3.3.5 - Alcohols Flashcards
Dehydration of alcohols products
Alcohol = alkene + water
Dehydration reaction catalysts
Conc Sulfuric/Phosphoric acid
Describe an elimination (dehydration) reaction
- Lone pair on oxygen attaches to H+
- Oxygen takes bond from C-O bond, forms carbocation
- Adjacent hydrogen leaves to carbon form double bond
- Products = alkene + water + H+
Cyclohexene preparation step 1
- Add conc sulphuric acid and cyclohexanol to the round bottom flask + bumping granules
Cyclohexene preparation steps 2-3
- Use heating mantle to wam reactants
- Chemicals with less than 83C boiling point evaporate and condense through the condenser
Cyclohexene preparation steps 4-5
- Put products into separating funnel and add water
- 2 layers form, drain off the bottom layer (water + soluble impurities
Cyclohexene preparation step 6
- Add cyclohexene + calcium chloride (drying agent) to round bottom flask, invert for 20-30 min
Hydration reaction conditions (3)
- H2SO4 + steam
- 300 degrees
- 30 atm
Hydration of alkenes to give alcohol reaction mechanism
- C=C attracts H+, breaks the double bond, forms carbocation
- +OH2 joins carbocation via lone pair
- OH2 loses H, forms alcohol + H+
Fermentation equation (2)
Glucose = Ethanol + carbon dixide
C6H12O6 = 2 C2H5OH + 2 CO2
What is fermentation used for?
Used to obtain pure ethanol, alternative to crude oil
Optimum conditions for fermentation
- Anaerobic condtions
- Yeast catalyst
Fermentation advantages (2)
- Cheap, little equipment needed
- Uses renewable resources
Biofuel advantages (2)
- Renewable
- Carbon neutral (CO2 released is absorbed by sugar cane)
Biofuel disadvantages (2)
- Expensive to convert engines
- Land usage = food shortages?
Why are biofuels carbon neutral?
Use up same amount of CO2 to make compared to how much is produced on combustion
Why are biofuels not necessarily carbon neutral?
Fossil fuels burned to transport biofuel, make fertilisers, machine harvesters.
Test for primary/secondary alcohols
Use acidified potassium dichromate (Cr2O7) - turns orange to green.
Fehling’s test for aldehydes
Aldehydes turn blue solution to brick red precipitate
Ketones = no change
Tollens reagent test
Add silver nitrate + warm solution
Aldehydes = silver mirror
Primary alcohol oxidation product(s)
Becomes aldehyde then carboxylic acid (under reflux)
Secondary alcohol oxidation product
Becomes ketone (under reflux)
How to figure out if a alcohol is primary, secondary, or tertiary?
Look at the number of carbons attached to the carbon with the OH group
Tertiary alcohols oxidation
Do not oxidise, not affected by acidified potassium dichromate
