Chemistry Reference
In-Depth Information
Mg anode in the shape of a pencil (Fig. 19.13) sur-
rounded by a conical steel cathode.
The following is a list of examples of other syn-
theses based on consumable anodes (see Fig. 19.14):
after acid hydrolysis, are obtained in an aprotic
solvent containing trimethylsilyl chloride [28].
(3)
Jubault
et al
. have used an Mg anode for syn-
thesis (Fig. 19.14b). As well as an improvement
in yield, the Mg anode also enabled production
rates greater than those expected from the stoi-
chiometric consumption of charge, because the
Mg becomes activated and acts as a reducing
agent [29].
(4)
Manufacture of the anti-inflammatory drug
Naproxen (Fig. 19.14c) with an Al anode and
lead cathode in dry DMF under a carbon dioxide
atmosphere [30].
(1)
Nozaki-Hiyama reaction (Fig. 19.14a). In the
electrochemical version of this reaction only cat-
alytic quantities of the transition metal ions are
required. The reaction involved regeneration of
Cr(II) intermediate and can be performed in an
undivided cell with an Al anode in DMF. The
chemical process produces large volumes of toxic
chromous chloride effluent [27].
(2)
Cathodic reduction of ethyl trifluoroacetate with
an Al anode in an undivided cell. With a steel
cathode good yields of fluorinated acetylacetate,
The cathodic generation of active metals is another
approach that has attractions for synthesis. Electro-
generated Ni powder, formed by reduction at a Pd
cathode as a black suspension in DMF, has been used
to reduce 4-substituted nitrobenzenes [31]. Electro-
generated Zn has been used to prepare organo-zinc
compounds as useful intermediates in the coupling
of alkyl and aryl halides [32].
Pencil Sharpener
Cell
6 Electrochemical Waste Minimisation
Pencil
anode
The process industries in their consumption and pro-
duction of materials and chemicals deal with a wide
range of liquors containing toxic and hazardous
materials. These materials, if not a direct product of
the plant, must be recycled or treated. In many cases
large quantities of effluents and dilute wastewaters
containing toxic (and non-biodegradable) com-
pounds can be produced. These compounds include
toxic metals, organic compounds, inorganic com-
pounds and waste and flue gases. The importance of
electrochemistry in recycling is now well appreciated.
The use of electrochemical techniques is increasing
rapidly for the treatment of a wide range of process
streams, both liquid and gaseous. Several of the elec-
trochemical methods described are used commer-
cially, notably metal deposition, whereas many more
are at the prototype stage. Methods described are
not always stand-alone techniques but often are
used in conjunction with other non-electrochemical
methods. For example, electrodeposition is an effec-
tive technique for the recovery of metal ions at rela-
tively high concentrations. At low concentrations
(< 1 ppm) the efficiency and cost effectiveness start to
fall and thus a method such as ion exchange, which
can deal effectively with lower metal ion concentra-
Electrolyte
Out
Cathode
Electrolyte
In
Fig. 19.13
Schematic diagram of the pencil sharpener cell.
