4'-Aminoacetophenone: Properties, Uses & Lab Guide

4'-Aminoacetophenone is a bifunctional aromatic compound bearing both a primary amine and a ketone group on a para-substituted benzene ring, making it a versatile and widely used building block in organic synthesis, pharmaceutical research, and dye chemistry.

CAS Number

99-92-3

Molecular Formula

C₈H₉NO

Molecular Weight

135.17 g/mol

Appearance

Light yellow to yellow crystalline powder

Melting Point

106–109 °C

Solubility

Soluble in ethanol, DMSO, and common organic solvents; sparingly soluble in water

Storage Condition

Store at room temperature, away from light and moisture, in a tightly sealed container

Chemical Identity and Physical Properties

4'-Aminoacetophenone (CAS 99-92-3), also known as para-aminoacetophenone or 4-acetylaniline, is a low-molecular-weight aromatic compound with the molecular formula C₈H₉NO and a molecular weight of 135.17 g/mol. Its structure features a benzene ring substituted at the para position with an amino group (–NH₂) at C-4 and an acetyl group (–COCH₃) at C-1.

The compound typically appears as a light yellow to yellow crystalline solid with a melting point in the range of 106–109 °C. It is moderately stable under ambient conditions but should be protected from prolonged exposure to light, heat, and moisture to prevent oxidative degradation or discoloration of the free amine. 4'-Aminoacetophenone is soluble in polar organic solvents such as ethanol, methanol, acetone, and DMSO, and has limited solubility in water, which is relevant for solution preparation in biological assays.

The coexistence of the electron-donating amino group and the electron-withdrawing carbonyl group on the same aromatic ring creates a push–pull electronic system that influences its UV absorption profile and reactivity, and makes it detectable by standard UV spectroscopy in the range of 280–310 nm.

Synthesis Routes and Reactivity

4'-Aminoacetophenone is most commonly prepared by the nitration of acetophenone to yield 4'-nitroacetophenone, followed by catalytic hydrogenation or chemical reduction (e.g., using iron/acetic acid or tin/hydrochloric acid) to afford the corresponding amine. The para selectivity in nitration is favored by the directing effect of the acetyl group. Alternatively, Friedel–Crafts acylation of acetanilide followed by hydrolysis provides another classical route.

The molecule's dual functionality makes it highly reactive in a range of transformations. The primary amine participates in diazotization reactions to form diazonium salts, which are key intermediates in azo dye synthesis. It undergoes acylation and sulfonylation to produce amide and sulfonamide derivatives, and condenses with aldehydes or ketones to form Schiff bases (imines), which are valuable scaffolds in medicinal chemistry.

The ketone moiety is amenable to nucleophilic addition, Baeyer–Villiger oxidation to yield 4-aminophenyl acetate, aldol-type condensations, and reductive amination. These diverse reaction pathways underline the compound's importance as a synthetic precursor.

Applications in Research and Industry

Pharmaceutical and Medicinal Chemistry: 4'-Aminoacetophenone serves as a key intermediate in the synthesis of a wide range of bioactive molecules. Its Schiff base derivatives have been investigated for antimicrobial, antifungal, anti-inflammatory, and anticancer activities. The scaffold is also employed in the preparation of heterocyclic compounds such as benzimidazoles, quinolines, and pyrimidines through condensation reactions with appropriate reagents.

Dye and Pigment Industry: Through diazotization and subsequent azo coupling, 4'-aminoacetophenone is converted into azo dyes used in textile and leather applications. The ketone group can also serve as an anchor for further chromophore modification.

Agrochemical Synthesis: Certain herbicide and pesticide intermediates incorporate the 4-aminoacetophenone moiety, and it has been used in the synthesis of sulfonyl urea-type compounds.

Analytical Chemistry: The compound has been explored as a derivatizing agent for carbonyl compounds and as a spectrophotometric reagent owing to its chromophoric properties.

Materials Science: Its use in the preparation of conducting polymers and as a monomer in polyimide synthesis has been reported in the literature.

Safe Handling, Storage, and Regulatory Notes

Hazard Classification: 4'-Aminoacetophenone is classified as an irritant. It may cause irritation to the skin, eyes, and respiratory tract upon contact or inhalation of dust. It is not currently listed as a carcinogen by major regulatory bodies (IARC, NTP) at the time of writing; however, standard laboratory precautions for aromatic amines should be observed.

