A critical investigation of the liebermann colour test: The formation and behaviour of phenolindophenol in strong acid media

A review of chemical ‘spot’ tests: A presumptive illicit drug identification technique

“…Widdop describes the many colors seen with Liebermann's, while other reports show its use in the detection of methcathinone analogs and synthetic cannabinoids containing an indole structure . A critical investigation into the chemical reaction of the Liebermann color test showed the mechanism occurring with phenols . The nitrous acid reagent produces carbocations and N‐nitrosamines with primary and secondary amines, respectively (Figure b).…”

“…42 A critical investigation into the chemical reaction of the Liebermann color test showed the mechanism occurring with phenols. 34 The nitrous acid reagent produces carbocations and N-nitrosamines with primary and secondary amines, respectively ( Figure 2b). The substituents present on the benzene ring will affect the color observed, and occasionally it is necessary to heat the test at 100°C to see the result.…”

Synthesis of a far-red fluorophore and its use as an esterase probe in living cells

“…Publications indicated that these compounds were formed as by-products in the Liebermann test for phenols. 16,17 Only limited spectral data exists for these compounds, 11,12,16,18,19 but carbazine-122 (l abs /l em = 654/694 nm, f = 0.45; Fig. 1) 11 was formerly sold as a laser dye by Lambda Physik AG and Exciton, Inc. 12 This led us to conclude that these molecules retain the fluorescent properties of simpler carbazines (i.e., DDAO).…”

“…Examination of the literature revealed an alternative reaction mechanism whereby the indophenol reacts not with phenol directly, but with p-nitrosophenol. 17,19 The formation of this intermediate occurs via nitrosation of phenol by sodium nitrite. Thus, we altered Hill's synthesis to include super-stoichiometric sodium nitrite and obtained DSACO in a 45% yield (Scheme 3).…”

Relationship between π-Conjugation Size and Electronic Absorption Spectrum: Novel π-Conjugation Size Dependence of Indoaniline Dyes

“…The relationship between the size of the π-system and the absorption spectrum is not yet well-known for the indoaniline dyes, and as far as we know, none of the research has been reported. However, 1,4-naphthoquinone type indoaniline dyes have been synthesized and the absorption wavelengths and intensities have been published . Analysis of these data shows a surprising hypsochromic shift, that is, the maximum absorption wavelength (λ max ) of the main band of 1,4-naphthoquinone type dyes is slightly shorter than that of the corresponding 1,4-benzoquinone type dyes (hypsochromic shift); 6h,i however, this has not yet been discussed in the literature .…”