Cycloalkylation reactions of fatty amines with α,ω-dihaloalkanes: Role of bis-quaternary ammonium salts as phase-transfer catalysts

Abstract

Bis-quaternary salts are effective phase-transfer catalysts in the cycloalkylation phase reactions of amines. The catalytic activity of these quats is similar to that of conventional quaternary ammonium catalysts, such as benzyltriethylammonium chloride and tetraethylammonium bromide. Bis-quaternary ammonium surfactants have attracted great interest. They are constituted of two hydrophilic groups per molecular unit, separated by a spacer. This is quite different from the catalytic behavior for the conventional surfactant, which leads to a more selective alkylation. Phase-transfer catalysis and micellar phase-transfer catalysis are two well-known methods of promoting reactions mainly between lipophilic and hydrophilic reactants. An intramolecular cycloalkylation of fatty amines, C 12 H 25 NH 2 and C 16 H 33 NH 2 , with several α,ω-dihaloalkanes, viz., 1,2-dibromoethane C 2 H 4 Br 2 , trans -1,4-dichloro-2-butene C 4 H 6 Cl 2 , 1,6-dibromohexane Br(CH 2 ) 6 Br, under PTC conditions are reported. In particular, the cycloalkylation of amine with an excess of α,ω-dihaloalkane has been studied in the presence of 1.9 × 10 −6 mol% bis-quaternary dihalide surfactants (I and II) as PT catalysts and sodium hydroxide (25%) as a base, at 50–60 °C. The reaction was completed in less than 4 h selectively yielding the desired cycloadduct. The structures of the synthesized cycloadducts formed were evidenced by elemental analyses, IR and 1 H NMR spectral analyses.