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S. Patel, B. K. Mishra / Tetrahedron Letters 45 (2004) 1371–1372
Table 1. Reflux time, yield, melting points and UV–vis (in ethanol) of the symmetrical diaryl diazo compounds
Substrate
Reflux (h)
Product
Yield (%)
Mp (°C)
kmax (nm)
Aniline
6
4
2
3
3
6
6
Azobenzene
95
90
95
80
85
75
65
68
185
320.5
329.5
356
p-Chloroaniline
p-Methoxyaniline
p-Methylaniline
p-Hydroxyaniline
o-Hydroxyaniline
2-Aminobenzothiazole
4,40-Dichloro-azobenzene
4,40-Dimethoxy-azobenzene
4,40-Dimethyl-azobenzene
4,40-Hydroxy-azobenzene
2,20-Dihydroxy-azobenzene
2,20-Azodibenzothiazole
160
144–145
190–192
173–175
294
328
361
431.5
424
Table 2. Reflux time, yield and melting point of the symmetrical disulfides
Substrate
Reflux (h)
Product
Yield (%)
Mp/bp (°C)
n-C4H9SH
C6H5SH
6
5
4
5
3
3
C4H9SSC4H9
C6H5SSC6H5
80
85
75
65
70
80
117–118(l)6
60–61(s)6
40–41(s)8
71–72(s)6
70–71(s)8
181–182(s)6
p-CH3C6H4SH
o-CH3C6H4SH
C6H5CH2SH
p-CH3C6H4SSC6H4CH3-p
o-CH3C6H4SSC6H4CH3-o
C6H5CH2SSCH2C6H5
2-Mercapto benzothiazole
2,20-Benzothiazolyl disulfide
for oxidant and substrate in both types of reactions.
When acrylonitrile was added to the reaction mixture
under nitrogen, turbidity appeared indicating the
involvement of free radicals in the reaction. No nitro-
anilines could be converted to corresponding azobenz-
enes even after 24 h of reflux. Possibly the free radicals
were captured by the nitro group.15 The reduced product
of chromium was found to be Cr(III).
Acknowledgements
B.K.M. thanks University Grants Commission, New
Delhi for financial support through a DRS Grant and
S.P. thanks the Council of Scientific and Industrial
Research, New Delhi for a Fellowship.
In conclusion, the reagent is found to be effective in
coupling amino and mercapto groups to give the cor-
responding diazo and disulfides, respectively.
References and notes
Synthesis of cetyltrimethylammonium dichromate:
Potassium dichromate (2.94 g, 0.01M) in 100 mL of
water was added slowly to an aqueous solution of
cetyltrimethylammonium bromide (7.38 g, 0.02 M) with
continuous stirring with a Teflon coated magnetic bar at
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room temperature.
A yellow colored compound
appeared immediately. Stirring was continued for 15 min
more after completion of the addition of dichromate
solution. The resulting yellow product was filtered off
and washed with water several times until no Brꢀ or
dichromate were detected in the filtrate. The product
was vacuum dried and kept in a desiccator in the dark.
Mp 212 °C (dec), yield: 98%. Elemental analysis: C,
58.14; H, 10.65; N, 3.54; Cr, 13.11. C38H84O7N2Cr2
requires C, 58.16; H, 10.71; N, 3.57; Cr, 13.26. IR
(cmꢀ1): 771, 879, 933, 1467, 2850, 2921, 3028, 3471.
NMR (CDCl3, 300 MHz): d 0.86 (t, 6H), 1.29 (m, 48H),
1.67 (m, 4H), 1.74 (m, 4H), 3.42 (s, 18H), 3.51 (m, 4H).
General procedure for oxidation of aromatic amino/thiol
compounds: To a solution of the substrate in chloroform,
half an equivalent of CTADC in chloroform was added
and the mixture was refluxed on a water bath. With
aniline substrates, the development of a red color in the
reaction mixture was observed. The volume of the
solution was reduced until a pasty mass remained and
this was then purified by silica gel column chromatog-
raphy to provide the azo compound. For mercaptans,
the color of reaction mixture was green.
15. Odian, G. Principles of Polymerization; McGraw Hill:
USA, 1970; p 225.