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8 Introduction to Organic Chemistry 2 ed William H. Brown 8-1 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Alcohols, Ethers, and Thiols Chapter 8 8-2 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Structure - Alcohols • The functional group of an alcohol is an -OH group bonded to an sp3 hybridized carbon • bond angles about the hydroxyl oxygen atom are approximately 109.5° • Oxygen is also sp3 hybridized • two sp3 hybrid orbitals form sigma bonds to carbon and hydrogen • the remaining two sp3 hybrid orbitals each contain an unshared pair of electrons 8-3 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Structure - Ethers • The functional group of an ether is an oxygen atom bonded to two carbon atoms • Oxygen is sp3 hybridized with bond angles of approximately 109.5°. In dimethyl ether, the C-OC bond angle is 110.3° H H •• H C H O •• C H H 8-4 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Structure - Thiols • The functional group of a thiol is an -SH (sulfhydryl) group bonded to an sp3 hybridized carbon • The bond angle about sulfur in methanethiol is 100.3°, which indicates that there is considerably more p character to the bonding orbitals of divalent sulfur than there is to oxygen 8-5 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Nomenclature-Alcohols • IUPAC names • the longest chain that contains the -OH group is taken as the parent. • the parent chain is numbered to give the -OH group the lowest possible number • the suffix -e is changed to -ol • Common names • the alkyl group bonded to oxygen is named followed by the word alcohol 8-6 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Nomenclature - Alcohols OH CH3 CH 2 CH 2 OH CH 3 CHCH 3 CH3 CH2 CH2 CH 2 OH 1-Propanol (Propyl alcohol) 2-Propanol (Isopropyl alcohol) 1-Butanol (Butyl alcohol) CH3 CH 3 OH CH3 CH 2 CHCH3 CH 3 COH CH 3 CHCH 2 OH CH3 2-Butanol 2-Methyl-1-propanol 2-Methyl-2-propanol (sec-Butyl alcohol) (Isobutyl alcohol) (tert-Butyl alcohol) 8-7 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Nomenclature - Alcohols • Problem: write IUPAC names for these alcohols CH 3 OH (a) CH 3 CHCH 2 CHCH 3 OH (b) CH3 CH 2 OH (c) CH 3 ( CH 2 ) 6 CH 2 OH (d) H3 C C CH 2 CH 3 H 8-8 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Nomenclature - Alcohols • Compounds containing more than one -OH group are named diols, triols, etc. CH 2 CH 2 HO OH 1,2-Ethanediol (Ethylene glycol) CH 3 CHCH 2 CH 2 CHCH 2 HO OH 1,2-Propanediol (Propylene glycol) HO HO OH 1,2,3-Propanetriol (Glycerol, Glycerin) 8-9 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Nomenclature - Alcohols • Unsaturated alcohols • the double bond is shown by the infix -en• the hydroxyl group is shown by the suffix -ol • number the chain to give OH the lower number 1 2 5 HOCH2 CH 2 3 4 6 CH2 CH 3 C C H H trans-3-Hexen-1-ol 8-10 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Nomenclature - Ethers • IUPAC: the longest carbon chain is the parent. Name the OR group as an alkoxy substituent • Common names: name the groups attached to oxygen followed by the word ether CH 3 CH 2 OCH 2 CH 3 Ethoxyethane (Diethyl ether) CH 3 OH CH3 OCCH 3 OCH 2 CH 3 CH 3 2-Methoxy-2-methylpropane trans-2-Ethoxycyclohexanol (methyl tert-butyl ether, MTBE) 8-11 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Nomenclature - Ethers • Although cyclic ethers have IUPAC names, their common names are more widely used O O Ethylene oxide O Tetrahydrofuran, THF O Tetrahydropyran O 1,4-Dioxane 8-12 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Nomenclature - Thiols • IUPAC names: • the parent is the longest chain that contains the -SH group • change the suffix -e to -thiol • Common names: • name the alkyl group bonded to sulfur followed by the word mercaptan SH CH3 CH 2 CH2 CH 2 SH 1-Butanethiol (Butyl mercaptan) CH3 CH2 CHCH3 2-Butanethiol (sec-Butyl