Download Organic Chemistry – Summary of Reactions and Conditions

565323042
Organic Chemistry
Reactions and Conditions
Alkane
1
Combustion in the presence of oxygen
General equation for non-cyclic alkanes
CnH(2n+2) + (1½n+½)O2  nCO2 + (n+1)H2O
Conditions: Ignition in the presence of plentiful oxygen.
Gives a cleaner flame than unsaturated hydrocarbons. Flame becomes increasingly sooty with
increasing chain length. In limiting oxygen, products may include C and CO.
2
Conversion to halogenoalkane
Reaction type: Free radical substitution
C2H6 + Cl2  C2H5Cl + HCl
Reagents:
Conditions:
chlorine or bromine
Ultraviolet light
Gas or liquid phase (inert solvent such as CCl4)
Further substitutions usually occur.
Knowledge of mechanism required.
Alkene
1.
Conversion to halogenoalkane
Reaction type: Electrophilic addition
H
H H
H
C C
H
Reagents:
Conditions:
+ HCl

H C C H
H
H Cl
hydrogen halide
Room temperature
Gas or liquid phase, or inert solvent (tetrachloromethane)
Markovnikov’s rule: When hydrogen halide adds to an unsymmetrical double bond, the
hydrogen adds to the carbon atom containing most hydrogen atoms.
Knowledge of mechanism and explanation of Markovnikov’s rule is required.
2.
Conversion to dihalogenoalkane
Reaction type: Electrophilic addition
1/16
565323042
H
H H
H
C C
H
+ Cl2

H C C H
H
Reagents:
Conditions:
Cl Cl
chlorine or bromine
room temperature, in dark.
gas phase or inert solvent (tetrachloromethane).
Knowledge of mechanism required.
3.
Conversion to alkyl sulphate and then to an alcohol
(i)
Addition of sulphuric acid
Reaction type: Electrophilic addition
H
H H
H
+ H2 SO4 
C C
H
H C C O S OH
H
H H
Reagents:
Conditions:
O
O
concentrated sulphuric acid.
0°C
Addition to unsymmetrical double bond follows Markovnikov’s rule.
(ii)
Conversion of alkyl sulphate to an alcohol
Reaction type: hydrolysis
H H
O
H C C O
H H
S OH + H2O  HO C C H
O
Reagents:
Conditions:
4.
H H
+ H2SO4
H H
water
warm under reflux
Conversion to diol
Reaction type: oxidation
H H
H
C C + 2 KOH + 2 KMnO4  HO C C OH + 2 K2MnO4
H
H
H H
H
Reagents::
Conditions:
5.
dilute aqueous alkaline potassium manganate (VII)
room temperature
Conversion to alkane
Reaction type: addition
H
+ H2 
C C
H
H H
H
H
Reagents:
Conditions:
H C C H
H H
hydrogen
nickel catalyst, 100C, 4 atm
2/16
565323042
6.
Polymerisation
H

C C
n
H H
H
H
H
C C
n
H H
Reagents and conditions:
Either
Free radical initiator such as organic peroxide, 100-300C, 1000-2000 atm (low density
polyethene produced, free radical mechanism)
or
Ziegler catalyst, 20-50C, 5-25 atm (high density polyethene produced, ionic mechanism)
Halogenoalkane
1.
Conversion into alcohol
Reaction type: nucleophilic substitution
H H
H H
H C C Cl
+ NaOH  H C C OH
H H
Reagents:
Conditions:
+ NaCl
H H
Aqueous sodium or potassium hydroxide.
Boil under reflux.
Knowledge of possible mechanisms required. Note the difference in reagent and conditions in
reaction 3.
H2O has a lone pair of electrons and can act as a nucleophile in a similar way to OH -. Lacking
an overall negative charge, H2O is a weaker nucleophile than OH-. One method of following
the reaction of a halogenoalkane with water is to carry out the reaction in the presence of
AgNO3 (aq). The Ag+ (aq) ions do not take part in the organic reaction. They do combine with
the halide ion product and the formation of a silver halide precipitate provides an indication of
the progress of the reaction.
2.
CH3CH2Cl
+
H2O
CH3CH2OH +
Cl- (aq)
+
Ag+ (aq)
H+ (aq)
+
Cl- (aq)
AgCl (s)
Conversion into amine
Reaction type: nucleophilic substitution
H H
H H
H C C Br + 2 NH3  H C C NH2 + NH4Br
H H
Reagents:
Conditons:
H H
Excess ammonia dissolved in ethanol.
Heat in a sealed tube.
Amines, having a lone pair of electrons on the nitrogen atom like ammonia, are themselves
nucleophiles. Therefore secondary and tertiary amines and quartenary amine salts also tend to
be formed which limits the usefulness of this reaction in synthesis.
CH3CH2Br + CH3CH2NH2
CH3CH2Br + (CH3CH2)2NH


