[Marvinthefish]

Hi. First post. I hope you can help. I made N-methyl-N-nitroso urea (http://en.wikipedia.org/wiki/ENU) last week, but I've no idea about the mechanism!
 
I've attached the first step (I hope the pic is attached!), which involves urea reacting with methylamine in aqueous acidic solution. I know methylamine is a pretty good nucleophile, but does it attack urea (which looks to me like a pretty bad electrophile) at the carbonyl carbon or...?

I reacted the product of that step with sodium nitrite in H2SO4 at -5 degrees Celcius. I presume this is some sort of diazotization? Anybody help me with the curly arrows for these two steps?

[jinclean]

 Anh! you use the chemsketch too!  the mechanism is in the figure

[Marvinthefish]

Aha! Thank you! It's so simple now. I can see the specific acid catalysis at work. *thinks aloud to himself* For some reason my mind didn't register that methylamine has a methyl group attached. I didn't know where the extra methyl was coming from.

 Yeah ChemSketch for the win

[stewie griffin]

Be careful with this stuff as it is nasty for you.
The second step should be pretty simple once you know what NaNO2 + H2SO4 does. It makes the nitrosonium ion (NO+, triple bond between N and O, formal positive on O). It's a pretty hot electrophile and you've got nucleophilic nitrogen sources in your starting material.
BTW, to make the nitrosonium ion, just use sulfuric acid to protonate one of the negatively charged oxygen of nitrate, then protonate it again to have water as your leaving group. Just use the other oxygen's lone pairs then to form the triple bond with nitrogen and kick out the water.
Hope that makes sense... I just didn't feel like making a chemdraw file and uploading it right now. 

[Marvinthefish]

Thanks stewie griffin. Yeah I know, I was using "a popular internet search engine" to try to find out the mechanism and all I got was dozens of studies giving mice tumours with the stuff! Dangerous. And I made diazomethane (!!) with it, so it was lab coat, safety goggles, gloves, screen fully down on the fumehood, and slow deliberate movements! It all worked out fine. My product is methylated. Now to activate that C-H bond over there...

Oh and thanks for the second reaction explanation. I wrote it out and it all made sense. Cool.

[stewie griffin]

I've used this stuff to make diazomethane as well. Are you distilling the resultant diazomethane? Some people do, but my advisor had an explosion doing that when he was a grad student and so I've always been told to be safe and not distill it. I didn't need super dry stuff anyways since I was just making a methyl ester. I just took my ether solution of diazomethane, dried it over some KOH pellets for 10 minutes, decanted the ether, dry over more KOH pellets, decant, and so on till I had dried it three times.

[Marvinthefish]

No I didn't distill it (although the PhD student whose procedure I'm using did). I made the diazomethane at -5 °C and made a cannula to my reaction flask. I then warmed the diazomethane flask (slightly!) and the diazomethane gas went over into my rxn flask through the cannula. I was making a methyl ester too. I didn't dry it at all! It still worked. The NMR was clean-ish. Hurray!

[stewie griffin]

Hey that's clever. I never thought of "cannulating" a gas like that. So simple and so effective.

[Marvinthefish]

I won't take credit for that one. A more experienced person in my lab suggested I do it that way. It is clever though. "in situ" formation of diazomethane, if you want to be fancy