Facile synthesis and properties of alkali-clearable azo disperse dye containing a carboxylic ester moiety

Article abstract of DOI:10.1016/j.cclet.2014.03.045

A yellow, alkali-clearable azo disperse dye containing a carboxylic ester moiety was readily synthesized from the reactant p-aminobenzoic acid by successive diazotization, coupling reaction, chlorination and esterification with ethanol. Then its molecular structure was characterized by FTIR, ¹H NMR, ¹³C NMR, mass spectrometry and elemental analysis. The synthesized dye and a similar control dye containing the acylamide moiety (I) were applied to dyeing poly(ethylene terephthalate) fabric and their washing and rubbing fastness properties with different post-treatment methods (reduction clearing and alkali clearing) were examined and compared. It is found that the ester-containing disperse dye shows good alkali-clear ability on poly(ethylene terephthalate) fabric and contaminates little to environment due to the absence of reductants, as well as low toxicity and easy recycling of the hydrolysates.

Full text of DOI:10.1016/j.cclet.2014.03.045

Accepted Manuscript
Title: Facile synthesis and properties of alkali-clearable azo
disperse dye containing a carboxylic ester moiety
Author: Zhi-Hua Cui Xiao-Hong Cheng Xin Li Hong-Hui Lu
Xi-Dong Wang Wei-Guo Chen
PII:
S1001-8417(14)00147-8
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.cclet.2014.03.045
CCLET 2931
To appear in:
Chinese Chemical Letters
Received date:
Revised date:
Accepted date:
23-12-2013
14-3-2014
19-3-2014
Please cite this article as: Z.-H. Cui, X.-H. Cheng, X. Li, H.-H. Lu, X.-
D. Wang, W.-G. Chen, Facile synthesis and properties of alkali-clearable azo
disperse dye containing a carboxylic ester moiety, Chinese Chemical Letters (2014),
http://dx.doi.org/10.1016/j.cclet.2014.03.045
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Graphical Abstract
Facile synthesis and properties of alkali-clearable azo disperse dye containing a carboxylic ester moiety
Zhi-Hua Cui a,b,∗ Xiao-Hong Chenga, Xin Lia, Hong-Hui Luc, Xi-Dong Wanga, Wei-Guo Chen a,b
a Engineering Research Center for Eco-Dyeing & Finishing of Textiles, Ministry of Education of China, Zhejiang Sci-Tech University, Hangzhou 310018,
China
b Key Laboratory of Advanced Textile Materials and Manufacturing Technology, Ministry of Education of China, Hangzhou 310018, China
c Zhejiang Jihua Group Co.,Ltd., Hangzhou 311228, China
CH3
N
N
O
N
H
O
Diazotization
NaNO2 / HCl
Coupling
O
H2N
N
OH
O
ONa
N
N
CH3
SOCl2/DMF
d
n
a
s
i
s
y
e
l
l
o
c
r
y
c
e
d
y
r
H
y
CH3
s
CH3
a
e
N
N
N
O
N
H
O
C2H5OH
N
N
N
N
O
H
Cl
O
OC2H5
A yellow, alkali-clearable azo disperse dye containing a carboxylic ester moiety was readily synthesized from reactant p-aminobenzoic acid by
successive diazotization, coupling reaction, chlorination and esterification with ethanol. The ester-containing disperse dye shows good
alkali-clear ability on poly(ethylene terephthalate) fabric and contaminates little to environment due to the absence of reductants, as well as
low toxicity and easy recycling of the hydrolysates.
∗ Corresponding author.
E-mail address: zhhcui@zstu.edu.cn
Page 1 of 7

