Posts Tagged ‘Al-H-Li bridge’

Mechanism of the Lithal (LAH) reduction of cinnamaldehyde.

Wednesday, April 1st, 2015
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The reduction of cinnamaldehyde by lithium aluminium hydride (LAH) was reported in a classic series of experiments[1],[2],[3] dating from 1947-8. The reaction was first introduced into the organic chemistry laboratories here at Imperial College decades ago, vanished for a short period, and has recently been reintroduced again. The experiment is really simple in concept; add LAH to cinnamaldehyde and you get just reduction of the carbonyl group; invert the order of addition and you additionally get reduction of the double bond. Here I investigate the mechanism of these reductions using computation (ωB97XD/6-311+G(d,p)/SCRF=diethyl ether).

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References

  1. R.F. Nystrom, and W.G. Brown, "Reduction of Organic Compounds by Lithium Aluminum Hydride. I. Aldehydes, Ketones, Esters, Acid Chlorides and Acid Anhydrides", Journal of the American Chemical Society, vol. 69, pp. 1197-1199, 1947. http://dx.doi.org/10.1021/ja01197a060
  2. R.F. Nystrom, and W.G. Brown, "Reduction of Organic Compounds by Lithium Aluminum Hydride. II. Carboxylic Acids", Journal of the American Chemical Society, vol. 69, pp. 2548-2549, 1947. http://dx.doi.org/10.1021/ja01202a082
  3. F.A. Hochstein, and W.G. Brown, "Addition of Lithium Aluminum Hydride to Double Bonds", Journal of the American Chemical Society, vol. 70, pp. 3484-3486, 1948. http://dx.doi.org/10.1021/ja01190a082