chemistry - organic chemistry reaction scheme
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ORGANIC CHEMISTRY REACTION SCHEME AN OVERVIEW ALKANES Preparation of Alkanes 1. Hydrogenation of Alkenes CnH2n H2 + Ni, Pd or Pt CnH2n+2 2. Reduction of Alkyl Halides a. Hydrolysis of Grignard Reagent RX + Mg dry ethyl ether RMgX water RH + Mg(OH)X *Note: RMgX is the Grignard reagent, alkylmagnesium halide. The alkyl group is covalently bonded to magnesium; and magnesium-halogen bond is ionic ie. [R:Mg]+[X]–. In the second step of the reaction, it is a displacement reaction in which water (the stronger acid) displacing the weaker acid (R–H) from its salt (RMgX).
b. Reduction by Metal and Acid +
RX Zn + H RH + Zn2+ + X– Reactions of Alkanes 1. Halogenation [Free Radical Substitution] CnH2n+1H + X2 heat, or UV CnH2n+1X + HX 2. Combustion CnH2n+2 + excess O2 heat nCO2 + (n+1)H2O 3. Pyrolysis Cracking 400-600 C catalyst H2 + smaller alkanes + alkenes alkane with or w/o
ALKENES Preparation of Alkenes 1. Dehydrohalogenation of Alkyl Halides H H
H
C
C
H
X
H OH
alcoholic KOH reflux
H
H
H
C
C
2. Dehydration of Alcohols H H
H
C
C
H
OH
H
excess conc H2 SO4 , 170 C or Al2 O3 , 400 C or H3PO4 , 200-250 C
3. Dehalogenation of Vicinal Dihalides H H
H
C
C
X
X
Zn H H
H
H
H
C
C
H+ K X + H 2 O
H
H
C
C
H+ Z n X
H+ H 2O
2
Reactions of Alkenes 1. Addition of Hydrogen. Catalytic Hydrogenation H + Ni, Pd or Pt CnH2n+2 CnH2n 2 Heat
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2. Addition of Halogens [Electrophilic Addition using bromine/ethene] H H H H
H
C
X2 /CCl4 H dark, room temperature
C
3. Addition of Aqueous Halogen. Formation of Halohydrin H H H
H
C
H X2 /H 2O H
C
H
C
C
X
X
H
H H+ H X
C
C
X
OH
Dark, room temp
4. Addition of Hydrogen Halides H
H
H
C
HX H H
C
5. Addition of Water. Hydration a) Industrial Method H H
H
C
C
concH 2HO(g) 3 PO 4
H
H
H
H
C
C
X
H
H
H
H
C
C
H
OH
H
300C, 60atm
b) Laboratory Method H H
H
C
C
H
H2 SO4 conc cold
H
H
H
C
C
H
OS O 3 H
H
H2 O, heat → H (hydrolysis)
6. Oxidation a) Cold, alkaline KMnO4 Solution H H
H
C
C
alkaline KMnO4 →H cold
H
b) Hot, acidic KMnO4 Solution H H
H
C
C
H
H
H
C
C
OH
OH
−
C
H
C
C
H
OH
H+ H 2S O
4
H
H
MnO4 /H2 SO4 H → hot
H
H O
+
O
C
H
*Note: Terminal carbons will be oxidized into carbon dioxide. *Note: Under such oxidizing conditions, the aldehydes will be oxidized to carboxylic acid very quickly. To extract the aldehyde only, we must use immediate distillation.