(CH3CH2)2NH + HBr
(CH3CH2)3N + HBr
3/16
565323042
CH3CH2Br + (CH3CH2)3N
3.

(CH3CH2)4N+ Br -
Conversion into alkene
Reaction type: Elimination (Acid/base)
H H
H
H C C Cl
+ KOH 
H
C C
H
H H
+ KCl + H2O
H
Reagents:
Potassium hydroxide dissolved in ethanol
Conditions:
Boil under reflux.
If several products are possible, the double bond tends to form between carbon atoms which
have fewest hydrogen atoms attached. Note the difference in reagent and conditions in
reaction 1.
4.
Alkylation (Friedel-Crafts reaction)
Reaction type: Electrophilic substitution
+ RCl 
Reagents:
Conditions:
R
+ HCl
benzene and anhydrous AlCl3 (catalyst).
heat under reflux.
Attachment of an alkyl group activates the arene ring, making it susceptible to further alkylations.
These occur at positions 2 and 4.
5.
Preparation of a nitrile
CH3CH2Br + KCN  CH3CH2C≡N + KBr
Reaction type :
Mechanism:
Conditions:
Substitution
Nucleophilic (CN- is nucleophile)
Heat under reflux in ethanol + water solvent
Alcohol
1
Formation of alcoxide salt
Reaction type: Redox
2 CH3CH2OH + 2 Na  2 CH3CH2O- Na+ + H2
Reagents:
Alkali metal
Conditions:
Room temperature.
The alcoxide salt can be used to prepare an ether by reaction with a halogenoalkane.
2.
4/16
565323042
(a)
Conversion of primary alcohol to aldehyde
Reaction type: Oxidation
H H
H O
3 H C C OH + Cr2O72- + 8 H+  3 H C C H + 2 Cr3+ + 7 H2O
H H
Reagents:
Conditions:
(b)
H
aqueous potassium dichromate (VI), acidified with dilute sulphuric acid.
alcohol reactant added to hot oxidation reactant, aldehyde product instantly
distilled to prevent further oxidation to carboxylic acid.
Conversion of primary alcohol to carboxylic acid
Reaction type: Oxidation
H H
H O
3 H C C OH + 2 Cr2O72- + 16 H+  3 H C C OH + 4 Cr3+ + 11 H2O
H H
Reagents:
Conditions:
(c)
H
aqueous potassium dichromate (VI), acidified with dilute sulphuric acid
heat under reflux, then distill
Conversion of secondary alcohol to ketone
Reaction type: Oxidation
OH
O
3 H3C C CH3 + Cr2O72- + 8 H+  3 H3C C CH3+ 2 Cr3+ + 7 H2O
H
Reagents:
Conditions:
(d)
3.
potassium dichromate (VI), acidified with dilute sulphuric acid.
heat under reflux.
The ketone produced is resistant to further oxidation.
Tertiary alcohols are resistant to oxidation.
Formation of ester
Reaction type: Condensation (nucleophilic addition followed by elimination)
H H
H O
H C C OH +
H C C OH
H H
Reagents:
Conditions:
4.
H

