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-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, which is its traditional source. It is a precursor to diverse fine chemicals. The mesityl group (Mes) is a substituent with the formula C₆H₂Me₃ and is found in various other compounds.^[4]

Mesitylene

Mesitylene Mesitylene
Names
Preferred IUPAC name 1,3,5-Trimethylbenzene[1]
Other names Mesitylene[1] sym-Trimethylbenzene
Identifiers
CAS Number	108-67-8 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:34833 Y
ChemSpider	7659 Y
ECHA InfoCard	100.003.278
EC Number	203-604-4
KEGG	C14508 Y
PubChem CID	7947
UNII	887L18KQ6X Y
UN number	2325
CompTox Dashboard (EPA)	DTXSID6026797
InChI InChI=1S/C9H12/c1-7-4-8(2)6-9(3)5-7/h4-6H,1-3H3 Y Key: AUHZEENZYGFFBQ-UHFFFAOYSA-N Y InChI=1/C9H12/c1-7-4-8(2)6-9(3)5-7/h4-6H,1-3H3 Key: AUHZEENZYGFFBQ-UHFFFAOYAK
SMILES Cc1cc(cc(c1)C)C
Properties
Chemical formula	C9H12
Molar mass	120.19 g/mol
Appearance	Colorless liquid[2]
Odor	Distinctive, aromatic[2]
Density	0.8637 g/cm3 at 20 °C
Melting point	−44.8 °C (−48.6 °F; 228.3 K)
Boiling point	164.7 °C (328.5 °F; 437.8 K)
Solubility in water	0.002% (20°C)[2]
Vapor pressure	2 mmHg (20°C)[2]
Magnetic susceptibility (χ)	-92.32·10−6 cm3/mol
Structure
Dipole moment	0.047 D[3]
Hazards
Flash point	50 °C; 122 °F; 323 K[2]
NIOSH (US health exposure limits):
PEL (Permissible)	none[2]
REL (Recommended)	TWA 25 ppm (125 mg/m3)[2]
IDLH (Immediate danger)	N.D.[2]
Safety data sheet (SDS)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Preparation

Mesitylene is prepared by transalkylation of xylene over solid acid catalyst:^[4]

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 via aldol condensation, which is catalyzed and dehydrated by sulfuric acid is another method of synthesizing mesitylene.^[5]

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).^[6] Bromination occurs readily, giving mesityl bromide:^[7]

(CH₃)₃C₆H₃ + Br₂ → (CH₃)₃C₆H₂Br + HBr

Mesitylene is a ligand in organometallic chemistry, one example being the organomolybdenum complex [(η⁶-C₆H₃Me₃)Mo(CO)₃]^[8] 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.^[9]

Niche uses

Structure of (mesitylene)molybdenum tricarbonyl, [(η⁶-C₆H₃Me₃)Mo(CO)₃]

Mesitylene is used in the laboratory as a specialty solvent. In the electronics industry, mesitylene has been used as a developer for photopatternable silicones 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 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.^[10]

Uvitic acid is obtained by oxidizing mesitylene or by condensing pyruvic acid with baryta water.^[11]

The Gattermann reaction can be simplified by replacing the HCN/AlCl₃ combination with zinc cyanide (Zn(CN)₂).^[12] Although it is highly toxic, Zn(CN)₂ is a solid, making it safer to work with than gaseous hydrogen cyanide (HCN).^[13] 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.^[14]

History

Mesitylene was first prepared in 1837 by Robert Kane, an Irish chemist, by heating acetone with concentrated sulfuric acid.^[15] He named his new substance "mesitylene" because the German chemist Carl Reichenbach had named acetone "mesit" (from the Greek μεσίτης, the mediator),^[16] and Kane believed that his reaction had dehydrated mesit, converting it to an alkene, "mesitylene".^[17] 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.^[18] In 1866 Adolf von Baeyer gave a correct mesitylene's empirical formula; however, with a wrong structure of tetracyclo[3.1.1.1^1,3.1^3,5]nonane.^[19] A conclusive proof that mesitylene was trimethylbenzene was provided by Albert Ladenburg in 1874; however, assuming wrong benzene structure of prismane.^[20]

• Historical mesitylene structures
• 
  Mesitylene by Adolf von Baeyer (tetracyclo[3.1.1.1^1,3.1^3,5]nonane)
• 
  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.^[21] 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 ((^tBu)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 (VOC) which results from combustion. It plays a significant role in aerosol and tropospheric ozone formation as well as other reactions in atmospheric chemistry.^{[citation needed]}

References

1. Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. p. 139. doi:10.1039/9781849733069-FP001. ISBN 978-0-85404-182-4.
2. NIOSH Pocket Guide to Chemical Hazards. "#0639". National Institute for Occupational Safety and Health (NIOSH).
3. Zhao, Jun; Zhang, Renyi (2004). "Proton transfer reaction rate constants between hydronium ion (H₃O⁺) and volatile organic compounds". Atmospheric Environment. 38 (14): 2177–2185. Bibcode:2004AtmEn..38.2177Z. doi:10.1016/j.atmosenv.2004.01.019.
4. 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. doi:10.1002/14356007.a13_227.
5. Cumming, W. M. (1937). Systematic organic chemistry (3E). New York, USA: D. Van Nostrand Company. p. 57.
6. Chambers, Richard D. (2004). "Functional Compounds Containing Oxygen, Sulphur or Nitrogen and their Derivatives". Fluorine in Organic Chemistry. CRC Press. pp. 242–243. ISBN 9780849317903.
7. Lee Irvin Smith (1931). "Bromomesitylene". Org. Synth. 11: 24. doi:10.15227/orgsyn.011.0024.
8. Girolami, G. S.; Rauchfuss, T. B. and Angelici, R. J. [de], Synthesis and Technique in Inorganic Chemistry, University Science Books: Mill Valley, CA, 1999. ISBN 0-93570248-2.
9. Gerald Booth (2007). "Nitro Compounds, Aromatic". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a17_411. ISBN 978-3527306732.
10. "Mesitylene (1,3,5-Trimethyl Benzene)".
11. "Definition of uvitic acid". merriam-webster.com. Retrieved 31 October 2016.
12. Adams R.; Levine, I. (1923). "Simplification of the Gattermann Synthesis of Hydroxy Aldehydes". J. Am. Chem. Soc. 45 (10): 2373–77. doi:10.1021/ja01663a020.
13. Adams, Roger (1957). Organic Reactions, Volume 9. New York: John Wiley & Sons, Inc. pp. 38 & 53–54. doi:10.1002/0471264180.or009.02. ISBN 9780471007265.
14. Fuson, R. C.; Horning, E. C.; Rowland, S. P.; Ward, M. L. (1955). "Mesitaldehyde". Organic Syntheses. doi:10.15227/orgsyn.023.0057; Collected Volumes, vol. 3, p. 549.
15. Robert Kane (1839) "On a series of combinations derived from pyroacetic spirit [acetone]" Transactions of the Royal Irish Academy, vol. 18, pages 99–125.
16. 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.
17. 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.
18. 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.)
19. Adolf von Baeyer (1866) "Ueber die Condensationsproducte des Acetons" (On condensation products of acetone), Annalen der Chemie und Pharmacie, vol. 140, pages 297–306.
20. Albert Ladenburg (1874) "Ueber das Mesitylen" (On mesitylene), Berichte der deutschen chemischen Gesellschaft, vol. 7, pages 1133–1137. doi:10.1002/cber.18740070261
21. Lee Irvin Smith (1931). "Isoodurene". Org. Synth. 11: 66. doi:10.15227/orgsyn.011.0066.