7. Combustion
ARENES Reactions of Benzenes 1. Nitration [Electrophilic Substitution in mononitration of benzene] NO2 conc. HNO3 → conc. H2 SO4
55oC
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2. Sulphonation
– AN
OVERVIEW
OSO 2H + H 2O
H2 SO 4 ( l ) → reflux
3. Halogenation
X + X
2
cold, dark → FeX3 , or AlX3
+ HX
Or Fe 4. Friedel-Crafts Alkylation
R + RX
FeX3 , or AlX3 → Lewis Acid
+ HX
5. Friedel-Crafts Acylation
COR Note: acyl group
→
+ R C O C l / [(R C O ) 2O ]
O
+ HX
FeX3 , or AlX3
R
C H
6. Hydrogenation
+ 3H
Ni → 150C
2
Preparation of Alkylbenzenes 1. Attachment of Alkyl Group. Friedal-Crafts Alkylation
+ RX
R
FeX3 , or AlX3 → Lewis Acid
2. Conversion of side chain R
+ HX
H
H C
C O
Zn(Hg), HCl, heat → or N2H4 , base, heat
R
+ HNX2 + H2O
Or H2/Pd, ethanol
*Note: This is known as the Clemmensen or Wolff-Kishner Reduction
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Reactions of Alkylbenzenes 1. Hydrogenation
R
R + 3H
OVERVIEW
2
Ni, Pt, Pd → 150C
2. Oxidation a. Mild Oxidation
CHO
R MnO2 → oxidation
b. Strong Oxidation
R
COOH −
MnO4 /H2 SO4 → or acidified K 2 Cr2 O7
w h ite c r y s ta ls 3. Free Radical Aliphatic Halogenation RCH3
RCH2X
→ X2 UV, light or heat
*Note: Reaction above is only a generic reaction. Actual position of the halogen is dependent on the stability of the carbocation intermediate.
4. Electrophillic Aromatic Halogenation by Electrophillic Addition R R
R
X X2 → FeX3 , FeX5
+
X 5. Electrophillic Aromatic Nitration by Electrophillic Addition R R
R NO2
conc HNO3 → conc H2 SO4
+
o
30 C
NO2 6. Electrophillic Aromatic Friedal-Crafts Alkylation by Electrophillic Addition R R R
R1
+
R1X → AlX3
R1 http://education.helixated.com An Open Source Education Project
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7. Electrophillic Aromatic Sulphonation by Electrophillic Addition R R
OVERVIEW
R
OSO 2H
+
H2 SO4 ( l ) →
OSO 2H 8. Electrophillic Aromatic Friedal-Crafts Acylation by Electrophillic Addition R R
R COR1
+ R 1C O C l / [(R 1C O )2O ]
+
FeX3 , or AlX3 →
COR1 Alkylbenzenes clearly offers two main areas to attack by halogens: the ring and the side chain. We can control the position of the attack simply by choosing the proper reaction conditions. Refer to Appendix for more details.
HALOGEN DERIVATIVES Preparation of Halogenoalkanes 1. Substitution in Alcohols a. Using HX (suitable for 3° alcohols) dry HX, ZnX2 (catalyst) → R–X + H2O R–OH Reflux b. Using PX3/PX5 (suitable for 1°, 2° alcohols) PX3 /PX 5 → R–X + POX3 + HX R–OH Reflux c. Using SOCl2 (sulphonyl chloride) SOCl2 , Pyridine(C5H5N) → R–Cl + SO2 + HCl R–OH Reflux *Note: This is the best method because it is very clean. SO2 can be bubbled off and HCl, being an acid, will react with pyridine.
2. Electrophillic Addition to Alkenes a) Addition of Hydrogen Halides H H
H
C
C
HX → H H
H
H
C
C
X
H
b) Addition of Halogens H H
H
C
C
X2 /CCl4 H → dark, room temperature
H
H
H
H
C
C
X
X
H
3. Free Radical Substitution of Alkanes heat, or UV CnH2n+1H + X2 → CnH2n+1X + HX
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Reactions of Halogenoalkanes 1. Alkaline Hydrolysis of Alcohols [Nucleophilic Substitution] aqueous KOH R–X + OH– reflux R–OH + X– *Note: Mechanism is SN2 for 1° halogenoalkane and SN1 for 3° halogenoalkane
2. Nitrile Synthesis aqueous ethanol R–C≡N + NaBr R–X + NaCN reflux
*Note: Nitriles are useful because they can be used to synthesize 1o amines and carboxylic acids. Reduction to Amine: LiAlH4 , dry ether 2 , Ni, heat RCH2NH2 R–C≡N or 2H Acidic Hydrolysis: HCl ( aq ) RCOOH + NH4+ R–C≡N reflux
