Benzyl alcohol

Benzyl alcohol is an aromatic alcohol with the formula C6H5CH2OH. The benzyl group is often abbreviated "Bn" (not to be confused with "Bz" which is used for benzoyl), thus benzyl alcohol is denoted as BnOH. Benzyl alcohol is a colorless liquid with a mild pleasant aromatic odor. It is a useful solvent due to its polarity, low toxicity, and low vapor pressure. Benzyl alcohol has moderate solubility in water (4 g/100 mL) and is miscible in alcohols and diethyl ether. The anion produced by deprotonation of the alcohol group is known as benzylate or benzyloxide.

Benzyl alcohol
Names
Preferred IUPAC name
Phenylmethanol
Other names
Phenylcarbinol
Benzenemethanol
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.002.600
EC Number
  • 202-859-9
E number E1519 (additional chemicals)
KEGG
RTECS number
  • DN3150000
UNII
Properties[1]
C7H8O
Molar mass 108.140 g·mol−1
Appearance Colorless liquid
Odor Slightly aromatic
Density 1.044 g cm−3
Melting point −15.2 °C (4.6 °F; 257.9 K)
Boiling point 205.3 °C (401.5 °F; 478.4 K)
3.50 g/100 mL (20 °C)
4.29 g/100 mL (25 °C)
Solubility in other solvents Soluble in benzene, methanol, chloroform, ethanol, ether, acetone
log P 1.10
Vapor pressure 0.18 kPa (60 °C)
Acidity (pKa) 15.40
−71.83·10−6 cm3/mol
1.5396
Viscosity 5.474 cP
1.67 D
Thermochemistry
217.8 J/(K·mol)
−352 kJ/mol
Pharmacology
P03AX06 (WHO)
Hazards
Safety data sheet External MSDS
NFPA 704 (fire diamond)
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g. canola oilHealth code 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
1
1
0
Flash point 93 °C (199 °F; 366 K)
436 °C (817 °F; 709 K)
Explosive limits 1.3–13%
Lethal dose or concentration (LD, LC):
1250 mg/kg (rat, oral)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

Natural occurrences

Benzyl alcohol is produced naturally by many plants and is commonly found in fruits and teas. It is also found in a variety of essential oils including jasmine, hyacinth and ylang-ylang.[2] It is also found in castoreum from the castor sacs of beavers.[3]

Preparation

Benzyl alcohol is produced industrially from toluene via benzyl chloride, which is hydrolyzed:

C6H5CH2Cl + H2O → C6H5CH2OH + HCl

Another route entails hydrogenation of benzaldehyde, a by-product of the oxidation of toluene to benzoic acid.[4]

For laboratory use, Grignard reaction of phenylmagnesium bromide (C6H5MgBr) with formaldehyde and the Cannizzaro reaction of benzaldehyde also give benzyl alcohol. The latter also gives benzoic acid, an example of an organic disproportionation reaction.

Reactions

Like most alcohols, it reacts with carboxylic acids to form esters. In organic synthesis, benzyl esters are popular protecting groups because they can be removed by mild hydrogenolysis.[5]

Benzyl alcohol reacts with acrylonitrile to give N-benzylacrylamide. This is an example of a Ritter reaction:[6]

C6H5CH2OH + NCCHCH2 → C6H5CH2N(H)C(O)CHCH2

Applications

Benzyl alcohol is used as a general solvent for inks, waxes, shellacs, paints, lacquers, and epoxy resin coatings. Thus it can be used in paint strippers, especially when combined with compatible viscosity enhancers to encourage the mixture to cling to painted surfaces.[7]

It is a precursor to a variety of esters and ethers, used in the soap, perfume, and flavor industries. E.g. benzyl benzoate, benzyl salicylate, benzyl cinnamate, dibenzyl ether, benzyl butyl phthalate.

It is also used in e-liquid for e-cigarettes to enhance the flavors used. When applied to damaged skin or mucous membranes at a 10% concentration, it acts as a local anesthetic and antimicrobial agent. It can be utilized as a degreaser in rug cleaning products. As a dye solvent, it enhances the process of dying wool, nylon, and leather.[8] It also has use as a photographic film developer and as an insect repellent.

