SYNTHESIS OF PENTAN-1-OL (Amyl alcohol)

• Fit the central neck of a 1-litre two-necked flask with an efficient double sur­face condenser and close the side-neck with a stopper. 

• Place 52 g (59.5 ml, 0.4 mol) of ethyl pentanoate and 800 ml of super-dry ethanol (1)  in the flask. 

• Add 95 g (4.1 mol) of clean sodium in small pieces through the aperture at such a rate that the vigorous refluxing is continuous (20-30 minutes). 

• Reflux the mixture in an oil bath for 1 hour in order to be certain that all the sodium has dissolved. 

• Re­place the reflux condenser by an efficient fractionating column (e.g. Hempel or all-glass Dufton column, etc.) and set the condenser for downward distilla­tion. 

• Fractionate the mixture from an oil bath; about 250 ml of absolute etha­nol are thus recovered. 

• Treat the residue, consisting of pentanol and sodium ethoxide, with 330 ml of water and continue the distillation (oil bath at 110­120 °C) until the temperature at the top of the column reaches 83 °C, indicat­ing that practically all the ethanol has been removed; about 600 ml of approx­imately 90 per cent ethanol are recovered. 

• Remove the fractionating column and steam distil the mixture; about 200 ml must be collected before all the pentan-1-ol is removed. 

• Separate the crude pentanol, dry it over anhydrous potassium carbonate or anhydrous calcium sulphate and distil through a short column. 

• Collect the fraction boiling at 137-139 °C. The yield of pentan-l-ol is 25 g (71%).

Notes to keep in mind:

1. The ethanol must be absolute; a lower grade gives a poor yield.



Cognate preparations. 2-Phenylethanol. 

• Prepare a suspension of 42 g (1.83 mol) of sodium in 120 ml of sodium-dried toluene in a 3-litre three-necked flask following the procedure described in Method 2 under Sodium. 

• Do not decant the toluene; when the mixture has cooled to about 60 °C, add a solution of 50 g (0.30 mol) of ethyl phenylacetate in 150 g (190 ml) of super-dry ethanol as rapidly as possible without allowing the reaction to get out of control. 

• Then add a further 200 g (253 ml) of super-dry ethanol. 

• When the reaction has sub­sided, heat the flask in a water bath until the sodium is completely dissolved Distil off the ethanol and toluene under reduced pressure using a rotary evap­orator. 

• Dilute the residue with water and extract the phenylethanol with ether, dry the extract with magnesium sulphate, remove the solvent and distil the residual oil under reduced pressure. 

• Collect the 2-phenylethanol at 116­118 °C/25 mmHg. The yield is 25 g (67%).

• The alcohol may be purified by conversion into the calcium chloride addi­tion compound. 

• Treat it with anhydrous calcium chloride; much heat is evolved and the addition compound is formed. 

• After several hours, remove any oil which has not reacted by washing with petroleum ether (b.p. 60-­80 °C). Decompose the solid with ice-water, separate the alcohol, dry and distil.

Butane-1 ,4-diol (Tetramethylene glycol). 

• Place 60 g (2.6 mol) of clean sodium in a 3-litre three-necked flask fitted with two efficient double surface con­densers and a dropping funnel protected by a calcium chloride tube. 

• Add from the dropping funnel a solution of 35 g (0.2 mol) of diethyl succinate in 700 ml of super-dry ethanol as rapidly as possible con­sistent with the reaction being under control; it may be necessary to immerse the flask momentarily in a freezing mixture. 

• When the vigorous action has subsided, warm the mixture on a water bath or in an oil bath at 130 °C until all the sodium has reacted (30-60 minutes). 

• Allow to cool and cautiously add 25 ml of water (1); reflux for a further 30 minutes to bring all the solid into solution and to hydrolyse any remaining ester. 

• Add 270 ml of concentrated hydrochloric acid to the cold reaction mixture, cool in ice, filter off the pre­cipitated sodium chloride and treat the filtrate with 300 g of anhydrous potas­sium carbonate to free it from water and acid. Filter the alcoholic solution through a large sintered glass funnel, and extract the solid twice with boiling ethanol. Distil off the ethanol from the combined solutions; towards the end of the distillation solid salts will separate. 

• Add dry acetone, filter and distil off the acetone. 

• Distil the residue under diminished pressure, and collect the butane-1,4-diol at 133-135 °C/18 mmHg. The yield is 13 g (72%). 

• Record the p.m.r. spectrum (DMSO-d₆) and assign the signals that are observed at 6 1.43 [m(A₂B₂), 4H], 3.39 (d of t, 4H) and 4.34 (t, 2H).

Notes to keep in mind:

1. Alternatively, the following procedure for isolating the diol may be used. Dilute the partly cooled mixture with 250 ml of water, transfer to a distilling flask, and distil from an oil bath until the temperature reaches 95 °C. Transfer the hot residue to an apparatus for continuous extraction with ether. The extraction is a slow process (36-48 hours) as the diol is not very soluble in ether. Distil off the ether and, after removal of the water and ethanol, distil the diol under reduced pressure.