Studies on Dyeing Performance of Novel Acid Azo Dyes and Mordent Acid Azo Dyes Based on 2 , 4-Dihydroxybenzophenone

Novel acid azo and mordent acid azo dyes have been prepared by the coupling of diazo solution of different aminonaphthol sulphonic acids and aromatic amino acids with 2,4-dihydroxybenzophenone. The resultant dyes were characterized by elemental analysis as well as IR and H NMR spectral studies. The UV-visible spectral data have also been discussed in terms of structure property relationship. The dyeing assessments of all the dyes were evaluated on wool and silk textile fibers. The dyeing of chrome pretreated wool and silk have also been monitored. The result shows that better hue was obtained on mordented fiber. Results of bactericidal studies of chrome pretreated fibers revealed that the toxicity of mordented dyes against bacteria is fairly good. Dyeing on wool and silk fibers resulted in yellowish pink to reddish brown colourations having excellent light fastness and washing fastness.

The area in which the acid azo dyes and mordent azo dyes formation based on this compound has not been developed except of few patents [13][14][15][16] .
The formation of dyes based on this compound may yield the dyes with good hue properties.Hence, in continuation of our earlier work 17 , it was thought interesting to explore the field of acid azo dyes based on 2,4-dihydroxybenzophenone. Thus, the present communication comprises the synthesis, characterizations and dyeing performance of novel acid azo and mordent acid azo dyes based on 2,4-dihydroxybenzophenone.

Experimental
All the chemicals used were of analytical grade and were further purified as and when required.The aminonaphthol sulphonic acids and aromatic amino acids listed in Scheme 1 were used for diazotization.Wool and silk fibers were gifted by Color Tax (Pvt) Ltd, Surat.Melting points were determined by open capillary method and are uncorrected.The visible absorption spectra were measured on a Carl Zeiss UV/VIS Specord spectrometer, and elemental analysis was carried out on Perkin Elmer CHNS/O Analyzer 2400 Series II.Infrared spectra were recorded in KBr pellets on a Perkin-Elmer Spectrum GX FT-IR model, proton NMR spectra were recorded on Hitachi R-1500 in DMSO-D 6 solvent and TLC (Thin layer chromatography) was run on a aluminum sheets precoated with silica gel 60 F 245, (Merck, Germany) using methanol-water-acetic acid (12:3:7) solvent system.Colour spot was visualized by UV chamber.HTHP dyeing machine (model-LL) was used for dying purpose.

Synthesis of acid azo dyes Diazotization
Diazotization of various aminonaphthol sulphonic acid and aromatic amino acid 1(a-g) (Scheme 1) was carried out by the method reported in literature 18,19 .

Coupling procedure
The coupling of above mentioned diazotized aminonaphthol sulphonic acid and aromatic amino acid 1(a-g) was carried out in the similar manner.The general procedure followed is given below: 2,4-Dihydroxybenzophenone (2.15 x 10 -3 kg, 0.01 mol) was dissolved in sodium hydroxide (1.2 x 10 -5 m 3 , 0.01 mol) solution.The clear solution was cooled in ice-bath and diazonium solution of aminonaphthol sulphonic acid and aromatic amino acid 1 (a-g) was added drop wise over a period of 30 min with vigorous stirring.The pH was maintained between 2.0 to 3.0 by simultaneous addition of 10 % w/v sodium carbonate solution.Stirring was continued for 2 h, allowing the temperature rise to ambient.The dyes was then filtered off and dissolved in distilled water after that acid azo dyes were obtained by evaporation procedure, and it was dried at room temperature.The dyes were designated as acid azo dye (D 1-7 ) and were recrystalised in acetone.

Acid azo dyeing method
Dyeing of wool and silk fiber, is convenient at 90 0 -130 0 C and at high pressure (165.6 kpa -207 kpa) in the laboratory.A model glycerin-bath high-temperature beaker and HTHP (model-LL) dyeing machine was used.For this purpose a paste of finely powdered acid azo dye (6 x 10 -5 kg) was prepared with dispersing agent dodamol (9 x 10 -5 kg), wetting agent Tween-80 (6 x 10 -6 kg) and water (2 x 10 -6 m 3 ) in a ball mill.To this paste, water (9.9 x 10 -5 m 3 ) was added with stirring and the pH was adjusted to 2.0 -4.0 using acetic acid, the previously mentioned dye suspension (1 x 10 -4 m 3 ) was added to a beaker provided with a lid and a screw cap.Before closing the lid and lightening the metal cap over the beaker a wetted pattern of wool and silk fiber was rolled in to the beaker, and then placed vertically on the rotatory carrier inside the tank and the clamp plate was firmly tightened.
The rotatory carrier was then allowed to rotate in the glycerin-bath and the temperature was raised to 90 0 C at the rate of 2 0 C/min.The dyeing was continued for 1 h under pressure.After cooling for 1 h, the beaker was removed from the bath and washed with distilled water.The dyed pattern was thoroughly washed with cold water and dried at room temperature.

