Chapter 8_Alcohols_16b4f829cbfe392b083261e97d951b36.pptx
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Alcohols, Phenols and Ethers CHAPTER 8 1 In This Chapter •Nomenclature of Alcohols, Phenols, and Ethers •Hydrogen Bonding •Acidity •Synthesis of Alcohols, Phenols and Ethers •Reactions of Alcohols, Phenols and Ethers 2 Introduction Alcohols contain an OH group connected to a saturated sp3 hybr...
Alcohols, Phenols and Ethers CHAPTER 8 1 In This Chapter •Nomenclature of Alcohols, Phenols, and Ethers •Hydrogen Bonding •Acidity •Synthesis of Alcohols, Phenols and Ethers •Reactions of Alcohols, Phenols and Ethers 2 Introduction Alcohols contain an OH group connected to a saturated sp3 hybridized Carbon They are important solvents and synthesis intermediates Phenols contain an OH group connected to a carbon in a benzene ring Methanol, CH3OH, called methyl alcohol, is a common solvent, a fuel additive, produced in large quantities Ethanol, CH3CH2OH, called ethyl alcohol, is a solvent, fuel, beverage Phenol, C6H5OH (“phenyl alcohol”) has diverse uses - it gives its name to the general class of compounds OH groups bonded to vinylic, sp2-hybridized carbons 3 Introduction An ether has two organic groups (alkyl, aryl, or vinyl) bonded to the same oxygen atom, R–O–R Diethyl ether is used industrially as a solvent Tetrahydrofuran (THF) is a solvent that is a cyclic ether Thiols (R–S–H) and sulfides (R– S–R ) are sulfur (for oxygen) analogs of alcohols and ethers 4 8.1 Naming Alcohols, Phenols and Ethers Naming of Alcohols: General classifications of alcohols based on substitution on C to which OH is bonded Alcohols can be classified as primary (1 ), secondary (2 ), or tertiary (3 ). 1o 2o 3o 5 8.1 Naming Alcohols, Phenols and Ethers I.U.P.A.C. Naming of Alcohols: 1. Select the longest carbon chain containing OH group as parent. 2. Number the chain from the end where OH group came first. 3. Number substituents according to position on chain. 4. Listing the substituents in alphabetical order and write the name of parent carbon chain while replacing –e with –ol. 5. If more then one –OH groups are present, list their position and write appropriate prefix (di, tri, etc.) before –ol. 6 8.1 Naming Alcohols, Phenols and Ethers Give IUPAC name of the following compounds: a) b) OH OH CH3 HO c) OH d) OH CH3 CH3 7 8.1 Naming Alcohols, Phenols and Ethers Draw structures of the following compounds: a) 2-Ethyl-2-butanol c) cis-2-Bromo-1-cyclopentanol b) 3-Cyclohexen-1-ol d) 2-Phenyl-2-butanol 8 8.1 Naming Alcohols, Phenols and Ethers Some common names of Alcohols 9 8.1 Naming Alcohols, Phenols and Ethers Naming of Phenols Use “phenol” (the French name for benzene) as the parent hydrocarbon name, not benzene. Name substituents on aromatic ring by their position from OH according to rules for naming disubstituted benzene. OH OH H 3C O 2N 4-Nitrophenol or p-Nitrophenol 4-Methylphenol or p-Methylphenol or p-Cresol 10 8.1 Naming Alcohols, Phenols and Ethers Draw structures of the following compounds: a) o-Bromophenol c) p-Hydroxyphenol b) 2,4,6-Trinitrophenol d) 4-Methylphenol 11 8.1 Naming Alcohols, Phenols and Ethers Naming of Ethers Simple ethers are named by identifying the two organic substituents and adding the word ether If other functional groups are present, the ether part is considered an alkoxy substituent 12 8.1 Naming Alcohols, Phenols and Ethers Give IUPAC name of the following compounds: C3H7 a) Br b) OH c) O O HO OCH3 d) OC2H5 CH3 13 8.2 Properties of Alcohols, Phenols, and Ethers: Hydrogen Bonding Bond Angles The structure around “O” of the alcohol, phenol or ether is similar to that in water, i.e. sp3 hybridized The C-O-H and C-O-R bond angles are 109and 112 respectively, which are approx. tetrahedral angle. 