Org. Synth. 1950, 30, 56
DOI: 10.15227/orgsyn.030.0056
2-MERCAPTOBENZIMIDAZOLE
[2-Benzimidazolethiol]
Submitted by J. A. VanAllan and B. D. Deacon
1.
Checked by Cliff S. Hamilton and Yao-Hua Wu.
1. Procedure
A mixture of
32.4 g. (0.3 mole) of o-phenylenediamine,
2 52.8 g. (0.33 mole) of potassium ethyl xanthate (Note 1),
300 ml. of 95% ethanol, and 45 ml. of water in a
1-l. flask is heated under reflux for 3 hours.
Norit (12 g.) is then added cautiously, and after the mixture has been heated at the reflux temperature for 10 minutes the
Norit is removed by filtration. The filtrate is heated to 60–70°, 300 ml. of warm tap water (60–70°) is added, and then
25 ml. of acetic acid in 50 ml. of water is added with good stirring. The product separates as glistening white crystals, and the mixture is placed in a
refrigerator for 3 hours to complete the crystallization. The product is collected on a
Büchner funnel and dried overnight at 40°. The yield is
37.8–39 g. (
84–86.5%) of
2-mercaptobenzimidazole melting at
303–304° (cor.)
(Note 2) and
(Note 3).
2. Notes
1.
The
potassium ethyl xanthate may be replaced by
19 g. of potassium hydroxide and
26 g. (21 ml., 0.34 mole) of carbon disulfide. The yield and quality of the product are the same.
2.
The quality of the product is excellent. Recrystallization may be effected from
95% ethanol as a solvent. Recovery is about 90%; there is no change in the melting point.
3.
2-Mercaptobenzoxazole, m.p.
193–195°, can be prepared in
80% yield by a similar procedure, using
o-aminophenol in place of
o-phenylenediamine.
3. Discussion
2-Mercaptobenzimidazole has also been prepared from
o-phenylenediamine by heating the
thiocyanate to 120–130°;
3 by heating with aqueous
potassium thiocyanate (in which case
2-aminophenylthiourea is a by-product);
4 by the action of
thiophosgene in
chloroform;
5 by heating with
carbon disulfide in alcohol
6 or in water;
7 and by heating the hydrochloride with
thiourea to 170–180°.
8
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
ethanol (64-17-5)
acetic acid (64-19-7)
chloroform (67-66-3)
o-aminophenol (95-55-6)
Norit (7782-42-5)
potassium hydroxide (1310-58-3)
carbon disulfide (75-15-0)
Thiophosgene (463-71-8)
potassium thiocyanate (333-20-0)
thiocyanate
potassium ethyl xanthate (140-89-6)
thiourea (62-56-6)
o-Phenylenediamine (95-54-5)
2-Mercaptobenzimidazole,
2-Benzimidazolethiol (583-39-1)
2-Mercaptobenzoxazole (2382-96-9)
2-aminophenylthiourea (3394-09-0)
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