ORGANIC CHEMISTRY CHM 207 CHAPTER 6: HYDROXYL COMPOUNDS (ALCOHOLS AND PHENOL) NOR AKMALAZURA JANI

SUBTOPICS Nomenclature of alcohols, phenols. Classification of alcohols. Physical properties of alcohols: - Physical state - Boiling points - Solubility of alcohols in water Acidity of alcohols and phenols Reactions of alcohols: - Reaction with sodium - Oxidation - Esterification - Halogenation and haloform reactions - Dehydration - Formation of ether (Williamson ether synthesis)

Reactions of phenols: - Reaction with sodium - Esterification - Halogenation of the ring - Nitration of the ring Tests to distinguish classes of alcohols: i) Lucas test ii) Oxidation Haloform test to identify methyl alcohol group - Iodoform - Bromoform Uses of alcohols and phenols.

ALCOHOLS Alcohols: Organic compounds containing hydroxyl (-OH) functional groups. Phenols: Compounds with hydroxyl group bonded directly to an aromatic (benzene) ring.

NOMENCLATURE OF ALCOHOLS

IUPAC RULES 1.Select the longest continuous chain of carbon atoms containing the hydroxyl group. 2.Number the carbon atoms in this chain so that the one bonded to the –OH group has the lowest possible number. 3.Form the parent alcohol name by replacing the final –e of the corresponding alkane name by –ol. When isomers are possible, locate the position of the –OH 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 branch chain (or other group) and designate its position by number.

Select this chain as the parent compound. This is the longest continuous chain that contains an hydroxyl group.

This end of the chain is closest to the OH. Begin numbering here.

methyl-2-butanol

Select this chain as the parent compound. This is the longest continuous chain that contains an hydroxyl group.

This end of the chain is closest to the OH. Begin numbering here.

3-methyl-2-pentanol

NOMENCLATURE OF CYCLIC ALCOHOLS Using the prefix cyclo- The hydroxyl group is assumed to be on C1.

NOMENCLATURE OF ALCOHOLS CONTAINING TWO DIFFERENT FUNCTIONAL GROUPS Alcohol containing double and triple bonds: - use the –ol suffix after the alkene or alkyne name. The alcohol functional group takes precedence over double and triple bonds, so the chain is numbered in order to give the lowest possible number to the carbon atom bonded to the hydroxyl group. The position of the –OH group is given by putting its number before the –ol suffix. Numbers for the multiple bonds were once given early in the name.

EXAMPLE 1) Longest carbon chain that contains –OH group - 5 carbon 2) Position of –OH group - Carbon-2 3) Position of C=C - Carbon-4 COMPLETE NAME = 4-penten-2-ol

Some consideration: - OH functional group is named as a hydroxy substituent when it appears on a structure with a higher priority functional group such as acids, esters, aldehydes and ketones. - Examples:

MAIN GROUPS Acids Esters Aldehydes Ketones Alcohols Amines Alkenes Alkynes Alkanes Ethers Halides decreasing priority

NOMENCLATURE OF DIOLS Alcohols with two –OH groups are called diols or glycols. Naming of diols is like other alcohols except that the suffix diol is used and two numbers are needed to tell where the two hydroxyl groups are located.

NOMENCLATURE OF PHENOLS The terms ortho (1,2-disubstituted), meta (1,3-disubstituted) and para (1,4-disubstituted) are often used in the common names.

Phenols may be monohydric, dihydric or trihydric according to the number of hydroxyl groups present in the benzene ring.

According to the type of carbinol carbon atom (C bonded to the –OH group). CLASSIFICATION Classes: i) Primary alcohol - -OH group attached to a primary carbon atom ii) Secondary alcohol - -OH group attached to a secondary carbon atom iii) Tertiary alcohol - -OH group attached to a tertiary carbon atom

TYPE STRUCTURE EXAMPLES i) Primary (1°) ii) Secondary (2°) iii) Tertiary (3°)

Alcohols that contain more than one OH group attached to different carbons are called polyhydroxy alcohols. Monohydroxy: one OH group per molecule. Dihydroxy: two OH groups per molecule. Trihydroxy: three OH groups per molecule. Polyhydroxy Alcohols

PHYSICAL PROPERTIES PHYSICAL STATES OF ALCOHOLS - simple aliphatic alcohols and lower aromatic alcohols (such as phenylmethanol, C 6 H 5 CH 2 OH) → liquids at room temperature. - highly branched alcohols and alcohols with twelve or more carbon atoms → solids.

BOILING POINTS - The boiling points of alcohols are higher than those of alkanes and chloroalkanes of similar relative molecular mass. - For example: C 2 H 5 OHCH 3 CH 2 CH 3 CH 3 Cl Relative molecular mass: Boiling point: 78°C -42°C -24°C - Reason: intermolecular hydrogen bonds exist between the –OH groups in the alcohol molecules. hydrogen bonding δ+δ+ δ-δ- δ+δ+δ-δ- δ-δ- δ-δ- - Branched chain alcohols boils at a lower temperature (more volatile) than the straight chain alcohols with the same number of carbon atoms.

