NOVELTY - Preparing 5-chloro-N-(((5S)-2-oxo-3-(4-(3-oxomorpholin-4-yl)phenyl)oxazolidin-5-yl)methyl)thiophene-2-carboxamide (rivaroxaban) (I) comprises reacting (S)-4-(4-(5-(aminomethyl)-2-oxooxazolidin-3-yl)phenyl)morpholin-3-one hydrochloride (II) with 5-chlorothiophene-2-carbonyl chloride (III) in the presence of 1-methylimidazole.    USE - The process is useful for preparing rivaroxaban (I) which is useful for treating thromboembolic diseases such as heart attack, angina pectoris, reocclusion and restenosis following angioplasty or bypass, cerebral apoplexy, transient ischemic attack, peripheral arterial obstructive diseases, pulmonary embolism or venous thrombosis.    ADVANTAGE - The process: provides (I) which has a uniform and well-defined morphology, a favorable dissolution rate, and improved bioavailability, inter-individual variability and chemical stability; provides (I) in high yield, purity and quality; is simple with less process steps; is carried out at lower temperature, requires less solvent and does not require addition of solid inorganic base to the reaction mixture; allows easily recovering and re-using the obtained mixture of solvents after the completion of the reaction; and is environmentally friendly.    DETAILED DESCRIPTION - Preparing 5-chloro-N-(((5S)-2-oxo-3-(4-(3-oxomorpholin-4-yl)phenyl)oxazolidin-5-yl)methyl)thiophene-2-carboxamide (rivaroxaban) of formula (I) comprises reacting (S)-4-(4-(5-(aminomethyl)-2-oxooxazolidin-3-yl)phenyl)morpholin-3-one hydrochloride of formula (II) with 5-chlorothiophene-2-carbonyl chloride of formula (III) in the presence of 1-methylimidazole. INDEPENDENT CLAIMS are also included for:    (1) (I) obtained by the process comprising less than 0.15 (preferably 0.07) area% of the 5-chloro-N-methylthiophene-2-carboxamide, and of polymorphic form K having peaks in its X-ray powder diffraction as given in the specification; and    (2) preparing (I) of polymorphic form K comprising dissolving (I) in the presence of acetic acid, crystallization (I) by addition of the solution to an anti-solvent, where the temperature of the crystallization medium is kept below 15 degrees C (preferably 0-5 degrees C), optionally ageing and isolation of the crystals, and optionally drying the crystals.