Synthesis of N-Octadecylsquarylium Dye

Abstract

The synthesis of N-octadecylsquarylium (SQ) dyes[3]and[4]was studied. A mixture of N-octadecylated intermediate[1]or[2](2 mol) and squaric acid (1 mol) was refluxed for 24 h in 1-pentanol-chlorobenzene (3: 2 vol.) (Method A), or heated at 160°C for 5 h in the presence of Nafion-H resin (Method B). Method B was superior to method A with respect to the yields of[3]and[4](Table 2). The yields of[3]were affected by the electron egativity of X and were in the order of X: CMe₂>Se>S>O. In the case of[4], good yields were attained for R⁴ which was an electron-releasing substituent such as OH or Me. IR and NMR measurements revealed that[3]and[4]have symmetrical 1, 3-bonded squarylium rings, which are consistent with the result of N-methyl SQ dyes reported by Treibs et al..