Question

How can u convert ethyl chloride to n butane

Answer 1

C2H5Br+Mg→C2H5Mgcl;

C2H5mgcl+H(O=C)CH3→H3C−CH2CH(OH)

H3C−CH2CH(OH)CH3+Δ+H3PO4→butylene + water

butylene+H2(g)→n-butane

Answer 2

Since you're gonna need a four-carbon chain, you will need to alkylate the initial ethyl chloride. 

Take a second equiv of ethyl chloride and hit it with Mg and a simple ether. The Mg will oxidatively insert between the 1-carbon and the Cl. 

Next, the C--MgCl bond itself will attack the initial (first equiv) 1-carbon...this will eject the Cl off of the initial equiv via Sn2 mechanism. 

And there you have it! 

Hope this helps...