1,2,4-Trimethylbenzene

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]

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]

Pseudocumene is a precursor to trimellitic 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]

• Cumene