I managed to form caffeine crystal by adding caffeine powder to hcl. But i cannot get rid of the excess hcl from my crystal. My crystal will release very strong smell of hcl when I heat it up. How to get caffeine hcl crystal without the strong smell of hcl?

just dry/evapoprate the solution or filter it

just dry/evapoprate the solution or filter it

I have tried but the access hcl still stick to the crystal.

Caffeine.HCl is a chemical compound, which inherently contains HCl. It is a hydrochloride salt of caffeine. Many compounds form such salts, e.g. hydrazine, N2H4.2HCl, cocaine.HCl.

 

When they are heated, then the HCl is released again and that is what you smell. The reason that many compounds are made into an acid salt is that these are much more resistant against aerial oxidation and they are well-crystallized solid compounds. This makes storage and transport easier.

actualy the main reason an acid salt is made if for administration of the medicine, some salts are better for injection and others for ingestion.

actualy the main reason an acid salt is made if for administration of the medicine, some salts are better for injection and others for ingestion.

Exactly. Acid salts are typically much more water soluble than their free-base counterparts and so are able to be absorbed through the digestive tract and intravenously much more efficiently than the free-base form. Free-base compounds are typically vaporized and inhaled as their boiling point is much lower than the acid salt which makes it much easier to vaporize them. (Hence why cocaine hydrochloride is snorted. It's an acid-salt and readily dissolves in the nasal pasages. Free-base cocaine is smoked because it vaporizes readily and so is easily absorbed through the lungs).