Step 1 of Scheme 4 illustrates the first step in the industrial scale production of chloroprene rubber. Chlorination of 1,3-butadiene leads to a mixture of products including HCO-1370 that is further processed in the production of chloroprene rubber and CHC-370 which must be separated and either further processed, or disposed of as a waste product. In Step 2, HCO-1370 can be further chlorinated to generate the key intermediate CHC-370. In Step 3, direct fluorination leads to the key intermediate to C4F6, CFC-316 which subsequently can be reductively dechlorinated to C4F6 using zinc as shown in Step 4.
There are a number of process disadvantages to using this route for the primary production of C4F6. First, the key intermediate (CHC-370) occurs only as a minor by-product in the chloroprene rubber production process. Thus, if the chloroprene rubber industry experiences a slowdown, the production of CHC-370 will similarly be reduced. Secondly, chlorination of HCO-1370 is problematic with formation of over chlorinated by-products (heavies) that must be separated and disposed of (incinerated). Thirdly, the fluorination Step 3 requires 6 equivalents of F2 per equivalent of CHC-370 and produces 6 equivalents of by-product HF that must either be disposed of (neutralization) or with great difficulty, separated, purified, and recycled to a F2 generator. In other words, only 50% of the fluorine atoms introduced in Step 3 are actually used in the production of CFC-316.
In light of the high dependence on the chloroprene production industry and the multiple waste generating chlorination and fluorination steps, this chlorobutane/F2 route (Alternative route C) to C4F6 is inferior to the preferred process described heretofore in Route 1.