Synthesis and Dyeing Performance of Some Novel Heterocyclic Azo Disperse Dyes

A síntese de novos azocorantes heterocíclicos derivados de 5-acetil-2-amino-4-metiltiazol (1) utilizando-se de vários N-alquil derivados da anilina (2a-e) e suas performances como corantes dispersos foram avaliadas em tecidos de poliester e nylon. As propriedades espectrais desses corantes foram determinadas. Os tecidos tingidos mostraram fixação moderada a boa na presença de luz, boa estabilidade à fricção, transpiração, lavagem e excelente estabilidade à sublimação. Esses corantes forneceram tonalidades de cor variando entre laranja e vermelho com boa profundidade e distribuição nos tecidos.


Introduction
Heterocyclic diazo components have been used extensively in the preparation of disperse dyes with outstanding dischargeability on cellulose acetate.These dyes are characterised also by having generally excellent brightness and high extinction coefficients, relative to azo dyes derived from substituted anilines.These properties encouraged work on dyes prepared from heterocyclic diazo components suitable for dyeing synthetic fabrics.
Early interest in heterocyclic diazo components was stimulated by the need for blue disperse dyes with improved dischargeability and gas fastness (oxide of nitrogen) for cellulose acetate.Before 1950, almost all the disperse dyes used were prepared from the anthraquinone class and had the limitations of poor dischargeability and sensitivity to oxides of nitrogen.Red and blue azo dyes with good dischargeability for use in printing were developed.Investigation of the use of heterocyclic diazo components was stimulated by the discovery of Dickey JB of Eastman Kodak in 1950.In 1953, they prepared bright blue heterocyclic azo disperse dyes 1 from 2-amino-5-nitrothiazole with adequate light fastness combined with excellent dischargeability, gas fastness and dyeability on cellulose acetate.The commercial success of such bright blue azo disperse dyes for cellulose acetate showing considerable interest in this class of dyes.With the exceptional of the 5nitro derivatives for discharge printing of dyeing cellulose acetate fabrics, 2-thiazolylazo dyes have so far achieved only secondary importance as bright blue dyes for polyester.Greenish blue dyes can be prepared by choosing a coupler containing electron donating groups such as 5-acetamido-2methoxyaniline derivatives.Additional early work on the 2thiazolylazo dyes resulted in violet dyes from 2-amino-5alkylsulphonylthiazole 2 and even more bathochromic dyes from 2-amino-4-alkylsulphonyl-5-nitrothiazole 3 .The pronounced bathochromic shift of the 5-nitro-2-thiazolylazo dyes, compared with the red azo dyes derived from the corresponding nitroaniline 4 , was of great interest.Early dyes showed moderate light fastness on cellulose acetate and polyesters, and light fastness on polyamides was very poor.Also, on polyesters the dyes had poor sublimation fastness for the thermofixation method of dyeing and showed loss of colour under high temperature exhaust dyeing conditions, particularly at high pH values.Dyes with increased light *e-mail:mardiahari@usa.net fastness and/or sublimation fastness were prepared from aniline type coupling components containing one or more N-alkyl groups substituted with groups such as cyano 5 , alkoxy 6 , pyridinium 7 and sulphato 8 were used as coupling components.
During the last ten years, the level of interest as indicated by the patent literature has grown in the field of thiazolylazo disperse dyes [9][10][11][12] .There has been a considerable growth in the volume of data reporting outside of patent literature [13][14][15][16][17][18][19][20] .It seems that no report is available on the use of 5-acetyl-2amino-4-methylthiazole in the synthesis of disperse dyes by coupling with various N-alkylanilines.Hence, it was thought worthwhile to synthesise a series of disperse dyes from 5acetyl-2-amino-4-methylthiazole (1) using various substituted N-alkyl-N-(2-hydroxyethyl) aniline derivatives 2a-e as coupling components.The resulting dyes were applied to polyester and nylon fabrics and their dyeing performance has been studied.

General
All of the chemicals and various coupling components used were of commercial grade and were further purified by recrystallisation and redistilled before use.The solvents used were spectroscopic grade.Melting points were determined by open capillary method.The visible absorption spectra were measured in a Carl Zeiss UV/VIS Specord spectrometer.The elemental analysis were carried out on a Carlo Erba Elemental Analyser 1108.Infrared spectra were recorded on a Perkin-Elmer model 983 spectrometer scanning between 4,000 to 400 cm -1 using a KBr pellets.Purification of the products was carried out by TLC (1 mm thickness glass plates 20 x 5 cm, using suspension of silica gel G in CHCl 3 ).The diazo component 5-acetyl-2-amino-4-methylthiazole (1) was prepared according to the literature 21 .Fastness to light, sublimation and perspiration were assessed in accordance with BS:1006-1978.The rubbing fastness test was carried out with a crockmeter (Atlas) in accordance with AATCC-1961 and the wash fastness test in accordance with IS:765-1979.The details of the method of colour fastness tests were described in the literature 22 .The dyeing of polyester and nylon fabrics were carried out according to the literature 22 .The percentage dyebath exhaustion of the dyed fabrics was determined according to the known method 23 .solution thus obtained was used immediately in the coupling reaction (see Scheme 1).Now N-(2hydroxyethyl)aniline (2a, 2.74 g, 0.02 mol), was dissolved in 10 cm 3 of AcOH, then cooled in an ice-bath at a 0 o C. The diazonium solution previously prepared was added dropwise over 1 h with vigorous stirring at 0-3 o C. The reaction mixture was stirred for further 2 h at 0-5 o C, then 10 % AcONa solution was dropped in slowly until the pH became 4-5.The product was then filtered off, washed with water until acid-free, dried at 50 o C in an oven to give azo dye 1a, which was recrystallised three times from EtOH (4.98 g, 82 %).The mp 208-209 o C (EtOH).

