Limestone or calcium carbonate (CaCO3) used as a sorbent in the removal of acid gas precursors (SO2) from combustion systems suffers from poor pore structural properties which causes low reactivity and incomplete utilization. The surface area and pore size distribution of CaCO3, if tailored appropriately, can considerably enhance its reactivity for SO2. This study focuses on the optimization of pore properties of CaCO3 particles and the enhancement of SO2 reactivity and ultimate utilization. The carbonate is produced by precipitation from an aqueous suspension of calcium hydroxide by injecting CO2. The influence of operating parameters, suspension concentration, gas flow rate, and additives (surfactant) on the surface area and pore volume is investigated. The surface area of the carbonate powder can be controlled in the range of 10−70 m2/g by varying the operating parameters. The SO2 reactivity and the ultimate utilization of the calcium carbonate indicate a dramatic improvement and can be correlated with the surface area and pore volume characteristics of the particles.

Easily accessible chiral sulfinamide 2 has been developed as the first highly efficient and enantioselective organocatalyst relying solely on a chiral sulfur center for stereochemical induction. In the presence of 20 mol % of 2, a broad range of N-aryl ketimines 1 were reduced by trichlorosilane to produce amines 3 in high yield and enantioselectivity.In recent years, there has been intense research interest in asymmetric organocatalysis, and significant progress has been made in the development of metal-free chiral organocatalysts. 1 The vast majority of the currently available enantioselective organocatalysts rely on chiral carbon centers for stereochemical induction. Although chiral sulfur centers have been well established as efficient and versatile stereocontrollers and have been extensively used as the chirality source of chiral auxiliaries and ligands, 2 organocatalysts incorporating chirality solely at sulfur have been rarely explored. Recently, several S-chiral sulfoxides were reported to activate allyltrichlorosilanes in asymmetric allylations, 3 and in one case, high enantioselectivities were obtained. 3a However, these sulfoxides were not catalytic and were all used in at least a stoichiometric amount. Herein, we report the first example of S-chiral compounds as highly effective organocatalysts (Figure 1), which promoted the asymmetric reduction of ketimines with trichlorosilane (HSiCl 3 ) in high yield and enantioselectivity.We recently initiated a program focusing on developing enantioselective Lewis base organocatalysts for the activation of HSiCl 3 for the asymmetric reduction of imines, 4,5 a useful yet challenging reaction for the production of chiral amines. 8 We were particularly interested in S-chiral sulfinamides due † Chengdu Institute of Biology. ‡ Xihua University.

L-Pipecolinic acid derived formamides have been developed as highly efficient and enantioselective Lewis basic organocatalysts for the reduction of N-aryl imines with trichlorosilane. Catalyst 4b afforded high isolated yields (up to 98%) and enantioselectivities (up to 96%) under mild conditions with an unprecedented substrate spectrum. Catalytic enantioselective reduction of imines represents one of the most important methods for preparing chiral amines, 1 a ubiquitous structural motif of natural products, drugs, and agrochemicals. Since the 1970s, considerable effort has been devoted to the development of this transformation, and remarkable progress has been made. 1,3 However, compared with the reduction of alkenes and ketones, relatively limited numbers of highly enantioselective procedures are currently available for the reduction of imines, and the development of efficient catalysts with high enantioselectivity has proven to be much more difficult. In particular, the highly enantio-selective catalyst with a satisfactorily broad substrate scope remains elusive. Factors contributing to the difficulty of this transformation include the difference in reactivity among imines containing different nitrogen substituents, the existence of acyclic imines as inseparable mixtures of E/Z