SOLUBILITY OF ALCOHOLS IN WATER i) alcohols with short carbon chains (such as methanol, ethanol, and propanol) dissolve in water. - when alcohols dissolve in water, hydrogen bonds are formed between the –OH group of the alcohol molecule and the –OH group of the water molecule. ii) the solubility of alcohols in water decreases sharply with the increasing length of the carbon chain. Higher alcohols are insoluble in water. - alcohol contains a polar end (-OH group) called ‘hydrophilic’ and a non- polar end (the alkyl group) called ‘hydrophobic’. - the water solubility decreases as the alkyl group becomes larger.

iii) alcohols with more than one hydroxyl group (polyhydroxy alcohols) are more soluble than monohydroxy alcohols with the same number of carbon atoms. This is because they can form more hydrogen bonds with water molecule. iv) branched hydrocarbon increases the solubility of alcohol in water. - reason: branched hydrocarbon cause the hydrophobic region becomes compact. * Phenol is unusually soluble (9.3%) because of its compact shape and the particularly strong hydrogen bonds formed between phenolic – OH groups and water molecules.

Alcohol is weakly acidic. In aqueous solution, alcohol will donated its proton to water molecule to give an alkoxide ion (R-O - ). ACIDITY OF ALCOHOLS AND PHENOLS R-OH + H 2 OR-O - + H 3 O + K a = ~ to alkoxide ion Example CH 3 CH 2 -OH + H 2 OCH 3 CH 2 -O - + H 3 O + The acid-dissociation constant, Ka, of an alcohol is defined by the equilibrium R-OH + H 2 OR-O - + H 3 O + KaKa Ka = [H 3 O + ] [RO - ] [ROH] pK a = - log (K a ) * More smaller the pK a value, the alcohol is more acidic

Acidity OF PHENOLS Phenol is a stronger acid than alcohols and water. R-OH + H 2 OR-O - + H 3 O + K a = ~ to alcohol alkoxide ion K a = 1.2 x H 2 O + H 2 OHO - + H 3 O + K a = 1.8 x hydroxide ion

Phenol is more acidic than alcohols by considering the resonance effect. i) The alkoxide ion (RO - ) - the negative charge is confined to the oxygen and is not spread over the alkyl group. - this makes the RO - ion less stable and more susceptible to attack by positive ions such as H + ions.

ii) The phenoxide ion - one of the lone pairs of electrons on the oxygen atom is delocalised into the benzene ring. - the phenoxide ion is more stable than the alkoxide ion because the negative charge is not confined to the oxygen atom but delocalised into the benzene ring. - the phenoxide ion is resonance stabilised by the benzene ring and this decreases the tendency for the phenoxide ion to react with H 3 O +.

The acidity decreases as the substitution on the alkyl group increase. - Reason: a more highly substituted alkyl group inhibits solvation of the alkoxide ion and drives the dissociation equilibrium to the left. - For example: methanol is more acidic than t-butyl alcohol. The present of electron-withdrawing atoms enhances the acidity of alcohols. - Reason: the electron withdrawing atom helps to stabilize the alkoxide ion. - For example: 2-chloroethanol is more acidic than ethanol because the electron-withdrawing chlorine atom helps to stabilize the 2-chloroethoxide ion. - alcohol with more than one electron withdrawing atoms are more acidic. For example, 2,2,-dichloroethanol is more acidic than 2-chloroethanol. - Example of electron-withdrawing atom/groups: Halogen atoms and NO 2. EFFECTS OF Acidity

Reaction with sodium Oxidation Esterification Halogenation and haloform reactions Dehydration Formation of ether (Williamson ether synthesis) REACTIONS OF ALCOHOLS

Reaction with sodium Alcohols reacts with Na at room temperature to form salts (sodium alkoxides) and hydrogen. 2R-O-H + 2Na → 2R-O - Na + + H 2 For example: CH 3 CH 2 OH + Na → CH 3 CH 2 O - Na + + 1/2H 2 alcohol sodium ethoxide Reactivity of alcohols towards the reactions with sodium: CH 3 > 1° > 2° > 3°

Oxidation 1° alcohol

Examples: 1° alcohol

2° alcohol 3° alcohol Example:

Esterification: - the reaction between an alcohol and a carboxylic acid to form an ester and H 2 O. Esterification H + = catalyst

Esterification also occurs when alcohols react with derivatives of carboxylic acids such as acid chlorides

Halogenation and haloform reactions 1) Hydrogen halides (HBr or HCl or HI) R-OH + H-X → R-X + H 2 O Example: C 2 H 5 -OH + H-Br C 2 H 5 -Br + H 2 O Reactivity of hydrogen halides decreases in order HI > HBr > HCl Reactivity of alcohols with hydrogen halides: 3° > 2° > 1° H+H+

2) Phosphorus trihalides, PX 3 3R-OH + PX 3 3R-X + H 3 PO 3 (PX 3 = PCl 3 or PBr 3 or PI 3 ) Example: (CH 3 ) 2 CHCH 2 -OH + PBr 3 → (CH 3 ) 2 CHCH 2 -Br isobutyl alcoholisobutyl bromide 3) Thionyl chloride (SOCl 2 ) R-OH + SOCl 2 → R-Cl + SO 2 + HCl Example: CH 3 (CH 2 ) 5 CH 2 -OH + SOCl 2 → CH 3 (CH 2 ) 5 CH 2 -Cl + SO 2 + HCl 1-heptanol 1-chloroheptane

Dehydration of alcohols will formed alkenes and the products will followed Saytzeff rules. Dehydration conc. H 2 SO 4 R-CH 2 -CH 2 -OHR-CH=CH 2 + H 2 O Saytzeff rule: - A reaction that produces an alkene would favour the formation of an alkene that has the greatest number of substituents attached to the C=C group.

