Annals of West University of Timisoara

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Annals of West University of Timisoara Series Chemistry 13 (1) (2004) 27-32 SYNTHESIS IN NON-AQUEOUS MEDIUM OF SOME SYMMETRICAL DISAZO DIRECT DYES DERIVED FROM 4,4 -DIAMINOSTILBENE-2,2 -DISULPHONIC

April 2004 Accepted: 15 May 2004 SUMMARY Three disazo direct dyes derived from 4,4 -diaminostilbene-2,2 -disulphonic acid were synthesized by a new procedure which involves coupling reactions of

1 Annals of West University of Timisoara Series Chemistry 13 (1) (2004) SYNTHESIS IN NON-AQUEOUS MEDIUM OF SOME SYMMETRICAL DISAZO DIRECT DYES DERIVED FROM 4,4 -DIAMINOSTILBENE-2,2 -DISULPHONIC ACID Maria Grad a, Georgeta Simu a, Simona Hora a a Institute of Chemistry Coriolan Dragulescu, Romanian Academy, Mihai Viteazul, 24, Timisoara, , Romania Received: 26 Mars 2004 Modified: 20 April 2004 Accepted: 15 May 2004 SUMMARY Three disazo direct dyes derived from 4,4 -diaminostilbene-2,2 -disulphonic acid were synthesized by a new procedure which involves coupling reactions of bis-diazotized 4,4 -diaminostilbene-2,2 -disulphonic acid with 2-hydroxybenzoic acid, 1,3- dihydroxybenzene and 2-naphthol in a non-aqueous medium. The three dyes were obtained in high yields and were isolated as free acids. The new procedure of synthesis has great advantages when pure and concentrated dyes free of salts are required. Keywords: Disazo dyes, 4,4 -diaminostilbene-2,2 -disulphonic acid, coupling reaction INTRODUCTION Azo dyes represent the largest class of organic colorants listed in the Color Index (60-70 % of the total). Among this class, direct dyes are second only to sulphur dyes in their textile usage, with vat and fiber reactive dyes far behind [1]. Practically, all azo dyes are produced from diazo compounds and coupling components by means of the azo coupling reaction [2]. The diazo component is usually an aromatic amine or diamine. For the synthesis of direct dyes, the diamine must fulfill the following requirements: it should ensure the 27

2 G RAD M., S IMU G., H ORA S. formation of a dye having a coplanar molecule and extended conjugated system, it should be capable of affording asymmetric dyes. The simplicity of their synthesis and the accessibility of the raw materials are also very important. In this regard, 4,4 -diaminostilbene-2,2 -disulphonic acid is an aromatic diamine suitable as diazo compound and was already been used in the synthesis of some diazo direct dyes [3]. SO 3 H HO 3 S H 2 N CH CH NH 2 Structure I. 4,4 -diaminostilbene-2,2 -disulphonic acid As coupling components, the benzene hydroxy derivatives, and some aromatic amines are the most used ones. Coupling reactions are carried out in aqueous medium at different ph values, depending on whether coupling is performed with a phenol (naphthol) or with an aromatic amine. In some cases, the addition of common salt before coupling gives a higher yield. In other cases, the coupling reaction occurs only in presence of pyridine or pyridine homologues. In every case, optimum coupling conditions must be established for each combination of diazo- and coupling components. Azo coupling in non-aqueous medium has not yet been investigated systematically. However, coupling reaction in mixtures of benzene and glacial acetic acid has been studied by Huisgen, in his work on the rearrangement of nitrosoacylanilines [4]. In this work, a new procedure of synthesis of some disazo dyes derived from 4,4 - diaminostilbene-2,2 -disulphonic acid is presented. The new procedure involves coupling reaction in non-aqueous medium and the isolation of the synthesized dyes as dyes free of salts. MATERIALS AND METHODS 1. Materials 4,4 -diaminostilbene-2,2 -disulphonic acid, 2-hydroxybenzoic acid, 1,3- dihydroxybenzene and 2-naphthol were provided from Aldrich Chemical Company. Electronic spectra were recorded on a Cecil CE7200 spectrophotometer from 0.1 M NaOH and 50% CH 3 COOH aqueous solutions. The extinction coefficient (ε) was 28