Basic Hydrolysis: NaOH ( aq ) RCOO–Na+ + NH3 R–C≡N reflux
3. Formation of Amines δ+
δ–
ethanol, reflux tube [H3N---R---X] NH3 RNH2 + NH4+X– R–X + excess conc NH3 sealed
*Note: NH3 acts as the nucleophile and the base. *Note: In the presence of excess RX, there will be polyalkylation of the halogenoalkane and 1°, 2°, 3° and even 4° ammonium salt will be formed. NH3 RX RNH2 RX R2NH RX R3N RX R4N+X–
4. Williamson Synthesis (Formation of Ether)Conc H SO , 140 C R–X + R'O–Na+ R–O–R' + NaX 2
4
o
*Note: The sodium or potassium alkoxide (anion of alcohol) is prepared by dissolving sodium and potassium in appropriate alcohol. ROH + Na RO–Na+ + ½H2
5. Dehydrohalogenation (Elimination) H H
H
C
C
H
X
− alcoholic KOH → H H + OH (aq ) reflux
H
H
C
C
Preparation of Halogenoarenes (Aryl Halides) 1. Electrophilic Aromatic Halogenation by Substitution
+ X
2
H + K X + H 2O
X
cold, dark → FeX3 , or AlX3
+ HX
Reactions of Halogenoarenes 1. Industrial Hydrolysis (Replacement of Halogen Atom, difficult due to strong C–X bond) + X O Na 2NaOH → 350C, 150atm
+ N aX
-
+ O Na
+ H 2O
OH +
H ( aq ) →
+ Na
+
2. Williamson Synthesis (Formation of Ether) R–X + ArO–Na+ → R–O–Ar + NaX Conc H2SO4, 140oC
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HYDROXY COMPOUNDS Preparation of Alcohols 1. Alkene Hydration. Addition of Water. H H
H
C
C
H
conc H2 SO4 → cold
H
H
H
C
C
H
OS O 3 H
H2 O, heat → H (hydrolysis)
H
H
H
C
C
H
OH
H+ H 2S O
4
2. Alkaline Hydrolysis of Halogenoalkanes aqueous KOH → R–OH + X– R–X + OH– reflux 3. Reduction of Carboxylic Acids, Aldehydes and Ketones a. Carboxylic Acids and Aldehydes are reduced to their primary alcohols. H R
C
O
+
4 [H ]
+
1. LiAlH4 (ethoxyethane), reflux 2.H /H2 0 → or H2 , Ni
R
C
HO
OH
+ H 2O
H H
R C
O
+
4 [H ]
+
1. LiAlH4 (ethoxyethane), reflux 2.H /H2 0 → or H2 , Ni
R
H
C
OH
H
b. Ketones are reduced to their secondary alcohols. R
C
O
+
4 [H ]
R +
1. LiAlH4 (ethoxyethane), reflux 2.H /H2 0 → or H2 , Ni
R1
C
R1
OH
H
*Note: Lithium aluminium hydride (or Lithium tetrahydridoaluminate(III)), LiAlH4, is one of the few reagents that can reduce an acid to an alcohol; the initial product is an alkoxide which the alcohol is liberated by hydrolysis. The –H ion acts as a nucleophile, and can attack the carbon atom of the carbonyl group. The intermediate then reacts with water to give the alcohol. OH R O H3C H3C H 2O C C O C H H – H H H H Carboxylic Acid: 4RCOOH + 3LiAlH4 4H2 + 2LiAlO2 + (RCH2O)4AlLi H2O 4RCH2OH Ketones: 4R2C=O + LiAlH4 (R2CHO)4AlLi H2O 4R2CHOH + LiOH + Al(OH)3
Reactions of Alcohols 1. Substitution in Alcohols a. Using HX (suitable for 3° alcohols) dry HX, ZnX2 (catalyst) R–X + H2O R–OH Reflux b. Using PX3/PX5 (suitable for 1°, 2° alcohols) PX3 /PX 5 R–X + POX3 + HX R–OH Reflux c. Using SOCl2 (sulphonyl chloride) SOCl , Pyridine(C5H5N) R–Cl + SO2 + HCl R–OH 2 Reflux *Note: This is the best method because it is very clean. SO2 can be bubbled off and HCl, being an acid, will react with pyridine.
2. Reaction with Sodium/Potassium H
H
C
O
H
H Sodium/Potassium →H
H
C
-
+
O Na
+
1 H 2
2
H
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3. Oxidation to Carbonyl Compounds and Carboxylic Acids a. Primary Alcohols are oxidized to aldehydes first, then carboxylic acids. R R R OH K 2 Cr2 O7 /H2 SO4 K 2 Cr2 O7 /H2 SO4 C O C → C → immediate or KMnO4 /H2 SO4 distillation H H HO H
O
*Note: MnO2 is also a milder oxidizing agent.
b. Secondary Alcohols are oxidized to ketones. R R OH K 2 Cr2 O7 /H2 SO4 C C → or KMnO4 /H2 SO4 R1 R1 H c.
