Этилен + Hbr - x - y+Na - хлорбутан

СH2=CH2 + HBr -> CH3-CH2-Br

CH3-CH2-Br + 2Na + Br-CH2-CH3 -> CH3-CH2-CH2-CH3 + 2NaBr

CH3-CH2-CH2-CH3 + Br2 -> CH3-CH2-CH2-CH2-Br + HBr