Tri phenylmethane dyes

Derivatives of N,N-dimethyl-4-methylaniline afford the iminomethine on anodic oxidation. This reaction allows the conversion of leucocompounds to the tri-phenylmethane dye, such as Malachite Green 55 [167]. 

Leuco compounds can be converted electrochemically into the corresponding tri-phenylmethane dyes (e.g. 203 204>). 

Finally, two or even three amino or dimethylamino groups in the para position stabilize trityl cations so efficiently because of their pronounced electron-donating resonance effect that the associated non-ionized neutral compounds are no longer able to exist at all but heterolyze quantitatively to salts. These salts are the well-known tri-phenylmethane dyes. 

Salicylic and cresotinic acids are used in the preparation of azo dyes and of tri-phenylmethane dyes of the aurine type (eriochrome azurol B). These acids confer upon the dyes the property of going onto metal mordants, particularly chromium mordants, and also of forming complex compounds, in substance, with suitable metal salts. Salicylic acid is also widely used in the pharmaceutical industry. 

It is also to be noted that chloranil is often very useful in the laboratory as a mild oxidizing agent, for example, in converting a leuco compound of the tri-phenylmethane series into the corresponding dye. In this reaction, the chloranil can be used in excess since it does not destrw the dye. Chloranil is too expensive to be used technically for such purposes (cL page 401). 

In pharmacy, the dyes used are azo dyes, quinoline dyes, tri-phenylmethane and xanthine dyes. They are not recommended in children because many colouring agents, mainly synthetic dyes, have been associated with hypersensitivity and other adverse reactions (gastrointestinal intolerance, dermatological reactions and carcinogenic concerns). Approximately 2-20% of people with asthma are sensitive to aspirin. Cross-reactions to azo dyes such as tartrazine produce similar effects. They have occurred in patients both with and without a history... 

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