3 SYNTHESIS IN NON-AQUEOUS MEDIUM OF SOME SYMMETRICAL DISAZO DIRECT DYES calculated from the Lambert-Beer law, using equation (1): A ε = c d where: ε is the extinction coefficient [L/g.cm]; A is the optical density, c is the concentration [g/l] and d is the layer thikness [cm]. The thin layer chromatographic (TLC) data were taken from silica gel plates (Merck 60F- 25) and the eluting system isopropanol: methyl-ethyl-ketone: NH 3 25% = 4:2:4, and isopropanol: methyl-ethyl-ketone: NH 3 25%: dimethylformamide = 8:6:3:8. 2. Dyes synthesis Step 1. Bis-diazotization of 4,4 -diaminostilbene-2,2 -disulphonic acid 4.35 g (0.01 mol) of 4,4 -diaminostilbene-2,2 -disulphonic acid (85%) was dissolved at 40 oc in a solution containing 0.8 g (0.02 mol) NaOH in 40 ml distillated water. 4 g ice were then added and the solution was cooled down to 15 o C. A 30 % HCl solution (6 ml, 0.5 mol) was added dropwise, under continuous stirring to the 4,4 - diaminostilbene-2,2 -disulphonic acid solution. The disulphonic compound of 4,4 - diaminostilbene-2,2 -disulphonic acid precipitated. The temperature was brought to 5 o C by addition of ice and 5 g (3.9 ml, 0.02 mol) 30% NaNO 2 solution was added dropwise during 2 hours. The ph of the mixture was kept acid. After the addition of NaNO 2, the mixture was stirred for another hour. Finally, the excess of nitrous acid was decomposed by urea. Thus, the obtained bis-diazonium salt was filtered and the precipitate was washed several times with distillated water for complete removal of salts. Step 2. Bis-azo coupling reactions Individual solutions of coupling components (e. g. 2-hydroxybenzoic acid, 1,3- dihydroxybenzene and 2-naphthol) were prepared by dissolving o.023 mol of compounds in dimethylforamide in a molar ratio of 1: mol of bis-diazonium salt obtained in Step 1 was suspended in 20 ml ethanol and was added dropwise to the individual solutions of coupling components at 5 o C, in about 1 hour. The mixtures were stirred at 5-10 o C during 12 hours. After completition of the coupling reactions, the dyes were precipitated by addition of dioxane to the reaction mixture. The overall yields were about 75-80%. The crude dyes were purified by several recrystalizations from dioxane:pyridine = 99:1 (v:v). (1) 29

4 G RAD M., S IMU G., H ORA S. RESULTS Three disazo dyes based on 4,4 -diaminostilbene-2,2 -disulphonic acid having the general structure II were synthesized first by the conventional manner and then by an original procedure. SO 3 H HO 3 S Ar N N CH CH N N Ar where Ar: IIa Structure II COOH OH HO IIb OH OH IIc The compounds were characterized by electronic spectra and their purity was checked by means of thin layer chromatography. The overall reaction yields obtained (by both procedures), the spectrophotometric properties of dyes II obtained by the new procedure, the R f coefficients and the color on cotton respectively are shown in Table I. Table I. Reaction yields, spectrophotometric properties, R f coefficients and color on cotton for dyes IIa, IIb and IIc. Dye Yield* [%] Yield [%] λ max** [nm] ε λ max*** [nm] ε R f**** Color on cotton IIa yellow IIb orange IIc violet * new procedure of synthesis; ** in 0.1 M NaOH solution; ***in 50% methanol solution; **** silica gel plates (Merck 60F-25) and isopropanol:methyl-ethyl-ketone:nh 3 25% = 4:2:4 (for dyes IIa and IIc), and isopropanol:methyl-ethyl-ketone:nh 3 25%:dimethylformamide = 8:6:3:8 (dye IIb) as eluting systems. 30

