Shweta thakur Asked a Question
February 13, 2021 4:55 pmpts 30 pts
2. Benzoin condensation. Aromatic aldehydes which do not contain o-hydrogen atoms aldol condensation. However, in presence of alcolhoiic potassium cyanide, they undergo seleOt une not under ondensatig the produg obtained from benzaldehyde) and the reaction is called benzoin condensation. For examnle Alc. KCN Het OH in a difer manner to form o-hydroxy ketones commonly called benzoins (after the name le, O O -Č-H Heat Benzoin Benzaldehyde 1de ig Mechanism. Kinetics of the reaction shows that benzoin condensation is first order in. and second order in benzaldehyde, i.e. Rate o [CN] ICH,CHO]2 steps benzaldehıyde to fon Step 1. The cyanide ion being a strong nuclcophile adds to the C= O group of benzaldehvde a anion () which being unstable undergoes a proton transfer to form carbanion (I). In vicw of the above rate law, benzoin condensation is believed to occur by the following sten OH OH :0: CH-C CH-C CN CH-CH CH-C CN CN C-N H Benzaldehyde () (11) The driving force for this proton transfer is the resonance stabilization of the resulting anion (). Step 2. The carbanion (I) subsequently adds to the C= O group of another benzaldehyde molecule the addition product (1I). This addition product then undergoes another proton transfer to affor IV) which subsequently eliminates cyanide ion to form benzoin. 0Dnogor 0242 :OH H-C. -CHs CH-C- C-CH CN H CN H (I) (III) :O5 CgHs-C-C-CH, CgH-C -C-CH-CHs :OH O OH CN H Benzoin VIng forçe for th
  • 3 Answer(s)
  • Shares
  • Priyanshu kumar thankyou
    check this mechanism shweta First formation of cyanohydrin takes place,then the OH- abstract acidic proton adjacent to electron withdrawing Cyanide group.
    • cropped4282149892379058293.jpg
    Likes(0) Reply(0)
  • Dinesh khalmaniya Best Answer
    to understand, check this mechanism here CN attack to carbonyl carbon charge goes on O atom so this O atom accept proton form H2O as given in the mechanism. here CN have -I effect ...
    Show more
    • cropped8043600813618221054.jpg
    Likes(0) Reply(0)
  • Achyut ranjan gogoi thankyou
    The encircled ion undergoes change into ion II because in structure II reasonance stabilization is possible. But in Structure I which is encircled reasonace stabilization is not po...
    Show more
    Likes(0) Reply(0)
Head Office :
MPA 44, 2nd floor, Rangbari Main Road,
Mahaveer Nagar II, Kota (Raj.) – 324005

Corporate Office:
212, F-1, 2nd Floor, Evershine Tower,
Amrapali Marg,
Vaishali Nagar, Jaipur (Raj.) – 302021

All Rights Reserved ©