMR (CF3CO2D), δ , J (Hz)
Prod- Yield mpd (°C)
(%)
(°C)
uct
(%)
found
133
reported
13313
C6H5
3a
3b
3c
3d
98
93
92
91
110
105
96
7.40–8.05, 8.05–8.35 (2 m, 7:2, 9H)
2.57 (s, 3H), 7.30–8.25 (m, 8H)
2.32 (s, 3H), 7.30–7.90 (m, 8H)
4a
4b
4c
4d
94
86
85
94
2-MeC6H4
3-MeC6H4
4-MeC6H4
131
132–13313
141–14213
135–13613
141
121
2.37 (s, 3H), 7.40, 8.06, (2d, 1:1, J = 8.5, 4H), 8.65
134
(m, 4H)
2-MeOC6H4
3e
98
146
3.82 (s, 3H), 6.80–7.20, 7.58, 7.60–8.00 (3m,
1:2:1, 8H)
4e
94
180
17818
3-MeOC6H4
4-MeOC6H4
3f
94
89
90
3.58 (s, 3H), 6.40–7.20, 7.30–7.80 (2 m, 1:3, 8H)
4f
88
99
140
137
14018
13718
3g
151
3.78 (s, 3H), 6.98, 8.08 (2d, 1:1, J = 8.5, 4H), 7.62
4g
(m, 4H)
2-ClC6H4
3h
3i
96
96
94
98
95
98
97
88
99
142
117
153
130
140
173
157
143
154
7.25–8.02, 8.10–8.40 (2m, 7:1, 8H)
4h
4i
90
88
92
88
89
83
91
94
84
163
158
162
172
174
211
194
251
181
16319
3-ClC6H4
7.30–8.00, 8.00–8.30 (2m, 7:1, 8H)
15819
4-ClC6H4
3j
7.55, 8.15 (2d, 1:1, J = 8.5, 4H), 7.65 (m, 4H)
7.30–7.90, 7.90–8.50 (2m, 5:3, 8H)
4j
162.519
3-BrC6H4
3k
3l
4k
4l
17219
4-BrC6H4
7.58 (m, 4H), 7.68, 8.02 (2d, 1:1, J = 8.5, 4H)
7.58, 7.82–8.80 (2m, 1:1, 8H)
172–17319
209–21019
193–19419
251–25219
180–18220
2-NO2C6H4
3-NO2C6H4
4-NO2C6H4
4-Me2NC6H4
3m
3n
3o
3p
4m
4n
4o
4p
7.40–8.10, 8.50–8.90, 9.00–9.35 (3m, 5:2:1, 8H)
7.62 (m, 4H), 8.32, 8.58 (2d, 1:1, J = 8.5, 4H)
2.92 (s, 6H), 6.53 (d, J = 8.5, 2H), 7.40–7.80
(m, 6H)
2,6-Me2C6H3
3q
3r
85
99
108
151
2.82 (s, 6H), 6.52, 7.62 (2m, 3:4, 7H)
4q
4r
94
91
147
204
14721
20322
2-MeO-
4.00 (s, 3H), 7.15 (d, J = 8.5, 1H), 7.50–7.85
5-ClC6H3
(m, 5H), 7.92 (s, 1H)
2,6-Cl2C6H3
3s
3t
95
95
183
122
7.40–8.10 (m)
4s
4t
92
89
141
230
140–14123
229–23013
1-naphthyl
7.30–8.10, 8.30–8.72 (2m, 9:2, 11H)
a
Satisfactory microanalyses were obtained: C ± 0.16; H ± 0.18; N ± 0.16; S ± 0.18; Cl ± 0.16; Br ± 0.13.
Yields obtained by carrying out the reactions in AcOH. Comparable yields were obtained when HCO2H or HCO2H/AcOH were used (see
b
experimental).
