In chemistry, a trimer is a molecule or an anion formed by combination or association of three molecules or ions of the same substance. In technical jargon, a trimer is a kind of oligomer derived from three identical precursors often in competition with polymerization.
Cyanogen bromide has an extended shelflife when refrigerated. Similar to some other cyanogen compounds, cyanogen bromide undergo an exothermic trimerisation to cyanuric bromide ((BrCN)3). This reaction is catalyzed by traces of bromine, metal salts, acids and bases. For this reason, experimentalists avoid brownish samples.
- 3 H2N-CO-NH2 → [C(O)NH]3 + 3 NH3
The endothermic synthesis of melamine can be understood in two steps.
First, urea decomposes into cyanic acid and ammonia in an endothermic reaction:
- (NH2)2CO → HOCN + NH3
Then in the second step, cyanic acid polymerizes to form cyanuric acid, which condenses with the liberated ammonia from the first step to release melamine and water.
- '3 HOCN → [C(O)NH]3
- [C(O)NH]3 + 3 NH3 → C3H6N6 + 3 H2O
This water then reacts with cyanic acid present, which helps drive the trimerization reaction, generating carbon dioxide and ammonia.
- 3 HOCN + 3 H2O → 3 CO2 + 3NH3
In total, the second step is exothermic:
- 6 HCNO + 3 NH3 → C3H6N6 + 3 CO2 + 3NH3
but the overall process is endothermic.
The 1,5,9-trans-trans-cis isomer of cyclododecatriene, which has some industrial importance is obtained by cyclotrimerization of butadiene with titanium tetrachloride and an organoaluminium co-catalyst:
Breaking carbon-hetero double bonds forms symmetrical saturated 1,3,5-heterocycles
1,3,5-Trithiane is the cyclic trimer of the otherwise unstable species thioformaldehyde. This heterocycle consists of a six-membered ring with alternating methylene bridges and thioether groups. It is prepared by treatment of formaldehyde with hydrogen sulfide.
Dimethylsilanediol dehydrates to a trimer of Me2SiO as well as polydimethylsiloxane. The reaction illustrates the competition between trimerization and polymerization. The polymer and trimer are formally derived from the hypothetical sila-ketone Me2Si=O, although this species is not an intermediate.
- Hillis O. Folkins (2005). "Benzene". Ullmann’s Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a03_475.
- Morris, Joel; Kovács, Lajos; Ohe, Kouichi (2015). "Cyanogen Bromide": 1–8. doi:10.1002/047084289X.rc269.pub3.
- Joel Morris; Lajos Kovács (2008). "Cyanogen Bromide". Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rc269.pub2.
- Klaus Huthmacher, Dieter Most "Cyanuric Acid and Cyanuric Chloride" Ullmann's Encyclopedia of Industrial Chemistry" 2005, Wiley-VCH, Weinheim. doi 10.1002/14356007.a08 191
- Industrial Organic Chemistry, Klaus Weissermel, Hans-Jurgen Arpe John Wiley & Sons; 3rd 1997 ISBN 3-527-28838-4
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- Cumming, W. M. (1937). Systematic organic chemistry (3E). New York, USA: D. Van Nostrand Company. p. 57.
- Bonamico, M.; Dessy, G.; Fares, V.; Scaramuzza, L. (1975). "Structural Studies of Metal Complexes with Sulphur-Containing Bidentate Ligands. Part I. Crystal and Molecular Structures of Trimeric Bis-(dithiobenzoato)-nickel(II) and -palladium(II)". Journal of the Chemical Society, Dalton Transactions: 2250–2255. doi:10.1039/DT9750002250.
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