Halochromism

The spectra and halochromism of thiophene analogs of triphenyl and diphenyl carbinol, " the spectra of anilides of 2- and 3-thenoyl-acetic acid, " and the fluorescence of some thiophene compounds have been investigated. 

Halochromie,/. halochromism, halochromy. Halogen-, halogen, halo- (as in Halogenbenr zoeadure, Halogenpyridin, etc.), halide of (as in Halogenailber, silver halide), -alkyl, n. alkyl halide, -aryl, n. aryl halide. 

The well-known BorntrAoer reaction for the detection of 1,8-dihydroxyanthraqui-nones is a characteristic example of such halochromism [36-38] ... 

The reaction between 4-nitrophenacyl esters and DMSO/diethylamine, described by Kallmayer et al., is also a halochromic reaction [39]. 

D) In the presence of an intramolecular nucleophile, the oquinones can evolve to cyclic indolic structures that evolve to halochrome and, finally, some polymeric structures can be formed. 

Reichardt, C. (1992). Solvatochromism, thermochromism, piezochromism, halochrom-ism, and chiro-solvatochromism of pyridinium IV-phenoxide betaine dyes. Chem. Soc. Rev. 21, 147-153... 

The formation from neutral substances (triphenylcarbinol) of coloured, salt-like reaction products which are more or less easily decomposed by water is a phenomenon called halochromism . The halo-chromic salts of triphenylcarbinol are regarded as carbonium salts this follows at once from the above discussion. A quinonoid formula, by which various authors explain the colour, seems less probable. Recently the attempt has been made to attribute complex formulae to the carbonium salts (Hantzsch), in accordance with Werner s scheme for ammonium salts. Such formulae express the fact that, in the ion, the charge is not localised at the methane carbon atom, but spread over the field of force of the whole radicle. The simplest carbonium salt of the group, the yellow perchlorate (K. A. Hofmann), would accordingly have the following structural formula ... 

Halochromism) Tribochromism Kezochromism (pH change) Mechanical friction Mechanical pressure (ditto)... 

Halochromism is a colour change brought about by a change in pH (see also acidochromism) (halochromic). 

Table 32 Properties of Halochromate(II) Dihydrates and a Diacetic Add Adduct...

The equilibria (111) to (115) exist only in HNO3 and HCIO4 and are modified when other anions are present because of the formation of substituted chromates, e.g. chlorochromate and sulfatochromate, as in equations (119) and (120). Dichromate is slow to oxidize, otherwise no halochromates could be isolated.2,222... 

Dimethylpyrazolinium fluorochromate,403 isoquinolinium fluorochromate (iQFC)404 and quinolinium bromochromate (QBC)405 have also been described as halochromates able to oxidize alcohols. 

Finally must be mentioned the interesting halochrome reaction of C-curarine similar color reactions are given by those derivatives of C-curarine which retain the chromophore of the parent molecule. This reaction has been studied most closely with tetrahydronorcurarine. In 40-80% aqueous sulfuric acid, the base dissolves to give a deep-violet solution. In concentrated sulfuric acid, the solution is yellow but, on dilution with water to 70%, the color becomes deep-violet and finally disappears on further dilution. Tetrahydronorcurarine can be recovered unchanged from these diluted acid solutions. A plausible explanation of... 

Furthermore, as a consequence of pronounced zwitterionic character of the computed electronic ground state, intense bathochromic halochromicity of the longest wavelength absorption bands with concomitant weak orange fluorescence can be observed upon protonation [221]. 

Azinium halochromates and bichromates as oxidants for organic synthesis 880PP533. 

F. J. Taboury, R. Thomassin, and Mile. Perrotin. Bull, soc. chim. France 1947, 783-9. UV, IR, Raman halochromism and complex formation of ketones and amines. 

The qualitative analysis of trityl compoimds takes advantage of the orange-yellow color of the halochromic salt formed when a trityl com-poimd is treated with a solution of concentrated sulfuric acid in glacial acetic acid. 

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