The Isolation of N-tert-Butyl-p-Toluidine Hydrochloride and the Synthesis of Mauveine

Abstract

Heating p-toluidine hydrochloride in tert-butanol gave a crystalline precipitate of N-tert-butyl-p-toluidine hydrochloride. This compound, now readily available by this simple procedure, was used to make mauveine, which was found by TLC analysis to be identical to authentic mauveine.

Studies on a Modern Method of Preparing Authentic Mauveine

“…Mauveine A and B have previously been characterised spectroscopically by others 14 and by us from our synthetic work. 17,18 We also separated small quantities of 18 Chart 3 is a mixture of the standard and the authentic mauveine. The A and B peaks align but the so-called fingerprint peak B x in authentic mauveine is not mauveine B 2 .…”

“…19 We have published photographs of TLC plates to try and give a visual indication of the experimentation since the chromophores are coloured. 17,18 So far we have not been able to make authentic mauveine by following Perkin's method. However, we were able to get a much better match to authentic mauveine by the potassium dichromate oxidation of tert-butylp-toluidine, o-toluidine and aniline followed by the deprotection of a mixture of intermediate tert-butylated chromophores.…”

WH Perkin, Patent AD 1856 No 1984: A Review on Authentic Mauveine and Related Compounds

“…The provenance of authentic mauveine is still disputed, 11 32 Our studies have centred upon the preparation of derivatives similar to or related to those found in mauveine, 16,18,33 and upon the synthesis of mauveine that has the same composition as authentic mauveine. 20,34 Finally we performed a detailed study on the oxidation products of p-toluidine to verify early literature studies. 35 …”

Synthesis and Analysis by Liquid Chromatography-Mass Spectrometry of a Mauveine Composition Similar to Museum-Stored Mauveine

“…14 As we found it impossible to convert the former to the latter by removing two chromophores B2 and C from the mixture, we have always maintained that the WHP mauveine was made by a modified method of synthesis which WHP did not reveal. 10,16,17 Our studies showed that replacing p-toluidine with N-tert-butyl-p-toluidine, and subsequently deprotecting the mauveine chromophores from the tert-butyl group, gave a mixture of mauveine chromophores rich in mauveine A and B. 10,16,17 Our studies were reported with highperformance liquid chromatography (HPLC) charts and were explained by assuming that capping the p-toluidine group blocks it from competing with aniline to form either mauveine B2 or mauveine C. 10 Hence only mauveine A and B dominate.…”

“…7 Discussion Figure 4 shows the structures of N-tert-butylmauveine A 6, N-tertbutylmauveine B 7 and N-tert-butyl-p-toluidine hydrochloride 8 used in these studies. 16,17,19…”