[magician4]

Hi y'all,

I was planning to modify the endgroups (i.e. both the -OH) of a PEG M ~ 35,000 by tosylating them

thinking of approx 1 g PEG in 10 ml of solution, the theoretical conc. for 1:1 reaction would be in the ballpark of 0.005 mole / L for both hydroxy and tosylchloride - which gave me concern about maybe very long reaction time required

on the other hand, grossly increasing the tosylchloride part (just to speed things up) would pose the problem of removal of the excess - which is a headscratcher in its own right


any ideas / reassurance / helpful remarks would be greatly appreciated

regards

Ingo

[Archer]

Have you considered a solid phase reaction of the excess onto, say, aminopropyl modified silica gel? Could get expensive!

Bit of a tough one this!

[magician4]

Have you considered a solid phase reaction of the excess onto, say, aminopropyl modified silica gel?

no, I didn't
with respect to any route involving removal of excess tosylchloride, my first idea was dry, fine powder of common household sugar  (and having a suspension with it , as I basically was thinking of some THF or thatlike as general solvent, where sugars should be next to insoluble)
as I said, the "excess" approach still is another headscratcher in its own right (and I would like to avoid it , of course)

my hope was that someone came along and said " 0.005 * 0.005 with tosylchloride / hydroxy: no problem" or something like that, or maybe had a suggestion for a catalyst ...

regards

Ingo

[Babcock_Hall]

I'm guessing that you already have seen this:
Convenient synthesis of α-tosyl-ω-tosyloxypoly(oxyethylene)
Die Makromolekulare Chemie, Rapid Communications
Volume 6, Issue 2, pages 53–56, February 1985
Rik J. De Vos, Eric J. Goethals
DOI: 10.1002/marc.1985.030060202

I don't know of any catalysts beyond the usual suspects.

[magician4]

I'm guessing that you already have seen this:(..)

thank you for the hint, and yes, I knew that one

problem is: this literature is dealing with M ~ 2,000 to 4,000
... and I wanted to modify PEG of ~ 35,000

this makes both relevant concentrations (i.e. hydroxy and tosylchloride) like 10 to 20 times smaller, and hence - given that the reaction most probably is second order - the speed like 100 to 400 times more slow
... i.e. would expand each and every "usual" hour to next to a week

anyway, thank you again


regards

Ingo