Benzophenone

This article is about the parent chemical. For the sunscreening-agent derivatives, see benzophenone-n.

Benzophenone is a naturally occurring organic compound with the formula (C₆H₅)₂CO, generally abbreviated Ph₂CO. Benzophenone has been found in some fungi, fruits and plants, including grapes.^[4] It is a white solid with a low melting point and rose-like odor^[5] that is soluble in organic solvents. Benzophenone is the simplest diaromatic ketone. It is a widely used building block in organic chemistry, being the parent diarylketone.^{[citation needed]}

Benzophenone

Names
Preferred IUPAC name Diphenylmethanone[1]
Other names Benzophenone[1] Phenyl ketone Diphenyl ketone Benzoylbenzene Benzoylphenyl
Identifiers
CAS Number	119-61-9 Y
3D model (JSmol)	Interactive image
Beilstein Reference	1238185
ChEBI	CHEBI:41308 Y
ChEMBL	ChEMBL90039 Y
ChemSpider	2991 Y
DrugBank	DB01878 Y
ECHA InfoCard	100.003.943
EC Number	204-337-6
Gmelin Reference	4256
KEGG	C06354 Y
PubChem CID	3102
RTECS number	DI9950000
UNII	701M4TTV9O Y
UN number	1224
CompTox Dashboard (EPA)	DTXSID0021961
InChI InChI=1S/C13H10O/c14-13(11-7-3-1-4-8-11)12-9-5-2-6-10-12/h1-10H Y Key: RWCCWEUUXYIKHB-UHFFFAOYSA-N Y InChI=1/C13H10O/c14-13(11-7-3-1-4-8-11)12-9-5-2-6-10-12/h1-10H Key: RWCCWEUUXYIKHB-UHFFFAOYAX
SMILES O=C(c1ccccc1)c2ccccc2
Properties
Chemical formula	C13H10O
Molar mass	182.222 g·mol−1
Appearance	White solid
Odor	Geranium-like[2]
Density	1.11 g/cm3[2]
Melting point	48.5 °C (119.3 °F; 321.6 K)[2]
Boiling point	305.4 °C (581.7 °F; 578.5 K)[2]
Solubility in water	Insoluble[2]
Solubility in organic solvents	1 g/7.5 mL in ethanol[2] 1 g/6 mL in diethyl ether.[2] Alkanes + tetrachloromethane: better with increasing tetrachloromethane content[3]
Magnetic susceptibility (χ)	-109.6·10−6 cm3/mol
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	Harmful (XN)
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H373, H411
Precautionary statements	P260, P273, P314, P391, P501
NFPA 704 (fire diamond)	1 1 0
Flash point	110 °C (230 °F; 383 K)
Safety data sheet (SDS)	External MSDS by Sigma-Aldritch
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

History

Carl Graebe of the University of Königsberg, in an early literature report from 1874, described working with benzophenone.^[5]

Uses

Benzophenone can be used as a photo initiator in ultraviolet (UV)-curing applications^[6] such as inks, imaging, and clear coatings in the printing industry. Benzophenone prevents UV light from damaging scents and colors in products such as perfumes and soaps.

Benzophenone can also be added to plastic packaging as a UV blocker to prevent photo-degradation of the packaging polymers or its contents. Its use allows manufacturers to package the product in clear glass or plastic (such as a PETE water bottle).^[7] Without it, opaque or dark packaging would be required.

In biological applications, benzophenones have been used extensively as photophysical probes to identify and map peptide–protein interactions.^[8]

Benzophenone is used as an additive in flavorings or perfumes for "sweet-woody-geranium-like notes."^[9]

Synthesis

Benzophenone is produced by the copper-catalyzed oxidation of diphenylmethane with air.^[10]

A laboratory route involves the reaction of benzene with carbon tetrachloride followed by hydrolysis of the resulting diphenyldichloromethane.^[11] It can also be prepared by Friedel–Crafts acylation of benzene with benzoyl chloride in the presence of a Lewis acid (e.g. aluminium chloride) catalyst: since benzoyl chloride can itself be produced by the reaction of benzene with phosgene the first synthesis proceeded directly from those materials.^[12]

Another route of synthesis is through a palladium(II)/oxometalate catalyst. This converts an alcohol to a ketone with two groups on each side.^[13]

Another, less well-known reaction to produce benzophenone is the pyrolysis of anhydrous calcium benzoate.^[14]

Organic chemistry

The Haller–Bauer reaction occurs between a non-enolizable ketone and a strong amide base. In this prototypical example involving benzophenone, the tetrahedral intermediate expels phenyl anion to give benzamide and benzene as the organic products.

