Use of the grignard solution, Chemistry

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Use of the Grignard solution to prepare 2,2,6-trimethyl-5-phenylheptan-3-one:

Prepare a solution of your enone (5.64 g; 0.030 moles) in dry ether (30 mL) and add it to the dropping funnel. Add it dropwise, over 30 min, to the stirred and ice-cooled solution of 2-propyl magnesium bromide. When addition is complete, remove the slush-bath and continue stirring for a further 30 min.

Hydrolyse the mixture by pouring it cautiously onto a mixture of ammonium chloride (16 g) and crushed ice (70 g) in a beaker, stirring as you do so with a glass rod. When the ice has melted, separate the two layers and extract the aqueous layer with ether (2 x 50 mL; there is no need to use dry ether at this stage: why not?) keep the ether layer. Back-wash the combined ethereal layers with saturated brine (40 mL)

Dry the ether layer over anhydrous magnesium sulphate, filter and evaporate thoroughly (use a clean rotary evaporator!) to dryness, in a tared RB flask. Determine the weight of the crude product obtained.

Recrystallise your product (even if it is at present a liquid) from a mixture of ethanol/water (95:5, v/v), using 2 mL of solvent for each gram of product. If no crystals appear on cooling the filtered solution in ice, add a seed crystal of product (available from a demonstrator) to induce crystallisation. After allowing a thick precipitate to form, collect it on a Hirsch funnel, filtering rapidly to avoid redissolving. Pull the cake as dry as possible, then finally dry (24 hr) on a watch glass, in air, in a cupboard.


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