organic synthesis Flashcards
1.
what is the functional group of a nitrile
CN
why are reactions that form carbon- carbon bonds important in organic chemistry
synthesis compounds containing more carbon atoms
describe the two ways of forming nitrile
- from haloalkanes
- from aldehydes and ketones
describe how to make a nitrile from a haloalkane
- reacting a haloalkane wiht sodium cyanide or potassium cyanide in ethanol
- nucleophillic substitution
describe how nitriles are formed from aldehydes and ketones
- react with hydrogen cyanide
- nucleophillic addition
what is used instead of hydrogen cyanide to obtain cyanide ions and why
- hydrogen cyanide is far too poisonous to use
- increased reaction rate can be obtaained in the presence of cyanide ions
- mixture of sodium cyanide and sulfuric acid is used which improve sadtey and increases reaction rate
what are nitriles used as intermediates to make
- amines
- carboxylic acids
describe the reduction of nitriles
- reduced to amines by reacting hydrogen in the prescence of a nickel catalsyt
describe the hydrolysis of nitriles
- form carboxylic acids
- heating with dilute aqueous acid eg HCl(aq)
describe how to form carbon-carbon bonds to benzene rings
- alkylation
- acylation
describe alkylation of benzene
- prescene of a freidel crafts catalyst such as aluminium chloride
- transfers an alkyl group from a haloalkane to a benzene ring
describe acylation reactions of benzene
- benzene reacts with an acyl chloride in prescence of aluminium chloride catalyst
- ketone formed
desribe the two organic solids that are prepared from what chemicals
- in preparation of aspiring reflux salicyclic acid, ethanoic anhydride and glacial ethanoic acid using quickfit apparatus
- preparing benzoic acid by alkaline hydrolusis use quickfit apparatus to reflux methly benxoate with aquous sodium hydroxide followed by acidification
- both preparations a solid forms which has to be seperated from the reaction mixture before it is purified
decribe hoow a solid product is seperated from solvent or liquid reaction mixture
filtration under reduced pressure
what is the apparatus for filtration under reduced pressure
- buchner flask
- buchner funnel
- pressure tubing
- filter paper
- access to filter or vaccum pump
describe the method for filtration under reduced pressure
- connecct one end of the pressure tubing to the vaccuum outlet or to the filter pump whilst attatching the other end of the rubber tubing to the buchner flask
- fit the buchner funnel to the buchner flask ensuring that there is a good tight fit this is usually obtained using a buchner ring or a rubber bung
- switch on the vacuum pump or the tap to which you filter pump is attatched
- check for good suction by placig your hand across the top of the funnel
- place a piece of filter paper inside the buchner funnel and wet this with the same solvent used in preparing your solid you should see the paper being sucked diwn against the holes in the funnel
- to filter your sample slowly pour the reaction mixture from a beaker into the centre of the filter paper
- rinse out the beaker with the solvent so that all of the solid crystals collect in the buchner funnel
- rinse the crystals in the buhner funnel with more solvent and leave them under suction fro a few mintues so that the crystals start to dry
what is recrystallisation
- solid product obtained after filtration will contain impurities which can be removed by carrying out recrystallisation
- purification by recrystallisation depends upon the desired product and the impurities having different solubilities in the chosen solvent
describe the method for recrystallisation
- pur a quantity of chosen solvent into a concial flask
- if the solvent is flammable warm the solvent over a water bath
- if the solvent is water place the conical flask on a tripod and gauze over a busem and warm solvent
- tip the impure sample into a second conical flask or beaker
- slowly add the solvent to the impure sample until it dissolved in the solvent
- add minimum volume of solvent needed to dissolve the solid
- once the solid has dissolved allow the solution to cool
- crystals of hte desired product should form in the conical flask or beaker
- when no more crystals form filter the crystals under reduced pressure to obtin the dry crystaline solid
describe why melting point determination i used to identify a compound
- chemists determine the melting point of solids to identify wether a solid compound is pure
what is the melting range
melting range is the difference between the temperature at which the sample stats to melt and the temperature at which melting is complete
how do you tell between a pure and impure sample of a compound with melting point determination
a pure organic substance usually has a very sharp melting range of one or two degree
* if compound contains impurities the solid melt over a wide range of temperatures
* an impure sample has a lower melting point than pure sample
describe how a sample is prepared before taking it melting point
- before taking the melting point of a solid you should ensure that the sample is completley dry and free flowing
- take a glass capillary tube or a melting point tube
- hold one end of the capillarry tube in the hot flame of a bunsen burner rotate the tube in the flame unti the end of the tube is sealed
- the capillary tube is allowed to cool and is then filled with crystals to about 3mm depth this is usually carried out by pushing the open end of the capillary into the solid sample to force some of the solid into the tube
- once you have prepared your sample you will need to take its melting point
describe the two ways melting point can be determines
- using electrically heated melting point apparatus
- use an oil bath or thiele tube method
describe how electrically heated melting point apparatus is used to determine melting point of a compound
- place the capillary tube containg the sample into a sample hole and a 0-300 degree thermometer in the thermometer hole of the mleting point apparatus
- usin the rapid heating setting start to heat up the sample whilst observing the sample through the magnifying window
- once the solid is seen to melt record the melting point
- allow melting apparatus to cool
- repare a second sample in a new capillary tube and place in the melting point apparatus and again heat up the sample
- as melting point is approached set to low and raise the temperature slowly whilst observing the sample
- an accurate determination of the melting point can hten be obtained
describe how using an oil bath or thiele tube method to determine the melting point of a compound
- set up the thielr tube or oil bath
- attatch the capillary tube containg the sample to a thermometer using a rubber band
- insert the temrometer through a hole in the cork if using theile tube or clamp the thermometer is using an oil bath
- the end of the thermometer and end of capitallry tube should dip into the oil
- using a micro burner slowy heat the side arm of the thiele tube or the oil bath whilst observing the solid
- when the solid starts to melt remove the heat and record the temperature at which all of the solid melting
- important to heat the oil slowly when approaching the melting point and it is advisable to repeat the melting point determination a second time to ensure that you obtain an accurate value
