ORGANIC CHEMISTRY REACTION SCHEME
Organic Chemistry Reaction Scheme
An Overview
Alkanes
Preparation of Alkanes
1. Hydrogenation of Alkenes
CnH2n [pic] CnH2n+2
2. Reduction of Alkyl Halides
a. Hydrolysis of Grignard Reagent
RX + Mg [pic] RMgX [pic]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 [pic] RH + Zn2+ + X–
Reactions of Alkanes
1. Halogenation [Free Radical Substitution]
CnH2n+1H + X2[pic]CnH2n+1X + HX
2. Combustion
CnH2n+2 + excess O2 [pic]nCO2 + (n+1)H2O
3. Pyrolysis Cracking
alkane [pic] H2 + smaller alkanes + alkenes
AlkEnes
Preparation of Alkenes
1. Dehydrohalogenation of Alkyl Halides
[pic]
2. Dehydration of Alcohols
[pic]
3. Dehalogenation of Vicinal Dihalides
[pic]
Reactions of Alkenes
1. Addition of Hydrogen. Catalytic Hydrogenation
CnH2n [pic] CnH2n+2
2. Addition of Halogens [Electrophilic Addition using bromine/ethene]
[pic]
3. Addition of Aqueous Halogen. Formation of Halohydrin
[pic]
4. Addition of Hydrogen Halides
[pic]
5. Addition of Water. Hydration
a) Industrial Method
[pic]
b) Laboratory Method
[pic]
6. Oxidation
a) Cold, alkaline KMnO4 Solution
[pic]
b) Hot, acidic KMnO4 Solution
[pic]
*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]
[pic]
2. Sulphonation
[pic]
3. Halogenation
[pic]
4. Friedel-Crafts Alkylation
[pic]
5. Friedel-Crafts Acylation
[pic]
6. Hydrogenation
[pic]
Preparation of Alkylbenzenes
1. Attachment of Alkyl Group. Friedal-Crafts Alkylation
[pic]
2. Conversion of side chain
[pic]
*Note: This is known as the Clemmensen or Wolff-Kishner Reduction
Reactions of Alkylbenzenes
1. Hydrogenation
[pic]
2. Oxidation
a. Mild Oxidation
[pic]
b. Strong Oxidation
[pic]
3. Free Radical Aliphatic Halogenation
[pic]
*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
[pic]
5. Electrophillic Aromatic Nitration by Electrophillic Addition
[pic]
6. Electrophillic Aromatic Friedal-Crafts Alkylation by Electrophillic Addition
[pic]
7. Electrophillic Aromatic Sulphonation by Electrophillic Addition
[pic]
8. Electrophillic Aromatic Friedal-Crafts Acylation by Electrophillic Addition
[pic]
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)
R–OH [pic] R–X + H2O
b. Using PX3/PX5 (suitable for 1°, 2° alcohols)
R–OH [pic] R–X + POX3 + HX
c. Using SOCl2 (sulphonyl chloride)
R–OH [pic] R–Cl + SO2 + HCl
*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
[pic]
b) Addition of Halogens
[pic]
3. Free Radical Substitution of Alkanes
CnH2n+1H + X2[pic]CnH2n+1X + HX
Reactions of Halogenoalkanes
1. Alkaline Hydrolysis of Alcohols [Nucleophilic Substitution]
R–X + OH– [pic]R–OH + X–
*Note: Mechanism is SN2 for 1° halogenoalkane and SN1 for 3° halogenoalkane
2. Nitrile Synthesis
R–X + NaCN [pic]R–C≡N + NaBr
*Note: Nitriles are useful because they can be used to synthesize 1o amines and carboxylic acids.
Reduction to Amine:
R–C≡N[pic] RCH2NH2
Acidic Hydrolysis:
R–C≡N[pic] RCOOH + NH4+
Basic Hydrolysis:
R–C≡N[pic] RCOO–Na+ + NH3
3. Formation of Amines
R–X + excess conc NH3 [pic] [H3---R---] [pic]RNH2 + NH4+X–
*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[pic] RNH2 [pic] R2NH [pic] R3N [pic] R4N+X–
4. Williamson Synthesis (Formation of Ether)
R–X + R'O–Na+ [pic]R–O–R' + NaX
*Note: The sodium or potassium alkoxide (anion of alcohol) is prepared by dissolving sodium and potassium in appropriate alcohol. ROH + Na [pic] RO–Na+ + ½H2
5. Dehydrohalogenation (Elimination)
[pic]
Preparation of Halogenoarenes (Aryl Halides)
1. Electrophilic Aromatic Halogenation by Substitution
[pic]
Reactions of Halogenoarenes
1. Industrial Hydrolysis (Replacement of Halogen Atom, difficult due to strong C–X bond)
[pic]
[pic]
