Synthesis And Alkaline Resistance Mechanism Of Azo Disperse Dyes Based On Hydrogen Bonding

The alkali-resistant disperse dyes enable polyester fabrics to be dyed under alkaline conditions.This helps to realize the dyeing of polyester/cotton blended fabrics in the same bath,and improves production efficiency.It reduces the use of water resources,dyeing auxiliaries,and the burden of printing and dyeing wastewater treatment.At present,most alkali-resistant disperse dyes generally have the problem of poor alkali resistance and unclear alkali resistance mechanisms.Based on this,we synthesized eight azo disperse dyes containing cyano and hydroxyl groups,investigated the relationship between molecular interactions-molecular coplanarity-dye properties,explored the mechanism of alkaline hydrolysis of disperse dyes containing cyano and hydroxyl groups,and finally analyzed the alkaline dyeing performance of the eight dyes on polyester and polyester/cotton blended fabrics.The study content and results are as follows:（1）Four azo disperse dyes（D1-D4）and four bis-azo disperse dyes（D5-D8）with 3-（Trifluoromethyl）aniline,2-amino-6-fluoro benzothiazole,resorcinol as diazo components and N,N-dihydroxyethyl aniline,N-（2-cyanoethyl）-N-hydroxyethyl aniline,3-（trifluoromethyl）aniline,4-（trifluoromethyl）aniline,3-methylaniline and 4-methylaniline as coupling components were designed and synthesized.The structure and maximum absorption wavelengths(λ_max)of the dyes were characterized using FT-IR,HPLC-MS,¹H NMR,¹³C NMR and UV-Vis.The results showed that disperse dyes D1-D8 were successfully prepared.Theirλ_max are 423 nm,428 nm,510 nm,494 nm,404 nm,406 nm,429 nm and 440 nm,respectively,where the color light of D3 and D4 is red and the rest of the dyes are in the yellow spectral range.（2）Structural optimization of disperse dyes D1-D8 by DFT.Two dyes single crystals were developed to corroborate with the calculated results,and the relationship between dyes spatial structure and properties was investigated.The results show that disperse dyes D1-D8 have excellent planar properties,and comparing the single crystal with the calculated optimized structure verifies that the DFT calculation method has good accuracy.The single crystals of dyes D6 and D7 are both monoclinic crystal systems with good molecular coplanarity and a tight,ordered stacking structure between the crystals.Intermolecular forces between dyes were analyzed by Hirshfeld surfaces and 2D Fingerprint plots.The D6 intermolecular forces are mainly composed of hydrogen bonds,van der Waals forces andπ-πinteractions,with the largest proportion of H…F/F…H interactions representing hydrogen bonds,about 34%.The dye D7intermolecular forces are also mainly composed of hydrogen bonds,van der Waals forces andπ-πinteractions.Among them,the representative H…H weak interactions account for the most,about 53%.At the same time,dyes D6 and D7 have intramolecular hydrogen bonds,which make the dye structure more stable.The intramolecular hydrogen bonding regulates the molecular planar properties and the intermolecular forces give the dyes a tight,ordered stacking structure,which hinders nucleophilic reagents from attacking the dyes.（3）The mechanism of alkaline hydrolysis of disperse dyes containing cyano or hydroxyl groups was investigated.The results showed that the cyano group in dye D4 is hydrolyzed to amide group and carboxyl group successively,this led to an increase in the water solubility of the dye,which was completely hydrolyzed after 30 min of treatment under high temperature and high pressure alkaline conditions.The transition state of propionitrile was calculated using DFT and the results were consistent with the experimental data.hydroxyl groups in D5 ionized under alkaline conditions and the polarity of the dye increased,but the dye was not completely hydrolyzed during the whole alkali treatment.After treatment,polyester fabrics were dyed using hydrolysis solutions of D4 and D5.the K/S value of D4 dyed fabric was only 2.085.However,the K/S value of D5 dyed fabric was 21.443 and the evenness was good,showing excellent alkali resistance.（4）The dyeing performance of disperse dyes D1-D8 on polyester fabrics and polyester/cotton blends under alkaline conditions was investigated.The results showed that the K/S values of the dyed fabrics were higher than 19 under different p H conditions,and the D1,D2,D6 and D8 had good alkaline dyeing performance,while D3,D5 and D7 had excellent acid and alkali stability.The color fixation rate of disperse dyes D1-D8 at 2 g/L Na OH（p H=12.7）was above 90%,similar to the conventional weak acidic（p H=4.5）condition.The dyes had good lifting power for dyeing polyester fabrics at p H=12.7,and the K/S values of dyed fabrics did not change significantly after the o.w.f reached 3%.The color fastness of dyed polyester fabrics to rubbing,washing and sublimation at p H=12.7 was above grade 4,with D1-D4 at grade 2-3and D5-D8 at grade 4,which was basically the same as that of dyed polyester fabrics at p H=4.5.In addition,the dyeing performance of dyeing polyester/cotton blended fabrics in one-bath one-step dyeing process is worse than two-bath two-step dyeing process,the colorfastness of the one-bath one-step dyeing performance of dyes D1,D5,D7 and D8 was better compared to the two-bath two-step dyeing with a color difference（ΔE）of 1.24,1.29,1.07 and 1.44,respectively.