Indian Journal of Fibre & Textile Research Vol. IS, September 1993,pp. 151-155 Syntheses of 3-aryl-5-[ 6-( a-picolyl)]rhodanines and 3-aryl-5- (2-pyridylmethylene )rhodanines and their dyeing performance on acetate and/or other fibres A A Fadda, M MAli, A S EI-Ahl & A Fouda Department of Chemistry, Faculty of Science, Mansoura University, Mansoura, Egypt Received 11 January 1993; accepted 2 April 1993 3-Aryl-5-[6-( a-picolyl)]rhodanines (Hla-g) and 3-aryl-5-(2-pyridylmethylene)rhodanines (IVa,b,f,g) were. prepared by treatment of a-picoline N-oxide (I) with 3-aryl rhodanines (II) at 90°C in presence of acetic anhydride and their dyeing performance of polyester, polyacrylic and wool fibres was as- sessed. The effect of nature and orientation of substituents on the colour of these compounds was also studied. All the compounds showed good affinity towards polyester fibres followed by polyac- rylic and wool fibres. Keywords: Disperse dyes, Dyeing, Polyacrylic fibre, Polyester fibre, Wool fibre 1 Introduction In the last two decades, interest in the cyanine dyes has been shown not only due to their use as textile dyes but also due to their unrivalled ability to impart light sensitivity to silver halides in that region of the spectrum where it is not normally sensitivet'. Most of the methods used for the preparation of cyanine dyes involve the reaction of 2-/4-me- thyl heterocyclic quaternary salt with some other reagents in the pfesence of' a basic condensing agent". On the other hand, Hamana and Yamaza- ki" found that when quinoline N-oxide is treated with some active methylene components in the presence of acetic anhydride it gives 2-substituted quinolines. In view of the above and as a further extension of our studies on exploring the synthetic poten- tialities of pyridinium salts=" and aromatic N-ox- ides", we have now synthesized some new 2-sub- stituted pyridine derivatives, structurally related to certain cyanioe dyes, by the reaction of c-picoline N-oxide with active methylene compounds of he- terocyclic series in the presence of acetic anhy- dride. The dyeing performance of these com- pounds on polyester l polyacrylic and wool fibres has also been assessed. 2 Materials and Methods 2.1 Preparation of 3-aryl-5-(6-(a-picolyl)rhodanines (llIa-g) and 3-aryl-5-(2-pyridylmethylene)rhodanines (IVa,b,f,g) A mixture of c-picoline N-oxide (1/,0.02 mol) and 3-aryl rhodanines (II, 0.02 mol) was heated with acetic anhydride at 90°C for 1 h in the pres- ence of fused sodium acetate. The reaction mix- ture was cooled and the precipitated solid was boiled with dioxane and filtered while hot to get IlIa-g. The dioxane filtrate was left to stand over- night and the precipitated crystals were recrystal- lized from dioxane to give IVa,b,f,g (Scheme 1). The characterization data of compounds I1Ia-g and IVa,b,f,g are given in Table 1. 2.2 Dyeing of Polyester, Polyacrylic and Wool Fibres The required amount of the dye (2% shade) was dissolved in a suitable solvent and poured in- to 4 g/I sodium lignosulphonate solution to give a fine dispel sion for use in dyeing. The material to be dyed was allowed to enter the dye bath containing 1-2% dye and 2 g/l Dekol-N (BASF dispersing agent) at 50-60°C, keeping the material-to-liquor ratio at 1:40, and the tempera- ture was raised to boiling within 45 min. The dye- ing was continued at the boil for about 2 h. the dyed material was first rinsed and then soaped with non-ionic detergent to improve the rubbing and wet fastness. 2.3 Colour Measurements The per cent reflectance (%R) of the dyed ma- terial was measured at different wavelengths in the visible region (400-700 nm) using ACS-600 colour control system. The K/S value at /.. was rnax calculated using the Kubelka-Munk equation: