14.2 : Reactions of Alcohols Flashcards

1
Q

What are the reactions alcohols can undergo ?

A

Combustion
Oxidation
Dehydration
Substitution

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2
Q

Describe combustion of alcohols

A

They burn completely in plentiful supply of oxygen to produce carbon dioxide and water.

This is an exothermic reaction, releasing a large quantity of energy in the form of heat. As the number of carbon atoms in the alcohol chain increases the quantity of heat released per mole also increase.

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3
Q

How can alcohols be distilled ? Include catalyst, result, method and any colour changes.

A

If the alcohol is primary.

Dilute sulfuric acid catalyst.

Result = aldehyde

Method :

Gently heat alcohol with acidified potassium dichromate.
Distill aldehyde out of the reaction mixture as it forms ( prevents any further reaction with oxidising agent .

Dichromate ions change colour from orange to green.

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4
Q

How can primary alcohols be refluxed ? Include catalyst, result and method

A

Catalyst = dilute sulfuric acid

Result : carboxylic acid

Method :

Strongly heat alcohol under reflux, with excess acidic potassium dichromate. Heating under reflux ensures that any aldehyde formed in the reaction undergoes oxidation to the carboxylic acid.

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5
Q

How can secondary alcohols be distilled ? Include catalyst, result, method and any colour changes

A

Result : ketones

Catalyst : dilute sulfuric acid

Method :

Strongly heat alcohol under reflux, with oxidising mixture.

Dichromate ions : orange to green

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6
Q

Describe oxidation of tertiary alcohols

A

They do not undergo oxidation reactions.

Acidified dichromate remains orange when added to alcohol.

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7
Q

Define ‘dehydration reaction’

A

Any reaction in which a water molecule is removed from the starting material.

It is a type of elimination reaction.

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8
Q

Describe dehydration of alcohols

A

Product : alkene and water

Catalyst = concentrated sulfuric acid or concentrated phosphoric acid

Method :

Alcohol is heated under reflux in the presence of an acid catalyst.

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9
Q

Describe substitution of alcohols

A

Product : haoalkane

Method :

When the alcohol is heated under reflux with sulfuric acid and a sodium halide, the hydrogen bromide is formed.

This HBr then reacts with the alcohol to produce the haloalkane.

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