The present invention is directed at the synthesis and characterization of recrystallized HI-6 dimethylsulfate (DMS). The method can comprise dissolving HI-6 DMS in an alkyl-based glycol and adding an antisolvent to recrystallize HI-6 DMS or dissolving HI-6 DMS in methanol and adding dimethoxy ethane or dimethyl formamide as the antisolvent to recrystallize HI-6 DMS. The recrystallized HI-6 DMS indicates a resistance to moisture absorption and/or a DSC melting point onset (MP Onset) at least at or above 160.0? C.

A novel agent for introducing a protecting group for a hydroxy group and/or a mercapto group that can be introduced and removed under mild conditions is provided. The agent for introducing a protecting group for a hydroxy group and/or mercapto group of a substrate compound having the hydroxy group and/or mercapto group is represented by the following formula (I), wherein A represents a ring structure having 1 to 5 rings in which two carbon atoms of an adjacent benzene ring are included, the ring structure comprises a substituted or unsubstituted five-membered ring or six-membered ring and optionally include a heterocycle; each of R.sup.1, R.sup.2, R.sup.3, and R.sup.4 is independently a hydrogen atom or a linear or branched alkyl group having 1 to 5 carbon atoms; and X is a halogen atom or OSO.sub.2R.sup.5 (R.sup.5=an aryl group or an alkyl group).

A novel agent for introducing a protecting group for a hydroxy group and/or a mercapto group that can be introduced and removed under mild conditions is provided. The agent for introducing a protecting group for a hydroxy group and/or mercapto group of a substrate compound having the hydroxy group and/or mercapto group is represented by the following formula (I), wherein A represents a ring structure having 1 to 5 rings in which two carbon atoms of an adjacent benzene ring are included, the ring structure comprises a substituted or unsubstituted five-membered ring or six-membered ring and optionally include a heterocycle; each of R.sup.1, R.sup.2, R.sup.3, and R.sup.4 is independently a hydrogen atom or a linear or branched alkyl group having 1 to 5 carbon atoms; and X is a halogen atom or OSO.sub.2R.sup.5 (R.sup.5=an aryl group or an alkyl group).