Question
Which is the most suitable reagent among the following to distinguish compound (iii) from rest of the compounds?
$$\eqalign{
& {\text{(i)}}\,C{H_3} - C \equiv C - C{H_3} \cr
& {\text{(ii)}}\,C{H_3} - C{H_2} - C{H_2} - C{H_3} \cr
& {\text{(iii)}}\,C{H_3} - C{H_2} - C \equiv CH \cr
& {\text{(iv)}}\,C{H_3} - CH = C{H_2} \cr} $$
A.
$$\frac{{B{r_2}}}{{CC{l_4}}}$$
B.
$$\frac{{B{r_2}}}{{C{H_3}COOH}}$$
C.
$$Alk.\,KMn{O_4}$$
D.
$${\text{Ammoniacal}}\,AgN{O_3}$$
Answer :
$${\text{Ammoniacal}}\,AgN{O_3}$$
Solution :
It may be noted that only the terminal alkynes react with ammoniacal silver nitrate. Therefore, this reaction can be used to distinguish between 1-alkynes and others such as alkane, alkenes and non-terminal alkynes.
$$C{H_3} - C{H_2} - C \equiv $$ $$CH + 2\left[ {Ag{{\left( {N{H_3}} \right)}_2}} \right]N{O_3} \to $$ $$\mathop {C{H_3}C{H_2}C \equiv CAg \downarrow }\limits_{{\text{White ppt}}{\text{.}}} $$