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Alcohols, Ethers, Phenols, and Thiols Chapter 22 Hein * Best * Pattison * Arena Version 1.0 Colleen Kelley Chemistry Department 1 College Pima Community © John Wiley and Sons, Inc. Chapter Outline 22.1 Functional Groups 22.2 Classification of Alcohols 22.4 Physical Properties of Alcohols 22.5 Chemical Properties of Alcohols 22.3 Naming Alcohols 2 Chapter Outline (continued) 22.6 Common Alcohols 22.7 Phenols 22.8 Properties of Phenols 22. 9 Production of Phenol 22.10 Ethers 22.11 Structures and Properties of Ethers 22.12 Preparation of Ethers 22.13 Thiols 3 Functional Groups 4 • The various classes of compounds are identified by the presence of certain characteristic groups called functional groups. • Through the chemical reactions of functional groups, it is possible to create or synthesize new substances. 5 O O H O H water R H alcohol H O R R ether phenol 6 Classification of Alcohols 7 • Alcohols are classified as primary (1°), secondary (2°), or tertiary (3°) depending on whether the carbon atom to which the –OH group is attached is directly bonded to one, two, or three other carbon atoms respectively. H C C C C OH C C OH H primary (1o) secondary (2 ) alcohol alcohol C C OH C H o tertiary (3o) alcohol 8 9 10 •Polyhydroxy alcohols and polyols are general terms for alcohols that have more than one –OH group per molecule. •Polyhydroxy compounds are very important molecules in living cells, as they include the carbohydrate class of biochemicals. 11 Structural Representations of Alcohols • An alcohol such as 2-butanol can be written in a single-line formula by enclosing the – OH group in parentheses and placing it after the carbon to which it is bonded. OH CH3CH2CHCH3 = CH3CH2CH(OH)CH3 12 Application to Biochemistry Blood sugar (glucose) contains five alcohol groups. Using the structure of glucose shown here, label each group as 1°, 2°, or 3°. O=CHCH(OH)CH(OH)CH(OH)CH(OH)CH2OH 13 Application to Biochemistry secondary H C O OH H OH OH C C C C H OH H CH 2OH primary H secondary 14 Naming Alcohols 15 IUPAC Rules for Naming Alcohols 1. Select the longest continuous chain of carbon atoms containing the –OH group. 2. Number the carbon atoms in this chain so that the one bearing the -OH group has the lowest possible number. 16 IUPAC Rules for Naming Alcohols 3. Form the parent alcohol name by replacing the final –e of the corresponding alkane by –ol. When isomers are possible, locate the position of the –OH group by placing the number (hyphenated) of the carbon atom to which the –OH is bonded immediately before the parent alcohol name. 4. Name each alkyl side chain (or other group), and designate its position by number. 17 Name CH3CH2CH2CH2OH 4 3 2 1 CH3CH2CHCH2OH 1-butanol 18 Nomenclature of Alcohols OH CH3 H3C CH CH3 2-propanol (isopropyl alcohol) OH cyclohexanol H3C CH CH2CH2OH 3-methyl-1-butanol HO OH 1,3-cyclohexanediol 19 Physical Properties of Alcohols 20 Physical Properties of Alcohols • The physical properties of alcohols are related to those of both water and alkane hydrocarbons. • An alcohol molecule is made up of a waterlike hydroxyl group joined to a hydrocarbonlike alkyl group. O H O H water R H alcohol 21 Boiling Points of Alcohols • Alcohols have relatively high boiling points. • The boiling points of the normal alcohols increase in a regular fashion with increasing number of carbon atoms. • Branched-chain alcohols have lower boiling points than corresponding straight-chain alcohols. 22 23 • Alcohols containing up to three carbon atoms are infinitely soluble in water. • The –OH group on the alcohol molecule is responsible for both the water solubility and relatively high boiling points of the low-molar-mass alcohols. 24 Hydrogen Bonding in Alcohols H O H H R O R O H O H H R H O O O H O R H R H H water-alcohol alcohol-alcohol 25 26 27 Glucose is one of the most important carbohydrates in biochemistry. It has six carbons and five alcohol groups (molar mass = 180.2 g). How would you predict the water solubility of glucose to differ from that of 1-hexanol? 