Hydrocarbons - Result Question 38
####21. Identify a reagent from the following list which can easily distinguish between 1-butyne and 2-butyne.
(2002, 3M)
(a) bromine, $CCl _4$
(c) dilute $H _2 SO _4$, $HgSO _4$
(b) $H _2$, Lindlar catalyst
(d) ammoniacal $CuCl _2$ solution
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Answer:
Correct Answer: 21. (b)
Solution:
- Ammoniacal $CuCl _2$ forms red precipitate with terminal alkynes, can be used to distinguish terminal alkynes from internal alkynes:
$$ \begin{aligned} CH _3-CH _2-C \equiv C-H+CuCl _2 \xrightarrow{NH _3(a q)} \ CH _3-\underset{\text { red ppt. }}{CH _2-C \equiv C^{-} Cu^{+} \downarrow} \end{aligned} $$
