An Improved Large-Scale Preparation of Benzimidazole-2-Sulfonic Acids and 2-Chlorobenzimidazoles.Footnote‡

‡ Dedicated to Henry Koppel.

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• The solvent system used was CHCl3:CH3OH 10:1 (V:V). Benzimidazol-2-thiones typically have very high Rf Values (>0.8) in this system whereas the Rf values for the benzimidazole-2-sulfonic acids are very low (<0.2)
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• This is needed to control the initial extremely exothermic reaction that occurs on heating
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• This is conveniently carried out by dividing the reaction mixture into two or three portions contained in 20 L plastic buckets. The time required for neutralization is reduced to approximately 2 hr
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