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In
chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a natural science that covers the elements that make up matter to the compounds made of atoms, molecules and ions: their composition, structure, proper ...
, a trimer (; ) is a
molecule A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and b ...
or polyatomic 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 In chemistry and biochemistry, an oligomer () is a molecule that consists of a few repeating units which could be derived, actually or conceptually, from smaller molecules, monomers.Quote: ''Oligomer molecule: A molecule of intermediate relati ...
derived from three identical
precursor Precursor or Precursors may refer to: * Precursor (religion), a forerunner, predecessor ** The Precursor, John the Baptist Science and technology * Precursor (bird), a hypothesized genus of fossil birds that was composed of fossilized parts of u ...
s often in competition with
polymerization In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many f ...
.


Examples


Alkyne trimerisation

In 1866, Marcellin Berthelot reported the first example of
cyclotrimerization In organic chemistry, an alkyne trimerisation is a +2+2nbsp; cycloaddition reaction in which three alkyne units () react to form a benzene ring. The reaction requires a metal catalyst. The process is of historic interest as well as being applica ...
, the conversion of
acetylene Acetylene ( systematic name: ethyne) is the chemical compound with the formula and structure . It is a hydrocarbon and the simplest alkyne. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in its pure ...
to
benzene Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms ...
. This process was commercialized: :


Nitrile trimerization

Symmetrical 1,3,5-triazines are prepared by trimerization of certain
nitrile In organic chemistry, a nitrile is any organic compound that has a functional group. The prefix '' cyano-'' is used interchangeably with the term ''nitrile'' in industrial literature. Nitriles are found in many useful compounds, including me ...
s such as cyanogen chloride or cyanimide. Cyanogen chloride and cyanogen bromide each trimerize at elevated temperatures over a carbon catalyst. The chloride gives cyanuric chloride: : The bromide has an extended shelflife when refrigerated. Like the chloride, it undergoes ab exothermic trimerisation to form cyanuric bromide. This reaction is catalyzed by traces of bromine, metal salts, acids and bases. For this reason, experimentalists avoid brownish samples. : An industrial route to
cyanuric acid Cyanuric acid or 1,3,5-triazine-2,4,6-triol is a chemical compound with the formula (CNOH)3. Like many industrially useful chemicals, this triazine has many synonyms. This white, odorless solid finds use as a precursor or a component of bleach ...
entails the
thermal decomposition Thermal decomposition, or thermolysis, is a chemical decomposition caused by heat. The decomposition temperature of a substance is the temperature at which the substance chemically decomposes. The reaction is usually endothermic as heat is re ...
of
urea Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid. Urea serves an important ...
, with release of ammonia. The conversion commences at approximately 175 °C: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 : 3 H2N-CO-NH2 -> (O)NH + 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 -> (O)NH : (O)NH + 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 In thermodynamics, an exothermic process () is a thermodynamic process or reaction that releases energy from the system to its surroundings, usually in the form of heat, but also in a form of light (e.g. a spark, flame, or flash), electricity ...
: : 6 HCNO + 3 NH3 -> C3H6N6 + 3 CO2 + 3NH3 but the overall process is
endothermic In thermochemistry, an endothermic process () is any thermodynamic process with an increase in the enthalpy (or internal energy ) of the system.Oxtoby, D. W; Gillis, H.P., Butler, L. J. (2015).''Principle of Modern Chemistry'', Brooks Cole. ...
.


Diene trimerisation

The 1,5,9-trans-trans-cis isomer of cyclododecatriene, which has some industrial importance is obtained by cyclotrimerization of
butadiene 1,3-Butadiene () is the organic compound with the formula (CH2=CH)2. It is a colorless gas that is easily condensed to a liquid. It is important industrially as a precursor to synthetic rubber. The molecule can be viewed as the union of two v ...
with
titanium tetrachloride Titanium tetrachloride is the inorganic compound with the formula . It is an important intermediate in the production of titanium metal and the pigment titanium dioxide. is a volatile liquid. Upon contact with humid air, it forms thick clouds ...
and an organoaluminium co-catalyst:''Industrial Organic Chemistry'', Klaus Weissermel, Hans-Jurgen Arpe John Wiley & Sons; 3rd 1997 :


Breaking carbon-hetero double bonds forms symmetrical saturated 1,3,5-heterocycles

Cyclotrimerization of
formaldehyde Formaldehyde ( , ) ( systematic name methanal) is a naturally occurring organic compound with the formula and structure . The pure compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde (refer to section ...
affords
1,3,5-Trioxane 1,3,5-Trioxane, sometimes also called trioxane or trioxin, is a chemical compound with molecular formula CHO. It is a white, highly water-soluble solid with a chloroform-like odor. It is a stable cyclic trimer of formaldehyde, and one of the t ...
: : 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 Formaldehyde ( , ) ( systematic name methanal) is a naturally occurring organic compound with the formula and structure . The pure compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde (refer to section ...
with
hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The under ...
. Three molecules of
acetaldehyde Acetaldehyde (IUPAC systematic name ethanal) is an organic chemical compound with the formula CH3 CHO, sometimes abbreviated by chemists as MeCHO (Me = methyl). It is a colorless liquid or gas, boiling near room temperature. It is one of the ...
condense to form paraldehyde, a cyclic trimer containing C-O single bonds. Catalyzing and dehydrating by sulfuric acid, trimerization of
acetone Acetone (2-propanone or dimethyl ketone), is an organic compound with the formula . It is the simplest and smallest ketone (). It is a colorless, highly volatile and flammable liquid with a characteristic pungent odour. Acetone is miscibl ...
via aldol condensation affords mesitylene


Trisiloxanes

Dimethylsilanediol dehydrates to a trimer of as well as
polydimethylsiloxane Polydimethylsiloxane (PDMS), also known as dimethylpolysiloxane or dimethicone, belongs to a group of polymeric organosilicon compounds that are commonly referred to as silicones. PDMS is the most widely used silicon-based organic polymer, as its ...
. The reaction illustrates the competition between trimerization and polymerization. The polymer and trimer are formally derived from the
hypothetical A hypothesis (plural hypotheses) is a proposed explanation for a phenomenon. For a hypothesis to be a scientific hypothesis, the scientific method requires that one can test it. Scientists generally base scientific hypotheses on previous obser ...
sila-ketone , although this species is not an intermediate.


Coordination chemistry

The dithiobenzoate complexes crystallize as trimers (M = Ni, Pd).


See also

*
Oligomer In chemistry and biochemistry, an oligomer () is a molecule that consists of a few repeating units which could be derived, actually or conceptually, from smaller molecules, monomers.Quote: ''Oligomer molecule: A molecule of intermediate relati ...
* Protein trimer


References

{{DEFAULTSORT:Trimer (Chemistry) Trimers (chemistry)