O
Tertiary alcohols are not readily oxidized.
4. Dehydration to Alkenes a. Excess conc H2SO4 H H
H
C
excess conc H2 SO4 , 170 ° C H → H or Al2 O3 , 400 ° C
C
H
H
C
C
H+ H 2O
or H3PO4 , 200-250 ° C
H
OH
b. Excess alcohol 140° C R–CH2OH + conc H2SO4 → R–CH2–O– CH2–R excess alcohol 5. Esterification
R
O O
R1
C
(can use acid or alkaline as catalyst)
H
OH
C
conc H2 SO4 heat
O
+
R1
R
+
H 2O
O
6. Acylation a. Acid Chloride
R
C
+
Cl
Note: acyl group
R1
OH
R
→ room temperature
C
O
R1
O
+ HCl R
O
C
O
H
b. Acid Anhydride
R
C
O
O
C
R
+ R1 OH
room temperature →
R
C
O
O
R1
+
R
C
O
OH
O H
7. Tri-Iodomethane (Iodoform) Formation *Note: Reaction is only positive for alcohol containing a methyl group and a hydrogen atom attached to the carbon at which the hydroxyl group is also attached.
H
CH3
H R
C
OH
I2 , NaOH ( aq ) → warm
CHI3
CH3
a. Step 1: Oxidation of Alcohol to the corresponding carbonyl compound by iodine.
R
CH
OH
+
I 2 + 2 HO
-
R
CH3 http://education.helixated.com An Open Source Education Project
C
O
+ 2 H2 O
+ 2 I
-
CH3
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b. Step 2: Further oxidation to carboxylate salt and formation of iodoform
R
C
O
+ 3 I2 + 4 HO
-
R
O
CH3 c.
R
H
C
O
+ CHI3 + 3 I
-
+ 3 H 2O
O
+ CHI3 + 5 I
-
+ 5 H 2O
-
Overall Equation:
C
OH + 4 I 2 + 6 HO
-
R
C O
CH3 Preparations of Phenols 1. Replacement of OH– group in diazonium salts N + N O
NH2
-
O -
S
OH
OH
O +
→ NaNO2 , H2 SO 4
water, H , heat →
Reactions of Phenols 1. Reaction with Reactive Metals (e.g. Na or Mg) +
-
O Na
OH
+
Na
+
1 H 2 2
2. Reaction with NaOH -
OH
+
O Na
+ NaOH
+
1 H O 2 2
*Note: Phenols have no reactions with carbonates
3. Esterifications -
OH
+
O Na NaOH →
RCOCl →
O
O C R
*Note: Phenols do not react with carboxylic acids but their acid chlorides to form phenyl esters. *Note: Esterification is particularly effective in NaOH(aq) as the alkali first reacts with phenol to form phenoxide ion which is a stronger nucleophile than phenol.
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4. Halogenation a. With bromine(aq)
– AN
OVERVIEW
OH
OH
Br
Br
+ 3HBr
3Br2 ( aq ) →
Br *Note: 2,4,6-tribromophenol is a white ppt.
