L-Arginine Solubility Help

Interesting idea.  I don't have experience with HMPT but I'll pitch the idea to my team.  It does have a relatively low BP though at about 50C, so it would just boil off in our reactor.

The only other solvent I can think of is propylene carbonate.

In that case, if it's not going into DMSO/DMF well enough and you can't use protic solvents, you might need to rethink your experiment approach.

Unfortunately I think the problem is now beyond the solvent.  I can't figure out why an amine rich L-arginine won't react with a diisocyanate?  That reaction should be lightning fast.

Try a glyme solvent e.g. tetraglyme triglyme...  They have a huge liquid range, they dissolve everything from water to non polar solvents.  DMPU, and PEG are other choices

L-Arginine in an amino acid and acids inhibit isocyanate reactions. 

Less than 10ppm of phosphoric acid can more than half the rate of reaction between a polyol and IPDI.

UPDATE:

Firstly, thanks for everyone's contribution to my first thread.  Really appreciate it.

I went forward with my synthesis as a slurry, using a diluted L-Arg/DMSO charged to an isocyanate rich reactant.  To my surprise, NOTHING happened.  The theory is that the amine rich L-Arg will react with the isocyanates to create a urea.  I am very experienced with the isocyanate and create a lot of urethanes with this reactant (using polyols instead of polyamines).  The amine/isocyanate reaction is typically lightning fast when compared to alcohol/isocyanate.  Instead, my slurry remained a slurry and the solids did not decrease in size.  The analytics didn't show urea formation so I knew my reaction was stalled.   This was all done at 85C with excellent mixing.

There's not a lot of literature for L-arginine used as a polyamine so I'm wondering if my theory is just not feasible.  I'm disappointed but there's a few other things I'm going to try.  Might even explore lysine as another option.

Any thoughts on my observations (or lack thereof)?

Is the arginine the free amine or the HCl salt?  I've only ever used R in one protected form or another, so the solubility was different.

Thanks for the response Unassuming.  We are currently using the free amine form as the acid can greatly affect our kinetics and we are avoiding any other associated compounds such as the HCl salt.

Have you tried HMPT?  What if you started with the free acid and added an equivalent of tetramethylammonium hydroxide?  I don't have personal experience with arginine, so these are just ideas.

Quote from:

L-Arginine in an amino acid and acids inhibit isocyanate reactions. 

Less than 10ppm of phosphoric acid can more than half the rate of reaction between a polyol and IPDI.

Yes, I agree acid is a very strong inhibitor for these reactions.  However, isn't arginine a basic amino acid?  pK = 12.5?  This is why I'm scratching my head.

http://www.thinkpeptides.com/aminoacidproperties.html

I'd try tetraalkylammonium hydroxide as Babcock_Hall suggested.

Oops just saw it's carcinogenic and mutagenic.  That's a big no-go in our product!

Germ cell mutagenicity
Hamster
Kidney
Morphological transformation

Carcinogenicity
IARC: 2B - Group 2B: Possibly carcinogenic to humans
NTP: Reasonably anticipated to be a human carcinogen

Yeah I think we've exhausted our solvents.  He had some luck with formic acid too, but I think I'm going to use a slightly acidic (~500 ppm H2SO4) with DMSO to create a slurry.  The reaction should be very fast and I don't anticipate residual L-Arg to be left behind (this is what I'm trying to avoid obviously).

I'll post back results next week.  Thanks again Unassuming.