Decomposition point.
c
d
Crystallization solvent was CHCl3/PE for compounds 4a–o, q–t and EtOH/PE for compound 4p.
two months underwent no decomposition; also at room ed in two products derived from the loss of nitrogen and
temperature (about 25°C) for two months, they underwent phenyl attack at the nitrogen atom of the imide (5, Scheme
no changes, the only exceptions being benzenediazonium 2) or at an oxygen atom of a sulfonyl group (6) which is
and o-, m-, and p-toluenediazonium o-benzenedisulfon- similar to the behaviour of salts containing fluorinated
imides (3a–d). Salts 3 have high, well defined and repro- N-anions.2,3 Products 5 and 6 are formed in percentages
ducible decomposition points (Table 1) and during more or less independent of the reaction conditions (5:6 =
decomposition nitrogen is gradually released. Two sam- 66:18 in the dry state and 79:14 in toluene, respectively).
ples of benzenediazonium o-benzenedisulfonimide (3a) In toluene the reaction gave also a small amount (7%) of
were heated, one in the dry state until the decomposition three isomers derived from phenylation of toluene at the
temperature (110°C), the other, suspended in toluene, to ortho, meta and para positions (ratio o:m:p = 2.2:1.0:1.1).
the boiling point of the hydrocarbon (110°C). Both result- Such a phenylation ratio is consistent with a heterolytic

SYNTHESIS
August 1998
1173
Table 2. Selected Bond Lengths and Angles for 3s
In conclusion, arenediazonium salts 3, where the counter-
ion of the arenediazonium cations is the anion derived from
the now readily accessible o-benzenedisulfonimide (2),
show the following characteristic advantages: i) they are
easily prepared; ii) they are easily purified; iii) they are nor-
mally very highly stable; iv) when salts 3 are reacted in wa-
ter or organic solvents they give rise, in yields often higher
than those obtained using known procedures, to numerous
classes of compounds such as azo compounds, phenols, sul-
fonates, halides, ethers, sulfides etc, as has been shown in
previous4 and current research; v) at the end of reactions us-
ing 3 there is nearly always excellent recovery (usually
greater than 90%) of o-benzenedisulfonimide;4 vi) most of
the salts 3 can be kept in a ready-to-use condition for a long
time; vii) the results already achieved,4 and others related to
work in progress, lead us to believe that salts 3 are excellent
laboratory reagents, and, furthermore, are valid candidates
for technological applications.
Bond Length
Å
Bond Angle
(°)
S1-O2
S1-N1
S2-O4
S2-N1
Cl1-C8
N2-N3
S1-O1
S1-C1
S2-O3
S2-C6
Cl2-C12
N2-C7
1.439(2)
1.577(2)
1.434(2)
1.586(2)
1.712(3)
1.088(3)
1.441(2)
1.773(3)
1.440(3)
1.775(3)
1.701(3)
1.387(3)
O2-S1-O1
O1-S1-N1
O1-S1-C1
O4-S2-O3
O3-S2-N1
O3-S2-C6
S1-N1-S2
C6-C1-S1
C1-C6-S2
C8-C7-N2
O2-S1-N1
O2-S1-C1
N1-S1-C1
O4-S2-N1
O4-S2-C6
N1-S2-C6
C2-C1-S1
C5-C6-S2
N3-N2-C7
N2-C7-C12
114.1(1)
113.7(1)
107.9(1)
115.6(2)
113.2(2)
107.6(2)
114.6(1)
110.7(2)
111.5(2)
118.3(2)
109.5(1)
110.6(1)
100.1(1)
109.2(2)
110.8(2)
99.3(1)
127.7(2)
127.7(2)
178.6(3)
118.3(3)
1H and 13C NMR spectra were recorded on a Bruker WP 80 SY spec-
trometer. Mass spectra were recorded on a quadrupole MS Engine HP
5989 B instrument, operating with a direct-inlet system at 70 eV. Pe-
troleum ether refers to the fraction boiling in the range 40–70°C and
is abbreviated as PE. All amines used are available commercially.
o-Benzenedisulfonimide (2) was prepared according to the literature
procedure,8 by reaction of o-benzenedisulfonyl chloride6 and NH3 gas
in EtOH / toluene instead of EtOH / benzene at 0°C.
