Five coals of different rank, in Coal/Metal-K/Diglyme system, were reductively methylated one tonine times in 3hr in an omitting extraction to obtain more detailed information about the solubilizationefficiencies of coals and the structural characteristics of solubilized products.
The benzene solubility of each coal increased almost exponentially with increasing of the number of methylation steps, and was as follows after nine methylation steps: Kairan (81%), Akabira (50%), Illinois no. 6 (39%), Daido (31%), Wandoan (16%).
Benzene soluble portion (BS) after each methylation step was separated by gel permeation chromatography (GPC) and structural parameters of these GPC. fractions were calculated. For Kairan coal, the amount of GPC. Fr. 1-3 including high molecular weight components gradually increased from 20% to 50% with the number of methylation steps, and it was clearly observed that part of benzene insoluble portion transfered to BS by step-wise methylation.
In general, reaction in this system is somewhat a less electron transferability which makes possible the formation of a “coal anion”. Consequently, repeated methylation process is more effective to be applied the coal such as Kairan coal that can largely be soluble in benzene in an incipient stage of repetition, since BS which has been dissolved, plays the role of an electron transfer agent. Because of this, it appeared that the effect of repeated methylation on the solubilization of low rank coal such as Wandoan coal can not be expected.
Thus, if it was necessary to dissolve the coal in large quantities in benzene by reductive alkylation, it seemed rather likely that coals were repeatedly alkylated, moreover using a large amount of naphthalene, and by Sternberg's procedure.
