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Unformatted text preview: yl chloride” C
OSO + NH
(“tosylate”) ester 10-20! Sulfonates in E2 Reactions!
2˚ and 3˚ sulfonates can participate in E2
reactions with strong bases:! 10-21! Alkyl Sulfonates!
Another commonly used sulfonyl chloride is
methanesulfonyl chloride (Ms-Cl)!
chloride + O
O-S-C H3 + H C l
(Cyclohexyl mesylate) Triﬂuoromethane sulfonyl chloride (CF3SO2Cl) is used to
prepare triﬂates (Tf-), which are excellent leaving groups !
10-22! Alcohols, Diols and Thiols!
Review: Formation of Sulfonate Esters!
R + OH R1 R1SO3R SO2Cl
R1 = HCl
CH3 Me CF3 Mechanism:!
O R + O H + R1 S O
R1 Cl O R -H
S R1 Cl
R O O O O S Cl O R1 S OR + Cl O H Characteristics!
• This is one of the best ways to activate an –OH group
for substitution or elimination!
• Is as good or better of a leaving group than I-!
10-23! Alcohols, Diols and Thiols!
Formation of Sulfonate Esters!
H3C OH + SO2Cl H3C O S
O O + OH H3C S O
Cl H3C O S O O F O F F F OH + F C S C
S F O O
O 10-24! Summary of Alkyl Sulfonate Reactions! 10-25! Alcohols, Diols, Thiols!
O O R OH + R
R' OH R' + H2O O Characteristics: !
• The reaction is catalyzed by acids (e.g. H2SO4)!
• The reaction is an EQUILIBRIUM, therefore unless
special methods are utilized, mixtures are produced.!
• “Special Methods”: !
• Add a drying agent or azeotrope off the H2O formed.!
• Use an acid chloride or acid anhydride !
10-26! Alcohols, Diols and Thiols!
R1 O O
R O H R1 OH -H C OH R1 OH O O H C R R H R1 C O OH O H H
OH R1 C OH O
R R1 C O R +
H O O O H R1 H2O + OR R 10-27! H Ethers and Epoxides!
! 2R OH R H2O Mechanism:!
H R + R O OH2 + H R R OH
R O O R + H2O R O R + H H
• Concentrated mineral acid catalyst!
• Driving force is removal of lower boiling ether by distillation!
• Works best for primary alcohols (rearrangement and elimination
with secondary and tertiary)!
10-28! Dehydration of ROH!
An alcohol can be converted to an alkene by acidcatalyzed dehydration (a type of β-elimination)!
C C acid catalyst
C C + H2O H • 1° alcohols must be heated at high temperature in the
presence of an acid catalyst, such as H2SO4 or H3PO4!
• 2° alcohols undergo dehydration at somewhat lower
• 3° alcohols often require temperatures at or slightly
above room temperature !
Base-catalyzed elimination?! 10-29! Ethers and Epoxides!
Synthesis: Base-Promoted Ring Closure of Halohydrins!
C C + C OH C + X X Mechanism:! !
C C + OH C C + H2O C C + X X X O O H Characteristics:!
• Internal SN2 (i.e. intramolecular Williamson)!
• Can be used to form epoxides, oxetanes, and tetrahydrofurans!
10-30! Cyclic Ether Synthesis!
H O O OH (CH2)n (CH2)n
Br CH2 O Br (CH2)n + Br CH2 • Note: Cyclic ether formation is typically much fa...
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