1)I am unable to understand how benzenesulfonyl chloride acts as a dehydrating agent in dehydration of amides? What is need of it loosing Chloride and taking hydroxide from amide?

2)Why I can't use other dehydrating agents like P4O10 , or H2SO4 , or CaCl2?

3)How can I estimate what is suitable dehydrating agent for a particular reactant? And last

4)Is it necessary to use only those dehydrating agents that go chemical change ? Or can I use dehydrating agents that adsorb water like silica gel?

I am really confused about it

Please provide a conceptual explanation.

Thanks in advance.

1. I am unable to understand how benzenesulfonyl chloride acts as a dehydrating agent in dehydration of amides? What is the driving force for losing chloride and taking the oxygen from the amide?

2. Why I can't use other dehydrating agents like $\ce{P4O10}$, $\ce{H2SO4}$, or $\ce{CaCl2}$?

3. How can I estimate what is suitable dehydrating agent for a particular reactant?

4. Is it necessary to use only those dehydrating agents that undergo chemical change? Or can I use dehydrating agents that adsorb water like silica gel?