Propose mechanisms for the following conversions in the proposed scheme for the

Question

Propose mechanisms for the following conversions in the proposed scheme for the synthesis of indigo given in the introduction to this experiment: Structure IV to structure V. the mechanism includes a series of Examples of tautomerization are illustrated below. Structure V to structure VI. think about the reversibility of the aldol condensation. Why must the indigo be reduced before it can be used as a dye? Write a balanced chemical equation for the reduction of indigo to leucoindigo and the reoxidation of leucoindigo to indigo. Identify the oxidizing agent and reducing agent pairs in each reaction. A laboratory chemist was interested to know if m-nitrobenzaldehyde would also produce an indigo like dye. What is your prediction and why? Why is indigo BLUE? Why is leucoindigo YELLOW?

Explanation / Answer

2. Indigo dye as prepared is not water soluble and thus cannot be used for dying purpose. The molecule is thus reduced to a more water soluble alcohol system prior to its use as a dye.

3. Reduction of indigo to leucoindigo by stannite ion,

C16H10N2O2 + SnO2^2- + 2H2O ----> C16H12N2O2 + SnO3^2-

Oxidant : C16H10N2O2 (indigo)

Reductant : SnO2^2- (stannite ion)

Oxidation of leucoindigo to indigo,

C16H12N2O2 + 1/2O2 ----> C16H10N2O2 + H2O

Oxidant : O2

Reductant : C16H12N2O2 (leucoindigo)

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