2-Chloro-2,2-Difluoroacetophenone: Properties & Applications

2-Chloro-2,2-difluoroacetophenone is a versatile α-halo ketone building block bearing both chlorine and two fluorine atoms on the carbonyl-adjacent carbon, making it a valuable electrophilic reagent in the synthesis of fluorinated heterocycles, pharmaceuticals, and agrochemicals.

Chemical Name

2-Chloro-2,2-difluoroacetophenone

Molecular Formula

C8H5ClF2O

Molecular Weight

194.57 g/mol

CAS Number

1450-76-6

Functional Class

α-Halo difluoro ketone

Key Applications

Fluorinated heterocycle synthesis, pharmaceutical intermediates, agrochemical research

Storage Recommendation

Cool, dry, well-ventilated area; away from moisture and incompatible materials

Chemical Identity and Structure

2-Chloro-2,2-difluoroacetophenone (CAS 1450-76-6) belongs to the class of α-halo ketones and is distinguished by the simultaneous presence of one chlorine atom and two fluorine atoms on the carbon alpha to the carbonyl group. Its molecular formula is C₈H₅ClF₂O, with a molecular weight of approximately 194.57 g/mol. The phenyl group attached to the carbonyl provides aromatic stabilisation, while the gem-difluoro and chloro substituents on the alpha carbon confer significant electrophilic reactivity at that centre.

The trifluoromethyl-like electronic environment created by the CClF₂ motif strongly withdraws electron density from the carbonyl, increasing electrophilicity and facilitating nucleophilic addition or substitution reactions. This structural feature is exploited extensively in organofluorine synthesis, where the introduction of fluorine atoms is known to modulate lipophilicity, metabolic stability, and bioavailability of drug candidates.

Synthesis and Reactivity

2-Chloro-2,2-difluoroacetophenone can be accessed through electrophilic fluorination or halogenation strategies applied to acetophenone derivatives. One classical route involves the reaction of phenacyl-type precursors with appropriate fluorinating agents or through chlorodifluoromethylation of benzaldehyde derivatives followed by oxidation. The compound is also obtainable via the reaction of difluorocarbene sources with benzoyl chloride-type substrates under controlled conditions.

In terms of reactivity, the alpha carbon bearing both halogens is highly susceptible to nucleophilic displacement. Nitrogen, oxygen, and sulfur nucleophiles can attack this site, enabling access to a wide range of α-difluoro ketone derivatives. The chlorine atom is generally more labile than the fluorines under standard nucleophilic substitution conditions, allowing selective mono-substitution while retaining the gem-difluoro unit. This chemoselectivity makes the compound particularly attractive for the stepwise construction of complex fluorinated architectures.

Applications in Research and Industry

The compound serves as a key building block in multiple research domains. In medicinal chemistry, the difluoromethyl ketone motif present after selective chlorine displacement is a recognised bioisostere for carboxylic acids and amides, and has been incorporated into protease inhibitor scaffolds and other bioactive molecules. Fluorine substitution at metabolically vulnerable positions can extend the half-life of drug candidates significantly.

In agrochemical research, α-halo difluoro ketones are employed as intermediates for fungicides and insecticides where fluorinated moieties enhance activity and environmental persistence profiles. Additionally, 2-Chloro-2,2-difluoroacetophenone is utilised in the preparation of fluorinated heterocyclic systems such as oxazoles, thiazoles, and triazoles by condensation with appropriate bifunctional nucleophiles, broadening its utility in heterocyclic chemistry.

Material science and polymer research also benefit from organofluorine building blocks such as this compound, where the introduction of fluorine into polymers can alter surface energy, chemical resistance, and thermal stability.

Handling, Safety, and Storage

As an α-haloketone, 2-Chloro-2,2-difluoroacetophenone is a reactive electrophile and should be handled with appropriate care. It is expected to be a lachrymator and skin/eye irritant; personal protective equipment including chemical-resistant gloves, safety goggles, and a laboratory coat should be worn at all times during handling. All manipulations should be performed in a well-ventilated fume hood to avoid inhalation of vapours.

The compound should be stored in a tightly sealed container in a cool, dry, and well-ventilated area, away from moisture, strong bases, and reducing agents, which can react with the electrophilic alpha carbon or the carbonyl group. Incompatibility with nucleophilic reagents should be considered during storage and waste disposal planning. Disposal must follow institutional and local regulatory guidelines for halogenated organic waste.

Note: Users should consult the current Safety Data Sheet (SDS) for this product prior to use for complete hazard, first-aid, and disposal information.

Frequently asked questions

What makes 2-Chloro-2,2-difluoroacetophenone useful in medicinal chemistry?

The compound contains a gem-difluoro ketone motif that, after selective displacement of the chlorine atom by nitrogen or oxygen nucleophiles, provides difluoromethyl ketone pharmacophores recognised as bioisosteres for carboxylic acids and amides. This structural feature can improve the metabolic stability and membrane permeability of drug candidates, making the compound a strategic building block for medicinal chemists.

How should 2-Chloro-2,2-difluoroacetophenone be stored to maintain stability?

It should be stored in a tightly sealed container under cool, dry, and well-ventilated conditions, away from moisture, strong bases, and nucleophilic reagents that could react with the electrophilic alpha carbon. Following the storage guidelines on the product label and current SDS is strongly recommended.

Can 2-Chloro-2,2-difluoroacetophenone be used to synthesise fluorinated heterocycles?

Yes. The compound reacts with bifunctional nucleophiles such as thioureas, amidines, and hydroxylamine derivatives to yield fluorinated five-membered heterocycles including thiazoles, oxazoles, and related systems. The retained gem-difluoro group in these products imparts unique electronic and physicochemical properties to the heterocyclic products.

What personal protective equipment is recommended when handling this compound?

Chemical-resistant gloves, safety goggles, and a laboratory coat are the minimum recommended PPE. Because the compound is expected to be a lachrymator and respiratory irritant, all handling must be conducted inside a fume hood. Consult the current SDS for full PPE and emergency response guidance.

Is 2-Chloro-2,2-difluoroacetophenone selective in nucleophilic substitution reactions?

Under standard nucleophilic substitution conditions, the chlorine atom on the alpha carbon is considerably more labile than the two fluorine atoms, allowing selective mono-substitution while preserving the gem-difluoro unit. This chemoselectivity is a key synthetic advantage that enables step-wise functionalisation of the molecule.

References

1. Meanwell, N. A. Fluorine and fluorinated motifs in the design and application of bioisosteres for drug design. Journal of Medicinal Chemistry, 2018.
2. O'Hagan, D. Understanding organofluorine chemistry. An introduction to the C–F bond. Chemical Society Reviews, 2008.
3. Gouverneur, V.; Seppelt, K. Introduction: Special Issue on Fluorine Chemistry. Chemical Reviews, 2015.

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