In the preparation of a griginard’s reagent great care must be taken that the reactants are absolutely dry and pure. The other experimental details are given below:
Magnesium: magnesium ribbon is washed with ether and dried in desicater.
Ether: it is distilled over sodium metal and P2O5.
Ethyl bromide: it is purified and then distilled over P2O5.
Take dry ether in a round bottom flask and add pieces of Mg ribbon in it. Fit it with water condenser and add ethyl bromide gradually through the condenser. Heat a little so that magnesium dissolves. Cool if necessary. A clear solution of griginard’s reagent – ethyl magnesium bromide, in ether appears. This ethereal solution is used as griginard’s reagent.
C2H5–Br + Mg à C2H5–Mg–Br
A chemical reaction in which two molecules react together in rate determining step is called bimolecular reaction. A bimolecular reaction may be SN2 or E2.
Rate of reaction of A bimolecular reaction is expressed as:
Rate = K[R–X][Nu]
A chemical reaction in which only one molecule takes part in rate determining step.is called an unimolecular reaction. An unimolecular reaction may be SN1 or E1.
Rate of reaction of an unimolecular reaction is expressed as:
Rate = K[R–X]