Preparation of n-ButylMgBr

The most important aspect of this experiment is to keep out water moisture from all the chemicals used as well as the system during the reaction. All reagents and solvents must be thoroughly dried and no air be allowed to enter the system unless it is first dried. So all outlets must be capped with drying tubes.

Measure 10 g of shining magnesium turnings (oxidised magnesium appears dull and is useless for this reaction) into a 250 ml round-bottom flask and fit a condenser and the dropping funnel to the flask. The set-up must have a thermometer to monitor the temperature. Add sufficient di-ethyl ether to cover the magnesium. Add a small crystal of iodine (to catalyse the reaction).

Prepare a solution of 44 ml of n-butyl bromide in 100 ml of di-ethyl ether and transfer it into a dropping funnel. Attach the funnel to the flask. Drop about 20 ml of the solution into the magnesium and stir the mixture. If there is no reaction (no increase in temperature) heat the mixture slightly. Once the reaction commerce add in the rest of the n-butyl bromide solution at a rate to maintain the temperature (more or less). Cool the reaction, if you have to, with ice-water. When all the bromide has been added, stir the mixture for a further 30 minutes, until all the magnesium has reacted (only a little magnesium should be left). This is a solution of n-butylMgBr.

n-Butyl bromide: M. Wt. = 137.03; B.Pt. = 100�C; and density = 1.273 g ml‾�. Mg: M.Wt = 24.3.
Di-ethyl ether: M.Wt. = 74.1; B.Pt. = 35�C; Density = 0.71 g ml‾�.

Reaction with Formaldehyde

Dry 20g of paraformaldehyde with phosphorus pentoxide in a vacuum desiccator. Add the paraformaldehyde into the Grignard reagent and stir for ca 2 hours. Pour the reaction mixture into 150 g of finely crushed ice and stir vigorously until the decomposition is complete. Dissolve the magnesium hydroxide with a 30% sulphuric acid.

Steam distill until no oil pass over (B.Pt. 1-pentanol=138˚C). Saturate the distillate with sodium chloride and extract with ether. Dry the ether portion with anhydrous potassium carbonate. Filter and distill off the ether over a warm water bath. Distill for the alcohol under reduced pressure. Yield is ca 40%.

Reaction with Ethylene Epoxide

Cool the ethylene oxide to 0�C before breaking the seal bulb (B.Pt. = 10.5�C). Dissolve 24 g of the ethylene oxide in 50 ml of ether. Cool the Grignard reagent in an ice-bath before adding the ethylene oxide solution. The rate of addition is such that the temperature is kept below 10�C. Excessively heating must be cooled using an ice-bath. Stir the mixture for a further 30 minutes after all the ethylene oxide has been added.

Distill off half the ether, then add about 100 ml of toluene. Continue the distillation until the residue becomes thick. Cool the mixture and add 100 ml of ice-water, then a 30% sulphuric acid to dissolve the magnesium hydroxide. Keep the mixture cold at all times by adding ice.

Steam distill to remove the product. Wash the aqueous distillate with 20% sodium hydroxide solution to remove the acid. Steam distill again for the product. Dry the distillate and then distill for the alcohol at 157�C. Yield is ca 60%.

Ethylene oxide: M.Wt. = 44.05; B.Pt. = 10.5�C; and sold in sealed bottle.

Reaction with Acetone

Dry the acetone over anhydrous calcium chloride.

Add 19 ml of the acetone into 15 ml of anhydrous ether. Cool the Grignard reagent in an ice-bath before adding the acetone solution drop by drop. The product will separate from the ethereal solution as a grey viscous solid.

When all the acetone has been added, dissolve the magnesium hydroxide with a 30% sulphuric acid, keeping the mixture cool with ice. Remove the ether portion. Extract the aqueous portion with 40 ml of ether. Repeat. Combine the ether portions and dry with anhydrous potassium carbonate. Filter and distill of the ether over a water bath. Finally distill for the dimethyl-1-butanol at 137˚C. Yield = 90%.

Reaction with Ethyl formate

Prepare a solution of 16 ml of ethyl formate in 35 ml of ether. Cool the Grignard reagent with an ice-water bath before adding the ethyl formate with vigorous stirring. The rate of addition is such that the temperature is kept at around 30�C. Excessively heating must be cooled using an ice-bath. Stir the mixture for a further 30 minutes after all the ethyl formate has been added.

Add 35 ml of water into the above reaction mixture and sit the flask in an ice-bath. Stir vigorously before adding 100 ml of a dilute sulphuric acid solution (15 ml to 85 ml water).

Isolate the ether layer. Wash the solid residue with 10 ml of ether and use this ether to extract the aqueous layer. Combine the ether extracts. Repeat this washing one more time.

Distill off the ether but not to dryness. Reflux what is left in the flask with 25 ml of 15% sodium hydroxide solution for about 3 hours.

Isolate the product using steam distillation (to about 500 ml of distillate). Isolate the organic layer, dry and vacuum distill (97-98�C/20mmHg) for the di-n-butyl carbinol. Yield is ca 40%.

Ethyl formate: M. Wt. = 74.1; B.Pt. = 53�C; and Density = 0.921 g ml‾�.