Use in health care

Benzyl alcohol is used as a bacteriostatic preservative at low concentration in intravenous medications, cosmetics, and topical drugs.[9] Some caution is necessary if a high percent of Benzyl alcohol is used as benzaldehyde arises from benzyl alcohol when used as preservative in an injectable formulation solution. [10][11]

Benzyl alcohol, sold under the brand name Ulesfia, was approved by the U.S. Food and Drug Administration (FDA) in 2009, as a 5% solution for the treatment of head lice in people 6 months of age and older.[12] It affects the louse's spiracles, preventing them from closing.[12] These then become clogged with water or mineral oil or other matter and cause the insect to die from asphyxiation.[12]

Benzyl alcohol is used effectively for treating lice infestations as the active ingredient in lotion shampoo with 5% benzyl alcohol.[12]

Other uses

Benzyl alcohol has nearly the same refraction index as quartz and wool fiber. If a clear quartz object is immersed in benzyl alcohol, it becomes almost invisible. This test has been used to determine non-destructively whether an object is truly made of quartz. Similarly, white wool immersed in benzyl alcohol also becomes almost invisible, clearly revealing contaminants such as dark and medullated fibers and vegetable matter.

Contact dermatitis
Illustration of allergic contact dermatitis

Benzyl alcohol is an ingredient used in the manufacture of soaps, topical creams, skin lotions, shampoos, and facial cleansers and is popular due to its anti-bacterial and anti-fungal properties. It is a common ingredient in a variety of household products and can cause severe allergic contact dermatitis in a significant percentage of the population.[13][14][15][16]

Safety

Benzyl alcohol has low acute toxicity with an LD50 of 1.2 g/kg in rats.[4] It oxidizes rapidly in healthy individuals to benzoic acid, conjugated with glycine in the liver, and excreted as hippuric acid. Very high concentrations can result in toxic effects including respiratory failure, vasodilation, hypotension, convulsions, and paralysis.

Benzyl alcohol is toxic to neonates and is associated with the gasping syndrome.[17][18]

Benzyl alcohol is severely toxic and highly irritating to the eye.[4] Pure benzyl alcohol produces corneal necrosis.[19]

Benzyl alcohol is not considered to be a carcinogen, and no data are available regarding teratogenic or reproductive effects.[4]

References
  1. "Benzyl alcohol". Archived from the original on 26 July 2009.
  2. The Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals (11th ed.), Merck, 1989, ISBN 091191028X, 1138
  3. Dietland Muller-Schwarze (2003). The Beaver: Its Life and Impact. p. 43. ISBN 9780801450105.
  4. Friedrich Brühne; Elaine Wright (2007). "Benzyl Alcohol". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a04_001.
  5. Furuta, Kyoji; Gao, Qing-Zhi; Yamamoto, Hisashi (1995). "Chiral (Acyloxy)borane Complex-Catalyzed Asymmetric Diels-Alder Reaction: (1R)-1,3,4-Trimethyl-3-Cyclohexene-1-Carboxaldehyde". Organic Syntheses. 72: 86.; Collective Volume, 9, p. 722
  6. Parris, Chester L. (1962). "N-benzylacrylamide". Organic Syntheses. 42: 16.; Collective Volume, 5, p. 73
  7. Benzyl alcohol, chemicalland21.com, archived from the original on 21 April 2009, retrieved 14 May 2006
  8. Michael Ash; Irene Ash (2004). Handbook of Preservatives. Synapse Info Resources. p. 292. ISBN 978-1-890595-66-1.
  9. DOI: 10.2116/analsci.27.865
  10. DOI: 10.2116/analsci.27.865
  11. DOI: 10.1016/j.jpba.2006.02.028
  12. "Ulesfia- benzyl alcohol lotion". DailyMed. 8 April 2019. Retrieved 27 April 2020.
  13. EJ Curry; EM Warshaw (2005), "Benzyl alcohol allergy: importance of patch testing with personal products.", Dermatitis (16): 203–8
  14. "NACDG Allergen: Benzyl Alcohol - The Dermatologist". www.the-dermatologist.com.
  15. "Benzyl Alcohol - Allergic Contact Dermatitis Database". www.contactdermatitisinstitute.com.
  16. Fisher, A. A. (1 October 1975). "Allergic paraben and benzyl alcohol hypersensitivity relationship of the "delayed" and "immediate" varieties". Contact Dermatitis. 1 (5): 281–284. doi:10.1111/j.1600-0536.1975.tb05436.x. PMID 139248. S2CID 29204040.
  17. Carl R. Baum (2008), "Examples of mass exposures involving the pediatric population", in Jerrold B. Leikin; Frank P. Paloucek (eds.), Poisoning and Toxicology Handbook (4th ed.), Informa, p. 726.
  18. Juan Gershanik; et al. (1982), "The gasping syndrome and benzyl alcohol poisoning", N Engl J Med, 307 (22): 1384–8, doi:10.1056/nejm198211253072206, PMID 7133084.
  19. Swarupa G. Kulkarni; Harihara M. Mehendale (2005), "Benzyl Alcohol", Encyclopedia of Toxicology, 1 (2nd ed.), Elsevier, pp. 262–264.
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