Alcohols and Analytical Techniques
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How do we make an alkane from an alkene?
Hydrogenation with H2 + a nickel catalyst
How do we make a haloalkane from an alkane?
Free radical substitution with a halogen in the presence of UV light
How do we make a haloalkane from an alkene? (2 methods)
• Electrophilic addition using hydrogen halide • Electrophilic addition with halogen molecule
How do we form alcohols from alkenes?
Hydration with water, using high temperatures with an acidic catalyst
How do we form alkenes from alcohols?
Dehydration in the presence of a concentrated acidic catalyst
How do we produce an alcohol from a haloalkane?
Hydrolysis (nucleophilic substitution) with OH- or NaOH under reflux
How do we produce a haloalkane from an alcohol?
Nucleophilic substitution with hydrogen halide/sodium halide+acid
What is the product of oxidation of primary alcohols under distillation?
Aldehyde
What is the product of oxidation of primary alcohols under reflux?
Carboxylic acid
What is the product of oxidation of secondary alcohols under reflux?
Ketone
What is the product of oxidation of tertiary alcohols under reflux?
n/a
What reactants are required for the oxidation of alcohols?
Potassium dichromate and sulphuric acid
What colour change occurs when potassium dichromate is reduced?
Orange - green
What reaction conditions are required for the formation of an alcohol?
• Water in the gaseous phase • High temperatures • Concentrated acidic catalyst
Why are the boiling pints of alcohols higher than other organic compounds?
• There are hydrogen bonds between the hydrogen atoms and lone pairs of oxygen atoms on another molecule. • These come in addition to instantaneous dipole-dipole forces. • So intermolecular bonding is much stronger in alcohols.
How is boiling point affected by chain length?
As chain length increases, the number of atoms increases, so more energy is required to overcome stronger London forces.
Why do alcohols dissolve in polar solvents?
Alcohols are polar molecules, and like dissolves like, as atoms with opposite partial charges attract.
Why does solubility decrease with increased chain length?
Only the single -OH group of the alcohol can form hydrogen bonds. The longer carbon chain does not form hydrogen bonds. So the influence of the single hydrogen bond decreases.
Why does solubility of alcohols increase with chain length for non-polar solvents?
The longer carbon chain forms stronger intermolecular bonds with solvent molecules. This weakens the lattice which breaks down more readily, and bonds form more easily between alcohol and solvent molecules.
How are alcohols classified?
They are classified as primary, secondary or tertiary, depending on the number of alkyl groups a carbon attached to the -OH is attached to.
What is the name of the process used to form alcohols? What conditions are required?
Electrophilic addition (hydration) of alkenes. H2O forms partial charges to produce a mixture of major and minor alcohol products. This process requires steam, high temps., and an acid catalyst
What is the name of the process used to form an alkene from an alcohol?
This is a nucleophilic elimination. It requires a source of H+ ions (acid catalyst).
What is the oxidising agent required for the oxidation of alcohols?
Acidified potassium dichromate
Why do we react sodium halides with sulphuric acid during nucleophilic substitution reactions?
Provides H+ ions to protonate the -OH group, making it a better H2O* leaving group and thus leaving the carbon atom more susceptible to nucleophilic attack.