A novel fast green method for the preparation of the squaraine dye 3-oxo-4[(1,3,3-trimethyl-3H-indol-1-ium-2-yl)methylene]-2-[(1,3,3-trimethylindolin-2-ylidene)methyl]cyclobut-1-enolate, inner salt

Unconventional and Sustainable Synthesis of Polymethine Dyes: Critical Overview and Perspectives within the Framework of the Twelve Principles of Green Chemistry

“…For this reason, in 2018, a new microwave-assisted protocol in ethyl lactate as a more sustainable reaction medium has been proposed by Minkovska et al for squaraine 3 b (Figure 9, synthesis analogous to the one reported in Scheme 5). [46] Even if the EcoScale score is very good (75.5) and comparable to those (75.0) obtained in DES (Figure 4), purification may be quite impacting from an environmental point of view (E factor = 137) if water and solvent recycling is not taken into consideration (no comment on this purpose could be found in the paper). Furthermore, the generality of the protocol has not been demonstrated on other substrates.…”

“…E factor and EcoScale scores for the synthesis of squaraine 3 b using microwaves as the energy source, in ethyl lactate as more sustainable solvent. [46] Scheme 7. Synthesis of unsymmetrical dimethinic cyanines using microwaves as the energy source, under solventless conditions.…”

“… E factor and EcoScale scores for the synthesis of squaraine 3 b using microwaves as the energy source, in ethyl lactate as more sustainable solvent [46] …”

Ethyl lactate and its aqueous solutions as sustainable media for organic synthesis

“…Ethyl lactate was used as a medium in the synthesis of squaraine dye 18 (Scheme 20) (Minkovska et al, 2018). The reaction was effectively performed under microwave irradiation affording desired product 18 in good yield after heating at 140 • C for 4 min only.…”