Alcohols: Nomenclature, Production, Oxidation, and Reactions

Alcohols: Nomenclature and Production

• Alcohols are a homologous series of organic compounds.
  • General formula: $C<em>nH</em>{2n+1}OH$
  • Names end with '-ol'.
  • Functional group: hydroxyl group (–OH).
  • Examples:
    • Methanol: $CH_3OH$
    • Ethanol: $C<em>2H</em>5OH$
    • Propanol: $C<em>3H</em>7OH$
    • Butanol: $C<em>4H</em>9OH$
    • Pentanol: $C<em>5H</em>{11}OH$
    • Hexanol: $C<em>6H</em>{13}OH$

Naming Alcohols

• Alcohols with three or more carbon atoms exhibit positional isomerism.
  • The carbon number to which the hydroxyl group is attached is written before '-ol'.
  • Examples:
    • Propan-1-ol
    • Propan-2-ol

Alcohols and Hydrogen Bonding

• The hydroxyl group (–OH) contains an electronegative oxygen atom, making alcohols polar.
• Alcohols can participate in hydrogen bonding.
• Boiling Point: Hydrogen bonding between alcohol molecules leads to higher boiling points compared to alkanes with similar molecular masses.
  • Example: Methanol (Mr = 32) boils at 64.7°C, while ethane (Mr = 30) boils at -88.6°C.
• Solubility: Alcohols can mix with water because they can form hydrogen bonds with water molecules.

Alcohol Production by Fermentation

• Alcohol production via sugar fermentation has been practiced for thousands of years.
• Process: Sugar from fruits or grains (e.g., wheat, barley) is mixed with yeast and water.
• Products: Ethanol and other compounds.

Industrial Fermentation

• Raw materials: Sugar cane, molasses (from sugar cane refining), or starch (from potatoes or corn).
• Product: A mixture of water and approximately 15% ethanol by volume.
• Limiting Factor: The yeast is denatured by the alcohol, which halts further alcohol production.
• Distillation: Used to remove most of the water from the ethanol.

Production of Ethanol from Ethene

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Fermentation vs. Hydration

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Oxidation of Alcohols

• A chain of carbon atoms can be represented by 'R' (an R group) when drawing structures.

Primary, Secondary, and Tertiary Alcohols

• Primary (1°) alcohols: Have one R group attached to the carbon to which the OH group is attached.
• Secondary (2°) alcohols: Have two R groups attached to the carbon to which the OH group is attached.
• Tertiary (3°) alcohols: Have three R groups attached to the carbon to which the OH group is attached.

Oxidation of 1° Alcohols: Aldehydes

• Primary alcohols can be oxidized to aldehydes using an oxidizing agent like acidified potassium dichromate(VI).
• Aldehydes contain a carbonyl group (C=O) at the end of the carbon chain.
• Nomenclature: Names end with the suffix '-al'.
• Symbol equation (oxidizing agent represented by [O]):
  • $RCH<em>2OH + [O] \rightarrow RCHO + H</em>2O$
  • Example: Propanal

Synthesis of Aldehydes

• Aldehydes are prepared by reacting a primary alcohol with acidified potassium dichromate(VI).
• The aldehyde is distilled off and collected to prevent further oxidation.

Oxidation of 1° Alcohols: Carboxylic Acids

• Primary alcohols can be oxidized to carboxylic acids by reacting them with an excess of oxidizing agent and refluxing.
• Carboxylic acids contain a carbonyl group (C=O) at the end of the carbon chain, with a hydroxyl group (OH) attached to the carbonyl carbon.
• Nomenclature: Names end with the suffix '-oic acid'.
• Symbol equations:
  • $RCH<em>2OH + [O] \rightarrow RCHO + H</em>2O$
  • $RCHO + [O] \rightarrow RCOOH$
  • Example: Propanoic acid

Synthesis of Carboxylic Acids

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Oxidation of 2° Alcohols: Ketones

• Secondary alcohols can be oxidized to ketones using an oxidizing agent such as acidified potassium dichromate(VI).
• Ketones contain a carbonyl group (C=O) attached to any carbon in the chain except a terminal carbon atom.
• Nomenclature: Names end with the suffix '-one'.
  • Example: Propanone
• Symbol equation:
  • $R<em>1CH(OH)R</em>2 + [O] \rightarrow R<em>1COR</em>2 + H_2O$
• Tertiary alcohols are resistant to oxidation due to the absence of hydrogen atoms on the carbon atom to which the hydroxyl group is attached.

Distinguishing Aldehydes and Ketones

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Esterification

• Esterification involves refluxing a carboxylic acid and an alcohol with a concentrated sulfuric acid catalyst.
• Ester names: Consist of two parts: an alkyl group (from the alcohol) and a carboxylate group (from the carboxylic acid).
• General reaction:
  • $R<em>1COOH + R</em>2OH \rightleftharpoons R<em>1COOR</em>2 + H_2O$
  • Example: Methanol and ethanoic acid react to form methyl ethanoate.

Oxidation of Alcohols

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Other Reactions of Alcohols

Making Alcohols from Aldehydes/Ketones

• Aldehydes and ketones can be reduced using a reducing agent, such as sodium borohydride ($NaBH_4$), to form alcohols.
• Symbol equation, reducing agent represented by [H].
• Aldehydes are reduced to primary alcohols:
  • $RCHO + 2[H] \rightarrow RCH_2OH$
• Ketones are reduced to secondary alcohols:
  • $R<em>1CHOR</em>2 + [H] \rightarrow R<em>1CH(OH)R</em>2$

Synthesis of Ethene from Ethanol

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Dehydration of Ethanol

• In the lab, dehydration of ethanol can be achieved by passing ethanol over a hot aluminum oxide catalyst.
• $CH<em>3CH</em>2OH \rightarrow C<em>2H</em>4 + H_2O$
• Ethene gas is collected by displacement.

Combustion of Alcohols

• Alcohols undergo complete combustion to form carbon dioxide and water.
• Example:
  • $CH<em>3CH</em>2OH + 3O<em>2 \rightarrow 2CO</em>2 + 3H_2O$
• Denatured alcohol is a useful portable fuel (e.g., for camping stoves) and is also used as a solvent.
• Denatured alcohol is ethanol made toxic and undrinkable by adding chemical additives.
• A traditional additive was methanol, forming methylated spirits (meths): 90% ethanol and 10% methanol.

Reaction with Sodium

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Forming Halogenoalkanes from Alcohols

• Primary, secondary, and tertiary alcohols all react with phosphorus(V) chloride to form a chloroalkane.
• Example:
  • $CH<em>3CH</em>2OH + PCl<em>5 \rightarrow CH</em>3CH<em>2Cl + POCl</em>3 + HCl$
• Adding solid phosphorus(V) chloride to an alcohol at room temperature produces white HCl fumes and the chloroalkane.
• This reaction can be used as a test for alcohols (the OH group) and as a method for producing halogenoalkanes.

Alcohol Reactions

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