I have an idea but it's to complicated and time-consuming....there can be in two steps:
1) CH3C(=O)CH3 ---H2-> CH3CH2(-OH)CH3 ---HCl-> CH3CH2(-Cl)CH3
(acetone) (2-propanol) (2-chloropropane)
2) CH3CH2(-Cl)CH3 + CH3Cl ---Na->
CH3CH(-CH3)CH3 + CH3CH(-CH3)CH(-CH3)CH3 + CH3CH3
(2-chloropropane) (chloromethane)
(isobutane) (2,3-dimethylbutane) (ethane)
But in this reaction there are other compounds besides isobutane
Help with something simpler . Greets