Dear Shu Er Tan, 

As stated by many people above, dry DMSO means, there is almost no water content in it. (greater than 99.9%)

From my experience I would definitely say that , some of the chemical reactions do not happen even with traces of water.  

And when you are dispensing the required volume of dry solvent, it should done under inert gas atmosphere (nitrogen inlet and sucking it with a syringe through the rubber stopper in the bottle), otherwise the atmospheric air will contaminate it with water, increasing the water content, thereby making it less effective in further reactions.

Good luck.

Arun 

Dear Shu,

Purification of Dimethyl sulfoxide (DMSO)

Dimethyl sulfoxide (CAS NO. 67-68-5) is colourless, odourless, very hygroscopic liquid, synthesised from dimethyl sulfide. The main impurity is water, with a trace of dimethyl sulfone. The Karl-Fischer test is applicable. It is dried with Linde types 4A or 13X molecular sieves, by prolonged contact and passage through a column of the material, then distd under reduced pressure. Other drying agents include CaH2, CaO, BaO and CaSO4. It can also be fractionally crystd by partial freezing. More extensive purification is achieved by standing overnight with freshly heated and cooled chromatographic grade alumina. It is then refluxed for 4h over CaO, dried over CaH2, and then fractionally distd at low pressure. For efficiency of desiccants in drying dimethyl sulfoxide.

Rapid purification: Stand over freshly activated alumina, BaO or CaSO4 overnight. Filter and distil over CaH2 under reduced pressure (~ 12 mm Hg). Store over 4A molecular sieves.

It depends, if you have to prepare dimsyl-soldium, you have to dry it. For a nucleophilic substitution it probably will work as it is unless you need high dilution: then the yield may drop. Just consider how much of your reagents may be destroyed by water, if any, and decide, whether it is worth it, to spend time for the purification.

Dear Shu Er Tan, 

As stated by many people above, dry DMSO means, there is almost no water content in it. (greater than 99.9%)

From my experience I would definitely say that , some of the chemical reactions do not happen even with traces of water.  

And when you are dispensing the required volume of dry solvent, it should done under inert gas atmosphere (nitrogen inlet and sucking it with a syringe through the rubber stopper in the bottle), otherwise the atmospheric air will contaminate it with water, increasing the water content, thereby making it less effective in further reactions.

Good luck.

Arun