14 8.2 Properties of Alcohols, Phenols, and Ethers: Hydrogen Bonding Hydrogen Bonding Alcohols and phenols have much higher boiling points than similar alkanes and alkyl halides A positively polarized OH hydrogen atom from one molecule is attracted to a lone pair of electrons on a negatively polarized oxygen atom of another molecule This produces a force that holds the two molecules together – Hydrogen Bonding Due to hydrogen bonding, more energy will be required to break the intermolecular attraction, thus increases the boiling point of compounds. These intermolecular attractions are present in solution but not 15in 8.2 Properties of Alcohols, Phenols, and Ethers: Hydrogen Bonding Hydrogen Bonding 16 8.3 Properties of Alcohols and Phenols: Acidity Acidity and Basicity Alcohols can act as weak basic and weak acid Alcohols are weak Lewis bases Protonated by strong acids to yield oxonium ions, ROH2+ 17 8.3 Properties of Alcohols and Phenols: Acidity Acidity and Basicity Alcohol can transfer a proton to water to a very small extent and act like acids Produces H3O+ and an alkoxide ion, RO, or a phenoxide ion, ArO 18 8.3 Properties of Alcohols and Phenols: Acidity Simple alcohols are about as acidic as water Alkyl groups make an alcohol a weaker acid The more easily the alkoxide ion is solvated by water the more its formation is energetically favored Steric effects are important 19 8.3 Properties of Alcohols and Phenols: Acidity Alcohols are weak acids – they react with alkali metal to form an alkoxide Alkoxides are bases used as reagents in organic chemistry 20 8.3 Properties of Alcohols and Phenols: Acidity Phenol Acidity Phenols (pKa ~10) are much more acidic than alcohols (pKa ~ 16) due to resonance stabilization of the phenoxide ion Phenols react with NaOH solutions (but alcohols do not), forming salts that are soluble in dilute aqueous solution A phenolic component can be separated from an organic solution by extraction into basic aqueous solution and is isolated after acid is added to the solution 21 8.3 Properties of Alcohols and Phenols: Acidity Phenoxide ion stability The negative charge of the oxygen can be delocalized over four atoms of the phenoxide ion. 22 8.4 Synthesis of Alcohols Alcohols are derived from many types of compounds The alcohol hydroxyl can be converted to many other functional groups This makes alcohols useful in synthesis 23 8.4 Synthesis of Alcohols Hydration of Alkenes: Reaction of Alkene with water in the presence of an acid, as catalyst, produces alcohol. Product follow the Markovnikov’s rule. CH3 OH H2O H2SO4 CH3 H 24 8.4 Synthesis of Alcohols Reduction of Carbonyl Compounds: The most common method of producing alcohol is reduction of carbonyl compounds (C=O). Aldehyde, Ketone, Ester and carboxylic acid are the examples of carbonyl compounds. O OH [H] H Carbonyl Alcohol 25 8.4 Synthesis of Alcohols Reduction of Aldehydes and Ketones: O OH [H] Reduction of Aldehyde gives primary (1 ) alcohol. Reduction of Ketone produces secondary (2 ) alcohol. R H R H H Aldehyde Primary alcohol O OH [H] A mild reducing agent sodium borohydrideR (NaBH4) is used as reducing agent. Ketone R R R H Secondary alcohol 26 8.4 Synthesis of Alcohols Reduction of Aldehydes O NaBH4, ethanol H H O+ 3 2-Methylbutanal Reduction of Ketones O NaBH4, ethanol H3C C 2H5 H3O+ 2-Butanone 27 8.4 Synthesis of Alcohols Reduction of Esters and Carboxylic acid: O OH Reduction of ester and carboxylic acid [H] R gives primary (1 ) alcohol. R OH Carboxylic acid These reactions are slow, so a strong H H Primary alcohol reducing agent like lithium aluminum hydride O (LiAlH4) is used. NaBH4 is not effective for this type of reduction. OH [H] OR' R Ester R H H R' + Primary alcohol 28 OH 8.4 Synthesis of Alcohols Reduction of Carboxylic acids O LiAlH4, ethanol OH H3O+ Propanoic acid Reduction of Ketones O LiAlH4, ethanol OC2H5 H3O+ Ethylbutanoate 29 8.5 Reaction of Alcohols Dehydration of Alcohols (Loss of Water) Alcohols loss one water molecule when treated with strong acids e.g. H2SO4. OH CH3 H2O, H2SO4 o H 50 C CH3 + H2O 30 8.5 Reaction of Alcohols Dehydration of Alcohols (Loss of Water) Acid catalyzed dehydration of alcohol usually follow the Zaitsev rule to give more substituted alkene as major product. OH H3C H2C C CH3 CH3 2-Methyl-2-butanol H2O, H2SO4 o 50 C H3C HC C CH3 CH3 2-Methyl-2-butene (major) + H3C H2C C CH2 CH3 2-Methyl-1-butene (minor) 31 8.5 Reaction of Alcohols Mechanism of Dehydration of Alcohols (Loss of Water) 32 8.5 Reaction of Alcohols Predict the product of following reaction. Indicate major and minor products also CH3 OH a) H3C HC C CH2CH3 CH3 H2O, H2SO4 50 oC OH H3C b) C CH3 CH3 H2O, H2SO4 50 oC 33 8.5 Reaction of Alcohols Oxidation of Alcohols Oxidation of alcohol produces carbonyl compounds Primary alcohols oxidized to aldehydes or carboxylic acids Secondary alcohols oxidized to ketones Tertiary alcohols do not react with oxidizing agents Can be accomplished by inorganic oxidizing gents, such as KMnO4, CrO3, and Na2Cr2O7 or by more selective, expensive reagents 34 8.5 Reaction of Alcohols Oxidation of Primary Alcohols Primary alcohols can be oxidized to aldehyde by using oxidizing agent pyridinium chlorochromate (PCC, C5H6NCrO3Cl) in dichloromethane. PCC is an expensive reagent and selective to produce aldehyde. Reaction with other reagents produce carboxylic acids 35 8.5 Reaction of Alcohols Oxidation of Primary Alcohols Oxidizing agents like CrO3 or Na2Cr2O7 oxidized primary alcohols to carboxylic acids. 