Bases carbinol

The preparation of triaryknethane dyes proceeds through several stages formation of the colorless leuco base in acid media, conversion to the colorless carbinol base by using an oxidising agent, eg, lead dioxide, manganese dioxide, or alkah dichromates, and formation of the dye by treatment with acid (Fig. 1). The oxidation of the leuco base can also be accompHshed with atmospheric oxygen in the presence of catalysts. 

The central carbon atom is derived from an aromatic aldehyde or a substance capable of generating an aldehyde during the course of the condensation. Malachite green is prepared by heating benzaldehyde under reflux with a slight excess of dimethyl aniline in aqueous acid (Fig. 2). The reaction mass is made alkaline and the excess dimethylaniline is removed by steam distillation. The resulting leuco base is oxidized with freshly prepared lead dioxide to the carbinol base, and the lead is removed by precipitation as the sulfate. Subsequent treatment of the carbinol base with acid produces the dye, which can be isolated as the chloride, the oxalate [2437-29-8] or the zinc chloride double salt [79118-82-4]. 

Carbinol bases are obtained by treating cationic triphenylmethine dyes with alkali.77 However, not all carbinol bases are stable. For example, 52 readily eliminates water to form the neutral quinonimide45 53 (Eq. 7). 

In view of the increasing interest in the radical ion chemiluminescence 71 has also been investigated to see whether radical ions play an essential role here, especially by E. G. Janzen et al. 136,137,138) The reaction pathway to N-methylacridone 72 was thought to proceed perhaps via a homolytic cleavage of the lucigenin carbinol base 74, yielding N-methylacridone radical anion 75. 

Michler s ketone is converted into the carbinol base of malachite green by the action of phenyl magnesium bromide (the Grignard reaction)... 

As long as the solution which has been made alkaline retains its colour the ammonium colow base, which preserves the quinonoid structure of the dye, is still present (Hantzsch). This base is stable for a short time only and can in no case be isolated. The disappearance of the quinonoid system, which rapidly follows, occurs either through a rearrangement of the genuine base to the so-called pseudo- or carbinol-base, accompanied by the wandering of the OH-group ... 

When the colourless carbinol base is treated with acid the quinonoid structure is re-formed and the dye produced. But on dissolving cautiously, with cooling, it can he seen that the colour attains its maximum depth only gradually. Hence the exceedingly unstable colourless carbinol salt is first formed it changes into the dye with spontaneous elimination of water ... 

Accdg to Refs 1 St 22, DPhA was Erst prepd in 1864 by A.W. Hofmann on heating rosaniline (fuchsin carbinol base),... 

Diazinium salts resemble pyridinium salts in their behavior. They form pseudo-bases with hydroxide ions which can disproportionate (e.g. 2-methylphthalazinium ion (199) — 2-methylphthalaz-l-one + 2-methyl-l,2-dihydrophthalazine) or undergo ring fission (e.g. 3-methylquinazolinium ion — (200). Aqueous acid converts (201) into (202), presumably by attack of a water molecule on a protonated species with subsequent intramolecular oxidative-reductive rearrangement of an intermediate carbinol base (201a) as shown. 

Benzo[6]thienylketones are reduced by lithium aluminum hydride to secondary alcohols.465, 526 The carbinol bases of a series of benzo-[6]thiophene analogs of malachite green have been prepared.621... 

Colorless derivatives of the carbinol bases of cationic dyes have recently found application for the manufacture of carbonless copy paper and for special paper used for thermal printers. Examples of such color formers are the crystal violet derivative 31 [29], which develops a blue color, and the black-developing fluorane lactone 32 [30] and benzoxazine 33 [31],... 

The triarylmethane dyes were also very important leather dyes in the past. The central carbon is sp2-hybridized (triarylmethine) and can add a hydroxyl group to form the respective carbinol base with spP-hybridized carbon. The dyes react like Lewis acids and some species act as pH indicators (e g., phenolphthaleine). The term cationic dyes is therefore recommended for this dye class instead of basic dyes. Nowadays only the sulfonated triphenylmethine dyes are used for leather. 

Alkaline blue carbinol base, one sulfo group Acid Blue 119 silk... 

It is understandable that, as is well known, the dye salt itself and the true colour base are coloured in contrast to the colourless carbinol base and the leuco base. In the latter there is no longer an electron hole55 at the central carbon atom. In addition we have probably a tetrahedral structure in contrast to the approximately plane structure of the ion compounds. 

Tri-amino Tri-phenyl Carbinol. Carbinol Base.— When tri-amino tri-phenyl methane is oxidized it yields a carbinol or alcohol just as tri-phenyl methane itself does, viz.. 

Para-rosaniline Chloride.—This carbinol is known as para-rosaniline, carbinol base. It is not a dye but when treated with acids it yields salts which are colored and which possess the properties of dyes. These salts result from one of the amino groups reacting with the acid, forming an ammonium salt, the tri-valent nitrogen of the amine becoming penta-valent in the salt, as in the formation of methyl ammonium chloride from methyl amine. 

Tri-amino tri-phenyl carbinol Para-rosaniline carbinol base)... 

Considering again what we have brought out in connection with para-rosaniline we should note that there are four distinct compounds, viz., the amine base or leuco base the carbinol base the hydrate salt and the anhydride salt or dye. Now these four types of compounds are known not only in the case of para-rosaniline but in the case of all triphenyl methane dyes. The general characters of these four types of triphenyl methane derivatives, including their color properties which are very important, may be given as follows ... 

Carbinol Base.—(2) The carbinol base is the alcohol or hydroxyl... 

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