Original article
Facile synthesis and properties of alkali-clearable azo disperse dye containing a carboxylic ester moiety
Zhi-Hua Cui a,b,∗ Xiao-Hong Chenga, Xin Lia, Hong-Hui Luc, Xi-Dong Wanga, Wei-Guo Chen a,b
a Engineering Research Center for Eco-Dyeing & Finishing of Textiles, Ministry of Education of China, Zhejiang Sci-Tech University, Hangzhou 310018,
China
b Key Laboratory of Advanced Textile Materials and Manufacturing Technology, Ministry of Education of China, Hangzhou 310018, China
c Zhejiang Jihua Group Co.,Ltd., Hangzhou 311228, China
ARTICLE INFO
ABSTRACT
A yellow, alkali-clearable azo disperse dye containing a carboxylic ester moiety was readily
synthesized from the reactant p-aminobenzoic acid by successive diazotization, coupling
reaction, chlorination and esterification with ethanol. Then its molecular structure was
characterized by FTIR, 1H NMR, 13C NMR, mass spectrometry and elemental analysis. The
synthesized dye and a similar control dye containing the acylamide moiety (I) were applied to
dyeing poly(ethylene terephthalate) fabric and their washing and rubbing fastness properties
with different post-treatment methods (reduction clearing and alkali clearing) were examined
and compared. It is found that the ester-containing disperse dye shows good alkali-clear ability
on poly(ethylene terephthalate) fabric and contaminates little to environment due to the absence
of reductants, as well as low toxicity and easy recycling of the hydrolysates.
Article history:
Received 23 December 2013
Received in revised form 14 March 2014
Accepted 19 March 2014
Available online
Keywords:
Alkali-clearable
Synthesis
Carboxylic ester
Disperse dye
PET
1. Introduction
Disperse dyes with little water solubility are largely produced and widely used for coloration of hydrophobic fibers, such
as polyester. Since disperse dyes have limited solubility in water, some dye particles may remain on the fiber surface after
the dyeing is completed and cause reduced color fastness on washing and rubbing [1,2]. Therefore, it is customary to
remove the insoluble dye particles by some clearing processes after dyeing. The commonly used method for polyester
fabrics is reduction clearing, namely, the dyed fabrics were treated by a solution containing 2 g/L sodium hydrosulfite (as
o
reductant) and 1 g/L sodium hydroxide at 70 C for 15 min [3], which decomposes dispersed dye particles into water
soluble small molecules. However, the reduction clearing process causes serious water pollution because of the addition of
chemicals and increases the treatment difficulty of the effluents [4]. Additionally, disperse dyes containing azo groups can
also be cleaved to aromatic amines and some of them might be toxic and carcinogenic. Therefore, elimination of treatment
of reduction clearing in the dyeing polyester process with disperse dyes can significantly reduce the costs of effluent
treatments. Encouragingly, alkali-clearable disperse dyes offer a means of resolving the problem [5].
Alkali-clearable dyes, which can be solubilized by the solo action of alkali, have been developed in recent years. Some
phthalimide and sulfonyl fluoride containing disperse dyes have been reported due to their alkali-clearable property [6].
Phthalimide containing, alkali-clearable disperse dyes undergo ring opening and convert to water soluble dyes under
relatively mild alkaline conditions. As for sulfonyl fluoride containing, alkali-clearable disperse dyes, the incorporated
fluorosulfonyl group of these dyes can also be converted to the water soluble dyes containing sulfonate groups under mild
alkaline conditions. These water soluble dyes generated after alkali clearing are readily washed off without generation of
∗ Corresponding author.
E-mail address: zhhcui@zstu.edu.cn
Page 2 of 7

