Hydrochloride

Trimethylammonium chloride as an example of an organic hydrochloride; the hydrogen bonds are drawn with dashed lines and marked in blue . Detailed investigations show that the structural formula at the top best describes this salt.

Hydrochlorides are salts of organic bases with hydrochloric acid . Hydrochlorides are often salts of primary, secondary or tertiary amines that are formed in a neutralization reaction with hydrochloric acid (HCl):

${\displaystyle \mathrm {R_{3}N+HCl\longrightarrow R_{3}NH^{+}+Cl^{-}} }$

The reaction proceeds analogously to the reaction of ammonia with HCl, in which ammonium chloride (NH ₄ Cl) is formed. Like all chlorides, hydrochlorides contain the chloride anion (Cl ^- ) and are therefore salts. Compared to their parent compounds (mostly amines), hydrochlorides are usually more water-soluble and can be cleaned more easily by recrystallization . The hydrochlorides of amines are significantly more stable and more resistant to aging - recognizable by their discoloration - than the free basic amines.

In the case of complex molecules with several basic reacting functional groups (see alkaloids , lysine ), in which the protonated group cannot be precisely defined, hydrochlorides are often represented graphically as follows:

${\displaystyle \mathrm {R_{3}N+HCl\longrightarrow R_{3}N\cdot HCl} }$

The reaction of organic diamines with excess hydrochloric acid results in dihydrochlorides (examples: arsphenamine , cetirizine , flunarizine , flurazepam , meclozin and sapropterin ), which contain two equivalents of hydrochloric acid (HCl) in a salt-like bond. If equimolar amounts of an organic di- or triamine are reacted with hydrochloric acid, a monohydrochloride is obtained .

use

Many basic medicinal products are used as hydrochlorides due to their mostly better water solubility and bioavailability. Water-soluble salts enable the production of aqueous solutions such as injection and infusion solutions , eye drops and nasal sprays . In the case of drug forms to be used orally , water solubility is often the prerequisite for the release of the drug from the drug form in the gastrointestinal tract . Only drugs released from the drug form (tablet, capsule, coated tablet, etc.) can be absorbed at all . Technical aspects (stability, solubility, processability) also often play a role in the use of the hydrochloride of medicinal substances.

Hydrochlorides in widely used drugs are, for example, those of xylometazoline , ambroxol and metformin . The European Pharmacopoeia alone describes a good 200 hydrochlorides as medicinal substances, the drug substance catalog (ASK) or the drug information system contains more than two thousand hydrochlorides.

Analog salts

The hydrochlorides belong to the class of hydrohalides . These also include the hydrofluorides , hydrobromides and hydroiodides .

Individual evidence

1. ↑ Glenn H. Penner, Renee Webber, and Luke A. O'Dell: A multinuclear NMR and quantum chemical study of solid trimethylammonium chloride. In: Canadian Journal of Chemistry . 89 (9), 2011, pp. 1036-1046, doi : 10.1139 / v11-034 .
2. ^ P. Heinrich Stahl (editor), Camille G. Wermuth (ed.): Pharmaceutical Salts: Properties, Selection, and Use. 2nd Edition. Wiley, 2011, ISBN 978-3-906390-51-2 .
3. ↑ European Pharmacopoeia 7th Edition 2011, EDQM.
4. ↑ German Institute for Medical Documentation and Information: Search for hydrochloric in the drug information system  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.