Question

The preferred reagent for the following conversion is $CH_3CH_2COOH \rightarrow CH_3CH_2COCl$

• A. HCl
• B. HOCl
• C. SOCl$_2$
• D. NaOCl

Hint:

Thionyl chloride ($SOCl_2$) is your go-to reagent for cleanly converting carboxylic acids to acyl chlorides. The gaseous byproducts simplify product isolation. Remember this key transformation in carboxylic acid chemistry.

Answer 1

The Correct Option is C

The conversion of a carboxylic acid to an acyl chloride involves replacing the -OH group with a -Cl group. Common reagents for this transformation include thionyl chloride (SOCl$_2$), phosphorus pentachloride (PCl$_5$), and phosphorus trichloride (PCl$_3$). Among these, thionyl chloride is often preferred due to its relatively clean reaction and gaseous byproducts (SO$_2$ and HCl), which are easily removed.
The reaction with thionyl chloride proceeds as:
$$CH_3CH_2COOH + SOCl_2 \rightarrow CH_3CH_2COCl + SO_2 \uparrow + HCl \uparrow$$ 
The other options are not suitable for this direct conversion:
HCl can react with carboxylic acids to form acyl chlorides under specific conditions, but it is not the preferred method.
HOCl is hypochlorous acid, an oxidizing agent and a source of chlorine, but not used for acyl chloride formation from carboxylic acids.
NaOCl is sodium hypochlorite, also an oxidizing agent and not typically used for this conversion.
Thus, the preferred reagent is $ \boxed{SOCl_2} $.