O H
H C C O C C H + H2O
H H
H
Appropriate pure carboxylic acid, small amount of conc. sulphuric acid
Heat and distill
Conversion to alkene
Reaction type: Elimination
H H
H C C OH
H H
5
H H
H

H
C C
H
+ H2O
H
Reagents:
excess concentrated sulphuric acid
Conditions:
heat to 170C
Where several products are possible, those in which the carbon atoms of the double bond
contain most alkyl groups are favoured.
Conversion to halogenoalkane
Reaction type: Substitution
5/16
565323042
Several reagents may be used.
Conversion to chloroalkane
CH3CH2OH + PCl5  CH3CH2Cl + POCl3 + HCl
Reagents:
phosphorus (V) chloride
Conditions:
room temperature
CH3CH2OH + SOCl2  CH3CH2Cl + SO2 + HCl
Reagents:
thionyl chloride (sulphur oxide dichloride)
Conditions:
room temperature
Conversion to bromoalkane
CH3CH2OH + HBr  CH3CH2Br + H2O
Reagents:
50% sulphuric acid and sodium bromide.
Conditions:
Heat under reflux.
The hydrogen bromide is generated by the reaction between sodium bromide and sulphuric
acid
NaBr + H2SO4  HBr + NaHSO4.
Conversion to bromo- or iodoalkane
3CH3CH2OH + PBr3  3CH3CH2Br + H3PO3
3CH3CH2OH + PI3  3CH3CH2I + H3PO3
Reagents:
Conditions:
moist red phosphorus and bromine or iodine
warm
phosphorus (III) halide is formed as the halogen reacts with the phosphorus.
Carbonyl Compounds (Aldehydes and Ketones)
1.
Conversion of aldehyde to carboxylic acid
Reaction type: oxidation
Preparation of carboxylic acid
H O
H O
3 H C C H
+ Cr2O72- + 8 H+  3 H C C OH
H
H
Reagents:
Conditions:
+ 2 Cr3+ + 7 H2O
aqueous potassium dichromate (VI) and dilute sulphuric acid
heat under reflux
Benedict's test for an aldehyde (not a preparative method)
H O
H C C H
H O
+ 2 Cu2+ + 5 OH- 
H
H C C O-
+ Cu2O + 3 H2O
H
Warm with Benedict's reagent. Formation of a red / brown precipitate indicates the presence
of an aldehyde. Fehling's solution behaves in a similary way. Both Benedict's and Fehling's
6/16
565323042
contain copper (II) complexes. These complexes enable Cu (II) to remain in solution in the
presence of alkali. Ketones are resistant to oxidation and do not react with Benedict's solution.
Tollen's reagent (ammoniacal silver nitrate) (not a preparative method)
Prepared by adding excess ammonia solution to silver nitrate solution so that the initially
formed precipitate redissolves. The solution formed contains Ag(NH 3)2+ (aq). Aldehydes are
oxidised by this reagent but not ketones:
RCHO + 2 Ag(NH3)2+ (aq) + 3 OH- (aq)  RCOO- + 2 Ag (s) + 4 NH3 (aq) + 2 H2O (l)
Formation of a silver mirror on the test tube indicates the presence of the aldehyde group.
2.
Formation of 2,4 dinitrophenylhydrazone
Reaction type: nucleophilic addition followed by elimination
O2N
H O
NH NH2
O2N
H H
+ H C C H 
NH N C C H
H
NO2
NO2
O2N
+ H2O
H
O2N
O
NH NH2
+
H3C C CH3
CH3

