Trisazo Direct Black dyes based on nonmutagenic 3,3 0 -disubstituted benzidines Guoliang Gong a , Xin Gao a , Jinlong Wang a , Defeng Zhao a, *, Harold S. Freeman b a State Key Laboratory of Fine Chemistry, Dalian University of Technology, Dalian 116012, China b Department of Textile Engineering, Chemistry and Science, North Carolina State University, Raleigh, NC 27695-8301, USA Received 28 September 2001; received in revised form 5 December 2001; accepted 15 December 2001 Abstract Using 3,3 0 -di-n-propoxybenzidine, 3,3 0 -di-n-butoxybenzidine and 3,3 0 -di-(b-hydroxyethoxy)-benzidine as diazo com- ponents, and 2,4-diamino-n-propoxybenzene, 2,4-diamino-n-butoxybenzene and 2,4-diaminophenyl-b-hydroxyethyl ether as coupling components, a series of new black trisazo dyes were prepared as homologues of C.I. Direct Black 38. Assessment of the resultant dyes indicated that their color and the dyeing properties were comparable or slightly better than the properties of C.I. Direct Black 38. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Nonmutagenic; Benzidine intermediates; Direct Black dyes; Synthesis; Dye application 1. Introduction C.I. Direct Black 38 (1) was one of the most important commercial direct dyes during the first half of 20th century. It was characterized by an economical price, a beautiful black hue and ease of application. However, because it is produced from benzidine (2), a known human carcinogen, all industrialized nations have stopped producing it. Similarly, benzidine homologues such as 3 were used prior to their identification as cancer suspect agents [1]. The aforementioned observations have led dye chemists to search for another simple aryldiamine as a benzidine substitute. In the search for nongenotoxic benzidine repla- cements, a number of approaches have been developed [2]. Studies in this area have included the synthesis of diamines (7) that contain a brid- ging group between the two phenylene rings [3]. In all but one case, extended conjugation is dis- rupted, causing a distinct hypsochromic effect. Moreover, most of these diamines give dyes of lower affinity for cellulose than benzidine-based dyes, and their synthetic routes lead to appreciably higher costs. Consequently, these diamines are not suitable benzidine substitutes. Similarly, heterocyclic diamines have been examined as potential benzidine substitutes. For example, 5,5 0 -diamino-2,2 0 -bipyridine and 4,5 0 - diamino-2,2 0 -phenylpyridine were used in the synthesis of C.I. Direct Black 38 analogues [4]. While the dyes were interesting from an academic viewpoint, it is clear that this approach is not technically feasible. Non-carcinogenic alkyl and alkoxy benzidine analogues have been developed, taking advantage of results from a prior study, which showed that 0143-7208/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0143-7208(02)00010-4 Dyes and Pigments 53 (2002) 109–117 www.elsevier.com/locate/dyepig * Corresponding author. Fax: +86-411-363-3080. E-mail address: zhaodfg@chem.dlut.edu.cn (D. Zhao).