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On the Formation Mechanism of Indigo Blue and Indigo Red from Vegetable Source

Received: 10 November 2021     Accepted: 27 November 2021     Published: 7 December 2021
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Abstract

In this communication a series of ionic reactions is advanced in order to explain not only indigo blue formation but also the continuous presence of indigo red as companion, and why this compound is always found in minority. Indican is the glycoside found in Indigofera tinctoria from which the mixture of indigo blue and indigo red is obtained by means of air oxidation in alkaline medium. A reaction mechanism for the hydrolysis of indican, which was advanced decades ago, is criticized in this paper. Fifty years ago a radical mechanism was suggested for indigo formation. However, the supposed reactive species, indoxyl radical, was not detected by electron spin resonance. Besides, there is no free radical promoter, and indirubin (indigo red) was not considered. A series of ionic reactions explain the formation of both indigoids, and why indigo red occurs in minor proportion. Indoxyl, 3-hydroxyindole, is the aglycone from indican. Reaction of indoxyl with oxygen is catalyzed by calcium hydroxide, indoxyl hydroperoxide being formed. Internal reaction in this intermediate produces 3-oxo-indolenine, which reacts with indoxyl carbanion to give leucoindigo. Further steps lead to indigo blue. Indirubin is formed from indoxyl hydroperoxide by dehydration to isatin, a keto lactam. Condensation of isatin salt with 3-indolinone affords indigo red. This step is retarded due to electric hindrance.

Published in Modern Chemistry (Volume 9, Issue 4)
DOI 10.11648/j.mc.20210904.14
Page(s) 88-91
Creative Commons

This is an Open Access article, distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution and reproduction in any medium or format, provided the original work is properly cited.

Copyright

Copyright © The Author(s), 2021. Published by Science Publishing Group

Keywords

Indigo Blue, Indirubin, Indican, Indoxyl, Organic Hydroperoxide, 3-Oxoindolenine, PeroxyHemiaminal

References
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[2] F. Sánchez. Viesca, and R. Gómez, “The chemistry of the Wellcome test for morphine”, OAR J. Chem. & Pharm., vol. 01 (02), pp. 001-004, 2021.
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  • APA Style

    Francisco Sánchez-Viesca, Reina Gómez. (2021). On the Formation Mechanism of Indigo Blue and Indigo Red from Vegetable Source. Modern Chemistry, 9(4), 88-91. https://doi.org/10.11648/j.mc.20210904.14

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    ACS Style

    Francisco Sánchez-Viesca; Reina Gómez. On the Formation Mechanism of Indigo Blue and Indigo Red from Vegetable Source. Mod. Chem. 2021, 9(4), 88-91. doi: 10.11648/j.mc.20210904.14

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    AMA Style

    Francisco Sánchez-Viesca, Reina Gómez. On the Formation Mechanism of Indigo Blue and Indigo Red from Vegetable Source. Mod Chem. 2021;9(4):88-91. doi: 10.11648/j.mc.20210904.14

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  • @article{10.11648/j.mc.20210904.14,
      author = {Francisco Sánchez-Viesca and Reina Gómez},
      title = {On the Formation Mechanism of Indigo Blue and Indigo Red from Vegetable Source},
      journal = {Modern Chemistry},
      volume = {9},
      number = {4},
      pages = {88-91},
      doi = {10.11648/j.mc.20210904.14},
      url = {https://doi.org/10.11648/j.mc.20210904.14},
      eprint = {https://article.sciencepublishinggroup.com/pdf/10.11648.j.mc.20210904.14},
      abstract = {In this communication a series of ionic reactions is advanced in order to explain not only indigo blue formation but also the continuous presence of indigo red as companion, and why this compound is always found in minority. Indican is the glycoside found in Indigofera tinctoria from which the mixture of indigo blue and indigo red is obtained by means of air oxidation in alkaline medium. A reaction mechanism for the hydrolysis of indican, which was advanced decades ago, is criticized in this paper. Fifty years ago a radical mechanism was suggested for indigo formation. However, the supposed reactive species, indoxyl radical, was not detected by electron spin resonance. Besides, there is no free radical promoter, and indirubin (indigo red) was not considered. A series of ionic reactions explain the formation of both indigoids, and why indigo red occurs in minor proportion. Indoxyl, 3-hydroxyindole, is the aglycone from indican. Reaction of indoxyl with oxygen is catalyzed by calcium hydroxide, indoxyl hydroperoxide being formed. Internal reaction in this intermediate produces 3-oxo-indolenine, which reacts with indoxyl carbanion to give leucoindigo. Further steps lead to indigo blue. Indirubin is formed from indoxyl hydroperoxide by dehydration to isatin, a keto lactam. Condensation of isatin salt with 3-indolinone affords indigo red. This step is retarded due to electric hindrance.},
     year = {2021}
    }
    

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    T1  - On the Formation Mechanism of Indigo Blue and Indigo Red from Vegetable Source
    AU  - Francisco Sánchez-Viesca
    AU  - Reina Gómez
    Y1  - 2021/12/07
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    N1  - https://doi.org/10.11648/j.mc.20210904.14
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    T2  - Modern Chemistry
    JF  - Modern Chemistry
    JO  - Modern Chemistry
    SP  - 88
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    PB  - Science Publishing Group
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    UR  - https://doi.org/10.11648/j.mc.20210904.14
    AB  - In this communication a series of ionic reactions is advanced in order to explain not only indigo blue formation but also the continuous presence of indigo red as companion, and why this compound is always found in minority. Indican is the glycoside found in Indigofera tinctoria from which the mixture of indigo blue and indigo red is obtained by means of air oxidation in alkaline medium. A reaction mechanism for the hydrolysis of indican, which was advanced decades ago, is criticized in this paper. Fifty years ago a radical mechanism was suggested for indigo formation. However, the supposed reactive species, indoxyl radical, was not detected by electron spin resonance. Besides, there is no free radical promoter, and indirubin (indigo red) was not considered. A series of ionic reactions explain the formation of both indigoids, and why indigo red occurs in minor proportion. Indoxyl, 3-hydroxyindole, is the aglycone from indican. Reaction of indoxyl with oxygen is catalyzed by calcium hydroxide, indoxyl hydroperoxide being formed. Internal reaction in this intermediate produces 3-oxo-indolenine, which reacts with indoxyl carbanion to give leucoindigo. Further steps lead to indigo blue. Indirubin is formed from indoxyl hydroperoxide by dehydration to isatin, a keto lactam. Condensation of isatin salt with 3-indolinone affords indigo red. This step is retarded due to electric hindrance.
    VL  - 9
    IS  - 4
    ER  - 

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Author Information
  • Organic Chemistry Department, Faculty of Chemistry, National Autonomous University of Mexico, Mexico City (CDMX), México

  • Organic Chemistry Department, Faculty of Chemistry, National Autonomous University of Mexico, Mexico City (CDMX), México

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