organic chemistry reacions summary
TRANSCRIPT
ORGANIC CHEMISTRY REACTIONS
Preparations of Alkyl Halides
Organic Halogen Compounds
1. Electrophilic Addition of Halogens or Hydrogen Halides to Alkenes
R
R
R
R+ X2 R
R
XR
R
X
R
R
R
R+ R
R
HR
R
XHX
H
CH3
H
H3C+ Cl2 H3C
H
ClCH3
H
Cl
HClH
CH3
H
H3C+ H3C
H
HCH3
H
Cl
Examples:
Examples:
1.
2.
2. Nucleophilic Substitution of Alcohols
General equation:
X = Cl, Br, I (Reagents: HCl, HBr, HI, SOCl2, PCl3, PBr3
H3PO3
OH+ HCl
Cl+ H2O
Examples:
OH + SOCl2 Cl + SO2
OH + PBr3Br +
HCl+
)
3. Preparation of Aryl Halides
+ X2FeX3
X+ HX
X = Cl, Br
+ Cl2FeCl3
Cl+ HCl
Example
Reaction of Alkyl Halides
H
XR
H
+ Nu-
H
NuR
H
+ X-
X = Cl, Br, I
Examples of nucleophiles: OH-, H2O, RO-, RCOO-, H2S, RSH, NHR2, NH2R, NH3
RX + HO- ROH + X-
alcohol
RX + H2O ROH + HXalcohol
RX + RO-Na ROR + X-
ether
RX + RCOO- + X-RCOORester
Br + NaOH OH + NaBr
ClH2O+
OH+ HX
Br++ O-Na+ O NaBr
Br ++ O-Na+ O NaBr
O
O
1.
2.
3.
4.
.
R'-X (excess)+ RNH2 R-N(R')3X+ -
RX + H2S RSH (thiol) + HX
Cl + H2S SH HCl+
R'X + RNH2 (excess) RNHR' + HX
CH3CH2NH2 + CH3Br CH3CH2NHCH3 + HBr
CH3CH2N+(CH3)3Br-CH3CH2NH2 + CH3Br
(excess)
(excess)
5.
6.
7.
Reaction Mechanism of Nucleophilic Substitutions
(i) SN
2 Reaction Mechanism
Example: Reaction of OH- with bromomethane (methyl bromide)
(ii) SN
1 Reaction Mechanism
C
Carbocation
+ XC X
CCNu Nu Enantiomer A
CC Nu Enantiomer BNu
Example: Reaction of water with (S)-3-bromo-2,3-dimethylpentane
Amines
Preparations of Amines
1. Reduction of Amides
Amides can be reduced to amines by using lithium aluminium hydride (LiAlH4
R NH2
O LiAlH4
AmideR NH2
then H2O
).
Example:
NH2
O
NH2Butanamide
LiAlH4then H2O
2. Reduction of Nitriles
Nitriles are compounds that contain group. Nitriles can be reduced to primary amines by using hydrogen in the presence of Ni catalyst.
RNitrile
R NH2C N
H2/ Ni
Example:
CNH2
NH2/ Ni
C N
3. Reduction of Aromatic Nitro Compounds to Aromatic Amines
Aromatic nitro compounds can be reduced to aromatic amines by using hydrogen/Pt or Sn/HCl.
NO2
H2/ Ptor
Sn/ HCl, then NaOHNH2
Reactions of Amines
1. Neutralisation with Acids As amines are basic, they can react with acids to form salts which are soluble in water.
R-NH2 + HCl RNH3+Cl-
Amine Alkyl ammonium chloride,
Example:
CH3NH2 + HCl CH3NH3+Cl
2. Reaction of Alkyl Halides
-
R'-X (excess)+RNH2 R-N(R')3X+ -
RNH2 (excess) + R'X RNHR' + HX
CH3CH2NH2 + CH3Br CH3CH2NHCH3 + HBr
CH3CH2N+(CH3)3Br-CH3CH2NH2 + CH3Br
(excess)
(excess)
3. Formation and Reaction of Diazonium Salts
NH2 N NCl
aniline diazonium salt
NaNO2, HCl
0 oC
The diazonium salt can undergo a coupling reaction with phenols or aromatic amines to give azodye compounds, which are highly coloured.
