4TH International Congress on Technology - Engineering & SCIENCE - Kuala Lumpur - Malaysia (2017-08-05)

Oxidative Transformation Of Organic Functional Groups With Silica Gel Supported Green Ruthenium Catalyst
Djerassi in 1993 reported use of RuO4 in oxidation of organic functional groups [1]. Since 1993, a number of reports addressed the reactivity and selectivity of RuO4 in various organic functional group transformation reactions [2]. RuO4 can be used as a stoichiometric reagent or as a catalyst regenerated in situ from a small amount of less expensive RuCl3 [3] or RuO2[4]. Due to the higher cost of RuO4, regeneration of RuO4 from RuCl3 is an attractive choice. RuO4 introduces oxygen in organic compounds. Oxygenated compounds are present in many fine chemicals and pharmaceuticals. They are also used extensively as starting materials in organic syntheses. Among others, oxidation of alkenes [5], alkynes [5], alcohols [6], sulphides [7], and aromatic rings [8], were carries out with RuO4 successfully. RuO4 catalyzed reactions traditionally do not employ environmentally safe procedures. Water is essential in RuO4 catalyzed reactions since RuO4 is regenerated from RuCl3 utilizing water soluble inorganic oxidizing reagent, such as, NaIO4 [2], H5IO6 [2], Oxone [9], or NaBrO3 [9]. Until recently, halogenated organic solvent-water bi-phasic reaction media used in RuO4 promoted reactions. Halogenated solvents are environmentally damaging and bi-phasic reaction produces large volume of halogenated liquid waste. Also, bi-phasic reactions prolong reaction times, involve multi-step product isolation, and expose workers to harmful chemicals. It is well documented that reactions utilizing solid supported reagents satisfy a number of the 12 green chemistry tenets [10]. Recently we have developed a solid supported RuO4 catalyst by mixing highly concentrated aqueous solution of RuCl3 and H5IO6 with silica gel. Hygroscopic silica gel immobilizes the reagents on its surface. This catalyst allowed us to use non-halogenated and environmentally benign dimethyl carbonate as the reaction media. This procedure also offers the following green chemistry benefits; (1) generates smaller amounts of waste, (2) produces shorter reaction times and higher product yields, (3) fast isolation of product, and (4) supporting reagent on solid prevent reagents from air-born thus eliminate potential exposure to the reagents. We have successfully carried out oxidative cleavage of alkenes, alkynes, and oxidation of alcohols and sulphides with this reagent. Preparation, applications, and efficacy of this reagent will be presented at the meeting.
Keywords: green chemistry, oxidation, Ruthenium tetroxide, solid supported reagent
Mohammed Ali, Rawshan Ripa, Tracy Rode, Haley Thompson