Disperse dyes derived from 2-amino-5-mercapto-1, 3, 4-thiadiazole

Article abstract of DOI:10.1007/s10593-010-0415-3

Some novel heterocyclic monoazo dyes based on 2-amino-5-mercapto-1, 3, 4-thiadizole have been synthesized by coupling with various N-phenylacrylamide derivatives. The dyeing performance of these dyes was assessed on polyester fabrics. IR and visible spect

Full text of DOI:10.1007/s10593-010-0415-3

Chemistry of Heterocyclic Compounds, Vol. 45, No. 10, 2009
DISPERSE DYES DERIVED FROM 2-AMINO-
5-MERCAPTO-1,3,4-THIADIAZOLE
Hari R. Maradiya*
Some novel heterocyclic monoazo dyes based on 2-amino-5-mercapto-1,3,4-thiadizole have been
synthesized by coupling with various N-phenylacrylamide derivatives. The dyeing performance of these
dyes was assessed on polyester fabrics. IR and visible spectra of the dyes were examined. The
percentage dye bath exhaustion, fixation, and various fastness properties of the dyes were also
determined. These dyes were found to give brownish-orange to reddish-pink shades on dyeing with good
depth, levelness, and brightness on fabric. The dyed fabric showed a good to excellent fastness to
washing, rubbing, perspiration, and sublimation.
Keywords: 2-amino-5-mercapto-1,3,4-thiadizole, N-phenylacrylamide, polyester, dyeing, exhaustion,
fixation.
Aminothiadiazoles were among the first heterocyclic diazo components for disperse dyes to be described in
the patent literature [1]. Such heterocyclic amines have been commercially used to produce dyes that provide brilliant
red shades on polyester fabrics. Depending on the substituent in the diazo component and the coupler used, brilliant
in the scarlet to bluish-red dyes were obtained [2–4]. These, however, still do not quite match the brightness of the
anthraquinone dyes. In spite of a great number of patent applications for structures with substituents such as
sulfonamide [5], halogen [6], trifluoromethyl [7], and various substituted mercapto groups [8-12], etc. these systems
have fallen short of expectations as far as their commercial exploitation is concerned. Some of the dyes produced
have been used to substitute for anthraquinone red and pink dyes, which have dominated this market area for so long.
During the last two decades the level of interest as indicated by the papers published in the literature [13-22]
has grown in the field of disperse thiadiazolylazo dyes. It seems that no report is available on the use of 2-amino-
5-mercapto-1,3,4-thiadiazole (1) in the synthesis of disperse dyes by coupling with various substituted
N-arylacylamides 2a–e. Hence, it was thought worthwhile to synthesize a series of disperse dyes 3a–e from 2-amino-
5-mercapto-1,3,4-thiadiazole using various substituted N-arylacylamides 2a–e and apply them on polyester fabrics as
disperse dyes.
_______
* To whom correspondence should be addressed, e-mail: mardiahariyahoo.com.
1 V.P. and R.P.T.P. Science College, Vallabh Vidyanagar-388120 Gujarat State, India.
__________________________________________________________________________________________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1558-1563, October, 2009.
Original article submitted November 3, 2008.
1252
0009-3122/09/4510-1252©2009 Springer Science+Business Media, Inc.

N
N
N
N
NaNO2/H2SO4
0–5°C
+
–
NHSO4
NH2
N
HS
HS
S
S
1
X
Y
H2N
NHCOCH=CH2
2a–e
X
Y
N
N
N
NHCOCH=CH2
N
HS
S
3a–e
2,3 a X = Y = H; b X = NO2, Y = H; c X = Cl, Y = H; d X = Me, Y = H; e X = H, Y = Me
TABLE 1. Characterization Data, Exhaustion (E), and Fixation (F)
Properties of Dyes 3a-e
Absorption maxima,
Rf
Mp (DMF),
oC
(λmax, nm)
Yield,
%
Dye
log ε
E,%
F,%
(AcOEt−PhH)
Conc.
H2SO4
DMF
3a
3b
3c
3d
3e
174-175
209-210
232-233
249-250
240-241
445
430
450
435
440
410
390
390
406
410
4.65
4.42
4.44
4.58
4.65
80
76
80
76
74
85
83
89
86
85
0.83
0.91
0.90
0.81
0.68
80
85
75
79
68
TABLE 2. Elemental Analysis of Dyes 3a-e
Found, %
——————
Dye
Empirical Formula
Calculated, %
H
C
N
3a
3b
3c
3d
3e
C11H9N5OS2
C11H8N6O3S2
C11H8N5OS2Cl
C12H11N5OS2
C12H11N5OS2
45.10
45.36
39.00
39.28
40.15
40.55
47.10
47.21
2.92
3.09
2.18
2.38
2.30
2.45
3.41
3.60
23.92
24.05
24.86
25.00
21.36
21.50
22.79
22.95
47.06
47.21
2.92
3.60
23.92
22.95
TABLE 3. Dyeing and Fastness Properties of Dyes 3a-e on Polyester Fabric
Fastness Properties
Perspiration
fastness
Acid Alkaline
Rubbing
fastness
Dye
Shade on polyester
Subli-
mation
Light
Wash
Dry
Wet
3a
3b
3c
3d
3e
Light-orange
Brown
4-5
3-4
4-3
4-3
3-4
5
5
5
5
5
5
5
5
5-4
5
5
5
5
5
5-4
5
Reddish-pink
Bright reddish-pink
Reddish-brown
5
4-5
4-5
5-4
4-5
5
5
5
5
5
4-5
5
5
5
1253

