Ammonium carbamate type self-derivative salts of (R-)- and racemic α-methylbenzylamine: Composition and thermal stability by evolved gas analyses (TG–FTIR and TG/DTA–MS)

• Published in: Journal of thermal analysis and calorimetry 2013, Vol.111 (1), p.567-574
• Main Authors: Madarász, János, Székely, Edit, Halász, Judit, Bánsághi, György, Varga, Dániel, Simándi, Béla, Pokol, György
• Format: Article
• Language: English
• Subjects: Analytical Chemistry; Chemistry; Chemistry and Materials Science; Exact sciences and technology; Inorganic Chemistry; Measurement Science and Instrumentation; Noncondensed benzenic compounds; Organic chemistry; Physical Chemistry; Polymer Sciences; Preparations and properties
• ISSN: 1388-6150; 1588-2926; 1572-8943
• DOI: 10.1007/s10973-011-2174-5

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 CO 2 . The crystalline solids have been characterized by elemental CHN analysis, X-ray diffraction (XRD), FTIR, 1 H, and 13 C NMR spectroscopy, and found to be α-methylbenzylammonium α-methylbenzylcarbamate self-derivative ionic salts 1 ( R / R ) and 2 ( rac RS ), respectively, of the corresponding amines. Compound 2 ( rac RS ) 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 ( rac RS )) 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 CO 2 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.