Nitrile reduction using Cobalt Chloride and NaBH4

[Chimimanie]

Optimum Reduction of Nitriles Using NaBH4 and CoCl2 in 2:1 THF:H2O

The following is a representative procedure. A pink solution of CoCl2.6H2O (0.445 g, 1.87 mmol) and benzonitrile (1.92g, 18.6 mmol) in THF (66 ml, distilled) and water (33 ml) was stirred vigorously and cooled intermittently with an ice-water bath while NaBH4 (1.40 g, 37.1 mmol) was added in portions over 8 min. The reaction was exothermic, producing a black precipitate and copious quantities of hydrogen. TLC analysis after 50 min indicated traces of starting material, so additional NaBH4 (0.41g) was added. After a total time of 2h 28% NH4OH solution (2ml) was added and the mixture transferred to centrifuge tubes. After centrifugation the supernatant (two liquid phases) was decanted and the sediment washed with more of the same solvent mixture. The combined supernatants were concentrated at reduced pressure to remove the bulk of THF, then the aqueous residue was extracted with 4 x 40 ml of DCM. The combined DCM layers were dried (MgSO4) and concentrated to afford benzylamine (1.82g 91%) as a pale oil, identical in every respect with an authentic sample.

   
ref: j am chem soc vol 108 no 1 1986 67-72

[Osmium]

So will this work with phenylacetonitriles too?
I'm not fat just horizontally disproportionate.

[Rhodium]

Read the full article at

https://www.thevespiary.org/rhodium/Rhodium/pdf/cobalt.boride.nitrile.reduction.pdf

[Barium]

I have a strong feeling that Raney-nickel and sodium borohydride will reduce phenylacetonitriles as well.
Catalytic hydrogenation freak

[karel]

Hi guys!
NaBH4/CoCl2 does reduce phenylacetonitriles, but in case of an ortho-substituted substrate (4-bromo-2,5-dimethoxyphenylacetonitrile) my yields were only about 20 % (rest was unreacted nitrile).
I recommend to your attention paper in Tetrahedron 2002, 2211-2213 - reduction of R-NO2 and RCN by HCOON2H5/Ra-Ni (yield 80% 2-phenethylamine from phenylacetonitrile).
Regards

Karel

[Rhodium]

karel: How did you synthesize the 4-bromo-2,5-dimethoxyphenylacetonitrile?

[Chimimanie]

see post

Post 299551

(karel: "Chloromethylation", Chemistry Discourse)
and react it with NaCN in DMSO and you will get the compound


Karel: you are freaking me: how do you do to get this shame rdt with this proc, can you give me ref? I'm very interested in this proc because of the good rdt and you are discouraging me ! Have you tested it, can you give us some more details???

[karel]

Chemimanie,
I reproduced journal procedure

Post 373778

(Chimimanie: "Nitrile reduction using Cobalt Chloride and NaBH4", Methods Discourse). I used 10 mmol RCN (2.56g; but it was mixture of isomers -

Post 299551

(karel: "Chloromethylation", Chemistry Discourse), note 4) and after amine isolation recycled 2.11g RCN back. So I did not further investigate this reaction , but used AlH3 in THF (see JACS 1968, 2927-2938), which gave 90% yield of amine.