Ammonium carbamate type self-derivative salts of (R-)- and racemic α-methylbenzylamine

Abstract

Two different compounds have formed from liquid enantiomeric (R-) and racemic α-methylbenzylamine (α-MBA, named also as 1-phenylethylamine, 1-FEA) with supercritical fluid CO2. The crystalline solids have been characterized by elemental CHN analysis, X-ray diffraction (XRD), FTIR, 1H, and 13C NMR spectroscopy, and found to be α-methylbenzylammonium α-methylbenzylcarbamate self-derivative ionic salts 1 (R/R) and 2 (racRS), respectively, of the corresponding amines. Compound 2 (racRS) has shown different XRD pattern from that of enantiomerically pure 1 (R/R), indicating a preferential formation of a 1:1 mixture of (R/S-) and (S/R-) or rather a racemate compound of (RS/SR-) ammonium carbamate salt (2 (racRS)) from racemate. For thermal stability, the compounds have been checked by differential scanning calorimetry (DSC), simultaneous thermogravimetry and differential thermal analysis (TG/DTA), and in situ coupled evolved gas analysis by mass spectroscopy (TG/DTA−EGA−MS) and FTIR-gas cell (TG−FTIR). No melting point is observed because of the low thermal stability of the compounds. Decomposition stages are tried to be separated with using semi-closed (sealed with a pinhole on the top) crucibles, thus different evolution courses of CO2 and organic vapors could be followed by MS and FTIR spectroscopy. The α-MBA vapors themselves, evolved from open crucibles could be identified by FTIR-gas cell, while vapors up to m/z = 164 have been detected by MS from semi-closed Al crucible.