28 H OH H OH OH C C C C C O H OH H H CH 2OH 95 g of glucose will dissolve in 100 g of water. OH 0.6 g of 1-hexanol will dissolve in 100 g of water.29 Chemical Properties of Alcohols 30 Chemical Properties of Alcohols • • • • Acidic and Basic Properties Oxidation Dehydration Esterification 31 Basic Properties • If an alcohol is mixed with a strong acid, it will accept a proton (act as a Brønsted-Lowry base) to form a protonated alcohol or oxonium ion. H H3C O H + H2SO4 H3C - + HSO4 O H 32 Acidic Properties • • 2 H3C Alcohols can also act as BrønstedLowry acids. The resulting anion in the alcohol reaction is known as an alkoxide ion (RO-). H2 C O H + 2 Na 2 H3C H2 C Na+ O + H2 (g) sodium ethoxide 33 Reactivity of Alcohols with Na or K • The order of reactivity of alcohols with sodium or potassium is: – primary > secondary > tertiary. • Reactivity decreases with increasing molar mass, since the –OH group becomes a relatively smaller, less significant part of the molecule. 34 Oxidation • Oxidation is the loss of hydrogen or the gain of bonds to oxygen by the organic reactant. • Carbon atoms exist in progressively higher stages of oxidation in different functional groups. Alkanes Alcohols Aldehydes Ketones Carboxylic Acids Carbon dioxide increasing oxidation state 35 36 H R C O O OH [O] R C H + H2O aldehyde H primary (1o) [O] R C OH carboxylic acid alcohol R R C O OH [O] R C R ketone H secondary (2o) alcohol The –OH group gives an organic compound the capability of forming an aldehyde, ketone, or carboxylic acid. R R C OH [O] No reaction R tertiary (3o) alcohol 37 Common Oxidizing Agents • KMnO4 • K2Cr2O7 • O2 38 Dehydration • Alcohols can be dehydrated with sulfuric acid to form alkenes. H H H C C H OH 96% H2SO4 H H heat H H C C H + H2O 39 Dehydration • For many alcohols, there is more than one way to remove water. Therefore the double bond can be located in different positions. • The major product in such cases is the alkene in which the C=C bond has the greatest number of alkyl substituents on it (or the least number of hydrogens). H H3C H H C C 96% H2SO4 CH2 H3C heat H OH H 2-butanol C H C CH3 + H3C 2-butene (major product) H2 C H C CH2 + H2O 1-butene 40 Saytzeff’s Rule During intramolecular dehydration, if there is a choice of positions for the carbon-carbon double bond, the preferred location is the one that generally gives the more highly substituted alkene – that is, the alkene with the most alkyl groups attached to the double-bond carbons. 41 Dehydration • Primary alcohols can be dehydrated with sulfuric acid to form ethers. H3C H3C H2 C H2 C OH OH 96% H2SO4 H3C heat H2 C O H2C CH3 + H2O diethyl ether • A reaction in which two molecules are combined by removing a small molecule is known as a condensation reaction. 42 Esterification (Conversion of Alcohols to Ethers) • An alcohol can react with a carboxylic acid to form an ester and water. O O + H R C OH carboxylic acid + H-OR' alcohol R C OR' + H2O ester 43 Utility of the Hydroxyl Functional Group 44 Common Alcohols 45 Three General Methods for Making Alcohols 1. Hydrolysis of an ester. 2. Alkaline hydrolysis of an alkyl halide (1° and 2° alcohols only). 3. Catalytic reduction of aldehydes and ketones. 46 Hydrolysis of an Ester • Hydrolysis is a reaction of water with another species in which the water molecule is split. O O + H H2O + R'O C ester R heat H-OR' + HO C R alcohol carboxylic acid 47 Alkaline hydrolysis of an alkyl halide (1° and 2° alcohols only). CH3CH2Cl + NaOH(aq) CH2CH3OH + NaCl 48 Catalytic Reduction of Aldehydes and Ketones • Produces primary and secondary alcohols. • Chapter 23 49 Methanol •Methanol is synthesized by the high-pressure catalytic hydrogenation of carbon monoxide. •The most economical nonpetroleum source of carbon monoxide for making methanol is coal. CO + 2 H2 ZnO-Cr2O3 300-400 C, 200 atm CH3OH 50 Uses of Methanol 1. Conversion to formaldehyde (use in manufacture of polymers). 2. Manufacture of other chemicals, especially various kinds of esters 3. Denaturing ethyl alcohol 4. Industrial solvent 51 Ethanol • Large quantities of ethanol are prepared by fermentation. – The conversion of simple sugars to ethanol is accomplished by yeast. • Industrially, ethanol is made by acidcatalyzed addition of water to ethylene. C6H12O6 yeast H2O 2 CH3CH2OH + 2 CO2 52 Uses of Ethanol • An intermediate in the manufacture of other chemicals such as acetaldehyde, acetic acid, ethyl acetate, and diethyl ether. • A solvent for many organic substances. • A compounding ingredient for pharmaceuticals, perfumes, flavorings, etc. • An essential ingredient in alcoholic beverages. 