Metallization of non-genotoxic direct dyes Jin-Seok Bae, Harold S. Freeman*, Ahmed El-Shafei Department of Textile Engineering, Chemistry, and Science, North Carolina State University, Raleigh, NC, 27695-8301, USA Accepted 1 October 2002 Dedicated to the memory of Professor Masaru Matsuoka Abstract Copper (II) salts were used as metallizing agents in the synthesis of new direct dyes for cotton. In this regard, direct dyes possessing ortho-propoxy, ortho 0 -hydroxy-substituted systems formed the corresponding dye–metal complexes. The complexes were characterized by neutron activation and spectrometric analyses and evaluated on cotton for color fastness. # 2003 Elsevier Science Ltd. All rights reserved. Keywords: Metallization; Direct dyes; Neutron activation; Synthesis; Lightfastness 1. Introduction It is well known that the treatment of suitably substituted azo dyes with metal ions (e.g. Cr 3+ , Cu 2+ , Fe 3+ ) can improve lightfastness and wash- fastness properties [1–12]. In this regard, the dyes often form ligand–metal complexes that are less soluble in water than the starting ligands, which contributes to the observed improvement in washfastness. In the case of medially metallized azo dye complexes, enhanced lightfastness arises from protection of the azo bond through back bonding, which utilizes the empty d-orbitals of the transition metals employed. The formation of copper complexes includes the metallization of direct dyes containing an ortho, ortho 0 -dihydroxyazo or ortho-methoxy-ortho 0 - hydroxyazo ligand system [5–12]. Well-known examples are C.I. Direct Blue 76 and C.I. Direct Blue 218, which are derivatives of C.I. Direct Blue 1 and C.I. Direct Blue 15, respectively (cf. Fig. 1). (It should be noted that, for simplicity, such metal complexes have been depicted throughout this paper in one isomeric form only, although in rea- lity they will be produced as isomeric mixtures.) In previous studies in our laboratories, a series of new direct dyes (cf. Fig. 2) was synthesized from non-genotoxic diamines and evaluated as potential alternatives to certain benzidine-based dyes [13]. Results from fastness testing indicated that the new dyes had comparable colors and inten- sities to structurally related commercial dyes but had low lightfastness. Bearing in mind that treat- ment with Cu 2+ ions can improve the lightfastness of metallizable direct dyes, we examined the suit- ability of dyes 1–12 for metal complex formation. 0143-7208/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved. PII: S0143-7208(02)00120-1 Dyes and Pigments 57 (2003) 121–129 www.elsevier.com/locate/dyepig * Correspondingauthor. Tel.: +1-919-515-6552;fax:+1-919- 515-6532. E-mail address: harold_freeman@ncsu.edu(H.S.Freeman).