ALCOHOLS Properties Preparation General formula R OH where R is alkyl or substitued alkyl Ar OH phenol different properties Nomenclature 1 Common names Name of alkyl group followed by word alcohol eg ethyl alcohol isopropyl alcohol 2 IUPAC a Parent structure longest chain containing OH group name by replacing e of alkane by ol b Position of OH is indicated by a number usually the lowest one possible OH takes precedence over double and triple bonds if any are present ie number from the end that gives the OH a lower number c Substituents on parent chain indicated by name and position number d More than one OH group diol triol etc eg C6H5 CH2 CHCl CH OH CH3 3 chloro 4 phenyl 2 butanol Physical Properties Up to 6 carbons soluble in water owing to hydrogen bonding and dipole dipole interactions with water The larger the alkyl group the more alkane like the alcohol and the less soluble it is in water H O H H O H H H O H HO H OH H OH H HO O H H H HO H HH O C C H HH O H H OH H OH H Alcohols can hydrogen bond OH H O H O H H HO H O H H O H H H O H O H H O H H O H H Small alkyl groups do not disrupt H bonding in water much large groups do Owing to H bonding and dipole dipole interactions the bps of alcohols are high compared to alkanes of same MW 2 Preparation 1 Reduction of Ketones Ketones can be reduced to secondary alcohols with lithium aluminum hydride or sodium borohydride C C C O eg NaBH 4 H2O followed by H3O or LiAlH 4 ether followed by H3O C C O C H H 1 NaBH 4 H2O 2 H3O CH3 C O CH3 C H OH 3 Limitations Sodium borohydride may reduce the C C p bond in conjugated ketones Lithium aluminum hydride is a powerful reducing agent and will reduce carboxylic acids esters nitriles amides and nitro groups it will replace alkyl halogens with hydrogen hydrogenolysis It is destroyed by even weakly acidic water and alcohols It may reduce the C C p bond in conjugated ketones It reacts violently with water and in general is nasty stuff 2 Reduction of Aldehydes Aldehydes can be reduced to primary alcohols with sodium borohydride or lithium aluminum hydride This reaction is analogous to 1 C H C O eg NaBH4 H2O followed by H3O or LiAlH4 ether followed by H3O C C O H H H H C O 1 2 NaBH4 H2O H3O 4 H C H OH 3 Reduction of Carboxylic Acids and Esters Both esters and carboxylic acids can be reduced to primary alcohols by lithium aluminum hydride O C OH 1 LiAlH4 H3O 2 H H C OH 5 Alcohols Reactions The alcohol functional group is O H and its reactions involve cleavage of the O H bond or the C O bond C O H or C O H In either case there can be a subsequent substitution or an elimination to form a double bond Substitution Elimination C O Y or C Y C O or C Alcohols As Acids Acidity is the result of the electronegativity of oxygen d R O H R O H 6 d Alcohols react with active metals R O H Na R O Na 1 2 H2 Acidity of Alcohols Compared to Other Compounds Compound HSO4H HCl ArSO3H pKa 10 7 6 5 RCH2 HOH H2OH 2 1 74 HNO3 HF Ar H2NH RCOOH H3NH 1 4 3 17 3 5 4 5 9 Compound ArOH HOH H H RCH2OH H C C H H2NH CH2 HCH Ph H CH3 H2CH J H pKa 8 11 15 74 16 18 25 34 36 5 37 42 100 7 pKa 15 7 Relative Acidities of Alcohols and Water Compound HO H CH3O H CH3CH2O H CH3 2CHO H CH3 3CO H 16 18 18 19 15 5 16 Oxidation of Alcohols Primary alcohols can be oxidized to aldehydes with care and carboxylic acids RCH2OH K2Cr2O7 or KMnO4 O RCOH Carboxylic Acids This oxidation occurs in two stages there is an aldehyde intermediate but aldehydes are usually more easily oxidized than alcohols many aldehydes are oxidized by air and under the conditions of the reaction the aldehyde is not isolated Aldehydes This reaction is successful under certain carefully controlled conditions C5H5NH CrO3Cl RCH2OH C5H5NH CrO3Cl is pyridinium chlorochromate PCC O RCH 8 Secondary alcohols can be oxidized to ketones R CR H OH KMnO4 or CrO3 or K2Cr2O7 R CR O Further oxidation does not take place because it would involve breaking a carbon carbon bond Tertiary alcohols are not oxidized under basic conditions and are converted to alkenes under acidic conditions Alkenes may react with oxidizing agents 9 Phenols Ar OH Phenols differ from alcohols in that the OH is directly attached to the aromatic ring Ph CH2 OH is an alcohol Physical Properties Phenol is somewhat soluble in water hydrogen bonding other phenols are not very soluble Boiling points are high compared to hydrocarbons owing to hydrogen bonding Reactions of Phenols Phenols are acidic Why are phenols acidic Ka 10 10 compared to alcohols Ka 10 16 10 Compared to a phenol the phenoxide ion is more stable than an alkoxide ion is compared to an alcohol R O H R O H OH OH O O OH OH OH O O O H charge separation no charge separation 11 Ethers Nomenclature name both groups followed by ether eg C6H5 O CH2 CH CH2 CH3CH2 O CH2CH3 allyl phenyl ether diethyl ether ether If one group has no simple name use alkoxy R O method eg 1 bromo 2 methoxycyclopentane Br OCH3 O R R Physical properties Weakly polar slightly soluble in water 12