Alcohols and Oxidation of Alcohols Flashcards
what are the 3 types of alcohols
primary, secondary and tertiary
what does R mean?
repeating carbon chain
position of OH in primary alcohol
joined to the end of a carbon chain (attached to carbon with 1 other carbon bonded
position of OH in secondary alcohol
joined to an intermediate carbon atom (attached to a carbon with 2 other carbons bonded)
position of OH in tertiary alcohol
joined to an intermediate carbon which also has a branch attached (attached to a carbon with 3 other carbons bonded)
alternative definition of oxidation (not loss of electrons)
a loss of H or gain of oxygen (increasing oxygen to hydrogen ratio)
oxidation of primary alcohol
aldehyde and carboxylic acid
oxidation of secondary alcohol
ketone
oxidation of tertiary alcohol
no products formed
aldehyde functional group and location
carbonyl C=O at start-end
general formula of aldehydes
CnH2nO
name of aldeydes
- ends in ‘al’
2. does not contain a number to show where the functional group is because C=O is always at start
ketone functional group and location
carbonyl C=O located in the middle
general formula of ketones
CnH2nO n=3 or more
name of ketones
- ends in ‘one’
2. position of C=O functional group must be included in the name
oxidation of ethanol experiment
- to facilitate oxidation reaction, an oxidising agent is used
- superwool soaked in ethanol
- copper oxide black –> orange/brown
- damp pH paper turns red (ethanoic acid)
reduction of alcohols
gain of H/loss of O
other way round from oxidation eg carboxylic acid –> aldehyde
how to distinguish between aldehydes
and ketones
aldehydes can be oxidised to carboxylic acids but ketones cannot be oxidised further
therefore you can tell them apart by oxidation
3 oxidising agents (tests) used to distinguish between aldehydes and ketones are:
- acidified potassium dichromate solution
- Fehling’s solution (aka Benedict’s solution)
- Tollen’s Reagent
Tollen’s Reagent
colourless –> formation of a silver mirror
tollen’s made from silver ions which are reduced Ag+ (aq) +e- –> Ag (s)
Fehling’s solution
blue –> brick red precipitate
Fehling’s made from copper oxide CuO Cu2+(aq) + 2e- –> Cu(s)
Acidified potassium dichromate
orange –> green
Cr2O72- + 14H+ + 6e- –> 2Cr3+ + 7H2O
acidic conditions to provide H+ ions
why would you not want something to oxidise?
if flavour/aroma molecules (aldehydes) are oxidised further they can change the taste and smell of the products
eg oxygen reacts with edible oils giving food a rancid flavour
what are antioxidants?
molecules which will prevent oxidation reactions taking place
they are easily oxidised in place of the compounds they have been added to
can be identified as the substance being oxidised in a redox reaction
