Chemistry Reference
In-Depth Information
Fig. 19.12
Cell for the production of
chlorine dioxide.
Table 19.4
Indirect electrochemical processes
Oxidation with metal salts
• Oxidation of aromatics with side chain, e.g. synthesis of substituted
benzyaldehydes with Mn
3
+
and Ce
4
+
• Oxidation at the aromatic nucleus, e.g. benzene to phenol with Fe
2
+
/H
2
O
2
• Olefin oxidations with Tl
3
+
, Pd
2
+
and Os
8
+
Oxidation with inorganic anions
• Oxidation of alkenes to epoxides and secondary alcohols to ketones with
halogens
• Dialdehyde starch production from starch by periodate
Reductions with metal salts and base metals
• Ti
3
+
, V
3
+
, Sn
2
+
, Cr
2
+
, Zn, Cu, Fe and Sn powder reduction of nitro
compounds and halogenated hydrocarbons
Reductions with metal complexes and metal salts
• Ni
o
, Ni
A
, Co
+
, Sn
o
, Pd
o
and Ph
l
complexes, e.g. reaction with alkylating
agents via oxidative addition
• Electrochemical reduction of alkyl complex cleaves the metal-carbon bond
Synthesis with organic redox catalysts
• Reductions with radical anions and dianions of mainly aromatics for
cleavage of alkyl (e.g. perylene), biphenyl, anthracene and aryl halides,
sulfonates, sulfides and, epoxides
• Dehalogenation of polychlorinated biphenyls with 1,9-diphenylanthracene
Reduction by viologen radical cations
• NAD to NADH and NADPH with methyl viologen
Oxidation with triarylamine radical cations
• Selective oxidations of arylalkanes to benzaldehyde dimethyl acetals
Oxidation with electrochemically regenerable
•
N
-Hydroxy phthalamide for oxidation of arylalkanes, benzylethers and
hydride or hydrogen-abstracting reagents
olefins
The range of syntheses performed in the laboratory
is vast and many (of the order of 100) have reached
industrial scale. This includes a range of reductive
and oxidative processes, cathodic and anodic cleav-
ages, cyclisations and couplings [22]. An important
developing area is the use of indirect electrochemi-
cal processes.
Many of these reagents can be prepared electro-
chemically and the appropriate regeneration of these
agents by electrochemical oxidation or reduction can
lead to simplifications in the process operation, a
reduction in any problems of effluent treatment and
can eliminate, or reduce, the need for bulk storage
of hazardous or toxic chemicals on site. There is con-
siderable commercial interest in the use of these
routes for the small-scale manufacture of high-value
and speciality chemicals [2,23]. Table 19.4 lists a
selection of the processes typically performed as
ex-cell processes.
Indirect electrosynthesis
Common methods of carrying out oxidation and
reduction in organic synthesis is by homogeneous
reaction with conventional oxidants or reductants.
