Fuchsin

Schiff s reagent is a dilute solution of fuchsin hydrochloride (p-rosaniline) that has been decolourised by sulphur dioxide. This decolourisation is the result of a... 

The triaryknethane dyes are broadly classified into the triphenyknethanes (Cl 42000—43875), diphenylnaphthyknethanes (Cl 44000—44100), and miscellaneous triphenylmethane derivatives (Cl 44500—44535). The triphenyknethanes are classified further on the basis of substitution in the aromatic nuclei, as follows (/) diamino derivatives of triphenylmethane, ie, dyes of the malachite green series (Cl 42000—42175) (2) triamino derivatives of triphenylmethane, ie, dyes of the fuchsine, rosaniline, or magenta series (Cl 42500—42800) (J) aminohydroxy derivatives of triphenylmethane (Cl 43500—43570) and (4) hydroxy derivatives of triphenylmethane, ie, dyes of the rosoHc acid series (Cl 43800—43875). Monoaminotriphenyknethanes are known but they are not included in the classification because they have Httie value as dyes. 

The first triaryknethane dyes were synthesized on a strictiy empirical basis in the late 1850s an example is fuchsine, which was prepared from the reaction of vinyl chloride with aniline. Thek stmctural relationship to triphenylmethane was estabHshed by Otto and Fmil Fischer (5) with the identification of pararosaniline [569-61-9] as 4,4, 4 -triaminotriphenyknethane and the stmctural elucidation of fuchsine. Several different stmctures have been assigned to the triaryknethane dyes (6—8), but none accounts precisely for the observed spectral characteristics. The triaryknethane dyes are therefore generally considered to be resonance hybrids. However, for convenience, usually only one hybrid is indicated, as shown for crystal violet [548-62-9] Cl Basic Violet 3 (1), for which = 589 nm. 

In a variation of this method, isolation of the ben2hydrol derivative is not required. The methane base undergoes oxidative condensation in the presence of acid with the same or a different arylamine direcdy to the dye. New fuchsine [3248-91 -7] Cl Basic Violet 2 (16), is prepared by condensation of two moles of o-toluidine with formaldehyde in nitrobenzene in the presence of iron salts to give the corresponding substituted diphenylmethane base. This base is also not isolated, but undergoes an oxidative condensation with another mole of o-toluidine to produce the dye. 

In the present work the acid-base surface properties of three Al O samples for a chromatography are investigated acidic (I), basic (II) and neutral (III) ones with the using of heterogeneous titration of their suspensions by HCl and NaOH solutions. To establish the correlations between the acid-base and adsoi ption properties studied Al O the representatives of cationic dyes -diamond green (DG), fuchsine (F) and anionic dyes - eriochrom black T and chromic dark blue have been used. 

The reaction depends, on the one hand, on the fact that fuchsin is decolorized by oxidizing agents (e.g. lead(IV) acetate) and, on the other hand, on the fact that lead(IV) acetate is reduced by compounds containing a-diol groups. It is, therefore, no longer available to decolorize the fuchsin. The fuchsin undergoes a Schiff reaction with the aldehydes that are formed [2]. 

Note The color of the zones persists for a long period, but changes to blue-violet [1]. Rosaniline [1, 2] can be employed instead of fuchsin. With sugar alcohols lead(IV) acetate alone yields white zones on a brown background (detection limit 1 — 2 pg per chromatogram zone) [3]. 

Tuduranine, CjgHjgOgN. This member of the aporphine group (p. 306) is the most recent addition to Sinomenium alkaloids and was isolated by Goto from the mother liquors of sinomenine. It is crystalline, has m.p. 125° (with softening at 105°), and yields a sparingly soluble hydrochloride, m.p. 286° (dec.), [a] f — 148° (dilute MeOH), is freely soluble in alkali, and gives feeble ferric chloride and diazo-colour reactions and a fuchsin-red colour with formaldehyde and sulphuric acid. It behaves as a secondary base and yields a diacetyl derivative, m.p. 170°, [a] / — 321-71° (MeOH), which does not form a methiodide, but can be hydrolysed to A -acetyl-tuduranine, m.p. 277°, — 395-24°, and this can be methylated to... 

Echt-rot, n. fast red. -sMurefuchsiQt n. fast acid fuchsine. -scbwarz, n. fast black. 

The presence of free bromine, and consequently the end-point, can be detected by its yellow colour, but it is better to use indicators such as methyl orange, methyl red, naphthalene black 12B, xylidine ponceau, and fuchsine. These indicators have their usual colour in acid solution, but are destroyed by the first excess of bromine. With all irreversible oxidation indicators the destruction of the indicator is often premature to a slight extent a little additional indicator is usually required near the end point. The quantity of bromate solution consumed by the indicator is exceedingly small, and the blank can be neglected for 0.02M solutions. Direct titrations with bromate solution in the presence of irreversible dyestuff indicators are usually made in hydrochloric acid solution, the concentration of which should be at least 1.5-2M. At the end of the titration some chlorine may appear by virtue of the reaction ... 

The titrations should be carried out slowly so that the indicator change, which is a time reaction, may be readily detected. If the determinations are to be executed rapidly, the volume of the bromate solution to be used must be known approximately, since ordinarily with irreversible dyestuff indicators there is no simple way of ascertaining when the end point is close at hand. With the highly coloured indicators (xylidine ponceau, fuchsine, or naphthalene black 12B), the colour fades as the end point is approached (owing to local excess of bromate) and another drop of indicator can be added. At the end point the indicator is irreversibly destroyed and the solution becomes colourless or almost so. If the fading of the indicator is confused with the equivalence point, another drop of the indicator may be added. If the indicator has faded, the additional drop will colour the solution if the end point has been reached, the additional drop of indicator will be destroyed by the slight excess of bromate present in the solution. 

Polarographic maxima. Current-voltage curves obtained with the dropping mercury cathode frequently exhibit pronounced maxima, which are reproducible and which can be usually eliminated by the addition of certain appropriate maximum suppressors . These maxima vary in shape from sharp peaks to rounded humps, which gradually decrease to the normal diffusion-current curve as the applied voltage is increased. A typical example is shown in Fig. 16.3. Curve A is that for copper ions in 0.1 M potassium hydrogencitrate solution, and curve B is the same polarogram in the presence of 0.005 per cent acid fuchsine solution. 

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