organic synthesis Flashcards
(26 cards)
what’s necessary for a quick fit apparatus
pear shaped flask
receiver
screw tap adaptor
condenser
still head
What equipment is necessary to heat under reflux?
Pear shaped flask Condenser Rubber tubing Stand and clamp Heat source (bunsen burner, tripod and gauze OR heating mantle)
Which method of heating is used when heating flammable liquids?
why do we use a bunsen burner and why not water bath
Heating mantle so there is no naked flames and provides safety if appratus cracks.
allows a reaction under reflux to be carried out at a fixed temp.
water bath used if reaction can be carried out below 100c.
What practical steps must be taken when setting up a reflux apparatus and why?
1)the flask is clamped by its neck. b4 fitting condenser you need to add reaction mixture + anti-bumping granules to the flask- added to the liquid b4 the flask is heated so the contents will boil smoothly. If not, large bubbles form at the bottom of liquid and make the glassware vibrate / jump violently.
2)apply a thin layer of grease to ground-glass joint on condenser . Place the condenser carefully into flask n gently rotate condenser back + forth to provide a good seal n ensure that apparatus comes apart easily at the end of experiment.
3)During reflux condenser is kept in the upright position.
Condensers should be clamped only loosely as glass outer jacket is v fragile + is easily broken. Never put a stopper in the top of the condenser as u would have a closed system n pressure would build up inside as the heated air expanded. ->apparatus exploding!
Rubber tubing used to connect inlet of condenser to the tap n the outlet to the sink. H20 always enters condenser at the bottom and leaves at the top to ensure that the outer jacket is full.
How does the condenser work during reflux and what is a common analogy for the process?
A: The vapour from the mixture rises up the inner tube of the condenser until it meets the outer jacket containing cold water. The vapour then condenses and drips back into the flask. The process is similar to putting a lid on a Saucepan when cooking.
What is heating under reflux and why is it used in reactions?
Heating under reflux enables a liquid to be continually boiled whilst the reaction takes place. This prevents volatile components from escaping and the flask from boiling dry.
What is the purpose of distillation?
Separate a pure liquid from its impurities.
What is the equipment necessary for distillation?
Pear shaped flask Condenser Rubber tubing Heat source Stand and clamp Screw cap adaptor, Receiver adaptor Still head Thermometer
how does distillation apparatus set up
The flasks clamped by its neck and still head is connected to the flask. The still-head adaptor is T shaped + has 2 ground-glass joints, one to fit screw-cap adaptor and one to fit condenser,
You should grease joints so that the apparatus comes apart easily after the experiment.
2nd clamp placed round receiver adaptor at the point at which its attached to condenser. This removes the need to clamp condenser, as it will be supported sufficiently at both ends.
As w reflux, rubber tubing is used to connect inlet of the condenser to the tap and the outlet to the sink. Water always enters the condenser at the lowest point. For distillation, this is the closest point to the receiver adaptor.
A flask is used to collect the distillate so that distillation apparatus is not completely airtight.
How does distillation work
Once the apparatus set up, the flask is heated and the mixture in the flask will start to boil. The different liquids in the mixture will have different boiling points. The liquid with the lowest boiling point is the most volatile and will boil first.
The vapour moves out of the flask up into the other parts of the apparatus, leaving behind the less volatile components of the mixture. When the vapours reach the cold condenser, they condense and become a liquid. This liquid then drips into the collecting flask.
in a distillation set up why is it necessary t o have continuous waterflow around the condenser
so the water remains cool in order for the mixture to be distilled.
Describe the process of purifying organic products
1)ensure tap of separating funnels closed
2)pour the mixture of liquids into separating funnel, place a stopper in the top of the funnel n invert to mix the contents.
3)allow layers to settle
4)add some h20 to see which layers inc in volume-this is the the aqueous layer
5)place a conical flask under the separating funnels, remove the stopper and open the tap until the whole of the lower layer has left the funnel.
6)place a second conical flask under the separating funnel to collect the other layer
7)you now have 1 conical flask containing the organic layer n another w aqueous,label so u don’t get muddled.
How can acid impurities be removed?
Adding aqueous sodium carbonate and shaking the mixture in the seperating funnel. CO2 gas is made and must be released via the tap (funnel upside down). Aqueous sodium carbonate layer is then removed and organic layer washed with water.
Describe the process of drying the organic product
1)add organic liquid to a conical flask
2)w spatula add some of drying agent(typically anhydrous inorganic salt) to the liquid n gently swirl contents to mix tg.
3)place a stopper on flask to prevent your product from evaporating away.leave for about 10 mins
4)if solid has all stuck tg in a lump then there’s some water present.add more drying agent until there’s some solid dispersed in solution as a fine powder.
5)decant the liquid from the solid into another flask.if the liquid is dry it should be clear.
what are the three common drying agents?
anhydrous calcium chloride, CaCl2 (drying hydrocarbons) anhydrous calcium sulfate CaSO4 (general drying)anhydrous magnesium sulfate, MgSO4(general drying)
How can a redistillation be used to purify a product when organic liquids have similar boiling points?
Sometimes organic liquids have boiling points that are relatively close together, so your prepared sample may still contain some organic impurities. The distillation apparatus is cleaned and dried and set up again so that a second distillation can be carried out. This time, only collect the product with the boiling point of the compound you are trying to make. The narrower the boiling range, the purer the product. You now will have separated your product from any impurities.
Draw a refulux diagram
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Draw a distillaition diagram
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What is a target molecule?
The compound that is being prepared by organic synthesis.
How would an aldehyde be formed from a halogenoalkane?
Stage 1: Add NaOH under reflux to form an alcohol Stage 2: Oxidise with acidified potassium dichromate under gentle heat and distill off
How would a ketone be formed from an alkene?
Stage 1: Add steam with acid catalyst to form an alcohol Stage 2: Oxidise with acidified potassium dichromate under reflux
to convert a starting molecule into the target molecule you need to
identify the functional groups in starting and target molecules
identify the intermediate that links starting and target molecules
state the reagents and conditions for each step
syntheiss of propanal
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synthesis pf butane
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