Question

Asked 19th Jun, 2015

Binghamton University

How can I oxidize a terminal PEG (MW:2000) hydroxyl group ?

I use this method:

A solution of PEG in DMSO was combined at RT with NaOH(40 wt%) under magnetic stirring for 30 min after that add chloroacetic acid and then solution stirring for 10h ,after that remove the DMSO and add Dichloromethan precipitated salt removed by filtration . But when I took the IR I didn't see the carboxylic acid peak.

Where is my mistake?

Chemical Oxidation

PEG Precipitation

Applied Organic Chemistry

Andrea Marchi

University of Bologna

Good reaction, I like it. You can start from Bromoacetaldehyde, make the diethyl acetal (or also you can buy it). Then you have to create the PEG alkoxide (also your way is correct, but I prefer organic phases), and after the reaction is complete (on TLC you won't see the PEG traces), drop in acid to reform the aldehyde (after that you can oxidize it).

On the second hand, if you want to synthesize carboxylic acid directly, I suggest you to put PEG and KMnO4 in alkalyne solution. The drawback is that this route gives appreciable amounts of chain cleavage, but you can try, and it is a cheaper way than yours. :-) Oh, another way is to use Alcohol dehydrogenases, but you know, it's hard to find the right one!!! Good luck and let me know the outcomes!!! :-)

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1 Recommendation

Danial Mousavi

Binghamton University

Thanks for answer

I used below method and I could see the carboxylic acid group in IR:

an aqueous solution of KOH (40wt%, 48 ml) was

added to a solution of mPEG (5 g, 1 mmol) in 72 ml dimethyl sulfoxide (DMSO). The solution was kept under magnetic stirring at

room temperature for 2 h. Chloroactic acid (0.5 g, 5.291 mmol) was

then added and the reaction mixture was heated to 60 C. The

reaction proceeded for an additional 24 h before adjusting its pH to

7.0 using HCl solution (37 wt %). The water was evaporated with

a rotary evaporator and the DMSO was removed by dialysis. The

residue was taken up in THF, ltered, precipitated in cold ethyl

ether twice and dried in vacuum overnight. Then white powder

mPEG-COOH was obtained.

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