Mesitylene or 1,3,5-trimethylbenzene is a derivative of benzene with three methyl positioned symmetrically around the ring. The other two isomeric trimethylbenzenes are 1,2,4-trimethylbenzene (pseudocumene) and 1,2,3-trimethylbenzene (hemimellitene). All three compounds have the chemical 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, which is its traditional source. It is a precursor to diverse . The mesityl group (Mes) is a substituent with the formula C6H2Me3 and is found in various other compounds.[
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Preparation
Mesitylene is prepared by transalkylation of xylene 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 xylene ⇌ C6H3(CH3)3 + toluene
- C6H4(CH3)2 + CH3OH → C6H3(CH3)3 + H2O
Although impractical, it could be prepared by trimerization of propyne, also requiring an acid catalyst, which yields a mixture of 1,3,5- and 1,2,4-trimethylbenzenes.
Trimerization of acetone via aldol condensation, which is catalyzed and dehydration by sulfuric acid is another method of synthesizing mesitylene.
Reactions
Oxidation of mesitylene with nitric acid yields trimesic acid, C6H3(COOH)3. Using manganese dioxide, a milder oxidising agent, 3,5-dimethylbenzaldehyde is formed. Mesitylene is oxidised by trifluoroperacetic acid to produce mesitol (2,4,6-trimethylphenol).
- (CH3)3C6H3 + Br2 → (CH3)3C6H2Br + HBr
Mesitylene is a ligand in organometallic chemistry, one example being the organomolybdenum complex which can be prepared from molybdenum hexacarbonyl.
Applications
Mesitylene is mainly used as a precursor to 2,4,6-trimethylaniline, 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 developer for photopatternable due to its solvent properties.
The three aromatic 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 group 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 with Barium hydroxide.
The Gattermann reaction can be simplified by replacing the HCN/AlCl3 combination with zinc cyanide (Zn(CN)2).
History
Mesitylene was first prepared in 1837 by Robert Kane, an Irish chemist, by heating acetone with concentrated sulfuric acid.[Robert Kane (1839) "On a series of combinations derived from pyroacetic spirit acetone" Transactions of the Royal Irish Academy, vol. 18, pages 99–125.] He named his new substance "mesitylene" because the German chemist Carl Reichenbach had named acetone "mesit" (from the Greek μεσίτης, the mediator),[Reichenbach's research is excerpted in: C. Reichenbach (1834) "Ueber Mesit (Essiggeist) und Holzgeist" (On mesit (spirit of vinegar) and wood spirits), Annalen der Pharmacie, vol. 10, no. 3, pages 298–314.] and Kane believed that his reaction had dehydrated mesit, converting it to an alkene, "mesitylene".[For an explanation of the original of the name "mesitylene", see also: Henry E. Roscoe, A Treatise on Chemistry (New York, New York: D. Appleton and Co., 1889), vol. III, page 102, footnote 2.] 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.[A.W. Hofmann (1849) "On the composition of mesitilole mesitylene, and some of its derivatives", The Quarterly Journal of the Chemical Society of London, vol. 2, pages 104–115. (Note: The empirical formula of mesitylene as stated in Hofmann's paper (C18H12 ) is incorrect; however, this happened because Hofmann used 6 as the atomic weight of carbon, instead of the correct atomic weight of 12. Once the correct atomic weight is used in Hofmann's calculations, his results give the correct empirical formula of C9H12.)] In 1866 Adolf von Baeyer gave a correct mesitylene's empirical formula; however, with a wrong structure of tetracyclo3.1.1.11,3.13,5nonane.[Adolf von Baeyer (1866) "Ueber die Condensationsproducte des Acetons" (On condensation products of acetone), Annalen der Chemie und Pharmacie, vol. 140, pages 297–306.] A conclusive proof that mesitylene was trimethylbenzene was provided by Albert Ladenburg in 1874; however, assuming wrong benzene structure of prismane.[Albert Ladenburg (1874) "Ueber das Mesitylen" (On mesitylene), Berichte der deutschen chemischen Gesellschaft, vol. 7, pages 1133–1137. ]
File:Mesitylen by Adolf von Baeyer.png|Mesitylene by Adolf von Baeyer (tetracyclo3.1.1.11,3.13,5nonane)
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, are typically prepared from the Grignard reagent (CH3)3C6H2MgBr.
Safety and the environment
Mesitylene is also a major urban volatile organic compound (VOC) which results from combustion. It plays a significant role in aerosol and tropospheric ozone formation as well as other reactions in atmospheric chemistry.
