SYNTHESIS OF HEXANE-1,6-DIOL

• All the apparatus and reagents must be thoroughly dry. 

• Set up a dry bowl to serve later as a cooling bath in a fume cupboard, a 1500-ml three-necked flask with a sealed stirrer unit, a 250 m1 dropping funnel and a double surface con­denser; attach guard-tubes containing calcium chloride to the open ends of the condenser and the dropping funnel. 

• The mechanical stirrer should be a powerful one. 

• It must be emphasised that all operations, includ­ing weighing, with solid lithium aluminium hydride must be conducted in the fume cupboard; during weighing, etc., the front of the fume chamber is pulled down so that there is a narrow opening to allow the hands to enter (for additional precautions and methods for removal of traces of reagent).

• Remove the dropping funnel from the flask neck and replace it by a funnel with a very short wide stem and introduce 10.5 g (0.263 mol) of powdered lith­ium aluminium hydride into the flask through this funnel, and use about 300 ml of sodium-dried ether to transfer the last traces into the flask. 

• Replace the dropping funnel and guard-tube. 

• Set the stirrer in motion, and place a solution of 50.5 g (0.25 mol) of freshly distilled diethyl adipate, b.p. 133­135 °C/14 mmHg, in 150 ml of anhydrous ether in the dropping funnel. 

• After stirring for 10 minutes (some of the lithium aluminium hydride may remain undissolved), add the diethyl adipate solution so that the ether refluxes gently; the reaction mixture rapidly becomes viscous and four 50 ml portions of anhydrous ether must be added during the reduction to facilitate stirring. 

• Continue the stirring for 10 minutes after the diethyl adipate has been added. 

• Decompose the excess of lithium aluminium hydride by the dropwise addition, with sitrring, either of 75 ml of water, or, preferably, by the more rapid addition of 22 g (24.5 ml) of ethyl acetate (1). 

• Filter the reaction product from the sludge through a sintered glass funnel; dry the ethereal solu­tion with magnesium sulphate and distil off the ether with a rotary evapor­ator. 

• The colourless viscous residue (18.5 g) solidifies completely on cooling and has m.p. 41-42 °C, i.e. is pure hexane-1,6-diol. 

• Dissolve the sludge remaining in the filter funnel in 20 per cent sulphuric acid, extract the result­ing solution with six 100 ml portions of ether, or use a continuous ether extractor. 

• Remove the ether by means of a rotary evaporator; the residue (6 g) crystallises completely on cooling, m.p. 41-42 °C. 

• The total yield of hexane-1,6-diol is 24.5 g (91%).

Notes to keep in mind:

1. Before adding water, remove the calcium chloride tubes and fit the reflux condenser with a long tube extending to the duct at the top of the fume cupboard; this will carry the escaping hydrogen above the motor of the stirrer. A spark-proof stirring motor is recommended and should be used, if available. The dropwise addition of water must be conducted while the mixture is stirred vigorously; foaming may occur and the reaction may be moderated by filling the bath surrounding the reaction vessel with cold water.