COLL 520 |
| K.C. Rajanna1, Mir Moazzam Ali2, and Tasneem Sajid2. (1) Department of Chemistry, Osmania University P.G. College, Mirzapur, Osmania University, Mirzapur(B),Medak(Dist), 502249, India, (2) Department of Chemistry, Anwarul Uloom College, Nawab Shah Alamkhan Institute for P.G.Studies and Research, Mallepally, Hyderabad, 500001, India |
| Vilsmeier Haack reagent(VHR) has recieved the attention of synthetic organic chemists all over the world ever since its discovery by Vilsmeier and Haack in 1927.It could be conveniently used as formylating agent when equimolar quantities of Dimethyl formamide(DMF)and Phoshorous oxy chloride were used for its preparation under chilled conditions(Preferably the temprature should be less than Zero (0) Celius degrees). VH reactions with organic substrates such as anisole are generally too sluggish even at elevated temperatures. However,the reactions underwent smoothly in micellar media even at mild temperatures.A variety of surfactants such as SDS, CTAB and Triton-X(100) are used as micelle forming compounds. The reactions underwent formylation when DMF and Phosphorous oxy chloride were used for the preparation of VH reagent. When DMF was replaced by Dimethyl acetamide (DMA) the reaction smoothly afforded acetyl derivatives.The reaction times are substantially reduced from several hours to few minutes from a native reaction to micellar mediated reaction followed by dramatic rate acceleraations and improvements in the yields of end products. The VH reactions followed second order kinetics with a first order dependance on the [Substrate] as well as [VHR]. In order to understand the nature of reactive VH species the reactions are studied in the binary solvent mixtures of dichloro ethane(DCE) and aceto nitrile(ACN) so as to obtain a large variation in the dielectric constant(D). On the basis of observed kinetic results a plausible mechanism is proposed. The kinetic observations of micellar mediated reactions are interpreted by Menger-Portnoy's enzymatic model and Piszckiewic's co-operativity model. |
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Environmental Colloids
2:00 PM-3:40 PM, Thursday, April 1, 2004 Marriott -- Grand Ballroom H, Oral
Division of Colloid and Surface Chemistry |