Hexamethylbenzene

Structural formula
General
Surname	Hexamethylbenzene
other names	Mellitol Mellites
Molecular formula	C 12 H 18
Brief description	orthorhombic prisms or needles
External identifiers / databases
CAS number 87-85-4 EC number 201-777-0 ECHA InfoCard 100.001.616 PubChem 6908 Wikidata Q413592
properties
Molar mass	162.28 g mol −1
Physical state	firmly
density	1.042 g cm −3
Melting point	165.5 ° C
boiling point	263.4 ° C
solubility	almost insoluble in water, soluble in ethanol, ether, acetone, benzene, acetic acid and chloroform
safety instructions
GHS labeling of hazardous substances no GHS pictograms H and P phrases H: no H-phrases P: no P-phrases
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Hexamethylbenzene ( Mellitol , Melliten ) is a benzene substituted with six methyl groups and thus an aromatic hydrocarbon .

History and characteristics

In 1880, J. Le Bel and WH Greene observed that the reaction of methanol over molten zinc chloride also formed hexamethylbenzene.

${\displaystyle {\ce {15 CH3OH -> C6(CH3)6 + 3 CH4 + 15 H2O}}}$

The reaction was interpreted as the dehydrocyclization of ethene to benzene with subsequent Friedel-Crafts alkylation by methyl chloride .

${\displaystyle \mathrm {2\ CH_{3}OH+ZnCl_{2}\longrightarrow 2\ CH_{3}Cl+Zn{(OH)}_{2}} }$

${\displaystyle \mathrm {C_{6}H_{6}+6\ CH_{3}Cl\longrightarrow C_{6}{(CH_{3})}_{6}+6\ HCl} }$

Hexamethylbenzene is a solid that forms orthorhombic prisms or needles. The melting point is 165.5 ° C, making it the highest of the methyl-substituted benzenes .

The common name Mellitol is derived from mellitic acid (benzene hexacarboxylic acid), which in turn was isolated from mellite ( honey stone ). In the same way, the common name of 1,2,3-trimethylbenzene ( Hemellitol , Hemi -Mellitol) is derived from it. The syllable hemi- denotes half of the substituents.

Mellitol (hexamethylbenzene)	Hemellitol

In 1929, Kathleen Lonsdale first demonstrated the shape of hexamethylbenzene and thus showed that the benzene ring is hexagonal and flat. In contrast, the hexamethylbenzene dication has a pentagonal-pyramidal structure in which the apical six-coordinate carbon atom is bonded to both a methyl group (bond length 1.479 (3) Å ) and the five basal carbon atoms (bond lengths 1.694 (2) -1.715 ( 3) Å).

presentation

A solution of phenol in methanol is added dropwise to an activated aluminum oxide catalyst at 530 ° C. over a longer period of time .

use

Because it is electron-rich, hexamethylbenzene can be used as a ligand in organometallic chemistry . It is used in numerous organometallic syntheses, e.g. B. with titanium, chromium, cobalt, rhodium and rhenium. Two further examples from organoruthenium chemistry are the sandwich complexes Ru (ɳ ⁴ -C ₆ (CH ₃ ) ₆ ) (ɳ ⁶ -C ₆ (CH ₃ ) ₆ ) and the dication [Ru (ɳ ⁶ -C ₆ (CH ₃ ) ₆ ) ₂ ] ²⁺ .

Hexamethylbenzene is also used as a solvent for ³ He-NMR spectroscopy.

literature

• HW Earhart, Andrew P. Komin: Kirk-Othmer Encyclopedia of Chemical Technology . John Wiley & Sons, Inc., 2000, ISBN 978-0-471-23896-6 , chapter Polymethylbenzenes , doi : 10.1002 / 0471238961.1615122505011808.a01 .

