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Experiment 5, page 4

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.

Figure 1

When the reaction is complete (> 10 min) cool the flask in water and ice and cautiously add 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!).

2. Reduction of Cinnamaldehyde to Cinnamyl alcohol: Inverse Addition.³

^LiAlH
inverse add⁴
ition

Dry, in an oven, a 250 ml three-necked flask, a 100 ml tap-funnel and a side arm adapter (see Figure 2). Make up a solution/suspension of lithium aluminium hydride (0.72 g, 1.1 H^-equiv) in dry ethyl ether (50 ml) in the 100 ml tap funnel. Set up the dried apparatus as in Figure 2 with a solution of cinnamaldehyde (redistilled, 10 g) in dry ether (25 ml) in the flask.