As an illustrative example 64.4 g of 5-iodo-2-benzyl thiouracil were deposited
in the reaction vessel and dissolved by adding 400 cc of glacial acetic acid
containing 10 cc of acetic anhydride and the reaction vessel was connected
tightly with the reflux condenser. The second vessel or generator was charged
with 95 cc of acetic anhydride and the vessel connected to a vessel such as a
dropping funnel or equivalent containing 75 cc of a 50% solution of hydroiodic
acid which was added slowly, as by dropwise addition, to the acetic anhydride
in the generator. The mixture in the generator soon became hot and the
hydrogen iodide which evolved passed continuously through the connecting
conduit into the reaction flask just above the level of liquid therein. As the
hydrogen iodide contacted the solution of the 2 benzyl derivative,a ring of the
debenzylated product formed under the inlet conduct. This operation was
continued until all of the hydroidic acid was added to the generator vessel.
The hydrogen iodide remaining in the generator was driven over into the
reaction vessel by heating the generator. It was ascertained that the reaction
is complete when no more precipitate forms in the main reaction vessel.
During the reaction vapors evolved were condensed in the condenser and
returned to the reaction vessel as reflux. The upper end of the reflux ispreferably connected with a vent leading to a drying chamber.
The reaction vessel was cooled and the precipitate separated by pouring or
decanting off the supernatant liquor. The precipitate of the 5-iodo-2-thiouracil
was then thoroughly washed, as, for example, on a Buchner funnel. The
precipitate was then extracted twice with hot glacial acetic acid to remove
unreacted material and then washed thoroughly by alternate washes with
alcohol and water. The product was then further purified by dissolving it in
warm dilute sodium hydroxide and after cooling was reprecipitated by careful
acidulation with acetic acid. Utilizing this procedure 37 g of purified 5-iodo-2-
thiouracil were obtained.
The supernatant liquid separated from the precipitate was concentrated in
vacuo and 7.4 g of the unreacted 5-iodo-2-benzyl thiouracil were recovered.
This obviously may be utilized for further debenzylation.
As pointed out previously, the 5-iodo-2-thiouracil is carefully dried, preferably
in a vacuum over P2O5.