Benzophenone is a common photosensitizer in photochemistry. It crosses from the S₁ state into the triplet state with nearly 100% yield. The resulting diradical will abstract a hydrogen atom from a suitable hydrogen donor to form a ketyl radical.

Benzophenone radical anion

Main article: Air-free technique

Addition of a solution of benzophenone in THF to a vial containing THF, sodium metal, and a stir bar, yielding the deep blue benzophenone anion radical. Playback speed 4x original recording. Notice that the stirbar is not Teflon-coated, which would be attacked by the ketyl.

A solvent pot containing dibutyl ether solution of sodium benzophenone ketyl, which gives it its purple color.

Alkali metals reduce benzophenone to the deeply blue colored radical anion, diphenylketyl:^[15]

M + Ph₂CO → M⁺Ph₂CO^•−

Generally sodium is used as the alkali metal. Sodium-benzophenone ketyl is used in the purification of organic solvents, particularly ethers, because it reacts with water and oxygen to give non-volatile products.^[16][17] Adsorbents such as alumina, silica gel, and especially molecular sieves are superior and far safer.^[18] The sodium-benzophenone method is common since it gives a visual indication that water, oxygen, and peroxides are absent from the solvent. Large scale purification may be more economical using devices which utilize adsorbents such as the aforementioned alumina or molecular sieves.^[19] The ketyl is soluble in the organic solvent being dried, which leads to faster purification. In comparison, sodium is insoluble, and its heterogeneous reaction is much slower. When excess alkali metal is present a second reduction may occur, resulting in a color transformation from deep blue to purple:^[15]

M + M⁺Ph₂CO^•− → (M⁺)₂(Ph₂CO)²⁻

Commercially significant derivatives and analogues

There are over 300 natural benzophenones, with great structural diversity and biological activities. They are being investigated as potential sources of new drugs. ^[20] Substituted benzophenones such as oxybenzone and dioxybenzone are used in many sunscreens. The use of benzophenone-derivatives which structurally resemble a strong photosensitizer has been criticized (see sunscreen controversy).

Michler's ketone has dimethylamino substituents at each para position. The high-strength polymer PEEK is prepared from derivatives of benzophenone.

2-Amino-5-chlorobenzophenone is used in the synthesis of benzodiazepines.^[21]

Safety

It is considered "essentially nontoxic."^[10] Benzophenone is however banned as a food additive by the US Food and Drug Administration, despite the FDA's continuing stance that this chemical does not pose a risk to public health under the conditions of its intended use.^[22][23]

The European Union permits it as a flavouring substance,^[24] having established a Total Dietary Intake of 0.3mg/kg of body weight per day.^[25]

Benzophenone derivatives are known to be pharmacologically active. From a molecular chemistry point of view interaction of benzophenone with B-DNA has been demonstrated experimentally.^[26] The interaction with DNA and the successive photo-induced energy transfer is at the base of the benzophenone activity as a DNA photosensitizer and may explain part of its therapeutic potentialities.

In 2014, benzophenones were named Contact Allergen of the Year by the American Contact Dermatitis Society.^[27]

Benzophenone is an endocrine disruptor capable of binding to the pregnane X receptor.^[28]

