Hexol


Hexol is the name for various salts of a coordination complex that has historical significance. The salts were the first synthetic non-carbon-containing chiral compounds. The sulfate salt has the formula 3.

Preparation and optical resolution

Salts of hexol were first described by Jørgensen. The salt is prepared by heating 3+ with dilute base such as ammonia followed by precipitation of the sulfate salt:
Depending on the conditions one obtains the 9-hydrate, the 6-hydrate, and the 4-hydrate. These salts exists as dark brownish-violet or black tabular crystals. The salts have low solubility in water. The cation can be quantitatively precipitated from its yellow-gray chromate and hexachloroplatinate salts. When treated with concentrated hydrochloric acid, hexol converts to cis-diaquotetramminecobalt sulfate. In boiling dilute sulfuric acid, hexol degrades with evolution of oxygen and nitrogen.

Optical resolution

In a historic set of experiments, Alfred Werner obtained chiral resolution by fractional crystallisation of the diastereomeric D--bromocamphorsulfonate salt. This ion has a high specific rotation of 2640°. More efficient methods involve the bisdiantimonate salt.

The "second hexol"

Werner also described a second achiral hexol that he incorrectly identified as a linear tetramer. The second hexol is hexanuclear, not tetranuclear.