Preparation of dimethylbutan, Chemistry

Preparation of dimethylbutan:


Prepare a mixture of 3,3-dimethylbutan-2-one (trivial name pinacolone; 20.0 g, 0.200 moles), redistilled benzaldehyde (24.0 g, 0.226 moles; see Note 1 if you need to redistil it yourself), 95% ethanol ( ‘rectified spirit'; 75 mL), water (26 mL) and 10% aqueous sodium hydroxide solution (20 mL) in a 500 mL round-bottomed flask equipped with a stirrer guide and overhead mechanical stirrer.

Stir for 6 hours at ambient temperature (this is important).

Dilute with an equal volume of water, and extract the organic product with three separate portions of diethyl ether (60 mL) using an appropriately sized separating funnel. Wash the combined ethereal extracts with water (4 x 60 mL; Note 3), then dry over anhydrous magnesium sulphate (Note 4).

Remove the desiccant by filtration (fluted filter paper, gravity) and the solvent by rotary evaporation over a water-bath using a tared RB flask (Note 5). Determine the mass of the crude product (Note 6).

It is critically important that you do the following distillation carefully: any residual starting materials will interfere with the next step in the reaction.

Purify your product by distillation under reduced pressure, using an efficient water-pump (Notes 7 and 8). Collect the lowish-boiling fore-run in receiver flask 1, and the constant-boiling pure product in receiver flask 2, over a temperature range of no more than 20.(See Note 6.) Record the bp/pressure at which the product distils, record its mass and calculate your percentage yield. Run a IR spectrum of your different fractions and check the purity of your product (marks will be awarded for purity and it will be worth repeating the distillation if your sample is contaminated).

Posted Date: 2/11/2013 6:27:32 AM | Location : United States

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