Patent ID: 7718799

Claim:
A process for preparation of linezolid form III characterized by an x-ray powder diffraction spectrum having peaks expressed as 2θ at about 7.6, 9.6, 13.6, 14.9, 18.2, 18.9, 21.2, 22.3, 25.6, 26.9, 27.9 and 29.9 degrees, wherein the crystalline linezolid form III is further characterized by an IR spectrum having main bands at about 3338, 1741, 1662, 1544, 1517, 1471, 1452, 1425, 1400, 1381, 1334, 1273, 1255, 1228, 1213, 1197, 1176, 1116, 1082, 1051, 937, 923, 904, 869, 825 and 756 cm −1 , which comprises the step of heating linezolid of a known crystalline form or in a mixture of known crystalline forms in a solvent selected from the group consisting of toluene, isopropyl alcohol, and ethyl acetate, at above about 90° C. for at least 30 mm until the known form/s are converted to form III.