NH N C
NO2
Reagents:
Conditions:
NO2
+ H2O
CH3
2,4 dinitrophenylhydrazine in concentrated hydrochloric acid or
concentrated phosphoric acid (H3PO4)
Room temperature
2,4 dinitrophenylhydrazones are characteristically orange crystalline solids at room
temperature. Determination of their melting points is often used to identify the aldehyde or
ketone from which they were prepared.
3
Reduction with LiAlH4 (lithium tetrahydridoaluminate)
LiAlH4 reduces an aldehyde to a primary alcohol and a ketone to a secondary alcohol. The
reaction conditions are the same as those used in the reduction of a carboxylic acid by LiAlH 4.
4
Addition of hydrogen cyanide to aldehydes and ketones
Reaction type:
Mechanism:
addition
nucleophilic
OH
O
+
CH3
C
HCN
CH3
CH3
C
CH3
CN
The highly toxic HCN gas is generated by adding dilute sulphuric acid to KCN. The actual
reaction mixture should be pH 8. The cyanohydrin product can be converted into a -hydroxy
carboxylic acid by heating with concentrated HCl (aq) under reflux.
7/16
565323042
OH
CH3
OH
CH3 +
C
2 H2O + H+
CH3
C
2 NH4+
COO-
CN
5
CH3 +
Reaction with iodine in the presence of alkali
Conditions: KI (aq) in the presence of NaOH (aq)
In these conditions, I- disproportionates to form IO-.
R
O
H
C
C
H + 3 IO-
R
O
I
C
C
H
R
O
I
C
C
I + 3 OH-
I
RCO2- + CHI 3
I + OH-
I
The CHI3 product of this reaction is a characteristic pale yellow precipitate. This reaction is
used to test for the -COCH3 and -CHOHCH3 groupings (secondary alcohol is initially oxidised
to the ketone).
Carboxylic Acid
1.
Formation of ester
Reaction type: Condensation (nucleophilic addition of alcohol to acid followed by
elimination of water)
H H
H O
H C C OH +
H H
Reagents:
Conditions:
2.
H H
H C C OH

