Alcohols Flashcards
Alcohols are a family of….
molecules that contain the hydroxyl functional group, -OH
general formula
CnH2n+1OH
what does the complete combustion of alcohol produce
carbon dioxide and water
Three ways to convert alcohols to halogenoalkanes
Chlorination
Bromination
Iodination
replacing the hydroxyl group in an alcohol molecule with a halogen atom
explain chlorination
Phosphorus(V) chloride is added to alcohol at room temperature
phosphoryl chloride and hydrogen chloride
CH3CH2CH2OH + PCl5 → CH3CH2CH2Cl + POCl3 + HCl
Chlorination of tertiary alcohols can be carried out in a different way by mixing (shaking) with hydrochloric acid at room temperatureThis reaction will not occur with primary or secondary alcohols.
(CH3)3CCl + H2O
explain bromination
warmed mixture of potassium bromide and 50% concentrated sulfuric acid with the reacting alcohol
2KBr + H2SO4 → K2SO4 +2HBr
CH3CH2CH2CH2OH + HBr → CH3CH2CH2CH2Br + H2O
explain iodination
using a mixture of red phosphorus and iodine with the alcohol whilst heating under reflux
2P + 3I2 → 2PI3
3C2H5OH + PI3 → 3C2H5I + H3PO3
formation of phosphoric acid
what is dehydration
done by heating the alcohol with concentrated phosphoric acid
similar to the elimination reaction of a halogenoalkene
The OH group and hydrogen of adjacent carbons are removed forming a C=C bond
CH3CH2OH → CH2=CH2 + H2O
What can primary alcohols oxidise to form
form aldehydes which can undergo further oxidation to form carboxylic acids
Secondary alcohols can be oxidised to form
ketones
what do tertiary alcohols form when oxidised
do not undergo oxidation
what are the oxidising agents of alcohols
Acidified potassium dichromate(VI), K2Cr2O7
what happens to dichromate ions when alcohols are oxidised
When alcohols are oxidised the orange dichromate ions (Cr2O72-) are reduced to green Cr3+ ions
what happens when primary alcohol is added to oxidising agent and warmed
The aldehyde product has a lower boiling point than the alcohol reactant so it can be distilled off as soon as it forms
If the aldehyde is not distilled off, further refluxing with excess oxidising agent will oxidise it to a carboxylic acid
what about ketone when distilling off
Since ketones cannot be further oxidised, the ketone product does not need to be distilled off straight away after it has been formed
formula for carboxylic acid
CnH2n+1COOH
formula for aldehydes
CnH2n+1CHO
Ketone formula
CnH2nO
how can you determine -OH group
If you add PCl5 to an unknown liquid the evolution of steamy fumes (HCl gas)
how can you determine the presence of an aldehyde group
oxidising agent Fehling
should go to red precipitate otherwise remain blue
what is Feeling’s solution
alkaline solution containing copper(II) ions which act as the oxidising agent
what happens when feelings solution is warmed with aldehyde
aldehyde is oxidised to a carboxylic acid and the Cu2+ ions are reduced to Cu+ ions
The carboxylic acid formed will be neutralised to a carboxylate ion (the -COOH will lose a proton to become -COO- )
The carboxylate ion (-COO-) will form a salt with a positively charged metal ion such as sodium (-COO-Na+)
clear blue solution turns opaque due to the formation of a red precipitate, copper(I) oxide
Can you do Fehling’s solution on ketone
Ketones cannot be oxidised and therefore give a negative test when warmed with Fehling’s solution
What is Tollens’ reagent
aqueous alkaline solution of silver nitrate in excess ammonia solution
what happens when Tollens is warmed with an aldehyde
the aldehyde is oxidised to a carboxylic acid and the Ag+ ions are reduced to Ag atoms
In the alkaline conditions, the carboxylic acid will become a carboxylate ion and form a salt
The Ag atoms form a silver ‘mirror’ on the inside of the tube
two techniques for oxidising aldehydes
Heating under reflux
Distillation with addition
what is heating under reflux
Producing a carboxylic acid for a primary alcohol
Producing a ketone for a secondary alcohol
any products of oxidation remain in the reaction mixture
Products which boil off condense in the vertical condenser then return to the heating flask
what does condenser help with
ensure vapour condense and return to the flask for further heating.
