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4th January 2013 @ 17:36

Reaction Scheme

Solid PT 1-1 (200 mg) was dissolved in chlorosulfonic acid (10 mL). The reaction was split into two equal parts A and C. A was stirred at room temperature and C was stored in a freezer at -25°C, both for 24 hours. Both parts were then subjected to an equal workup as follows:

The reaction mixture was dripped into a rapidly-stirred mixture of DCM (50 mL) and ice-water (50 mL), taking care to avoid excessive splashing. The layers were quickly separated and the aqueous extracted once more with DCM. The combined organic layers were dried over magnesium sulfate and evaporated to dryness, then stored under nitrogen in a freezer. Portion A gave 44.7mg of dark solid, and portion C gave 55.3mg of a tan oil. Re-extraction of the aqueous from portion A gave a further 14 mg of dark solid (portion B). Each portion was extremely soluble (>20 mg per ml CDCl3). Each portion was dissolved in methanol and held at 5°C for 72h, and re-analysed.

Analysis:

Portions A and B were found to have reacted to the same material as in Chlorosulfonation of aryl pyrrole PMY 1-6 (PMY 54-1), and portion C had partially reacted to the same compound with significant starting material, indicating that double sulfonation is unlikely. At first glance, the product pyrrole is symmetrical since there is only one singlet at ca. 2.5 ppm, however the integral of this peak relative to the aromatic region is insufficient by a factor of approximately 2, suggesting single substitution obfuscated by odd chemical shifts. After derivatisation with methanol, a new peak appeared at ca. 4.0ppm, with the same relative abundance as the proton resonance corresponding to a 1:1 ratio. Mass Spectroscopy indicated the presence of a doubly-sulfonated species only.

Conclusion:

When chlorosulfonic acid is used neat, isolation of a singly-sulfonated intermediate is probably not possible, even when the temperature was reduced until significant starting material remained.


NMR:

PT-1-2A.pdf
PT-1-2B.pdf
PT-1-2C.pdf

 

 

 

 

After methanolysis:

PT-1-2A-methanol.pdf
PT-1-2B-methanol.pdf
PT-1-2C-methanol.pdf

 

 

 

 

TLC:

TLC indicated the creation of a new compound which did not move from the baseline even when subjected to very polar conditions (5% CHCl3 in MeOH).

References:

  1. Moranta, C.; M. Molins-Pujol, A.; Dolors Pujol, M.; Bonal, J. Journal of the Chemical Society, Perkin Transactions 1 1998, 3285. http://pubs.rsc.org/en/content/articlelanding/1998/P1/a803239d

Risk and Hazard Assessment:

PT-1-2 Risk Assessment.pdf

 

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Attached Files
PT-1-2B.pdf
PT-1-2C.pdf
PT-1-2 scheme.png
PT-1-2 Risk Assessment.pdf
PT-1-2A.pdf
PT-1-2C-methanol.pdf
PT-1-2B-methanol.pdf
PT-1-2A-methanol.pdf
Comments
Re: Attempted direct chlorosulfonation of Arylpyrrole PT 1-1 (PT 1-2) by Patrick Thomson
4th January 2013 @ 18:03
I have a hunch the new compound (which paul also prepared) is actually the acid chloride. The NMR suggests that the pyrrole H has been moved downfield into the mess at 7ppm, while the fluorophenyl ring has barely been touched at all thanks to that non-conducting twist. Also, one of the methyl groups could be non-visible due to intramolecular hydrogen bonding or hindered rotation, since the integral is insufficient. The NMR samples shown here have all been diluted with an equal volume of methanol, and will be evaporated and re-analysed after the weekend.

If there's a sulfonyl chloride, it's readily hydrolysed (<50% mass recovery after a workup, plus decomposes on TLC silica). So, I'd expect it to react with an alcohol.