H
O H
H C C O C C H + H2O
H H
H
alcohol and concentrated sulphuric acid.
heated under reflux to form equilibrium mixture.
Conversion to alcohol
Reaction type: Reduction
H O
4 H C C OH + 3 LiAlH4
 LiAl (OCH2CH3)4 + 4 H2 + 2 LiAlO2
H
LiAl(OCH2CH3)4 + 4 H2O  4 CH3CH2OH + Al(OH)3 + LiOH
These equations do not need to be learnt. The reducing agent can be described notionally in
the equation as [H].
H O
H C C OH
H
H H
+ 4 [H]
 H C C OH
H H
8/16
+ H2O
565323042
Reagents and conditions:
i)
Lithium tetrahydridoaluminate (III) (lithium aluminium hydride) in dry ether solvent
ii)
Water (caution – hydrogen released / fume cupboard)
It is easier to reduce an ester than a carboxylic acid. Therefore, a carboxylic acid may be first
esterified with an alcohol and then reduced as above (to form 2 alcohols).
H H
O H
H H
H C C O C C H
H H
+ 4 [H]
 2 H C C OH
H
H H
It is not possible to produce an aldehyde directly from a carboxylic acid by reduction.
3.
Conversion to acid chloride
Reaction type: Substitution
H O
H O
+ PCl5  H C C Cl
H C C OH
H
H
Reagents:
Conditions:
4.
+ POCl3 + HCl
phosphorus (V) chloride
room temperature
Conversion to a salt
Reaction type: Acid-base
H O
H O
H C C OH
+ NaOH 
H C C O- Na+
H
2 H
+ H2O
H
H
OH
C
C
O + Na2CO3 (aq)
2H
H
H
O-Na+
C
C
O + CO2 (g) + H2O (l)
H
Reagents:
Conditions:
aqueous alkali
room temperature
Carboxylic Esters
1.
Conversion to alcohol and carboxylic acid
Reaction type: Hydrolysis (addition of water followed by elimination of alcohol)
i)
Acid catalysed
H H
O H
H C C O C C H
H H
Reagents:
Conditions:
H H
+ H2O  H C C OH +
H
H H
dilute sulphuric acid
heat under reflux
9/16
H O
H C C OH
H
565323042
The reaction reaches equilibrium – simply the reverse of ester synthesis from carboxylic acid
and alcohol.
ii)
In alkali
H H
O H
H H
H C C O C C H
H H
+ OH-  H C C OH + H C C O-
H
Reagents:
Conditions:
H O
H H
H
aqueous sodium or potassium hydroxide
heat under reflux
Unlike acid catalysed hydrolysis, the reaction goes to completion. The carboxylate salt is
converted into the protonated acid by adding dilute hydrochloric acid.
This is how soaps are made from triglycerides.
O
O
H
H C O
C
R'
O
+
O
O
+
-
O
O
+
-
Na
H C O H
H C O C R''
+ 3 NaOH  H C O H
H C
O
O
H
C
R'''
H C O H
-
C R''
Na
C R'''
H
Na
triglyceride
2
C R'
H
glycerol
O
fatty acid salts
Transesterification
(i)
Reaction with a carboxylic acid
Reaction type: substitution
Mechanism: nucleophilic
Acid catalyst required
CH3COOCH2CH3 + HCOOH ⇌ HCOOCH2CH3 + CH3COOH
This type of reaction is used to increase the proportion of saturated acids (e.g. stearic acid) in
margarine to increase its melting point.
(ii)
Reaction with an alcohol
CH3COOCH2CH3 + CH3OH  CH3COOCH3 + CH2CH3OH
A catalyst such as solid sodium hydroxide is required for this reaction. Biodiesel is
made from vegetable oils but the triglycerides in the oils need to be converted into methyl or
ethyl esters in order for the oil to be a suitable fuel for the engine. e.g.
O
CH2O
HCO
C
C
R
O
R
CH2OH
O
+
3
CH3OH
3
+
CH3O
CH2O
C
C
CHOH
R
CH2OH
R
O
10/16
565323042
Acyl Chloride (Acid chloride)
1.
Conversion to carboxylic acid
Reaction type: hydrolysis
H O
H O
H C C Cl
+ H2O 
H C C OH
H
H
Reagents:
Conditions:
2.
water
room temperature, reaction is vigorous
Conversion to ester
Reaction type: addition followed by elimination
H H
H O
H C C Cl + H C C OH
H H

Reagents:
Conditions:
H H
Conversion to amide
Reaction type: addition followed by elimination
H O
H C C Cl
H
Reagents:
Conditions:
+ 2 NH3  H C C NH2
+ NH4Cl
H
aqueous ammonia.
room temperature (care needed).
Conversion to N-substituted amide
Reaction type: addition followed by elimination
H O
H O
H C C Cl
+ H2NR  H C C NH R
H
Reagents:
Conditions:
5.
H
alcohol
room temperature
H O
4.
O H
H C C O C C H + HCl
H H
H
3.
+ HCl
+ HCl
H
primary amine.
room temperature.
Reduction with lithium tetrahydridoaluminate (III)
Acyl chlorides are reduced to primary alcohols by LiAlH 4 in the same way that the
corresponding carboxylic acids are reduced.
Arene
1.
(i)
Nitration
Reaction type: Electrophilic substitution
+ HNO3 
Reagents:
NO2 + H2O
concentrated nitric acid and concentrated sulphuric acid mixture.
11/16
565323042
Conditions:
55°C with constant agitation (reactants are immiscible).
Knowledge of mechanism is required (not shown above).
Above 60°C, a second nitration may take place at position 3.
(ii)
Reduction of nitro group to amine
+ 7 H+
NO2 + 3 SnCl2
+ 12 Cl-
2-
N+H3 + 3 SnCl6 + 2 H2O
Reagents:
Reaction conditions:
Tin and concentrated hydrochloric acid
These react together to form SnCl2 (with H2).
Cold water bath to form the amine salt.
The salt is then neutralised with concentrated NaOH (aq) to give
the amine which is then steam distilled.
N+H3 (aq) + NaOH (aq)
NH2 + H2O (l) + NaCl (aq)
(l)
2
Sulphonation
Reaction type:
Mechanism:
Reagent:
Substitution
Electrophilic
Fuming sulphuric acid (oleum)
+ SO3
3
Halogenation
Reaction type:
SO3H
Electrophilic substitution
+ Br2 
Reagents:
Conditions:
4.
Br
+ HBr
R
+ HCl
FeBr3 catalyst, bromine
heat
Alkylation (Friedel-Crafts reaction)
Reaction type: Electrophilic substitution
+ RCl 
12/16
565323042
Reagents:
Conditions:
chloroalkane and anhydrous AlCl3 (catalyst).
heat under reflux.
Attachment of an alkyl group activates the arene ring, making it susceptible to further
alkylations. These occur at positions 2 and 4.
5.
Conversion to an aromatic ketone (Friedel-Craft acylation)
Reaction type: Electrophilic substitution
O
+
O

