A Fourier transform-Raman and IR vibrational study of flurazepam base and the mono- and dihydrochloride salts.

Fourier transform (FT) Raman and IR spectra of flurazepam base and the mono- and dihydrochloride salts have been recorded. The parent compounds is 7-chloro-1-[2-(diethylamino)ethyl]-5-(2-fluorophenyl)-1,3-dihydro-[2H]- 1,4-benzodiazepin-2-one and is closely related to diazepam. The spectra show characteristic features associated with both the diazepine ring and substituents. Very strong lines near 1615 cm-1 in the Raman spectra of the base and the monohydrochloride are assigned to the C = N stretch of the diazepine ring. The C = N group becomes a C = N+ group in the dihydrochloride and the frequency shifts to 1635 cm-1. A very strong absorption near 1680 cm-1 in the IR spectra of the three compounds is attributed to the C = O stretching mode. The hydrochlorides are characterized by very strong broad bands in the IR spectra between 2600 and 2200 cm-1. Various IR and Raman vibrational features serve to characterize and differentiate the salts from each other and the free base. Raman and IR spectra have also been recorded for the related compound desalkylflurazepam [7-chloro-5-(2-fluorophenyl)-1,3-dihydro-[2H]-1,4-benzodiazepin-2- one], in which a hydrogen atom replaces the (diethylamino)ethyl group at position 1 of the diazepine ring. Comparison of the spectra of this compound with those of flurazepam has enabled some vibrations of the (diethylamino)ethyl group to be identified.