Thionyl chloride

Thionyl chloride is a chemical compound with the formula . It is related to sulfurous acid by replacing the  groups in its structure with chlorine (an acyl chloride). It is mostly used in the chemical industry and research to add chlorine atoms to other molecules (chlorination) or to remove water from mixtures or hydrates (dehydration).

 Uses 
 Removing water 
Thionyl chloride is a reactive desiccant: it reacts strongly with water and will remove it from a solution or the air. Thionyl chloride reacts with water to make sulfur dioxide and hydrogen chloride:

Because both of the products are gases, it is easy to purify anything left after the reaction. This makes  useful for removing water from hydrated chlorine compounds like magnesium chloride and iron(III) chloride.

 Adding chlorine 
Thionyl chloride is very reactive with chemicals containing an  functional group. This includes not only water and hydroxides, but also organic chemicals like alcohols and carboxylic acids. These reactions almost always involve replacing the  with a chlorine atom, and the release of  and .

With an alcohol like ethanol, it normally makes the matching organic chloride:

If a lot of alcohol is used, and the reaction temperature is controlled, it can make sulfite esters instead:

With a carboxylic acid like acetic acid, it makes the matching acyl chloride:

 Other reactions 
Thionyl chloride also reacts with primary amides to make nitriles.

It can also react with secondary amides in a name reaction called the von Braun amide degradation. This produces a nitrile and organic chloride:

 References 

Category:Sulfur compounds
Category:Oxychlorides