[mahesh]

Hi all,
I am new to this forum, but it looks really informative.
I am working on synthesis of synthesis of carbamates by aminolysis of DMC with various amines.
RNH2 + MeO-COOMe------- RNHCOOMe + MeOH
I am using lead compounds as catalysts. After I finish the reaction, I am getting colored reaction mixtures. I can understand that aromatic amines will give colored reaction mixtures, but even amines like butylamine and benzylamine are giving color (yellowish-brown). I feel this may be due to lead compounds (lead methoxide or others). Since I need to purify the carbamates, is there any way of removing the lead before isolating the carbamates? By the way, can someone please suggest the reaction mechanism if I am using lead oxide (Pb3O4) as catalyst? Amine, Pb3O4 (as catalyst) and DMC (excess) are the only reaction components, and the reaction results in carbamates only at higher temperatures (120-160C).

[AWK]

Pb3O4 is a strong oxidizer. It can oxidize organic compounds to tarry products (especially amines).

[mahesh]

Thanks a lot for responding. However, I have still no clue as to how I can remove lead from my reaction mixture     I am having difficulty in isolating my carbamate products because of this, can someone help please?

[Mitch]

Water/ether extractions not working?

[mahesh]

No, I guess some organic derivative of lead is forming (may be something like lead methoxide), which is not dissolving in water. Besides, carbamate easters can be treated with water for much time and under harsh conditions (warm water, etc.), as these compounds tend to hydrolyse. 

[AWK]

But you will extract carbamate to organic phase

[mir]

is there any way of removing the lead before isolating the carbamates?

Try filtrate the mixture through active coal or some silica.

[mahesh]

Silica column is working fine when I used aromatic amines as substrates, but there was problem for aliphatic amines, the carbamates decomposed... I tried charcolization too, but thats not removing the reddish color at all..  I think i will have to drop the aliphatic amines... i could isolate the aromatic amine carbamates by silica gel coulmn chromat., You know, I could see the lead oxide particles moving down my column and clogging at the bottom on the cotton swab !!. The soluble colored lead compound came down first as a separate fraction!!

[mahesh]

Anyway, thanks a lot dear people for the kind *delete me*!

[mahesh]

hey i had typed help, not delete me!!!

[Quimex]

Have you tried EDTA?