Crystal Structure of n-Propyl GallateUsed as the Charge-Control Agent of the Negative Type

抄録

n-Propyl gallate (PG) is a charge-control agent (CCA) of the negative type used for toners in the electrophotographic process. Suganami et al. found that PG enhances greatly the charge-control power of triphenyl-pararosaniline (TPPR: an electron donor due to amino groups) used as the positive type, where PG works as an electron acceptor (i.e. acid) due to three phenolic hydroxides to form a 1:2 charge-transfer complex of TPPR/PG. However, judging from the 1:2 ratio of the complex and the number of hydroxides in PG, the effective acidity of PG seems to be quite weak. For this reason, the present structure analysis has been carried out in order to characterize the acidity of PG from the structural point of view. Three kinds of solvated single crystals are isolated from solution in dichloromethane, chloroform and acetonitrile. In all crystals, there observed strong OH…O intramolecular as well as intermolecular hydrogen bond network throughout the crystal. These results lead us to conclude that the formation of OH…O intramolecular hydrogen bonds weakens considerably the acidity of PG toward surroundings.