A bis-phosphonium salt represented by the following formula (1) is
provided:
##STR1##
wherein R.sup.1, R.sup.2, R.sup.3, and R.sup.4 each represent a linear or
branched alkyl group, a cycloalkyl group, an aryl group, or an aralkyl
group; A represents an alkylene group; Y represents an anion; R.sup.1 and
R.sup.2 may form a ring; R.sup.3 and R.sup.4 may form a ring; and R.sup.1,
R.sup.2, R.sup.3, and R.sup.4 may be the same or different. A process for
producing such a bis-phosphonium salt includes a step of allowing a first
secondary phosphine and second secondary phosphine to react with a
compound in an alcohol solvent selected from a secondary alcohol and
tertiary alcohol. The compound is represented by the following formula
(5):
Y--A--Y (5)
