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D. L. Astolfi, F. C. May6ille, Jr. / Tetrahedron Letters 44 (2003) 9223–9224
carbonate (1.1 gram/50 ml). Sodium nitrite (1.5 g) and
chilled 2 M hydrochloric acid (5.0 ml) are then added
and stirred. After 10 min the precipitation of the sul-
fanilic acid as a diazonium salt occurs (white precipi-
tate). The diazonium salt was allowed to react with a
solution containing N,N-dimethylaniline (2.7 ml) and
the ionic liquid (2.0 ml). The mixture was cooled in an
ice bath for 15 min to completely form the helianthin
precipitate. The helianthin was the first product of the
coupling reaction and the red acidic form of methyl
orange. At this point the helianthin solid was collected
by vacuum filtration. The filtrate contained the ionic
liquid which was separated from the aqueous layer and
dried over 4–8 mesh molecular sieves. The helianthin
solid was finally dissolved in 10.0% sodium hydroxide
(30.0 ml) by heating the solution to boiling. After all
the helianthin had dissolved, solid sodium chloride (10
g) was added to the solution and cooled in an ice bath
to precipitate the final sodium salt (basic form) of
methyl orange. The basic form of methyl orange was
collected through vacuum filtration and allowed to dry.
Acetic acid was used to stabilize the reaction intermedi-
ates for the control reactions and the ionic liquids were
used in the experimental reactions for the same
purpose.
were between 2.9 and 4.5 pH units, while the literature
reported transition ranges between 3.1 and 4.4 pH
units. The ionic liquids were quantitatively recovered
(1.5–1.8 ml/2.0 ml) from the product for each reaction
and the purity confirmed by proton NMR.
The ionic liquids enhanced the methyl orange reaction
mechanism by improving charge stabilization, which
allowed an increased product yield of more than 30%
when compared to the traditional reaction solvent.
Both ionic liquids reacted in a similar fashion and by
stabilizing the high-energy charged intermediates they
ran at lower temperatures than the control reaction.
Future and ongoing work will include more diazo
coupling, bromination, oxidation and addition reac-
tions in ionic liquids. The synthesis of new ionic liquids
will also be a future goal.
References
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acetic acid and in both ionic liquids suggests an
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