Ventsi Posted December 27, 2009 Posted December 27, 2009 I'm grabbing some Copper Carbonate, and I was wondering if Copper Sulfate wold be a better substitute as far as synthesis of Cu Benz/Saly. goes. And some tips on making the salts wouldn't be bad either!
Miech Posted December 27, 2009 Posted December 27, 2009 I'd rather react the copper carbonate with hydrochloric acid first, because copper chloride is way more soluble. Making copper benzoate can easily be done by adding a solution of a random copper salt to a solution of potassium benzoate. Do not use a test tube for this, or you'll have a very hard time getting your product out. Then simply filter, wash a few times with cold water and dry. For a higher purity, recrystallization from ether or a similar solvent can give you nearly 100% purity, given that your potassium benzoate was pure.
firetech Posted December 27, 2009 Posted December 27, 2009 Is that really all it takes? It seems pretty simple when the price of CuBenz is so high.
Miech Posted December 27, 2009 Posted December 27, 2009 That's how I made it. Most reactions are pretty simple to do, but scaling it up to an industrial scale is the real challenge. Drying is the part where it may or may not become tricky. It forms a foamy sort of lump when dried in a dessicator, which is why I would prefer recrystallizing the next time. Ether is gone in a blink of the eye (or in a flash if you aren't careful).
Mumbles Posted December 28, 2009 Posted December 28, 2009 No one makes it industrially, presumably because it isn't good for anything, so all of it has to be made on custom small scale batches. This corresponds with expensive. I never thought about it, but I would have to second the chloride method. Not for solubility reasons, but for cleaning reasons. When I made my CuO last time, I used CuSO4 and NaOH. The sodium sulfate was such a bitch to wash out of the solid. I can only imagine that potassium is about as bad. On the other side, it's not as clean to start from the carbonate, as it doesn't have as defined of a molecular formula as the sulfate. It will have numerous impurities as well.
Ventsi Posted December 28, 2009 Author Posted December 28, 2009 Interesting, so would the best way to go be using straight Benzoic Acid and Copper Carbonate? That way, in theory you should end up with CuBenz and water. Also, many, if not all sources I've read said that they got pure, perfectly usable CB using a sodium salt, either the benzoate or saly. and repeated washing. This is from both AFNII and Skylighter. I don't exactly understand, why is recrystallization needed? Is the particle size/shape so small/odd shaped that it doesnt let go of the water? Is there any other solvent I could use rather than ether, its extremely expensive?
Mumbles Posted December 28, 2009 Posted December 28, 2009 Honestly, I don't even know if it's soluble in ether. I think it's soluble in alcohol at least, probably with boiling. The reaction isn't as clean using benzoic acid and copper carbonate. Firstly, you can't filter any insoluble contaminates from the starting materials. Secondly, you have to heat it to keep the benzoic acid in solution, and there is a slow foaming mess. It's hard to tell when the reaction is done. You have to rememer that copper carbonate is insoluble in water too, and actually exists as a complex salt of copper carbonate and copper hydroxide. Even with a dessicator, I don't know that you will remove all of the waters of hydration, of which there are at least 2 if not 3. There is a definitive darkening upon drying at heat to almost a teal color IIRC.
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