Question

What reagents would you use for the following synthesis? Please Explain

fte fllosuteare? rate woul d What use (z)-2-haxene fom 3-hexyna (t)-3-haxsn Prom 3-aryua ) exane from 3-hexyna

Answer 1

We can reduce alkynes to their alkene or alkane form by hydrogenation of alkyne. But the strong reducing agent can reduce alkyne to alkane. So in order to stop at alkene stage we need to modify the reagents so that the reduction process can stop at alkene stage.
solution (a) Synthesis of (2)-3-hexene from 3-hexyne. сн cң, с= ccңн, Н., снясно сносни catalyst H H Lindlar's Lindlar's Catalyst= 5%.Pd-CaCO₃ Pb(OCOCH3)2 2.2.222222222 + Quinoline. - Lindlar's catalyst consists deposited of on Caco, and Pd to is used to convert alkynes to alkenes. → Pb deactivate the sites of Palladium . Also the catalyst get deactivated in the presence of quinoline that leads to its selectivity and also prevent formation of alkanes. One most important property of this reagent is that it is stereospecific Occurring via syn addition & it gives cis-alkene b) Synthesis of (E)-3-hexene from 3-hexyne - CH₂-CHC=CCHCH₂ Na/ NH3 CH₂ CH₂ H 5 c → Sodium metal has lone electrons in its a valence shell & it can give quite easily any molecule that can accept m to y sgt leads to anti addition & form trans - alkene.

(C) synthesis of hexame from 3-hexyne снясняс Есенен усн, сн,-cң, -сненс Hydrogenation of alkyne in the presence of Palladium dispersed on carbon lead to the complete reduction of alkyne to alkane Some other reagents also can be used to completely reduce the alkynes to alkane that are Raney-Ni (dispersed Ni) and ptle (Pilatinum dispersed on carbon).