R C
C R
+ HCl
Cl
Reagents:
Conditions:
6
acyl chloride and anhydrous aluminium chloride catalyst.
heat under reflux.
Reduction
+ 3 H2
Reaction type:
Conditions:
addition
Finely divided nickel, 150C
Phenol
1
Reaction with alkali (but not with carbonates)
Reaction type: Acid-base
2
O- Na+
+ NaOH 
OH
Conditions:
Aqueous solution, room temperature
Nitration
Reaction type:
Electrophilic substitution
NO2
OH
Reagent:
Conditions:
3
+ HNO3 
OH
4 mole dm-3 (dilute) nitric acid
room temperature
Halogenation
Reaction type:
Electrophilic substitution
13/16
+ H2O
565323042
Br
+ 3 Br2 
OH
Br
OH
+ 3 HBr
Br
Conditions:
Aqueous bromine, room temperature
Amine
1.
Conversion to amine salt
Reaction type: Acid base
R3N + HCl  R3NH+ ClReagent:
Conditions:
2.
(R = alkyl, aryl or H group)
dilute hydrochloric or sulphuric acid
room temperature
Reaction with transition metal ions
Reaction type: complexation
4 R3N + Cu2+  [Cu(R3N)4]2+ (R = alkyl, aryl or H group)
Reagent:
Conditions:
3.
Aqueous copper (II) sulphate solution
Room temperature
Conversion to N-substituted amide
Reaction type: addition followed by elimination
H O
H O
H C C Cl
+ H2NR  H C C NH R
H
Reagents:
H
acyl chloride
14/16
+ HCl
565323042
Conditions:
4.
room temperature.
Formation azo dye (from aromatic amines only)
(i)
Formation of diazonium salt
NH2 + NaNO2 (aq) + 2 HCl (aq)
N+ N
Cl- (aq)
Reagents:
Conditions:
(ii)
+ NaCl (aq) + 2 H2O
sodium nitrite and dilute HCl (aq)
less than 10°C
Coupling of diazonium salt to aromatic amine or phenol
N+ N
Cl- (aq)
N
+
NH2
NH2 + HCl
N
or
15/16
565323042
HO
-
N+ N
Cl- (aq)
O3S
Na+
+
HO
-
O3S
N
N
+
+ HCl (aq)
Na
Nitrile
1
Conversion to carboxylic acid
Reaction type:
Hydrolysis
Reaction conditions:
Heat under reflux with NaOH, then neutralise with HCl (can
also be hydrolysed with an acid catalyst)
CH3CH2CN + OH- (aq) + H2O (l) → CH3CH2COO- (aq) + NH3 (aq)
CH3CH2COO- (aq) + HCl (aq) → CH3CH2COOH (aq) + Cl- (aq)
2
Reduction to an amine
Reagents: LiAlH4 in dry ether followed by H2O
CH3CH2CN [ + 4 H] →
CH3CH2CH2NH2
16/16