Study On The Synthesis And Properties Of Azo Pigment Based On Barbituric Acid

The azo pigment is a vital colorant,widely used in ink,paint,plastic products,and educational products coloring.Conventional azo pigment is made by diazotization of aromatic amine orheteroaromatic amine to make diazonium salt and then coupled with acetoacetanilide,2-hydroxynaphthalene,pyrazolone,and 3-hydroxy-2-naphthoic acid and other coupling components,most of which contain color-emitting group aryl azo group in their structure.Besides,amide groups are introduced in the molecular design to enhance intermolecularhydrogen bonding and improve theheat,light,and solvent-resistance of pigments.In recent years,much attentionhas been paid to improving the application properties of pigments by extending the molecular conjugation system,introducing different substituent groups,or changing the morphological characteristics of solid powder particles.In this paper,p-aminobenzaldehyde and barbituric acid-containing polyamide bonds were used as raw materials to prepare organic Azo pigment with bright color and good resistance and to provide a technical reserve for the development of products.(1)5-[(4-aminophenyl)methylene]-2,4,6(1H,3H,5H)-pyrimidinetrione inte-rmediates were synthesized by knoevenagel condensation reaction using p-aminobenzaldehyde and barbituric acid as starting materials.The effects of the reaction solvent system,reaction temperature,and reaction time on the yield of intermediates were investigated.The intermediate was characterized by 1H NMR,FT-IR,elemental analysis and TGA.The results showed that the intermediate yield reached 89.7%with anhydrous ethanol as the solvent and the reaction at 78? for 5h,and the thermal decomposition temperature was greater than 210? by TGA.(2)5-[(4-aminophenyl)methylene]-2,4,6(1H,3H,5H)-pyrimidinetrione was synthesized as a diazo component,and a series of new azo pigment molecules containing barbituric acid structure were prepared by coupling acetoacetanilide(AAA),o-methoxyacetoacetanilide(AAOA),5-acetoacetylamino benzimidazolo-ne(AABI),2-hydroxy-3-naphthalene formylaniline(chromophenol AS),?-naphth-ol,1-phenyl-3-methyl-5-pyrazolone(PMP)and 3-hydroxy-2-naphthoic acid,res-pectively.It was also characterized using 1H NMR,FT-IR,elemental analysis,UV-Vis and SEM.The effects of inorganic acid and dosage,coupling reaction time,reaction temperature and pH on the reaction products of the diazotization reaction were investigated.It was found that the efficiency of diazotization reaction washigh when sulfuric acid was selected and n(intermediate):n(NaNO2)n(H2SO4)was 1:3.5:30;Thehighest product yield was 86.9%when the coupling component was acetoacetanilide;The reaction pH was 4.5?6 and the product yield was up to 86.9%with stirring at 15? for 0.8h.When the coupling component was o-methoxy acetoacetanilide,the ?max of the resulting pigment UV spectrum was 392 nm,and the ?max was 3.0 × 104 L·mol-1·cm-1.It was found that when the coupling components were acetoacetanilide,5-acetylacetamido benzimidazolone,?-naphthol,etc,the resulting pigments were modified by m-nitrophenol in aqueous solution,and the resulting solid powderhad a regular shape and bright color.When the coupling component was o-methoxy acetoacetanilide,the resulting pigmentshad a rice-like solid shape and bright color after 6h modification by DMF.(3)An intermediate for the preparation of bis-azo organic pigments were synthesized from p-nitroaniline and barbituric acid,and a coffee-colored bis-azo organic pigment was synthesized by coupling acetoacetanilide with this intermediate as the diazo component,which was characterized by 1H NMR,FT-IR,elemental analysis and UV-Vis.The conditions of nitro reduction of the first step coupling product were investigated,and the conditions of pigment synthesis were optimized.It was found that the molar ratio of p-nitrophenazobar-bituric acid to sodium sulfide was 1:1.7,100? for 48h,and the yield was 84.6%.For diazotization,10mL concentrated sulfuric acid was used to dissolve 0.3g intermediate.The yield was 88.5%when the pH of the coupling solution was 4.5?6 and the reaction time was 0.8h at 8?10 ?.