b. With bromine(CCl4) OH
OH
OH
+
Br2 (CCl4 ) →
Br
Br 5. Nitration a. With conc nitric acid
OH
OH O 2N
NO2
conc HNO3 →
NO2 b. With dilute nitric acid OH
OH
OH
+
dil HNO3 →
NO2
O 2N
6. Reaction with FeCl3(aq) *Note: This is a test for phenol. Violet complex upon adding iron(III) chloride will confirm presence of phenol. Colour may vary depending on the substitution on the ring. 3 --
O
OH 3+
Fe →
Fe 6
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– AN
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CARBONYL COMPOUNDS Preparation of Aldehydes 1. Oxidation of Primary Alcohols R OH K 2 Cr2 O7 /H2 SO4 → C immediate distillation H H
R C
2. Oxidative Cleavage of Alkenes R2 R3
R1
+ H 2O
O
R2
R3
−
MnO4 /H2 SO4 → hot
C
H 2O
H
Preparations of Ketones 1. Oxidation of Secondary Alcohols R R OH K 2 Cr2 O7 /H2 SO4 C C → or KMnO4 /H2 SO4 R1 R1 H
C
+
O
+
C R1
R4
C
O
O
R4
Reactions of Carbonyl Compounds 1. Addition of Cyanide. Cyanohydrin formation. [Nucleophilic Addition of Hydrogen Cyanide to Aldehyde and Ketone] H H H C HCN, small amount of base + CN C CN → H
O
OH
*Note: Cyanohydrins can be hydrolysed to form 2-hydroxy acids. Acidic Hydrolysis R
H
R
C
CN
water, HCl (aq) → heat
H
OH
Basic Hydrolysis
C OH
R H
C
+ NH4Cl
COOH
R CN
water, NaOH ( aq ) → H heat
OH
C
-
+
COO Na
+
NH3
OH
*Note: Cyanohydrins can undergo reduction. R
H
C
R CN
LiAlH4 in dry ether → or H2 , Ni, heat
H
OH
R2
C
CH2NH2
OH
2. Reaction with 2,4-Dinitrophenylhydrazine (Brady’s Reagent). Condensation Reaction. R2 C
O + H2N
NH
NO2
C
N
NH
NO2 +
H2O
R1
R1 O 2N
O 2N
*Note: 2,4-dinitrophenylhydrazones formed are orange or yellow crystalline solids with characteristic melting points. They are useful for identifying individual aldehydes and ketones.
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3. Oxidation Reactions *Note: Aldehydes are easily oxidized to carboxylic acids. Ketone are not.
a. Oxidation of Aldehydes using hot, acidified potassium dichromate(VI) *Note: K2Cr2O7 turned from orange to green if test is positive.
R
H
R
C
OH C
K 2 Cr2 O7 /H2 SO 4 → heat
O
O O
O K 2 Cr2 O7 /H2 SO 4 → heat
C
C
H R1
R C
OH K 2 Cr2 O7 /H2 SO4 → N o R e a c tio n heat
O b. Oxidation of Aldehydes using hot, acidified potassium manganate(VII) *Note: KMnO4 turned from purple to colourless if test is positive.
R
H
R
C
OH C
→ K 2MnO4 /H2 SO 4 heat
O
O O
O C
C
K 2MnO4 /H2 SO 4 → heat
H c.
OH
Oxidation of Aliphatic Aldehydes using Fehling’s Solution (Fehling’s Test)
R
H C
R
O
-
C
Fehling's Solution → warm
O
+
Cu2O (s)
O O C
Fehling's Solution → N o R e a c tio n warm
H R C
R1 Fehling's Solution → N o R e a c tio n warm
O *Note: Aliphatic aldehydes reduce the copper(II) in Fehling’s solution to the reddish-brown copper(I) oxide. R–CHO + 2Cu2+ + 5OH– R–COO– + Cu2O (s) + 3H2O *Note: Methanal (strongest aldehyde reducing agent) produces metallic copper as well as copper(I) oxide. HCHO + Cu2O + OH– HCOO– + 2Cu (s) + H2O
d. Oxidation of Aldehydes using Tollen’s Reagent (Silver Mirror Test)
R
H C
R Tollen's Reagent → warm
O
O C
-
+
Ag (s)
O O
O C
Tollen's Reagent → warm
H
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+ Ag (s)
C O
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d. Oxidation of Aldehydes using Tollen’s Reagent (Silver Mirror Test) (Cont’d) R R1 Tollen's Reagent C → N o R e a c tio n warm
O *Note: Aldehydes redyce the Ag(I) in Tollen’s reagent to Ag, forming a silver mirror. RCHO + 2[NH3→Ag←NH3]+ + 3OH– heat RCOO– + 2Ag (s) + 4NH3 + 2H2O
4. Reduction Reactions a. Reduction of Aldehydes to Primary Alcohols LiAlH4 in dry ether 4 ( aq ) R–CH2OH R–CHO + 2[H] or NaBH Ni catalyst R–CH2OH R–CHO + H2 heat b. Reduction of Ketones to Secondary Alcohols
R
H
R1
C
+
H2
LiAlH 4 in dry ether or NaBH4 ( aq )
R
C
O R
OH H
R1
C
R1
+
H2
R
Ni catalyst heat
C
O
R1
OH
5. Reaction with Alkaline Aqueous Iodine (Tri-Iodomethane (Iodoform) Formation)
H
*Note: Reaction is only positive for alcohol containing a methyl group attached to the carbon at which the carbonyl group is also attached i.e. methyl carbonyl compounds. For aldehydes, only ethanal will form iodoform. All methyl ketones will form iodoform. NaOH, warm R C O + CHI3 + 3I + 3H2O R C O + 3 I 2 + 4 HO →
O
CH3
-
6. Chlorination using Phosphorus Pentachloride (PCl5) *Note: Aldehydes and ketones react with phosphorus pentachloride to give geminal-dichloro (cf. vicinal) compounds. The oxygen atom in the carbonyl group is replaced by two chlorine atoms.
