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What type of reaction is characterized by electrophilic substitution?
What type of reaction is characterized by electrophilic substitution?
What are the reagents and conditions for the halogenation of alkenes?
What are the reagents and conditions for the halogenation of alkenes?
X2 in organic solvent at room temperature
The observation during halogenation involves an orange-red bromine decolourising.
The observation during halogenation involves an orange-red bromine decolourising.
True
What type of reaction is hydrohalogenation?
What type of reaction is hydrohalogenation?
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What is the product formed from the hydrohalogenation of alkenes?
What is the product formed from the hydrohalogenation of alkenes?
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What is the condition required for direct hydration of alkenes?
What is the condition required for direct hydration of alkenes?
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Match the type of reaction with its corresponding description:
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Match the following types of reactions with their corresponding conditions:
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Match the following reagents with their specific reaction types:
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Match the following observations with the corresponding reactions:
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Match the following reactions with their corresponding observations:
Match the following reactions with their corresponding observations:
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Match the following types of reactions with their respective reagents and conditions:
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Match each reaction type with the correct reaction formula:
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Study Notes
Free Radical, Chain Substitution
- A reaction where a halogen molecule, X2, reacts with an alkene in the presence of UV light
- The reaction results in the formation of a dihalogenoalkane
- Mechanism is an electrophilic substitution
Halogenation
- A reaction where a halogen molecule, X2(g), reacts with an alkene in an organic solvent at room temperature
- The reaction results in the formation of a dihalogenoalkane
- The halogen, X2, is typically bromine, Br2, which is orange-red, indicating that the reaction is occurring by observing the disappearance of the orange-red color
- An example of an electrophilic addition reaction
- Halogenation in Water*
- Variation of halogenation that involves the addition of a halogen molecule, X2(g), and water to an alkene
- Produces a halohydrin as the product
- The presence of water influences the reaction mechanism
- The halogen is typically bromine, Br2, which is orange-red, indicating that the reaction is occurring by observing the disappearance of the orange-red color
Hydrohalogenation
- A reaction where a hydrogen halide, HX(g), reacts with an alkene
- The reaction is typically conducted in a dry environment at room temperature.
- The reaction results in the formation of a halogenoalkane.
- An example of an electrophilic addition reaction
- Indirect Hydration*
- An indirect process for adding water to an alkene
- Involves two steps:
- First, the alkene is reacted with concentrated sulfuric acid (conc. H2SO4) at a low temperature, which forms an alkyl hydrogen sulfate
- Then the alkyl hydrogen sulfate is reacted with water and heat to produce an alcohol
- An example of electrophilic addition reaction
- Direct Hydration of Alkenes*
- A reaction that directly adds water to an alkene, resulting in the formation of an alcohol.
- The reaction proceeds in the temperature range of 300 degrees Celsius to 350 degrees Celsius.
- The reaction can be catalyzed by the use of an acid catalyst, and requires high pressure.
