Avobenzone

History

Avobenzone was patented in 1973 and was approved in the EU in 1978. It was approved by the FDA in 1988. As of 2021, the FDA announced that they do not support avobenzone as being generally recognized as safe and effective (GRASE) citing the need for additional safety data. Avobenzone was banned in 2020 by the Palau government citing reef-toxicity concerns.

Properties

Pure avobenzone is a whitish to yellowish crystalline powder with a weak odor, dissolving in isopropanol, dimethyl sulfoxide, decyl oleate, capric acid/caprylic, triglycerides and other oils. It is not soluble in water.

Avobenzone is a dibenzoylmethane derivative. Avobenzone exists in the ground state as a mixture of the enol and keto forms, favoring the chelated enol.{{cite journal

Safety

Avobenzone is not generally recognised as safe and effective (GRASE) by the FDA for lack of sufficient data to support this claim. However, it is still the only FDA approved UVA filter (up to 3% concentration). Avobenzone is also approved in all other jurisdictions, such as EU (up to 5%), Australia, and Japan.

A 2017 study at Lomonosov Moscow State University found that chlorinated water and ultraviolet light can cause avobenzone to disintegrate into various other organic compounds, including; phenolic acids, aldehydes, phenols, and acetophenones which can cause adverse health effects.

Stability

Avobenzone is sensitive to the properties of the solvent, being relatively stable in polar protic solvents and unstable in nonpolar environments. Also, when it is irradiated with UVA light, it generates a triplet excited state in the keto form which can either cause the avobenzone to degrade or it can transfer energy to biological targets and cause deleterious effects.

Avobenzone has been shown to degrade significantly in light, resulting in less protection over time.[[Image:Free text.png]] {{cite journal| title = Changes in ultraviolet absorption of sunscreens after ultraviolet irradiation| date = October 1999| pmid=10504439| vauthors = Tarras-Wahlberg N, Stenhagen G, Larko O, Rosen A, Wennberg AM, Wennerstrom O

• 4-Methylbenzylidene camphor (USAN Enzacamene)
• Tinosorb S (USAN Bemotrizinol, INCI Bis-Ethylhexyloxyphenol Methoxyphenyl Triazine)
• Tinosorb M (USAN Bisoctrizole, INCI Methylene Bis-Benzotriazolyl Tetramethylbutylphenol)
• Butyloctyl Salicylate (Tradename HallBrite BHB - https://web.archive.org/web/20111002150609/http://www.hallstar.com/pis.php?product=12231)
• Hexadecyl Benzoate
• Butyloctyl Benzoate
• HallBrite PSF (INCI Undecylcrylene DimethiconeE)
• Mexoryl SX (USAN Ecamsule, INCI Terephthalylidene Dicamphor Sulfonic Acid)
• Synoxyl HSS (INCI Trimethoxybenzylidene Pentanedione)RK Chaudhuri, MA Ollengo, P Singh and BS Martincigh, 3-(3,4,5-Trimethoxybenzylidene)-2,4-pentanedione: Design of a Novel Photostabilizer with In-vivo SPF Boosting Properties and Its Use in Developing Broad-spectrum Sunscreen Formulations, International Journal of Cosmetic Science, 39(1):25-35, 2017; First published 29 June 2016 | doi: 10.1111/ics.12344
• Corapan TQ (INCI Diethylhexyl 2,6-Naphthalate)
• Parsol SLX (INCI Polysilicone-15)
• Oxynex ST (INCI Diethylhexyl Syringylidene Malonate{{cite journal
• Polycrylene (INCI Polyester-8)
• SolaStay S1 (INCI Ethylhexyl Methoxycrylene)
• Octyl Salicylate (INCI Ethylhexyl Salicylate)

Complexing avobenzone with cyclodextrins may also increase its photostability.{{cite journal

The photostability of avobenzone is further increased when sunscreens are formulated with antioxidant compounds. Mangiferin, glutathione, ubiquinone, vitamin C, vitamin E, beta-carotene and trans-resveratrol have all demonstrated some ability to protect avobenzone from photodegradation. The stability and efficacy of avobenzone seems to continue to increase as a greater amount of antioxidants are added to the sunscreen.

According to some studies, "the most effective sunscreens contain avobenzone and titanium dioxide."{{cite journal |access-date=2007-06-03 |archive-url=https://web.archive.org/web/20070226040442/https://www.fda.gov/cder/otcmonographs/Sunscreen/sunscreen_avobenzone_enforc_policy_19970420.pdf |archive-date=2007-02-26 |url-status=dead

Various

As an enolate, avobenzone forms with heavy metal ions (such as Fe3+) colored complexes, and chelating agents can be added to suppress them. Stearates, aluminum, magnesium and zinc salts can lead to poorly soluble precipitates. Manufacturers also recommend to avoid the inclusion of iron and ferric salts, heavy metals, formaldehyde donors and PABA and PABA esters.

