remains on the iron surface for a sufficiently long period of time. There are two
reaction paths considered—sequential hydrogenolysis and β-elimination (Janda
et al. 2004; Liu et al. 2005).
1.8.1 Sequential Hydrogenolysis
During sequential hydrogenolysis, C-Cl bonds in halogenated hydrocarbons are
gradually replaced by the C-H bonds under sufficiently strong reducing conditions
to form Cl
À and less chlorinated hydrocarbon according to Eq. (1.25). The feasibility
of hydrogenolysis depends on the type of hydrocarbon and decreases from aliphatic
to aromatic hydrocarbons. Hydrogenolysis is also influenced by the presence and
location of substituents and heteroatoms.
1.8.2 Reductive β-Elimination
During reductive β-elimination of halogenated organic substances, multiple bonds
(e.g., triple) between carbon atoms are created, and halogens are simultaneously
removed from molecules in the form of halides. For the multiple bond formation, the
halogen atoms must be bound to two adjoining carbon atoms. The reaction of
halogenated ethene (e.g., 1,2-DCE) can be generally described by the equation
CHX ¼ CHX þ 2e
À
! CH CH þ 2X
À
ð1:36Þ
where acetylene is the final product.
Fig. 1.5 Principles of reduction of R-Cl by Fe compounds
16
M. Černík and J. Zeman