How is propanoic acid is prepared starting from
an alkene

Explanation

From an alkene : Propene adds on to borane `(BH_(3))` to give tripropyl borane.
`underset("Propene")(3CH_(3)-CH=CH_(2)+BH_(3))tounderset("Tripropyl borane")((CH_(3)CH_(2)CH_(3))_(3)B)overset(H_(2)O_(2)//OH^(-))(to)underset("Propyl alcohol")(CH_(3)CH_(2)CH_(2)OH+H_(3)BO_(3))`
This reaction is hydroboration
`underset("Propanol")(CH_(3)CH_(2)CH_(2)OH)underset((O))overset(K_(2)Cr_(2)O_(7)//H^(+))(to)underset("Propanoic acid")(CH_(3)CH_(2)COOH)`
Alternate method :
`CH_(3)CH=CH_(2)+HBroverset("peroxide")(to)underset("(Anti-markovnikos rule)")underset("n propyl bromide")(CH_(3)CH_(2)CH_(2)Br`
This kharasch peroxide effect
`CH_(3)CH_(2)CH_(2)Br+NaOHoverset(H_(2)O)(to)underset("Propanol")(CH_(3)CH_(2)CH_(2)OH`
`underset("Propanol")(CH_(3)CH_(2)CH_(2)OH)underset(K_(2)Cr_(2)O_(7)//H^(+))overset((O))(to)underset("Propanoic acid")(CH_(3)CH_(2)COOH`