Facile dehalogenation of halogenated anilines and their
derivatives using Al-Ni alloy in alkaline aqueous solution
compared with ethanol (no precipitation of BCAN after
mixing with aq. NaOH).
4. Conclusions
From an applicability standpoint, methylal as a
co-solvent especially represents a good choice for
the following reasons: a) excellent solubility of XAN’s
in DMM; b) solubility of DMM in water is ca. 30 wt.%
(better mass transfer); c) the boiling point of DMM,
42°C, enables simple distillation and recycling of DMM;
d) contrary to usual ethers or DEM, DMM does not form
explosive peroxides; e) DMM has an extremely low
toxicity and ecotoxicity [31-33].
Based on the findings described above, we decided
to investigate the behaviour of the Raney Al–Ni alloy
in the mixture of DMM and aqueous NaOH for the
dehalogenation of water-insoluble polyhalogenated
anilines and their G-NH-Ar-Xn derivatives. For this
purpose, we used industrially important halogenated
ureas used as herbicides, such as Monuron (N´-(4-
chlorophenyl)-N,N-dimethylurea), Bromuron (N´-(4-
bromophenyl)-N,N-dimethylurea), Chlorotoluron (N´-(3-
chloro-4-methylphenyl)-N,N-dimethylurea).
In conclusion, we have reported a general method
for dehalogenation of halogenated anilines and their
derivatives using Al-Ni alloy in alkaline aqueous
solutions at room temperature. Under these conditions,
dimethoxymethane was shown to be a suitable green co-
solvent for the dehalogenation of sparingly water-soluble
XANs and their derivatives in a dimethoxymethane-
aqueous NaOH-Al/Ni alloy multiphase reaction system.
We successfully reduced aluminium and nickel from the
effluents generated using neutralization. This simple
method enables recovery of most of the Al and Ni from
the water solution.
From the point of view of environmental protection,
this process shows potential advantages in reducing the
adverse impact of AOX dissolved in industrial effluents.
We hope that this simple approach enables broader
utilization of Al-Ni alloy as a cheap and commercially
available dehalogenation agent applicable in aqueous
or multi-phase reaction mixtures.
The molar ratios of the reactants used for the
dehalogenation were Al : Ni : NaOH : G-NH-Ar-Xn = 5n
: 2.3n : 20n : 1, the conversion to aniline (or appropriate
aniline derivative) being 100 % in all cases (Table 5,
entries 6-16).
Easily available ortho-acylated- or ortho-alkylated
4-chloroanilines [6,7] serve as starting materials for
the simple preparation of ortho-alkylated-anilines used
as intermediates for drug or pesticide synthesis. As a
result, the efficiency of the dehalogenation method
described above was proven using appropriate
commercially available derivatives of XANs (2-amino-5-
chlorobenzophenone, 2-trifluoromethyl-aniline).
Acknowledgements
The authors wish to thank the Grant Agency of the
Czech Republic (203/07/P248) and the Ministry of
Education of the Czech Republic for financial support
(MSM 0021627502).
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