Six novel monoazo dyes were derived from diazotized 2-amino-5-mercapto-1,3,4-thiadiazole 1 and
coupled with various N-phenylacrylamides 2a-e. Diazotization in concentrated acids was used for the diazo
component, since hydrolysis of the diazonium salt occurs in diluted acid. Here, the acid of choice is
concentrated H2SO4, used in admixture with glacial AcOH. A particularly important reagent combination is
nitrosylsulfuric acid (NOHSO4), which is used extensively as a nitrosating agent for the diazo component. The
amino compound 1 was diazotized satisfactorily at 0-5°C by nitrosylsulfuric acid in AcOH. In order to
determine the diazotization end point, it was useful to check the presence of the unreacted diazo component on
TLC by sampling the diazotization mixture. Thus, when the unreacted diazo component no longer persisted on
TLC, the diazotization ended. The diazonium salt solution was used immediately since it decomposed on
standing even when cold. Subsequent coupling reaction took place readily on adding the resulting diazonium
salt continuously to the solution of the coupling component in AcOH, and good dye yields of 68-85% were
usually obtained.
The purity of the dyes was evaluated by TLC using AcOEt-benzene (1:4) as the eluting system. When
adsorbed onto silica chromatography plates, the dyes produced a single color spot. All the recrystallized dyes
exhibited well-defined melting points. The characterization data are given in Table 1.
The visible adsorption maxima λmax of dyes 3a–e were recorded in concentrated H2SO4 and DMF
(Table 1). Their values are directly proportional to the electronic power, and the nature and position of the
substituent in the phenyl ring of a coupler moiety. The logarithm values of the molar extinction coefficient
(log ε) of dyes 3a-e were in the range of 4.42–4.65, consistent with their high absorption intensity. One reason
for the increased intensity might be attributed to the greater planarity of the thiadiazole dyes because of the
lower steric interaction of a five-membered ring.
The IR spectra of dyes reveal the characteristic bands around 2960-3010, 1580-1610, and 1500 cm–1 due
to the aromatic stretching vibration of the phenyl ring, and the bands at 600–660 and 675-700 cm–1 (C–S–H
stretching), 1070 (C–N stretching), 1200 (NHCOCH=CH2 group), and 1435 cm–1 (S–C stretching). The bands at
800-870 (a para-disubstituted phenyl ring), 960-990, and 870-900 cm–1 are due to the out-of-plane C-H bending
of the vinyl group. The azo group (N=N) indicates the stretching vibration at 1540-1560 cm–1. Two strong bands
observed at 1650-1690 cm–1 are assigned to the stretching vibration of the C=O group of the acrylamido group.
The amide grouping N–H stretching vibration was observed around 3275-3350 cm–1. The band at 1320-1350
cm–1 is due to the symmetric stretching of the NO2 group. The bands at 620-685 and 1385-1450 cm–1 are due to
the C–Cl and C–CH3 stretching vibration, respectively.
All the dyes were applied at 2% depth on polyester fabric as disperse dyes. Their dyeing properties are
given in Table 3. These dyes gave a narrow range of color varying from orange to pink with excellent levelness,
brightness, and depth on fabric and a deeper shade with high tinctorial and excellent levelness. The variation in
the shade of the dyed fabric results from alteration in the coupling components. The dyed fabric has good (3-4)
to excellent (5) light, washing, rubbing, perspiration, and sublimation fastness properties. A remarkable degree
of levelness and brightness after washing indicates good penetration and excellent affinity of dyes to the fabric.
The value obtained for the given colorant in any fading test depends on many factors, the most important of
which are: Dye concentration and/or aggregation degree within the fabric; the nature of fabric in which it is
dispersed; characteristics of the incident radiation, molecular structure, molecular size, and substantivity. The
substantivity of the dyes for polyester fabric is such that they conferred almost similar depth of shade (close
fixation values), which had the same rating, implying that the intrinsic photostabilities of dyes on the fabric are
similar. This suggests that smaller molecular size and higher substantivity factors hold more importance than
those concerning a slight difference in molecular structure of dyes.
Table 1 shows exhaustion and fixation of all the dyes on fabric. Very good exhaustion on the fabric may
be expected because dye diffusion within the fabric proceeds rapidly under the dyeing condition. Hence, the
diffusion rate of the dye molecules into fabric is higher, which increases the exhaustion value. Also the smaller
thiadiazole dye molecule penetrates deeper into the fabric, which closes easily on fabric after dyeing and so
1254

