CD 9, 10, 11 Flashcards
what is reacted with aldehyde and ketones to extend their carbon chain
HCN
what is a nitrile group and what are the two ways to get rid of it
C=N
(TRIPLE BOND)
- nitrile group can be hydrolysed into a carboxylic acid or dehydrated into an amine
what is a carbonyl group and what compounds contain them
- C=O
- aldehydes and ketones
why do aldehydes and ketones differ in terms of oxidation
- aldehydes contain a hydrogen atom attached to the carbonyl group, this means that aldehydes react with a range of oxidising agents whereas ketones will not
how do you distinguish an aldehyde from a ketone, what is the problem with this method
- heat the sample under reflux with acidified potassium dichromate
- aldehyde sample will turn from orange to green
- problem is that this result would also be produced for a primary/ secondary alcohol
How is Fehling’s test conducted and what is it used to test for
- a mixture of Fehling’s A and B is warmed in a water bath with an aldehyde and the solution should change from blue to brick red precipitate
describe in detail what Fehling’s solution is comprised of
- made from a mixture of Fehling’s A and Fehling’s B
- Fehling’s A contains the weak oxidising agent Cu 2+
- Fehling’s B which is an alkaline solution containing a bidentate ligand
- Cu 2+ ions are reduced to copper (I) ions, precipitated as copper oxide Cu2O, forming the brick red precipitate
How is the test will Tollen’s reagent conducted
- aldehydes are oxidised into carboxylate ions
- Tollen’s reagent is warmed with aldehyde in a test tube using a water bath
- a silver mirror forms on the inside of the tube
Explain what Tollen’s reagent is formed from
- Formed by dissolving silver (I) oxide, Ag2O in ammonia to form the complex ion [Ag(NH3)2]+
- when tollen’s reagent is added to an aldehyde, Ag+ ions are reduced to elemental silver, which appears as a silvery layer on the surface of the test tube
what are aldehydes and ketones reduced to and what is used in this process
- aldehydes are reduced to primary alcohols
- ketones are reduced to secondary alcohols
- the powerful reducing agent NaBH4, sodium tetrahydridoborate (III)
what addition reactions do aldehydes and ketones take part in
- undergo addition reactions with hydrogen cyanide in acidic conditions across the C=O bond to form cyanohydrins / 2-hydroxynitriles
define
- nitrile
- cyanohydrin
nitrile - a functional group in which a carbon is triple bonded to a nitrogen
cyanohydrin - a functional group where a cyanide group and an alcohol group is bonded to the same carbon atom
what is hydrogen cyanide replaced with in laboratories and why
- cyanide is too hazardous to use the laboratory
- acidified potassium cyanide is used to replace it, as it is a source of CN- and H+ ions
what occurs in the mechanism of the addition reaction of HCN and aldehyde/ ketone
- two stages
1. cyanide ion CN- is a nucleophile and attracted to carbon in the carbonyl group as it has a partial positive charge
2. New carbon-carbon bond forms and electrons from C=O move to oxygen which then carries a negative charge, the it takes up a proton from the solvent (water) to become OH
how to choose a starting material for synthesis
- available in suitable quantities
- cost is low enough to make synthesis economic
benzene —> halogenated benzene
- electrophilic substitution
- benzene reacts with liquid bromine or chlorine gas
- presence of FeBr3 or AlCl3
- both reactions occur at room temperature
- bromine is decolourised and fumes of HBr are given off
benzene —> nitrobenzene
- electrophilic substitution
benzene + HNO3 (nitric acid)
- in the presence of concentrated H2SO4 and at 55 degrees
- produces nitrobenzene
- nitrating mixture is a mix of concentrated nitric acid and concentrated sulphuric acid
nitrobenzene —> phenylamine
- electrophilic substitution
nitrobenzene heated under reflux with HCl, in the presence of tin
forms benzene and NH2
benzene —> acyl-substituted benzene
- electrophilic substitution
benzene + acyl chloride (or acid anhydride) + AlCl3
—> C6H5COR + HCl
- occurs under anhydrous conditions
benzene —> sulfonated benzene
- electrophilic substitution
- benzene + conc. H2SO4 —> benzene sulfonic acid + H+
- heated under reflux
benzene —> alkyl substituted benzene
- electrophilic substitution
benzene + chloroethane —> ethyl benzene + HCl
- heated under reflux in the presence of anhydrous aluminium chloride (AlCl3)
define the type of reaction and give an example of a functional group that takes part in this reaction
- addition
- two molecules that react together to form a single product
- aldehydes ad ketones
define the type of reaction and give an example of a functional group that takes part in this reaction
- elimination
- a small molecule, such as water or HCl is removed from a larger molecule, leaving an unsaturated molecule
- alcohols
- haloalkanes
define the type of reaction and give an example of a functional group that takes part in this reaction
- condensation
- two molecules reacting together to form a larger molecule, and a smaller molecule
- carboxylic acids and alcohols
- acyl chlorides, alcohols and amines
