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Formation and Characterization of Melam, Melam Hydrate, and a Melam–Melem Adduct
Author(s) -
Wirnhier Eva,
Mesch Maria B.,
Senker Jürgen,
Schnick Wolfgang
Publication year - 2013
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201203340
Subject(s) - hydrate , adduct , hydrogen bond , molecule , ammonia , crystallography , chemistry , reactivity (psychology) , melamine , condensation , hydrothermal circulation , chemical engineering , organic chemistry , medicine , physics , alternative medicine , pathology , thermodynamics , engineering
Until recently, melam, [C 3 N 3 (NH 2 ) 2 ] 2 NH, has been regarded as a short‐lived intermediate in the condensation process of melamine that is only detectable under special reaction conditions owing to its high reactivity. A new synthetic approach has allowed a closer look at the formation and condensation behavior of melam by using elevated ammonia pressure in autoclaves. Whereas the thermal treatment of dicyandiamide at 450 °C and 0.2 MPa ammonia yielded melam in large amounts, prolonged treatment under these conditions (9 days) led to the formation of a melam–melem adduct, thus enabling the first insight into the condensation process of melam into melem. The hydrothermal treatment of melam at 300 °C (24 h) yields melam hydrate, [C 3 N 3 (NH 2 ) 2 ] 2 NH ⋅ 2 H 2 O (space group P 2 1 / c ; a =676.84(2), b =1220.28(4), c =1394.24(4) pm; β =98.372(2)°; V =1139.28(6)×10 6 pm 3 ; Z =4), which crystallizes as a layered structure that is composed of almost‐planar melam molecules, thereby forming ellipsoidal rosette‐like motifs. The resulting voids are filled with four water molecules, thus forming a dense network of hydrogen bonds.