The crystal structure of free base cocaine, C17H21NO4

Abstract

The crystal structure of free base cocaine has been determined in order to compare the conformation with that observed in its salts, and to clarify the powder pattern of the pure compound. Crystals of (−)-cocaine are monoclinic, space group P21, a = 10.130(1), b = 9.866(2), c = 8.445(1) Å, β = 106.92(1)°, Z = 2, Dx = 1.25 g cm−3. Data were collected with MoKα radiation on a modified Picker diffractometer using the NRCC diffractometer control system. The structure was solved by direct methods and refined by least squares to final R and Rw. of 0.065 and 0.062 (w = 1/σ2 (F)) using the 1818 independent reflections with sin θ/λ < 0.7048 and |F|/σ(|F|) ≤ 3.0.The free base exists in a piperidine chair conformation similar to the methiodide salt and the hydrochloride salt. However, the piperidine ring carbon–nitrogen bonds in the free base are shorter than those in the salts; 1.460(7) and 1.467(6) Å in the free base compared to 1.55(2) and 1.51(2) Å in the methiodide salt and 1.50(1) and 1.49(1) Å in the hydrochloride salt. Further, the orientations of the benzoxy group and the methoxycarbonyl group, with respect to the piperidine rings, are significantly different from that common to both salts. The calculated powder diffraction pattern of (−)-cocaine showed that several previously reported weak lines in powder diffraction data for this alkaloid should not be present.