Reactions with Alcohols Section 10.4

Combustion of Alcohols Strongly exothermic Amount of energy released increases as you go up the homologous series Amount of CO 2 increases and it is the strength of this bonding that contributes to the exothermic nature

Example Reactions 2CH 3 OH (l) + 3O 2(g) → 2CO 2(g) + 4H 2 O (l) Δ H = -726 kJ mol -1 2C 5 H 11 OH (l) + 10 O 2(g) → 10CO 2(g) + 12H 2 O (l) Δ H = kJ mol -1 Alcohols are less efficient than hydrocarbons

Oxidation Reactions Can be viewed as the loss of H Different products for primary, secondary, and tertiary alcohols Most common oxidizing agent used is acidified potassium (VI) dichromate This agent is bright orange and turns dark green when the Cr(VI) is reduced to Cr(III) When writing equations, the oxidizing agent is shown as [O]

Primary Alcohol Oxidized first to an aldehyde Secondly to a carboxylic acid See example reactions on the board

Obtaining the Aldehyde Aldehydes have a lower boiling point than either alcohols or carboxylic acids (no H- bonding with each other) Excess alcohol over the oxidizing agent will favor production of the aldehyde Process of distillation is used

Obtaining the Carboxylic Acid Have to leave the aldehyde in contact with the oxidizing agent for a prolonged period Excess oxidizing agent will favor production of the carboxylic acid Reflux apparatus is used

Reflux Apparatus

Secondary Alcohols Have only a single H attached to the carbon with the hydroxyl group There is only one product possible: a ketone See the board for example reaction

Tertiary Alcohols Have no H atoms attached to the carbon atom with the hydroxyl group Are not easily oxidized No color change when mixed with acidified potassium (VI) dichromate

Determine if an Aldehyde or Ketone have been Produced Standard test is to react the chemical with 2,4-dinitrophenylhydrazine solution Both aldehydes and ketones form orange cystalline precipitates Melting point of the precipitate can be found and used to identify a particular ketone or aldehyde Works because both functional groups contain a C=O

Differentiate Between an Aldehyde or a Ketone Aldehydes can be oxidized while ketones cannot 2 common chemicals are used as mild oxidizing agents Fehling's solution produces an orange-brown precipitate with aldehydes or carboxylic acids Tollen's reagent produces a “silver mirror” effect on the inside of a test tube containing an aldehyde

Test for Aldehydes Fehlings SolutionTollen’s reagent