Reactivity of alcohols towards dehydration: 3° > 2° > 1° Reagents for dehydration: i) Concentrated H 2 SO 4 conc. H 2 SO 4 CH 3 -CH 2 -OHCH 2 =CH 2 + H 2 O ii) With phosphoric (v) acid iii) Vapour phase dehydration of alcohols CH 3 CH 2 OHCH 2 =CH 2 + H 2 O Al 2 O 3 heat

Involves the S N 2 attack of an alkoxide ion on an unhindered primary alkyl halides. The alkoxide is made by adding Na, K or NaH to the alcohol. R-O - + R’-X → R-O-R’ + X - alkoxide (R’ must be primary) Formation of ether (Williamson ether synthesis) The alkyl halides (or tosylate) must be primary, so that a back-side attack is not hindered. If the alkyl halides is not primary, elimination usually occurs to form alkenes.

Reaction with sodium Esterification Halogenation of the ring Nitration of the ring REACTIONS OF PHENOLS

REACTION WITH SODIUM REACTION WITH AQUEOUS SODIUM HYDROXIDE ROH + NaOH no reaction

ESTERIFICATION H+H+

More reactive towards electrophilic substitution than benzene. ortho-para director. HALOGENATION

Monobromophenols are obtained if the bromine is dissolved in a non-polar solvent such as CCl 4.

NITRATION Dilute nitric (v) acids reacts with phenol at room temperature to give a mixture of 2- and 4-nitrophenols.

By using concentrated nitric (v) acid, the nitration of phenol yields 2,4,6-trinitrophenol (picric acid). Picric acid is a bright yellow crystalline solid. It is used in the dyeing industry and in manufacture of explosives.

1)Lucas Test - The alcohol is shaken with Lucas reagent (a solution of ZnCl 2 in concentrated HCl). - Tertiary alcohol - Immediate cloudiness (due to the formation of alkyl chloride). - Secondary alcohol - Solution turns cloudy within about 5 minutes. - Primary alcohol - No cloudiness at room temperature. TESTS TO DISTINGUISH CLASSES OF ALCOHOLS

2)Oxidation of alcohols - only primary and secondary alcohols are oxidised by hot acidified KMnO 4 or hot acidified K 2 Cr 2 O 7 solution. - the alcohol is heated with KMnO 4 or K 2 Cr 2 O 7 in the presence of dilute H 2 SO o or 2 o alcohol: → the purple colour of KMnO 4 solution disappears. → the colour of the K 2 Cr 2 O 7 solution changes from orange to green. - 3 o alcohol do not react with KMnO 4 or K 2 Cr 2 O 7.

HALOFORM TEST TO IDENTIFY METHYL ALCOHOL GROUP 1) Iodoform: Ethanol and secondary alcohols containing the group methyl alcohol group which react with alkaline solutions of iodine to form triiodomethane (iodoform, CHI 3 ). Triiodomethane – a pale yellow solid with a characteristic smell.

The iodoform test can distinguish ethanol from methanol positive iodoform test negative iodoform test

The iodoform test can distinguish 2-propanol from 1-propanol positive iodoform test negative iodoform test * TERTIARY ALCOHOLS DO NOT GIVE POSITIVE IODOFORM TEST

2) BROMOFORM sample iodoform reagent

As solvents: - examples: the lower alcohols such as methanol, ethanol and propanol. - methanol is used as a solvent for varnish and paints. As fuels: - biofuel (fuel derived from a biological source). - ethanol can be produced from sugars such as sucrose from sugar cane, through fermentation and distillation. It can be blended with petrol and used as fuel in motor vehicles. - methylated spirit is ethanol made undrinkable by the addition of a little methanol. It is used as a fuel in camping stoves. USES OF ALCOHOLS

In alcoholic drinks: - ethanol is used for making wine, beer and etc. As intermediates: - methanol can be oxidised to methanal (HCHO), a chemical feedstock (starting material) for the manufacture of thermosetting plastics such as bakelite. - methanol is used to make methyl methacrylate which is used in the manufacture of another plastic called perspex. In cosmetics: - ethanol is used as solvent for fragrances in perfumes and after- shave lotions. - polyhydroxyl alcohols (for example, glycerol) are used in moisturising creams.

Making plastics such as bakelite (phenol-methanal plastic). The synthesis of cyclohexanol and hexanedioic acid to make nylon 6,6. Making dyes. Making antiseptics such as 4-chloro-3,5- dimethylphenol which is active ingredient in ‘Dettol’. USES OF PHENOLS