2. Williamson Synthesis (Formation of Ether)
R–X + ArO–Na+ [pic] R–O–Ar + NaX
Hydroxy compounds
Preparation of Alcohols
1. Alkene Hydration. Addition of Water.
[pic]
2. Alkaline Hydrolysis of Halogenoalkanes
R–X + OH– [pic]R–OH + X–
3. Reduction of Carboxylic Acids, Aldehydes and Ketones
a. Carboxylic Acids and Aldehydes are reduced to their primary alcohols.
[pic]
[pic]
b. Ketones are reduced to their secondary alcohols.
[pic]
*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.
[pic]
Carboxylic Acid: 4RCOOH + 3LiAlH4[pic]4H2 + 2LiAlO2 + (RCH2O)4AlLi [pic]4RCH2OH
Ketones: 4R2C=O + LiAlH4[pic](R2CHO)4AlLi [pic]4R2CHOH + LiOH + Al(OH)3
Reactions of Alcohols
1. Substitution in Alcohols
a. Using HX (suitable for 3° alcohols)
R–OH [pic] R–X + H2O
b. Using PX3/PX5 (suitable for 1°, 2° alcohols)
R–OH [pic] R–X + POX3 + HX
c. Using SOCl2 (sulphonyl chloride)
R–OH [pic] R–Cl + SO2 + HCl
*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
[pic]
*Note: Alcohols are too weak to react with hydroxides and carbonates.
3. Oxidation to Carbonyl Compounds and Carboxylic Acids
a. Primary Alcohols are oxidized to aldehydes first, then carboxylic acids.
[pic]
*Note: MnO2 is also a milder oxidizing agent.
b. Secondary Alcohols are oxidized to ketones.
[pic]
c. Tertiary alcohols are not readily oxidized.
4. Dehydration to Alkenes
a. Excess conc H2SO4
[pic]
b. Excess alcohol
R–CH2OH + conc H2SO4[pic] R–CH2–O– CH2–R
5. Esterification
[pic]
6. Acylation
a. Acid Chloride
[pic]
b. Acid Anhydride
[pic]
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.
[pic]
a. Step 1: Oxidation of Alcohol to the corresponding carbonyl compound by iodine.
[pic]
b. Step 2: Further oxidation to carboxylate salt and formation of iodoform
[pic]
c. Overall Equation:
[pic]
Preparations of Phenols
1. Replacement of OH– group in diazonium salts
[pic]
Reactions of Phenols
1. Reaction with Reactive Metals (e.g. Na or Mg)
[pic]
2. Reaction with NaOH
[pic]
*Note: Phenols have no reactions with carbonates
3. Esterifications
[pic]
*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.
4. Halogenation
a. With bromine(aq)
[pic]
*Note: 2,4,6-tribromophenol is a white ppt.
b. With bromine(CCl4)
[pic]
5. Nitration
a. With conc nitric acid
[pic]
b. With dilute nitric acid
[pic]
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.
[pic]
carbonyl compounds
Preparation of Aldehydes
1. Oxidation of Primary Alcohols
[pic]
Preparations of Ketones
1. Oxidation of Secondary Alcohols
[pic]
2. Oxidative Cleavage of Alkenes
[pic]
Reactions of Carbonyl Compounds
1. Addition of Cyanide. Cyanohydrin formation.
[Nucleophilic Addition of Hydrogen Cyanide to Aldehyde and Ketone]
[pic]
*Note: Cyanohydrins can be hydrolysed to form 2-hydroxy acids.
Acidic Hydrolysis
[pic]
Basic Hydrolysis
[pic]
*Note: Cyanohydrins can undergo reduction.
[pic]
2. Reaction with 2,4-Dinitrophenylhydrazine (Brady’s Reagent). Condensation Reaction.
[pic]
*Note: 2,4-dinitrophenylhydrazones formed are orange or yellow crystalline solids with characteristic melting points. They are useful for identifying individual aldehydes and ketones.
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.
[pic]
[pic]
[pic]
b. Oxidation of Aldehydes using hot, acidified potassium manganate(VII)
*Note: KMnO4 turned from purple to colourless if test is positive.
