chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds made of atoms, molecules and ions ...

, 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 bioch ...

polyatomic anion A polyatomic ion, also known as a molecular ion, is a covalent bonded set of two or more atoms, or of a metal complex, that can be considered to behave as a single unit and that has a net charge that is not zero. The term molecule may or may no ...

formed by combination or association of three molecules or

ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

s 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 relativ ...

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, monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are ...

Examples

Alkyne trimerisation

In 1866,

Marcellin Berthelot Pierre Eugène Marcellin Berthelot (; 25 October 1827 – 18 March 1907) was a French chemist and Republican politician noted for the ThomsenBerthelot principle of thermochemistry. He synthesized many organic compounds from inorganic substance ...

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 ...

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 met ...

s such as

cyanogen chloride Cyanogen chloride is a highly toxic chemical compound with the formula CNCl. This linear, triatomic pseudohalogen is an easily condensed colorless gas. More commonly encountered in the laboratory is the related compound cyanogen bromide, a room-te ...

cyanimide Cyanimides are a group of chemical compounds sharing a common functional group with the general structure R1R2N-C≡N. This group can be regarded as a secondary amine with a cyano Cyanide is a naturally occurring, rapidly acting, toxic che ...

Cyanogen chloride Cyanogen chloride is a highly toxic chemical compound with the formula CNCl. This linear, triatomic pseudohalogen is an easily condensed colorless gas. More commonly encountered in the laboratory is the related compound cyanogen bromide, a room-te ...

and

cyanogen bromide Cyanogen bromide is the inorganic compound with the formula (CN)Br or BrCN. It is a colorless solid that is widely used to modify biopolymers, fragment proteins and peptides (cuts the C-terminus of methionine), and synthesize other compounds. ...

each trimerize at elevated temperatures over a carbon catalyst. The chloride gives

cyanuric chloride Cyanuric chloride is an organic compound with the formula (NCCl)3. This white solid is the chlorinated derivative of 1,3,5-triazine. It is the trimer of cyanogen chloride. Cyanuric chloride is the main precursor to the popular but controver ...

: :

The bromide has an extended shelflife when refrigerated. Like the chloride, it undergoes ab exothermic trimerisation to form

cyanuric bromide Cyanuric bromide is a heterocyclic compound with formula C3N3Br3. It contains a six-membered ring of alternating nitrogen and carbon atoms, with a bromine atom attached to each carbon. It is formed by the spontaneous trimerisation of cyanogen brom ...

. This reaction is catalyzed by traces of bromine, metal salts, acids and bases. For this reason, experimentalists avoid brownish samples. : Cyanuric bromide synthesis

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 req ...

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 r ...

, 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 Melamine is an organic compound with the formula C3H6N6. This white solid is a trimer of cyanamide, with a 1,3,5-triazine skeleton. Like cyanamide, it contains 67% nitrogen by mass, and its derivatives have fire retardant properties due t ...

can be understood in two steps. : First, urea decomposes into

cyanic acid Isocyanic acid is a chemical compound with the structural formula HNCO, which is often written as . It is a colourless, volatile and poisonous substance, with a boiling point of 23.5 °C. It is the predominant tautomer of 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 (e ...

: : 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. p. ...

Diene trimerisation

The 1,5,9-trans-trans-cis isomer of

cyclododecatriene Cyclododecatrienes are cyclic trienes with the formula C12H18. Four isomers are known for 1,5,9-cyclododecatriene. The ''trans'',''trans'',''cis''-isomer is a precursor in the production of nylon-12. : Production The ''trans'',''trans'',''cis'' ...

, 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 vi ...

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 o ...

and an organoaluminium

co-catalyst Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

:''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 F ...

affords 1,3,5-Trioxane: : 1,3,5-Trithiane is the cyclic trimer of the otherwise unstable species thioformaldehyde. This

heterocycle A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different chemical element, elements as members of its ring(s). Heterocyclic chemistry is the branch of organic chemistry dealing with the synthesis ...

consists of a six-membered ring with alternating

methylene bridge In organic chemistry, a methylene bridge, methylene spacer, or methanediyl group is any part of a molecule with formula ; namely, a carbon atom bound to two hydrogen atoms and connected by single bonds to two other distinct atoms in the rest of ...

s and thioether groups. It is prepared by treatment of

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 unde ...

. 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 mos ...

condense to form

paraldehyde Paraldehyde is the cyclic trimer of acetaldehyde molecules. Formally, it is a derivative of 1,3,5-trioxane, with a methyl group substituted for a hydrogen atom at each carbon. The corresponding tetramer is metaldehyde. A colourless liquid, it ...

, 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 miscib ...

via

aldol condensation An aldol condensation is a condensation reaction in organic chemistry in which two carbonyl moieties (of aldehydes or ketones) react to form a β-hydroxyaldehyde or β-hydroxyketone (an aldol reaction), and this is then followed by dehydration to ...

affords

mesitylene Mesitylene or 1,3,5-trimethylbenzene is a derivative of benzene with three methyl substituents positioned symmetrically around the ring. The other two isomeric trimethylbenzenes are 1,2,4-trimethylbenzene (pseudocumene) and 1,2,3-trimethylbenze ...

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). DTBNIT11

References

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