N NCl
diazonium salt
R
R = OH, NH2, NHR, NR2
+ NN
R
Azodye
Example:
N NCl
diazonium salt
N+ NN
N
AzodyeN.N-dimethylaniline
Preparations of Alcohols
Alcohols, Phenols and Ethers
1. Hydration of Alkenes
Example: Hydration of trans-but-2-ene
2. Nucleophilic substitution of alkyl halides
R X + OH- R OH + X-
OH- can be obtained from H2
Example:
CH3CH2Br NaOH CH3CH2OH + NaBr+
O, NaOH, KOH and X = Br, Cl, I
+ H2O
H OH
H+
+ H2O
H
OHH+ H
H
3. Reduction of Aldehydes and Ketones
(i) Catalytic hydrogenation
R R'
OH2+
R R'
HO HNi catalyst
Reaction conditions: hydrogen + nickel catalyst
Example:
OH2+
HO HNi catalyst
(ii) Reduction by lithium aluminium hydride (LiAlH4
)
R' R"
O
R' R"
OHHthen H2O
LiAlH4
then H2OLiAlH4
Example:
H
O
H
OHH
(iii) Synthesis using Grignard reagents
R' R
O
R' R
OHR"+ R"MgX
Grignardreagent
then H2O
R = alkyl or aryl X = Cl, Br, I
Examples:
H
O
H
OHCH3+ CH3MgBr
CH3
O
CH3
OHCH3
+ CH3MgBr
then H2O
then H2O
Reactions of Alcohols
1. Reaction with Hydrogen Halides R-OH + HX R-X + H2
Alcohol Alkyl halide
O
Reactivity of R-OH: Tertiary OH > Secondary OH > Primary OH
Example:
H3C CH3
H OH
H3C CH3
H Cl+ HCl + H2O
2. Dehydration to Alkenes
OH
RR
R
HR H2SO4 (concentrated)
Concentrated H2SO4 is a dehydrating reagent
alcoholR
R
R
R+ H2O
alkene
3. Oxidation to Carbonyl Compounds
(i) Oxidation of primary alcohol
Primary alcohol Aldehyde Carboxylic acid
Oxidation of primary alcohol with PCC
R OH
HH
Primary alcohol
PCCR O
H
Aldehyde
OH
Primary alcohol
PCCO
H
Aldehyde
1-Propanol Propanal
Example
HR
H
OH[O]
R
H
Ofurther [O]
R
HO
O
Oxidation of primary alcohol with CrO
3
R OH
HH
Primary alcohol
CrO3
R O
H
Oxidation doesnot stop here!
R O
OH
Carboxylicacid
Example
OHOH
OCrO3
OH OH
O
CrO3
(ii) Oxidation of secondary alcohol
Secondary alcohol Ketone
OH
Secondary alcohol
PCCO
Ketone2-Pentanol Pentan-2-one
R OH
HR'
Secondary alcohol
PCC or CrO3
R O
R'
Ketone
PCC = Pyridinium chlorochromate
CrO3 = Chromic acid
Example
(iii) Oxidation of tertiary alcohol
Tertiary alcohol
R'R
H
OH[O]
R
R'
O
no further [O]
R'R
R''
OH[O]
no reaction
Preparation of Phenol SO3H OH
H2SO4 NaOH
300 oCbenzene benzenesulfonic
acidphenol
concentrated
Reactions of Phenols
1. Neutralisation OH
phenol
+ NaOH
O-Na+
sodiumphenoxide
+ H2O
2. Electrophilic Substitution with Halogens
OH
phenol
+ Br2 (aq)
OH
2,4,6-Tribromophenol
Br Br
Br
Preparation of Ethers
Ethers can be prepared by Williamson synthesis.
2 ROH + 2 Na 2 RO-Na+ + H
RO
2
-Na+
Example:
+ R’-Br ROR’ + NaBr
2 CH3OH + 2 Na 2 CH3O-Na+ + H2
CH
3O-Na+ + CH3CH2Br CH3OCH2CH3
+ NaBr
Preparations of Aldehydes
Aldehydes and Ketones
R OH
HH
Primary alcohol
PCCR O
H
Aldehyde
OH
Primary alcohol
PCCO
H
Aldehyde
1-Propanol Propanal
Example
Preparations of Ketone
OH
Secondary alcohol
O
Ketone2-Pentanol Pentan-2-one
R OH
HR'
Secondary alcohol
PCC or CrO3
R O
R'
Ketone
PCC = Pyridinium chlorochromate
CrO3 = Chromic acid
Example
PCC or CrO3
Reactions of Aldehydes and Ketones
1. Oxidation of Aldehydes to Form Carboxylic Acids
R H
O
Aldehyde
R OH
OCrO3 orTollen's reagent
Carboxylic acid
Example:
H
O
OH
O+ Ag
Tollen's reagent
Tollen’s reagent (AgNO3 + NH3 (aq)
2. Reduction to Alcohols
) is used as a test to distinguish aldehydes from ketones. Upon treatment with Tollen’s reagent, only aldehydes will give a silver mirror. No silver mirror is formed for ketones.
