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Ch 10 and 11 Chemistry of alcohols and thiols

Ch 10 and 11 Chemistry of alcohols and thiols - Chemistry...

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10-1 Chemistry of Alcohols and Thiols Chapters 10 & 11
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10-2 Reactions of Alcohols, Diols and Thiols C C O H Cleavage of OH bond dissolving metal reduction tosylation esteriFcation etheriFcation Cleavage of C-O bond oxidation substitution elimination
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10-3 Formation of Alkoxides Alcohols can be converted to metal alkoxides by reaction with bases stronger than the alkoxide ion, e.g., NaH Alcohols also react with Li, Na, K, and other active metals to liberate hydrogen gas and form the metal alkoxide CH 3 O H 2 + Na 0 CH 3 O Na + + H 2 2 Sodium methoxide O H + K 0 O K + + H 2 2 2 Potassium tert -butoxide CH 2 O H + Na + H CH 2 O Na + + H 2 Sodium ethoxide CH 3 CH 3
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10-4 Synthesis of Alcohols (Review) Nucleophilic substitution alkyl halide by OH - (or synthetic equivalent) Cl + K + – OH O tetrahydrofuran (THF) OH + KCl Br NaOH THF OH + + + Zaitsev E2 Hofmann E2 S N 2
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10-5 50% H 2 SO 4 HO + OH + OH major minor negligible 1. Hg(OAc) 2 , H 2 O 2. NaBH 4 OH 1. BH 3 ·THF 2. H 2 O 2 , NaOH OH Synthesis of Alcohols (Review) Hydration of alkenes water in acid solution (rearrangements possible) oxymercuration - demercuration (Markovnikov product) hydroboration - oxidation (anti-Markovnikov product)
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10-6 Alcohols as Nucleophiles New O-H bond breaks, O-C bond forms: ROH is weak nucleophile (Chapter 9) RO - is strong nucleophile (Chapter 9) C H O R O H C + weak nucleophile strong electrophile C R O H R O H C R O R O H Na R O weak nucleophile strong nucleophile C X Na + + weak electrophile C R O
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10-7 Conversion into Ethers Alcohols can be converted into ethers by nucleophilic substitution reactions ( Williamson ether synthesis ): Step 1: formation of a nucleophilic alkoxide ion (NaH or Na 0 /K 0 ) Step 2: reaction with alkyl halide (S N 2) How would you prepare tert -butyl methyl ether? O
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10-8 Ethers and Epoxides Williamson Synthesis Mechanism Characteristics S N 2 mechanism Elimination competes if hindered halide (i.e. secondary or tertiary halide) RO + R 1 X R O R 1 X + RO + C H D Me X OR H D CH 3 + X RO + C Me Et nPr X Elimination
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10-9 Williamson Ether Synthesis O CH 3 O + I O + CH 3 I 1 2 1 2
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10-10 Williamson Ether Synthesis O CH 3 O + I O + CH 3 I 1 2 1 2
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10-11 Alcohols as Electrophiles C-Nu bond forms, C-O bond breaks: OH - is not a good leaving group unless it is protonated but most nucleophiles are strong bases which would remove H + (not suitable for C-C bond formation). C H O C O H weak electrophile H Br C O H strong electrophile H C Br + H 2 O C O H H C: HC + X CH HC + C H O
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10-12 Oxidation 1˚ alcohols can be oxidized to aldehydes or carboxylic acids 2˚ alcohols can only be oxidized to ketones 3˚ alcohols cannot be oxidized (under normal conditions)
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10-13 Oxidation of ROH A common oxidizing agent for this purpose is chromic acid, prepared by dissolving chromium(VI) oxide or potassium dichromate in aqueous sulfuric acid Potassium dichromate Chromic acid K 2 Cr 2 O 7 H 2 SO 4 H 2 Cr 2 O 7 H 2 O 2H 2 CrO 4 + Chromic acid Chromium(VI) oxide 3 H 2 O H 2 4 H 2 4
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10-14
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