2,5-Dibromofluorobenzene
[CAS 1435-52-5]

Identification

• Classification: Organic raw materials >> Hydrocarbon compounds and their derivatives >> Hydrocarbon halide
• Name: 2,5-Dibromofluorobenzene
• Synonyms: 1,4-Dibromo-2-fluorobenzene
• Molecular Formula: C₆H₃Br₂F
• Molecular Weight: 253.89
• CAS Registry Number: 1435-52-5
• EC Number: 629-432-3
• SMILES: C1=CC(=C(C=C1Br)F)Br

Properties

• Density: 2.0±0.1 g/cm³ Calc.^*
• Melting point: 33 - 36 °C (Expl.)
• Boiling point: 213.9±20.0 °C 760 mmHg (Calc.)^*, 216 °C (Expl.)
• Flash point: 101.7 °C (Calc.)^*, 102 °C (Expl.)
• Index of refraction: 1.575 (Calc.)^*

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Safety Data

• Hazard Symbols: GHS07 Warning
• Risk Statements: H315-H319-H335
• Safety Statements: P261-P264-P264+P265-P271-P280-P302+P352-P304+P340-P305+P351+P338-P319-P321-P332+P317-P337+P317-P362+P364-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Skin irritation	Skin Irrit.	2	H315
Eye irritation	Eye Irrit.	2	H319
Specific target organ toxicity - single exposure	STOT SE	3	H335

chemBlink Chemical Story

2,5-Dibromofluorobenzene, CAS 1435-52-5, is a halogenated aromatic compound used mainly as a building block in organic synthesis and materials chemistry. It is also systematically named 1,4-dibromo-2-fluorobenzene and has the molecular formula C₆H₃Br₂F and a molecular weight of 253.89. Its structure consists of a benzene ring bearing two bromine atoms in a para relationship and one fluorine atom adjacent to one of them. This apparently simple substitution pattern creates an interesting problem in synthetic chemistry: when a molecule contains two similar carbon-bromine bonds, can a chemist choose which one reacts first?

Aryl bromides are among the most useful starting materials for modern transition-metal-catalyzed cross-coupling chemistry. In the Suzuki-Miyaura reaction, an aryl halide reacts with an organoboron compound, typically in the presence of a palladium catalyst and base, to form a new carbon-carbon bond. The reaction has become one of the fundamental methods for assembling biaryls and larger aromatic structures used in pharmaceuticals, agrochemicals, electronic materials, and chemical research.

With a dibrominated compound, however, another possibility appears. One bromine can be replaced first while the second remains available for a later reaction. This allows a single benzene ring to function as a central platform from which a larger molecule can be constructed in stages.

2,5-Dibromofluorobenzene provides a particularly instructive example because its two brominated positions are not electronically identical. The fluorine atom lies next to one carbon-bromine bond but is farther from the other. Although fluorine is small, it strongly influences electron distribution within the aromatic ring. Consequently, the two sites can display different reactivity under carefully selected catalytic conditions.

This behavior was investigated directly in a 2010 study of site-selective Suzuki-Miyaura reactions. Researchers showed that 1,4-dibromo-2-fluorobenzene could undergo controlled sequential coupling with arylboronic acids to produce fluorinated terphenyls. Rather than treating both bromine atoms as equivalent handles that react indiscriminately, the reaction sequence exploited differences between the two sites.

The first coupling produces a brominated biphenyl intermediate. Because one carbon-bromine bond remains, a second Suzuki-Miyaura reaction can introduce another aryl group. If different arylboronic acids are used in the two stages, unsymmetrical terphenyl structures can be assembled from the same dibromofluorobenzene starting material.

This is an elegant example of site selectivity. Chemoselectivity asks which type of functional group will react; site selectivity asks which of two or more similar positions will react. The distinction becomes particularly important in molecules containing repeated functional groups. If every reactive site behaved identically under all conditions, constructing unsymmetrical molecules would often require additional protection, deprotection, or alternative synthetic routes.

The fluorine substituent plays another role after the carbon-carbon bonds have been constructed. Unlike bromine, which is commonly used as a temporary synthetic handle and removed during coupling, fluorine frequently remains in the final molecule. The strong carbon-fluorine bond can survive many reaction conditions, allowing fluorine to become a permanent structural feature while the bromine atoms serve as temporary connection points.

Fluorinated oligophenyl structures are of interest not only in medicinal chemistry but also in molecular and materials research. Introducing fluorine into conjugated aromatic systems can alter electronic distribution, molecular packing, dipole moments, and other physical properties. The precise consequences depend on the complete molecular structure, but fluorinated aromatic building blocks provide researchers with a convenient way to study these effects systematically.

2,5-Dibromofluorobenzene has also been used to prepare 1,4-diethynyl-2-fluorobenzene derivatives through palladium-catalyzed alkynylation chemistry. Such compounds have been investigated in studies of poly(phenyleneethynylene)-related chromophores, where molecular geometry, conjugation, aggregation, and crystal packing influence optical behavior. In this case, the two bromine atoms provide positions for installing carbon-carbon triple-bond-containing substituents.

More recent patent literature demonstrates another direction for the same building block: organic electronic materials. 1,4-Dibromo-2-fluorobenzene has been reacted under palladium-catalyzed conditions with nitrogen-containing aromatic systems such as carbazole and acridine derivatives during the construction of larger compounds intended for organic light-emitting devices. Here again, the dibrominated fluorobenzene ring serves as a compact molecular junction from which a much larger conjugated architecture can be assembled.

The compound therefore illustrates how halogens can perform very different jobs in synthetic chemistry even when they occupy the same small aromatic ring. Bromine is frequently temporary: it marks a carbon where another molecular fragment can later be installed. Fluorine is often permanent: it survives the construction process and becomes part of the properties of the finished molecule.

Most interestingly, even the two bromine atoms need not be treated as identical. Their surrounding molecular environments allow chemists to distinguish between them and, under suitable conditions, decide which connection to make first.

2,5-Dibromofluorobenzene is thus more than a benzene ring decorated with three halogens. It is a compact example of programmable molecular construction. Two bromines provide two potential exits from the ring, fluorine helps make those exits chemically distinguishable, and sequential cross-coupling allows a simple six-carbon starting material to grow into an unsymmetrical, highly substituted aromatic structure. Modern synthesis becomes powerful not merely when chemists know how to make a bond, but when they can decide which apparently similar bond should be made first.

References

1. NIST Chemistry WebBook, SRD 69. 1,4-Dibromo-2-fluorobenzene. CAS 1435-52-5.
https://webbook.nist.gov/cgi/cbook.cgi?ID=C1435525

2. Sharif, M. et al. (2010). "One-pot synthesis of fluorinated terphenyls by site-selective Suzuki-Miyaura reactions of 1,4-dibromo-2-fluorobenzene." Tetrahedron Letters, 51, 2810-2812.

3. Miyaura, N.; Suzuki, A. (1995). "Palladium-Catalyzed Cross-Coupling Reactions of Organoboron Compounds." Chemical Reviews, 95, 2457-2483.
https://doi.org/10.1021/cr00039a007

4. Levitus, M. et al. (2001). "Steps to demarcate the effects of chromophore aggregation and planarization in poly(phenyleneethynylene)s. 2. The photophysics of 1,4-diethynyl-2-fluorobenzene in solution and in crystals." Journal of Organic Chemistry, 66, 3188-3195.

5. CN 111620900 A. Organic light-emitting compounds and synthetic intermediates prepared using 1,4-dibromo-2-fluorobenzene.