process (ratio o:m:p = 2.4:1.0:1.0)9 and not a homolytic
one (ratio o:m:p = 4.0:1.0:0.7).10 This clue, together with
the gradual and non-violent formation of 5 and 6, drew us
to the conclusion that the decomposition of the salts oc-
curs likely via a heterolytic mechanism; decomposition by
this route being due to the insufficient electron donor
properties of the anion derived from o-benzenedisulfon-
imide. Thus homolytic reactions, also violent ones, which
many arenediazonium salts undergo in the dry state would
be avoided for salts 3. In any case the salts fall in line with
other empirical rules that give indexes of diazonium salts
stability in the dry state: i) with only two exceptions (3c,f),
decomposition points are greater than 100°C;11 ii) the ox-
ygen content is insufficient to convert more than half of
the carbon atoms present into CO;1d iii) the C/N ratio is
>3.1d Still on the subject of stability: it was ascertained
that salts 3 can be handled in air and light without decom-
position; in our laboratory there was no case of violent de-
composition during the preparation, purification and
handling of the said salts. Nevertheless it must be borne in
mind that there is always a potential danger of explosion
for diazonium salts 3 in the dry state, as for all other
known diazonium salts in the dry state, even those be-
lieved to be quite stable.1,11,12
CAUTION! All dry diamonium salts are potentially explosive.
Therefore they must be carefully stored and handled.
Diazotization of Amines 1: Benzenediazonium o-Benzenedisulf-
onimide (3a); Typical Procedure:
A solution of o-benzenedisulfonimide (2; 2.63 g, 12 mmol) in glacial
AcOH (40 mL) was slowly added, over a period of 10 min, to a stirred
solution of aniline (1, Ar = Ph; 0.93 g, 10 mmol) in the same solvent
(20 mL), previously cooled to 0–5°C in an ice bath. i-Pentyl nitrite
(1.28 g, 11 mmol) was added dropwise at such a rate that the temper-
ature did not exceed 5°C (about 10 min). A white precipitate of 3a be-
gan to separate at once. After the addition was complete, the cooling
bath was removed and the mixture was maintained under stirring for
a further 5 min. Then anhyd Et2O was added to complete the precipi-
tation of the diazonium salt that was gathered by filtration on a Büch-
ner funnel and washed several times on the funnel with anhyd Et2O
(6 × 5–6 mL) to complete the elimination of AcOH. After drying un-
der reduced pressure, the dry title compound 3a was obtained in 98%
yield (3.18 g). It was virtually pure (NMR). For analyses, a sample
was dissolved in hot anhyd MeCN and then precipitated again with
anhyd Et2O, after cooling; dp (decomposition point) 110°C.
1H NMR (CF3COOD): δ = 7.40–8.05 and 8.05–8.35 (2 m, 7 : 2, 9 H).
13C NMR (CF3COOD): δ = 123.35, 123.94, 136.57 (d, CH), 131.77
+
(2 d, CH overlapped), 140.10 (s, CS), 163.83 (s, CN2 ).
Anal. C12H9N3O4S2 (323.3): calcd C, 44.58; H, 2.81; N, 13.01; S,
19.80; found: C, 44.45; H, 2.76; N, 12.99; S, 19.91.
Salts 3b–s were prepared in the same way. All the salts were recrys-
tallized as reported above for 3a. They melted with decomposition,
1
but none exploded. Yields, decomposition points and H NMR data
are reported in Table 1.
Diazotization of amines 1a,d,g,j,q,r was also carried out in HCO2H
(20 mL to dissolve 2 and 10 mL to dissolve 1) or in a mixture HCO2H/
AcOH (20 mL of HCO2H to dissolve 2 and 20 mL of AcOH to dis-
solve 1). Yields and purity of corresponding salts 3a,d,g,j,q,r were
comparable with those obtained when AcOH was used.
