CD - Organic reactions *01 *02 Flashcards
electrophilic substitution reactions of aromatic compounds: halogenation of the ring
eg. chlorination
reactants and conditions:
- X2 (any halogen)
- AlCl3 catalyst
- warm
to make electrophile
eg. Cl2 + AlCl3 —> Cl+ + AlCl4-
overall reaction
C6H6 + Cl2 —[AlCl3]—> C6H5Cl + HCl (makes chlorobenzene)
electrophilic substitution reactions of aromatic compounds: nitration
Reactants and conditions:
- conc. H2SO4 catalyst
- HNO3
- 55 degrees (so only one group)
to make electrophile: NO2+
- HNO3 + 2H2SO4 —> NO2+ + 2HSO4- + H3O+
products
nitrobenzene and water
mechanism
- NO2+ attacks benzene ring
- unstable intermediate forms
- the H+ ion is lost
- reacts with HSO4- to regenerate H2SO4 catalyst
electrophilic substitution reactions of aromatic compounds: sulfonation
reactants and conditions - fuming H2SO4 - 40 degrees - 30 mins OR - boil benzene under reflux for several hours with conc. H2SO4
Making electrophile: (SO3)
- H2SO4 —> H2O + SO3
products:
benzene-sulfonic acid and water
same mechanism as Nitration
electrophilic substitution reactions of aromatic compounds: friedel-crafts ALKYLATION
conditions and reactants:
- RCL
- AlCl3 cataylst
- reflux
making electrophile: R+ (eg CH3+) in this case its a carbocation
CH3Cl + AlCl3 —–> CH3+ + AlCl4-
products:
methylbenzene and HCl
(AlCl4- reacts with the H+ that is lost with makes HCl and regenerates catalyst)
overall reaction:
C6H6 + RCl —[AlCl3]—> C6H5 + HCl
electrophilic substitution reactions of aromatic compounds: freidel-crafts ACYLATION
conditions and reactants
- RCOCl
- AlCl3 catalyst
- reflux
making electrophile: (RCO+ eg. CH3CO+)
- CH3COCl + AlCl3 —-> CH3CO+ + AlCl4-
products:
phenylethanonoe and HCl
Making a Diazonium Salt
phenylamine and nitrous acid
nitrous acid is unstable so has to be made in situ
- NaNO2 + HCl —> HNO2 + NaCl
(sodium nitrate + Hydrochloric acid)
Nitrous acid + phenylamine + HCl —–> benezenediazonium chloride
TEMP BELOW 5 DEGREES to prevent phenol forming
Making an Azo Dye
coupling reaction
diazonium salt + phenol
- phenol dissolved in NaOH solution —-> sodium phenoxide solution
- stood on ice and chilled benzene-diazonium chloride added
- azo dye precipitates out of solution immediately
reactions of carbonyl compounds: making aldehydes
distil primary alcohol with acidified potassium dichromate (VI)
reactions of carbonyl compounds: making carboxylic acids
heat a primary alcohol (or aldehyde) under reflux with acidified potassium dichromate (VI)
reactions of carbonyl compounds: making ketones
reflux a secondary alcohol with acidified potassium dichromate (VI)
testing for aldehydes and ketones: what can be used
- Fehling’s solution
- tollen’s reagent
testing for aldehydes and ketones: Fehling’s solution
Fehling’s solution is a blue solution of copper (II) ions dissolved in sodium hydroxide
- If heated with an aldehyde the copper (II) ions are reduced to a brick red precipitate of Copper (I) oxide, Cu2O
method
- add 2cm3 of Fehling’s solution to a test tube
- add 5 drops of aldehyde or ketone
- put the test tube in a hot water bath for a few minutes
aldehyde - brick red precipitate
( Cu2+ + e- —> Cu+) the aldehyde is oxidised to the carboxylate ion ( RCHO —> RCOO-)
ketone - nothing happens
testing for aldehydes and ketones: Tollen’s reagent
- put 2cm3 of 0.1moldm-3 silver nitrate solution into a test tube
- add a few drops of dilute sodium hydroxide solution, a light brown precipitate should form
- add drops of dilute ammonia solution until the brown precipitate dissolves completely
- this solution is tollen’s regent - place the test tube in a hot water bath and add 10 drop of aldehyde or ketone, wait for a few mins.
results:
aldehyde - a silver mirror (a thin coating a silver) form on the walls of the test tube
Ag(NH3)2+ (aq) + e- —-> Ag (s) + 2NH3 (aq), aldehyde –> carboxylate ion
ketone - nothing happens
why cant aldehydes and ketones be put over a flame
they are flammable
so must be heated in a water bath
PAG7