Results and Discussion
Preparation of Dyes 5-Acetyl-2-amino-4-methylthiazole (1) was diazotised satisfactorily at 0-5 o C by nitrosylsulphuric acid in AcOH.In order to determine the end point of diazotisation, it was found useful to check for the presence of unreacted diazo component on TLC by sampling the diazotisation mixture.Thus, when unreacted diazo component no longer persisted on TLC, the diazotisation was ended.The diazonium salt solution was used immediately since this decomposed on standing, even when cold.Subsequent coupling reactions took place readily on adding the resulting diazonium salt continuously to the solution of coupling component in acetic acid.Coupling was usually accompanied by some evidence of decomposition; however 80-85 % yield of dye were usually obtained by careful addition of the diazonium salt solution at 0-3 o C to a solution of the coupling component in an acetic acid..To complete coupling, particularly for reactions using nitrosylsulphuric acid in the previous diazotisation, the pH of the reaction mixture was adjusted to approximately 4-5.Thus, an appropriate amount of 10 % sodium acetate solution was slowly added below 5 o C.

Physical properties of dyes
The purity of all the dyes was checked by TLC using methanol/water/acetic acid (12:3:7 v/v) as the solvent system.When adsorbed on silica chromatography plates, the dyes produced orange-red colours.All the recrystallised dyes exhibited well-defined melting points characteristic of pure compounds but it would be unwise to attempt to explain in detail their relative values, because of the complex dependence of the melting points on a number of factors (e.g.polarity, size, geometry, interaction etc).
The following dyes 1b-e were prepared in similar manner using various coupling components 2b-e.The characterisation data of dyes 1a-e are given in Table 1.

Spectral properties of dyes
Absorption maxima of dyes 1a-e were recorded in DMF solution and are shown in Table 1.As far as absorption maxima are concerned, λ max values are directly proportional to the electronic power of the substituents in the coupled ring system.The value of the logarithm of molar extinction coefficient (log ε) of the dyes were in the range of 4.13-4.83,consistent with their high intensity of absorption.The introduction of electrondonating or electron-attracting groups at suitable positions in the coupled ring affect the absorption characteristics of the dyes.As can be seen from the data in Table 1, the bathochromic shift can be obtained by enhancing the electron donor properties of the coupled ring, e.g. by introducing a methyl group ortho to the azo group, as in dye 1d.This gave considerable shift of 15 nm relative to dye 1e.Thus, electron displacement can be enhanced by electron donating substituents on the coupled ring.The resulting increase polarisability should result in bathochromism.An additional small bathochromic shift of 3 nm also resulted from increasing the alkyl chain length of dye 1c; for example, when replacing the methyl group by ethyl group, the resulting dye 1c absorbed at 508 nm.

Infrared spectra of dyes
The infrared spectra of dyes 1a, 1d and 1e are shown in Figure 1.The characteristic band at 3400-3420 cm -1 indicates the N-H and O-H stretching.The strong bands observed at 1600-1610 cm -1 indicate stretching vibration of the C=O.The bands at 820-830 cm -1 and 1320-1360 cm -1 correspond to para disubstituted ring and -C-N-C stretching, respectively.The azo group is confirmed at 1515-1520 cm -1 .The band at 1450-1460 cm -1 is due to the alkyl chain.The methyl group is confirmed at 2895-2900 cm -1 .

Dyeing properties of dyes
The disperse dyes 1a-e were applied at 2 % depth on polyester and nylon fabrics.Their dyeing properties are given in Tables 2 and 3. Change for these dyes are gave red hues with good levelness, brightness and depth on the fabrics.The variation in the hues of the dyed fabric result from both the nature and position of the substituent present on the coupler ring.The dyeings showed good to very good fastness to light, washing, rubbing and perspiration and excellent fastness to sublimation.A remarkable degree of levelness after washing indicates good penetration and affinity of these dyes to the fabrics.

Conclusion
The diazo component 5-acetyl-2-amino-4-methylthiazole (1) possessed sufficiently basicity to warrant the employment of various condition for diazotisation.It was found that nitrosylsulphuric acid was needed for satisfactory diazotisation.A series of azo disperse dyes containing various N-alkyl-N-(2-hydroxyethyl)aniline coupling moiety have been synthesised by conventional method and their colour properties examined in solution, and applied to polyester and nylon fabrics.
These dyes derived from 1 provided reddish orange rather than blue hues on polyester and nylon fabrics.These dyes, however, are noteworthy in its excellent affinity and intensity of colour.Outstanding characteristics of these dyes are that they give deep and bright hues with level dyeing.The bright hue might be attributed to the greater planarity of the thiazole dyes, because of the lower steric interaction of a five membered ring.

Table 1 .
Characterisation data for dyes 1a-e

Table 2 .
Colour fastness properties and exhaustion of dyes 1a-e on polyester fabric

Table 3 .
Colour fastness properties and exhaustion of dyes 1a-e on nylon fabric