Carboxylic acids can be converted into acid chlorides by treatment with phosphorous chlorides (PCl5, Pcl3) or thionyl chloride (SOcl2) in pyridine.
Acetic acid + Phosphorous Pentachloride = Acetyl chloride + POCl3 + HCL
acetic acid + PCl3 = Acetyl chloride + HePO3
acetic acid + thionyl chloride = acetyl chloride + sulphur dioxide + HCl
From benzoic acid we get benzoyl chloride