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

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℃ 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℃ 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.