Mixtures of gaseous hydrogen chloride and gaseous l, &butadiene at total pressures less than 1 atm and at temperatures between 294 and 334 K yield mixtures of 3-chloro-l-butene and (E)-and (Z)-l-chloro-2-butene. The ratio of the product of putative l, &addition to those of 1, 4-addition is approximately unity with only the amount of (Z)-l-chloro-2-butene increasing from ca. 2% of the total reaction product mixture at the lower temperature to ca. 4% at the ...