harmful primary aromatic amines, even if there are some azo groups in their chromophores.
In view of the lower toxicity of the hydrolysate of carboxylic ester group than sulfonyl fluoride and phthalimide groups
under alkaline conditions, in this work, a yellow, azo disperse dye containing a carboxylic ester moiety was readily
synthesized (see Scheme 1) and its structure was confirmed. The synthesized, ester-containing dye 4 and a similar control
dye (I, Fig. 1) containing acylamide moiety [7] were then applied to dyeing poly(ethylene terephthalate) (PET) fabric and
their wash and rubbing fastness properties with different after-treatment methods (reduction clearing and alkali clearing)
were examined and compared.
2. Experimental
All reagents were of analytic grade and obtained from commercial suppliers and used without further purification. Melting
1
points were measured on a Mel-Temp capillary melting point apparatus and were uncorrected. H NMR and 13C NMR
spectra were recorded on a Varian INOVA 400 NMR Spectrometer with TMS as internal standard in CDCl3. IR spectra
were measured with an FT/IR-430 spectrophotometer. Mass spectra (MS) were determined by using a HP1100 mass
spectrometer. Ultraviolet-visible (UV-vis) absorption spectra were recorded on a Lambda 900 UV/vis spectrophotometer.
The synthetic route of the target ester-containing dye is outlined in Scheme 1 which mainly contains three steps as
follows.
Synthesis of acid dye 2 by diazo coupling reaction: Acid dye 2 was synthesized by conventional diazo-coupling methods.
Initially, p-aminobenzoic acid (1.37 g, 10 mmol) was dissolved in a 5% sodium hydroxide aqueous solution (10 mL, 10
mmol) at room temperature and a 12% sodium nitrite (6 mL, 11 mmol) aqueous solution was rapidly mixed with the
amine solution. Subsequently, the amine–nitrite mixture was cooled to 0 – 5 oC and then rapidly poured into the ice-cooled
dilute hydrochloric acid (13 mL, 2.3 mol/L) solution already in the vessel. The coupling reaction was carried out by
adding the prepared diazonium salt solution to the coupling component (3-methyl-1-phenyl-2-pyrazoline-5-one) solution
(1.76 g, 10.1 mmol) at 0 – 5 oC, pH 8.5–9.0 for 3 h. The pH value of the coupling liquor was controlled by adding sodium
carbonate powder. The dye was salted out by adding 2.0 g sodium chloride. Crude yield: 4.0 g (116.3%); FTIR (KBr,
cm-1): 2850 (CH3), 1656 (C=O, pyrazolone), 1537, 1366 (C=O, COONa); MS (ESI, negative): m/z 321.1 [M-Na]–. The
crude dye 2 was then purified by the N,N-dimethylformamide/ether (3:20, v/v) purification method [8]. Yield: 1.9 g
(55.2%).
Synthesis of acyl chloride 3: N,N-dimethylformamide (0.2 mL) was added to a stirred suspended mixture of acid dye 2
(3.5 g, 10 mmol) and thionyl chloride (20 mL, 270 mmol) at room temperature. The mixture was heated to 60 oC and
stirred for 1.5 h. The solvent thionyl chloride was removed by vacuum distillation, and then the residue was transferred
into ice water (1:2 (w/w), 150 mL). After it was cooled to room temperature, the product was collected by filtration. The
filter was washed with ice-cooled water until the filtrate was colorless and neutral, then dried in a vacuum. The crude
product 3 was purified by recrystallization from toluene. Yield: 2.8 g (77.1%); mp 164–165oC; FTIR (KBr, cm-1): 1765
(C=O, acyl chloride), 1672 (C=O, pyrazolone); 1H NMR (400 MHz, CDCl3): δ 13.58 (s, 1H, =N–NH), 8.18 (d, 2H, Ar–H),
7.94 (d, 2H, Ar–H), 7.49–7.53 (m, 2H, Ar–H), 7.42–7.47 (m, 3H, Ar–H), 2.40 (s, 3H, N=C-CH3); MS (ESI, negative): m/z
339.1 [M-H]–, 341.1 [M+2-H]–; Element analysis: Found (%): C, 59.85, H, 3.93, N, 16.28; Calcd. (%): C, 59.92, H, 3.85,
N, 16.44.
Synthesis of ester-containing dye 4: To a stirred suspension of acyl chloride 3 (1.7 g, 5 mmol) in dry ethanol (30 mL),
K2CO3 (0.7 g, 5 mmol) and a few zeolites were added. The reaction mixture was heated to the boiling point and refluxed
for 1.5 h, then the solvent was entirely distilled and the residue was poured into 10 % dilute hydrochloric acid (100 mL).
The product was collected by filtration, the filter cake was washed with water until the filtrate was colorless and neutral,
then the ester-containing dye 4 was air dried at room temperature. The pure dye 4 was obtained by recrystallization in
ethanol. Yield: 1.5 g (85.7%); mp 143–145 oC; FTIR (KBr, cm-1): 2975, 2923, 2900 (CH3, CH2), 1707 (C=O, carboxylic
Page 3 of 7