CH3CHO + PCl5 → CH3CHCl2 + POCl3 CH3COCH3 + PCl5 → CH3CCl2CH3 + POCl3
CARBOXYLIC ACIDS & DERIVATIVES Preparation of Carboxylic Acids 1. Oxidation a. Oxidation of Primary Alcohols and Aldehydes R R R OH K 2 Cr2 O7 /H2 SO4 K 2 Cr2 O7 /H2 SO4 C O C → C → immediate or KMnO4 /H2 SO4 distillation H H HO H b. Oxidative Cleavage of Alkenes H H
C H
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C
H
KMnO4 /H2 SO4 , heat →
O C OH
H
13
O
+
O
H C OH
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C CH3
O
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– AN
Oxidation of an Alkylbenzene (Formation of Benzoic Acid)
CH3
OVERVIEW
O C
+ 3 [O ]
OH
KMnO4/H2 SO 4 , heat →
+ H 2O
2. Hydrolysis a. Hydrolysis of Nitriles (R–C≡N) Acidic Hydrolysis HCl ( aq ) RCOOH + NH4+ R–C≡N reflux
Basic Hydrolysis NaOH ( aq ) RCOO–Na+ + NH3 R–C≡N reflux b. Hydrolysis of Esters (RCOOR’)
Acidic Hydrolysis HCl ( aq ), reflux RCOOR’ + H2O RCOOH + R’OH conc H2 SO4
Basic Hydrolysis NaOH ( aq ) RCOO–Na+ + R’OH RCOOR’ + H2O reflux +
H RCOOH RCOO–Na+ reflux
Reactions of Carboxylic Acids 1. Salt Formation a. Reaction with Metal RCOOH + Na RCOO–Na+ + ½H2 b. Reaction with Bases RCOOH + NaOH RCOO–Na+ + H2O c. Reaction with Carbonates 2RCOOH + Na2CO3 2RCOO–Na+ + H2O + CO2 2. Esterification
R
O
O C
R1 conc H2 SO4 heat
O
+
H
OH
(can use acid or alkaline as catalyst)
C R
R1 O
+
H 2O
3. Conversion into Acyl Chlorides (RCOCl) RCOOH + PCl5 RCOCl + POCl3 + HCl 3RCOOH + PCl3 3RCOCl + H3PO3 RCOOH + SOCl2 RCOCl + HCl + SO2 4. Reduction to Alcohols 1. LiAlH in dry ether RCOOH + 4[H] 2. H24 SO4 ( aq ) RCH2OH + H2O
Preparation of Acyl Chlorides 1. From Carboxylic Acid RCOOH + PCl5 RCOCl + POCl3 + HCl 3RCOOH + PCl3 3RCOCl + H3PO3 RCOOH + SOCl2 RCOCl + HCl + SO2
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Reactions of Acyl Chlorides 1. Conversion into Acid. Hydrolysis RCOCl + H2O RCOOH + HCl ArCOCl + H2O ArCOOH + HCl *Note: Benzoyl chloride reacts much slower than acyl chlorides because of the reduce in the positive nature of the carbonyl carbon caused by resonance.
