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only McMurray coupling products were readily detected when Ti and Zn
were used.
El-Eskandarany et al. have reported a unique process for obtaining carbon-
free metallic iron via a single-step reduction and described how a single-step
displacement reaction occurred during the mechanical milling (using a
Fritsch P6 ball mill) of a mixture of haematite (Fe
2
O
3
) and magnesium
powders at room temperature under moderate rotation speed (2.2 s
1
).
During the early milling stage (0-12 h), the Fe
2
O
3
particles were embedded
in the soft Mg matrix (reducing agent) particles to form coarse reactant
material composite powders as a result of the repeated impact and shear
forces generated by the balls. After 24 h of milling, a mechanical solid-state
reduction takes place between the fresh Fe
2
O
3
and Mg. Complete solid-state
reduction is successfully achieved after 120 h. The end product, obtained
after 150 h, is a nanocrystalline mixture of metallic Fe and MgO powders
with average grain size of
o
20 nm in diameter.
25
On the other hand, metallic
Fe particles and non-magnetic oxide were prepared by reducing MgFe
2
O
4
with Al or Mg in a ball mill, in work by Takacs et al. (2002) (Scheme 3.21). The
reaction took place as a fast self-propagating process at some point between
0.5 and 1 h of milling. It was shown, using XRD and M¨ssbauer spec-
troscopy, that the Fe phase contains a small percentage of dissolved Al, that
it shows high defect concentration and that the surface tension of the
ultrafine (about 15 nm) grains results in local compressive strains. Mag-
netization is 25% less than expected for pure ferromagnetic Fe.
26
A kinetic study using dichloro- and monochlorobenzene (DCB, MCB) as
model pollutants and an excess of magnesium and n-butylamine as reagents
in a laboratory centrifugal ball mill at 25 1C was carried out by Birke et al. to
investigate the reaction mechanisms for mechanochemical dehalogenation
reactions using magnesium and slightly acidic hydrogen donors. The focus
of the study was on polyhalogenated aromatics, such as PCBs or hexa-
chlorobenzene, which have chlorine-aromatic ring carbon bonds, which
display higher bond strengths than chlorine-aliphatic carbon bonds. An
analysis of the findings strongly suggested that one-pot, consecutive
Grignard-Zerewitinoff-like reactions occur; firstly, the Grignard intermedi-
ates are formed from DCB or MCB and then, in a stepwise manner, their
protonation to monochlorobenzene or benzene, respectively, occurs via the
amine. Furthermore, a rationale was derived to explain the observation of
complete reductive dechlorination to benzene, which was formed in ap-
proximately 100% yield (mole/mole, based on DCB or MCB).
27
Mack et al. have reported a practical method for the solvent-free reduction
of aldehydes and ketones via high speed ball milling (using a Spex CertiPrep
mixer/mill 8000 M apparatus) in an open atmosphere. Using NaBH
4
(1 eq.),
MgAl
2
O
4
+2Fe
MgFe
2
O
4
+2Al
MgFe
2
O
4
+ 3 MgAl
4MgO + 2 Fe
Scheme 3.21 MgFe
2
O
4
ball mill reduction in presence of Al or Mg.
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