Preparation of dimsyl sodium

Dimsyl sodium is used for the alkylation of polysaccharide and sometimes oligosaccharides. It is a very strong base and it converts the polysaccharide to the polyanion. Treatment of DMSO with NaH gives dimsyl sodium, under the evolution of hydrogen gas. Because of its flammability NaH is kept in oil which must be washed away before the reaction with DMSO. The NaH-suspension should be grey, if it is white that is a sign of NaOH coming from moisture. Petroleum ether or hexane is used for this. The resulting solution of dimsyl sodium is 2M.

• Sodium hydride in oil (50%)
• Petroleum ether
• DMSO pro analysi
• serum flasks 10 and 25 mL
• Needles 0.9 mm, or somewhat larger.

Full list of chemicals

1. Put the NaH/oil dispersion (1 g) in a 25 mL septum flask and seal it. Wash with petroleum ether/hexane (15 mL) by stirring with a magnetic rod. Crush big lumps of dispersion with a glass rod. Repeat twice.
2. Remove the last traces of petroleum ether/hexane by flushing with a gentle stream of N₂ or dry compressed air. Some heating of the flask may be necessary.
3. Add DMSO (10 mL), cap, and put a needle through the septum. Stir with magnetic rod. If gentle reaction heat to 40-45 �C, if not leave until the reaction calms down, then heat. You may ultrasonicate for some minutes.
4. Transfer the dimsyl sodium solution to screw cap tubes and centrifuge for a couple of minutes at ca. 3000 rpm.
5. Transfer to 10 mL serum flasks.

• The less moisture and oil that comes into the reaction the better.
• Some heat is required to start the hydrogen evolution, which must be led out via the needle. If there is water in the DMSO and bubbling in the flask takes place the needle may get clogged with NaOH and the flask can explode.
• A sediment is often obtained in the centrifugation.
• If dry gas is blown around the place of transfer no seals are required.