Alcohols Flashcards
(15 cards)
Primary, secondary and tertiary alcohols
Primary - The OH group is on a carbon with one alkyl group
Secondary - The OH group is on a carbon with two alkyl groups
Tertiary - The OH group is on a carbon with three alkyl groups
Combustion of alcohols (equation and details)
- Alcohols burn in excess oxygen to product CO₂ and H₂O
- Burn readily with a light blue flame
CH₃OH(l) + 1.5O₂ –> CO₂ + 2H₂O
Chlorination of alcohols (producing chloroalkanes)
Alcohols can be chlorinated by HCl or PCl₅
Using PCl₅:
ROH + PCl₅ –> RCl + HCl + POCl₃
Using HCl:
ROH + HCl –> RCl + H₂O
(Tertiary alcohols react the fastest with HCl)
Bromination of alcohols (producing bromoalkanes)
- An inital reaction needs to take place for HBr to be produced
Initial reaction: KBr + H₂SO₄ –> HBr + KHSO₄
(A 50% conc sulfuric acid is used)
Bromination reaction: HBr + ROH –> RBr + H₂O
Iodination of alcohols (producing iodoalkanes)
- Phosphorus triodide (red phosphorus - PI₃) is used, produced in situ
How PI₃ is made: 2P + 3I₂ –> 2PI₃
Iodination reaction: SP + 3I₂ –> 2PI₃
Dehydration of alcohols/forming alkenes by elimination (eliminating water)
- Uses an acid catalyst (either H₂SO₄ or phosphoric acid, H₃PO₄)
Alcohol –> alkene + H₂O
ex. C₂H₅OH –> C₂H₄ + H₂O
How many different alkenes are produced by the dehydration of non-primary alcohols?
Non primary alcohols can produce 3 different alkenes
The double bond (made when the alkene forms) can form either side of the carbon that had the OH group
E/Z isomerism forms two different versions of the same positioned alkene
Reaction of alcohols with potassium dichromate (IV) (oxidising PRIMARY alcohols)
Primary alcohols are oxidised to an aldehyde and then with excess oxidising agent to a carboxylic acid
Primary alcohol —(distillation)–> aldehyde —(heating under reflux)–> carboxylic acid
Reaction of alcohols with potassium dichromate (IV) (oxidising SECONDARY alcohols)
Secondary alcohols are oxidised to ketones only.
Secondary alcohol —(heating under reflux)–> ketone
Why can tertiary alcohols not be oxidised under normal conditions?
The carboon with the OH group must also have a hydrogen atom attached to be oxidised
Explain the process of heating under reflux
What is the point of heating under reflux:
it enables you to heat a reaction mixture for a long time without losing volitile substances
How it works:
* Condenser is placed vertically above the reaction flask
* As vapours rise, they cool and condense back into the liquid, dripping back into the flask
Purpose:
ensures the reaction goes to completion without loss of reactants or products due to evapouration
Explain the process of extraction with a solvent in a seperating funnel
- A separating funnel is used to extract a solute from one solvent into another solvent in which it is more soluble
- the two solvents form seperate layers due to immiscibility
- mixture is shaken and allowed to settle
- the layer containing the desired solute is then run off
Explain the process of distillation
- Heat the mixture in a flask
- the component with the lowest boiling point vapourises first
- the vapour passes into a condenser, cools and condenses
- the condensed liquid is collected in a beaker
Explain the process of drying with an anhydrous salt
- A drying agent is added (MgSO₄ or CaCl₂) to the organic solution
- swirl and observe: the drying agent will clump if water is present
- keep adding the drying agent until there is no more clumping
- allow to stand
- seperate organic liquid by filtration
Explain the process of boiling temperature determination
- using a round-bottom flask with the liquid sample, connected to a condenser and thermometer positioned at the flask neck
- heat the flask
- when the liquid starts to boil, and the vapours rise and pass the thermometer, record the temperature
