WM Flashcards
5What can primary alcohols be oxidized to?
Aldehydes
And then carboxylic acids
What can secondary alcohols be oxidized to?
Ketones
Using acidified potassium dichromate
The orange dichromate ion is reduced to the green chromium (III) ion
Heat under reflux
What can tertiary alcohols be oxidized to?
No reaction
How to make aldehyde
Acidified potassium dichromate
Heat
Distillation apparatus
The aldehyde boils at a lower temperature than the alcohol so evaporates and distills off
How to make carboxylic acid
Heat primary alcohol under reflux with excess acidified potassium dichromate
What does it mean to heat under reflux?
To heat without loss of products or reactants
How to make a ketone
Heat under reflux with acidified potassium dichromate
Dehydration of alcohols to form alkenes
Alcohol vapour is passed over a catalyst of aluminium oxide heated by bunsen burner
or can reflux ethanol with excess conc sulfuric acid at 170c. The ethene produced is then collected over water - this is an elimination reaction
What is an elimination reaction
Where a small group of atoms break away from a larger molecule. The group is not replaced by anything else
Alcohol + carboxylic acid –>
Esters
Heat carboxylic acid with an alcohol in the presence of an acid catalyst
Called esterification reaction
Concentrated sulfuric acid or hydsrocholoric acid
Alcohols and acid anhydrides form…
Esters
+ carboxylic acid
Alcohols reaction with halide ion containing compounds
In a substitution reaction
The hydroxyl (-OH) group is replaced by the halide so the alcohol becomes a haloalkane
Test for phenols
Iron (III) chloride solution
Shake
Turns purple
What functional groups does a phenol contain?
Benzene ring and -OH group
Number the carbons from the one with the -OH group
Phenols reaction with strong alkalis
Phenols are weak acids
They dissolve a little bit in water to form a phenoxide ionand a H+ ion so the solution formed is weakly acidic
Phelos react with alkalis to produce salt and water
Pheonls don’t react with carbonate solutions as its not strong enough tore move the hydorgen ion from the phenol
Carboxylic acids react with alkalis and cabonates so a good way to tell apart - giving of CO2 gas
Volatile liquids can be purified by redistillation
After distillation, the product will probably still contain impurities
If product and impurities have different boiling points redistillation can be used to separate them.
Use distillation apparatus but this time heat the impure product instead of the reaction mixture
When the liquid boils place a flask at the open end of the condenser to collect the pure product
When the thermometer shows a change in temperature a different liquid will be delivered
Why is the choice of solvent important
Solid must be very soluble in hot solvent but nearly insoluble when the solvent is cold.
If the product is too soluble in the cold solvent most of it will stay in the solution even after cooling. So when you filter it, you’ll lose must of your product, giving a very low yield. If it isn’t soluble enough in the hot solvent you won’t be able to dissolve it at all
Measuring melting point is a good way to determine purity
Determine the melting point of an organic solid
Pack a small sample of the solid into glass capillary tube inside the heating element
Increase temperature slowly until the sample turns from solid to liquid
Compare melting point of a substance to those in data books
Impurities in the sample will lower the melting point and increase the melting range
Filtration is used to isolate solid organic products
Organic solids can be purified by recrystallisation
As the solution cools the solubility of the product falls. It reaches a point where it can’t stay in solution and forms crystals
1) Add very hot solvent to the impure solid until it just dissolves. This gives a saturated solution of the impure product
2) Allow solution to cool slowly. Crystals of the product will form
3) The impurities stay in solution
4) Remove the crystals by filtration and wash with ice cold solvent. The crystals then need to be dried
Phenol + acid anhydride =
Just like other alcohols, phenols react with acid anhydrides to from an ester and carboxylic acid
Though unlike other alcohols, they will not react with carboxylic acids to form an ester
What does it mean to distill a compound?
To separate substances based on boiling point
The substances will evaporate out in order of increasing boiling point
If the boiling point of the pure product is known you can use the thermometer to find out when it’s evaporating and therefore when to collect it
How are volatile liquids purified after distillation?
After distillation the product will probably still contain impurities
Redistillation can be used to separate the pure and impure products if they have different boiling points
Reheat the impure product
When the liquid you want boils, place a flask at the end of the condenser and collect the pure product
Separation method
If a product is insoluble in water then separation can be used to dissolve soluble impurities
Pour the mixture into a separating funnel and add water
Shake the funnel and allow products to settle
The organic layer is less dense than the aqueous layer so will float on top
Soluble impurities will have dissolved in the lower aqueous layer
Open the stopper and run of the aqueous layer
How to dry the purified product
If separation was used to purify the product it will contain trace amounts of water
Add an anhydrous salt (e.g. calcium chloride or magnesium sulfate)
The salt is a drying agent and binds to water to become hydrated
You know all the water has been removed when the mixture is swirled and appears cloudy
The mixture is then filtered to remove the solid drying agent
How do you isolate solid organic products
Filtration
Pour the reaction into a Buchner funnel with filter paper lining the bottom
The reduced pressure inside the flask caused by the removal of air through the vacuum line will force the liquid through the funnel leaving the solid product on the filter paper
What is infrared spectroscopy
A beam of IR radiation is passed through a sample
It’s absorbed by the covalent bonds which increases their vibrational energy
Different bonds absorb different frequencies
3 aspects of green chemistry
Using renewable resources - using renewable raw materials and renewable energy sources, reducing energy usage where possible
Minimise waste and use biodegradable or recyclable products - the atom economy should be as high as possible, use of catalysts, chemical reactions should be designed to be biodegradable, removal of unnecessary steps
Ensuring all the chemicals and processes involved are as safe as possible - non-toxic to the environment, minimise the risk of chemical spills, explosion and fires. Technologies for monitoring processes should be improved
The colour change
Orange to green
As Cr2O72- is reduced to the Cr3+ ion
Testing for an aldehyde
Tollen’s reagent
Positive result silver mirror
OR
Fehlings solution
Contains complex Cu3+ ions which are reduced by the aldehyde to form red Copper(II) oxide
Ketones don’t react with fehling’s
