Benzoin Condensation
Presented by Ellie Roberts
Reaction Overview
-
Two cyclic aldehydes reacted with a cyanide ion to form benzoin
NaCN
CH3OH
Spectra
Mass Spectroscopy
Molecular weight of benzoin: = 212.24 g/mol
13
C NMR
Ketone or aldehyde: δ 198.9
Alkenes: δ 139.0, 133.9, 133.4, 129.1, 128.7,
128.6, 127.7
Alcohol, ether, or ester: δ 76.1
IR
Alcohol (3403.27 cm-1)
Conjugated ketone (1678.14 cm-1)
Aromatic alkene (1594.60 cm-1)
1
H NMR
Differences in the literature:
- The c, d, and e protons
were grouped
1H NMR (400 MHz, CDCl3): δ
7.93–5.54 (m, 2H), 7.52–7.40 (m, 1H),
7.38–7.23 (m, 7H), 5.95 (d, J = 6.3 Hz,
1H), 4.55 (d, J = 6.3 Hz, 1H).
Masaki Hayashi; Masatoshi Shibuya; and Yoshiharu Iwabuchi; The Journal of Organic Chemistry. 2012, 77 (6), 3005-3009.
Mechanism
The mechanism is split into four main steps
1)
2)
3)
4)
Formation of a cyanohydrin
Nucleophile formation
New C-C bond formation via nucleophilic attack
Formation of benzoin via leaving group dissociation
Formation of a cyanohydrin 1
Nucleophile Formation 2
Formation of new C-C bond 3
Formation of benzoin 4