Synthetic Derivatives of Mauveine

Abstract

Oxidation of phenosafranin and an excess of aniline gave a novel hydroxylated derivative of pseudo-mauveine. N-Methyl-p-toluidine and bis(4-methylphenyl)amine are efficient building blocks for making mauveine-related chromophores. Their oxidation with K 2 Cr 2 O 7 is believed to form nitrogen centred radicals which then couple with an aromatic amine by homolytic aromatic substitution of hydrogen. The N-methyl substituent and the p-methyl substituents are essential for the reaction to proceed. N-Methyl substituted chromophores were not demethylated in the reaction or by oxidation with K 2 Cr 2 O 7 in dilute H 2 SO 4 . N-Nitroso-bis(4-methylphenyl)amine rearranges smoothly to the orange compound, (2-nitro-4-methylphenyl)-4-methylphenylamine, when a solution in CH 2 Cl 2 is treated with montmorillonite at room temperature for 24 h. 2,4-Dimethylaniline has been used to make a mauveine homologue. The colour of silk dyed with mauveine chromophores has been compared to the colour of silk dyed with authentic 1862 mauveine. Synthesis with bis(4-methylphenyl)amine (5)Since the four main components of mauveine (A, B, B 2 , C) 13 contain a key building block derived from p-toluidine (at Scheme 1 The synthesis of p-hydroxypseudo-mauveine 2. The numbering scheme of the phenazine ring is shown.

1-(Phenylamino)Pseudo-Mauveine: A New Water Soluble Phenazine Dye

“…However, we showed previously that acetone/water mixtures can be used in these syntheses for poorly water soluble building blocks. [6][7][8] The oxidation of compound 9 and p-phenylenediamine 1 with K 2 Cr 2 O 7 in water/ acetone (1.5 : 1.0) was successful as the building block is easily dissolved in a water/acetone mixture (Scheme 3). The acetone must be evaporated before filtration of the reaction mixture as it solubilises the mauveine-like product 10.…”

Syntheses and Structures of Pseudo-Mauveine Picrate and 3-Phenylamino-5-(2-Methylphenyl)-7-Amino-8-Methylphenazinium Picrate Ethanol Mono-Solvate: The First Crystal Structures of a Mauveine Chromophore and a Synthetic Derivative

“…Attempts were made to crystallise a number of picrate salts of various synthetic derivatives of mauveine 22 Symmetry codes: (i) 1+x, y, z; (ii) -x, 1-y, 1-z; (iii) ½-x, y-½, ½-z; (iv) ½+x, 3/2-y, ½+z. N H…”

“…The two compounds pseudo-mauveine 1 and the synthetic derivative 6 were made from N-phenyl-p-phenylenediamine 9 (Scheme 4) because it is cheap and readily available (1 kg costs £37). 25,22 For complete clarity we prepared pseudo-mauveine by three different methods and checked that the spectroscopic data of the products were the same. The methods were (i) the oxidation of a mixture of N-phenyl-p-phenylenediamine 9 and aniline with K 2 Cr 2 O 7 ; 25 (ii) the oxidation of pure aniline with K 2 Cr 2 O 7 ; (iii) the oxidation of pure aniline with CuCl 2 .…”

“…They also provide information on electronic structure (in terms of bond-lengths within the ring system) and the molecular conformation in the solid state. Despite mention of crystalline phases by Perkin himself, our attempts to accomplish the crystallisation of mauveine chromophores, and some synthetic derivatives 22 met with failure until we began an investigation into the use of picrate as the counter-ion. Picrate salts of aromatic compounds are often crystalline and the method was widely used in the past, but seems to be less fashionable today.…”

Liquid chromatography-mass spectrometry analysis of mauveine from the historical London suburb of Sudbury (W.H. Perkin's home and factory) and Bradford

“…4 Studies on the mechanism of mauveine formation by Plater investigated the replacement of p-toluidine by N-alkyl-p-toluidines (alkyl = Me, Et, i Pr and t Bu). [5][6][7][8] This makes the starting material more electron-rich and facilitates its oxidation. The first coupling step of an N-alkyl-p-toluidine to either aniline or o-toluidine then occurs more readily and the product yields of N-alkylmauveine chromophores are higher.…”