Organic synthesis Flashcards
What is the formation of nitriles from haloalkanes?
Reacting haloalkanes with sodium cyanide or potassium cynanide in ethanol increases the length of the carbon chain.
Nucleophilic substitution.
CH3CH2Cl + KCN –> CH3CH2CN + KCl
What is the formaiton of nitriles from aldehydes and ketones?
Aldehydes and ketones react with hydrogen cyanide in a nucleophilic addition reaction to increase the number of carbon atoms, forming a hydroxynitrile.
Hydrogen cyanide is poisonous so a mixture of NaCN and H2SO4 is used to improve safety and reaction rate.
What is the reduction of nitriles?
Nitriles are reduced to amines by reacting hydrogen in the presence of a nickel catalyst.
CH3CH2CN + 2H2 –Ni–> CH3CH2CH2NH2
What is the hydrolysis of nitriles?
Nitriles are hydrolysed to carboxylic acids by heating with dilute aqueous acid.
CH3CH2CN + 2H2O + HCl –> CH3CH2COOH + NH4Cl
What is alkylation of benzene rings?
An alkyl group from a haloalkane is transferred to a benzene ring using a Friedel Crafts catalyst like AlCl3.
What is acylation of benzene rings?
Benzene reacts with an acyl chloride in the presence of AlCl3 to form a ketone.
What is filtration under reduced pressure?
Used to separate a solid product from a solvent or liquid reaction mixture.
Diagram:
Buchner flask
Buchner funnel
Pressure tubing
Filter paper
Filter / vacuum pump
What is the method of filtration under reduced pressure?
Slowly pour the reaction mixture from the beaker into the filter paper in the funnel.
Rinse the beaker with cold solvent to collect all the crystals.
Rinse the crystals in the funnel with more solvent and let dry for a few minutes.
What is recrystallisation?
The solid product formed from filtration contains impurities which can be removed by recrystallisation.
Purification depends upon the desired product and the impurities having different solubilities in the chosen solvent.
What is the method of recrystallisation?
If flammable, heat the solvent in a water bath. If water, place the conical flask on a tripod over a bunsen burner to warm.
Tip the impure sample into a conical flask.
Slowly add the minimum volume of hot solvent to the sample until it dissolves.
Once dissolved, allow to cool. Crystals should form (scratch with glass rod if not), then when no more form, filter under reduced pressure to obtain dry crystalline solid.
What is melting point used for?
The melting point can determine if a sample is pure.
A pure organic substance has a very sharp range of 1 or 2 degrees.
An impure sample has a lower melting point than a pure sample.
How do you prepare a sample for melting point determination?
The sample must be dry and free flowing.
Take a glass capillary tube and hold one end in the flame of a bunsen burner. Rotate the tube until the end of the tube is sealed.
Allow to cool, then fill with crystals at 3mm depth, by pushing the open end into the solid sample.
What is the method of melting point determination using electrically heated melting point apparatus?
Place the filled capillary tube into a sample hole and a thermometer into the thermometer hole of the apparatus.
Using the rapid heating setting, heat the sample while observing through the magnifying window.
Once the solid starts melting, record the temperature, allow the apparatus to cool.
Prepare a second sample and repeat, but as the melting point is approached, set to low and raise the temperature slowly for accurate determination.
What is the method of using an oil bath / Thiele tube for melting point determination?
Attach the capillary tube to the thermometer using a rubber band.
Insert the thermometer through a hole in the cork (thiele) or clamp (oil bath).
The end of the thermometer should dip into the oil.
Using a micro-burner, slowly heat the arm of the thiele tube whilst observing the solid.
When the solid starts to melt, remove the heat, and record the temp at which all the solid has melted.
What are the 2-, 4-, directing groups?
NH2
OH
OR
R
C6H5
Halogens