mercaptan) 8-13 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Physical Prop - Alcohols • Alcohols are polar compounds H + C O H H H + • Alcohols are associated in the liquid state by hydrogen bonding 8-14 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Physical Prop - Alcohols • Hydrogen bonding: the attractive force between a partial positive charge on hydrogen and a partial negative charge on a nearby oxygen, nitrogen, or fluorine atom • the strength of hydrogen bonding in water is approximately 5 kcal/mol • hydrogen bonds are considerably weaker than covalent bonds • nonetheless, they can have a significant effect on physical properties 8-15 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Physical Prop - Alcohols • Ethanol and dimethyl ether are constitutional isomers. • Their boiling points are dramatically different • ethanol forms intermolecular hydrogen bonds which increases attractive forces between its molecules, which results in a higher boiling point CH 3 CH2 OH Ethanol bp 78°C CH 3 OCH 3 Dimethyl ether bp -24°C 8-16 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Physical Prop. - Alcohols • In relation to alkanes of comparable size and molecular weight, alcohols • have higher boiling points • are more soluble in water • The presence of additional -OH groups in a molecule further increases boiling points and solubility in water 8-17 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Physical Prop. - Alcohols Formula Name CH 3 OH methanol CH 3 CH 3 ethane CH 3 CH 2 OH ethanol propane CH 3 CH 2 CH 3 CH 3 CH 2 CH 2 OH 1-propanol CH 3 CH 2 CH 2 CH 3 butane HO ( CH 2 ) 4 OH CH 3 ( CH 2 ) 4 OH CH 3 ( CH 2 ) 4 CH 3 1,4-butanediol 1-pentanol hexane Solubility in Water MW 32 30 bp (°C) 65 -89 46 78 44 -42 insoluble 60 58 97 0 infinite insoluble 90 88 86 230 138 69 infinite 2.3 g/100 g insoluble infinite insoluble infinite 8-18 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Physical Prop. - Ethers • Ethers are polar molecules; • the difference in electronegativity between oxygen (3.5) and carbon (2.5) is 1.0 • each C-O bond is polar covalent • oxygen bears a partial negative charge and each carbon a partial positive charge 8-19 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Physical Prop. - Ethers • Ethers are polar molecules, but because of steric hindrance, only weak attractive forces exist between their molecules in the pure liquid state • Boiling points of ethers are • lower than alcohols of comparable MW and • close to those of hydrocarbons of comparable MW • Ethers hydrogen bond with H2O and are more soluble in H2O than are hydrocarbons 8-20 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Physical Prop. - Thiols • Low-molecular-weight thiols have a STENCH • the scent of skunks is due primarily to these two thiols CH3 CH 3 CHCH 2 CH 2 SH CH3 CH= CH CH 2 SH 3-Methyl-1-butanethiol 2-Butene-1-thiol 8-21 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Physical Prop. - Thiols • The difference in electronegativity between S (2.5) and H (2.1) is 0.4. Because of the low polarity of the S-H bond, thiols • show little association by hydrogen bonding • have lower boiling points and are less soluble in water than alcohols of comparable MW Thiol bp (°C) methanethiol 6 ethanethiol 35 1-butanethiol 98 Alcohol bp (°C) methanol 65 ethanol 78 1-butanol 117 8-22 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Acidity of Alcohols • In dilute aqueous solution, alcohols are weakly acidic CH 3 O-H + O H CH 3 O - + + H O H H H [CH 3 O - ] [H 3 O + ] Ka = = 15.5 [CH 3 OH] 8-23 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Acidity of Alcohols Compound Formula pKa hydrogen chloride HCl -7 acetic acid CH 3 CO2 H methanol CH 3 OH 15.5 water H2 O 15.7 ethanol CH 3 CH2 OH 15.9 2-propanol (CH 3 ) 2 CHOH 17 2-methyl-2-propanol (CH 3 ) 3 COH 18 4.8 Stronger acid Weaker acid 8-24 