Basic green

A further strong bathochromic shift is observed as the basicity of the primary amines is increased by A/-alkylation, eg, malachite green [569-64-2] Cl Basic Green 4, =621 nm (5). 

Several examples of typical triarylmethane dyes have already been mentioned, in particular, pararosaniline (6.161), malachite green (6.162) its o-chloro derivative (6.169), crystal violet (6.164), rosaniline (6.165) and diphenylamine blue (6.173). Cl Basic Green 1 (6.168 R = C2H5), the ethyl analogue of malachite green, is prepared by the aldehyde route and is isolated as the sulphate. The ethyl analogue of crystal violet is Cl Basic Violet 4 (6.167 R = C2H5) and is obtained by the ketone route. 

After isolation, the compound is insoluble in water and in common organic solvents. Aqueous ammonia and acid decompose the salt, yielding the free amino arid hot water converts the copper aminomethanesulfonate into an insoluble basic green salt. Because of its insolubility and its color, a chelate ring structure has been proposed similar to that of the alpha-amino acids with copper. 

Cationic dyes form positively charged dye ions by dissociation, and the positive electric charge is delocalized over the entire molecule. They are usually di- and triarylmethine dyes such as C.I. Basic Green 4, 42000 [569-64-2] (31), which are also known as triarylmethane dyes or triaryl carbenium ions [15], oxazine dyes such as C.I. Basic Blue 3, 51005 [2787-91-9] (32), orthiazine dyes. 

Triphenylmethane dyes are usually prepared in two steps 1) condensation of an N,N-dialkylaniline with a benzaldehyde compound and 2) oxidation of the resultant leuco base (27). The synthesis of C.I. Basic Green 4 (Malachite Green) is given as an example in Fig. 13.106. Alternatively, C.I. Acid Green 50 is prepared in three steps 1) condensation of... 

Fig. 13.106. Two-step synthesis of Malachite Green (Basic Green 4). Three-step synthesis of Acid Green 50.

Solabannavar, S. B., Desai, U. V., Mane, R. B. Heck reaction in aqueous medium using Amberlite IRA-400 (basic). Green Chem. 2002,4,... 

In practice mixtures of indicators are often used, for example the universal indicator which provides preliminary information on acidic (red), neutral (yellow to yellow-green) or basic (green and blue) behavior. In our experiment we shall also use some mixed indicators. 

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