How to predict the acidity or alkalinity of drugs though pKa values?

[Dina Mahmoud]

Hi, how are you all? Hoping to be fine
I tried to get information about pka and pkb of some chemical agents, but I don't understand how to know the nature of a certain drug, I mean Is it an acidic or basic drug? And Is it a weak or strong one? For example, Levamisole Hcl (its structure is presented in the link below); is an anthelmintic drug, in the hydrocholide salt, freely soluble in water and has pKa value of 8.

1- Is it an acidic or basic agent?
2- Is there a general rule or pKa range helps me to detect the acidic or alkaline nature of other drugs?

Hoping to help and simplify this issue to me. Thanks in advance

https://www.caymanchem.com/app/template/Product.vm/catalog/14874

 

[Black]

1. the hydrochloride salt is acidic. levamisole itself is a base.
2. no, pka will tell you nothing about if the compound you're looking at is an acid or base.

but it's really quite simple. since any acid-base reaction is characterised by the transfer of a proton, there will always be a protonised and deprotonised form (the corresponding acids and bases) - in this case the HCl salt of levamisole and levamisole. the pka value gives you the pH at which both forms will be present in equal concentrations.
but not every acid even has a pka value. strong acids, which are fully dissociated from H+ in water (like HCl) fall in this category.
most organic compounds however are weak acids/bases.

but there are some things you can say about compounds based on the pka. since levamisole has a pka of 8 (which is above 7), you can say that levamisole is a weaker acid than levamisole is a base. on the other hand something like acetic acid (with a pka of around 5) is a stronger acid than the corresponding acetate anion is a base.

some general rules of thumb: if a compound has an amine, it's likely a base. if a compound has a COOH group, it's an acid. if a compound can build a salt with an acid like for instance HCl (and if it only has one pka), it's a base.
most psychoactive drugs are bases.

 

[sekio]

http://chemicalize.org

this site predicts pKa etc.

like so

 

[Dina Mahmoud]

Thanks a lot. It's clear now