Current Catalysis - Volume 4, Issue 2, 2015

The importance of cytochrome P450 enzymes (P450) and their contribution to the majority of xenobiotic phase I metabolism is well established; as such, P450 is the only family of enzymes required by the FDA to be fully evaluated for any interaction(s) with all new chemical entities. The traditional methods used to screen potential therapeutics, generally involving biological systems, present numerous intrinsic issues that have led researchers to explore alternative means. Moreover, the highly selective nature of enzymes has created a type of “gold standard” for catalysis, leading to many attempts to develop systems with similar capabilities, or mimics. The fields of biocatalysis and biomimetic catalysis have grown considerably in the past decade; the objective of this review is to discuss two such catalysts employed in the biomimetic area: metalloporphyrins and metallosalens. These catalysts are often used as P450 mimics, metalloporphyrins in particular, as they are structurally and therefore mechanistically similar to heme B, the activesite common to all P450 enzymes. The focus herein will be on the biomimetic oxidations of compounds that are of biological relevance to humans, ranging from pollutants, to current and potential therapeutics. Additionally, successful applications utilizing metalloporphyrin and salen catalysts for the regio- or enantiospecific oxidation of an advanced intermediate to generate [high-purity] chiral natural products will be briefly discussed.

The present work deals with the characterization and comparison of ceramic foam (dimension 40×40×15mm, 30 pores per inch) supported mesoporous alumina(prepared by the surface hydrolysis of 99% Al metal plate as well as by hydrothermal synthesis of Al(NO3)3.9H2O using pluronic F-127 as structure directing agent), and H-ZSM-5 for the methylation of toluene reaction. The characterization of the catalyst was done by XRD, SEM, Particle size distribution, Ammonia TPD, BET surface area, and pore size distribution. It was observed that alumina prepared with pluronic F-127 shows higher BET surface area (320 m2/g) compared to commercial H-ZSM-5(260 m2/g). Toluene alkylation reaction with methanol was carried out with catalyst coated foam and also with catalyst extrudates (both1g). Conversion obtained was 25-30% at a catalyst loading of 8% on foam for H-ZSM-5 whereas it was 1.26% for alumina coated one. It can also be concluded that catalyst coated ceramic foam exhibits higher conversion compared to pelleted one due to less mass transfer resistance and uniform distribution of catalyst active sites. For any chosen reaction like alkylation, the greater surface area for any catalyst is not the only reason for higher conversion, but the bronsted and lewis acid sites play an important role.

The synthesis and characterization of a novel aminophenyl benzimidazole Pd (II) complex is reported. The complex proved as an efficient catalyst for the Sonogashira crosscoupling reaction of ten different aryl bromides with trimethylsilylethyne to yield a wide range of aryl trimethylsilylethynes. The reaction involves use of the novel complex and triethylamine

Ring opening of various epoxides with different alcohols was studied at room temperature using methanolic solution of trifluoromethane sulphonic acid which in situ generates methyloxonium triflate. The methyloxonium trifalte (0.0625 mol%) was found to be an efficient and selective catalyst for the reaction giving excellent conversions of epoxide/ yields of product (81–>99%) under optimized reaction condition. The turnover number of the catalyst for ring opening of styrene oxide with methanol was found to be 1568, which is better than most of the reported methods.

The effect of three different zeolites: ZSM-5, zeolite-β and zeolite-Y on 1-(1- propylsulfonic)-3-methylimidazolium chloride catalyzed one-pot conversion of cellulose to ethyl levulinate and levulinic acid in 40 % (v/v) aq. ethanol was studied by measuring ethyl levulinate, levulinic acid and 5-hydroxymethylfurfural yields with and without zeolites. The zeolite type ZSM-5 as a co-catalyst produced the highest enhancement in yields and more pronounced effect is observed in ethyl levulinate yields. The highest improvement is seen at 180 °C, 24 h experiment; for instance, the reaction carried out with ZSM-5 as a co-catalyst produced 29.5 % yield of ethyl levulinate, whereas the reaction without zeolite produced 16.3 % yield under similar conditions.