, 2005, 15(5), 207–208
N,N'-Diiodo-N,N'-1,2-ethanediylbis(p-toluenesulfonamide) as a reagent for
conversion of aldehydes to methyl esters
Ramin Ghorbani-Vaghei,* Elham Shahbazee and Hojat Veisi
Department of Chemistry, Faculty of Science, Bu-Ali Sina University, 65174 Hamadan, Iran.
Fax: +98 811 827 2404; e-mail: ghorbani@basu.ac.ir
DOI: 10.1070/MC2005v015n05ABEH002091
N,N'-Diiodo-N,N'-1,2-ethanediylbis(p-toluenesulfonamide) (NIBTS) can be used for the oxidation of aldehydes to the corre-
sponding methyl esters with high efficiency in a single step.
The selective oxidation of aldehydes to esters is very important
in organic chemistry.1 For example, NIS is used for the oxida-
tion of aldehydes to esters.2 Ester formation can be performed
under various conditions,3 which are not always satisfactory in
yield and/or simplicity of operation. The presence of strong
acids, bases or catalysts and the application of heat or electricity
are required.1(a) Simple processes for esterification under mild
conditions are very desirable.
prevent the light induced homolytic decomposition of the inter-
mediate hypoiodite.9
Note that α,β-unsaturated aldehydes such as crotonaldehyde
(Table 1, entry 12) converted to an ester with high chemo-
selectivity without addition of the reagent to the C=C bond.
Furthermore, functional groups such as chloro, methoxy and
†
The IR and NMR spectra were recorded using a Shimadzu 435-U-04
spectrophotometer (KBr pellets) and a 90 MHz Jeol FT-NMR spectrometer,
respectively.
Me
I
Procedure for preparation of N,N'-1,2-ethanediylbis(p-toluenesulfon-
amide). p-Toluenesulfonyl chloride (30 g) was placed in a three-necked
round bottom flask and melted. Then, ethylenediamine (8 ml) was added
dropwise (for 30 min). The mixture was heated at 90 °C for 2 h. Then, it
was cooled to room temperature and 100 ml of distilled water was added
and filtered off. Crude product was recrystallised from ethanol.
Procedure for the preparation of N,N'-diiodo-N,N'-1,2-ethanediylbis-
(p-toluenesulfonamide) 1. N,N'-1,2-ethanediylbis(p-toluenesulfonamide)
(1 g, 0.006 mol) was dissolved in an excess of a sodium hydroxide
solution (6 M) at room temperature and transferred to a beaker. Iodine
(10 g) dissolved in carbon tetrachloride (15 ml) was added to the solution
with vigorous stirring at –10 °C and immediately a yellow precipitate
was formed. The product (yellow precipitate) was collected on a Buchner
funnel and washed with cold distilled water (10 ml) and then dried in a
vacuum desiccator at room temperature for 6 h. The reaction gives 1
(0.9 g, 90%). 1H NMR ([2H6]DMSO) d: 2.40 (s, 6H), 2.70 (s, 4H),
7.50–7.76 (dd, 8H). 13C NMR (DMSO) d: 20.2 (Me), 45.1 (CH2),
126.20–141.19 (four peaks of benzene carbons). IR (KBr, n/cm–1): 1600,
1460, 1340, 1150.
N
S
CH2
O
O
2
NIBTS 1
Scheme 1
Here we report a convenient method for the conversion of
aldehydes to the corresponding methyl esters with high efficiency
in a single step1(b),4 using a new reagent N,N'-diiodo-N,N'-1,2
ethanediylbis(p-toluenesulfonamide) 1 (NIBTS)5 (Scheme 1).†
The advantages of NIBTS are as follows: (i) the preparation
of NIBTS is easy; (ii) NIBTS is stable for six months under
atmospheric conditions; (iii) after reaction of NIBTS with a
substrate, the sulfonamide is recovered and can be reused many
times without decreasing the yield.
‡
The oxidation of aldehydes to esters with NIBTS under
General procedure for conversion of aldehydes to methyl esters with
ambient conditions is shown in Scheme 2.‡
NIBTS. A mixture of benzaldehyde (0.106 g, 1 mol), methanol (10 ml),
NIBTS (0.620 g, 0.5 mol) and sodium carbonate (0.333 g, 3.1 mol) was
stirred at room temperature for 2.5 h. The reaction was performed in the
dark to prevent the light-induced homolytic decomposition of intermediate
hypoiodite 4. The reaction was monitored by TLC (carbon tetrachloride–
acetone, 9:1). After completion of the reaction, 3 ml of Na2S2O3·5H2O
(5%) was added to destroy remaining NIBTS or hypoiodite species. The
resultant mixture was extracted with 2×10 ml of a solution of 50% diethyl
ether in hexane. The organic layer was dried with MgSO4. The removal
of the solvent under reduced pressure gave the crude product. The crude
product was chromatographed on a silica gel column with 1% ethyl acetate
in hexane. The evaporation of the solvent gave methyl benzoate (90%).
The results of the conversion of various aldehydes to esters
are presented in Table 1.
Since NIBTS contains two iodine atoms, which are attached
to nitrogen atoms, this reagent can in situ release I+, which
can act as an electrophilic species.5,6 Therefore, the following
mechanism can be suggested for the conversion of aldehydes to
esters (Scheme 3). Initially formed methyl hemiacetal 3 is
oxidised by NIBTS to corresponding hemiacetal hypoiodite 4.7
The subsequent elimination of hydrogen iodide produces the
observed product.8 The reaction is performed in the dark to
Mendeleev Commun. 2005 207