The Anhydrous Racemate of the Carcinostatic Agent Cyclophosphamide and the Bicyclic Degradation Product 1-(2-Chloroethyl)tetrahydro-1H,5H-1,3,2-diazaphospholo[2,1-b][1,3,2]oxazaphosphorine 9-Oxide

Anhydrous racemic cyclo­phosphamide, [(±)-N,N-bis­(2-chloroethyl)-tetrahydro-2H-1,3,2-oxazaphosphorin-2-amine 2-oxide C₇H₁₅Cl₂N₂O₂P, (1)], displays a chair conformation with axial phosphoryl oxygen and close to planar geometry at the N atoms. The molecules are linked by N-H...O=P hydrogen bonds into chains. One chloroethyl side chain is extended, the other is gauche. The C—Cl bond lengths are Cl1-C5 1.789 (2) and Cl2-C7 1.791 (2) Å. The bicyclic degradation product, 1-(2-chloroethyl)tetrahydro-1H,5H–1,3,2-diazaphospholo[2,1-b][1,3,2]oxazaphosphorine 9-oxide, C₇H₁₄ClN₂O₂P, (2), is formed by intramolecular alkylation at the ring N atom of (1). The major change of bond length upon annelation is observed for P—N2, the ring P—N bond in (1), which is lengthened from 1.633 (2) to 1.6593 (14) Å. The angle N1—P—N2, incorporated into the five-membered ring in (2), narrows from 105.84 (8) to 97.36 (7)°. The remaining chloroethyl side chain is gauche. The C—Cl bond length is 1.790 (2) Å.

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