Sciencemadness Discussion Board

Copper(II) Anthranilate.....red??

DraconicAcid - 30-9-2021 at 11:21

So, a couple of years ago, I introduced a new lab to my students- quantitative analysis of copper by precipitation with anthranilate (as I mention here: http://www.sciencemadness.org/talk/viewthread.php?tid=45838#... ).

The other day, I was looking at the students' products, and one of them had some lovely little dark red crystals in with the green copper(II) anthranilate. WTF?

Possibly a nitrosobenzoic acid derivative? I haven't tried picking any of them out to find out what they are yet, but suggestions of possibilities are welcome. The solutions of sodium anthranilate aren't exactly fresh, so some of the anion may have oxidized, but the copper salts were pure (so it shouldn't contain some other metal).

Amos - 30-9-2021 at 14:41

Sounds like oxidized anthranilic acid crystallizing with a small amount of its oxidized products in tow.

Boffis - 30-9-2021 at 21:20

Some Cu(I) complexes of colourless organic ligands are red or violet so maybe as Amos suggests the anthranilate portion has been oxidized to something and the copper reduced accordingly.

Amos - 2-10-2021 at 10:11

I was just referring to air oxidation or impurities already contained in the material; I've seen impressive reddish-brown crystals of anthranilic acid posted here and in other amateur scientific communities before multiple times. But I won't completely discount the possibility of copper(I) formation.

DraconicAcid - 2-10-2021 at 10:39

I'll have the samples back on Monday- only one of them had the red crystals. I'll check to see if they are soluble in alcohol.