Mesitylene or 1,3,5-trimethylbenzene is a derivative of
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, ...
with three
methyl
In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula . In formulas, the group is often abbreviated as Me. This hydrocarbon group occurs in many ...
substituent
A substituent is one or a group of atoms that replaces (one or more) atoms, thereby becoming a moiety in the resultant (new) molecule. (In organic chemistry and biochemistry, the terms ''substituent'' and ''functional group'', as well as ''side ...
s positioned symmetrically around the ring. The other two isomeric
trimethylbenzenes
The trimethylbenzenes constitute a group of substances of aromatic hydrocarbons, which structure consists of a benzene ring with three methyl groups (–CH3) as a substituent. Through their different arrangement, they form three structural iso ...
are
1,2,4-trimethylbenzene
1,2,4-Trimethylbenzene, also known as pseudocumene, is an organic compound with the chemical formula CH(CH). Classified as an aromatic hydrocarbon, it is a flammable colorless liquid with a strong odor. It is nearly insoluble in water but soluble ...
(pseudocumene) and
1,2,3-trimethylbenzene (hemimellitene). All three compounds have the
formula
In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwee ...
C
6H
3(CH
3)
3, which is commonly abbreviated C
6H
3Me
3. Mesitylene is a colorless liquid with sweet aromatic odor. It is a component of
coal tar
Coal tar is a thick dark liquid which is a by-product of the production of coke and coal gas from coal. It is a type of creosote. It has both medical and industrial uses. Medicinally it is a topical medication applied to skin to treat psoriasi ...
, which is its traditional source. It is a precursor to diverse
fine chemical
In chemistry, fine chemicals are complex, single, pure chemical substances, produced in limited quantities in multipurpose plants by multistep batch chemical or biotechnological processes. They are described by exacting specifications, used f ...
s. The mesityl group (Mes) is a substituent with the formula C
6H
2Me
3 and is found in various other compounds.
[
]
Preparation
Mesitylene is prepared by transalkylation
In organic chemistry, transalkylation is a chemical reaction involving the transfer of an alkyl group from one organic compound to another. The reaction is used for the transfer of methyl and ethyl groups between benzene rings. This is of particul ...
of xylene
In organic chemistry, xylene or xylol (; IUPAC name: dimethylbenzene) are any of three organic compounds with the formula . They are derived from the substitution of two hydrogen atoms with methyl groups in a benzene ring; which hydrogens are sub ...
over solid acid catalyst
In acid catalysis and base catalysis, a chemical reaction is catalyzed by an acid or a base. By Brønsted–Lowry acid–base theory, the acid is the proton (hydrogen ion, H+) donor and the base is the proton acceptor. Typical reactions catalyze ...
:[Karl Griesbaum, Arno Behr, Dieter Biedenkapp, Heinz-Werner Voges, Dorothea Garbe, Christian Paetz, Gerd Collin, Dieter Mayer, Hartmut Höke “Hydrocarbons” in Ullmann's Encyclopedia of Industrial Chemistry 2002 Wiley-VCH, Weinheim. .]
:2 C6H4(CH3)2 ⇌ C6H3(CH3)3 + C6H5CH3
:C6H4(CH3)2 + CH3OH → C6H3(CH3)3 + H2O
Although impractical, it could be prepared by trimerization of propyne
Propyne (methylacetylene) is an alkyne with the chemical formula . It is a component of MAPD gas—along with its isomer propadiene (allene), which was commonly used in gas welding. Unlike acetylene, propyne can be safely condensed.Peter Päs ...
, also requiring an acid catalyst
In acid catalysis and base catalysis, a chemical reaction is catalyzed by an acid or a base. By Brønsted–Lowry acid–base theory, the acid is the proton (hydrogen ion, H+) donor and the base is the proton acceptor. Typical reactions catalyze ...
, yields a mixture of 1,3,5- and 1,2,4-trimethylbenzenes.
Trimerization
In chemistry, a trimer (; ) is a molecule 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 derived from three identical precursors ofte ...
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 ...
, which is catalyzed and dehydrated
In physiology, dehydration is a lack of total body water, with an accompanying disruption of metabolic processes. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental temperature. Mil ...
by sulfuric acid
Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...
is another method of synthesizing mesitylene.
Reactions
Oxidation of mesitylene with nitric acid
Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available nitri ...
yields trimesic acid
Trimesic acid, also known as benzene-1,3,5-tricarboxylic acid, is an organic compound with the formula C6H3(CO2H)3. It is one of three isomers of benzenetricarboxylic acid. A colorless solid, trimesic acid has some commercial value as a precursor t ...
, C6H3(COOH)3. Using manganese dioxide
Manganese dioxide is the inorganic compound with the formula . This blackish or brown solid occurs naturally as the mineral pyrolusite, which is the main ore of manganese and a component of manganese nodules. The principal use for is for dry-cell ...