2. Ester Formation. Alcoholysis. RCOCl + R’OH room temperature RCOOR’ + HCl *Note: Reaction is slow when phenol is directly reacted with acyl chloride. RCOCl + ArOH slow RCOOAr + HCl *Note: Because phenol is a weaker nucleophile (lone pair of electron delocalizes into the ring), it is converted to phenoxide to increase nucleophilic strength. ArOH + NaOH ArO–Na+ + H2O RCOCl + ArO– RCOOAr + Cl–
3. Amide Formation. Ammonolysis. RCOCl + NH3 RCONH2 + HCl RCOCl + R’NH2 RCONHR’ + HCl RCOCl + R’R’’NH RCONR’R’’ + HCl 4. Reduction to Aldehyde, then Alcohol LiAlH in dry ether LiAlH in dry ether RCOCl 4 RCHO H 24SO 4 ( aq ) RCH2OH Preparations of Esters 1. Condensation Reaction of Acid and Alcohol a. Ethyl Ethanoate
R
O C
O
R1
+
OH
conc H2 SO4 heat
O H
(can use acid or alkaline as catalyst)
C R
R1 O
+
H 2O
b. Phenyl Benzoate ArOH + NaOH ArO–Na+ + H2O ArCOCl + ArO–Na+ ArCOOAr + NaCl Reaction of Esters 1. Hydrolysis a. Acidic Hydrolysis HCl ( aq ), reflux RCOOR’ + H2O RCOOH + R’OH conc H2 SO4
b. Basic Hydrolysis NaOH ( aq ) RCOO–Na+ + R’OH RCOOR’ + H2O reflux
2. Reduction to Primary Alcohols LiAlH in dry ether RCOOR’ H 24SO 4 ( aq ) RCH2OH
Preparation of Polyesters 1. Condensation Reaction acid nHOOCRCOOH + nHOR’OH reflux ( OCRCOOR’O )
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NITROGEN COMPOUNDS Preparation of Amines 1. Reaction of Halides with Ammonia or Amines. Ammonolysis δ+ δ– ethanol, reflux tube [H3N---R---X] NH3 RNH2 + NH4+X– R–X + excess conc NH3 sealed NH3 RX RNH2 RX R2NH RX R3N RX R4N+X– 2. Reduction a. Reduction of Amide
LiAlH in dry ether RCONH2 H 24/ Ni or Pt RCH RNH22NH2
b. Reduction of Nitrile R–C≡N c.
LiAlH 4 , dry ether or 2H2 , Ni, heat
RCH2NH2
Reductive Amination
H
H
H C
O
+ NH3 →
H
H
C NH imine
H2 , Ni →H or NaBH3 CN
C
NH2
H
Reactions of Amines 1. Salt Formation RNH2 + HCl → RNH3+ Cl– RNH2 + R’COOH → RNH3+ –OOCR’ +
NH2
NH3 Cl
+
HCl
-
→
*Note: Phenylamine is not soluble in water but dissolves in acid.
2. Formation of Amides. Acylation. R'COCl → R'CONHR + HCl ArSO2 Cl → ArSO 2NHR + HCl
RNH2 RR'NH
R''COCl → R''CONRR' + HCl ArSO2 Cl → ArSO 2NRR' + HCl
RR'R''N
R'''COCl → no reaction ArSO2 Cl → no reaction
*Note: Since HCl is formed, some of the ammonia/amine will be protonated and cannot act as a nucleophile. Hence, at least double the amount of ammonia / amine must be used. *Note: Acylation of 1° and 2° amines leads to the formation of substituted amides. 3° do not undergo acylation because they do not have any replaceable H atoms. CH3CH2NH2 + CH2COCl CH3CH2NHCOCH3 + HCl ArNH2 + Ar’COCl ArNHCOAr’ + HCl ArNH2 +RCOCl ArNHCOR + HCl
3. Ring Substitution Reactions of Aromatic Amines a. Halogenation NH2
NH2 Br
+
3Br2 (aq)
Br
→
(s)
+ 3HBr
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*Note: To get monosubstituted compounds, react phenylamine with ethanoyl chloride to reduce the ‘strongly activating’ nature of the amino group to form phenylacetamide. NH2
NHCOCH3
+
→ CH3COCl
*Note: NHCOCH3 is also 2,4-directing but moderately activating. Halogenation of ArNHCOCH3 will give N-(2bromophenyl)acetamide or N-(4-bromophenyl)acetamide. Reacting this with aqueous NaOH and heating will give 2-bromophenylamine or 4-bromophenylamine.
