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Mesitylene or 1,3,5-trimethylbenzene is a derivative of
]
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 silicones due to its solvent properties.
The three
File:Mesitylen by Adolf von Baeyer.png, Mesitylene by Adolf von Baeyer (tetracyclo .1.1.11,3.13,5onane)
File:Mesitylen by Albert Ladenburg.png, Mesitylene by Albert Ladenburg (1,2,6-trimethylprismane)
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 ato ...
with three methyl 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 '' ...
s positioned symmetrically around the ring. The other two isomeric trimethylbenzenes 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 C6H3(CH3)3, which is commonly abbreviated C6H3Me3. 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 psoria ...
, 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 ...
s. The mesityl group (Mes) is a substituent with the formula C6H2Me3 and is found in various other compounds.
Preparation
Mesitylene is prepared bytransalkylation
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 partic ...
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: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, also requiring an acid catalyst, yields a mixture of 1,3,5- and 1,2,4-trimethylbenzenes.
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 miscible wi ...
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 ...
, 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. Mi ...
by sulfuric acid is another method of synthesizing mesitylene.
Reactions
Oxidation of mesitylene withnitric 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 ni ...
yields trimesic acid, 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-cel ...
, 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 oxid ...
, 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 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 call ...
(2,4,6-trimethylphenol). Bromination occurs readily, giving mesityl bromide:
:(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 ele ...
in organometallic chemistry, one example being the organomolybdenum complex which can be prepared from molybdenum hexacarbonyl.
Applications
Mesitylene is mainly used as a precursor to2,4,6-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 silicones 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 sat ...
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 protons, which give a singlet near 2.3 ppm. For this reason, mesitylene is sometimes used as an internal standard in NMR samples that contain aromatic protons.
Uvitic acid 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 ac ...
with baryta water.
The Gattermann reaction can be simplified by replacing the HCN/AlCl3 combination with zinc cyanide (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 had named acetone "mesit" (from the Greek μεσίτης, the mediator), and Kane believed that his reaction had dehydrated mesit, converting it to analkene
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 or ...
gave a correct mesitylene's empirical formula; however, with a wrong structure of tetracyclo .1.1.11,3.13,5onane. A conclusive proof that mesitylene was trimethylbenzene was provided by Albert Ladenburg in 1874; however, assuming wrong benzene structure of prismane.
Mesityl group
The group (CH3)3C6H2- is called mesityl (organic group symbol: Mes). Mesityl derivatives, e.g. tetramesityldiiron, are typically prepared from the Grignard reagent (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 urbanvolatile 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. Combust ...
. It plays a significant role in aerosol and tropospheric ozone 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, mete ...
.
References