Ch 10 and 11 Chemistry of alcohols and thiols

Sulfonates in e2 reactions 2 and 3 sulfonates can

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Unformatted text preview: yl chloride” C HO OSO C O OSO + NH Cl– ROTs, a toluenesulfonate (“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)! O OH Cyclohexanol !   pyridine Cl-S-CH3 O Methanesulfonyl chloride + O O-S-C H3 + H C l O Cyclohexyl methanesulfonate (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 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! •  Ex:! O 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 O Cl S F O O O 10-24! Summary of Alkyl Sulfonate Reactions! 10-25! Alcohols, Diols, Thiols!   Esterification! 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!   Esterification Mechanism:! O + 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!   Synthesis:! H ! ! 2R   OH R H2O Mechanism:! H R + R O OH2 + H R R OH R O O R + H2O R O R + H H H   Characteristics:! •  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)! OH 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 temperatures! •  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! O OH C C + C OH C + X X   Mechanism:! ! O 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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This note was uploaded on 01/27/2014 for the course BIOL 241 taught by Professor Henrychang during the Winter '10 term at Purdue University-West Lafayette.

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