ester), 1665 (C=O, pyrazolone); 1H NMR (400 MHz, CDCl3): δ 13.25 (s, 1H, =N–NH), 8.01 (d, 2H, Ar–H), 7.90 (d, 2H,
Ar–H), 7.74 (d, 2H, Ar–H), 7.47 (t, 2H, Ar–H), 7.24 (t, 1H, Ar–H), 4.33 (q, 2H, CH2), 2.32 (s, 3H, N=C-CH3), 1.33 (t, 3H,
CH3); 13C NMR (125 MHz, CDCl3): δ 165.8, 157.3, 148.6, 144.6, 137.8, 131.3, 129.9, 128.9, 127.1, 125.3, 118.3, 115.1,
61.1, 14.4, 11.8; MS (ESI, negative): m/z 348.8 [M-H]–; Element analysis: Found (%): C, 65.09, H, 5.24, N, 16.03; Calcd.
(%): C, 65.13, H, 5.18, N, 15.99.
3. Results and discussion
Generally, the commercial, azo disperse dyes are synthesized by a coupling reaction at the last step with the diazo and
coupling components prepared in the previous steps (see Scheme 2). The shortcoming of the route focuses on the amino
deprotection reaction which probably generates unwanted by-product 5 due to the hydrolysis of the carboxylic ester group,
either under acidic or alkaline conditions, and finally fails to yield the target product 4 in high yield.
Considering the defect of the traditional synthetic route on synthesis of the ester-containing dye, a facile, synthetic route
was designed by avoiding amino protection and deprotection reactions and only proceeds by successive diazotization,
coupling reaction, chlorination, and esterification from reactant p-aminobenzoic acid. The detailed synthesis procedure of
the ester-containing dye is shown in Scheme 1.
The chemical structure of dye 4 was confirmed by FTIR, 1H NMR, 13C NMR, mass spectrometry and elemental analysis.
It is known that azopyrazolone dyes predominantly exist in the hydrazone form over the azo form in the solid state and
1
acidic solutions [9]. The FTIR and H NMR spectra of the dye provide some characteristic results to prove this. The
stretching vibration band of carbonyl appears at 1665 cm-1 in the FTIR spectrum. The hydrogen-bonded NH proton
appears at δ 13.25 in the 1H NMR spectrum and its hydrogen integral is close to 1.0. The results suggest that dye 4 nearly
completely exists in the hydrazone form (see Scheme 3).
In order to prove the alkali-clearing ability of dye 4, dye I has been used for color fastness comparison with different
after-treatment methods. First of all, dye 4 and dye I had been milled for 8 h with pea gravel at room temperature in the
presence of dispersing agent NNO (Dye:NNO = 1:1, w/w). Then the dyes were utilized in the dyeing of PET fabric
samples in stainless steel sealed dye pots in an infrared high temperature (130 oC) dyeing machine, using a liquor ratio of
50:1. In the next step, reduction clearing (1 g/L NaOH and 2 g/L Na2S2O4, liquor-to-goods ratio 80:1, at 70 oC, for 15 min)
and alkali clearing (1 g/L NaOH, liquor-to-goods ratio 80:1, at 70oC, for 15 min) were carried out on the dyed samples.
After clearing, the samples were rinsed with cold water and air dried. The color fastness properties of various PET
samples were then assessed according to ISO standard [10,11].
The dye sorptions and K/S values of dye 4 and dye I on PET fabric at 130 oC for 1 h are listed in Table 1. It can be seen
that both of them show high sorption (>94%) and satisfied K/S values (>14) for color fastness tests at 0.5% owf. Table 1
also shows the washing and rubbing fastness test results of dye 4 and dye I on PET fabrics with various treatment methods.
Clearly, the treated samples of dye 4 and dye I by reduction clearing and alkali clearing show superior rubbing fastness
and washing fastness for cotton staining in comparison with those of the untreated samples. It confirms the effectiveness
of the clearing processes to remove the insoluble dye particles on the fiber surface. For dye 4, the sample treated by alkali
clearing shows equal fastness properties with the sample treated by reduction clearing. While for the control dye without
carboxylic ester group, the sample treated by alkali clearing shows inferior wet rubbing fastness and wash fastness for
cotton staining in comparison with the sample treated by reduction clearing. It means dye 4 has good alkali-clear ability
than that of dye I due to its easy hydrolysis and washability. In a word, the reductant-free treatment method could get the
same color fastness results and simplify the after-treatment process of dyeing wastewater.
Additionally, ester-containing dye 4 has some other advantages on application and after-treatment of dyeing effluents. The
hydrolysates of dye 4, namely acid dye 2 and ethanol, in which ethanol is of low toxic and acid dye 2 can easily be reused
by acidification, precipitation, filtration and then recycled (see Scheme 4).
4. Conclusion
Page 4 of 7