, a milder oxidising agent
An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or " accepts"/"receives" an electron from a (called the , , or ). In other words, an oxi ...
, 3,5-dimethylbenzaldehyde
Benzaldehyde (C6H5CHO) is an organic compound consisting of a benzene ring with a formyl substituent. It is the simplest aromatic aldehyde and one of the most industrially useful.
It is a colorless liquid with a characteristic almond-like odor. ...
is formed. Mesitylene is oxidised by trifluoroperacetic acid
Trifluoroperacetic acid (trifluoroperoxyacetic acid, TFPAA) is an organofluorine compound, the peroxy acid analog of trifluoroacetic acid, with the condensed structural formula . It is a strong oxidizing agent for organic oxidation reactions, suc ...
to produce mesitol
Mesitol (2,4,6-trimethylphenol) is an organic compound with the formula (CH3)3C6H2OH. It is one of several isomers of trimethylphenol. The name and structure of mesitol derives from the combination of mesitylene and phenol
Phenol (also calle ...
(2,4,6-trimethylphenol). Bromination occurs readily, giving mesityl bromide
Mesityl bromide is an organic compound with the formula (CH3)3C6H2Br. It is a derivative of mesitylene (1,3,5-trimethylbenzene) with one ring H replaced by Br. The compound is a colorless oil. It is a standard electron-rich aryl halide In organic ...
:
:(CH3)3C6H3 + Br2 → (CH3)3C6H2Br + HBr
Mesitylene is a ligand
In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electr ...
in organometallic chemistry
Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and so ...
, one example being the organomolybdenum
Organomolybdenum chemistry is the chemistry of chemical compounds with Mo-C bonds. The heavier group 6 elements molybdenum and tungsten form organometallic compounds similar to those in organochromium chemistry but higher oxidation states tend to ...
complex which can be prepared from molybdenum hexacarbonyl
Molybdenum hexacarbonyl (also called molybdenum carbonyl) is the chemical compound with the formula Mo(CO)6. This colorless solid, like its chromium and tungsten analogues, is noteworthy as a volatile, air-stable derivative of a metal in its zero ...
.
Applications
Mesitylene is mainly used as a precursor to 2,4,6-trimethylaniline
2,4,6-Trimethylaniline is an organic compound with formula (CH3)3C6H2NH2. It is an aromatic amine that is of commercial interest as a precursor to dyes. It is prepared by selective mononitration of mesitylene, avoiding oxidation of the methyl grou ...
, a precursor to colorants. This derivative is prepared by selective mononitration of mesitylene, avoiding oxidation of the methyl groups.
Niche uses
]
Mesitylene is used in the laboratory as a specialty solvent. In the electronics industry, mesitylene has been used as a photographic developer, developer for photopatternable silicone
A silicone or polysiloxane is a polymer made up of siloxane (−R2Si−O−SiR2−, where R = organic group). They are typically colorless oils or rubber-like substances. Silicones are used in sealants, adhesives, lubricants, medicine, cooking ...
s due to its solvent properties.
The three aromatic
In chemistry, aromaticity is a chemical property of cyclic ( ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to satur ...
hydrogen atoms of mesitylene are in identical chemical shift environments. Therefore, they only give a single peak near 6.8 ppm in the 1H NMR spectrum; the same is also true for the nine methyl
In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula . In formulas, the group is often abbreviated as Me. This hydrocarbon group occurs in many ...
protons, which give a singlet near 2.3 ppm. For this reason, mesitylene is sometimes used as an internal standard An internal standard in analytical chemistry is a chemical substance that is added in a constant amount to samples, the blank and calibration standards in a chemical analysis. This substance can then be used for calibration by plotting the ratio of ...
in NMR samples that contain aromatic protons.
Uvitic acid
Uvitic acid (5-methylisophthalic acid) is an organic compound with the formula CH3C6H3(COOH)2. The name comes from Latin ''uva'' which means a grape. The acid is called so because it may be produced indirectly from tartaric acid, which is found in ...
is obtained by oxidizing mesitylene or by condensing pyruvic acid
Pyruvic acid (CH3COCOOH) is the simplest of the alpha-keto acids, with a carboxylic acid and a ketone functional group. Pyruvate, the conjugate base, CH3COCOO−, is an intermediate in several metabolic pathways throughout the cell.
Pyruvic aci ...
with baryta water.
The Gattermann reaction
The Gattermann reaction, (also known as the Gattermann formylation and the Gattermann salicylaldehyde synthesis) is a chemical reaction in which aromatic compounds are formylated by a mixture of hydrogen cyanide (HCN) and hydrogen chloride (HCl ...
can be simplified by replacing the HCN/AlCl3 combination with zinc cyanide
Zinc cyanide is the inorganic compound with the formula Zn( CN)2. It is a white solid that is used mainly for electroplating zinc but also has more specialized applications for the synthesis of organic compounds.
