Valerophenone: Reactivity and Safety

General Description

Valerophenone is an aromatic ketone with significant photoreactive properties, especially in aqueous environments, where it undergoes Norrish type reactions that involve the formation of a 1,4-biradical upon photoexcitation. The interaction with water alters its excited states, contributing to a long triplet lifetime of 52 ns. Despite the computational models aligning with experimental results regarding its reactivity, discrepancies in absolute quantum yield values indicate a need for further study. Safety considerations are crucial, as valerophenone can cause skin and eye irritation, necessitating protective measures. Regulatory oversight, such as REACH, ensures safe usage in formulations, highlighting the importance of compliance in industrial and consumer applications.

Figure 1. Valerophenone

Reactivity

Photoreactivity

Valerophenone is a significant aromatic ketone that exhibits unique photoreactive properties, particularly under aqueous conditions. Research has shown that valerophenone undergoes Norrish type reactions, where photochemical behavior is influenced by solvent interactions. When valerophenone interacts with water, intermolecular hydrogen bonds form, leading to a blue shift in the n,pi* excited states. In contrast, the Coulomb interaction between the valerophenone and water causes red shifts in the pi,pi* excited states. This intriguing dynamic makes the (3)pi pi* state the lowest triplet state in valerophenone, contributing to its notably long triplet lifetime. ¹

Norrish Type Reactions

The Norrish type II reactions of valerophenone demonstrate its reactivity through the formation of a 1,4-biradical upon photoexcitation. The free energy perturbation (FEP) method, integrating quantum mechanics (QM) and molecular mechanics (MM), has been utilized to study these reactions. Notably, the α C-C bond cleavages are not in competition with the 1,5-H shift, highlighting the efficiency of these pathways in valerophenone. The experimental quantum yield results support these findings, indicating nearly complete efficiency upon irradiation in specific wavelength ranges. The prediction of a triplet lifetime of 52 ns aligns with the computational models, showcasing the reliability of the methods used to analyze valerophenone's behavior. ²

Implications of Valerophenone's Reactivity

The unique response of valerophenone to photonic stimuli has far-reaching implications in photochemistry and material science. The interactions between valerophenone, water, and the resultant biradical formations significantly impact the branching ratios of the subsequent reactions, such as cyclization or further molecular cleavage. This adds complexity to the understanding of valerophenone's pathways during photoreactivity. Although computational predictions align closely with experimental observations, there remains a discrepancy in the absolute quantum yield values for the reactions, indicating a need for further exploration in the photophysical characteristics of valerophenone. This ongoing research on valerophenone will enhance our understanding of photochemical processes and could lead to advancements in related applications.

Safety

Safety Considerations

Valerophenone is a chemical compound that poses various safety considerations, notably in terms of its irritant properties. According to hazard classifications, Valerophenone is identified as causing skin irritation (Skin Irrit. 2) and eye irritation (Eye Irrit. 2A). These classifications indicate that exposure to Valerophenone can lead to significant adverse effects, necessitating the use of appropriate personal protective equipment when handling this substance. Precautionary measures should be taken to prevent skin and eye contact, as these are the primary routes of irritation associated with Valerophenone. ³

Regulatory Compliance

The European Chemicals Agency (ECHA) recognizes Valerophenone as an active substance under the REACH regulation, which mandates comprehensive safety evaluations for chemical substances. This regulatory oversight ensures that users of Valerophenone are aware of its safety implications and compliance requirements. Furthermore, while Valerophenone may be utilized in various formulations, it is subject to specific restrictions and guidelines. For instance, it does not have an individual approval for use as a standalone chemical in New Zealand; instead, it can only be incorporated as a component in products covered by a group standard. Thus, proper understanding and adherence to regulatory guidelines are essential for the safe use of Valerophenone in industrial and consumer products. ³

Reference

1. Ding L, Shen L, Chen XB, Fang WH. Solvent effects on photoreactivity of valerophenone: a combined QM and MM study. J Org Chem. 2009 Dec 4; 74(23): 8956-8962.

2. Shen L, Fang WH. The reactivity of the 1,4-biradical formed by Norrish type reactions of aqueous valerophenone: a QM/MM-based FEP study. J Org Chem. 2011 Feb 4; 76(3): 773-779.

3. National Center for Biotechnology Information (2024). PubChem Compound Summary for CID 66093, Valerophenone.

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