NOVELTY - Preparation (P1) of pure armodafinil (I) or its salt involves (a) reacting (-)-2-(R)-((diphenylmethyl)sulfinyl) acetic acid (II) with a chloroformate compound of formula R1O-C(O)-Cl (III), optionally in the presence of a suitable base in a suitable solvent to produce a mixed anhydride compound (IV); and (b) amidating the mixed anhydride compound (IV) with ammonia in a suitable solvent to produce pure armodafinil (I) and optionally converting the armodafinil formed into its salt.    USE - For preparation of armodafinil (claimed) use as an antidepressant or stimulant agent, in the treatment of hypersomnia, disorders associated with Alzheimer's, idiopathic narcolepsy.    ADVANTAGE - The process is less hazardous, environmentally friendly, easy to handle reagents, reduced cost, greater simplicity, increased purity i.e. greater than 99 (preferably 99.9)%, and increased yield of the product, and commercially viable. The 2-((diphenylmethyl)sulfinyl) acetic acid comprises sulfone impurity (less than 0.1 (preferably less than 0.05) wt.%).    DETAILED DESCRIPTION - Preparation (P1) of pure armodafinil (I) or its salt involves (a) reacting (-)-2-(R)-((diphenylmethyl)sulfinyl) acetic acid (II) with a chloroformate compound of formula R1O-C(O)-Cl (III), optionally in the presence of a suitable base in a suitable solvent to produce a mixed anhydride compound of formula (IV); and (b) amidating the mixed anhydride compound (IV) with ammonia in a suitable solvent to produce pure armodafinil (I) and optionally converting the armodafinil formed into its salt.    R1=alkyl, aryl or aralkyl.    INDEPENDENT CLAIMS are included for following:    (1) preparation (P2) of modafinic acid or 2-((diphenylmethyl)sulfinyl) acetic acid substantially free of sulfone impurity, involving (a) reacting 2-((diphenylmethyl)thio) acetic acid with a suitable oxidizing agent in a first solvent, optionally in the presence of a suitable base to produce a reaction mass; (b) combining the reaction mass obtained in step-(a) with a second solvent; (c) optionally, acidifying the reaction mass with a suitable acid; and (d) isolating pure 2-((diphenylmethyl)sulfinyl) acetic acid substantially tree of sulfone impurity from the reaction mass; and    (2) a mixed anhydride compound (IV) is new intermediate.