The crystal structure of the title compound (orthorhombic a = 26.724, b = 10.899, c = 9.483 Å, space group Pna21, Z = 12) has been determined by X-ray analysis. The structural units consist of hydrogen-bonded trimers with approximate C3 h symmetry. The results are discussed in relation to the Beckmann rearrangement of the title compound, which yields exclusively the mirror-symmetric diamide.