required vs mandatory

required is not a noun while mandatory is a noun.

Word	Noun	Adjective	Verb	Adverb
required	No	Yes	No	No
mandatory	Yes	Yes	No	No

As adjectives, required and mandatory are synonyms defined as:

Other synonyms of required include compulsory.

required (noun)	mandatory (noun)
	a territory surrendered by Turkey or Germany after World War I and put under the tutelage of some other European power until they are able to stand by themselves
	the recipient of a mandate

required (adjective)	mandatory (adjective)
necessary for relief or supply	required by rule
required by rule