it from sublimation. The sublimation fastness observed shows that all the dyes exhibit very good (5-4) to excellent
(5) rating on fabric. The other fastness properties are found to be good to excellent (5).
The efficient diazotization of amino compound 1 can only be achieved using nitrosylsulfuric acid obtained
from NaNO2 and concentrated H2SO4. A series of thiadiazole-based disperse dyes containing various N-aryl-
acrylamide residues has been synthesized by conventional methods and their color properties examined both in
solution and on application to polyester fabric. A gamut of color shades narrowly by ranging from orange to pink
was obtained by applying variously substituted dyes. The small size of thiadiazolylazo dyes provides good dye
ability. The intrinsic conjugation in the dye structure results in very good color strength. The nature of the substituent
in coupling components has little influence on the visible absorption. These dyes give very good exhaustion, fixation,
and economy (as compared with anthraquinones, which could only provide up to blue shades). An outstanding
characteristic feature of these dyes is that they give a level dyeing and excellent dispersability. The remarkable
levelness degree after dyeing indicates good penetration and affinity of these dyes to the fabric.
The results suggest that polyester fabric dyeing with thiadiazolylazo disperse dyes may be promising for
practical use, chiefly on account on facility and cheapness of the dye synthesis, the application ease, and the
overall versatility of their use.
EXPERIMENTAL
All the melting points were determined by the capillary method. The visible absorption spectra were
measured in a Carl Zeiss UV/VIS Specord spectrometer. The elemental analysis was carried out on a Perkin-
Elmer 240 elemental analyzer. IR spectra were recorded in the KBr pellets on a Perkin-Elmer 983 spectrometer.
The solvents and reagents were obtained from commercial sources. They were further purified by a standard
method [23]. The diazo component 1 was prepared as reported in the literature [24].
The coupling components 2a-e were prepared by the method reported in the literature [25]. All the dyes
were applied to polyester fabrics adopting the general dyeing method [26]. Fastness to light, sublimation, and
perspiration were assessed in accordance with BS: 1006-1978 (British Standard Institute, Dictionary of Quality
Standards) and the wash fastness test in accordance with IS: 765-1979. The rubbing fastness test was carried out
using a crockmeter (Atlas) in accordance with AATCC-1961. The percentage dye bath exhaustion (%E) and
fixation (%F) of the dyed fabric was also determined by the known method [27].
2-(N-Phenylacryamido)azo-5-mercapto-1,3,4-thiadiazole (3a). The synthesis of compound 3a involves
two steps:
a) Diazotization of 2-amino-5-mercapto-1,3,4-thiadiazole (1). The compound 1 was diazotized by the
general method reported in the literature [17].
b) Coupling with N-phenylacrylamide (2a). Compound 2a (2.94 g, 0.02 mol) was dissolved in AcOH
(10 ml)and cooled to 0-5°C in an ice bath. A freshly prepared diazonium salt solution was added at 0-5°C
sufficiently slowly to prevent liberation of nitrous gases. The coupling occurred rapidly. The reaction mixture
was stirred at 0-5°C for 45 minutes, maintaining the pH 4.5-5.0 by adding 10% AcONa solution. The mixture
was stirred further at 0-5°C for 1 h and then diluted with 100 ml water, and the solid product was filtered off,
washed with water, and finally dried in an oven at 50°C. The crude product thus obtained was recrystallized
from the minimum amount of DMF to provide 3a as a brown powder.
The above procedure was used for the preparation of dyes 3b-e using various coupling components 2b-e.
The whole procedure for the synthesis is given in the Scheme. The characterization data of dyes 3a–e are given in
Tables 1-3.
The author thanks Professor V. S. Patel, Ex-Vice Chancellor of Sardar Patel University, for providing
research facilities and valuable guidance.
1255

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