An alkali-clearable azo disperse dye containing a carboxylic ester moiety was facilely synthesized from
carboxylic-containing azo acid dye as reactant by chlorination and esterification with ethanol in high yield. The defect of
the traditional synthetic route of azo dyes, which could generate unwanted by-products, was avoided. The ester-containing,
alkali-clearable dye could be applied to PET fabric and attain the same excellent wet color fastnesses after alkali clearing
treatment without the utilization of reductants in comparison with that after reduction clearing treatment. The
ester-containing, disperse dye shows good alkali-clear ability and results in little contamination to the environment due to
the absence of reductants, as well as low toxicity and easy recycling of the hydrolysates.
Acknowledgements
The work was supported by the National Natural Science Foundation of China (Nos. 51173168, 21106135), Zhejiang
Provincial Key Innovation Team (No. 2010R50038), Zhejiang Provincial Top Key Academic Discipline of Chemical
Engineering and Technology, and “521” Talent Project of Zhejiang Sci-Tech University.
References
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group, Color. Technol. 120 (2004) 156-160.
J. Koh, Alkali-hydrolysis kinetics of alkali-clearable azo disperse dyes containing a fluorosulphonyl group and their fastness properties on PET/cotton blends,
Dyes and Pigm. 64 (2005) 17-23.
Standardization Administration of the People's Republic of China, Disperse dyestuff − Determination of shade and relative strength, GB/T 2394-2013.
J.H. Choi, J.Y. Choi, E.M. Kim, et al., Coloration properties and clearability of phthalimide-derived monoazo disperse dyes containing ester groups, Color.
Technol. 129 (2013) 352-359.
J.S. Koh, J.P. Kim, Synthesis of phthalimide-based alkali-dischargeable azo disperse dyes and analysis of their alkali-hydrolysis mechanism, Dyes and Pigm. 37
(1998) 265-272.
J.S. Koh, J.P. Kim, Application of phthalimide-based alkali-clearable azo disperse dyes on polyester and polyester/cotton blends, J. Soc. Dyer. Colour. 114 (1998)
121-124.
Z.H. Cui, X.D. Wang, W.G. Chen, E.L. Hua, K. Liu, Synthesis, spectral and dyeing properties of phenylazopyrazolone-containing acylamide disperse dyes
designed for poly(lactic acid), Color. Technol. 128 (2012) 283-289.
J. Yang, Analysis and Anatomy of Dyes, Chemical Industry Press, Beijing, 1989.
K. Hunger, Industrial Dyes: Chemistry, Properties, Applications, Wiley-VCH Verlag GmbH & Co. KgaA, Weinheim, 2003.
ISO 105-C03:1989 Textiles - Tests for colour fastness-Part C03: Colour fastness to washing: Test 3 (ISO, 1989).
ISO 105-X12:1993 Textiles - Tests for colour fastness-Part X12: Colour fastness to rubbing (ISO, 1993).
CH3
N
N
O
N
H
O
Coupling
O
Diazotization
NaNO2/HCl
H2N
N
OH
O
ONa
1
N
2
N
CH3
SOCl2/DMF
CH3
CH3
N
N
N
O
N
H
O
C2H5OH
N
N
N
N
O
H
Cl
O
OC2H5
4
3
Scheme 1. Facile synthetic route of an alkali-clearable azo disperse dye containing the carboxylic ester moiety.
Page 5 of 7

O
O
H
N
Acetylation
Chlorination
H
N
H3C
C
O
1
H3C
C
O
OH
Cl
C2H5OH
NH2
O
O
H
N
Coupling
Diazotization
NaNO2/HCl
H
N
Hydrolysis
Hydrolysis
H3C
C
O
4
H3C
C
O
OH
OC2H5
O
N
5
N
O
CH3
C2H5O
Scheme 2. Traditional synthetic route of an alkali-clearable azo disperse dye containing the carboxylic ester moiety and its defect.
O
O
OC2H5
OC2H5
H3C
N
H3C
N
N
O
N
N
H
N
N
N
OH
hydrazone form (predominant)
azo form (few)
Scheme 3. Changes between hydrazone and azo forms of ester-containing phenylazopyrazolone dyes 4.
CH3
CH3
N
N
N
H
O
N
H
O
NaOH
N
N
+
N
C2H5OH
N
O
ONa
O
OC2H5
low toxicity
4
2
HCl
CH3
N
N
H
O
Precipitation,
easy to recycle
N
N
O
OH
6
Scheme 4. The hydrolysis of alkali-clearable azo disperse dye containing the carboxylic ester moiety in alkali medium and the recycling process of hydrolyzate
dye.
CH3
N
N
H
O
N
N
O
NHC2H5
Control dye (I)
Fig. 1. The structure of the control dye containing the acylamide moiety.
Table 1
Dyeing and color fastness properties of ester-containing dye 4 and dye I on PET fabrics at 0.5% owf.
Washing fastness
Rubbing fastness
Dry Wet
Dye
Dye sorption (%)
K/S
Aftertreatment
Staining of cotton
Staining of PET
Page 6 of 7

Untreated
3
4-5
4-5
4-5
4-5
4-5
4-5
3-4
4-5
4-5
3-4
4-5
4-5
3
95.6
94.5
15.6
14.7
4
I
Reduction clearing a
Alkali clearing b
Untreated
3-4
3-4
3
4-5
4-5
3
Reduction clearing a
Alkali clearing b
4
4-5
4
3-4
a 1 g/L NaOH and 2 g/L Na2S2O4, liquor-to-goods ratio 80:1, 70 oC,15 min.
b 1 g/L NaOH, liquor-to-goods ratio 80:1, 70 oC, 15 min.
Page 7 of 7