References

1. "Front Matter". Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. pp. 723–724, 726. doi:10.1039/9781849733069-FP001. ISBN 978-0-85404-182-4.
2. Merck Index (11th ed.). p. 1108.
3. Azizian, Saeid; Haydarpour, Afshin (November 2003). "Solubility of Benzophenone in Binary Alkane + Carbon Tetrachloride Solvent Mixtures". Journal of Chemical & Engineering Data. 48 (6): 1476–1478. doi:10.1021/je0340497.
4. Surana, Khemchand; Chaudhary, Bharatkumar; Diwaker, Monika; Sharma, Satyasheel (2018). "Benzophenone: a ubiquitous scaffold in medicinal chemistry". MedChemComm. 9 (11): 1803–1817. doi:10.1039/C8MD00300A. ISSN 2040-2503. PMC 6238883. PMID 30542530.
5. "Molecule of the Week Archive: Benzophenone". American Chemical Society. 11 March 2024. Retrieved 20 May 2024.
6. Carroll, G.T.; Turro, N.J.; Koberstein, J.T. (2010). "Patterning dewetting in thin polymer films by spatially directed photocrosslinking". Journal of Colloid and Interface Science. 351 (2): 556–560. Bibcode:2010JCIS..351..556C. doi:10.1016/j.jcis.2010.07.070. PMID 20728089.
7. Dornath, Paul John (2010). "Analysis of Chemical Leaching from Common Consumer Plastic Bottles Under High Stress Conditions" (PDF). p. 32. Archived from the original (PDF) on 26 February 2015. Retrieved 26 February 2015.
8. Dorman, Gyorgy; Prestwich, Glenn D. (1 May 1994). "Benzophenone Photophores in Biochemistry". Biochemistry. 33 (19): 5661–5673. doi:10.1021/bi00185a001. PMID 8180191.
9. Arctander, Steffen. Perfume And Flavor Chemicals: (Aroma Chemicals).
10. Siegel, Hardo; Eggersdorfer, Manfred. "Ketones". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a15_077. ISBN 978-3527306732.
11. Marvel, C. S.; Sperry, W. M. (1941). "Benzophenone". Organic Syntheses; Collected Volumes, vol. 1, p. 95.
12. "Synthesis of benzoic acid and benzophenone". Journal of the Chemical Society, Abstracts. 34: 69–70. 1878. doi:10.1039/CA8783400019.
13. Dornan, L.; Muldoon, M. (2015). "A highly efficient palladium(II)/polyoxometalate catalyst system for aerobic oxidation of alcohols". Catalysis Science & Technology. 5 (3): 1428–1432. doi:10.1039/c4cy01632g.
14. Lee, C. C. (1953). "The Mechanism of the Ketonic Pyrolysis of Calcium Carboxylates". The Journal of Organic Chemistry. 18 (9): 1079–1086. doi:10.1021/jo50015a003.
15. Connelly, Neil; Geiger, William (28 March 1996). "Chemical Redox Agents for Organometallic Chemistry". Chemical Reviews. 96 (2): 877–910. doi:10.1021/cr940053x. PMID 11848774.
16. Armarego, W. L. F.; Chai, C. (2003). Purification of laboratory chemicals. Oxford: Butterworth-Heinemann. ISBN 978-0-7506-7571-0.
17. Harwood, L. M.; Moody, C. J.; Percy, J. M. (1999). Experimental Organic Chemistry: Standard and Microscale. Oxford: Blackwell Science. ISBN 978-0-632-04819-9.
18. Williams, D. B. G.; Lawton, M. (2010). "Drying of Organic Solvents: Quantitative Evaluation of the Efficiency of Several Desiccants". The Journal of Organic Chemistry. 75 (24): 8351–4. doi:10.1021/jo101589h. PMID 20945830. S2CID 17801540.
19. Simas, Alessandro B. C.; Pereira, Vera L. P.; Barreto Jr., Cleber B.; Sales, Daniel L. de; Carvalho, Leandro L. de (2009). "An expeditious and consistent procedure for tetrahydrofuran (THF) drying and deoxygenation by the still apparatus". Química Nova. 32 (9): 2473–2475. doi:10.1590/S0100-40422009000900042. ISSN 0100-4042.
20. Wu, Shi-Biao; Long, Chunlin; Kennelly, Edward J. (2014). "Structural diversity and bioactivities of natural benzophenones". Nat. Prod. Rep. 31 (9): 1158–1174. doi:10.1039/C4NP00027G. ISSN 0265-0568. PMID 24972079.
21. Massah, Ahmad R.; Gharaghani, Sajjad; Lordejani, Hamid Ardeshiri; Asakere, Nahad (1 August 2016). "New and mild method for the synthesis of alprazolam and diazepam and computational study of their binding mode to GABAA receptor". Medicinal Chemistry Research. 25 (8): 1538–1550. doi:10.1007/s00044-016-1585-z. ISSN 1554-8120.
22. "FDA Bans Use of 7 Synthetic Food Additives After Environmental Groups Sue". NPR.org. Retrieved 9 October 2018.
23. 83 FR 50490
24. Risk management approach for benzophenone (Report). Health Canada. January 2001.
25. Silano, Vittorio; et al. (14 November 2017). "Safety of benzophenone to be used as flavouring". EFSA Journal. 15 (11): e05013. doi:10.2903/j.efsa.2017.5013. hdl:2164/9927. PMC 7010149. PMID 32625332.
26. Consuelo Cuquerella, M.; Lhiaubet-Vallet, V.; Cadet, J.; Miranda, M. A. (2012). "Benzophenone Photosensitized DNA Damage". Acc. Chem. Res. 45 (9): 1558–1570. doi:10.1021/ar300054e. PMID 22698517.
27. Doug Brunk (14 March 2014). "Benzophenones named 2014 Contact Allergen of the Year : Dermatology News". Skinandallergynews.com. Archived from the original on 22 March 2016. Retrieved 16 June 2016.
28. Mikamo, Eriko; Harada, Shingo; Nishikawa, Jun-Ichi; Nishihara, Tsutomu (2003). "Endocrine disruptors induce cytochrome P450 by affecting transcriptional regulation via pregnane X receptor". Toxicology and Applied Pharmacology. 193 (1): 66–72. Bibcode:2003ToxAP.193...66M. doi:10.1016/j.taap.2003.08.001. PMID 14613717.