Oxygen-Containing Organic Compounds

Alcohol

hydroxyl group (OH: polar) bonded to carbon chain

How is methanol obtained?

pyrolysis (thermal decomposition of wood at high temperatures in absence of oxygen)

What are the properties of methanol?

• colourless, odourless, liquid at rtp

• toxic - can cause blindness and death if ingested

What are the uses of methanol

• common solvent (e.g. perfumes)

• industrial starting material

• fuel for car racing

properties of ethanol

• colourless, odourless, liquid at rtp

• toxicity - can ingest small amount, if blood conc. >1% → coma and death

Uses of ethanol

alcoholic beverages

perfume/lotion solvent

industrial starting material

How is alcohol obtained

Hydration of alkenes

- alkene + H2O(steam) -- alcohol (may have >1 possible structure)

- conditions: 300C, 60-70atm, H3PO4 catalyst

Fermentation (ethanol)

- C6H12O6 -- 2CH3CH2OH + 2CO2

- requires yeast enzymes

- waste product of yeast metabolism (anaerobic respiration)

Alcohol to alkene

alcohol -- alkene + H2O

- dehydration, removes OH group and H from adjacent carbon

- Conditions: 180C, excess conc H2SO4

What is a phenol

Hydroxyl group (OH) bonded to benzene ring

Properties of phenols

colourless solid

weak acid

low melting point

What are the properties of alcohols (boiling point and solubility)

boiling point

• increases as chain length increases (LDF)

• higher than alkane (HB), difference decreases (LDF)

Solubility

• 1-4: Highly soluble

• 5-7: Moderately soluble

• >7: Slightly soluble/insoluble

Classifying alcohols

no of alkyl groups attached to C which is bonded to OH (methyl, primary, secondary, tertiary)

Nomenclature of alcohols

1. Find longest C chain with -OH

2. replace -e with -ol (keep -e for diol/triol)

3. number

4. indicate -OH position on parent chain

5. name and number substituents

Dissociation of phenols

C6H5-OH <> C6H5O- + H+

• resonance makes ring stable

• phenoxide allows more resonance - stable

Phenol examples

• Cresol - antiseptic

• Hexylresorcinol - lozenge

• Pentachlorophenol - wood preservative

• Salicylic acid - anti-inflammatory

Carboxylic acid formation

alcohol + 2[O] → carboxylic acid + H₂O

- oxidation

- conditions: acidified KMnO₄ or K₂Cr₂O₇

- color change: purple → colourless or orange → green

Oxidation of secondary alcohols

alcohol + [O] → ketone + water

• conditions: acidified KMnO₄ or K₂Cr₂O₇

Oxidation of tertiary alcohols

cannot be oxidised

Dissociation of carboxylic acids

RCOOH → RCOO^- + H⁺

Nomenclature of carboxylic acids

1. Find longest C chain with -OH

2. replace -e with -oic acid (keep -e for multiple)

3. Number carboxyl group as 1

4. name and number substituents

Aliphatic

with carbon chain

aromatic

with benzene

When does carboxylic acid undergo neutralisation

• with reactive metals, bases & carbonates

• completely neutralised by strong bases/carbonates

• qualitative test

Uses of salts of carboxylic acids (carboxylate salt)

1. Food preservatives

   • inhibit bacteria, fungi and microorganism growth to slow food spoilage

   • calcium propanoate prevents bread mould

2. MSG - monosodium glutamate

   • flavour enhancer

Natural sources of carboxylic acids

• methanoic acid - ants

• ethanoic acid - vinegar

• oxalic acid (ethanedioic acid)

• Lactic acid - yoghurt

• Citric acid - citrusy fruits

Esterification

carboxylic acid + alcohol → ester + water

• conditions: conc. H2SO4

• done in reflux (force vapour to condense back)

• note position of ester link (especially in polyesters)

Uses of esters

• Fruity flavours for sweets, drinks, cakes

• Solvent for organic compounds (e.g. in glue, varnishes, paints)

Properties of ester

• Pleasant odour

• Slightly polar; low molecular weight esters are water soluble

• Volatile

Nomenclature of esters

1. Alkyl portion of alcohol in front

2. Replace -oic acid → -oate

   e.g. ethanol + butanoic acid → ethyl butanoate

Application of esterification

1. Fats and oils - naturally occurring esters

   • energy storing compound by plants & animals

   • lipids - insoluble in water, soluble in organic solvent

   • tri-esters glycerol and fatty acids (condensation)

2. Polyesters - condensation polymerisation

   • 1 monomer - 1 alcohol, 1 carboxylic acid end

   • 2 monomers - alcohol (2 alcohol ends) and carboxylic acid (2 carboxylic acid ends)

   • water also formed; if C chain <5C, may form ring

terylene

• Polyester, used in clothing, curtains, sleeping bags

• Fibres of terylene + cotton → polyester-cotton

• Condensation of ethane-1,2-diol and benzene-1,4-dicarboxylic acid