b. Nitration
NH2
NH2 O 2N
NO2
conc HNO3 + conc H SO → 2 4
NO 2 *Note: The same steps as above can be taken if we want monosubstituted nitrophenylamine. Preparations of Amides 1. Ammonolysis of Acid Derivatives RCOCl + NH3 → RCONH2 + HCl RCOCl + R’NH2 → RCONHR’ + HCl RCOCl + R’R’’NH → RCONR’R’’ + HCl 2. Reaction between Amine and Acid Chloride R'COCl → R'CONHR + HCl RNH2 ArSO2 Cl → ArSO 2NHR + HCl RR'NH
R''COCl → R''CONRR' + HCl ArSO2 Cl → ArSO 2NRR' + HCl
Reactions of Amides 1. Acidic Hydrolysis HCl, H2 O → R–COOH + NH4+ RCONH2 heat
2. Basic Hydrolysis NaOH, H2 O → R–COO– + NH3 RCONH2 heat
Preparations of Amino Acids 1. Hell-Volhard-Zelinsky Reaction H Br2 , PBr3 → heat
C H
H
R
COOH
C Br
H excess conc NH3 → COOH H2N R
C R
COOH
Reactions of Amino Acids 1. Salt Formation a. Reaction with H+. Cationic + H3N–CH2–COO–(aq) + H+(aq) → +H3N–CH2–COOH (aq) – b. Reaction with OH . Anionic + H3N–CH2–COO–(aq) + OH– (aq) → H2N–CH2–COO– (aq) + H2O(l) *Note: The above two equations explains the buffering capability of amino acids.
2. Acylation (Formation of Amides) CH3COCl + H2N–CH2–COOH → CH3–CO–NH–CH2COOH + HCl http://education.helixated.com An Open Source Education Project
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3. Esterification HCl H2N–CH2–COOH + ROH
+
H3N–CH2–COOR + H2O
4. Peptide Formation *Note: A peptide is any polymer of amino acids linked by amide bonds between the amino grup of each amino acid and the carboxyl group of the neighbouring amino acid. The –CO–NH– (amide) linkage between the amino acids is known as a peptide bond.
H2N
CH
C
R
O
OH
+ H2N
CH
C
R1
O
OH
H2N
5. Hydrolysis of Peptides a. Acidic Hydrolysis H O H
------
C
C
R
H ------
C R
N
C
H
R1
H2 SO4 ( aq ) → ----------- heat
N
C
H
R1
C
N
CH
C
R
O
H
R1
O
H
O
C
C
OH
NaOH ( aq ) → ----------- heat
+
OH
+
H3N
C
------
R1
H
O
C
C
R
+ H2 O
H
R
b. Basic Hydrolysis O H
C
CH
H O
-
+
H2N
C
------
R1
*Note: A peptide bond can be cleaved by hydrolysis in the presence of a suitable enzyme (trypsin, pepsin etc) or by heating in acidic or alkaline medium.
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APPENDIX Halogenation of Alkylbenzenes: Ring vs Side chain Alkylbenzenes clearly offer two main areas to attack by halogens: the ring and the side chain. We can control the position of attack simply by choosing the proper reaction conditions. Halogenation of alkanes requires conditions under which halogen atoms are formed, that is, high temperature or light. Halogenation of benzene, on the other hand, involves transfer of positive halogen, which is promoted by acid catalysts like ferric chloride (FeCl3). heat or light CH4 + Cl2 → CH3Cl + HCl + Cl2
FeCl3 , cold →
Cl
+ HCl
We might expect, then, that the position of attack in, for example, methylbenzene would be governed by which the attack particle is involved, and therefore by the conditions employed. This is so: if chlorine is bubbled into boiling methylbenzene that is exposed to ultraviolet light, substitution occurs almost exclusively in the side chain; in the absence of light and in the presence of ferric chloride, substitution occurs mostly in the ring.
CH3
Cl●
Atom: Attacks side chain
Cl+
Ion: Attacks ring
Markovnikov’s Rule In the ionic addition of an acid to the carbon-carbon double bond of an alkene, the hydrogen of the acid attaches itself to the carbon atom that already holds the greater number of hydrogens. Saytzeff’s Rule For elimination reactions, the preferred product is the alkene with the most alkyl groups attached to the doubly bonded carbon atoms i.e. the most substituted product.
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