16) Organic synthesis Flashcards
Name 5 key quickfit apparatus that are often used in organic synthesis
round-bottom or pear-shaped flask receiver screw-tap adaptor condenser still head
Define reflux
the continual boiling and condensing of a reaction mixture back to the original container to ensure that the reaction takes place without the contents of the flask boiling dry
State 3 key things that heating under reflux helps to achieve
overcome activation energy
increase rate of reaction
prevent volatile components from escaping
Name 5 key apparatus used in a reflux
rubber tubing Liebig condenser clamp + stand pear-shaped flask heat source
In reflux, what should the direction of water flow ensure?
that the outer jacket of the condenser is full
In reflux, what is the rubber tubing connected to?
the inlet of the condenser
the outlet of a sink
Why should a Liebig condenser be clamped loosely?
very fragile
Why should a stopper not be placed on a Liebig condenser when undergoing reflux?
may explode
Why are the joints of some quickfit apparatus greased before use and then rotated back and forth when connecting to another piece of apparatus?
to ensure a good seal which comes apart easily after the experiment
What should be added to the reaction mixture in reflux to allow it to boil smoothly?
anti-bumping granules
What heat source without a naked flame could be used for reflux when heating flammable liquids?
a heating mantel
For reflux, should water go into a Liebig condenser at the top or the bottom?
at the bottom
Define distillation
common method to separate a pure liquid from its impurities (once reflux is complete)
Name 5 pieces of apparatus not used for reflux, that will be needed to carry out a distillation
thermometer screw-cap adaptor / thermometer pocket still head receiver conical flask
What is important about the use of a conical flask in a distillation?
means that the apparatus is not completely airtight
What property of a mixture of liquids is important for distillation to work? Why?
different boiling points
the liquid with the lowest boiling point is the most volatile and will boil first, when the vapours reach the condenser they will condense
Describe the steps for purifying an organic product after distillation
1) ensuring separating funnel tap is closed, pour in mixture, place in stopper and invert to mix contents. allow to settle
2) identify aqueous layer (increases in volume when water is added)
3) place a conical flask under the separating funnel, remove the stopper and open the tap to allow the lower layer to be collected. repeat with a second conical flask for the other layer. label flasks
What extra steps would be needed for the purification of an organic product if the preparation has used acids?
1) add aqueous sodium carbonate and shake the mixture in the separating funnel to remove an acid impurities
2) slowly open the tap whilst holding the funnel upside down to release any pressure as CO2 is produced
3) remove the aqueous carbonate layer and wash the organic layer with water
Define drying agent
an anhydrous inorganic salt that readily takes up water to become hydrated
Name a drying agent for drying hydrocarbons
anhydrous CaCl2
Name 2 drying agents for general drying
anhydrous CaSO4
anhydrous MgSO4
Give the 4 steps for drying an organic product
1) using a spatula, add drying agent to the organic layer in the conical flask and gently swirl to mix together
2) place on a stopper (prevent evaporation) and leave for 10 mins
3) If the solid has stuck together in a lump there is still water present - so add more drying agent until some solid is dispersed in the solution as a fine powder
4) decant the liquid from the solid into another flask. if the liquid is dry it should be clear
Why would you dry an organic product?
to remove traces of water
When carrying out a second distillation what change would you make?
collect only the product with the boiling point of the compound you are trying to make
The _ the boiling range, the purer the product.
narrower
Define organic synthesis
the preparation of complex molecules from simple starting materials
haloalkane -> alcohol
NaOH(aq)
reflux
alkane -> haloalkane
halogen/UV
alkene -> haloalkane
hydrogen halide
alkene -> alcohol
H2O(g)
H3PO4 catalyst
alkene -> alkane
H2
Ni catalyst
alcohol -> haloalkane
sodium halide + H2SO4
alcohol -> alkene
conc. H2SO4
primary alcohol -> carboxylic acid
K2Cr2O7/H2SO4 reflux
primary alcohol -> aldehyde
K2Cr2O7/H2SO4 distil
secondary alcohol -> ketone
K2Cr2O7/H2SO4 reflux
Define target molecule
the compound the chemist is attempting to prepare by organic synthesis
Describe how you would prepare to carry out a two-step synthesis
identify functional groups in starting and target molecules
identify the intermediate
state reagents and conditions for each step