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Basicity of Alcohols • In the presence of strong acids, the oxygen atom of an alcohol behaves as a weak base • proton transfer from the strong acid forms an oxonium ion CH 3 •• O •• H H An acid + O H + •• CH 3 H An oxonium ion •• •• A base H + + H2 SO 4 O H •• O H H 8-25 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Reaction with Metals • Alcohols react with Li, Na, K, and other active metals to liberate hydrogen gas and form metal alkoxides 2 CH 3 OH + 2 Na Methanol 2 CH 3 O - Na + + H2 Sodium methoxide 8-26 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Conversion of ROH to RX • Conversion of an alcohol to an alkyl halide involves substitution of halogen for -OH at a saturated carbon • the most common reagents for this purpose are the halogen acids, HX, and thionyl chloride, SOCl2 8-27 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Reaction with HX • Water-soluble 3° alcohols react very rapidly with HCl, HBr, and HI. Low-molecular-weight 1° and 2° alcohols are unreactive under these conditions CH 3 CH 3 COH + CH 3 HCl 2-Methyl-2propanol 25°C CH 3 CH 3 CCl + H2 O CH 3 2-Chloro-2methylpropane 8-28 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Reaction with HX • Water-insoluble 3° alcohols react by bubbling gaseous HX through a solution of the alcohol dissolved in diethyl ether or THF OH + HCl CH 3 1-Methylcyclohexanol 0 oC ether Cl + CH 3 1-Chloro-1-methylcyclohexane H2 O 8-29 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Reaction with HX • 1° and 2° alcohols require concentrated HBr and HI to form alkyl bromides and iodides H2 O CH3 CH 2 CH 2 CH 2 OH + HBr reflux 1-Butanol CH3 CH 2 CH 2 CH 2 Br + H 2 O 1-Bromobutane 8-30 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Mechanism: 3° ROH + HCl • An SN1 reaction • Step 1: rapid, reversible acid-base reaction that transfers a proton to the OH group CH 3 CH 3 - C •• O- H •• + H H CH 3 H •• •• CH 3 H + + CH 3 - C O •• CH 3 2-Methyl-2-propanol (tert-Butyl alcohol) + O H •• rapid and reversible O H H An oxonium ion 8-31 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Mechanism: 3° ROH + HCl • Step 2: loss of H2O to give a carbocation intermediate CH 3 rate-limiting step H An oxonium ion CH3 CH 3 -C + CH3 + •• •• •• CH 3 H + CH 3 -C O O H H A 3° carbocation intermediate 8-32 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Mechanism: 3° ROH + HCl • Step 3: reaction of the carbocation intermediate (a Lewis acid) with halide ion (a Lewis base) CH 3 CH 3 Cl •• CH 3 rapid •• CH 3 - C- Cl •• •• •• + •• CH 3 - C + •• CH 3 2-Chloro-2-methylpropane (tert-Butyl chloride) 8-33 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Mechanism: 1°ROH + HBr • An SN2 reaction • Step 1: rapid and reversible proton transfer + CH 3 CH 2 CH2 CH 2 - O-H + H O H •• H •• •• rapid and reversible An oxonium ion H + •• •• •• + CH 3 CH 2 CH2 CH 2 -O H O H H 8-34 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Mechanism: 1° ROH + HX • Step 2: displacement of HOH by halide ion Br •• + + CH3 CH2 CH2 CH2 -O •• •• •• •• H H rate-limiting step S N2 H + •• •• •• CH3 CH2 CH2 CH2 -Br •• •• O H 8-35 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Mechanisms: SN1 vs SN2 • Reactivities of alcohols for SN1 and SN2 are in opposite directions SN 1 Increasing stability of cation intermediate 3° alcohol 2° alcohol 1° alcohol Increasing ease of access to the reaction site SN 2 8-36 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Reaction with SOCl2 • Thionyl chloride is the most widely used reagent for the conversion of 1° and 2° alcohols to alkyl chlorides • a base, most commonly pyridine or triethylamine, is added to neutralize the HCl CH 3 (CH 2 ) 5 CH 2 OH + SOCl 2 1-Heptanol Thionyl chloride pyridine CH 3 (CH 2 ) 5 CH 2 Cl + SO 2 + HCl 1-Chloroheptane 8-37 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Dehydration of ROH • An alcohol