A Publication
of Reliable Methods
for the Preparation
of Organic Compounds
Annual Volume
Page
GO
GO
?
^
Top
Org. Synth. 1950, 30, 56
DOI: 10.15227/orgsyn.030.0056
2-MERCAPTOBENZIMIDAZOLE
[2-Benzimidazolethiol]
Submitted by J. A. VanAllan and B. D. Deacon1.
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 alcohol6 or in water;7 and by heating the hydrochloride with thiourea to 170–180°.8

References and Notes
  1. Eastman Kodak Company, Rochester, New York.
  2. Org. Syntheses Coll. Vol 2, 501 (1943).
  3. Lellmann, Ann., 221, 9 (1883).
  4. Frerichs and Hupka, Arch. Pharm., 241, 165 (1903).
  5. Billeter and Steiner, Ber., 20, 231 (1887).
  6. Gucci, Gazz. chim. ital., [1] 23, 295 (1893).
  7. Kawaoka, J. Soc. Chem. Ind., Japan 43, Suppl. binding 223 (1940) [C. A., 35, 2368 (1941)].
  8. Kym, J. prakt. Chem., [2] 75, 324 (1907).

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)