Synthesis of alkynyl-substituted camphor derivatives and their use in the preparation of paclitaxel-related compounds

Compounds containing two alkyne groups in close vicinity at the rigid skeleton of camphorsulfonamide show unique reactivities when treated with electrophiles or catalytic amounts of platinum(II). The formed product structures depend not only on the reagents used but also on the substituents attached to the triple bonds. Cycloisomerisations with perfect atom economy lead to polycyclic heterocycles that resemble to some extent the AB ring system of paclitaxel. Herein, we present practical synthetic methods for the selective synthesis of precursor dialkynes bearing different substituents (alkyl, aryl) at the triple bonds, based on ketals or an imine as protecting groups. We show for isomeric dialkynes that the reaction cascade induced by Pt(II) includes ring annulation, sulphur reduction, and ring enlargement. One isomeric dialkyne additionally allows for the isolation of a pentacyclic compound lacking the ring enlargement step, which we have proposed as a potential intermediate in the catalytic cycle.

Sulphur reduction in fluid catalytic cracking using a kaolin in situ crystallization catalyst modified with vanadium

Sulphur reduction catalysts represent a viable option for S reduction in the fluid catalytic cracking (FCC) process. In this paper, a kaolin in situ crystallization catalyst was modified with vanadium and evaluated in a fixed fluid bed (FFB) reactor. The relation between the acidity of the catalyst, the S reduction rate and the catalyst activity is discussed. The results show that increasing weak Lewis acid acidity favours S reduction in the FCC process. Increasing the V content enhances the weak Lewis acidity, so causing the S reduction rate to increase. The kaolin in situ crystallization catalyst modified with 0.6 wt.% of V leads to a 34.5% reduction in the S content of the liquid product. Comprehensive evaluation of the FFB results and the S reduction ability indicates that the catalyst modified with 0.45 wt.% V provided the best performance.

Sulphur reduction additive prepared from caustic-modified kaolin

The performance of a fluidized cracking catalyst additive prepared from caustic-modified kaolin microspheres for gasoline S reduction was investigated using N2 adsorption, infrared acid-site characterization, X-ray diffraction and small-scale fluid bed reactor tests. The additive exhibited improved coke selectivity and yield distribution, and the S content of cracked gasoline was reduced significantly. The results indicated that a reactive mesoporous structure was formed in the modified kaolin.