[mahesh]

Hello guys!!
I have a query. What would happen if you heat lead oxide (Pb3O4) suspended in excess aniline at 160C for say 3 hrs? I got a thick purple liquid, which is miscible in organic solvents. There was also Pb3O4 left at the bottom, which remained unchanged in color or form. I am doing mechanistic study, and so need your help in this.

[Kryolith]

Have a look at

http://en.wikipedia.org/wiki/Mauveine

Perhaps you've just done the same with Pb₃O₄

[AWK]

Mauveine cannot be formed from pure aniline. Instead aniline black is formed. Oxidation with Pb3O4 goes better under acidic condition

[mahesh]

So what should be happening in the reaction? The conditions are basic (due to excess aniline) and not acidic... So I don't get it.. The mole ratio of aniline to Pb in the reaction was nearly 6. Importantly, at the end of the reaction, I found that about half the aniline was consumed, and the weight of the solid had increased by approx 6%, which I guess could be due to the adsorption of the dye on the oxide. The slight change in the color of the solid (slightly darker orange) also indicated in the same direction. I feel from these observations that Pb is not getting into the solution, rather, the dark purple liquid is some oxidation (coupling product, if I am not wrong) product.
Is there some way for me to identify or confirm the formation of such a dye in my reaction?

[AWK]

Aniline even in closed bottle become brown after time being. It is easily oxidized by air at RT
http://en.wikipedia.org/wiki/Aniline

[ARGOS++]

Dear Mahesh;

Aniline oxidizes with a numerous of metal salts as catalysts to different oxidation/coupling “states” with a Lot of different colors. Some of them you are able to isolate quite pure.

One of several “Aniline Blacks” you may see on:  "Aniline Black”

At least a numerous names of Dyes/Oxidation-states you will get an the German page:  "Anilinschwarz”
(Maybe a hint for future searches.)


Good Luck!
                    ARGOS⁺⁺