36 8.5 Reaction of Alcohols Oxidation of Secondary Alcohols Secondary alcohols easily oxidized to ketone with any oxidizing agent. 37 8.5 Reaction of Alcohols Williamsons Ether Synthesis Ethers can be synthesized by the reaction of alkoxide ions with primary alkyl halides in what is known as the Williamson ether synthesis. This is an SN2 displacement reaction and as such, works better with primary alkyl halides to facilitate back-side attack. If a secondary or tertiary alkyl halide is used, the alkoxide will act as a base and an elimination will take place. 38 8.6 Synthesis and Reactions of Phenols Synthesis of Phenol Phenols can be prepared from aromatic compounds by first treating them with SO3/H2SO4. The sulfonic acid produced will then react with NaOH at high temperature to produce phenol. SO3H SO3 1. NaOH, 300 oC H2SO4 CH3 Toluene OH CH3 2. H3O+ p-Toluenesulfonic acid CH3 p-Methylphenol 39 8.6 Synthesis and Reactions of Phenols Reactions of Phenol Phenols are different then alcohol. Phenol can’t be dehydrated by reaction with acids nor they converted to aryl halides by treating with HX. OH HCl No Reaction Phenol H2SO4, H2O OH OCH CH CH Phenols can be converted to ethers by reaction with alkyl halides in the presence of base. K CO 2 + CH3CH2CH2Br O2N 2 2 3 3 Acetone O2N 40 8.6 Synthesis and Reactions of Phenols Electrophilic Aromatic Substitution Reactions of Phenol OH in phenol, activate aromatic ring and is ortho and para directing group. OH Phenol undergo electrophilic halogenation, nitration and Br sulfonation. Br , FeBr 2 3 OH OH NO2 HNO3 , H2SO4 OH SO3 , H2SO4 SO3H 41 8.6 Synthesis and Reactions of Phenols Oxidation of Phenol: Quinones Oxidation of phenol with strong oxidizing agent produce cyclohexadienedione – Quinone. 42 8.6 Synthesis and Reactions of Phenols Quinones in nature: Quinone are interesting compounds. These can reduced to hydroquinones by NaBH4 and oxidized back to quinones using Na2Cr2O7. O OH NaBH4 Na2Cr2O7 O OH Ubiquinones – a biooxidizing agent- mediate electrontransfer processes involved in energy production through their redox reactions 43 8.7 Synthesis and Reactions of Ethers Synthesis of Ethers: Reaction of alkoxide anion with primary alkyl halide produces ethers. Alkoxide anions are produced by reaction of alcohols with metal or metal hydrides. 44 8.7 Synthesis and Reactions of Ethers Reactions of Ethers: Ethers are generally unreactive Strong acid will cleave an ether at elevated temperature Reaction of ethyl isopropyl ether with HI. HI, HBr produce an alkyl halide from less hindered component by SN2 (tertiary ethers undergo SN1). Halide will attack from less hindered side of protonated ether. The product of reaction is alcohol and alkyl halide. 45 8.7 Synthesis and Reactions of Ethers Reactions of Ethers: Tertiary ethers undergo SN1 because of the formation of stable carbocation. Halide will attack from more hindered side of protonated ether. 2 3o o O C CH3 CH3 CH3 HBr , H2O SN1 CH3 OH + H3C CBr CH3 Oxygen with stay with less substituted alkyl group and halide will bond with more substituted alkyl group. 46 Ethyl Alcohol: Chemical, Drug and Poison Ethanol Production: Fermentation of sugar and grain is the oldest way of preparing ethanol. To carry out this reaction yeast is use. C6H12O6 + Yeast 2 CH3CH2OH + 2 CO2 Industrially, ethanol is produced acid catalyzed hydration of ethylene. CH2=CH2 + H2O Acid catalyst 2 CH3CH2OH 47 Ethyl Alcohol: Chemical, Drug and Poison Effects of Ethanol on Human Body: Ethanol is Dangerous. Ethanol is CNS depressant. High intake of ethanol, increases the alcohol level in blood which effects the respiration and cardiovascular regular, which may lead to death. In stomach ethanol increase the production of acid, which ultimately reduce the body temperature. Ethanol produces aldehydes in the liver which damages liver. 48 Homework 8.24, 8.25, 8.26, 8.28, 8.31, 8.32, 8.33, 8.35, 8.37, 8.40, 8.41, 8.48 49