5 SYNTHESIS IN NON-AQUEOUS MEDIUM OF SOME SYMMETRICAL DISAZO DIRECT DYES DISCUSSION New coupling reaction conditions were established for the synthesis of three disazo dyes with general structure II. The three disazo dyes were first synthesized by the conventional manner [5]. Thus, the coupling reaction was carried out in an alkaline aqueous medium, in presence of Na 2 CO3 and NaOH. The suspension of bis-diazotised 4,4 -diaminostilbene-2,2 -disulphonic acid was directly added to the individual alkaline solutions of the corresponding coupling components. The coupling reactions occurred at ph values ranging between (IIa, IIb) to 9.5 (IIc). In the case of the coupling reactions of bis-diazotized 4,4 -diaminostilbene-2,2 - disulphonic acid with 2-hydroxy benzoic acid and 1,3-dihydroxybenzene respectively, an increased alkalinity of the reaction medium was avoided because it gives rise to the formation of undesirable by-products. This is due to the fact that in a strong alkaline medium, both 2-hydroxybenzoic acid and 1,3-dihydroxybenzene can react consequently not only in the 4- position to the OH group but also in the 2- position (2-hydroxybenzoic acid) or in the 2- and 5-positions (1,3-dihydroxybenzene). The dyes were obtained as sodium salts, with high overall yields (see Table I). The new procedure involves an original way to conduct the coupling reactions of bis-diazotized 4,4 -diaminostilbene-2,2 -disulphonic with the coupling components. As reaction medium, an organic solvent, e.g. dimethylformamide was chosen. Furthermore, the diazonium salt was isolated by filtration, washed for several times with distillated water and suspended in ethanol prior to its use in the coupling reactions. During the syntheses it was noticed that longer reaction time were necessary for the completition of the coupling reaction (as compared to the conventional manner). However, no by-products were formed and the overall reaction yields were slightly better (see Table I) than those obtained by conducting the coupling reaction in aqueous medium. According to the new procedure, dyes II were isolated as free acids. This is a great advantage when pure and concentrated dyes free of salts are required. On the other hand, the filtrates which result after dye synthesis contain none or only small amounts of dye, which are easy to remove. 31

6 G RAD M., S IMU G., H ORA S. CONCLUSION New coupling reaction conditions in a non-aqueous medium were established for the synthesis of three disazo symmetric dyes derived of 4,4 -diaminostilbene-2,2 - disulphonic. According to the new procedure, the disazo dyes with structure II were obtained in high yields and were isolated as free acids. REFERENCES 1. Aspland J. R., Direct Dyes and their Application, Text. Chem. Color., 23(11)(1991) Rys P., Zollinger H., Fundamentals of the Chemistry and Application of Dyes, Wiley- Interscience, London, New York, Sydney, Toronto, 1970, p Chao Y. C., Pan Y. I., Trisazo Dyes Derived from 4,4 -Diaminodiphenylsulphide: Substitutes for C. I. Direct Black 38 and C. I. Direct Green 1, Dyes Pigments, 31 (1996) Zollinger H., Azo and Diazo Chemistry. Aliphatic and Aromatic Compounds, Interscience Publishers Inc. New York, 1961, p Sanielevici H., Urseanu F., Sinteze de Coloranti Azoici, Ed. Tehnica Bucuresti, 1987, Vol. II, p

THERMODYNAMIC STUDY OF A SYMMETRICAL DISAZO DIRECT DYE DERIVED FROM 4,4 -DIAMINO-BENZANILIDE ON MERCERIZED COTTON

THERMODYNAMIC STUDY OF A SYMMETRICAL DISAZO DIRECT DYE DERIVED FROM 4,4 -DIAMINO-BENZANILIDE ON MERCERIZED COTTON THERMODYAMIC STUDY OF A SYMMETRICAL DISAZO DIRECT DYE DERIVED FROM 4,4 -DIAMIO-BEZAILIDE O MERCERIZED COTTO SIMU Georgeta Maria, FUAR-TIMOFEI Simona, BALŞ Gianina Institute o Chemistry Timişoara, Romanian