Important old mechanis-m

Important old mechanis-m思维导图，包括：SN1、SN2、E1、E2、E1cB、SOCL2等板块。

Important old mechanisms application

• SN1
  • 3' alcohol +HCl/HBr
    • produce alkyl halides
  • some ether cleavage
    • p 531
• SN2
  • ester production
    • SN2
      • carboxylate ion+ R'X(primary alkyl hilide)
  • acid chloride synthesis
    • treat carboxylic acid with thionyl chloride; SOCl2
      • in CHCl3
    • strategy:
      • SN2 replaces -OH into -O-S=O-Cl, a much better leaving group, and use Cl- as a nucleophile to nucleophilic acyl substitute it.
  • Alkly halide production
    • 1'/2' alcohols + SOCl2/PBr2
      • produce alkyl halides
  • Nitriles formation
    • El: primary/secondary alkyl halide
    • Nu: CN-
      • NaCN
    • Usually followed by heats them in aqueous acid/base solution to form acids
  • Alkyl ammine formation
    • SN2 reaction of ammonia or an amine with an alkyl halide
  • Ether synthesis
    • industiral
      • only 1' alcohol can be used, other wise it will produce alkenes by E1 reaction
      • sulfaric acid -catalyzed reaction of alcohols
        • produce simple, symmetrical ethers
    • williamson ether synthesis
      • alkoxide ion + 1'alkyl halide/tosylate
        • alkoxide ion is derived from treating alkohol with strong base NaOH
          • Ag2O is a better base used here, because no alkoxide ion need
      • compete E2 elimination can accur with more hindered substrates
        • require more hindered alcohol partner
          • Why???
        • less hindered alkyl halide partner
  • epoxide ring opening
    • acid/base catalyst hydration
      • a diol is produced
      • acid first protonates ring oxygen, base hydroxyl anion act as nucleophile
    • React with HCl
      • H+ as acid catalyst, Cl- act as nucleophile to attack the less hindered carbon
        • produce chloride + alcohol
    • epoxidation
      • Alkene + peroxyacid
        • single stepped mechanism
      • Alkene + halohadrine, then eliminate HX with base
        • electrophilic addition
  • sulfides+alkylhalide
    • produce suldonium ions R3S+
    • readily react
      • S is much more nucleophilic than O
  • Acidic ether cleavage？
• E1
  • 3' alcohol's acid catalyst dehydration
    • acid catalyst
      • -OH2+ is a better leaving group than -OH
    • 1. protonation, 2. water lose----C+intermediate---- 3. deprotonation
    • ex. aldo dehydration when acid catalyst
  • E1 like
    • second step of acid catalyst keto-enol transformation
      • protonated resonace stabalized Cation is deprotonated by a base in its alpha posation, then generate a double bond.
  • some ether cleavage
  • dehydrohalogenation, and some dehydration
• E2
  • E2 like
    • followed by some SOCl2 nucleophylic attack
      • nitrile production by dehydration of primary amide
        • C=O double bond nucleophilic attack S
          • SOCl2 converts Carbonyl oxygen into -O-SOCl
        • Base remove proton on N
        • base catalyst E2 like to yield nitrile
        • p624
      • soCl2 make a good leaving group
    • laboratory oxidation
      • alcohol
        • closely related to E2
          • first is the oxidant substites H of hydroxyl group
          • then generates a C=O by elimination of intermediate, leaving group is a reduced iodine (DMP) or metcal (Cr)
            • therefore require at least one H attach to the hydroxyl attached carbon
      • aldehyde
        • through intermediate 1,1 diol/ hyrates
          • formed by hydration of aldehyde
            • equilibrium amount
          • then hydrate is oxidized through the alcohol mechanism
            • therefore require at least one H attach to the carnonyl carbon
            • the 1,1 diol produced by ketone hydration do not have more H attached on the hydroxyl attached carbon..
      • phenol
        • radical
  • 2'/3' alcohol's POCl3 dehydration
    • add POCl3 in pyridine solvent
      • in 0 degree
    • mechanism,
      • Pocl3 's phosphate is an electrophile
      • OH nucleophilic attack POCl3's phosphate, and it substitute 0H into a good leaving group
        • dichlorophosphate intermediate
      • E2 accours: pyridine act as a base here, to remove the proton
    • sometimes acid catalyst may have the same effect
      • ex, acid catalyst dehydration of aldo product
  • hofmann elimination
    • produce alkenes from ammines
    • they are first quaternized by treatment with idomethane(ICH3) and then heated with silver oxide（Ag2O)
  • dehydrohalogenation, and some dehydration
• E1cB
  • certain alcohol dehydration
    • happened in which -OH group is 2 carbons away from a carbonyl group
      • because it near the acidic alpha hydrogen
    • ex. base catalyst dehydration of aldo products
    • common in biological system
  • biological alcohol dehydration
• SOCL2
  • very electrophilic S in S=O
    • so first a nucleophilic addition on SOCl
  • -SOCl is a very good leaving group
  • converts OH into Cl
    • Then Cl- nucleuphile SN2 -SOCl
  • Dehydration of amides to yield nitriles
    • amides+SOCl2 also yields SO2 and 2HCl
    • amides C=O double bond as a nucleophile!
    • then followed by E2 like dehydration
  • Converts -OH into Cl
    • produce alkyl chloride from alcohol
    • produce acid chlorides from carboxylate acids