[redfox]

Ok, am at a reealy basic level of chemistry...I need to react C6H5C=OOH with SOCl2. I don't know where to begin as I'm not sure what would go where, and if anything would be bumped off and what would be left over.
I don't just want the answer to this question as I need to do quite a few like it, but I need to know how it's done, what the rules are, etc. I would look it up but I don't know what it's called!
Can I please get some advice on where to begin/where online is a good tutorial site/what this 'reaction method' is called?

Ta very much:)

[english]

Carboxyic acids are tranformed into acyl halides by way of thionyl chloride (SOCl₂) or PCl₃, or P₂O₅. 


This is an acyl nucleophilic substitution reaction. 

If you've been introduced to reactions of alcohols with thionyl chloride, then you already know how this reaction will go.  It is the same, except for the tetrahedral intermediate that is formed.

Try the mechanism now.

[redfox]

Cool, thanks for the answer.

How would I know which bit to substitute in a reaction? Is it just the functional group that goes?

[english]

Generally, OH is substituted for Cl.

You first must convert OH into a good leaving group.  This can be done by converting it into —OSOCl.

So your hydroxy group must react with thionyl chloride.  The protonated form will rapidly deprotonate (designated as "workup").  


The resulting tetrahedral intermediate collapses to the acyl chloride.



Compare this reaction to the chlorination of alcohols.