Avobenzone in sunscreen may stain clothes yellow-orange and make them sticky if washed in iron-rich water, as it reacts with iron to produce rust. The damage can be undone with a rust remover or stain remover. The staining properties of sunblock made with avobenzone are particularly noticeable on fiberglass boats with white gelcoat.

Avobenzone also reacts with boron trifluoride to form a stable crystalline complex that is highly fluorescent under UV irradiation. The emission color of the crystals depends on the molecular packing of the boron avobenzone complex. The photoluminescence may also be altered by mechanical force in the solid state, resulting in a phenomenon called "mechanochromic luminescence". The altered emission color recovers itself slowly at room temperature or more swiftly at higher temperatures.

Absorbance spectrum

Avobenzone has a peak absorbance around 360 nm when dissolved. The peak may shift slightly depending on the solvent.

Preparation

The compound is prepared by reacting 4-tert-butylbenzoic methyl ester (from 4-tert-butylbenzoic acid by esterification with methanol) with 4-methoxyacetophenone in toluene in the presence of sodium amide via Claisen condensation.

According to a recent patent application, yields of up to 95% are obtained with the same starting materials in toluene in the presence of potassium methoxide.

It is subject to keto-enol tautomerism and exists predominantly enol when dissolved. Upon UV radiation, it may convert to keto form, while converting back to enol form after placing in dark.

Notes

References

1. (2020). "REGULATIONS PROHIBITING REEF-TOXIC SUNSCREENS". The Palau Government.
2. "Making Cosmetics®, Avobenzone".
3. Research, Center for Drug Evaluation and. (2021-11-16). "Questions and Answers: FDA posts deemed final order and proposed order for over-the-counter sunscreen". FDA.
4. "After More Than A Decade, FDA Still Won't Allow New Sunscreens".
5. "Sunscreen creams break down into dangerous chemical compounds under the sunlight".
6. (September 2017). "Stability and removal of selected avobenzone's chlorination products". Chemosphere.
7. (2016-09-15). "Transformation of avobenzone in conditions of aquatic chlorination and UV-irradiation". Water Research.
8. (September 2001). "Photostabilization of Butyl methoxydibenzoylmethane (Avobenzone) and Ethylhexyl methoxycinnamate by Bis-ethylhexyloxyphenol methoxyphenyl triazine (Tinosorb S), a new UV broadband filter". Photochemistry and Photobiology.
9. "CTFA letter re: Tentative Final Monograph for OTC Sunscreen". Food and Drug Administration.
10. "Hallbrite® PSF".
11. Bonda C.. (2000). "A new photostabilizer for full spectrum sunscreens". Cosmetics & Toiletries.
12. "Archived copy".
13. http://www.hallstar.com/techdocs/Polycrylene&CorapanTQAvobenzoneStabilization.pdf {{dead link. (March 2024)
14. "Product Information Sheet: SolaStay S1". The HallStar Company.
15. (2021). "Synthesis of phenylalanine and leucine dipeptide functionalized silica-based nanoporous material as a safe UV filter for sunscreen". Journal of Sol-Gel Science and Technology.
16. (October 2015). "Mangiferin and naringenin affect the photostability and phototoxicity of sunscreens containing avobenzone". Journal of Photochemistry and Photobiology B: Biology.
17. (2019-01-01). "Glutathione as a photo-stabilizer of avobenzone: an evaluation under glass-filtered sunlight using UV-spectroscopy". Photochemical & Photobiological Sciences.
18. (November 2014). "Photodegradation of avobenzone: stabilization effect of antioxidants". Journal of Photochemistry and Photobiology B: Biology.
19. (2015-10-12). "Photostability evaluation of five UV-filters, trans-resveratrol and beta-carotene in sunscreens". European Journal of Pharmaceutical Sciences.
20. Stability Study of Avobenzone with Inorganic Sunscreens, ''Kobo Products Poster'', 2001, [http://www.koboproductsinc.com/Downloads/NYSCC-Avobenzone.pdf Online version] {{webarchive. link. (May 7, 2007)
21. (July 2004). "The effects of manganese doping on UVA absorption and free radical generation of micronised titanium dioxide and its consequences for the photostability of UVA absorbing organic sunscreen components". Photochem Photobiol Sci.
22. (17 August 2022). "How to Remove Summer Stains From Your Clothes". Consumer Reports.
23. (18 July 2022). "The secret to removing sunscreen stains is this unexpected cleaning product". CNN.
24. Zhang G. (February 2010). "Polymorphism and Reversible Mechanochromic Luminescence for Solid-State Difluoroboron Avobenzone". Journal of the American Chemical Society.
25. {{Patent
26. {{Patent
27. (2008). "Photostability of the sunscreening agent 4-tert-butyl-4-methoxydibenzoylmethane (avobenzone) in solvents of different polarity and proticity".