# Indigo Beyond Tradition: Scalable Derivatization, Extraction from Waste Denim Textiles, and Boc-Protected Intermediates

## TL;DR

This paper introduces a scalable method to synthesize Boc-protected indigo derivatives and repurpose waste denim textiles, offering a sustainable solution for the textile industry.

## Contribution

The first scalable, column-free synthesis of Boc-protected indigo derivatives and their use in recycling waste denim textiles.

## Key findings

- N-mono-Boc indigo was synthesized under mild conditions with moderate yield.
- The oxidation mechanism of di-Boc indigo was elucidated using experimental and theoretical methods.
- Indigo-dyed textile waste can be repurposed as a starting material for Boc-protected indigo derivatives.

## Abstract

This study demonstrates
the feasibility of industrial-scale, column-free
synthesis of tert-butoxycarbonyl (Boc)-protected
indigo derivatives and highlights their application potential in the
textile industry for the dyeing of previously undyeable synthetic
textiles with indigo. The direct synthesis of N-mono-tert-butoxycarbonyl (Boc) indigo, an important intermediate
for indigo substitution studies, was achieved under very mild conditions
and in a moderate yield. For the first time, the molecular structures
of all synthesized compounds were comprehensively characterized through
detailed NMR and HRMS analyses as well as the single-crystal X-ray
diffraction method. The influence of the Boc groups on the photophysical
and thermal properties, oxidation–reduction behavior, and dyeing
performance was thoroughly investigated and defined. Importantly,
the oxidation mechanism of dihydro-di-Boc indigo (i.e., reduced di-Boc
indigo) was elucidated by combined experimental and theoretical approaches.
Furthermore, this study shows that indigo-dyed textile waste can serve
as valuable starting materials for the synthesis of Boc-protected
indigo derivatives. This innovative methodology offers significant
promise not only for textile-to-textile recycling technologies but
also as a sustainable strategy to address global waste management
and environmental pollution challenges.