R' R"
O
R' R"
OHH
Aldehydes
Ketones
Primary alcohols
Secondary alcohols
then H2OLiAlH4
then H2OLiAlH4
then H2OLiAlH4
H
OOH
Butanal 1-Butanol
O
3-Methylpentan-2-one
OH
aldehyde
ketone
primary alcohol
3-Methylpentan-2-olsecondary alcohol
then H2OLiAlH4
then H2OLiAlH4
Example
Reaction mechanism of carbonyl compounds with LiAlH
R R
O
H
O-
RR H
O
RR
HH-OH
H-
4
3. Reaction with Grignard Reagents
Aldehydes Secondary alcoholsthen H2OR"MgX
H
O+ CH3MgBr
Butanal Methyl magnesiumbromide
HOH
CH3
Pentan-2-ol
then H2O
Example
then H2OKetones Tertiary alcoholsR"MgX
O
+ CH3MgBrPentan-2-one Methyl magnesium
bromide
CH3
OH
CH3
2-Methylpentan-2-ol
then H2O
Example
Reaction mechanism of carbonyl compound with Grignard reagent
H-OHR R
O
R'
OMgX
RR R
O
RR
H
R'MgX
4. Reaction with Amines or Hydrazines
Reaction of aldehydes and ketones with 2,4-dinitrophenylhydrazine
H3C
HO + NH2N
O2N
NO2
H
H3C
HNN
O2N
NO2
H
+ H2O
H3C
H3CO + NH2N
O2N
NO2
H
H3C
H3CNN
O2N
NO2
H
+ H2O
Aldehydes and ketones react with 2,4-dinitrophenylhydrazine to produce 2,4-dinitrophenylhydrazone (orange precipitate). This reaction used as a test for aldehydes and ketones.
Reaction mechanism of ketones with primary hydrazines:
R R
O
NH2NHR'
O-
RR
Tetrahedralintermediate
NHNHR'
O-
RR
H- H2O
R R
N
R'NHNH2
Protontransfer
NHR'
5. Iodoform Reaction
A chemical test for aldehyde and ketone with a CH3CO- group will gives CHI3
H3C R
O
+ 3I2 + NaOH CHI3 + RCOO-Na+ + 3HIwarm
yellow ppt
(iodoform), a yellow ppt.
General properties of carboxylic acids
Carboxylic Acids and Their Derivatives
1. Carboxylic acids can react with sodium to form salts and water.
2 RCOOH + 2 Na 2 RCOO-Na+ + H
O
OH +2 2NaO
O-Na+ + H22
2
2. Carboxylic acids can react with inorganic bases to form salts and water.
RCOOH + NaOH RCOO-Na+ + H2
O
OH + NaOH
O
O-Na+ + H2O
O
3. Carboxylic acids can react with carbonate to form salts, carbon dioxide and water.
2 RCOOH + Na2CO3 2 RCOO-Na+ + CO2 + H2
O
OH +2 Na2CO3
O
O-Na+ + CO2 + H2O2
O
Preparations of Carboxylic Acids
1. Oxidation of Primary Alcohols
R OH
HH
Primary alcohol
CrO3
R O
H
Oxidation doesnot stop here!
R O
OH
Carboxylicacid
Example:
OHOH
OCrO3
OH OH
O
CrO3
2. Oxidation of Alkylbenzenes
R COOHKMnO4
Alkylbenzene Benzoic acid
Examples:
COOHKMnO4
Benzoic acid
OH COOHKMnO4
3. Carboxylation of Grignard Reagents
RMgX + CO2 RCOOHthen H2O
Examples:
+ CO2
MgBr
MgBr
+ CO2
COOH
COOH
then H2O
then H2O
Reactions of Carboxylic Acids
1. Reduction to Form Alcohols
LiAlH4,
then H2OR OH
Oheat
R OH
Example:
LiAlH4,
then H2O
heatOH
OOH
Propanoic acid 1-Propanol
2. Formation of Acid Chlorides
R OH
O SOCl2R Cl
O
Example:
OH
O SOCl2Cl
O
Propanoic acid Propanoyl chloride
3. Formation of Acid Anhydrides
R OH
O
R O
O
R
O
acid anhydride
H2ORHO
O+
heat+
4. Formation of Esters
Carboxylic acids can react with alcohols to give esters. This process is called Fishcher esterification. The esterification is catalysed by dilute sulphuric acid. One water molecule is also formed: OH from carboxylic acid, H from alcohol.
R OH
O
R O
OR'
Ester
H2OHO+heat
+R'
Carboxylicacid
Alcohol
H+
Example:
Benzoic acid
O
OH
O
O
Ethyl benzoate
OH+ + H2Oheat
H+
Preparation of Acid Chlorides
Acid Chlorides
Acid chlorides can be prepared by reacting carboxylic acids with thionyl chloride (SOCl2
).
