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ULTRASOUND-ASSISTED ORGANIC SYNTHESIS: ALCOHOL OXIDATION AND OLEFIN EPOXIDATION
Citation:
Pillai**, U R., E SahleDemessie*, V Namboodiri**, A Q. Zhao*, AND J Enriquez*. ULTRASOUND-ASSISTED ORGANIC SYNTHESIS: ALCOHOL OXIDATION AND OLEFIN EPOXIDATION. Presented at AIChE Annual Conference, Indianapolis, IN, November 03, 2002 - November 08, 2004.
Impact/Purpose:
To inform the public.
Description:
Ultrasound-assisted Organic Synthesis: Alcohol Oxidation and Olefin Epoxidation
Unnikrishnan R Pillai, Endalkachew Sahle-Demessie , Vasudevan Namboodiri, Quiming Zhao, Juluis Enriquez
U.S. EPA , 26 W. Martin Luther King Dr. , Cincinnati, OH 45268
Phone: 513-569-7739, Fax: 513-569-7677 Email: sahle-demessie.endalkachew@epa.gov
Abstract:
Catalytic epoxidation of carbon-carbon double bonds is a versatile transformation in synthetic organic chemistry due to the synthetic utility of the ensuing epoxides and their further functionalization. Epoxidation using hydrogen peroxide (H2O2) is very attractive as this cheap and readily available oxidant forms only water as the by-product. This is mostly achieved in the presence of transition metal catalysts. The main drawbacks of most of these processes is the long reaction time required to achieve the desired product yield and the use of organic solvents to achieve optimum rate and product yield. Liquid phase oxidation of alcohols into aldehydes and ketones is also a ubiquitous transformation in organic chemistry. In most cases, oxidizing reagents are needed in stoichiometric amounts that generate heavy-metal waste and are usually run in chlorinated solvents. Separation of the reaction products from the solvent and catalyst mixture is usually demanding and laborious. The growing environmental concerns and awareness these days has resulted in greater demand for environmentally friendly protocols that use relatively benign oxidants such as molecular oxygen and hydrogen peroxide in combination with reusable and recyclable solid catalysts.We will be presenting results of studies on the application ultrasound assisted reactions. An efficient ultrasound-assisted epoxidation of olefins and a,b-unsaturated ketones over hydrotalcite catalysts in the presence of hydrogen peroxide and acetonitrile. This general and selective protocol is relatively fast and is applicable to a wide variety of substrates.
The scarcity of alcohols oxidation processes that simply use oxygen or air as the ultimate stoichiometeryic oxidant is particularly notable. We have evaluated the merits of combining two advanced oxidation processes, viz., sonolysis and photocatalysis, by investigating the conversion of various primary and secondary alcohols to ketones using a high-frequency ultrasonic generator and UV-photolysis. An additive effect on the degradation rate of the parent compound is observed when the sonolysis and photocatalysis experiments were carried out in a simultaneous or sequential manner. Sonolysis is effective for inducing faster degradation of the parent compounds, while reducing the required amount of TiO2 for photocatalysis