1,204,553. Chlorinated hydrocarbons. KNAPSACK A.G. 8 Aug., 1968 [17 Aug., 1967], No. 37849/68. Heading C2C. The invention relates to a modification of the process of Specification 1,111,023 wherein a mixture of 1,2-dichlorobutene-2, 1,3-dichlorobutene-2 and 2,3-dichlorobutene-1 is prepared by subjecting a mixture of the substituted phosphine or phosphonium catalyst and 1,2,3-trichlorobutane containing 5-20% by weight of 2,2,3,3 - tetrachlorobutane to dehydrochlorination by reflux-boiling in a reactor having an associated fractionating column, removing the evoved hydrogen chloride near the column head and subjecting the organic vapours to total reflux until a temperature of 127‹ Œ 1‹ C. is attained (at 760 mm. Hg), whereupon the dichlorobutene mixture is removed overhead at a constant head temperature of 127‹ Œ 1‹ C. The modification comprises withdrawing the dichlorobutene mixture at a reflux ratio of R = 1-20, withdrawing the completely condensed matter or reflux matter near the column base, introducing said matter into a circulation evaporator and recycling it in vapour form from said evaporator to the reactor, continuously supplying the circulation evaporator with metered quantities of fresh 2,2,3,3-tetrachlorobutane-containing 1,2,3-trichlorobutane, the latter coming from a reservoir and being evaporated in the said circulation evaporator, and the said 2,2,3,3-tetrachlorobutane-containing 1,2,3-trichlorobutane being supplied at the same rate as produced dichlorobutene mixture is withdrawn from the system; and, when the concentration of 2,2,3,3-tetrachlorobutene in the 1,2,3-trichlorobutane in the reactor has been found by continuous or periodical analysis to have attained a value of 30% by weight, introducing a portion of the reflux matter withdrawn near the column base into a stirrable cooler; centrifuging the 2,2,3,3 - tetrachlorobutane, which is found partially to crystallize in the said cooler, the cooler being cooled to a temperature of 0‹ C., and withdrawing it; and recycling mother liquor to the said circulation evaporator. Other dichlorobutenes are obtained as byproducts. The dichlorobutene mixture may be thermally dehydrochlorinated to chloroprene without further purification.
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