can be converted to an alkene by elimination of H and OH from adjacent carbons (a b-elimination) • 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 only at or slightly above room temperature 8-38 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Dehydration of ROH CH 3 CH 2 OH OH H2 SO 4 o 180 C CH 2 =CH 2 + H 2 O H2 SO 4 + H 2O 140oC Cyclohexanol CH3 CH 3 COH CH3 Cyclohexene H2 SO 4 o 50 C CH 3 CH 3 C= CH 2 + H2 O 2-Methylpropene (Isobutylene) 8-39 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Dehydration of ROH • Where isomeric alkenes are possible, the alkene having the greater number of substituents on the double bond generally predominates (Zaitsev rule) OH CH 3 CH 2 CHCH3 2-Butanol 85% H 3PO4 heat CH 3 CH= CH CH 3 + CH 3 CH 2 CH= CH2 2-Butene 1-Butene (80%) (20%) 8-40 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Dehydration of ROH • A three-step mechanism • Step 1: proton transfer from H3O+ to the -OH group to form an oxonium ion •• •• HO CH 3 CHCH 2 CH 3 + H + O H •• rapid and reversible H H •• + H O An oxonium ion •• •• CH 3 CHCH 2 CH3 + O H H 8-41 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Dehydration of ROH • Step 2: the C-O bond is broken and water is lost, giving a carbocation intermediate H + H O •• CH 3 CHCH 2 CH 3 slow and rate limiting •• •• + CH3 CHCH 2 CH3 + H2 O A 2o carbocation 8-42 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Dehydration of ROH • Step 3: proton transfer of H+ from a carbon adjacent to the positively charged carbon to water. The sigma electrons of the C-H bond become the pi electrons of the carbon-carbon double bond H •• •• + CH 3 - CH -CH - CH 3 + O H rapid H CH 3 - CH = CH - CH 3 + + H O H •• H 8-43 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Dehydration of ROH • Acid-catalyzed alcohol dehydration and alkene hydration are competing processes C C + H2 O An alkene acid catalyst C C H OH An alcohol • large amounts of water favor alcohol formation • scarcity of water or experimental conditions where water is removed favor alkene formation 8-44 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Oxidation: 1° ROH • A primary alcohol can be oxidized to an aldehyde or a carboxylic acid, depending on the oxidizing agent and experimental conditions OH CH 3 -CH 2 A primary alcohol [O] O CH 3 -C- H An aldehyde [O] O CH 3 -C- OH A carboxylic acid 8-45 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Oxidation: chromic acid • Chromic acid is prepared by dissolving chromium(VI) oxide or potassium dichromate in aqueous sulfuric acid CrO 3 + Chromium(VI) oxide K2 Cr 2 O7 Potassium dichromate H2 O H2 SO 4 H2 SO 4 H2 Cr 2 O7 H2 CrO 4 Chromic acid H2 O 2 H2 CrO 4 Chromic acid 8-46 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Oxidation: 1° ROH • Oxidation of 1-octanol by chromic acid gives octanoic acid • the aldehyde intermediate is not isolated CrO3 CH 3 ( CH 2 ) 6 CH 2 OH H2 SO4 , H 2 O 1-Octanol O O CH 3 ( CH 2 ) 6 CH CH3 ( CH2 ) 6 COH Octanal (not isolated) Octanoic acid 8-47 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 PCC • Pyridinium chlorochromate (PCC): a form of Cr(VI) prepared by dissolving CrO3 in aqueous HCl and adding pyridine to precipitate PCC CrO 3 Cl - N+ H • PCC is selective for the oxidation of 1° alcohols to aldehydes; it does not oxidize aldehydes further to carboxylic acids 8-48 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Oxidation: 1° ROH • PCC oxidation of a 1° alcohol to an aldehyde O CH 2 OH Geraniol PCC CH Geranial 8-49 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Oxidation: 2° ROH • 2° alcohols are oxidized to ketones by both chromic acid and and PCC CH(CH 3 ) 2 OH CH(CH 3 ) 2 H2 CrO 4 acetone CH 3 2-Isopropyl-5-methylcyclohexanol (Menthol) O CH 3 2-Isopropyl-5-methylcyclohexanone (Menthone) 8-50 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Reactions of ethers • Ethers, R-O-R, resemble hydrocarbons