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Grignard reaction in aroma chemical industryGRIGNARD REACTION in Aroma chemical industry. In general terms, addition of Grignard reagent to Aldehydes and Ketones is known as the Grignard reaction. I Formaldehyde gives primary alcohol, other Aldehydes give secondary alcohols, and Ketones give tertiary alcohols by this reaction. The reaction is of ve GR is used in Alkylation, in coupling reactions, for making Esters of Different Functional Groups, Aromatic & Tertiary Thiols etc ACs like DMBC/DMBCA, DIMETOL, DAMASCONES etc are prepared by GR from many years. Diethyl ether is used as the solvent in many processes in spite of the potential hazards of flammability and formation of explosive peroxides. THF, Dibutyl ether and Diamyl ether have also been used, but these solvents present problems as well. GR is becoming an important Industrial Process for many ACs productions now a days Criticalities associated with the Grignard ReactionInitiation of the reactionInitiation of the reaction should occur within the first 10-20% addition of the RX solution in ethereal solvent. Evidence for the initiation is large exotherm and a visual change of the magnesium turnings from a bright shiny silver color to a dull gray black. Agitation should be strong enough to shear the magnesium turnings in the reaction mass. Until initiation has been confirmed, no more than 20% of the RX charge should be added to the reactor. Otherwise the large exotherm will release the reaction contents to the atmosphere. Effect of moisture & Oxygen Problems are homocoupled product, intra molecular reactions, formation of RMgO2X and noninitiated reaction. Proper manipulation and drying of each component must be carried out. Water in RX and Solvent and Mg must be less than 0.02% and free of Oxygen. Presence of water typically leads to the sudden initiation after all RX has been added. This takes place because the residual water is azeotroped out of the mixture during reflux Or is actually used up by residual Grignard reagent. To prevent this, dry the components properly and manipulate under nitrogen. Addition of small quantity of GR may help for the initiation. Oxygen will react with GR to form RMgO2X. This peroxo-species can oxidize the other reactants, ligands and catalyst or final product. And the purification problems will arise. RMgX + H2O ---------à RH + MgX[OH] Ether and non-polar Hydrocarbons are the generally used solvents, Solvent is selected for yield improvement, stereo chemical and regiochemical control and formation of dialkyl Mg species. The solvent effect is attributed to the solvent’s polarity, basicity, steric hindrance etc. | Related Tags            |
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