Comparison of reactors for oxygen-sensitive reactions: reductive dechlorination of chlorophenols by vitamin b(12s)

Serum bottles are frequently used for studies of reductive dechlorination by vitamin B(12), but reducing conditions can be maintained only for several days. This time period is inadequate for evaluating the reductive dechlorination of some slow-reacting aromatic compounds. Sealed glass ampoules maintain reducing conditions for many months, but this method has the disadvantage of disallowing subsampling of the reaction mixture. A glass serum tube was modified for these experiments which not only maintained anoxic conditions for several days but also allowed subsamples to be removed during experiments. The modification was a restriction placed in the middle of the tube by heating in a flame, creating two chambers separated by a narrow neck. The lower chamber contained the oxygen-sensitive reaction mixture. The upper chamber, sealed with a septum and screw cap, was purged with purified nitrogen or argon introduced and vented through fused silica capillaries. Reductive dechlorination of chlorophenols by vitamin B(12) reduced with Ti(III) citrate was monitored in all three reactor types. Sealed ampoules maintained reducing conditions for up to 12 months. The two-chambered reactor maintained reducing conditions longer than the serum vials when frequent samples were taken.