R OH
O SOCl2R Cl
O
Example:
OH
O SOCl2Cl
O
Propanoic acid Propanoyl chloride
Reactions of Acid Chlorides
1. Acid chlorides can react with water to form carboxylic acids. This reaction with water is called hydrolysis of acid chlorides.
R Cl
O
Acid chlorideR OH
O
Carboxylic Acid
H2O
Example:
Cl
O
OH
OH2O
Propanoylchloride
Propanoic acid
2. Acid chlorides can also react with alcohols to form esters.
R Cl
O
Acid chlorideR OR'
O
Ester
R'OH+
Alcohol
Example:
Cl
O
O
OOH+
3. Acid chlorides can react with ammonia/amines to form amides.
R Cl
O
Acid chloride
R N
O
Secondary amide
2 R'NH2+ R'
H
R Cl
O
Acid chlorideR N
O2 NH3+ H
HAmmonia
NH4+Cl-+
R'NH3+Cl-+
Primary amide
Primaryamine
R Cl
O
Acid chloride
R N
O
Tertiary amide
2 R'NHR"+ R'
R"
R'NR"H2+Cl-+
Secondaryamine
Examples:
Cl
O
N
OCH3NH2+ CH3
H
Cl
O
N
ONH3+ H
H
NH4+Cl-+
CH3NH3+Cl-+
Preparation of Acid Anhydrides
Acid Anhydrides
The most general method for preparing acid anhydrides is by reacting sodium salt of carboxylic acids (sodium alkanoates) with acid chlorides.
R' Cl
O
Acidchloride
R O
O
Acid anhydride
R O-Na+
O
Sodium alkanoate
+R'
O
Example:
Cl
O
Ethanoyl chloride(acetyl chloride)
O
O
Acetic anhydride
O-Na+
O
Sodium ethanoate(sodium acetate)
+O
Reactions of Acid Anhydrides
1. Acid anhydrides can be hydrolysed by water to form carboxylic acid.
R O
O
Acid anhydrideR OH
OH2OR'
O
R' OH
O+
Example:
O
O
OH
OH2OO
OH
O+
2. Acid anhydrides can also react with alcohols to form esters. This reaction requires a base (eg. pyridine)
R OR'
O
Ester
R'OH+R O
O
Acid anhydrideR
O pyridine
Example:
O
O O
O
O
OH+pyridine
3. Acid anhydrides can react with ammonia/amines to form amides.
R N
O 2R''NH2+ R''
H
R N
O2 NH3+ H
HR O
O
R'
O
R O
O
R'
O
Ammonia
Primary amide
Primaryamine Secondary amide
+R O
O
R'
O
R N
O
Tertiary amide
2R''NHR"' R''
R"'Secondaryamine
R' O-NH4+
O+
R' O-N
O+
R''
R' O-NH2
O
R''
R'''+
+
+
Examples:
O
O O
N
O
2CH3NH2+
H
H
N
O
2NH3+
CH3
HO
O O
O-NH4+
O
+
O-NH3CH3
O+ +
Preparations of Esters
Esters
1. Fishcher esterification
R OH
O
R O
OR'
Ester
H2OHO+heat +R'
Carboxylicacid
Alcohol
H+
Example:
Benzoic acid
O
OH
O
O
Ethyl benzoate
OH+ + H2Oheat
H+
2. Esters can also be synthesized from acid chlorides and alcohols. Pyridine is used as a base to remove HCl that is formed during the reaction
R Cl
O
Acid chlorideR OR'
O
Ester
R'OH+Alcohol
pyridine
Reactions of Esters
1. Esters can be hydrolysed by water under acidic condition to form carboxylic acid and alcohols.
R OH
O
Carboxylic acid
Ester
R O
OR' R'OH+
Alcohol
+ H2OH+
Example:
OH
OO
O
++ H2O
Methyl benzoate
CH3OHH+
2. Esters can also react with base (NaOH) to carboxylic acid salts and alcohols. The basic hydrolysis is called saponification.
R O-Na+
O
Carboxylic salt
Ester
R O
OR' R'OH+
Alcohol
+ NaOH
Example:
O-Na+
O
O
O
++ NaOH
Methyl benzoate
CH3OH
Sodium benzoate
3. Esters can react with ammonia/amines to form amide and alcohols.
R N
O R"NH2+ R"
H
R N
O NH3+ H
H
R O
OR'
R O
OR'
R'OH+
R'OH+
Examples:
N
O CH3NH2+ CH3
H
N
O
NH3+ H
HO
O
O
O
+
+
OH
OH
4. Esters can be reduced with lithium aluminium hydrides (LiAlH4
R OH
Ester
R O
OR' R'OH+
AlcoholAlcoholthen H2O
LiAlH4
) to form alcohol.
Example:
then H2OLiAlH4 OHO
O+
Methyl benzoate
CH3OH
Benzylalcohol
Methanol