[JSUCY232]

I would like to try to make the tosylate of polyvinyl alcohol so I can subsequently substitute it with a thiol group with NaSH. I can't find any of good methods for simply doing this. I have a high molecular weight PVOH, tosyl chloride, pyridine, THF, and pretty much whatever else I need. How do I perform a simple tosylation reaction? I am thinking 1.2 equiv of TSCl, 2.5 equiv pyridine, lots of THF at 0C. Any advice? I will be doing this under Argon with dry/purged reagents. Thanks a lot!

Donna

[OrganicDan96]

that sounds ok, dropwise addition of pyridine is typical. I would chose DCM for such a reaction. you should be able to find common conditions online

[JSUCY232]

Ok. Thanks. I might try DCM instead.

[wildfyr]

A warning, this will not go to full conversion. You will not tosylate every last alcohol group. I would suggest you use a very large excess of tosyl chloride and long reaction time to get as much as you can.

Dan, I'm pretty sure PVA has garbage solubility in DCM. For reference, its very soluble in water, but poorly soluble in alcohols, and totally insoluble in acetone. It depends a little on the degree of acetylation still present, most commonly its 20% still acetylated. I would use hot DMF to give myself the best chance.

[JSUCY232]

Thanks for the advice. I started the reaction with only pyridine as the solvent. I am hoping that the solubility of the product will be better than the solubility of the PVA. Of course, I will not achieve complete substitution, but I used an approximately 1:1 equivalent of TSCl, because that's all I had. I started in an ice bath under an Argon balloon, and will allow it to warm to room temp and possibly stir overnight. I have DMF. I could add some and heat it??? It seems to be slowly dissolving, but I'm not 100% sure. For workup, I have been instructed to wash with saturated ammonium chloride, then possibly use 1M NaOH to remove the resulting sulfonamide. Does this sound good? I'm a computational chemist primarily, so my synthetic results have been hit and miss. This is an undergraduate research project with a student I am instructing, so I'd like things to go well. Thanks again. Donna.

[wildfyr]

I would definitely suggest adding like a few more equivalent of TsCl. I've played this exact game before, tosylation of polymers is just a crummy reaction. I'm sure every organic chemist at your school has a big old' 500 g container of it sitting around to get from. Neat pyridine isn't a bad idea, but if you feel like nothing is dissolving, adding some DMF and heating it a bit (remember pyridine's BP!) should help.

That workup would work for a small molecule, but is doomed to fail on a polymer. I bet it came from a small molecule guy. I'll give you a crash course in polymer workup from someone who has made a couple hundred novel ones.

Polymers virtually always need to be precipitated and redissolved a few times to clean up. Small molecules become caught in the polymer matrix, so just doing liquid liquid extraction won't fully transfer contaminants from one phase to another like in a small molecule reaction. Also, polymers make great surfactants, so extractions can easily emulsify.

Once you think the reaction is pretty complete, take a drop of it and put it in some cold ether, methanol, and isopropanol. Pick the one the precipitates best. I can't explain exactly why, but those 3, (plus water, when appropriate) are just really terrible solvents for polymers, but decent ones for small molecules. Hexane could work in this case too. You should see a solid precipitate out that is not a very fine powder. This judgment unfortunately requires some experience with polymers, but you want the precipitated solid to be easily captured on a filter and able to be redissolved and precipitated again. 3x is typical. Each cycle should drastically reduce the amount residual pyridine/DMF/TsCl left. It may seem a little silly, but I would smell your solid. If you can detect pyridine, keep precipitating. If you smell pyridine, the other two are likely still there too. Often each cycle will lower your yield, but it's worth it for purity.

[rolnor]

I think heat could be used to push the reaction? 80°C? The polymer needs to move a bit to let it react. Also, could moisture be a problem here, is maybe the polymer hygroskopic? It could be sonicated in the pyridine with molecular sieves for a few hours before adding tosyl chloride. Or co-evaporated with pyridine a few times.