Structure
In Zn(CN)2, zinc adop ...
(Zn(CN)2). Although it is highly toxic, Zn(CN)2 is a solid, making it safer to work with than gaseous hydrogen cyanide (HCN). The Zn(CN)2 reacts with the HCl to form the key HCN reactant and ZnCl2 that serves as the Lewis-acid catalyst ''in-situ''. An example of the Zn(CN)2 method is the synthesis of mesitaldehyde from mesitylene.
History
Mesitylene was first prepared in 1837 by Robert Kane, an Irish chemist, by heating acetone with concentrated sulfuric acid. He named his new substance "mesitylene" because the German chemist Carl Reichenbach
Carl Ludwig von Reichenbach (full name: Karl Ludwig Freiherr von Reichenbach; February 12, 1788January 1869) was a German chemist, geologist, metallurgist, naturalist, industrialist and philosopher, and a member of the Prussian Academy of Scienc ...
had named acetone "mesit" (from the Greek μεσίτης, the mediator), and Kane believed that his reaction had dehydrated mesit, converting it to an alkene
In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond.
Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, an ...
, "mesitylene". However, Kane's determination of the chemical composition ("empirical formula") of mesitylene was incorrect. The correct empirical formula was provided by August W. von Hofmann in 1849. In 1866 Adolf von Baeyer
Johann Friedrich Wilhelm Adolf von Baeyer (; 31 October 1835 – 20 August 1917) was a German chemist who synthesised indigo and developed a nomenclature for cyclic compounds (that was subsequently extended and adopted as part of the IUPAC org ...
gave a correct mesitylene's empirical formula; however, with a wrong structure of tetracyclo 1,3.13,5">.1.1.11,3.13,5onane. A conclusive proof that mesitylene was trimethylbenzene was provided by Albert Ladenburg
Albert Ladenburg (July 2, 1842August 15, 1911) was a German chemist.
Early life and education
Ladenburg was a member of the well-known Jewish in Mannheim. He was educated at a Realgymnasium at Mannheim and then, after the age of 15, at the tec ...
in 1874; however, assuming wrong benzene structure of prismane
Prismane or 'Ladenburg benzene' is a polycyclic hydrocarbon with the formula C6H6. It is an isomer of benzene, specifically a valence isomer. Prismane is far less stable than benzene. The carbon (and hydrogen) atoms of the prismane molecule are a ...
.
File:Mesitylen by Adolf von Baeyer.png, Mesitylene by Adolf von Baeyer (tetracyclo 1,3.13,5">.1.1.11,3.13,5onane)
File:Mesitylen by Albert Ladenburg.png, Mesitylene by Albert Ladenburg (1,2,6-trimethylprismane)
Mesityl group
The group (CH3)3C6H2- is called mesityl (organic group symbol: Mes). Mesityl derivatives, e.g. tetramesityldiiron
Tetramesityldiiron is an organoiron compound with the formula Fe2(C6H2(CH3)3)4. It is a red, air-sensitive solid that is used as a precursor to other iron complexes. It adopts a Molecular symmetry, centrosymmetric structure. The complex is a Lewis ...
, are typically prepared from the Grignard reagent
A Grignard reagent or Grignard compound is a chemical compound with the general formula , where X is a halogen and R is an organic group, normally an alkyl or aryl. Two typical examples are methylmagnesium chloride and phenylmagnesium bromide ...
(CH3)3C6H2MgBr. Due to its large steric demand, the mesityl group is used as a large blocking group in asymmetric catalysis (to enhance diastereo- or enantioselectivity) and organometallic chemistry (to stabilize low oxidation state or low coordination number metal centers). Larger analogues with even greater steric demand, for example 2,6-diisopropylphenyl (Dipp) and the analogously named Tripp ((iPr)3C6H2, Is) and supermesityl ((''t''Bu)3C6H2, Mes*) groups, may be even more effective toward achieving these goals.
Safety and the environment
Mesitylene is also a major urban volatile organic compound
Volatile organic compounds (VOCs) are organic compounds that have a high vapour pressure at room temperature. High vapor pressure correlates with a low boiling point, which relates to the number of the sample's molecules in the surrounding air, a ...
(VOC) which results from combustion
Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combusti ...
. It plays a significant role in aerosol and tropospheric ozone
Ground-level ozone (O3), also known as surface-level ozone and tropospheric ozone, is a trace gas in the troposphere (the lowest level of the Earth's atmosphere), with an average concentration of 20–30 parts per billion by volume (ppbv), with cl ...
formation as well as other reactions in atmospheric chemistry
Atmospheric chemistry is a branch of atmospheric science in which the chemistry of the Earth's atmosphere and that of other planets is studied. It is a multidisciplinary approach of research and draws on environmental chemistry, physics, meteoro ...
.
References
{{Hydrocarbons
Hydrocarbon solvents
Alkylbenzenes
C3-Benzenes
Aromatic solvents