The production of biodiesel as a fuel in diesel engines greatly increased in recent years and is expected to grow more and more in the near future. Increasing biodiesel consumption requires optimized production processes allowing high production capacities, simplified operations, high yields, and the use of more economic feedstocks such as waste oils and fats. However, the latter often contain large amounts of free fatty acids and cannot be processed with the commonly practiced technology based on the use of alkaline catalysts in the homogeneous phase that requires the use of highly refined oil as raw materials. Therefore, the development of processes for low-cost biodiesel production requires the individuation of heterogeneous catalysts that are very efficient in promoting the transesterification reaction also in the presence of free fatty acids and water, allowing the prompt separation of pure glycerol and not requiring expensive purification of this byproduct. In the present contribution, the performances of different heterogeneous catalysts are compared both in the absence and in the presence of free fatty acids. In some cases, the resistance of the catalysts to the presence of water and the eventual deactivating effects after the first use have also been tested. The catalysts considered are both basic and acidic in nature, such as hydrotalcite, MgO, TiO 2 grafted on silica, vanadyl phosphate, and different metals-substituted vanadyl phosphate of the type Me(H 2 O) x VO 1-x PO 4 ‚2H 2 O, where Me is a trivalent cation such as Al, Ga, Fe, and Cr and where x ) 0.18-0.20. Finally, the understanding of the kinetic behavior of the most stable catalyst TiO 2 /SiO 2 has been deepened.

The first catalytic version of the stannylene-mediated benzylation and allylation of polyols is reported. The methodology is based on a simple solvent-free protocol that significantly advances, in terms of both experimental ease and synthetic scope, the applicability of tin-promoted selective protections. The described approach is indeed endowed with a very large number of advantages over routine protocols: use of a low catalytic loading of cheap Bu 2 SnO, a single-step process with avoided use of solvents, a minimally demanding experimental procedure with reactions performed under air, reduced reaction times, a much simpler work up, a wide target scope, and yields that, in many cases, compare favorably to routine protocols. In addition, the catalytic solvent-free approach extends the scope of stannylene chemistry to unprecedented applications to reducing sugars and in the synthesis of highly benzylated building blocks otherwise accessed through much more demanding procedures. From a conceptual point of view, the described results indicate that solvent-free conditions can assist the development of catalytic approaches otherwise ineffective in solution.

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Three alternative protocols were developed to carry out the selective installation of acetal groups on carbohydrates and polyols under mildly acidic, solvent-free conditions. One protocol is based on a diol/aldehyde condensation at room temperature, with an acetolysis process serving for the activation of the carbonyl component. A second approach is based on an orthoester-mediated activation of the carbonyl component at high temperature. The third protocol is instead entailing a transacetalation mechanism. Combination of these methods allows a wide set of acetal-protected building blocks to be accessed in short times under very simple experimental conditions working under air. The scope of the latter two approaches was also extended to unusual one-pot synthetic sequences leading to concomitant Fischer glycosidation/acetal protection of reducing sugars