Individual evidence

1. ↑ ^{a b c d e} David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Physical Constants of Organic Compounds, pp. 3-280.
2. ^ LO Brockway, JM Robertson: "The Crystal Structure of Hexamethylbenzene and the Length of the Methyl Group Bond to Aromatic Carbon Atoms", in: J. Chem. Soc. , 1939, pp. 1324-1332; doi: 10.1039 / JR9390001324 .
3. ↑ ^{a b} data sheet for hexamethylbenzene from Sigma-Aldrich , accessed on January 17, 2017 ( PDF ).
4. ↑ Clarence D. Chang: "Hydrocarbons from Methanol", in: Catal. Rev. Sci. Closely. , 1983, 25  (1), pp. 1-118; Abstract .
5. ↑ Kathleen Lonsdale: "The Structure of the Benzene Ring in C ₆ (CH ₃ ) ₆ ", in: Proceedings of the Royal Society , 1929, 123A , pp. 494-515; doi: 10.1098 / rspa.1929.0081 .
6. ↑ Moritz Malischewski, K. Seppelt: The molecular structure of the pentagonal-pyramidal hexamethylbenzene dication C ₆ (CH ₃ ) ₆ ²⁺ in the crystal . In: Angewandte Chemie . tape 129 , no. 1 , 2017, p. 374–376 , doi : 10.1002 / anie.201608795 .
7. ↑ NM Cullinane, SJ Chard, CWC Dawkins: Hexamethylbenzene In: Organic Syntheses . 35, 1955, p. 73, doi : 10.15227 / orgsyn.035.0073 ; Coll. Vol. 4, 1963, p. 520 ( PDF ).
8. ↑ Phillip S. Landis, Werner O. Haag: "Formation of Hexamethylbenzene from Phenol and Methanol", in: The Journal of Organic Chemistry , 1963, 28  (2), pp. 585-585; doi: 10.1021 / jo01037a517 .
9. ^ HH Zeiss, W. Herwig: "ACETYLENIC π-COMPLEXES OF CHROMIUM IN ORGANIC SYNTHESIS", in: J. Am. Chem. Soc. , 1958, 80  (11), pp. 2913-2913; doi: 10.1021 / ja01544a091 .
10. ↑ B. Franzus, PJ Canterino, RA Wickliffe: "TITANIUM TETRACHLORIDE-TRIALKYLALUMINUM COMPLEX - A CATALYST FOR CYCLIZING Acetylenic COMPOUNDS", in: J. Am. Chem. Soc. , 1959, 81  (6), pp. 1514-1514; doi: 10.1021 / ja01515a061 .
11. ↑ Ernst Otto Fischer , Hans Hasso Lindner: "About aromatic complexes of metals. LXXVI. Di-hexamethylbenzene-metal-π-complexes of monovalent and divalent cobalt and rhodium", in: Journal of Organometallic Chemistry , 1964, 1  (4), Pp. 307-317; doi: 10.1016 / S0022-328X (00) 80056-X .
12. ^ Ernst Otto Fischer, Manfred Wilhelm Schmidt: "About Aromatic Complexes of Metals, XCI. About monomeric and dimeric bis-hexamethylbenzene-rhenium", in: Chemischeberichte , 1966, 99  (7), pp. 2206-2212; doi: 10.1002 / cber.19660990719 .
13. ^ MA Bennett, TN Huang, TW Matheson, AK Smith: "(η ⁶ -Hexamethylbenzene) Ruthenium Complexes", in: Inorganic Syntheses , 1982, 21 , pp. 74-78; doi: 10.1002 / 9780470132524.ch16 .
14. ↑ M. Saunders, HA Jimenez-Vazquez, A. Khong: "NMR of ³ He Dissolved in Organic Solids", in: J. Phys. Chem. , 1996, 100  (39), pp. 15968-15971; doi: 10.1021 / jp9617783 .

Web links

Commons : Hexamethylbenzene  - Collection of pictures, videos and audio files

• Entry on hexamethylbenzene . In: P. J. Linstrom, W. G. Mallard (Eds.): NIST Chemistry WebBook, NIST Standard Reference Database Number 69 . National Institute of Standards and Technology , Gaithersburg MD, accessed December 19, 2012.