Question of 90
Q.(i) Give only the chemical equation of the following reactions: (A) Wurtz Reaction (B) Friedel-Crafts reaction (C) Kolbe electrolytic synthesis
(ii) How will you obtain: (A) Benzene from Ethylene (B) Prop-1-ene from Propan-2-ol
OR
(i) Write (A) and (B) for the following:
(i) CH3-CH(Br)-CH3 --[Alc. KOH]--> (A) --[ROOR / +HBr]--> (B)
(ii) 3 CH(triple bond)CH --[3Cl2 / Sunlight]--> (A) --> (B)
(iii) CH3-CH2-Cl --[Alc. KOH]--> (A)
(ii) Write the isomeric structures of C5H12.
Rajasthan RbseRajasthan Board Senior Secondary Part-I Examination 2018Subjective· 5mImportance★★★★★
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Start your 14-day free trial to unlock the full solution →Wurtz, Friedel-Crafts and Kolbe reactions are given by equation; benzene is obtained by the cyclic trimerization of ethyne (the stem's 'ethylene' is treated as a scan artifact for 'ethyne'); and prop-1-ene is obtained by acid-catalysed dehydration of propan-2-ol. (This is the primary part of an OR question; the alternative, on a halide reaction sequence and the isomers of C5H12, is not separately solved since the primary part is fully answerable.)
- Chemical equations: (A) Wurtz Reaction — two molecules of an alkyl halide react with sodium metal in dry ether to give a higher alkane with double the carbon atoms (via free-radical coupling): 2 CH3CH2Br + 2Na --(dry ether)--> CH3CH2CH2CH3 + 2NaBr (B) Friedel-Crafts (alkylation) reaction — benzene reacts with an alkyl halide in the presence of anhydrous AlCl3 (Lewis acid catalyst) to give an alkylbenzene: C6H6 + CH3Cl --(anhyd. AlCl3)--> C6H5CH3 + HCl (C) Kolbe's electrolytic synthesis — electrolysis of an aqueous solution of the sodium salt of a carboxylic acid gives a higher alkane at the anode, along with CO2, and H2 at the cathode: 2 CH3COONa + 2H2O --(electrolysis)--> CH3CH3 + 2CO2 + 2NaOH + H2
- Conversions: (A) Benzene: the stem asks for benzene 'from Ethylene', but there is no standard single-step (or simple multi-step) NCERT-level synthesis of benzene from ethylene (ethene) — this is almost certainly a scan/transcription artifact for 'Ethyne' (acetylene), since the standard, well-known preparation of benzene taught at this level is the cyclic trimerization of ethyne. That reaction is used here: three molecules of ethyne combine on passing through a red-hot iron (or copper) tube at about 873 K, cyclizing to form benzene: …
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