Chapter 16 Flashcards
What does Quickfit Appartus include
Round bottom/pear shaped flask Condenser Receiver Screw cap adaptor Still head
How do you heat organic reactions?
They are heated ro overcome the activation energy and increase the rate of reaftion ; heating under reflux is a common procedure used to prepare an organic liquid without boiling off rhe solvent, reactants or products
Equipment needed to heat under reflux
Round bottom/pear shaped flask Condenser Rubber tubinf Stand and clamo Heat source (tripod/bunsen burner/gauze/heating mantle)
When is a water bath used when heating under reflux?
If the reaction can be carried out at less than 100 degrees celsius
Precaution taken when heating flammable liquids?
Heating mantle used so there is no naked flame present ; added level of safety should an apparatus crack
Purpose of anti-bumping granules?
To ensure that the lquid boils smoothly and if the granules are not used rhen large bubbles form at the bottom of the liquid and make the glassware vibrate/jump violently
Purpose of grease?
Applied to the ground-glass joints on the condenser so it comes apart easily at the end ; also provides a good seal by rotating it
Position of equipment when heating under reflux?
Condenser is kept upright with water coming in at the bottom and out through the top ; condenser is clamped loosely as the glass outer jacket is fragile and easily broken. NO STOPPER AT TOP OTHERWISE THERE WOULD BE A CLOSED SYSTEM AND PRESSURE WOULD BUILD UP INSIDE AS THE HEATED AIR EXPANDED - apparatus could explode
Water in the condenser?
Rubber tubing connects inlet of the condenser to the tap and outlet to the sink ; water enter condenser at the bottom and leaves at rhe rop to ensure the outer jacket is full
Purpose of heating under reflux?
Enables a liquid to be continually boiled whilst the reaction takes place - prevents volatile components from escaping and the flask boiling dry as the vapour rises unril it meets the outer jacket of cold water causing it to condense and drip back into the flask
Distillation?
Separates a pure liquid from its impurities - only works due to differences in boiling point. Many reactions may not go to completion/produce by-products as well as the desired product (crude oil needs to be purified)
How is flask in distillation?
Clamped by its neck (pear shaped) and still hesd is connected to the flask. Still head has 2 ground glass joints ; 1 to fit the screw cap adaptor and the other to fit the condenser - SHOULD BE GREASED
Where is second clamp placed in distillation?
Around the receiver adaptor where it is attached to the condenser thus no need to clamp the condenser as it is supported sufficiently at both ends
Where does water enter for distillation?
ALWAYS lowest point ; this is the closest ro receiver adaptor for distillation (inlet)
Once appartus for distillation is set up?
Flask is heated and the mixture starts ro boil - different liquids have different boiling points and most volatile liquids will boil first. They will move out if the flask, condense, become a liquid and fhen drip info the collecting flask
What else can happen when purifiying organic products?
Water may be obtained along with the product - will see two liquid layers inside collection flask ; one the organic layer and the ofher the aqueous/water layer. Easy to separate these two by adding in more water and whichever one gets bigger v aqueous
How to spearate our the two layers?
Ensure tap of separating funnel is closed and add in mixture - then invert to mix and make sure two layers have formed… identify the organic (add more water). Open tap and take off stopper allow lower layer to leave the funnel
Which organic solvents are at bottom?
Dichloromethane
How to get rid of any acidic impurities?
Add aqueous soidum carbknage and shake in separatinf dunnel - acid will react and release CO2 gas ; tap needs to be slowly opened holding it upside down to release any gas pressure and then the aqous sodium carbonate layer is removed. The organic layer is then washed with wayer before running both layers off into two separate flasks
How to remove water in organic product?
Add drying agent ; an anhydrous inorganic salt that readily takes up water to become hydrated.
Common drying agents
CaCl2 - drys hydrocarbons
CaSO4 - general dryinf
MgSO4 - general drying
How to dry an organic loquid?
Add liquid to conical flask and then add drying agent to the liquid. Place a stopper on the flask to prevent product from evaporating away. If solid has stuck together in a lump there is still water pressnt ; add more drying agent until solid is dispersed in the solution as a fine powder
Decant (pour slowly) into another container and if liquid is clear then NO MORE WATER
Purpose of redistillation?
To get rid of any impurities which have very close boiling points - distillation apparatus is set up again - this time to only collect the product with the boiling point you are trying to make - NARROWER THE boiling range, the purer the product (now have separated product from impurities)
Ester funcyional group
C=O and same carbon attached to single O which is attached to another alkyl group
Organic synthesis
Preparation of complex molecules from simple starting ones
Alkane -> Haloalkane
UV radiation required for radical substitution - homolytic fission occurs forming halogen radicals
CH4 + Br. -> .CH3 + HBr
.CH3 + Br2 -> CH3Br + Br.
LIMITATION IS FURTHER SUBSTITUTION/AT DIFFERENT POINTS
Alkene -> alkane
H2 and Nickel Catalyst at 423 K
Hydrogenation
Addition reaction - saturated product
Each double bond = 1 H2 molecule
Alkene -> Haloalkane
Hydrogen halide
Electrophilic addition (can also just be bromination for example)
Unsymmetrical reactants thus two prosucts can be formed - major or minor
Major is when carbocation created is the more stable out of the two carbons in C=C - Halogen attaches itself to carbon with most alkyl groups attached to it
Occurs at room temperature
Alkene -> alcohol
Steam (H2O (g)) in the presence of phosphoric acid catalyst H3PO4
Electrophiloc addition - major minor products with OH bonding to most stable carbocation
Haloalkane -> alcohol
Nucleophilic substitution
Add NaOH (aq) - OH- ions
Heat under reflux
Alcohol -> alkene
Dehydration
Elimination reaction
Concentrated Sulfuric Acid catalyst
Produces water
Alcohol -> Haloalkane
Subsitution reaction
Sodium halide is added
H2SO4 concentrated
Sodium halide + H2SO4 -> hydrogen halide and soodim hydrogen sulfate
Hydrogen halide reacts with slochol to produce haloalkane - substituion reaction
Nucleophilic substitution
Primary alcohol -> carboxylic acid
K2Cr2O7 (colour change from orange to green) - escess… all of fhe alocjol is oxidised and any aldehyde formed originally oxidises ahain to turn into the carboxylic acid H2O by product 2[O] reactant H2SO4 Heated under reflux
Primary alcohol -> aldehyde
Gentle heating and distillation - orevents any further oxidation into carboxylic acid
K2Cr2O7 acidified with H2SO4
[O] used and H2O produced
Secondary alcohol -> ketone
Add K2Cr2O7 (acidified with sulfuric acid) and then heat under reflux to form a ketone ; cannot further oxidise ketones - change from oranhe to green H2O created and [O] used
Tertiary alcohols
NO
Target molecule
The compound that the chemist is attempting to prepare by organic synthesis
1-chloropropane to propanal
Nucelophilic substitution
K2Cr2O7 distilled
But-2-ene to butanone
Hydration (steam)
K2Cr2O7/H2SO4 reflux
What must you do in all organic syntheses?
WRITE DOWN CONDITIONS AND REACTANTS OF EACH STEP
DO GREEN BOX QS 248 AND QS 249
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