Chlorosulfonation without chlorosulfonic acid
For some reason I was needing some 2,5-dimethoxybenzenesulfonyl chloride and I was without chlorosulfonic acid, so I decided to try first sulfonate
the 1,4-dimethoxybenzene and then get the chloride using PCl5. Of course there is nothing new here but it is a good way to show a path using PCl5
instead of POCl3.
The 1,4-dimethoxybenzene can be made using the methyl bromide technique already discussed here as well the PCl5.
I know it is not so OTC but if someone has some red phosphorus and a Cl2 generator, the rest of it is very easy.
The way presented by Ullmann at 4-alkylthio-2,5-dimethoxybenzaldehyde, Sulfuric Duff reaction is good indeed but it cannot be used to make an
asymmetric molecule like 2,5-dimethoxyphenyl ethyl sulphide, so I tried the way it follows:
Potassium 2,5-dimethoxybenzenesulfonate – To 40.00 g (0.29 mol) of 1,4-dimethoxybenzene was added 43.00 g of conc. H2SO4 for 15 min and then the
mixture was heated to 80 Celsius for a period of 2.5 hours. (when to stop is easy to know: just put some sample (0.1 ml) to 4 ml H20 and shake it,
when there was no more precipitate the reaction is over).
After cooling to RT the reaction product was carefully poured over a K2CO3 saturated solution (500 ml) with good stirring, the solids were filtered
by vacuum and washed with 20 ml MeOH, after dried it well, it will get 66.21 g ( 88.88 % on 1,4-dimethoxybenzene) of potassium
2,5-dimethoxybenzenesulfonate.
2,5-dimethoxybenzenesulfonyl chloride – 36.00 g of PCl5 and 20.00 g (0.08 mol) of the anhydrous potassium sulfonate were mixed well in a RBF adapted
with an exit to allow the escape of the HCl produced and it was heated using an oil bath at 130 Celsius for 3 hours. The solids will partially melt
with a brown colour. After cooling to RT there was added 200 ml H2O with care and good stirring (HCl protection!). There was a yellow precipitate that
was extracted with 3x100 ml DCM, the organics were washed with 100 ml H2O, dried with MgSO4, and rotovaped to get 12.23 g of a yellow crystalline
powder (yield 66.45% over the sulfonate). The product has a mp 113 Celsius (lit. 115 to 117 Celsius), its sulfonamide has a mp 148.0 Celsius (lit.
147.5 to 148.5 Celsius).
Hope it can help someone.
[Edited on 29-5-2012 by DrNoiZeZ]
[Edited on 29-5-2012 by DrNoiZeZ]
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