PCl5 / SOCl2 and carboxylic acids

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In summary, the equations given in the chemistry notes involve reactions between R-COOH and either PCl5 or SOCl2, which produce R-COCl and various byproducts including HCl and gases such as POCl3 and SO2. In an open system, the reaction with SOCl2 will go to completion due to the escape of all products except for the acyl chloride. However, the reaction with PCl5 does not go to completion because HCl is also a gas and can escape, but in reality a base is added to these reactions and they are performed under schlenk conditions.
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trollcast
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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?
 
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trollcast said:
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.
 

FAQ: PCl5 / SOCl2 and carboxylic acids

1. What are PCl5 and SOCl2?

PCl5 and SOCl2 are both chemical compounds commonly used in organic chemistry reactions. PCl5 is known as phosphorus pentachloride, while SOCl2 is sulfur oxychloride.

2. How are PCl5 and SOCl2 used in organic chemistry?

Both PCl5 and SOCl2 are used as reagents in organic chemistry reactions. They are often used to convert carboxylic acids into acyl chlorides, which are important intermediates in many organic synthesis reactions.

3. How do PCl5 and SOCl2 react with carboxylic acids?

In the presence of PCl5 or SOCl2, carboxylic acids undergo a nucleophilic acyl substitution reaction. The chlorine atoms from PCl5 or SOCl2 replace the hydroxyl group of the carboxylic acid, forming an acyl chloride.

4. What are the advantages of using PCl5 and SOCl2 in these reactions?

One advantage of using PCl5 and SOCl2 is that they are both relatively inexpensive and readily available reagents. They also typically react faster and more efficiently than other reagents, making them popular choices for organic synthesis reactions.

5. Are there any safety concerns when working with PCl5 and SOCl2?

Both PCl5 and SOCl2 are corrosive and can cause severe burns if they come into contact with skin or eyes. They should be handled with caution and proper protective equipment should be worn. Additionally, they can release toxic gases when heated, so proper ventilation is important when working with these compounds.

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