53 2-Propanol (Isopropyl Alcohol) • 2-Propanol is made from propene. + CH3CH=CH2 + H2O H CH3CH(OH)CH3 2-propanol 54 Uses of 2-Propanol (Isopropyl Alcohol) 1. To manufacture other chemicals (especially acetone). 2. As an industrial solvent. 3. As the principal ingredient in rubbing alcohol formulations. 55 Ethylene Glycol (1,2-Ethanediol) • Industrial synthesis Ag catalyst 2 CH2=CH2 + O2 2 200-300 C O + H2O O H+ ethylene oxide (oxirane) HOCH2CH2OH 1,2-ethanediol (ethylene glycol) 56 Uses of Ethylene Glycol (1,2-Ethanediol) 1. In the preparation of the synthetic polyester fiber Dacron and film Mylar 2. As a major ingredient in “permanenttype” antifreeze cooling systems 3. As a solvent in the paint and plastic industries 4. In the formulations of printing ink and ink for ballpoint pens. 57 Glycerol (1,2,3-Propanetriol) • Glycerol (also known as glycerine) is an important trihydroxyalcohol. • It is obtained as a by-product of the processing of animal and vegetable fats to make soap and other products. • It is synthesized commercially from propene. 58 Uses of Glycerol • Each directly related to the three –OH groups. 1. As a raw material in the manufacture of polymers and explosives. 2. As an emollient in cosmetics. 3. As a humectant in tobacco products. 4. As a sweetener. 59 Phenols 60 Phenols • The term phenol is used for the class of compounds that have a hydroxy group attached to an aromatic ring. • The parent compound is also called phenol, C6H5OH. OH 61 Naming Phenols • Many phenols are named as derivatives of the parent compound, via the general methods for naming aromatic compounds. OH OH OH Br phenol m-bromophenol NH2 p-aminophenol 62 Common Phenols OH OH OH HO HO resorcinol catechol (m-dihydroxybenzene) (o-dihydroxybenzene) OH hyrdroquinone (p-dihydroxybenzene) 63 Properties of Phenols 64 Properties of Phenols • Colorless, crystalline solid, mp = 41 °C • Highly poisonous • More acidic than alcohols and water - O Na+ OH + NaOH phenol ROH + NaOH alcohol + H2O sodium phenoxide no reaction 65 Production of Phenol 66 Production of Phenol • Phenol is obtained from coal tar. • Several commercial methods are used to produce phenol synthetically. 67 Ethers 68 Ethers Ethers have the general formula ROR’ 69 70 71 Naming Ethers • Individual ethers may be known by several names. H3C O CH3 H3C ether methyl O CH2CH3 ether methyl dimethyl ether methyl ethyl ethyl methyl ether 72 IUPAC Nomenclature of Ethers 1. Select the longest carbon continuous chain and label it with the name of the corresponding alkane. 2. Change the –yl ending of the other hydrocarbon group to –oxy to obtain the alkoxy group name. e.g. CH3O- is called methoxy. 73 IUPAC Nomenclature of Ethers 3. Combine the two names from Steps 1 and 2, giving the alkoxy name and its position on the longest carbon chain first, to form the ether name. H3C O CH3O- is the alkoxy group (methoxy) CH2CH3 This is the longest C-C chain, so call it ethane. methoxyethane 74 IUPAC Nomenclature of Ethers H3CH2CH2C O CH2CH2CH2CH3 1-propoxybutane CH3 CH3 H3CHC O CH3 CHCH2CHCH3 2-isopropoxy-4-methylpentane 75 Structures and Properties of Ethers 76 Properties of Ethers • Ethers are somewhat more polar than alkanes, but are much less polar than alcohols. • Ethers – especially diethyl ether – are exceptionally good solvents for organic compounds. H SO H 3 O O H H hydrogen bond O H3C CH2CH3 ether-water O H3C CH2CH3 ether-acid 77 78 Formation of Peroxides from Ethers • Oxygen of the air slowly reacts with ethers to form unstable peroxides that are subject to explosive decomposition. O H3CH2C CH2CH3 + O2 O H3CH2C CHCH3 O-O-H diethyl ether hydroperoxide 79 Preparation of Ethers 80 Williamson Synthesis of Ethers • The alkyl halide, RX, may be a methyl or primary group, but not a secondary or tertiary alkyl group or an aryl group. • The alkoxide, R’ONa, may be methyl, primary, secondary, tertiary, or an aryl group. RX + R’ONa alkyl halide alkoxide ROR’ + NaX ether 81 Thiols 82 Thiols • Organic compounds that contain the -SH group are known as thiols or mercaptans. S H3C H methanethiol (methyl mercaptan) SH H3C CH2CH3 2-propanethiol 83 Properties of Thiols 1. Foul odors. 2. Oxidation to disulfides: [O] 2 RSH R-S-S-R thiol disulfide 84 85