1,2,4-Trimethylbenzene

1,2,4-Trimethylbenzene, also known as pseudocumene, is an organic compound with the chemical formula C₆H₃(CH₃)₃. Classified as an aromatic hydrocarbon, it is a flammable colorless liquid with a strong odor. It is nearly insoluble in water but soluble in organic solvents. It occurs naturally in coal tar and petroleum (about 3%). It is one of the three isomers of trimethylbenzene.

1,2,4-Trimethylbenzene^[1]

Skeletal formula Ball-and-stick model
Names
Preferred IUPAC name 1,2,4-Trimethylbenzene
Other names Pseudocumene, Asymmetrical trimethylbenzene, ψ-Cumene
Identifiers
CAS Number	95-63-6 Y
3D model (JSmol)	Interactive image
Beilstein Reference	1903005
ChEBI	CHEBI:34039 Y
ChEMBL	ChEMBL1797280
ChemSpider	6977 Y
ECHA InfoCard	100.002.216
EC Number	202-436-9
KEGG	C14533 Y
PubChem CID	7247
RTECS number	DC3325000
UNII	34X0W8052F Y
UN number	1993 2325
CompTox Dashboard (EPA)	DTXSID6021402
InChI InChI=1S/C9H12/c1-7-4-5-8(2)9(3)6-7/h4-6H,1-3H3 Y Key: GWHJZXXIDMPWGX-UHFFFAOYSA-N Y InChI=1/C9H12/c1-7-4-5-8(2)9(3)6-7/h4-6H,1-3H3 Key: GWHJZXXIDMPWGX-UHFFFAOYAF
SMILES c1c(ccc(c1C)C)C
Properties
Chemical formula	C9H12
Molar mass	120.19 g/mol
Appearance	Colorless liquid
Density	0.8761 g/cm3
Melting point	−43.78 °C (−46.80 °F; 229.37 K)
Boiling point	169 to 171 °C (336 to 340 °F; 442 to 444 K)
Magnetic susceptibility (χ)	−101.6·10−6 cm3/mol
Hazards
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H226, H315, H319, H332, H335, H411
Precautionary statements	P210, P233, P240, P241, P242, P243, P261, P264, P271, P273, P280, P302+P352, P303+P361+P353, P304+P312, P304+P340, P305+P351+P338, P312, P321, P332+P313, P337+P313, P362, P370+P378, P391, P403+P233, P403+P235, P405, P501
Flash point	44.4 °C (111.9 °F; 317.5 K)
Explosive limits	0.9%–6.4%[2]
NIOSH (US health exposure limits):
PEL (Permissible)	none[2]
Safety data sheet (SDS)	Sigma-Aldrich MSDS
Related compounds
Related compounds	1,2,3-Trimethylbenzene; 1,3,5-Trimethylbenzene
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

History

In 1849, Charles Blachford Mansfield rectified coal tar and identified fractions which he hypothesized to be cumole and cymole. The latter fraction boiled slightly above 170°C and had specific density of 0.857.^[3]

In 1862, Warren De la Rue and Hugo Müller (1833-1915) proposed the term pseudocumole for the fractions heavier than xylole.^[4]

When three years later American chemist Cyrus Warren (1824-1891) attempted to reproduce Mansfield's results, he determined that the oil boiling at 170° has the same formula as cumole, not cymole, and suggested to name it isocumole.^[5]

The structure of the compound was determined by Th. Ernst and Wilhelm Rudolph Fittig, who first prepared it from bromoxylene and iodomethane in 1866 by a Wurtz–Fittig reaction developed two years earlier.^[6]

In the next year, Fittig et al. adopted the pseudocumol terminology,^[7] in 1869 Fittig and B. Wackenroder proved that the fraction is a mixture of mesitylene with another trimethylbenzene, for which the name of pseudocumol was retained,^[8] and in 1886 Oscar Jacobsen [de] showed that the third trimethylbenzene he discovered earlier is also present.^[9]

Production

Industrially, it is isolated from the C₉ aromatic hydrocarbon fraction during petroleum distillation. Approximately 40% of this fraction is 1,2,4-trimethylbenzene. It is also generated by methylation of toluene and xylenes and the disproportionation of xylene over aluminosilicate catalysts.^[10]

Uses

Pseudocumene is a precursor to mellitic anhydride, from which high performance polymers are made. It is also used as a sterilizing agent and in the making of dyes, perfumes and resins. Another use is as an antiknock agent,^[11] since its research and motor octane numbers are well above 100.^{[12]: Fig. II.1 [13]}

In automobile fuel it is a minor additive, with its share in US gasoline rising from 0.03–0.5% in early 1990s^[14] to 1.1–2.6% in 2011.^[15] It may be a major component of some avgas formulations.^[16]

Scintillator

1,2,4-Trimethylbenzene dissolved in mineral oil is used as a liquid scintillator^[17] in particle physics experiments such as NOνA and Borexino.

See also

• Cumene