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What is alkane substitution reactions ? Give different types of substitution reactoins name and possibilities. |
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Answer» Solution :In alkane, one or more hydrogen is substituted can be substituted with halogen, nitro group and sulphuric acid group. These reactions in which hydrogen atoms of alkanes are substituted are known as substitution reactions. (a) Nitration : Hydrogen of alkane is substituted with `_NO_(2)` group, Known as nitration. (b) Sulphonation : Hydrogen of alkane is substituted with `-SO_(3)H` group, known as sulphonation. (c) Halogenation : Hydrogen of alkane is replaced with halogen (F, Cl, Br, I) Known as halogenation. Rate of reaction of alkanes are : `F_(2) gt Cl_(2) gt Br_(2) gt I_(2)` (d) Fluorination : Fluorination is too violent to be controlled. `(CH_(4)+F_(2)(N_(2) " or " Ar) rarr CH_(3)F + HF)` (e) Iodination : Iodination is vert slow and a reversible reaction. It can be carried out in the PRESENCE of oxidizing aganets like `HIO_(3)` or `HNO_(3)`. `CH_(4) + I_(2) hArr CH_(3)I + HI` `HIO_(3) + 5HI rarr 3I_(2) + 3H_(2)O` (f) Chlorination and bromination : They are easy reactions. If chlorine is in required amount then all the hydrogens are substituted with -Cl ATOM. `CH_(4) underset(-HCl)overset(hv, Cl_(2))rarr CH_(3)Cl underset(-HCl)overset(hv, Cl_(2))rarrCH_(2)Cl_(2)` `underset(-HCl)overset(hv, Cl_(2))rarrCHCl_(3) underset(-HCl)overset(hv, Cl_(2))RARRC Cl_(4)` ....(i) `underset("Ethane")(CH_(3))-CH_(3)+Cl_(2) overset(hv) rarr underset("Chloroethane")(CH_(3))-CH_(2)Cl+HCl` ...(ii) Chlorination and bromination takes place either at temperature 573 to 773 K or in presence of diffused sunlight or UV light. In alkane, series of substitution of H is `3^(@) gt 2^(@) gt 1^(@)`. e.g., `CH_(3)CH_(2)CH_(3) underset(-HCl)overset(hv, Cl_(2))rarrunderset("1-Chloropropane")underset(45%)(CH_(3)H_(2)CH_(2)Cl)+underset("1-Chloropropane")underset(55%)(CH_(3)CHCLCH_(3))` Substitution of `2^(@)` - hydrogen `gt` Substitution of `1^(@)` hydrogen rate (g) Bromination : Reaction is slow than that of chlorine and mainly monobromo is formed. |
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