weigh out lithium aluminium hydride (2.9 g) and introduce it into a
3-necked flask viaa powder funnel. Rinse in any residues with dryTHF (~20 ml) and at once fit a
stirrer, condenser and tap-funnel and set up the apparatus as in Figure 1. Use a Citenco brushless
motor for the stirrer, a magnetic stirrer is not sufficiently powerful.
Pass a slow stream of purified nitrogen into the reaction flask, switch on the stirrer and heat the
flask to a gentle reflux. From the dropping funnel add a solution of redistilled cinnamaldehyde (5
g) in dry THF (50 ml), very slowly and at such a rate that the THF in the flask maintains the gentle
reflux. At intervals check the reaction mixture by tlc using silica plates developed in
dichloromethane.
saturated aqueous sodium sulfate (12 ml) dropwise to the stirred reaction mixture to decompose the
excess of reagent. An aqueous solution is safe here because only a small quantity of reagent is
present and it is in solution under an atmosphere of nitrogen. It is important to ensure that all of the
excess reagent is destroyed before continuing (ask a demonstrator if in doubt). Then add 10%
(v/v) sulfuric acid (95 ml). Separate the two layers (if present) and re-extract the aqueous layers
with ether (4 x 30 ml). Dry the combined organic layers over anhydrous sodium sulfate.
Evaporate the solvent under reduced pressure (Rotavapor) and distil the residual oil under reduced
pressure. Isolate the hydrocinnamyl alcohol (b.p. 120-121ºC/13 mm Hg pressure). Record the
yield, b.p. refractive index and i.r. and n.m.r. spectra and so confirm (or otherwise) the absence
of cinnamaldehyde.
In the fume cupboard, clean any contaminated glassware by decomposing the lithium aluminium
hydride with ethyl acetate (see above for details; contact a demonstrator if you are unsure what to
do!).
Figure 2). Make up a solution/suspension of lithium aluminium hydride (0.72 g, 1.1 H – equiv) in
LiAlH4
inverseaddition