- An example of electrophilic addition reaction
Free Radical Substitution
- Occurs with limited X2(g) in the presence of UV light
Halogenation of Alkenes
- Electrophilic addition of X2 to an alkene forms a dihalogenoalkane
- Reagents: X2 in an organic solvent at room temperature
- Observations: Orange-red bromine decolourises
- Electrophilic Addition of X2 in water to an alkene forms -halohydrins
- Reagents: Xe in water at room temperature
- Observations: Orange bromine water decolourises
Hydrohalogenation of Alkenes
- Electrophilic addition of HX to an alkene forms a halogenoalkane
- Reagents: Dry HX(g) at room temperature
Indirect Hydration
- Electrophilic addition of H2O to an alkene after reaction with concentrated H2SO4 followed by water and heat forms an alcohol
- Reagents: Concentrated H2SO4 cold, followed by H2O and heat
Dirct Hydration
- Electrophilic addition of H2O to an alkene with high temperature and pressure in the presence of concentrated phosphoric acid forms an alcohol
- Reagents: H2O(g), heat, conc. H3PO4
Reduction of Alkenes
- Reduction of an alkene with hydrogen gas and a catalyst (nickel or platinum) forms an alkane
- Reagents: H2(g), heat, nickel catalyst or platinum catalyst at room temperature
Mild Oxidation of Alkenes
- Mild oxidation of an alkene with potassium permanganate in potassium hydroxide (cold) forms a diol
- Reagents: KMnO4(aq), KOH(aq)
- Observations: Purple KMnO4 decolourises, brown ppt of manganese(IV) oxide formed
Strong Oxidation of Alkenes
- Strong oxidation of an alkene with potassium permanganate in sulfuric acid under reflux forms a carboxylic acid
- Reagents: KMnO4(aq) in H2SO4, heat under reflux
- Observations: Purple KMnO4 decolourises, effervescence of CO2 gives white ppt in lime water
Dehydration of Alcohols
- Elimination of an alcohol forms an alkene and water
- Reagents: Excess concentrated H2SO4, heat OR concentrated H3PO4, heat OR Al2O3, heat
Dehydrohalogenation
- Elimination of HX from a halogenoalkane forms an alkene
- Reagents: KOH in ethanol, heat under reflux
Halogenation of Benzene
- Electrophilic substitution of X2 with a catalyst (FeX3, AlX3, Fe) forms a halogenoalkane and HX
- Observations: Yellowish-green Cl2 decolourised, white fumes of HCl
- Observations: Reddish-brown Br2 decolourised, white fumes of HBr
Alkylation of Benzene
- Electrophilic substitution of RX, with a catalyst (FeX3, AlX3, Fe) forms an alkylbenzene and HX
- Observations: White fumes of HX
Nitration of Benzene
- Electrophilic substitution with concentrated HNO3 and concentrated H2SO4 at 55 degrees celcius forms nitrobenzene, water and HX
- Reagents: Conc HNO3, conc H2SO4
Halogenation of Methylbenzene
- Same as benzene
Nitration of Methylbenzene
- Electrophilic substitution with concentrated HNO3 and concentrated H2SO4 at 30 degrees celcius forms nitrobenzene, water and HX
- Reagents: Conc HNO3, conc H2SO4
Free Radical Substitution of Methylbenzene
- Occurs in the presence of UV light with limited X2
Side Chain Oxidation of Methylbenzene
- Strong oxidation of methylbenzene with potassium permanganate in sulfuric acid under reflux forms a carboxylic acid
- Same as strong oxidation of alkenes
Nucleophilic Substitution
- Formation of Alcohol: RX + NaOH(aq) or KOH(aq) → ROH + NaX or KX (heat under reflux)
-
Formation of Ether: RX + R'O- → R-O-R' + X-
- This reaction requires an alkoxide, which is formed by reacting an alcohol with a strong base (Na or K)
- Formation of Nitrile: RX + KCN or NaCN → RCN + KX or NaX (ethanol, heat under reflux)
- Formation of Amine: RX + 2NH3 → RNH2 + NH4+X- (excess NH3 in ethanol, heat in sealed tube) or RX + NH3 → RNH2 + X- (limited NH3 in ethanol, heat in sealed tube)
Reduction
- Formation of Amine (from Nitrile): RCN + 2H2 → RCH2NH2 (H2(g), Ni catalyst, heat) or RCN + 4[H] → RCH2NH2 (LiAlH4 in dry ether, r.t.p.)
