PAG 6 - Synthesis of Organic Solid (6.2.5a, 6.3.1a) Flashcards
During the organic synthesis of a solid, state the procedures used to
I. Separate a solid product from a liquid/solvent
II. Purify a sample
III. Check purity of a sample
I. Filtration under reduced pressure
II. Recrystallisation
III. TLC; Melting pt. Determination;
What equipment is required for filtration under reduced pressure?
- Buchner flask
- Buchner funnel
- Pressure tubing
- Filter paper
Describe the practical procedure for filtration under reduced pressure
- Attach the tubing out of the Buchner flask to the suction pump connected to the tap
- Tap your hand against the end of the pipe to check if there is suction
- Place filter paper in the Buchner funnel and add crystals on top
- Wet filter paper with same solvent used when preparing the solid
- Turn the tap on to begin suction, rinse the crystals with more solvent repeatedly
Describe the process of recrystallisation
- Even after filtration the products may be contaminated
- Gently warm a solvent to boiling
- Keep adding the solvent to impure sample until it dissolves
- Do slowly as you want to dissolve the impure sample in the minimum amount of solvent
- Minimum amount to ensure solution is saturated for max amount of crystals upon cooling
- Allow solution to cool until crystals appear
- Once no more crystals from, filter under reduced pressure to obtain dry crystalline solid
- Wash with an ice cold solvent and dry - to prevent crystals from dissolving again and to remove any soluble impurities
How do you determine melting point of crystals?
- Use a capillary tube with one open and one sealed end
- Tap the open end into the sample to move it up the tube
- Place in an electronic melting point meter
- Place capillary tube in sample hole
- Begin to heat, and watch through the magnifying glass to see when the crystals melt
- Record the temperature
- Compare to known values
what are the general steps of synthesis of an organic solid
preperation: react suitable amount of reactant to make product
**seperation of the impurities : ** the solid is seperated from the reaction by suction filtration
purification of products: removes impurities and it is carried out by recrystallisation
drying the product : this is done by sucking air over the solid in the buckner flask , and drying in a low temp oven
check purity : by carrying out melting point determination
draw how we seperate an organic solid from impurities
describe the process for purification of an organic solid, recrystallisation
- Dissolve the impure compound in a minimum volume of hot (near boiling) solvent.
- Hot filter solution through (fluted) filter paper quickly.
- Cool the filtered solution by inserting beaker in ice
- Suction filtrate with a Buchner flask to separate out crystals
5 Wash the crystals with distilled water
- Dry the crystals between absorbent paper
what is an appropriate solvent for purifying organic solid by recrystallisation
An appropriate solvent is one which will dissolve both compound and impurities when hot and one in which the compound itself does not dissolve well when cold.
The minimum volume is used to obtain saturated solution and to enable crystallisation on cooling
what do you dissolve impure compound in
minimum volume of hot solvent
what is used to do a hot filtration and why
gravity filtration using a hot funnel and fluted filter paper to remove insoluble impurities
how do you check the melting point of a substance
- place some solid in a melting point tube sealed at one end
- place in melting point apparatus and heat slowly
- record the temperatures at which solids start to melt and the temperature at which it finishes melting
- compare to a known database
why is percentage yeild less than 100%
- some solid is lost in purification steps e.e some solid could dissolve in solvent during recrytallisation
-some product is lost when transferring between vessels
