How could organic synthesis help the understanding of the problems of deephydrodesulfurization of gasoils?

Various alkyldibenzothiophenes bearing bulky groups in positions 4 and 6 we re synthesized and their sensitivity to HDS compared over a NiMo/Al2O3 indu strial catalyst in a batch reactor at 573 K and under 5 MPa H-2 pressure. I t was demonstrated that their reactivity is correlated to the steric hindra nce near the sulfur atom. A new method for removing these refractory compou nds is described, involving the selective formation of insoluble charge tra nsfer complexes between dibenzothiophene derivatives and tetranitrofluoreno ne in synthetic solutions. Following the same procedure, the global sulfur level was lowered in gasoils. (C) 2000 Academie des sciences / Editions sci entifiques et medicales Elsevier SAS.