4.4 organic compounds containing oxygen

prefix of alcohols

hydroxy-

suffix of alcohols

-ol

suffix of aldehydes

-al

prefix of phenols

phen-

suffix of ketones

-one

suffix of carboxylic acids

-oic acid

suffix of esters

(alcohol)-yl (carboxylic acid)-oate

suffix of acid chlorides

-oyl chloride

suffix of acid anhydrides

-oic anhydride

suffix of nitriles

-nitrile

suffix of amines

-amine

suffix of amides

-amide

primary alcohol

1 alkyl group attached to C-OH

secondary alcohol

2 alkyl groups attached to C-OH

tertiary alcohol

3 alkyl groups attached to C-OH

carboxylic acid acidity

• weak acids

• negative charge of the carboxylate ion is delocalised, which stabilises the ion allowing H+ to form

alcohol acidity

• less acidic than carboxylic acids and phenols

• the charge on anion cannot be delocalised to another electronegative atom

alcohol solubility

as the carbon chain length increases the contribution of the polar -OH or the -COOH group decreases due to the larger non-polar section of the molecule

phenol acidity

• less acidic than carboxylic acids

• the negative charge of the phenoxide ion is stabilised by being delocalised around the ring

testing for carboxylic acids

• universal indicator; colour change from green to red

• sodium carbonate; effervescence passed through limewater turns milky

testing for alkenes

bromine water; colour change from orange brown to colourless

alkene → alkane

• electrophilic addition

• reagents; hydrogen gas (H₂), Ni catalyst

aldehyde → primary alcohol

• reduction

• reagents; sodium borohydride (NaBH₄)

• conditions; reflux

ketone → secondary alcohol

• reduction

• reagents; sodium borohydride (NaBH₄)

• conditions; reflux

carboxylic acid → aldehyde

• reduction

• reagents; lithium aluminium hydride (LiAlH₄), dry ether

• conditions; room temperature

carboxylic acid → primary alcohol

• reduction

• reagents; lithium aluminium hydride (LiAlH₄), dry ether

• conditions; room temperature

halogenoalkane → alcohol

• nucleophilic substitution

• reagents; NaOH (aq)

• conditions; reflux

halogenoalkane → alkene

• elimination

• reagents; NaOH in ethanol

• conditions; reflux

halogenoalkane → nitrile

• nucleophilic substitution

• reagents; KCN in ethanol

alcohol → bromoalkane

• bromination

• reagents; NaBr/H₂SO₄

• conditions; reflux

alcohol → chloroalkanes

• chlorination

• reagents; hydrogen chloride gas (HCl), anhydrous zinc chloride (ZnCl₂)

• conditions; heat

carboxylic acid + alcohol → ester

• esterification

• reagents; H⁺ catalyst

• conditions; reflux

acyl chloride + alcohol → ester

• esterification

• conditions; room temperature, dropwise

primary alcohol → aldehyde

• oxidation

• reagents; H⁺/Cr₂O₇²⁻ or H⁺/MnO₄⁻

• conditions; gentle heating, immediate distillation

primary alcohol → carboxylic acid

• oxidation

• reagents; H⁺/Cr₂O₇²⁻ or H⁺/MnO₄⁻

• conditions; reflux

secondary alcohol → ketone

• oxidation

• reagents; H⁺/Cr₂O₇²⁻ or H⁺/MnO₄⁻

• conditions; heating

alcohol → alkene

• elimination

• reagents; concentrated H₂SO₄

• conditions; reflux

testing for primary and secondary alcohols

• acidified potassium dichromate (H⁺/Cr₂O₇²⁻); colour change from orange to green

• acidified potassium permanganate (H⁺/MnO₄⁻); colour change from pink to colourless

testing for secondary alcohols (iodoform)

warmed iodine in aqueous sodium hydroxide; pale yellow precipitate forms (CHI₃), antiseptic smell

phenol → 2,4,6-tribromophenol (white solid)

• electrophilic substitution

• reagents; Br₂

phenol → ester

• electrophilic substitution

• reagents; acyl chloride

phenol → sodium phenoxide

reagents; sodium hydroxide

testing for phenols

neutral iron(III) chloride solution; purple/violet colour forms

aldehyde → carboxylic acid

• oxidation

• reagents; H⁺/Cr₂O₇²⁻

• conditions; heat

aldehyde/ ketone → nitrile

• nucleophilic addition

• reagents; potassium cyanide (KCN), dilute sulphuric acid (H₂SO₄)

testing for aldehydes

• 2,4-dinitrophenylhydrazine (2,4-DNPH); forms red crystals

• Tollens' reagent; forms silver mirror

• Fehling's reagent; colour change from blue solution to brick-red precipitate

• acidified dichromate (Cr₂O₇²⁻); colour change from orange to green

identifying an aldehyde with pure crystals

the crystals have very sharp melting points which can be compared with known values in a database

identifying an aldehyde with impure crystals

the melting point will be lower than the actual value and the crystals will melt over a temperature range

Tollen's reagent

• silver nitrate in aqueous ammonia

• Ag⁺(aq) + e⁻ → Ag(s)

Fehling's reagent

• Cu²⁺ ions dissolved in aqueous alkali

• 2Cu²⁺(aq) + 2e⁻ + 2OH⁻(aq) → Cu₂O(s) + H₂O(l)

testing for ketones (+ethanal)

warmed iodine in aqueous sodium hydroxide; pale yellow precipitate forms (CHI₃), antiseptic smell

ester → carboxylic acid + alcohol

• hydrolysis

• reagents; water, dilute hydrochloric acid

• conditions; reflux

ester → carboxyate + alcohol

• hydrolysis

• reagents; sodium hydroxide

• conditions; reflux

amides → carboxylic acid

• hydrolysis

• reagents; sodium hydroxide

• conditions; reflux, followed by acidification

acyl chloride → carboxylic acid

• hydrolysis

• reagents; water

• conditions; room temperature

nitrile → carboxylic acid

• hydrolysis

• reagents; water, dilute hydrochloric acid

• conditions; reflux, heat

benzene → carboxylic acid

• oxidation

• reagents; alkaline potassium manganate (VII) solution (MnO₄⁻)

• conditions; heat, followed by acidification

carboxylic acid → acyl chloride

• reagents; phosphorus pentachloride (PCl₅)

• conditions; anhydrous

carboxylic acid → alkane

• decarboxylation

• reagents; soda lime (NaOH)

• conditions; heat

carboxylic acid → amide

• oxidation

• reagents; ammonia (NH₃)

• conditions; heat/ reflux

amide → nitrile

• reagents; phosphorus(V) oxide (P₄O₁₀)

• conditions; heat