Benzophenone

Benzophenone is the organic compound with the formula (C6H5)2CO, generally abbreviated Ph2CO. It is a white solid that is soluble in organic solvents. Benzophenone is a widely used building block in organic chemistry, being the parent diarylketone.

This article is about the parent chemical. For the sunscreening-agent derivatives, see benzophenone-n.
Benzophenone
Names
Preferred IUPAC name
Diphenylmethanone[1]
Other names
Benzophenone[1]
Phenyl ketone
Diphenyl ketone
Benzoylbenzene
Benzoylphenyl
Identifiers
3D model (JSmol)
1238185
ChEBI
ChEMBL
ChemSpider
DrugBank
ECHA InfoCard 100.003.943
EC Number
  • 204-337-6
4256
KEGG
RTECS number
  • DI9950000
UNII
UN number 1224
  • InChI=1S/C13H10O/c14-13(11-7-3-1-4-8-11)12-9-5-2-6-10-12/h1-10H checkY
    Key: RWCCWEUUXYIKHB-UHFFFAOYSA-N checkY
  • InChI=1/C13H10O/c14-13(11-7-3-1-4-8-11)12-9-5-2-6-10-12/h1-10H
    Key: RWCCWEUUXYIKHB-UHFFFAOYAX
  • O=C(c1ccccc1)c2ccccc2
Properties
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]
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]
-109.6·10−6 cm3/mol
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 Harmful (XN)
GHS labelling:
GHS08: Health hazardGHS09: Environmental hazard
Warning
H373, H411
P260, P273, P314, P391, P501
NFPA 704 (fire diamond)
NFPA 704 four-colored diamond
1
1
0
Flash point 110 °C (230 °F; 383 K)
Safety data sheet (SDS) External MSDS by JT Baker
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)
Infobox references

Uses

Benzophenone can be used as a photo initiator in UV(Ultra-violet)-curing applications[4] such as inks, imaging, and clear coatings in the printing industry. Benzophenone prevents ultraviolet (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).[5] 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.[6]

Benzophenone is used as an additive in flavorings or perfumes for "sweet-woody-geranium-like notes."[7]

Synthesis

Benzophenone is produced by the copper-catalyzed oxidation of diphenylmethane with air.[8]

A laboratory route involves the reaction of benzene with carbon tetrachloride followed by hydrolysis of the resulting diphenyldichloromethane.[9] 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.[10]

Another route of synthesis is through a palladium(II)/oxometalate catalyst. This converts an alcohol to a ketone with two groups on each side.[11]

Another, less well-known reaction to produce benzophenone is the pyrolysis of anhydrous calcium benzoate.[12]

Organic chemistry

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
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:[13]

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.[14][15] Adsorbents such as alumina, silica gel, and especially molecular sieves are superior and far safer.[16] 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.[17] 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:[13]

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. [18] 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.[19]

Safety

It is considered "essentially nontoxic."[8] 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.[20][21] 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.[22] 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.[23]

Benzophenone is an endocrine disruptor capable of binding to the pregnane X receptor.[24]

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. 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.
  5. 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.
  6. Dorman, Gyorgy; Prestwich, Glenn D. (1 May 1994). "Benzophenone Photophores in Biochemistry". Biochemistry. 33 (19): 5661–5673. doi:10.1021/bi00185a001. PMID 8180191.
  7. Arctander, Steffen. Perfume And Flavor Chemicals: (Aroma Chemicals).
  8. Siegel, Hardo; Eggersdorfer, Manfred. "Ketones". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a15_077.
  9. Marvel, C. S.; Sperry, W. M. (1941). "Benzophenone". Organic Syntheses.; Collective Volume, vol. 1, p. 95
  10. "Synthesis of benzoic acid and benzophenone". Journal of the Chemical Society, Abstracts. 34: 69–70. 1878. doi:10.1039/CA8783400019.
  11. 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.
  12. 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.
  13. Connelly, Neil; Geiger, William (March 28, 1996). "Chemical Redox Agents for Organometallic Chemistry". Chemical Reviews. 96 (2): 877–910. doi:10.1021/cr940053x. PMID 11848774.
  14. Armarego, W. L. F.; Chai, C. (2003). Purification of laboratory chemicals. Oxford: Butterworth-Heinemann. ISBN 978-0-7506-7571-0.
  15. 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.
  16. 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.
  17. 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.
  18. 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.
  19. Massah, Ahmad R.; Gharaghani, Sajjad; Lordejani, Hamid Ardeshiri; Asakere, Nahad (2016-08-01). "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.
  20. "FDA Bans Use of 7 Synthetic Food Additives After Environmental Groups Sue". NPR.org. Retrieved 2018-10-09.
  21. 83 FR 50490
  22. 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.
  23. Doug Brunk (2014-03-14). "Benzophenones named 2014 Contact Allergen of the Year : Dermatology News". Skinandallergynews.com. Archived from the original on 2016-03-22. Retrieved 2016-06-16.
  24. 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. doi:10.1016/j.taap.2003.08.001. PMID 14613717.
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