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Nicotinoyl chloride is only available as its hydrochloride salt.

Why can't nicotinoyl chloride be synthesized in free form? How can we seperate nicotinoyl chloride from its salt form? Can we try any base for this purpose?

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  • $\begingroup$ I suppose (but am far from sure) that it's because acyl chlorides are very reactive, and the hydrochloride is here for stabilization… $\endgroup$
    – F'x
    Aug 27, 2013 at 18:26
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    $\begingroup$ hydrochloride salts are typically made to address solubility issues, and that might be the case here as well. $\endgroup$ Aug 27, 2013 at 19:19
  • $\begingroup$ Hydrochlorides are also often more crystalline and easier to purify: chemistry.stackexchange.com/questions/2627/… $\endgroup$
    – Ben Norris
    Aug 27, 2013 at 21:41

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Unfortunately, i don't have access to the original reference from 1928 Über die Einwirkung von Thionylchlorid auf die Pyridin-monocarbonsäuren by Meyer and Graf, but it's cited in The Preparation of Nicotinyl Chloride from 1953.

In this later note, where dried and grounded potassium nicotinate was reacted with oxalyl chloride in anhydrous benzene and the resulting nicotinyl chloride eventually destilled off under reduced pressure (75-90 °C, 10-12 mm), the authors state:

On exposure to the air, the oily acyl chloride soon solidified to nicotinic acid hydrochloride.

With other words, the combination of moisture and the basicity of the pyridine moiety results in the decomposition of the product. This is apparently prevented by deactivation of the pyridine upon conversion to its hydrochloride.

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