ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

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

Stela Minkovska, Nikola Burdzhiev, Alexi Alexiev, and Todor Deligeorgiev

Bulgarian Academy of Sciences, Sofia, Bulgaria

E-mail: stelamin@ic.bas.bg

Abstract: A novel green method was developed for the preparation of a squaraine dye, on an 8-mmol scale, by microwave irradiation of two equivalents of 1,3,3-trimethyl-2-methyleneindoline with one equivalent squaric acid in the green solvent, ethyl l-lactate. The time required for this green synthesis is only 4 min. The target squaraine dye was isolated in excellent yield (81%) and with high purity.

Keywords: Green method ; 1,3,3-Trimethyl-2-methyleneindoline ; Squaric acid ; Ethyl l-lactate ; Microwave irradiation 

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-018-0398-6

Chemical Papers 72 (6) 1549–1552 (2018)