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To aldehydes
[edit]Nitriles can also be reduced to aldehydes. The Stephen aldehyde synthesis uses Tin(II) chloride and hydrochloric acid to yield an aldehyde via the hydrolysis of a resulting iminum salt. Aldehydes can also form using a hydrogen donor followed by in-situ hydrolysis of an imine. Useful reagents for this reaction include formic acid with a hydrogenation catalysis[1] or metal hydrides which are used to add one mol of hydrogen to the nitrile. For example, sodium borohydride reduces nitriles in alcoholic solvents with a CoCl2 catalyst or Raney nickel.[2] Reducing agent Diisobutylaluminium hydride, or DIBAL-H, is another commonly used metal hydride. DIBAL-H acts as a proton source, adding a hydride ion to the carbon of the nitrile. The resulting imine is a relatively stable intermediate that can be hydrolzed to the aldehyde.[3]
Mechanism
[edit]
DIBAL-H is added in controlled amounts at low temperatures to achieve partial reduction of the nitrile.[4] The aluminum atom in DIBAL acts as a Lewis acid, accepting an electron pair from the nitrile. The nitrile is then reduced by the transfer of a hydride ion to the carbon of the carbon-nitrile triple bond, producing an imine. After a workup with water, the aluminum complex is hydrolyzed to produce the desired aldehyde.[5] Because the hydrolytic workup generates the aldehyde at the end, the nitrile does not undergo over-reduction.
- ^ van Es, T.; Staskun, B. (1971). "4-Formylbenzenesulfonamide". Organic Syntheses. 51: 20. doi:10.15227/orgsyn.051.0020.
- ^ 17-, Smith, Michael, 1946 October (2001). March's advanced organic chemistry : reactions, mechanisms, and structure. March, Jerry, 1929-1997., March, Jerry, 1929-1997. (5th ed. ed.). New York: Wiley. ISBN 9780471585893. OCLC 43936853.
{{cite book}}:|edition=has extra text (help);|last=has numeric name (help)CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link) - ^ Carey, F. A.; Sundberg, R. J.; Advanced Organic Chemistry, Part B: Reactions and Synthesis
- ^ 1937-, Carey, Francis A., (2000). Advanced organic chemistry. Sundberg, Richard J., 1938- (4th ed ed.). New York: Kluwer Academic/Plenum Pub. ISBN 0306462435. OCLC 43555205.
{{cite book}}:|edition=has extra text (help);|last=has numeric name (help)CS1 maint: date and year (link) CS1 maint: extra punctuation (link) CS1 maint: multiple names: authors list (link) - ^ Solomons, T W. G, Craig B. Fryhle, and S A. Snyder. Organic Chemistry. , 2014. Print.