Scheme 2

SYNTHESIS
Papers
1174
Azo Coupling Reactions: (2-Hydroxy-1-naphthyl)phenyldiazene
(4a); Typical Procedure:
X-ray Analysis of Compound 3s:
Crystals of 3s (C12H7Cl2N3O4S2), grown by slow evaporation from
MeCN, are monoclinic: a = 7.360(1), b = 16.391(2), c = 13.173(2) Å,
b = 99.6(1)°, V = 1566.9 Å3, Dcalc = 1.663 g/cm3, Z = 4, space group
P21/c. The unit-cell parameters and intensities of 3791 independent
reflections were measured on a Philips PW110 four-circle diffracto-
meter, using graphite monochromated MoKα radiation (λ= 0.71073 Å),
θ –2θ scan mode up to θmax = 28°. The structure was solved by direct
methods of SHELXS-86 program.16 Refinement was carried out by
full-matrix least-squares on F2, using the full dataset, with anisotropic
displacement parameters for all non-hydrogen atoms, by application
of the SHELXL-93 program.17 Hydrogen atoms were included at cal-
culated positions with idealized geometry, and during the refinement
A solution of 2-naphthol (0.72 g, 5 mmol) in 10% aq NaOH solution
(4.4 mL, 11 mmol) was added dropwise over a period of 5 min to a
suspension of benzenediazonium o-benzenedisulfonimide (3a;
1.61 g, 5 mmol) in H2O (20 mL), under vigorous stirring. A red pre-
cipitate of 4a began to separate at once. Stirring was continued for 15–
20 min until completion of the reaction. Then the mixture was extracted
with CHCl3 (3 × 60 mL) and the organic extracts were separated from
the aqueous solution and washed with H2O (2 × 50 mL). After drying
(Na2SO4) and solvent removal in vacuo, the residue was virtually pure
4a (1.15 g, 93%). The product was furthermore purified by column
chromatography (silica gel, CHCl3); yield unchanged; mp 133°C
(CHCl3/PE) (Lit.13 mp 133°C). Using the same workup as previously
described,14 o-benzenedisulfonimide (2) was recovered from the aque-
ous solution. This was acidified with concd HCl, concentrated in vacuo
until 4–5 mL and then passed through a 15 g column of Dowex 50 × 8
ion-exchange resin (Fluka), eluting with H2O (about 15 mL). After re-
moval of H2O in vacuo, virtually pure (NMR) 2 was recovered in 94%
yield (1.03 g); mp 192–194°C (toluene) (Lit.8,14 mp 192–194°C).
Also diazenes 4b–t were prepared according to the above procedure.
In all the cases o-benzenedisulfonimide (2) was recovered in yields
usually greater than 90%. Yields and mp are reported in Table 1.
they were allowed to ride on their carrying atom, with U set equal
iso
to 1.2 times the U of the atom to which they are bonded. Refine-
eq
ment converged to R1 = 0.039 [on F, for 2407 reflections with Fo
≥4(σ)Fo] and wR2 = 0.125 (on F2) for all data. The data / restraints /
parameters ratio was 3791 / 0 / 208. Goodness of fit = 0.970. Maxi-
mum shift / e.s.d.s. 0.001. Maximum and minimum ∆ρ in the final
difference Fourier map: +0.45 and –0.32 e/Å3. Selected bond lenghts
and bond angles are listed in Table 2. Complete lists of fractional
atomic coordinates, bond distances, bond angles, and anisotropic dis-
placement parameters have been deposited and are available at the
Cambridge Crystallographic Data Centre.
Thermal Decomposition of Benzenediazonium o-Benzenedisulf-
onimide (3a):
This work was supported by the National Research Council of Italy
(CNR), Legge 95/95 and by Ministero dell’Università e della Ricerca
Scientifica e Tecnologica (MURST).
Procedure A: Salt 3a (1 g) was heated in an oven-dried 10-ml flask
equipped with a drying tube, at 110°C (oil bath) for 10 min, until the
release of nitrogen ceased and a proof of azo coupling reaction with 2-
naphthol was negative. CHCl3 (5 mL) was added to the solid residue
and the mixture was heated under reflux for 5 min. The organic solution
was separated by decantation and the insoluble solid substance was
washed again with the same solvent (2 × 2 mL). The crude residue ob-
tained after evaporation of the solvent under reduced pressure was
chromatographed on a silica gel column with CHCl3 as eluent. Com-
pound 6 was obtained in 18% yield (0.16 g). Anhyd MeOH (5 mL) was
added to the solid substance which was insoluble in CHCl3 and the mix-
ture was heated under reflux for 5–10 min. The organic solution was
separated by decantation and evaporated under reduced pressure to af-
ford virtually pure (NMR) compound 5 in 66% yield (0.60 g).
