Chemistry Evaluative

Primary alcohol

In a primary alcohol, the carbon which carries the -OH group is only attached to one alkyl group.

Secondary alcohol

In a secondary alcohol, the carbon with the -OH group attached is joined directly to two alkyl groups, which may be the same or different.

Tertiary alcohol

In a tertiary alcohol, the carbon atom holding the -OH group is attached directly to three alkyl groups, which may be any combination of same or different.

Carboxylic acids can be identified by using potassium carbonate

Observations:

• Fizzing
• Solid dissolves 

Detecting a carbonyl group

• use 2,4-DNPH (Bradys reagent)
• If added to an aldehyde or ketone a yellow or orange precipitate will be formed.
• confirms the presence of a C=O bond.

Aldehyde or Ketone?

• Tollens reagent added
• Oxidise aldehydes to carboxylic acids
• Aldehyde = silver precipitate / silver mirror
• Ketone = no reaction

Primary alcohols

Alcohol to aldehyde

CH3CH2OH + [O] --> CH3CHO + H2O

Aldehyde to carboxylic acid

CH3CH2OH + 2[O] --> CH3COOH + H2O

Secondary alcohols

Alcohol to ketone

CH3CHOHCH3 + [O] --> CH3COCH3 + H2O

ORANGE TO GREEN

What is important when carrying out oxidation reactions to ensure correct observations?

Excess of reagent to ensure you observe the full colour change or reaction that is taking place.

Acid hydrolysis of esters:

• Heated under reflux with dilute sulfuric acid or dilute hydrochloric acid.

CH3COOCH2CH2CH3 + H2O --> CH3COOH + HOCH2CH2CH3

Ester + Water --> Carboxylic acid + Alcohol 

Alkaline hydrolysis of esters: 

• Sodium hydroxide is refluxed with the ester.

CH3CH2COOCH2CH3 + NaOH --> CH3CH2COO-Na+ + HOCH2CH3

Ester + Sodium hydroxide --> sodium salt + alcohol