PCl5 / SOCl2 and carboxylic acids

[trollcast]

In my chemistry notes it gives the equations,

$R-COOH + PCl_5 \rightleftharpoons R-COCl + POCl_3 + HCl$

$R-COOH + SOCl_2 \rightleftharpoons R-COCl + SO_2 + HCl$

It then says that in an open system the reaction with thionyl chloride will go to completion as all the products except the acyl chloride can escape as they are gases, so the equilibrium keeps moving right. However why does the reaction with PCl5 not go to completion since the HCl will escape as its a gas?

 

[monodisperse]

In my chemistry notes it gives the equations,

$R-COOH + PCl_5 \rightleftharpoons R-COCl + POCl_3 + HCl$

$R-COOH + SOCl_2 \rightleftharpoons R-COCl + SO_2 + HCl$

It then says that in an open system the reaction with thionyl chloride will go to completion as all the products except the acyl chloride can escape as they are gases, so the equilibrium keeps moving right. However why does the reaction with PCl5 not go to completion since the HCl will escape as its a gas?

Phosphoryl chloride is a liquid, ergo...

In reality we as a base, usually triethylamine, to these reactions and perform them under schlenk condition.