Which of the following reagents can distinguish between propene and propyne?
(i) `Na` (in hexane)
(ii) `Na^(+)NH_2` (in liquid `NH_3`)
(iii) `Ag(NH_3)_2^(+)OH^(-)`
(iv) `Cu(NH_3)_2^(+)OH^(-)`

Options

A. (i),(ii),(iii),(iv)
B. (i),(ii)
C. (iii),(iv)
D. (ii),(iii),(iv)

Answer

A

Explanation

All these tests are based on the acidity of the terminal H of a terminal alkyne.
`2CH_3C-=CH+2Natounderset("sodium propynide")(2CH_3C-=C)`:` .^(-)Na^(+)+H_2uarr`
`CH_3C-=CH+NaNH_2overset("liq.NH_3")toCH_3C-=C`:` .^(-)Na^(+)+NH_3uarr`
`CH_3C-=CHunderset("ammoniacal silver nitrate")(+Ag(NH_3)_2^(+)OH^(-))toCH_3C-=CAg(s)+2NH_3+H_2O`
`CH_3C-=CH+underset("Ammoniacal cuprous chloride")(AG(NH_3)_2^(+)OH^(-))toCH_3C-=CAg(s)+2NH_3+H_2O`
Similar chemical tests can be used to distinguish propane from propyne.