[pic]
[pic]
c. Oxidation of Aliphatic Aldehydes using Fehling’s Solution (Fehling’s Test)
[pic]
[pic]
[pic]
*Note: Aliphatic aldehydes reduce the copper(II) in Fehling’s solution to the reddish-brown copper(I) oxide.
R–CHO + 2Cu2+ + 5OH– [pic] R–COO– + Cu2O (s) + 3H2O
*Note: Methanal (strongest aldehyde reducing agent) produces metallic copper as well as copper(I) oxide.
HCHO + Cu2O + OH– [pic] HCOO– + 2Cu (s) + H2O
d. Oxidation of Aldehydes using Tollen’s Reagent (Silver Mirror Test)
[pic]
[pic]
d. Oxidation of Aldehydes using Tollen’s Reagent (Silver Mirror Test) (Cont’d)
[pic]
*Note: Aldehydes redyce the Ag(I) in Tollen’s reagent to Ag, forming a silver mirror.
RCHO + 2[NH3(Ag(NH3]+ + 3OH– [pic]RCOO– + 2Ag (s) + 4NH3 + 2H2O
4. Reduction Reactions
a. Reduction of Aldehydes to Primary Alcohols
R–CHO + 2[H] [pic]R–CH2OH
R–CHO + H2 [pic] R–CH2OH
b. Reduction of Ketones to Secondary Alcohols
[pic]
[pic]
5. Reaction with Alkaline Aqueous Iodine (Tri-Iodomethane (Iodoform) Formation)
*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.
[pic]
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 [pic]CH3CHCl2 + POCl3
CH3COCH3 + PCl5 [pic]CH3CCl2CH3 + POCl3
Carboxylic Acids & Derivatives
Preparation of Carboxylic Acids
1. Oxidation
a. Oxidation of Primary Alcohols and Aldehydes
[pic]
b. Oxidative Cleavage of Alkenes
[pic]
c. Oxidation of an Alkylbenzene (Formation of Benzoic Acid)
[pic]
2. Hydrolysis
a. Hydrolysis of Nitriles (R–C≡N)
Acidic Hydrolysis
R–C≡N[pic] RCOOH + NH4+
Basic Hydrolysis
R–C≡N[pic] RCOO–Na+ + NH3
b. Hydrolysis of Esters (RCOOR’)
Acidic Hydrolysis
RCOOR’ + H2O [pic] RCOOH + R’OH
Basic Hydrolysis
RCOOR’ + H2O [pic] RCOO–Na+ + R’OH
RCOO–Na+ [pic] RCOOH
Reactions of Carboxylic Acids
1. Salt Formation
a. Reaction with Metal
RCOOH + Na [pic] RCOO–Na+ + ½H2
b. Reaction with Bases
RCOOH + NaOH [pic] RCOO–Na+ + H2O
c. Reaction with Carbonates
2RCOOH + Na2CO3 [pic] 2RCOO–Na+ + H2O + CO2
2. Esterification
[pic]
3. Conversion into Acyl Chlorides (RCOCl)
RCOOH + PCl5 [pic] RCOCl + POCl3 + HCl
3RCOOH + PCl3 [pic] 3RCOCl + H3PO3
RCOOH + SOCl2 [pic] RCOCl + HCl + SO2
4. Reduction to Alcohols
RCOOH + 4[H] [pic]RCH2OH + H2O
Preparation of Acyl Chlorides
1. From Carboxylic Acid
RCOOH + PCl5 [pic] RCOCl + POCl3 + HCl
3RCOOH + PCl3 [pic] 3RCOCl + H3PO3
RCOOH + SOCl2 [pic] RCOCl + HCl + SO2
Reactions of Acyl Chlorides
1. Conversion into Acid. Hydrolysis
RCOCl + H2O [pic] RCOOH + HCl
ArCOCl + H2O [pic] 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 [pic] RCOOR’ + HCl
*Note: Reaction is slow when phenol is directly reacted with acyl chloride.
