Microwave Synthesis of Quaternary Ammonium Salts

Abstract

The microwave synthesis of several quaternary ammonium salts is described. The synthesis provides comparable or better yields than published methods with reduced reaction times and in the absence of solvent.

Spectral fine tuning of cyanine dyes: electron donor—acceptor substituted analogues of thiazole orange

“…Two new methoxy-substituted TO derivatives, CH 3 O-TO and CH 3 O-TO-CF 3 (Chart 1) were synthesized as their iodide salts by a standard route 50 : (A) N -methylation of 5-methoxy-2-methylbenzothiazole, (B) methylation of either 7-(trifluoromethyl)quinoline-4-thiol or 4-chloroquinoline, and (C) condensation in the presence of triethylamine to yield the final dyes (Scheme 1). …”

Polymethine Dyes in Hybrid Photovoltaics: Structure–Properties Relationships

“…The required grafting group, which allows binding with the semiconductor surface, is usually introduced in either the 1‐ or 5‐position. Position 1 is generally functionalized through reaction with alkyl halides43 (Figure 1) and sometimes can also form supramolecular structures with other co‐sensitizers, as proposed by Etgar et al44 Usually, for a fast and inexpensive synthesis, unsubstituted indolenines (R 1 = H in Figure 1) and 5‐carboxy‐substituted indolenines (R 1 = COOH in Figure 1) are the most used building blocks. Moreover, starting from para ‐substituted hydrazines, it is possible to obtain indolenines with different groups in the 5‐position.…”

“…As recently reported by our group,66 by exploiting MW heating it is possible to minimize the need for anhydrous conditions and to improve synthetic pathways. Thus, formation of indolenine from hydrazine, quaternarization of indolenine nitrogen (as reported also by Winstead et al43), squaraine formation, and even further reaction on the formed squaraine (such as coupling on Br squaraines) have been improved because of microwave‐assisted organic synthesis (MAOS), which also allows us to reduce the number of reaction steps and to avoid hemisquarate hydrolysis before unsymmetrical squaraine formation (Scheme ). The ease of preparation and the possibility of providing good amounts of pure dyes in a short time could lead to the construction of a large variety of novel structures that can be easily tested in technological applications.…”

Microwave-Assisted Synthesis of Near-Infrared Fluorescent Indole-Based Squaraines

“…10,21 For example, in the synthesis of 3a, reaction times decreased from 24 h (entry 1) 17d to 9 min (entry 4). In the synthesis of 3b, the yield increased from 79 19 to 94%, while reaction times decreased from 24 h to 20 min.…”