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In chemistry, a trimer (//) (tri-, "three" + -mer, "parts") is an oligomer derived from three identical precursors. An example is the procedure of production of polymers. At first, a monomer is made. By combining two monomers, a dimer is produced. With further additions, a trimer and eventually a polymer is made. Often, trimerization competes with polymerization; for example, dimethylsilanediol polymerizes to polydimethylsiloxane, even though a trimer is made:
- Me2Si(OH)2 + (HO)2SiMe2 → Me2(OH)Si-O-Si(OH)Me2 – dimer
- Me2(OH)Si-O-Si(OH)Me2 + (HO)2SiMe2 → Me2(OH)Si-O-SiMe2-O-Si(OH)Me2 – trimer
- Me2(OH)Si-O-SiMe2-O-Si(OH)Me2 + (HO)2SiMe2 → Me2(OH)Si-O-SiMe2-O-SiMe2-O-Si(OH)Me2 – tetramer
- et cetera, until Me2(OH)Si-O-[SiMe2-O-]nSi(OH)Me2 (n>100) – polymer
- 1 Trimerisation via breaking triple bond
- 2 -Ene trimerisation
- 3 References
Trimerisation via breaking triple bond
In 1866, Marcellin Berthelot reported the first example of cyclotrimerization leading to aromatic products, the cyclization of acetylene to benzene. In the Reppe synthesis, the trimerization of acetylene gives benzene:
Breaking carbon-hetero triple bonds forms symmetrical unsaturated 1,3,5-heterocycles
Cyanuric chloride is prepared in two steps from hydrogen cyanide via the intermediacy of cyanogen chloride, which is trimerized at elevated temperatures over a carbon catalyst:
In 2005, approximately 200,000 tonnes were produced.
- 3 BrCN → (BrCN)3
- 3 H2N-CO-NH2 → [C(O)NH]3 + 3 NH3
Synthesis of melamine
- (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 C12H18 has some industrial importance  and 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.
- Schetter, M. C. R. (1866). Hebd. Seances Acad. Sci. 62: 905.
- Klaus Huthmacher, Dieter Most "Cyanuric Acid and Cyanuric Chloride" in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim. doi:10.1002/14356007.a08_191.
- 1995 figures for global annual capacity 8000 ton
- Industrial Organic Chemistry, Klaus Weissermel, Hans-Jurgen Arpe John Wiley & Sons; 3rd 1997 ISBN 3-527-28838-4
- Bost, R. W.; Constable, E. W. "sym-Trithiane" Organic Syntheses, Collected Volume 2, p.610 (1943). http://www.orgsyn.org/orgsyn/pdfs/CV2P0610.pdf
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