RCOCl + ArOH [pic] 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 [pic] ArO–Na+ + H2O
RCOCl + ArO– [pic] RCOOAr + Cl–
3. Amide Formation. Ammonolysis.
RCOCl + NH3 [pic] RCONH2 + HCl
RCOCl + R’NH2 [pic] RCONHR’ + HCl
RCOCl + R’R’’NH[pic]RCONR’R’’ + HCl
4. Reduction to Aldehyde, then Alcohol
RCOCl [pic] RCHO [pic] RCH2OH
Preparations of Esters
1. Condensation Reaction of Acid and Alcohol
a. Ethyl Ethanoate
[pic]
b. Phenyl Benzoate
ArOH + NaOH [pic] ArO–Na+ + H2O
ArCOCl + ArO–Na+ [pic] ArCOOAr + NaCl
Reaction of Esters
1. Hydrolysis
a. Acidic Hydrolysis
RCOOR’ + H2O [pic] RCOOH + R’OH
b. Basic Hydrolysis
RCOOR’ + H2O [pic] RCOO–Na+ + R’OH
2. Reduction to Primary Alcohols
RCOOR’ [pic] RCH2OH
Preparation of Polyesters
1. Condensation Reaction
nHOOCRCOOH + nHOR’OH [pic] ( OCRCOOR’O ) n + 2nH2O
nitrogen compounds
Preparation of Amines
1. Reaction of Halides with Ammonia or Amines. Ammonolysis
R–X + excess conc NH3 [pic] [H3---R---] [pic]RNH2 + NH4+X–
NH3 [pic] RNH2 [pic] R2NH [pic] R3N [pic] R4N+X–
2. Reduction
a. Reduction of Amide
RCONH2 [pic] RNH2
b. Reduction of Nitrile
R–C≡N[pic] RCH2NH2
c. Reductive Amination
[pic]
Reactions of Amines
1. Salt Formation
RNH2 + HCl [pic] RNH3+ Cl–
RNH2 + R’COOH [pic] RNH3+ –OOCR’
[pic]
*Note: Phenylamine is not soluble in water but dissolves in acid.
2. Formation of Amides. Acylation.
[pic]
[pic]
[pic]
*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[pic]CH3CH2NHCOCH3 + HCl
ArNH2 + Ar’COCl[pic]ArNHCOAr’ + HCl
ArNH2 +RCOCl[pic]ArNHCOR + HCl
3. Ring Substitution Reactions of Aromatic Amines
a. Halogenation
[pic]
*Note: To get monosubstituted compounds, react phenylamine with ethanoyl chloride to reduce the ‘strongly activating’ nature of the amino group to form phenylacetamide.
[pic]
*Note: NHCOCH3 is also 2,4-directing but moderately activating. Halogenation of ArNHCOCH3 will give N-(2-bromophenyl)acetamide or N-(4-bromophenyl)acetamide. Reacting this with aqueous NaOH and heating will give 2-bromophenylamine or 4-bromophenylamine.
b. Nitration
[pic]
*Note: The same steps as above can be taken if we want monosubstituted nitrophenylamine.
Preparations of Amides
1. Ammonolysis of Acid Derivatives
RCOCl + NH3 [pic] RCONH2 + HCl
RCOCl + R’NH2 [pic] RCONHR’ + HCl
RCOCl + R’R’’NH[pic]RCONR’R’’ + HCl
2. Reaction between Amine and Acid Chloride
[pic]
[pic]
Reactions of Amides
1. Acidic Hydrolysis
RCONH2 [pic] R–COOH + NH4+
2. Basic Hydrolysis
RCONH2 [pic]R–COO– + NH3
Preparations of Amino Acids
1. Hell-Volhard-Zelinsky Reaction
[pic]
Reactions of Amino Acids
1. Salt Formation
a. Reaction with H+. Cationic
+H3N–CH2–COO–(aq) + H+(aq)[pic] +H3N–CH2–COOH (aq)
b. Reaction with OH–. Anionic
+H3N–CH2–COO–(aq) + OH– (aq)[pic] 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 [pic] CH3–CO–NH–CH2COOH + HCl
3. Esterification
H2N–CH2–COOH + ROH [pic] +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.
[pic]
5. Hydrolysis of Peptides
a. Acidic Hydrolysis
[pic]
b. Basic Hydrolysis
[pic]
*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.
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).
CH4 + Cl2 [pic] CH3Cl + HCl
[pic] + Cl2 [pic] [pic] + 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.
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.
-----------------------
Note: acyl group
[pic]
[pic]
–H
Note: acyl group
[pic]
[pic]
[pic]
ClÏ% Atom: Attacks side chain
Cl+ Ion: Attacks ring
[pic]
Dark, room temp
55oC
Or Fe
Or H2/Pd, ethanol
N [pic]
[pic]
Cl● Atom: Attacks side chain
Cl+ Ion: Attacks ring
[pic]
Dark, room temp
55oC
Or Fe
Or H2/Pd, ethanol
N2 + H2O
30oC
Conc H2SO4, 140oC
Conc H2SO4, 140oC
RCH2NH2
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