dehydration of primary amide
with Thionyl chloride (SOCl2)
mechanism. Socl2 nucleophylic attack, followed by E2 like
Imine and Enamine formation(Nu addition followed by dehydration)
Imine R2=NR
neucleophile is primary amines
ex. Schiff base in our body
can produced by Alanine react with PLP
a common way of its metabolism
nitriles can added by grignard reagent to yield Imine ion, then it adds a water to yield a ketone, by a machanism that is exact reverse of immine formation
enamine R2N-CR=CR2
neucleophile is secondary amines
dehydration of alcohol
products
E1Cb in biological system
Followed zaister's rule: major product is more stable alkene, due to C+ rearrangement
dehydration after adol reaction
between β-hydroxyl group and α-hydrogen
generate conjugated enones or α，β-unsaturated products
they have sharing pi electrons system/ holistic pi MO
more stable than nonconjugated enones
just like conjugated diene
condition
temperature
a bit higher than idol formation
hard to isolate adol, usually the product of carbonyl condensation
Value
move the idol formation equilibrium to product
even though the initial equilibrium is unfavored
Hemiacetal dehydration to oxonium ion(C=O:+-R)
acid protonates hemiacetal's hydroxyl group, it then leaves to gave oxonium ion
double bond of oxonium ion is then added by another alcohol
water deprotonate the added alcohol, regenerate H3O+
usually E1,E2,E2like,E1cB: depends on substrate and nucleophiles you applied
often convert -OH a better leaving group
or substitute it by another group
