Alcohols Flashcards
What is the functional group of alcohols?
OH - hydroxyl group
What is an alcohol called when there are 2 hydroxyl groups present?
A diol
When is an alcohol classified as primary?
When the C bonded to the OH is attached to one other carbon atom or alkyl group
(same with secondary and tertiary)
What must happen for an alcohol to undergo combustion and what does it produce?
Must react with oxygen in the air and be ignited - produces CO2 and H2O
How do we carry out the chlorination of on alcohol?
Phosphorus (V) chloride is added resulting in a vigorous reaction
What conditions does chlorination occur under?
Room temperature - no heating needed
How is chlorination used as a qualitative test for the presence of an OH group?
If you add PCl5 to an unknown liquid the evolution of steamy fumes (HCl) is evidence for the presence of the OH group
What is formed in the chlorination of alcohols?
The halogenoalkane and 2 inorganic products - Phosphoryl chloride and Hydrogen chloride
What is the formula for phosphoryl chloride?
POCl3
How can the chlorination of tertiary alcohols also be carried out?
By mixing (shaking) the alcohol with HCl acid at room temperature
How is bromination carried out?
Using a warmed mixture of potassium bromide and 50% concentrated sulfuric acid with the reacting alcohol
Why do we not use more concentrated sulfuric acid in bromination?
It would oxidise bromide ions to bromine resulting in different products
What is the first reaction in bromination?
The inorganic reactants react first to form HBr and Potassium sulfate
What is the second reaction in bromination?
The HBr from the first reaction reacts with the alcohol to form the halogenoalkane and water
How is iodination carried out?
Using a mixture of red phosphorus and iodine with the alcohol
What conditions is iodination carried out under?
The mixture is heated under reflux
What is the first reaction in iodination?
The inorganic reactants react to form phosphorus (lll) iodide
2P + 3I2 = 2PI3
What is the second reaction in iodination?
The alcohol reacts with the phosphorus iodide to form the halogenoalkane and phosphoric acid
How is dehydration of alcohols carried out?
By heating the alcohol with concentrated phosphoric acid
How is the dehydration of alcohols similar to an elimination reaction?
The OH group and hydrogen of adjacent carbons are removed forming a C=C bond
Why does phosphoric acid not appear in the equation for the dehydration of an alcohol?
The water formed dilutes the concentrated phosphoric acid
What can primary alcohols be oxidised to form?
Aldehydes
What can aldehydes undergo further oxidation to form?
Carboxylic acids
What can secondary alcohols be oxidised to form?
Ketones
Do tertiary alcohols undergo oxidation?
No
What do the oxidising agents of alcohols include?
Acidified potassium dichromate (VI)
K2Cr2O7
What is the colour of acidified potassium dichromate?
Orange
What does acidified mean in acidified potassium dichromate?
The potassium dichromate is in a solution of dilute acid
What must happen for potassium dichromate to act as an oxidising agent?
It needs to be reduced itself
What does the reduction of potassium dichromate require?
Hydrogen ions - which are produced by the acidic medium
What happens when alcohols are oxidised (colour change)?
The orange dichromate ions (Cr2O7-) are reduced to green Cr3+ ions
How is the oxidation of a primary alcohol carried out?
It is added to the oxidising agent and warmed
Why usually happens to the aldehyde product as soon as it is formed in the oxidation of an alcohol?
It is distilled off
Why can the aldehyde product be distilled off as soon as it is formed in the oxidation of an alcohol?
It has a lower boiling point than the alcohol reactant
What happens if the aldehyde is not distilled off after the oxidation of an alcohol?
Further reducing with excess oxidising agent will oxidise it to a carboxylic acid
Why do ketones not have to be distilled off as soon as it is formed?
Since they cannot be further oxidised
What is the equation of reacting a secondary alcohol with an oxidising agent?
Alcohol + oxidising agent = Ketone + water
How can be the presence of an aldehyde group in an unknown compound be determined?
By the oxidising agents Fehling’s and Tollen’s reagent
What is Fehling’s solution?
An alkaline solution containing copper (ll) ions which act as the oxidising agent
What happens when Fehling’s solution is warmed with an aldehyde?
The aldehyde is oxidised to a carboxylic acid and the Cu2+ ions are reduced to Cu+ ions
What will happen to the carboxylic acid in the alkaline conditions (Fehling’s solution)?
The carboxylic acid will be neutralised to a carboxylate ions - COO-
What will happen to the carboxylate ions (neutralisation with Fehling’s solution)?
It will form a salt with a positively charged metal ion
What colour is Fehling’s solution?
Clear blue
What colour will Fehling’s solution turn when an aldehyde is added?
Turns opaque due to the formation of copper (l) oxide which is a red precipitate
What happens when Fehling’s solution reacts with a ketone?
Ketones cannot be oxidised so there is a negative test
What is Tollen’s reagent?
An aqueous alkaline solution of silver nitrate in excess ammonia solution
What is Tollen’s reagent also called?
Ammoniacal silver nitrate solution
What happens when tollen’s reagent is warmed with an aldehyde?
It is oxidised to a carboxylic acid
The Ag+ ions are reduced to Ag atoms
What happens in the alkaline conditions to carboxylic acid in tollen’s reagent?
They become carboxylate ions and form a salt
What do the Ag atoms form in tollen’s reagent?
A silver mirror on the inside of the tubes
When is heating under reflux used?
When we want full oxidation
Primary alcohol - carboxylic acid
Secondary alcohol - ketone
What does reflux involve?
Heating the chemical reaction for a specific amount of time, while continually cooling the vapour produced back into liquid form, using a condenser
What does the heating under reflux set up mean for the products of oxidation?
They remain in the reaction mixture
When do we use distillation with addition?
When we do not want to complete oxidation
Primary alcohol - aldehyde
How do we carry out distillation with addition?
Only the oxidising agent is heated whilst the alcohol is slowly added
What happens when the aldehyde is formed in the distillation with addition reaction?
It immediately distils off as it has a much lower boiling point than the alcohol used to make it
What is solvent extraction?
This method uses a solvent to remove a desired organic product from a reaction mixture
Can various solvents be used for solvent extraction?
Yes but they must have certain features
What features do solvent used in solvent extraction need to have?
- Immiscible(doesn’t mix) with the solvent containing the desired organic product
- The desired organic product should be much more soluble than the added solvent
What is the 1st step of solvent extraction?
Place the reaction mixture in a separating funnel and add the chosen solvent forming a separate layer
What should one do after adding the solvent to the reaction mixture in solvent extraction?
- Place a stopper in the neck of the funnel
- Gently shake the contents for a while
What should one allow to happen after shaking the contents of the funnel in solvent extraction?
Allow the contents to settle into 2 layers
How should one remove the layer without the organic product in solvent extraction after the contents have settled into 2 layers?
Remove the stopper and open the tap, allowing the lower layer to drain into a flask
What should one do with the remaining layer once the lower layer has been removed in solvent extraction?
Pour it into a clean dry conical flask and add 2 spatulas of magnesium sulfate (it should be added until there is no further clumping)
What will magnesium sulfate do to the organic layer in solvent extraction?
Remove the water
How can magnesium sulfate be removed from the organic layer in solvent extraction?
By gravity filtration
How can the organic compound also be extracted from the organic layer in solvent extraction?
By distillation
How can a liquids purity be measured?
By measuring its boiling point
What will impurities present in liquid do its boiling point?
Raise it
What has been done to the boiling points of pure organic compounds?
Have been measured and are available in data books and online
How do we determine how pure a compound is?
Compare the measured boiling point to its data book value
