The -OH group of an alcohol or the -COOH group of a carboxylic acid can be replaced by -Cl using
- phosphorus pentachloride
- hypochlorous acid
- chlorine
- hydrochloric acid
Answer
(1) phosphorus pentachloride
Solution
As per NCERT, phosphorus pentachloride replaces the –OH group of alcohols and of carboxylic acids by –Cl:
R-OH + PCl5 R-Cl + POCl3 + HCl
R-COOH + PCl5 R-COCl + POCl3 + HCl
(In -COOH it is the –OH part that is replaced, giving the acid chloride.)
HCl works only with alcohols (needs ZnCl2 for 1° and 2°) and does not convert acids into acid chlorides; HOCl and Cl2 do not replace –OH.
Answer: (1)