alcohols Flashcards
(21 cards)
how do you name alcohols?
- have the ending -ol and the the position number for the oh group is added between the name stem and the -ol
- if the compound has another functional group than hydroxy- can be used.
-if there are two or more -OH groups then di- tri- are used. - add the e onto the stem name though
What are the bond angles in alcohols?
- H-C-H And C-C-O are 109.5 because there are 4 bonding pairs
- H-O-C is 104.5 because there are 2 bonding pairs of electrons
what are the boiling points of alcohols?
- low boiling points due to their ability to form hydrogen bonds between alcohol molecules.
what are the different types of alcohols?
-Primary alcohols are alcohols where 1 carbon is attached to the carbon adjoining the oxygen
- Secondary alcohols are alcohols where 2 carbons are attached to the carbon adjoining the oxygen.
- Tertiary alcohols are alcohols where 3 carbon are attached to the carbon adjoining the oxygen.
what is potassium di chromate?
Potassium dichromate K2Cr2O7 is an oxidising agent
that causes alcohols to oxidise
What happens in the partial oxidation of primary alcohols with potassium dichromate?
-a primary alcohol is turned into an aldehyde
- the orange dichromate ion reduces to the green cr3+
CH3CH2CH2OH + [O]
(propan-1-ol)
+ [O] CH3CH2CHO+ H2O (propanal)
what are the conditions for the oxidation of primary alcohols?
- use a limited amount of dichromate , warm gently and distil out the aldehyde as it forms.
what happens in the distillation of primary aldehydes?
- this is used as a separation technique to separate an organic product from its reacting mixture.
- you only collect the distillate at the approximate boiling point of the desired aldehyde and not higher.
what happens in the full oxidation of primary alcohols?
- A primary alcohol turns into a carboxylic acid
- C3H7OH (propan-1-ol) + [o] -> C2H5COOH (propanoic acid)
- The orange dichromate ion reduces to the green cr3+ ion
what are the conditions needed for the full oxidation of primary alcohols?
- an excess of potassium dichromate and heat under reflux
What is reflux?
- Reflux is used when heating organic reaction mixtures for long periods of time. It prevents organic vapours from escaping by condensing them back to liquids.
- Anti-bumping granules are added to prevent uneven boiling.
What happens in the oxidation of secondary alcohols?
- The secondary alcohols are made into ketones under reflux with potassium dichromate and dilute sulfuric acid.
- e.g propan-2-ol -> propanone
What happens in the oxidation reaction of tertiary alcohols?
They cannot be oxidised by potassium dichromate because no hydrogen atom is bonded to the carbon with the —OH group.
How do you distinguish between aldehydes and ketones?
- Tollens reagent. and Fehling’s solution
What happens in the reaction with Tollens reagent?
- Aqueous ammonia and silver nitrate are heated gently with the substance. Aldehydes are only oxidised by Tollens reagent into a carboxylic acid, the silver ions are reduced to silver atoms
- A silver mirror will form
- Ketones result in no visible change.
What happens in the reaction with Fehling’s solution?
- Blue Cu2+ ions are heated gently with the substance.
Fehlings oxidises only aldehydes into carboxylic acid. The copper 2 ions are reduced to copper 1 oxide, and the solution turns from blue to red.
How do you test for a carboxylic acid?
Add sodium carbonate. It will fizz and produce carbon dioxide.
How do you reduce carbonyls?
- aldehydes and ketone can be reduced to primary and secondary alcohols using reducing agents such as sodium borohydride and lithium aluminium hydride
- we show reducing agents using the symbol [H]
What happens in the elimination reactions of alcohols?
- dehydration
- The lone pair on the oxygen will attach to the H+ ion, which comes from the acid catalyst
- An oxygen intermediate is formed with a positive charge, oxygen pulls electrons in the C-O bond strongly to break the bond, leaving an unstable carbonation intermediate
- The carbocation loses a H+, and the electrons in C-H move to form a CC bond
What happens in the dehydration of non-primary alcohols?
- The double bond can be formed on either side of the carbon that has the -OH hydroxyl group.
How is the dehydration of alcohols done?
- Alcohol vapour is passed over a hot (600 °) catalyst of aluminium oxide powder.
- Excess hot, sulfuric acid is used as a catalyst.
- Alkenes produced by this method can also be used to produces monomers for polymerisation without using monomers from crude oil.
