[Procyan]

I have prepared immobilized Cibacron Blue silica gel for enzyme binding studies.  I would like to convert the sulphonic acid groups to sulfonamides using thionyl chloride and ethanolamine.  Safely

Using a fume cupboard, I plan to put a measured amount of dry blue silica gel in a sintered glass funnel, cover it with neat SOCl2 for several minutes, draw off the excess and rinse with DMF.  Then simply flush with straight ethanolamine and leave for several hours. 

1. Does this sound reasonable? 
2. Can I use diluted SOCl2?  Solvent?
3. Could someone suggest a method of measuring extent of reaction (besides titration of remaining acid groups)...is there a direct test for sulfonic acid groups?

Any/all suggestions appreciated more than somewhat.

[Two00proof]

I would not wash with DMF.  DMF can be reactive towards SOCl2, much like in the Vilsmeier reaction.  If you want to dilute the SOCl2, use methylene chloride.  I would also dilute the ethanolamine with methylene chloride.  You don't want to risk a violent reaction.

Doing the reaction in a sintered glass funnel might not allow for complete conversion.  Usually when you do heterogenous reactions, you need heavy stirring.  Just something to consider.

[Procyan]

I would not wash with DMF.  DMF can be reactive towards SOCl2, much like in the Vilsmeier reaction.  If you want to dilute the SOCl2, use methylene chloride.  I would also dilute the ethanolamine with methylene chloride.  You don't want to risk a violent reaction.

Thanks for the tip! Avoiding [any more] violent reactions is foremost at this stage.  I would rather use DMSO in stead of methylene chloride (I have 4 bottles that are getting old and no methylene chloride).  Any potential problem there? 

I use some powerful reagents occasionally with no fear, but SOCl2 is quite scary when it gets out of the bottle.  My sintered funnel seemed to offer a measure of control, but mixing is important so I will not use it as reaction vessel.

[Two00proof]

DMSO is potentially worse.  Look up Swern Oxidation. 

[Procyan]

Right, the order for Methylene Chloride goes in today. 

Do you think this is a good way to block/eliminate sulfonic acid?

[Two00proof]

It does sound reasonable.  One thing, keep in mind that generation of a sulphonyl chloride may not go quickly.  Sometimes you have to have long reaction times and possibly elevated temperatures.  If this is the case, you may need to change solvents to toluene and do the reaction under reflux conditions.
Let hope this is not the case.

[Procyan]

Thanks, it is important that I get this right.  I'll get a reflux apparatus ready just in case.  Lots of toluene on hand.  One thing still bothering me is tracking extent of reaction.  I have no direct quant or even qualitative test for immobilized sulfonate groups.  For amines I use TNBS or OPA, but I can't find anything for acids.

I hate putting my immobilized dye in reflux for long times.  Seems so harsh. 

[Two00proof]

Sorry, I honestly don't know of a good way to figure it out.  My first thought is a titration, but that may not tell you much.

[Procyan]

Thanks you've been a big help.  Always good to avoid violence in the lab!