Procedure B: A suspension of salt 3a (1 g) in anhyd toluene (5 mL)
was heated at 110°C as described above. The release of N2 ceased af-
ter 2 h. The organic solution was separated by decantation from the
insoluble solid substance which was washed again with toluene (2 ×
2 mL). The crude residue obtained after evaporation of the solvent un-
der reduced pressure was chromatographed on a silica gel column
with CHCl3 as eluent. Two fractions were collected. After evapora-
tion under reduced pressure of the first fraction, a solid substance was
obtained. GC and GC/MS analyses showed the presence of three
products, i.e. o-, m- and p-methyldiphenyl, each with m/z 168 (M+),
in a 2.2:1:1.1 ratio; yield: 7% (0.036 g). Structure of the three isomers
was confirmed by comparison with authentic samples (Aldrich).
Evaporation of the second fraction afforded compound 6 in 14% yield
(0.13 g). The solid substance insoluble in toluene was virtually pure
compound 5 (0.72 g, 79%).
(1) General references:
a) Zollinger, H. Diazo Chemistry I; VCH: Weinheim, 1994; pp
24, 25.
b) Engel, A. In Houben-Weyl, 4th ed., Vol. 16a, Part 2; Kla-
mann, D., Ed.; Thieme-Verlag: Stuttgart, 1990; p 1052.
c) Hertel, H. In Ullmann’s Encyclopedia of Industrial Chem-
istry, 5th ed., Vol. A8; Gerhartz, W., Ed.; VCH: Weinheim,
1987; p 506.
d) Wulfman, D. S. In The Chemistry of Diazonium and Diazo
Groups, Part 1; Patai, S., Ed.; Wiley: New York, 1978; pp 250–
252.
e) Putter, R. In Houben-Weyl, 4th ed., Vol. 10/3, Part 3; Stroh,
R., Ed.; Thieme-Verlag: Stuttgart, 1965; pp 32–34.
f) Zollinger, H. Azo and Diazo Chemistry; Interscience Pub-
lishers: New York, 1961; pp 51–53.
g) Roe, A. In Organic Reactions, Vol. 5; Adams, R., Ed.; Wiley:
New York, 1949; pp 194–200.
(2) Haas, A.; Yagupolskii, Y. L.; Klare, C. Mendelev Commun.
1992, 70.
(3) Zhu, S.-Z.; DesMarteau, D. D. Inorg. Chem. 1993, 32, 223.
(4) a) Barbero, M.; Degani, I.; Fochi, R.; Perracino, P. IT Patent
MI97A 000473; 1997. PCT/EP98/01145.
b) Barbero, M.; Degani, I.; Fochi, R.; Perracino, P. 2nd Ger-
man-Italian Symposium, Goslar (Germany), 29.5–1.6.1997, ab-
stract p 32.
Compound 5: mp 194–195°C (from MeOH/PE) (Lit.15 mp 195°C).
1H NMR (CF3 COOD): δ = 7.10–7.35 and 7.50–7.80 (2 m, 5:4, 9 H).
13C NMR (CD3OD): δ = 122.85, 124.61, 130.67, 131.68, 134.71 (d,
CH), 143.30 (s, CS), 213.73 (s, CN).
(5) For the preparation of (CF3SO2)2NH, see:
a) Foropoulos, J.; DesMarteau D. D. Inorg. Chem. 1984, 23,
3720.
MS: m/z = 295 (M+ ).
b) DesMarteau, D. D.; Witz, M. J. Fluorine Chem. 1991, 52, 7.
For the preparation of O2S(CF2)3SO2NH, the following note is
reported in Ref. 3:
Zuberi, S.; DesMarteau, D.D., manuscript in preparation. To
our knowledge, until today no preparation of the reagent is re-
ported in the literature.
Compound 6: mp 106°C (CHCl3/PE).
1H NMR (CDCl3): δ = 7.05–7.70 and 7.95–8.20 (2 m, 5:4, 9 H).
13C NMR (CDCl3): δ = 122.74, 123.58, 128.79, 130.31, 134.35,
136.87 (d, CH), 131.66 (s, CO), 145.12 (s, CS), 148.32 (s, CS).
MS: m/z = 295 (M+).
Anal. C12H9NO4S2 (295.3): calcd C, 48.80; H, 3.07; N, 4.74; S,
21.71; found: C, 48.72; H, 3.04; N, 4.69; S, 21.65.
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Ital. 1986, 116, 165.

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