Mordent dyeing method
The dye pattern of wool and silk fibers obtained from the above mentioned process was treated with potassium dichromate solution equal to half of the weight of dye and it was allowed to roll into the beaker and again, the beaker was then placed vertically on the rotatory carrier inside the tank and the dyeing was continued for 1 h under the pressure.After cooling for 1 h, the beaker was removed from the bath and washed with cold distilled water.The dyed pattern was thoroughly washed with warm water and air dried at room temperature.

Determination of the percentage exhaustion and fixation
The dye bath percentage exhaustion and fixation of the dyed fabric was determined according to the known method 20 and is shown in Table 1.

Fastness property
The fastness to light, sublimation and perspiration of dye pattern was assessed according to British standard: 1006-1978 and the wash fastness test according to Indian standard: IS: 765-1979.The rubbing fastness was tested by using Crock meter (Atlas) AATCC-1961, shown in Table 2 to 5.

Physical properties of dyes
All the dyes are obtained as crystal powder ranging from yellowish pink to pinkish blue in colours.The purity of the dyes were checked by TLC using methanol-water-acetic acid (12:3:7) solvent system.The TLC results show that only single spot observed for each dye.The purified dyes have melting point measured by open capillary tube.The melting points were uncorrected.
The results of elemental analysis content of each dyes are consistent with the predicted structure as shown in Scheme 1.The number of azo group is almost one for each dye.The nitrogen content and number of azo group for each dye are co-related with each other.The IR spectrum of each dye comprises the important features of aromatic, azo, hydroxyl and keto groups.The 1 H NMR spectra of all the diazo compounds based on 2,4dihydroxybenzophenone shows an important signals at their respective positions confirmed the structures of various dyes as shown in Scheme 1.
The visible absorption spectroscopic properties of dyes were recorded in double distilled water.The absorption maxima (λ max ) of all the dyes fall into the range of 422-465 nm in water, as shown in Table 1.The value of the logarithm of molar extinction coefficient (log ε) of all the dyes were in the range of 4.21 -4.60, consistent with their high intensity of absorption.
Moreover, the presence of electron donating or electron attracting groups did not bring about any marked increase or decreased in λ max in the visible region and that log ε remained nearly constant.However, electron attracting substituents like -SO 3 H and -COOH in the substituent group of the coupler increase polarizability, and will results in bathochromic shifts.This leads to decrease in energy between the highest occupied molecular orbital and lowest unoccupied molecular orbital and thus π→π* electronic transition takes place at lower frequency photon, resulting in the bathochromic shift of the visible absorption band.

Dyeing properties of dyes
The acid azo dyes were applied at 2% depth on wool and silk fabric respectively.Their dyeing properties are given in Table 2 to Table 5.These dyes gave a wide range of colours varying from yellowish pink to pinkish blue shades with good levelness, brightness and depth on the fabrics.The variation in the shades of the dye fabric results from both the nature and position of the substituent present on the diazotized compound.The dyeing showed an excellent fastness to light, with very good to excellent fastness to washing, perspiration and sublimation, however it shows poor rubbing fastness.
A remarkable degree of levelness after washing is observed.This may be attributed to good penetration and affinity of the dye molecule in to fiber structure.The most prominent features of these dyes is that, the dye patterns treated with Cr (III) salt solution afford excellent shining shade of dyes.This might be due to the chrome complex formation on fiber matrix.The bacterial activities of chrome complexes of dyes were monitored against the plant pathogens.The results show that these dyes are inhibiting the bacteria about 70 to 80% and are shown in Table 6.The dye pattern of chrome treated dye may be affordable for human body.

Conclusions
Produced acid azo dyes have good fastness to light, sublimation and perspiration but show poor rubbing fastness properties.The nature of the substituent in the coupling components has a little influence on the visible absorption and shade of the dyeing.Comparison of above two dyes reveals that mordent acid azo dyes have better shades than acid azo dyes.

Table 5 .
Results of mordent acid azo dyeing and various fastness properties of dyes on silk.

Table 2 .
Results of acid azo dyeing and various fastness properties of dyes on wool.

Table 3 .
Results of acid azo dyeing and various fastness properties of dyes on silk.

Table 4 .
Results of mordent acid azo dyeing and various fastness properties of dyes on wool.