CD - Organic reactions *01 *02 Flashcards

1
Q

electrophilic substitution reactions of aromatic compounds: halogenation of the ring

A

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)

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2
Q

electrophilic substitution reactions of aromatic compounds: nitration

A

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

  1. NO2+ attacks benzene ring
  2. unstable intermediate forms
  3. the H+ ion is lost
    - reacts with HSO4- to regenerate H2SO4 catalyst
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3
Q

electrophilic substitution reactions of aromatic compounds: sulfonation

A
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

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4
Q

electrophilic substitution reactions of aromatic compounds: friedel-crafts ALKYLATION

A

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

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5
Q

electrophilic substitution reactions of aromatic compounds: freidel-crafts ACYLATION

A

conditions and reactants

  • RCOCl
  • AlCl3 catalyst
  • reflux

making electrophile: (RCO+ eg. CH3CO+)
- CH3COCl + AlCl3 —-> CH3CO+ + AlCl4-

products:
phenylethanonoe and HCl

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6
Q

Making a Diazonium Salt

A

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

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7
Q

Making an Azo Dye

A

coupling reaction
diazonium salt + phenol

  1. phenol dissolved in NaOH solution —-> sodium phenoxide solution
  2. stood on ice and chilled benzene-diazonium chloride added
  3. azo dye precipitates out of solution immediately
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8
Q

reactions of carbonyl compounds: making aldehydes

A

distil primary alcohol with acidified potassium dichromate (VI)

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9
Q

reactions of carbonyl compounds: making carboxylic acids

A

heat a primary alcohol (or aldehyde) under reflux with acidified potassium dichromate (VI)

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10
Q

reactions of carbonyl compounds: making ketones

A

reflux a secondary alcohol with acidified potassium dichromate (VI)

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11
Q

testing for aldehydes and ketones: what can be used

A
  • Fehling’s solution

- tollen’s reagent

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12
Q

testing for aldehydes and ketones: Fehling’s solution

A

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

  1. add 2cm3 of Fehling’s solution to a test tube
  2. add 5 drops of aldehyde or ketone
  3. 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

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13
Q

testing for aldehydes and ketones: Tollen’s reagent

A
  1. put 2cm3 of 0.1moldm-3 silver nitrate solution into a test tube
  2. add a few drops of dilute sodium hydroxide solution, a light brown precipitate should form
  3. add drops of dilute ammonia solution until the brown precipitate dissolves completely
    - this solution is tollen’s regent
  4. 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

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14
Q

why cant aldehydes and ketones be put over a flame

A

they are flammable

so must be heated in a water bath

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15
Q

PAG7

A
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16
Q

reactions of carbonyl compounds: reaction with cyanide ions

A

Nucleophilic addition
hydrogen cyanide reacts with carbonyl compounds to produce CYANOHYDRINS (molecules with a -CN and -OH group)

hydrogen cyanide is a weak acid
HCN < —> H+ + CN-

  1. the CN- attacks the partially +ve carbon atom and donates a pair of electrons
    - two electrons from the double bond transfer to the oxygen
  2. H+ (for HCN or H2O) bonds to the oxygen tp form the hydroxyl group
17
Q

dangers of hydrogen cyanide

A

highly poisonous gas

so reaction needs to be done in fume cupboard