2'-Bromoacetophenone
[CAS 2142-69-0]

Identification

• Classification: Chemical reagent >> Organic reagent >> Aromatic ketone
• Name: 2'-Bromoacetophenone
• Synonyms: 1-(2-Bromomphenyl)ethanone; 1-(2-Bromophenyl)ethanone; 1-Acetyl-2-bromobenzene
• Molecular Formula: C₈H₇BrO
• Molecular Weight: 199.04
• CAS Registry Number: 2142-69-0
• EC Number: 218-398-1
• SMILES: CC(=O)C1=CC=CC=C1Br

Properties

• Density: 1.5±0.1 g/cm³ Calc.^*, 1.476 g/mL (Expl.)
• Boiling point: 249.0±23.0 °C 760 mmHg (Calc.)^*, 262.4 °C (Expl.)
• Flash point: 86.6±9.9 °C (Calc.)^*, 110 °C (Expl.)
• Solubility: water: practically insoluble (Expl.)
• Index of refraction: 1.554 (Calc.)^*, 1.568 (Expl.)

^* 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
Acute toxicity	Acute Tox.	4	H302
Acute toxicity	Acute Tox.	4	H312
Acute toxicity	Acute Tox.	4	H332

Discovery and Applications

2'-Bromoacetophenone is an aromatic ketone consisting of an acetophenone framework with a bromine substituent located at the 2' position of the benzene ring relative to the acetyl group. It belongs to the class of halogenated acetophenones and is characterized by the combination of an aromatic ring, a carbonyl group, and a reactive aryl bromide functionality.

The molecular structure is based on acetophenone, which contains a phenyl group directly attached to an acetyl group (–COCH₃). In 2'-bromoacetophenone, one hydrogen atom on the aromatic ring is replaced by bromine at the ortho position relative to the carbonyl-containing acetyl substituent. This arrangement places the bromine atom adjacent to the carbonyl group and influences the electronic and steric properties of the molecule.

The benzene ring is a planar aromatic system containing a delocalized π-electron network. The acetyl group is conjugated with the aromatic ring, allowing partial overlap between the carbonyl π-system and the aromatic π-system. This conjugation stabilizes the molecule and affects the distribution of electron density across the ring.

The carbonyl group of the acetyl substituent contains a carbon atom that is sp²-hybridized and adopts trigonal planar geometry. The carbon–oxygen double bond is strongly polarized because of the electronegativity difference between carbon and oxygen. The carbonyl oxygen carries a partial negative charge and acts as a hydrogen bond acceptor, while the carbonyl carbon is electrophilic and can undergo nucleophilic addition reactions.

The bromine atom is attached directly to the aromatic carbon through a carbon–bromine bond. Bromine has a strong inductive electron-withdrawing effect because of its electronegativity, but it can weakly donate electron density through resonance involving its lone pairs. In the ortho position, the inductive effect generally influences the electron distribution more strongly than resonance donation.

The ortho arrangement of the bromine and acetyl groups creates steric interaction between the bromine atom and the carbonyl-containing substituent. This steric effect can influence the preferred conformation of the acetyl group relative to the aromatic ring, reducing complete coplanarity in comparison with less hindered acetophenone derivatives.

From an electronic perspective, 2'-bromoacetophenone contains two important functional regions: the conjugated aromatic ketone system and the aryl bromide bond. The aromatic ketone system controls many of the molecule’s electronic properties, while the bromine substituent provides a potential site for further chemical transformation.

Physicochemically, the molecule is moderately polar. The carbonyl group provides a significant dipole moment and hydrogen-bond acceptor capability, while the brominated aromatic ring contributes hydrophobic character and increased molecular polarizability. The compound lacks hydrogen bond donor groups because it contains neither hydroxyl nor amino functionalities.

Chemically, the ketone group undergoes reactions typical of aromatic ketones, including reduction to secondary alcohols, nucleophilic addition reactions, and condensation reactions involving the methyl group adjacent to the carbonyl. The α-hydrogen atoms of the acetyl methyl group can be removed under basic conditions to generate enolate intermediates, which participate in carbon–carbon bond-forming reactions.

The aryl bromide bond is also chemically significant. The carbon–bromine bond can participate in transition-metal-catalyzed coupling reactions, such as carbon–carbon or carbon–heteroatom bond formation, allowing modification of the aromatic framework. Under appropriate conditions, the bromine substituent can also undergo nucleophilic aromatic substitution, although the reactivity depends strongly on the electronic environment of the ring.

The aromatic ring itself retains the stability characteristic of benzene derivatives and can undergo electrophilic aromatic substitution reactions. The acetyl group generally acts as an electron-withdrawing substituent and directs substitution toward positions influenced by its meta-directing effect, while the bromine substituent has both inductive and weak resonance effects.

Overall, 2'-bromoacetophenone is an ortho-brominated acetophenone derivative containing a conjugated aromatic ketone and an aryl bromide functional group. Its polarized carbonyl group, halogen substituent, and sterically influenced ortho arrangement determine its physical properties and chemical reactivity, making it a useful intermediate in aromatic organic synthesis.

References

2025. Bioreduction of N-(3-oxobutyl)heterocycles with flexible ring by yeast whole-cell biocatalysts. Applied Microbiology and Biotechnology.
DOI: 10.1007/s00253-025-13486-2

2025. Asymmetric Reductive Heck Cyclization of 3-(Adamantan-1-yl)-1-(2-bromophenyl)prop-2-en-1-one: Highly Enantioselective Synthesis of 3-(Adamantan-1-yl)indan-1-one. Russian Journal of Organic Chemistry.
DOI: 10.1134/s1070428024604023

2025. Annulation of 2-Bromophenyl Methyl Ketones with 2-Aminobenzohydrazides. Science of Synthesis.
URL: https://science-of-synthesis.thieme.com/app/text/?id=SD-116-01442