what is distillation with addition
when we do not want to complete oxidation
To obtain an aldehyde rather than carboxylic acid for primary alcohol
what is simple distillation
separate a liquid and soluble solid from a solution
or a pure liquid from a mixture of liquids
what is fractional distillation
separate two or more liquids that are miscible with one another
what is solvent extraction and conditions
This method uses a solvent to remove a desired organic product from a reaction mixture
Immiscible (does not mix) with the solvent containing the desired organic product
The desired organic product should be much more soluble than the added solvent
process of solvent extraction
Place the reaction mixture in a separating funnel and add the chosen solvent forming a separate layer
Place a stopper in the neck of the funnel and gently shake the contents of the funnel for a while
Allow the contents of the funnel to settle into two layers
Remove the stopper and open the tap to allow the lower layer to drain into a flask
Pour the remaining layer into a clean dry conical flask and add two spatulas of anhydrous magnesium sulfate
This will remove water
It should be added until there is no further clumping and it can then be removed by gravity filtration
explain crystallisation
separate a dissolved solid from a solution, when the solid is much more soluble in hot solvent than in cold
The solution is heated, allowing the solvent to evaporate, leaving a saturated solution behind
The saturated solution is allowed to cool slowly
Crystals begin to grow as solids will come out of solution due to decreasing solubility
The crystals are collected by filtering the solution, they are washed with cold distilled water to remove impurities and are then allowed to dry
how can you test if the solution is saturated after crystallisation
dipping a clean, dry, cold glass rod into the solution
If the solution is saturated, crystals will form on the glass rod
what happens to temperature from impurities
Impurities present in the liquid will raise its boiling temperature
Can you do tollens reagent on Ketones
Ketones cannot be oxidised and therefore give a negative test when warmed with Tollens’ reagent
what is stereoisomerism
compounds with same structural formula but atoms have different arrangement
how to achieve high yield of aldehyde
distill off immediately
give one reason why yield is less than 100%
transfer loss
incomplete reaction
side reactions
6 test for alcohols
reagents and observations
bromine water - orange / yellow / brown solution goes colourless
carboxylic acid and H2SO4 - smell of an ester
acidified potassium manganate - purple to colourless
alkaline potassium manganate - purple to green
neutral potassium manganate - purple to brown
acidified potassium dichromate - orange to green
how can you obtain pure dry sample of cyclohexene
when reacting cyclohexanol with phosphoric acid and this mixture is warmed in water bath for 15 minutes before distilling the mixture of cyclohexene and water
separate cyclohexene from water using separating funnel
IP2 remove the lower aqueous layer because it has a higher density
* IP3 suitable drying agent
* IP4 separate the cyclohexene from the drying agent
* IP5 redistil product
* IP6 collect the distillate boiling over between 80 and 86 °C to
collect the pure cyclohexene
how can alcohol be converted to nitrile
via intermediate product called
1-bromobutane
halogenoalkane is heated under reflux with a solution of sodium or potassium cyanide in ethanol. The halogen is replaced by a -CN group and a nitrile is produced
why do anti bumping granules give a smoother boil
because it provides a surface area for bubbles to form and prevent large bubbles from forming
hydrogen bromide plus alcohol
what is
cooling a mixture
antibumping granules
heating under reflux used for
cool the mixture because the reaction (with concentrated sulfuric acid /
H2504) is (very) exothermic
anti-bumping granules are added to prevent violent / sudden / localised boiling
to make sure the vapour / gas condenses
Or
to prevent vapour escaping
(1)
describe how to dry the organic layer to prepare for distillation
add magnesium sulfate and leave until solution becomes clear and drying agent dont clump together
