Reactions of 1, 2, 3, 4-Tetrachlorobutanes with Sodium Hydroxide in Aqueous Methanol

Abstract

1, 2, 3, 4-Tetrachlorobutanes (TCB) were dehydrochlorinated by sodium hydroxide in aqueous methanol to give 2, 3-dichloro-1, 3-butadiene (2, 3-DCB-1, 3) and 1, 2-dichloro-1, 3-butadiene. Dehydrochlorination of meso-TCB gave cis-1, 2, 4-trichloro-2-butene together with the substi- tution products, cis-1, 2-dichloro-4-methoxy- and cis-1, 4-dimethoxy-2-chloro-2-butenes. On the other hand, dl-TCB was converted into trans-1, 2, 4-trichloro-, trans-1, 2-dichloro-4-methoxy-, and trans-1, 4-dimethoxy-2-chloro-2-butenes. meso-TCB was converted into 2, 3-DCB-1, 3 in a good yield, whereas a fairly large amount of the methoxy compounds was obtained from dl-TCB. Since 2, 3-elimination took place by the trans-elimination of hydrogen chloride from dl-TCB as a starting material, 2-alkenes were favorably formed.1, 2-Elimination dominated in meso-TCB because of steric requirement and, as a result, 2, 3-DCB-1, 3 was obtained in a good yield. Further results obtained are summarized as follows. (1) The yield of 2, 3-DCB-1, 3 depended on the ratio of methanol to water, and showed a maximum in the range 75-85 vol%. (2) As the concentration of sodium hydroxide increased, the yield of 2, 3-DCB-1, 3 from meso-TCB decreased, and that from dl-TCB increased. (3) With the increasing reaction temperature, the selectivity for the formation of 2, 3- DCB-1, 3 from meso-TCB decreased and that from dl-TCB increased.