(564a) Immobilisation of Eosin Y on Wool for the Photocatalytic Synthesis of Fine Organic Chemicals

Recently, the interest in solar photocatalysis for the synthesis of organic compounds has grown as a more sustainable alternative than traditional synthesis routes. Moreover, transition metals have been replaced by metal-free dyes, which are cheaper and non-toxic. In this field, Eosin Y has shown a great potential as a photocatalyst for applications in organic synthesis reactions such as cyclisation, dehydrogenation or redox reactions, among others.¹ However, these reactions have been performed with the catalyst in solution, which increases the cost of the process due to the difficulty to handle and separate the catalyst from the reaction mixture.² The immobilisation of Eosin Y on a robust/renewable material allows the continuous illumination of the catalyst during the reaction and its recovery and reuse, making the process more sustainable.

Natural wool was chosen as support of Eosin Y and different immobilisation methods were investigated. The oxidative homocoupling of benzylamine was selected as a model reaction and it was performed under a solar light simulator (40 cm*40 cm). The results demonstrated that acidic conditions are the most favourable to immobilise Eosin Y. This is due to the negative charge of Eosin Y and the wool in water. Treating the wool with an acid creates a positively charged wool surface and an ionic bonding between the negative charge of the catalyst and the wool surface. The stirring of the reaction mixture and low volumes achieved a conversion of 39 % after 5 h. A reusability study was performed, showing that Eosin Y was stable on the wool after 3 cycles. Further investigations have been carried out pre-treating the wool with a cationic reagent to increase the amount of catalyst immobilised, achieving conversions of 43 %. The pre-treatment allowed the increase of positively charged functionalities on the surface of the wool and therefore more ionic bonding sites were created for the catalyst. Further work will be to scale up the reaction with the Eosin Y on wool using a Spinning Mesh Disc Reactor. In summary, this research has demonstrated that the immobilisation of Eosin Y on wool under acidic conditions creates a strong bonding between the catalyst and the support and it is a cheap and sustainable catalyst to carry out photocatalytic synthesis of fine organic compounds.

REFERENCES

1. Prasad Hari and B. König, Chem. Commun, 2014, 50, 6688-6699.
2. Shivaprasad, M. D. Jones, D. A. Patterson and E. A. C. Emanuelsson, Chem. Eng. Process., 2017, 122, 550–559.