“GRIGNARD REACTION- AS POTENTIAL ROUTE FOR
AROMA CHEMICAL SYNTHESIS”
GRIGNARD REACTION Basically phrases, addition of Grignard reagent to Aldehydes and Ketones is named the Grignard response. It’s a response of a carbonyl compound with alkyl or arryl Magnesium/Zinc Halide to offer an alcohol. Main, Secondary or Tertiary alcohols could also be ready by the response of an appropriate carbonyl-containing compound with an alkyl magnesium halide-so referred to as Grignard reagent. The reagent is often obtained fairly readily by including an alkyl halide to a suspension of magnesium turnings in anhydrous ethers. Initiation of the response could require the addition of some crystals of iodine, the aim of which can be to kind a catalytic quantity of Magnesium Iodide or presumably merely to etch the metallic floor. As it’s important that the iodine must be concentrated on the metallic floor the combination shouldn’t be stirred at this stage. Usually used solvents are THF, Dibutyl ether and so forth.
Formaldehyde offers main alcohol, different Aldehydes give secondary alcohols, and Ketones give tertiary alcohols by this response. The response is of very broad scope, and tons of of alcohols have been ready by this response. The metallic used typically is magnesium. However typically Moreover Grignard reagents, alkyl-and aryl lithiums and alkyl zinc reagents are additionally used for assault of carbon on organo-metallic compounds. Organo-tin reagents, aryl lithium, titanium, alluminium are additionally employed
GR is utilized in Alkylation, in coupling reactions, for making Esters of Completely different Practical Teams, Fragrant & Tertiary Thiols and so forth
ACs like DMBC/DMBCA, DIMETOL, DAMASCONES and so forth are ready by GR from a few years. Diethyl ether is used because the solvent in lots of processes despite the potential hazards of flammability and formation of explosive peroxides. THF, Dibutyl ether and Diamyl ether have additionally been used, however these solvents current issues as properly.
GR is turning into an vital Industrial Course of for a lot of ACs productions now a days
Criticalities related to the Grignard Response
Initiation of the response
Initiation of the response ought to happen inside the first 10-20% addition of the RX resolution in ethereal solvent. Proof for the initiation is giant exotherm and a visible change of the magnesium turnings from a vibrant shiny silver coloration to a boring grey black. Agitation must be sturdy sufficient to shear the magnesium turnings within the response mass. Till initiation has been confirmed, not more than 20% of the RX cost must be added to the reactor. In any other case the big exotherm will launch the response contents to the ambiance.
Impact of moisture & Oxygen
Issues are homocoupled product, intra molecular reactions, formation of RMgO2X and noninitiated response. Correct manipulation and drying of every part have to be carried out. Water in RX and Solvent and Mg have to be lower than zero.02% and freed from Oxygen. Presence of water sometimes results in the sudden initiation in spite of everything RX has been added. This takes place as a result of the residual water is azeotroped out of the combination throughout reflux Or is definitely used up by residual Grignard reagent. To forestall this, dry the elements correctly and manipulate below nitrogen. Addition of small amount of GR could assist for the initiation.
Oxygen will react with GR to kind RMgO2X. This peroxo-species can oxidize the opposite reactants, ligands and catalyst or ultimate product. And the purification issues will come up.
RMgX + H2O ——————————à RH + MgX[OH]
Ether and non-polar Hydrocarbons are the commonly used solvents, Solvent is chosen for yield enchancment, stereo chemical and regiochemical management and formation of dialkyl Mg species. The solvent impact is attributed to the solvent’s polarity, basicity, steric hindrance and so forth.
LIST OF SOME PERFUMERY & FLAVOUR PRODUCTS IN WHICH GRIGNARD REACTION IS USED
FREESIOL -H&R MATSUTAKE ALCOHOL -TAKASAGO (MORILLOL-BASF) UNDECAVERTOL -GIVAUDAN ROURE ALPHA DAMASCONE BETA DAMASCONE DELTA DAMASCONE BETA DAMASCENONE DYNASCONE-10-FIRMENICH DIHYDRO DAMASCONE PHENYL METHYL ETHYL CARBINOL ALPHA, ALPHA DIMETHYL PHENETHYL CARBINOL DIMETHYL BENZYL CARBINOL ACETATE IRONES DOREMOX-FIRMENICH FLOROSA-QUEST CLARYCET-IFF