Introduction
Sodium dithionite (also known as sodium hydrosulfite) is a versatile,
inexpensive, safe and readily available reagent, which has been
employed for more than 70 years. It has been used in biochemistry
for the reduction of a variety of coenzymes and enzymes, and in
organic synthesis to reduce several types of functional groups,
such as aldehydes, ketones, imines, pyrazine, vinyl sulfones, nitro
[¹]
and azo groups,
[²]
oximes,
[³]
enones,
[4]
quinones,
[5]
and azides.
[6]
It was also found to be an efficient
reagent for the reductive displacement of iodine
[7]
and reductive coupling of benzylic
and allylic halides.
[8]
It has been
also used as radical initiator to promote coupling of CF3CHClBr
with 1,3,5-trimethoxybenzene,
[9]
the
addition of 1-bromo-1-chloro-2,2,2-triuoroethane
to the terminal double bond of allylbenzenes,
[¹0]
addition
reaction of peruoroalkyl iodides with allenes,
[¹¹]
the reaction
of polyfluoroalkyl iodides with alkenes,
[¹²]
addition
of dialkyl phosphonodifluoromethyl radical onto unsaturated ketones,
[¹³]
fluoroalkylation
of porphyrins
[¹4]
and vinyl
ethers.
[¹5]
This reagent
is found to be a useful reagent in the intramolecular Marschalk cyclization
[¹6]
and Claisen rearrangement.
[¹7]
Sodium dithionite is now commercially available, but can also
be prepared readily by the reaction of sodium bisulfite with zinc.
[¹8]
It is obtained as a
white crystalline powder with a weak sulfurous odor. This compound
is stable under most conditions, but it will decompose in hot water
and in acid solutions.
Scheme 1