Personal Protective Equipment (PPE): Always wear appropriate chemical-resistant gloves (nitrile recommended), safety goggles, and a laboratory coat when handling this compound. Work in a well-ventilated area or fume hood, particularly when weighing out powders, to minimize inhalation exposure.

Storage: Store in a tightly sealed container at room temperature (15–25 °C), away from direct light, heat sources, and moisture. Keep away from strong oxidizing agents, strong acids, and strong bases. Shelf life is typically adequate for at least 2 years under proper storage conditions.

Disposal: Dispose of waste material in accordance with local, regional, and national regulations governing aromatic amine-containing waste. Do not pour into drains or waterways.

First Aid: In case of skin or eye contact, flush thoroughly with water for at least 15 minutes. If inhaled, move to fresh air immediately. Seek medical attention as appropriate.

Preparation Tips for Common Laboratory Uses

Stock Solution Preparation: Due to limited water solubility, prepare stock solutions in DMSO or ethanol first (e.g., 100 mM), then dilute into aqueous buffer as required. Ensure the final DMSO concentration in biological assays does not exceed 0.1–0.5% (v/v) to avoid solvent-related cytotoxicity artifacts.

Weighing: Use a closed powder-transfer protocol when weighing to minimize dust generation. Tare the container beforehand and handle in a fume hood.

Reaction Setup for Schiff Base Synthesis: Dissolve 4'-aminoacetophenone in ethanol, add equimolar aldehyde, and stir with a catalytic amount of acetic acid at reflux or room temperature depending on the aldehyde reactivity. Monitor by TLC (silica gel, ethyl acetate/hexane system).

Diazotization: Cool a solution of 4'-aminoacetophenone in dilute HCl to 0–5 °C using an ice bath, then add sodium nitrite solution dropwise with stirring. Verify completion with starch–iodide paper before proceeding to coupling. Diazonium solutions should be used immediately and not stored.

Analytical Grade Verification: Confirm purity by HPLC (C18 column, acetonitrile/water gradient) and identity by ¹H NMR (characteristic NH₂ broad singlet ~5.7 ppm, COCH₃ singlet ~2.5 ppm, aromatic protons 6.6 and 7.7 ppm in DMSO-d₆).

Frequently asked questions

What solvents are recommended for dissolving 4'-Aminoacetophenone?

4'-Aminoacetophenone dissolves readily in polar organic solvents including DMSO, ethanol, methanol, and acetone. For biological applications, prepare a concentrated stock in DMSO and dilute into aqueous media, keeping the final DMSO content below 0.5% (v/v).

What are the main chemical reactions of 4'-Aminoacetophenone?

The primary amine group undergoes diazotization, acylation, sulfonylation, and Schiff base formation, while the ketone moiety participates in nucleophilic addition, reductive amination, aldol-type condensations, and Baeyer–Villiger oxidation. This dual reactivity makes it an exceptionally versatile synthetic building block.

How should 4'-Aminoacetophenone be stored to ensure maximum shelf life?

Store in a tightly sealed container at room temperature (15–25 °C), away from light, moisture, heat, and strong oxidizers. Under these conditions, the compound typically remains stable for at least two years. Yellowing or darkening of the solid may indicate oxidation of the amine group.

Is 4'-Aminoacetophenone the same as 4-acetylaniline?

Yes. 4'-Aminoacetophenone, para-aminoacetophenone, and 4-acetylaniline are all synonymous names for the same compound with CAS number 99-92-3. The primed notation (4') refers to the para position on the phenyl ring relative to the carbonyl carbon.

What safety precautions are needed when handling 4'-Aminoacetophenone?

Wear nitrile gloves, safety goggles, and a lab coat, and work in a fume hood to avoid inhaling dust. The compound is classified as an irritant. Although not currently listed as a carcinogen, standard precautions for aromatic amines should be observed, and waste should be disposed of per local regulations.

References

1. March, J. Advanced Organic Chemistry: Reactions, Mechanisms, and Structure. 4th ed. Wiley-Interscience, 1992.
2. Clayden, J.; Greeves, N.; Warren, S. Organic Chemistry. 2nd ed. Oxford University Press, 2012.
3. PubChem Compound Summary for CAS 99-92-3, 4'-Aminoacetophenone. National Library of Medicine. https://pubchem.ncbi.nlm.nih.gov/compound/4-Aminoacetophenone
4. Sigma-Aldrich / Merck Product Data Sheet for 4'-Aminoacetophenone, CAS 99-92-3.

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