Important Reactions in Haloalkanes and Haloarenes
Important Name Reactions organic chemistry class 12 by gtctuition
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1. Groove's Process
Primary and Secondary alcohols form chloroalkanes when hydrochloric acid gas is passed through alcohol in the presence of anhydrous zinc chloride.
2. Reaction of alcohols with thionyl chloride
Chloroalkanes can be prepared from alcohols by refluxing alcohols with thionyl chloride in the presence of pyridine.
3. Markovnikov's Rule and Antimarkovnikov's Rule ( Peroxide Effect )
Addition of HBr to unsymmetrical alkenes is occur in accordance to Markovnikov Rule i.e negative part of attacking reagent attached itself to the carbon atom carrying lesser number of hydrogen atom.
In the presence of Peroxide addition of HBr to unsymmetrical alkenes is occur in accordance to antiMarkovnikov's Rule i.e negative part of attacking reagent attached itself to the carbon atom carrying more number of hydrogen atom.
4. Finkelstein Reaction ( Halogen Exchange )
This reaction is particularly useful for preparing iodoalkanes. The iodoalkanes are obtained by heating chloro or bromoalkanes with a concentrated solution of sodium iodide in acetone.
5. Swarts Reaction
This reaction is particularly useful for preparing fluoro alkanes. The fluoro alkanes are obtained by treating chloro or bromoalkanes with salts such as mercurous fluoride ( Hg2F2) or silver fluoride ( AgF ) .
6. Borodine Hunsdiecker Reaction
Bromoalkanes can be prepared by decomposing silver salts of carboxylic acids with bromine in CCl4.
7. Diazotisation Reaction
This reaction is used to prepare benzene diazonium chloride salt by treating ice-cold solution of aniline in excess of dilute HCl with an aqueous solution of sodium nitrite at low temperature ( 0 - 5 degree Celsius )
8. Sandmeyer's Reaction
Chloro and bromoarenes are prepared by treating a freshly prepared diazonium salt solution with cuprous chloride or cuprous bromide dissolved in corresponding halogen acid.
9. Gattermann Reaction
Chloro and bromoarenes are prepared by treating a freshly prepared diazonium salt solution with Copper powder in presence of corresponding halogen acid.
10. Balz Schiemann Reaction
Fluoro arenes are prepared by treating benzene diazonium chloride with fluoroboric acid followed by heating.
11. Mendius Reaction
Alkyl cyanides can be reduced by nascent hydrogen evolved from sodium and alcohol to form primary amines.
12. SN2 Reaction ( Substitution Nucleophilic Bimolecular )
These are the substitution reaction in which rate of reaction depends upon concentration of both the reactants alkyl halide and nucleophile. For example the reaction between methyl bromide and hydroxide ion to form methanol follow second order kinetics.
Reactivity of Alkyl Halides towards SN2 Reaction
13. SN1 Reaction ( Substitution Nucleophilic Unimolecular )
These are the substitution reaction in which rate of reaction depends upon concentration of only one reactant ( alkyl halide ) . For example the reaction between tert-butyl bromide and hydroxide ion to form tert-butyl alcohol follow first order kinetics.
Reactivity of Alkyl Halides towards SN1 Reaction
14. Dehydro halogenation Reaction ( 𝛃-Elimination Reaction )
When alkyl halides with 𝛃- hydrogen atom are boiled with alcoholic solution of potassium hydroxide they undergo elimination of hydrogen halide ( HX ) resulting in the formation of alkenes.
Alkene will be preffered in which carbon atoms joined by the double bond are maximum alkylated ( Saytzeff rule )
15. Wurtz Reaction
Two molecules of alkyl halides react with metallic sodium in the presence of ether to form alkanes.
This reaction fails for tertiary alkyl halides and give mixture when two different alkyl halides are used.
16. Dows Process ( Chlorobenzene to Phenol )
Aryl halides when heated with aqueous solution of sodium hydroxide under 300 atm pressure, the halogen atom is replaced by hydroxyl group to form phenol.
17. Chlorobenzene to Aniline
Chlorobenzene on heating with aqueous ammonia in the presence of cuprous oxide under pressure give aniline.
18. Wurtz Fitting Reaction
When aryl halide is heated with alkyl halide in the presence of sodium in anhydrous ether, halogen atom is replaced by alkyl group.
19. Fitting Reaction
When haloarenes react with sodium in the presence of ether, diphenyl is formed.
20. Ulmann Reaction
Iodobenzene when heated with copper powder in sealed tube it gives diphenyl.
21. Friedel Craft Reactions
Friedel Craft Alkylation : Aryl halides are treated with alkyl chloride in the presence of anhydrous aluminium choride.
Friedel Craft Acylation : Aryl halides are treated with acyl chloride in the presence of anhydrous aluminium choride.
Important Questions From Haloalkanes and Haloarenes
Q. Out of HCl(g) and SOCl2 ( Thionyl Chloride ) which is preffered for converting ethanol into Chloroethane ?
Q. Why is sulphuric acid not used during the reaction of alcohols with KI?
Q. Arrange each set of compounds in order of increasing boiling points.
(i)Bromomethane, Bromoform, Chloromethane, Dibromomethane.
(ii)1-Chloropropane, Isopropyl chloride, 1-Chlorobutane.
Q. In the following pairs of halogen compounds, which would undergoSN2 reaction faster?
Q. In the following pairs of halogen compounds, which compound undergoes faster SN1 reaction?
Q. What are ambident nucleophiles? Explain with an example.
Q. Explain why
(i)the dipole moment of chlorobenzene is lower than that of cyclohexyl chloride?
(ii)alkyl halides, though polar, are immiscible with water?
(iii)Grignard reagents should be prepared under anhydrous conditions?
Q. Haloarenes are insoluble in water but soluble in benzene. Explain.
Q. Alkyl Halides give Cyanide with KCN but isocyanides with AgCN as the products. Explain.
Q. Allyl chloride is more reactive than n-propyl chloride towards nucleophilic substitution reaction. Explain why ?
Q. p-Dichlorobenzene has higher m.p. than those of o- and m-isomers. Discuss.
Q. The treatment of alkyl chlorides with aqueous KOH leads to the formation ofalcohols but in the presence of alcoholic KOH, alkenes are majorproducts. Explain.
Q. What is Chirality ?
Q. What are enantiomers ? Draw the structures of the possible enantiomers of 3-methylpent-1-ene.
Q. Chloroform contains chlorine but gives no reaction with AgNO3 solution. Why ?
Q. Why is chloroform stored in Dark coloured bottles ?
Q. A small amount of ethyl alcohol is usually added to chloroform bottles. why ?
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