Patent ID: 8541591

Claim:
A phosphorus compound represented by formula (3): R 1 —Ar + —R 2 —B—PO(OR 3 ) (OR 4 ).X − (3) where Ar + represents an imidazolium cation, B represents a single bond or an oxygen atom, R 1 represents a hydrogen atom or a substituted or unsubstituted alkyl group having 1 to 30 carbon atoms, R 2 represents a single bond or a substituted or unsubstituted alkylene group having 1 to 30 carbon atoms, R 3 represents a hydrogen atom or a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, R 4 represents a hydrogen atom or a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, at least one of R 3 and R 4 represents a hydrogen atom, and X − represents an anion produced by dissociation of a proton from a protonic acid.