Química Orgánica 2 · Sustitución electrofílica aromática
Benzenesulfonyl chloride from benzene and chlorosulfonic acid
Condiciones: ClSO3H (2 equiv)
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Arrastra desde los electrones que se mueven hasta donde van, o toca uno y luego el otro. Cada flecha se revisa; Pista te ayuda cuando te atascas. No necesitas cuenta.
El mecanismo, paso a paso
Siguiente reproduce las flechas curvas de cada paso y las explica. Los pasos escritos están abajo.
Leer los 8 pasos escritos
One chlorosulfonic acid protonates another
Chlorosulfonic acid is a very strong acid. One molecule protonates the OH oxygen of a second, turning that OH into a water leaving group.
Las flechas curvas
- The OH oxygen of the first chlorosulfonic acid takes the acidic proton of the second.
- The O–H electrons stay on oxygen, giving the chlorosulfate anion.
Lose water to form ClSO₂⁺
The S–OH₂⁺ bond breaks and water leaves, giving the chlorosulfonyl cation ClSO₂⁺, the electrophile.
Las flechas curvas
- The S–O bond pair moves onto the protonated oxygen, which leaves as water.
The ring attacks ClSO₂⁺
A ring π pair bonds to the cationic sulfur, which becomes neutral; the ring loses aromaticity in this slow step.
Las flechas curvas
- The ring π pair at the carbon bearing the drawn hydrogen forms the new C–S bond; the neighboring carbon becomes cationic.
Delocalize the charge to the para carbon
The arenium charge is shared by the two ortho carbons and the para carbon, as in every EAS.
Las flechas curvas
- The neighboring ring π pair shifts toward the cationic carbon, moving the positive charge to the carbon para to the new bond.
Return the charge beside the sp³ carbon
The arenium ion is one hybrid; redraw the contributor with the positive charge back on the carbon next to the sp³ C–H. That contributor shows which π bond the C–H electrons will re-form in the deprotonation.
Las flechas curvas
- The π pair shifts back toward the para carbon, leaving the positive charge on the ortho carbon next to the sp³ C–H.
Why two equivalents?
One equivalent supplies the electrophile, the other acts as the acid and its conjugate base takes the ring proton.
Chlorosulfate removes the ring proton
The chlorosulfate anion removes the proton from the sp³ carbon bearing sulfur, regenerating chlorosulfonic acid and restoring aromaticity.
Las flechas curvas
- The negative oxygen of chlorosulfate takes the ring proton.
- The C–H bond electrons form the ring π bond to the neighboring cationic carbon, restoring aromaticity.
Benzenesulfonyl chloride
The SO₂Cl group has replaced a ring hydrogen, giving benzenesulfonyl chloride. Water is released and one chlorosulfonic acid is regenerated.
Qué vas a practicar
Draw formation of the ClSO₂⁺ electrophile from two chlorosulfonic acid molecules and its substitution onto benzene to give benzenesulfonyl chloride.
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