NOVELTY - Preparation (P1) of isoxazolyl penicillin compound (I) and its salt, involves: in-situ preparation of 5-methyl-3-phenyl-isoxazole-4-carbonyl chloride intermediate (III) followed by dissolution in an ester; condensation of acid chloride solution with a basic solution of 6-aminopenicillanic acid, followed by addition of a saturated salt solution; crystallization with sodium salt of ethyl hexanoic acid; filtration at a reduced pressure and inert atmosphere; and drying under mechanical stress and reduced pressure and temperature.    USE - For preparation of isoxazolyl penicillin compound (claimed), useful for treating gram positive bacteria.    ADVANTAGE - The process is less polluting and hence eco-friendly. The reaction is carried out without isolating the intermediate at any stage i.e. reaction is carried out in an in-situ manner, which is very useful on commercial scales. Thus, the process is economical. The process incurs less capital costs since the cost of equipments/machinery used otherwise for purification of the intermediate is completely eliminated.    DETAILED DESCRIPTION - Preparation (P1) of isoxazolyl penicillin compound of formula (I) and its salt, involves: in-situ preparation of 5-methyl-3-phenyl-isoxazole-4-carbonyl chloride intermediate of formula (III) followed by dissolution in an ester; condensation of acid chloride solution with a basic solution of 6-aminopenicillanic acid, followed by addition of a saturated salt solution; crystallization with sodium salt of ethyl hexanoic acid; filtration at a reduced pressure and inert atmosphere; and drying under mechanical stress and reduced pressure and temperature.    X1 and X2=H or halo.    An INDEPENDENT CLAIM is included for preparation (P2) of cloxacillin and its salt involving: preparing intermediate of formula (III), where X1 is H and X2 is chlorine, and the preparation of the intermediate is in-situ and is involving reacting ortho-chlorobenzaldehyde with hydroxylamine salt at a pH of 9-10, passing chlorine gas in the presence of triethylamine in an inert atmosphere at -10 to 10 (preferably 0-5) degrees C, adding methylacetoacetate in the presence of sodium methoxide, adding phosphorus pentachloride and thionyl chloride under vacuum; dissolving the intermediate directly in an ester, without isolating the intermediate from the reaction mixture; reacting with basic solution of 6-aminopenicillanic acid followed by addition of a saturated salt solution; crystallizing with sodium salt of ethyl hexanoic acid; filtering at a reduced pressure and inert atmosphere; and drying under mechanical stress and reduced pressure and temperature.