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Sikdar et al.
Ion exchange resin are the earliest known support for reagents and
catalysts in organic synthesis.[1] Among the advantages of supported
reagents in organic synthesis are easy work-up procedure, mild reaction
condition, site specific reactions, and high turn over. Supported reagents
are also environment friendly.[2–6]
In continuation of our work in the field of ion exchange resin
supported reagents in organic synthesis, we had earlier reported the use
of bromate exchange resin as an oxidizing agent for the oxidation of
aldehyde to the carboxylic acids.[7] We now report the use of bromate
exchange resins for the oxidation of alcohols and benzylhalides to the
corresponding carbonyl compounds in biphasic condition. An important
observation is that primary alcohols were oxidized only to the aldehydes
and overoxidation to the carboxylic acid was not observed.
In our earlier communication, we had reported a method of
immobilizing Bromate ion onto ion exchange resin namely Amberlite
IRA-400(Clꢀ). The extent of loading of bromate ions was likewise
reported to be 0.9 mequivalent per gram of resin.
The bromate exchange resin so obtained was used for the oxidation
alcohols and benzyl halides to the corresponding carbonyl compounds.
Primary alcohols and halides were oxidized to aldehydes, a transformation
which is synthetically useful. The reaction were carried out under biphasic
condition in organic solvents. Work-up procedure is simple and involves
filtration and removal of solvent. Conversion was found to be as high as
90% in some cases. The products were identified by comparing their m.p.,
1
IR, UV, and H NMR spectra with authentic samples. Identification of
products were also done by conversion to their 2,4-DNP derivatives and
the percentage yield ascertained by this procedure.
EXPERIMENTAL
The anion exchange resin used was AmberliteIRA-400(Clꢀ), 20–50
mesh, according to Rohm and Hass specification obtained from Loba
Cheme (India). The resin was washed several times with deionized water
and dried. All starting materials were purified before use and sodium
bromate was used as a source of bromate ions.
Five grams dry bromate exchange resin was eluted several times with
the same volume (100 ml) of 1 M aqueous KCl to ensure complete
exchange of BrOꢀ3 with Cl. The resin was further washed with distilled
water. The combined volume of the elutent and washing collected and
made up to 250 ml. The bromate present in this solution was estimated by