Acyl Bromide

Definition

Acyl bromides are a class of organic compounds that contain an acyl functional group (derived from a carboxylic acid by replacing the hydroxyl group with a halogen) directly attached to a bromine atom. The general formula for an acyl bromide is RCOBr, where R is an alkyl or aryl group and COBr represents the acyl bromide functionality[5][16].

Preparation

Acyl bromides can be prepared by reacting carboxylic acids with phosphorus tribromide (PBr3). For example, acetyl bromide, a specific acyl bromide, can be synthesized by the reaction of acetic acid with PBr3, as shown in the following equation:

\[ 3 CH_3COOH + PBr_3 \rightarrow 3 CH_3COBr + H_3PO_3 \]

This reaction yields acetyl bromide and phosphorous acid (H3PO3) as a byproduct[6]. Another method involves the reaction of carboxylic acids with bromine in the presence of a catalyst[7].

Reactions

Acyl bromides are highly reactive and can undergo various chemical reactions due to the presence of the electron-withdrawing bromine atom, which makes the carbonyl carbon more susceptible to nucleophilic attack. Some common reactions include:

• Hydrolysis: Acyl bromides react with water to form carboxylic acids and hydrobromic acid[6].
• Reaction with alcohols: They react with alcohols to form esters[6].
• Reaction with amines: They react with amines to produce amides[6].
• Friedel-Crafts Acylation: Acyl bromides can react with aromatic compounds in the presence of a Lewis acid catalyst to form aromatic ketones[5].
• Reduction: Acyl bromides can be reduced to alcohols using reducing agents like lithium aluminum hydride (LiAlH4)[11].

Uses

Acyl bromides are used as intermediates in organic synthesis due to their high reactivity. They are involved in the synthesis of various chemical compounds, including:

• Esters and amides, which are important in the production of pharmaceuticals and polymers[6].
• Aromatic ketones, which are used in the manufacture of dyes and fragrances[5].
• Acetyl bromide is specifically used to mediate reactions like the Nazarov cyclization, which is important in the synthesis of complex organic molecules[4].

In summary, acyl bromides are versatile reagents in organic chemistry, used to synthesize a wide range of chemical compounds. Their preparation typically involves the reaction of carboxylic acids with phosphorus tribromide or bromine, and they participate in numerous reactions due to their high reactivity.

Citations:

[1] https://www.merriam-webster.com/dictionary/acetyl%20bromide

[2] https://pubs.acs.org/doi/pdf/10.1021/ja01858a502

[3] https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Map:_Organic_Chemistry_(Wade)_Complete_and_Semesters_I_and_II/Map:_Organic_Chemistry_(Wade)/22:_Carboxylic_Acid_Derivatives_and_Nitriles/22.04:_Acid_Halide_Chemistry

[4] https://www.sigmaaldrich.com/US/en/product/aldrich/135968

[5] https://en.wikipedia.org/wiki/Acyl_halide

[6] https://en.wikipedia.org/wiki/Acetyl_bromide

[7] https://www.masterorganicchemistry.com/2020/09/30/the-hell-volhard-zelinsky-reaction/

[8] https://www.sciencedirect.com/topics/chemistry/acyl-halide

[9] https://pubchem.ncbi.nlm.nih.gov/compound/Acetyl-bromide

[10] https://patents.google.com/patent/CN104529745A/en

[11] https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Organic_Chemistry_(Morsch_et_al.)/21:_Carboxylic_Acid_Derivatives-_Nucleophilic_Acyl_Substitution_Reactions/21.04:_Chemistry_of_Acid_Halides

[12] https://www.spectrumchemical.com/acetyl-bromide-tci-a0080

[13] https://www.nj.gov/health/eoh/rtkweb/documents/fs/0012.pdf

[14] https://www.tandfonline.com/doi/abs/10.1080/10426509508042564

[15] https://www.organic-chemistry.org/namedreactions/hell-volhard-zelinsky-reaction.shtm

[16] https://www.wordnik.com/words/acyl%20bromide

[17] https://journals.iupui.edu/index.php/ias/article/view/5210

[18] https://youtube.com/watch?v=EjwUzk42XCA

[19] https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Supplemental_Modules_(Organic_Chemistry)/Acid_Halides/Properties_of_Acyl_Halides

[20] https://pubs.acs.org/doi/10.1021/ja01858a502

[21] https://study.com/academy/lesson/acyl-group-definition-structure.html

[22] https://patents.google.com/patent/CN104086403A/en

[23] https://www.definitions.net/definition/acyl+bromide

[24] https://www.prepchem.com/synthesis-of-acetyl-bromide/