Trimethylbenzenes

The trimethylbenzenes form a group of substances whose structure consists of a benzene ring with three methyl groups  (–CH ₃ ) as substituents . Their different arrangement results in three constitutional isomers with the empirical formula C ₉ H ₁₂ . Depending on the position, one speaks of vic. -, asym. - or sym. trimethylbenzene. They also belong to the group of C ₃ benzenes . The sym. -Trimethylbenzene mesitylene is the best known of the three isomers.

Representative

The trimethylbenzenes group of substances includes:

• Hemellitol (1,2,3-trimethylbenzene)
• Pseudocumene (1,2,4-trimethylbenzene)
• Mesitylene (1,3,5-trimethylbenzene)

Trimethylbenzenes
Surname	Hemellitol	Pseudocumene	Mesitylene
other names	1,2,3-trimethylbenzene vic. -Trimethylbenzene	1,2,4-trimethylbenzene asym. -Trimethylbenzene	1,3,5-trimethylbenzene sym. -Trimethylbenzene
Structural formula
CAS number	526-73-8	95-63-6	108-67-8
	25551-13-7 (unspecified isomer or mixture of isomers)
PubChem	10686	7247	7947
Molecular formula	C 9 H 12
Molar mass	120.19 g mol −1
Physical state	liquid
Brief description	colorless liquid
Melting point	−25 ° C	−44 ° C	−45 ° C
boiling point	176 ° C	169 ° C	165 ° C
Density (20 ° C)	0.89 g cm −3	0.88 g cm −3	0.87 g cm −3
Vapor pressure (25 ° C)	2.25 mbar (25 ° C)	2.8 mbar (25 ° C)	2.69 mbar (20 ° C)
solubility	insoluble in water
GHS labeling	Caution	Caution	danger
H and P phrases	226-315-319-335	226-304-332-319-335-315-411	226-304-315-319-335-411
	no EUH phrases	no EUH phrases	no EUH phrases
	261-305 + 351 + 338	261-273-301 + 310-331-302 + 352-304 + 340 + 312	210-273-301 + 310-331-302 + 352-304 + 340 + 312
MAK	Switzerland: 20 ml m −3 or 100 mg m −3

properties

The melting points behave rather inconsistently. Mesitylene is unusual. The most symmetrical representative in this group has a melting point of −45 ° C and is therefore the lowest of all three isomers.

literature

• HW Earhart, Andrew P. Komin: Polymethylbenzenes . In: Kirk-Othmer Encyclopedia of Chemical Technology , 2000, doi: 10.1002 / 0471238961.1615122505011808.a01 .

Web links

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

Individual evidence

1. ↑ ^{a b c d e} Entry on 1,2,3-trimethylbenzene in the GESTIS substance database of the IFA , accessed on March 4, 2020(JavaScript required) .
2. ↑ ^{a b c d e} Entry on 1,2,4-trimethylbenzene in the GESTIS substance database of the IFA , accessed on March 4, 2020(JavaScript required) .
3. ↑ ^{a b c d e} Entry on 1,3,5-trimethylbenzene in the GESTIS substance database of the IFA , accessed on March 4, 2020(JavaScript required) .
4. ↑ Swiss Accident Insurance Fund (Suva): Limit values ​​- current MAK and BAT values (search for trimethylbenzene (all isomers) ), accessed on March 4, 2020.