The Gewald reaction in dye chemistry

Abstract

This review presents the most elegant and promising set of synthetic routes for the synthesis of 2‐aminothiophenes by the Gewald reaction. This reaction has applications in several applied fields, such as pharmaceuticals/biomedicine, agrochemicals, carbohydrate conjugates, sugar cane ripeners, peptide analogues, dyestuffs, and electronic materials; however, the present review will focus on the use of Gewald chemistry in the synthesis of conventional and functional colourants. The Gewald reaction produces 2‐aminothiophene, which is a key intermediate for the diazotisation reaction and for the synthesis of azo dyes, and thus opened the door for new dye chemistry. The reaction produces electron‐withdrawing groups such as CN, COOEt, COOMe, CONH2, and COPh in the 3‐ and/or 5‐position, resulting in bathochromic shifts for the deeper colours of the dyes. The review further reveals the importance of this reaction in the synthesis of azo dyes, fluorescent dyes (coumarin dyes, styryl dyes, thieno[2,3‐d]pyrimidine dyes, bithiophene dyes), thiophene analogues of phthalocyanines, and fluorescent whitening agents.

Microbial degradation of dyes: An overview

“…The synthesis involves many unit processes like reduction, oxidation, nitration, sulfonation, hydroxylation, amination, alkylation, halogenation, hydrolysis, condensation, alkoxylation, esterification, carboxylation, acylation, phosgenation, diazotization and coupling. In this section we have discussed few unit processes (Gregory, 2000;Freeman and Mock, 2007;Sabnis, 2016).…”

2-Amino-4,5-dihydrothiophene-3-carbonitriles: A New Synthesis, Quantum Chemical Studies, and Mannich-Type Reactions Leading to New Hexahydrothieno[2,3-d]pyrimidines

“…In addition, the 2-aminothiophene motif is present in drugs and bioactive molecules such as T-62 (a selective allosteric modulator of the adenosine A receptor), bentazepam (Tiadipona), and brotizolam (Lendormin); − anxiolytic/anticonvulsant agents and skeletal muscle relaxants; and the anticancer drug raltitrexed (Tomudex) − (Figure ). 2-Aminothiophenes are able to act as starting points for the synthesis of a variety of thiophene-containing heterocycles and polycyclic hybrid molecules. − , Moreover, as shown recently, 2-aminothiophenes might find an application in the preparation of functional materials such as electrochemically color switching azomethines, − liquid crystalline materials, oligothiophene-BODIPY hybrids as NIR dyes, organic photovoltaic cells, azodyes, nonlinear optical materials, and azomethine-bridged polythiopheneferrocenes …”

“…2-Aminothiophenes are able to act as starting points for the synthesis of a variety of thiophenecontaining heterocycles and polycyclic hybrid molecules. [3][4][5][6]42 Moreover, as shown recently, 2-aminothiophenes might find an application in the preparation of functional materials such as electrochemically color switching azomethines, 43−46 liquid crystalline materials, 47 oligothiophene-BODIPY hybrids as NIR dyes, 48 organic photovoltaic cells, 49 azodyes, 50 nonlinear optical materials, 51 and azomethine-bridged polythiopheneferrocenes. 52 Such a diversity of available structures and applications is due to the synthetic availability of 2-aminothiophenes.…”

Synthesis and Application to Polyester and Nylon 6 Fabrics of Hetaryl Bis-Azo Disperse Dyes Based on 6-Amino-2,4-Dihydroxypyrimidine and 4-Methoxy-2-Nitroaniline Moieties

“…They have also been found useful in the detection of cancer, and as a chemotherapeutic agent. Furthermore, they are important precursors in the synthesis of many fused heterocyclic compounds of biological importance [11].…”