Cuiming Yuan

Derivatization and structural studies by spectroscopic methods of humic acids from Leonardite

Abstract Humic acids (HA) from Leonardite were methylated with CH 3 I/Ag 2 O in a methanol suspension (yield 261±23.6 g kg −1 ; N =4) and dimethylformamide (DMF) (yield 839±57.6 g kg −1 ; N =4) solution. Methylated humic acids are soluble in organic solvents and have been examined by IR-FT, 1 H and 13 C-NMR spectroscopy methods. The OCH 3 /COOCH 3 ratio was calculated by 13 C-NMR for HA methylated in methanol suspension and DMF solution obtaining values of 0.38 and 0.82, respectively. Methylated acids molecular weight distribution was measured by Size-Exclusion Chromatography (SEC). The product obtained in methanol suspension has a molecular weight ( M n ) of 2918 Da and a dispersion index ( D = M w / M n ) of 1.13. The methylated product prepared in DMF solution is characterized both by higher molecular weight, ( M n =3623 Da) and dispersion index ( D =2.10).

PHASE DIAGRAMS OF PERHYDROTRIPHENYLENE AND AROMATIC COMPOUNDS II. Terthiophene and related thiophene oligomers

Terthiophene included in a perhydrotriphenylene (PHTP) adduct exhibits an UV spectrum different from that observed in the bulk or in solution. The X-ray diffraction pattern also differs significantly from that of pure PHTP. The UV spectrum is interpreted as due to an isolated molecule in a vacuum-like space, in agreement with a model developed from X-ray diffraction data. Knowledge of the phase diagram was essential for an interpretation of the optical properties and of some kinetic aspects of the formation of the inclusion compound phase. In this work, the phase diagrams of terthiophene (T3) are presented, and DSC evidence of the inclusion of quater- (T4), penta- (T5)and α,ω-dihexylquaterthiophene (DH4T) is discussed.