- Reduction of Aldehyde: R-CHO → R-CH2OH (LiAlH4 in dry ether, NaBH4 in methanol, or H2 with Ni catalyst, heat under high pressure)
- Reduction of Carboxylic Acid: R-COOH → R-CH2OH (LiAlH4 in dry ether)
- Reduction of Ketone: R-CO-R' → R-CHOH-R' (LiAlH4 in dry ether, NaBH4 in methanol, or H2 with Ni catalyst, heat under high pressure)
- Reduction of Nitrobenzene: C6H5NO2 + 6[H] → C6H5NH2 + 2H2O (Sn or Fe in excess conc. HCl, heat under reflux, followed by addition of NaOH(aq))
Elimination
- Formation of Alkenes: RX + KOH(aq) → alkene + HX (ethanol, heat under reflux)
Oxidation
- 1° Alcohol to Aldehyde: R-CH2OH + [O] → R-CHO + H2O (K2Cr2O7 in dilute H2SO4, heat with immediate distillation)
- 1° Alcohol to Carboxylic Acid: R-CH2OH + [O] → R-COOH + H2O (K2Cr2O7 in dilute H2SO4, heat under reflux, or KMnO4 in dilute H2SO4, heat under reflux)
- Aldehyde to Carboxylic Acid: R-CHO + [O] → R-COOH (K2Cr2O7 in dilute H2SO4, heat under reflux, or KMnO4 in dilute H2SO4, heat under reflux)
- 2° Alcohol to Ketone: R-CHOH-R' + [O] → R-CO-R' + H2O (K2Cr2O7 in dilute H2SO4, heat under reflux, or KMnO4 in dilute H2SO4, heat under reflux)
Other Reactions
- Alcohol to Halogenalkane: R-OH + HX(g) → R-X + H2O (HX(g), heat, or PX3, r.t.p., or PCl5, r.t.p., or SOCl2 in pyridine)
-
Alcohol to Alkoxide: R-OH + Na(s) → R-O-Na + 1/2H2
- Can also be formed by reacting an alcohol with NaOH(aq)
- Iodoform Test: Alcohol or ketone + I2 + 4OH- → Carboxylate + CHI3 + 3H2O (add I2 in NaOH to a solution of alcohol or ketone, warm with water bath)
- Acylation of Benzene: Benzene + R-COX → C6H5COR + HX (anhydrous AlCl3 or FeCl3, with R-COX)
- Ketone/Aldehyde to Cyanohydrin: R-CHO + HCN → R-CH(OH)-CN or R-CO-R' + HCN → R-C(OH)(CN)-R' (HCN and trace amounts of NaOH/KOH, cold)
-
Carboxylic Acid to Carboxylate Salt: R-COOH + Na(s) or Mg(s) → R-COO-Na+ or R-COO-Mg+ + 1/2H2
- Neutralisation reaction with NaOH(aq) or KOH(aq) also forms carboxylate salts
- Reaction with Na2CO3(aq) also forms carboxylate salts, along with CO2 and H2O
- Carboxylic Acid to Acyl Chloride: R-COOH + PCl3 or PCl5 or SOCl2 → R-COCl + HCl or H2SO4 (heat)
- Oxidation of Methanoic Acid: HCOOH + [O] → CO2 + H2O (KMnO4 in H2SO4(aq), heat under reflux)
- Acyl Chloride to Carboxylic Acid: R-COCl + H2O → R-COOH + HCl
- Acyl Chloride to Amides: R-COCl + NH3/RNH2/RNHR → R-CONH2/R-CONHR'/R-CONR'2 + HCl (ammonia or amine, r.t.p.)
- Ester to Carboxylic Acid and Alcohol: R-COOR' + H2O → R-COOH + R'OH (HCl or H2SO4, heat under reflux)
- Ester to Carboxylate Salt and Alcohol: R-COOR' + NaOH/KOH → R-COO-Na+/K+ + R'OH (NaOH/KOH(aq), heat under reflux)
- Ester to Two Alcohols: R-COOR' → R-OH + R'-OH (LiAlH4 in dry ether)
- Amide to Carboxylic Acid: R-CONH2 + H2O → R-COOH + NH3 (H2SO4(aq) or HCl(aq), heat under reflux)
- Amide to Carboxylate Salt and Amine: R-CONH2 + NaOH/KOH → R-COO-Na+/K+ + NH3 (NaOH/KOH(aq), heat under reflux)
- Amide to Amine: R-CONH2 + 4[H] → R-CH2NH2 + H2O (LiAlH4 in dry ether)
- Amine to Ammonium Salt: R-NH2 + HX → R-NH3+ X- (any acid)
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Description
This quiz covers the reactions of alkenes with halogens, specifically focusing on free radical and electrophilic substitution mechanisms. Understand the processes involved in halogenation, including the variations that occur in different solvents and the formation of products like dihalogenoalkanes and halohydrins.
