Reductions of cyanohydrins

[Rhodium]

Is there any other method for reducing the cyanohydrin of a benzaldehyde (or an ester thereof) to a phenethylamine without using catalytic hydrogenation? If not, what about CTH with Pd/C and ammonium formate?

http://rhodium.lycaeum.org

[WizardX]

Rhodium: Yes, I will post an electrochemical reduction. I forgot to send it to you.

[obituary]

yes, please post it. (why not add it to your site also)

[obituary]

could you use benzonitrile + MeMgBr to produce PhEtAm? 
assuming this is possible, run sandmeyer on Br-benzene to yeild the nitrile and thus get any number of PhEtAm's.

[Rhodium]

PhCN + MeMgBr would give acetophenone after hydrolysis, or 1-PEA (not the desired 2-PEA) if one would reduce the ketimine intermediate.

http://rhodium.lycaeum.org

[jim]

Why wouldn't metal hydrides work?

[Rhodium]

As far as I know, reduction with LAH would afford the 1-phenyl-2-amino-ethanol, not the fully reduced phenethylamine.

http://rhodium.lycaeum.org

[WizardX]

Rhodium: I remember an electrochemical reduction!! I have too look it up again and get back too you.

[WizardX]

Mandelonitriles C6H5-CH(-OH)-CN ==> C6H5-CH2-CN

Refs
(1) J. Electrochem. Soc. Vol 106 Pg 325 (1959)
(2) J. Org. Chem Vol 35 Pg 1604 (1970)

Reduction of Amides to Amines.

Catalytic hydrogenation of amides does not take place with noble metal catalysts under gentle conditions but is accomplished at 210-250 at 100-300 Atm using copper chromite and dioxane.

Reduction of amides is best performed with metal hydrides and electrochemically.

Lithium Aluminium Hydride, LiAlH4. Yield around 90%

Refs.
(1) J. Org Chem Vol 18 pg 1190 (1953)
(2) Org. Syn. Coll. Vol 4 pg 339, 564 (1963)

Magnesium Aluminium Hydride, Mg(AlH4)2. Yield 100%

Ref. (1) J. Chemical & Industrial, Year 1971 pg 227

Alane AlH3. Yield 46-93%

Ref. (1) J. Amer. Chem. Soc. Vol 90 pg 2927 (1968)

Electrochemically using a lead Pb cathode in dilute sulphuric acid at 5 degC. Yield 63-76%

Ref.
(1) J. Chem. Ber Vol 32 pg 68 (1899) in German. Pb cathode, dil H2SO4.
(2) CA (Chemical Abstracts) 105: 215 760v (1986). Pb cathode, dil H2SO4, Ti(3+) salt.
(3) CA 81: 105 975 x (1974). Hg cathode, CH3OH/HOAc solvent, (CH3)4NCl electrolyte.

[Rhodium]

Cyanohydrins can be reduced to phenylacetonitriles by the aid of commercially available phosphorous pentasulfide. 0.2-1.1 moles of P2S5 per mole of cyanohydrin is employed, preferably around 0.5 moles, but larger amounts are not deleterious to the yields. The reaction is performed in an inert solvent, preferably an intert hydrocarbon having a boiling point between 50-150°C, such as hexane, heptane, benzene and toluene.

As an example 2 mmol of a cyanohydrin in 5ml toluene is heated to 85°C with 1 mmol phosphorous pentasulfide for one hour, and the reaction was quenched with water (H2S evolution!) and the reaction mixture was extracted with a non-polar solvent, dried and filtered, the solvent evaporated and the residue distilled to give the phenylacetonitrile in high yield.

Reference: US Pat 4,952,718