Preparation of high-carbon-yield pitches from 1-methylnaphthalene through I2O5-assisted electrophilic iodination

Abstract Novel high-carbon-yield pitches were prepared through the iodination of 1-methylnaphthalene (1-MNP) followed by dehydroiodination/polycondensation. 1-MNP was first iodinated by I2 with the aid of I2O5, yielding mainly 1-iodo-4-MNP. Then, a thermal-dehydroiodination reaction at a comparatively low temperature of 130–180 oC was carried out to condense the iodinated products to obtain the pitches. The structures of the iodinated products and pitches were investigated by TG, GC-MS, 1H-NMR and FT-IR. Results indicated that the iodination selectivity (Smb) reached 96.4% when 0.75 mol I2 and 0.18 mol I2O5 reacted with 1 mol 1-MNP at 60 oC for 24 h in acetic acid. Ring-hydrogenation products (tetralin, 5-methyltetralin) and methyl migration products (2-MNP, dimethylnaphthalene and trimethylnaphthalene) were found in the pitches by analyzing their methanol-soluble fractions. Dehydroiodination substantially increased the degree of polymerization and carbon yield of the pitches. The pitches exhibited high polymerization degrees (toluene soluble fraction less than 12 wt%), high carbon yields (54–66 wt%) and complicated 1-MNP molecular assembly patterns including α-α′, α-β′, β-β′, depending on dehydroiodination temperature and time. The iodination/dehydroiodination approach is simple, mild and clean for preparation of high quality pitches for high performance carbon materials.