1,4-Bis(diethylphosphono)-2-butene 1,4-Bis(diethylphosphonyl)-2-butene 1112-96-5 NSC131765 Phosphonic acid, 2-butene-1,4-diylbis-, tetraethyl ester Phosphonic acid, 2-butenylenedi-, tetraethyl ester Tetraethyl 2-butene-1,4-diphosphonate