Hydroxyazobenzenes

Hydroxyazophenols
Surname	2-hydroxyazobenzene	3-hydroxyazobenzene	4-hydroxyazobenzene
other names	o -hydroxyazobenzene	m -hydroxyazobenzene	p -hydroxyazobenzene
Structural formula above: ( E ) -isomer below: ( Z ) -isomer
CAS number	2362-57-4 [( E , Z ) mixture] 35983-15-4 [( E ) -isomer] 889457-23-2 [( Z ) -isomer]	2437-11-8 [( E , Z ) mixture] 20714-71-0 [( E ) -isomer] 1356827-79-6 [( Z ) -isomer]	1689-82-3 [( E , Z ) mixture] 20714-70-9 [( E ) -isomer] 37790-28-6 [( Z ) -isomer]
PubChem	6506404	15723297	5354198
Molecular formula	C 12 H 10 N 2 O
Molar mass	198.22 g mol −1
Physical state	firmly
Melting point	83 ° C	114-115 ° C	157.5-159.5 ° C
boiling point			230 ° C
solubility			practically insoluble in water , good in diethyl ether and ethanol
GHS labeling	no GHS pictograms	no GHS pictograms	Caution
H and P phrases	no H-phrases	no H-phrases	315-319-335
	no EUH phrases	no EUH phrases	no EUH phrases
	no P-phrases	no P-phrases	261-305-338-351

Hydroxyazobenzenes are organic compounds from the group of azobenzenes . They also belong to the azo dyes . They have a characteristic azo group and two benzene rings . The hydroxy group on one of the benzene rings acts as a substituent . Theoretically, three constitutional isomers with the empirical formula C ₁₂ H ₁₀ N ₂ O are possible, each of which occurs in two ( E , Z ) isomers .

presentation

Hydroxyazobenzenes can be prepared from diazonium salts and phenols or aromatic amines by coupling reactions . They are also the product of the Gelding rearrangement . In this case, azoxybenzenes react in an acidic environment to form hydroxyazobenzenes, more precisely to p- hydroxyazobenzene. O -hydroxyazobenzene is formed in addition to p -hydroxyazobenzene when benzene diazonium chloride is coupled with phenol. The product contains only at most 1% of the ortho - isomer . This can be separated from the less volatile para isomer by steam distillation . In addition, the ortho connection is created when the para position is occupied.

Isomerism

In addition to structural isomers m - o - p -Hydroxyazobenzol there to each of the individual isomers another E - and Z isomer. All the information in the table below relates to the E , Z -isomer mixture, since it is difficult to separate the isomers from one another. Due to steric hindrances , the E isomers are more stable, but rearrangement into the Z isomers is possible.

The hydroxyl group on the benzene ring can increase the electron density in the benzene ring through the mesomeric effect (+ M effect). The electron-withdrawing inductive (- I ) effect is superimposed by the mesomeric effect. Because of these effects, p- hydroxyazobenzene is the most stable. The m -hydroxyazobenzene is therefore the most unstable. The o -hydroxazobenzene lies in between.

properties

The hydroxyazobenzenes are classified as highly hazardous to water ( WGK 3 ). Due to their azo group, the hydroxyazobenzenes appear colored. The p- hydroxyazobenzene has a yellowish-orange color and crystallizes in the form of prisms. The o- hydroxyazobenzene appears in an orange hue.

use

Like many other azo dyes, hydroxyazobenzenes are used to color soaps , varnishes , fats and resins .

Individual evidence

1. ^ ^{A b c} Louis F. Fieser, Mary Fieser: Textbook of organic chemistry . Chemie, Weinheim 1957, p. 713 .
2. ↑ ^{a b c} Gavriella Gabor, Yael F. Frei, Ernst Fischer: Tautomerism and Geometric Isomerism in Arylazophenols and Napthols IV. - Spectra and Reversible Photoreactions of m- and p-Hydroxyazobenzene , J. Phys. Chem. 72: 3266-3272 (1968).
3. ↑ ^{a b} Entry on 4- (phenylazo) phenol at TCI Europe, accessed on May 7, 2014.
4. ↑ ^{a b} Data sheet 4-Phenylazophenol from Sigma-Aldrich , accessed on May 8, 2014 ( PDF ).
5. ^ M. Windholz: The Merck Index . Merck & Co., Rahway 1976, ISBN 978-0-911910-26-1 , pp. ONR-92 .
6. ↑ ^{a b} Dietrich Schulte-Frohlinde: About the thermal catalytic cis - trans rearrangement of substituted azobenzenes , Liebigs Ann. Chem. 612: 138-152 (1958).
7. ↑ Charles E. Mortimer ; Ulrich Müller: Chemistry . Thieme, Stuttgart 2010, ISBN 978-3-13-484310-1 , p. 549-550 .
8. ↑ Beyer, Walter: Textbook of organic chemistry . S. Hirzel Verlag, Stuttgart 2004, ISBN 3-7776-1221-9 , p. 630 ff .
9. ^ Zerong Wang: Comprehensive Organic Name Reactions and Reagents . John Wiley & Sons, New Jersey 2009, ISBN 978-0-471-70450-8 , pp. 2942-2945 .