alcohols Flashcards
What are alcohols
Molecules which have an -OH functional group
Fermentation of ethanol
Glucose -> ethanol + carbon dioxide
Conditions: yeast, 30-40 degrees C and no air.
Yeast catalyses the reaction, optimum temp is 38 degrees C, no air to prevent further reaction
+ glucose is renewable and cheap
- batch process therefore slow, expensive not pure production of ethanol
Hydration of ethene
Ethene + water -> ethanol
Hydration/addition reaction
Conc H3PO4 or conc H2SO4
High temp and pressure - 300 degrees C and 70atm
+faster, pure production and continuous
- expensive and non renewable source
How is Ethanol a biofuel and carbon neutral
Biofuel is fuel produced from plants.
Ethanol is produced from glucose which comes from photosynthesis of plants.
Fermentation releases 2CO2
Combustion of ethanol releases of 4CO2
Photosynthesis takes in 6 CO2
Input and output of carbon dioxide is equal
No net release of carbon dioxide.
How can ethanol be considered not carbon neutral
Reactions don’t take into account CO2 released during travel and machinery processes.
Different types of alcohols
Primary, secondary and tertiary
What is a primary alcohol
Primary alcohols when the 1 carbon is attached to the carbon adjoined to the oxygen of the OH group
What is a secondary alcohol
When 2 carbons are attached to the carbon adjoined to the oxygen of the OH group
What is a tertiary alcohol
When 3 carbons are attached to the carbon adjoined to oxygen of the OH group
Oxidation of alcohols
Primary: alcohol - aldehyde - carboxylate acid
Secondary: alcohol - ketone
Tertiary: no oxidation
Oxidising agent and colour change
[O] = potassium dichromate / K2Cr2O7
Orange to green when oxidation occurs
Oxidation of a primary alcohol e.g. ethanol
Ethanol + [O] -> ethanal + water
C2H5OH + [O] -> CH3CHO + H2O
Heat and distill
Ethanal + [O] -> ethanoic acid
CH3CHO + [O] -> CH3COOH
Heat under reflux
Potassium dichromate solution and dilute H2SO4
Why is reflux used in the oxidation of alcohols to produce a carboxylic acid
Ensures carboxylic acid is produced as any vapour will condense back into the flask and be reoxidised.
Oxidation of a secondary alcohol e.g. propanol
Propanol +[O] -> propanone
Heat under reflux
Reagent: potassium dichromate solution and dilute sulphuric acid
Why are tertiary alcohols unable to be oxidised
No hydrogen bonded to the carbon adjoined to the oxygen of the OH group.
The oxidising agent would remove the hydrogen, oxidising the alcohol
