Converting e.g. HCL-Salt into Base and/or another Salt like Citrate

[Soulfake]

I have a few questions about the conversion of (for example) an HCL-salt form of a chemical into the free base and/or converting the base further into another salt like citrate, ascorbate, acetate etc.

I also have some problems understanding the chemical properties of amino acids which are zwitterion/dipolar ions and I haven´t found articles that explain how those dipolar amino acids react with bases/acids. For example Arginine which has a ph of 10,5-12 as the free base and a ph of ~6 as the common HCL salt, would Arginine with it´s basic nature yield a "arginate salt" if mixed with a acidic substance like Phenibut which has a ph of 2,5?

What does the ph-value tell about the probably best salt form for the substance? For example Phenibut with it´s very sour PH of 2,5 would give quite different dissociation rates etc. if either made into an basic salt like arginate (or wouldn´t it be basic/would the low ph of Pheni and the high ph of Arginine cancel each other out to some degree?) or citrate? (the citrate form is used as "Citrocard" in russia, a paper states that the citrate is quite better than the hcl).
What about "semi-neutral" substances like Caffeine with a ph of 6-8? If anyone has general informations about the difference and properties of salts I would be thankful. I know that there are some drugs sold as a lysine-salt like Ibuprofen-lysinate, can you use any amino acid to produce a salt?
How can there be salts of a substance and also be salts with the substance? For example Lysine HCL and Ibuprofen lysinate? Is this because of the dipolar properties of Lysine?

If anyone knows an article that explains how exactly the negative and positive pole of the molecule reacts with bases/acids and how the binding with those would look like as a picture of the molecule/salt please let me know.

If I want to convert a HCL salt of a substance into the free base I can simply add Sodium Bicarbonate in the right amount, the only problem with this is the NaCl byproduct which would be problematic if one needs a certain amount of the chemical or uses it often. Is there a different technique to convert something into a base which doesn´t involve special lab equipment or hardly obtainable substances? I guess the procedure with a stronger base than Sodium Bicarbonate would need more precision and safety measurements, testing of the final ph-value etc.?

If I have the free base I can simply convert it for example into the citrate or ascorbate salt by simply adding adequate amounts of ascorbic or citric acid? Does this work with other acids like Acetic acid too?
It´s not possible to convert an HCL salt into a different salt directly/without converting it into a base in between, right?

And my last question would be what happens if I mix e.g. Phenibut with Citric Acid in water, then adding some Bicarbonate? Would this work too?

I hope this questions are allowed but as it´s just converting the salt-form of substances and not substances themselves I guess it´s ok.

 

[sekio]

pH is not something that is associated with substances themselves, it's a measurement of the acidity of a known volume of solution. pKa is the number that decides how acidic/basic the compounds are without regards to concentration. You can imagine a concentrated solution of sodium bicarbonate having a pH of 10 but also a very dilute solution of sodium hydroxide could also have a pH of 10 too.

If anyone knows an article that explains how exactly the negative and positive pole of the molecule reacts with bases/acids and how the binding with those would look like as a picture of the molecule/salt please let me know.

There's no "negative pole" of a molecule. There are however certain functional groups that can either donate or accept protons from other molecules (proton donors are called acids and proton acceptors are called bases). For instance, carboxylic acid groups and sulfonic acid groups are proton-donating moieties, and amines or negatively charged oxygen/sulfur atoms are proton acceptors. Depending on where exactly these groups are located on a molecule and how many there are, one can determine how a compound will likely behave when in various environments.

Amino acids are special because they are "zwitterions", which means they have both acidic and basic groups on them, and can hence act as either aproton donor (acid) or proton acceptor (base) depending on conditions. It's not correct to call these "dipolar" as that term has a quite different meaning in chemistry!

In general when you combine an acid and a base to produce a salt, the measured pH will be somewhere between the two compounds, as some of the protons that would normally remain free in solution (from the acid) are accepted and "stick" to the base provided.

Sodium bicarbonate can be used in some cases to break salts apart to the sodium salts of the acid and the free base molecule, however for some compounds it may not be strong enough and stronger bases must be used like sodium carbonate or hydroxide. Likewise combining a base with an acid will produce a salt.

 

[Scrofula]

OP: please be careful around concentrated acids and bases. You probably know the two don't mix well, not without a lot of heat and splashing back into faces. I have witnessed this (by proxy, but close enough).

For amino acids, let's take glycine since it has no functional group to worry about. You have a carboxyl acidic end and a basic amino end. The numbers you're interested in are the pKa values of these groups (and they are molecule specific). pKa is the pH in which it will be half-ionized in solution. For glycine I'm guesing the acid has a pKa of about 4, and the amino group a pKa of around 9.

The rule of thumb, is that if the pH is two units away from the pKa, the group will be all protonated or all unprotonated.

That means at pH 4, half of the molecules will have a proton on the acid and half won't. OK, now, it takes a while for students to figure which way it would go, so be prepared, the amino group at pH 4, would be all protonated, meaning every molecule has a charged amino group.

So at pH 4, half the molecules have a negative acid and a positive amine for zero charge, and half have a neutral acid and a postive amine for a net positive charge.

So, pH 7, two units away from both, you have all negative acids and positve amines.

pH 11, you have all negative acids and all neutral amines, for a net negative molecule.

For less than two units, there's an equation to work it out.

THese are all different from the pH you'd get dissolving powdered glycine into water; that would depend on the final concentration of glycine.

OK, I'll let that sit, and feel free to say that's too simplistic you actually work for NASA and mean something different.