in their resistance to chemical reaction • they do not react with strong oxidizing agents such as chromic acid, H2CrO4 • they are not affected by most acids and bases at moderate temperatures • Because of their good solvent properties and general inertness to chemical reaction, ethers are excellent solvents in which to carry out organic reactions 8-51 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Epoxides • Epoxide: a cyclic ether in which oxygen is one atom of a three-membered ring • Common names are derived from the name of the alkene from which the epoxide is formally derived CH 2 CH 2 O Ethylene oxide CH 2 CHCH 3 O Propylene oxide 8-52 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Synthesis of Epoxides-1 • Ethylene oxide, one of the few epoxides manufactured on an industrial scale, is prepared by air oxidation of ethylene 2 CH 2 =CH 2 + O 2 Ag 2 CH 2 CH 2 O Oxirane (Ethylene oxide) 8-53 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Synthesis of Epoxides-2 • The most common laboratory method for the synthesis of epoxides is oxidation of an alkene using a peroxycarboxylic acid (a peracid) such as peroxyacetic acid O CH3 COOH Peroxyacetic acid (Peracetic acid) 8-54 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Synthesis of Epoxides-2 • Epoxidation of cyclohexene O + Cyclohexene RCOOH A peroxycarboxylic acid CH 2 Cl 2 H O O + RCOH H 1,2-Epoxycyclohexane A carboxylic (Cyclohexene oxide) acid 8-55 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Hydrolysis of Epoxides • In the presence of an acid catalyst, an epoxide is hydrolyzed to a glycol CH2 CH2 + H2 O O Ethylene oxide H + HOCH2 CH2 OH 1,2-Ethanediol (Ethylene glycol) 8-56 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Hydrolysis of Epoxides • Step 1: proton transfer to the epoxide to form a bridged oxonium ion intermediate H2 C CH2 O H2 C + H O H CH 2 O+ H H 8-57 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Hydrolysis of Epoxides • Step 2: attack of H2O from the side opposite the oxonium ion bridge H H2 C O CH 2 O+ H H H H +O H2 C CH 2 O H 8-58 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Hydrolysis of Epoxides • Step 3: proton transfer to solvent to complete the hydrolysis H O H H H +O H2 C CH 2 H H2 C O CH 2 + O O H H + H O H H 8-59 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Hydrolysis of Epoxides • Attack of the nucleophile on the protonated epoxide shows anti stereoselectivity • hydrolysis of an epoxycycloalkane gives a trans-diol H O OH + H 1,2-Epoxycyclopentane (Cyclopentene oxide) H2 O H+ OH trans -1,2-Cyclopentanediol 8-60 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Hydrolysis of Epoxides • Compare the stereochemistry of the glycols formed by these two methods H + RCO3 H OH H O H2 O OH H trans-1,2-Cyclopentanediol OH Os O4 ROOH OH cis-1,2-Cyclopentanediol 8-61 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Thiols • Thiols are stronger acids than alcohols CH 3 CH 2 SH + H2 O pKa = 8.5 pKa = 15.9 CH 3 CH 2 OH + H 2 O - CH 3 CH 2 S + H3 O+ - CH 3 CH 2 O + H 3 O + 8-62 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Thiols • When dissolved an aqueous NaOH, they are converted completely to alkylsulfide salts CH 3 CH 2 SH + Na + OH pKa = 8.5 Stronger Stronger + acid base CH 3 CH 2 S Na + H2 O pKa = 15.7 Weaker base Weaker acid 8-63 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Thiols • Thiols are oxidized to disulfides by a variety of oxidizing agents, including O2. • they are so susceptible to this oxidation that they must be protected from air during storage 2 RSH + A thiol 1 2 O2 RSSR + A disulfide H2 O • The most common reaction of thiols in biological systems in interconversion between thiols and disulfides, -S-S8-64 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved. 8 Alcohols, Ethers, and Thiols End of Chapter 8 8-65 Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.