Benzyl chloride
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| IUPAC name
chlorophenylmethane
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| Other names
α-Chlorotoluene
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3D model (JSmol)
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| ECHA InfoCard | 100.002.594 | ||
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PubChem CID
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CompTox Dashboard (EPA)
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| Properties | |||
| C7H7Cl | |||
| Molar mass | 126.58 g/mol | ||
| Density | 1.100 g/cm3 | ||
| Melting point | −39 °C | ||
| Boiling point | 179 °C | ||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Benzyl chloride, or α-chlorotoluene, is an organic compound with the formula C6H5CH2Cl. This colourless liquid is a reactive organochlorine compound that is a widely used chemical building block.
Preparation
Benzyl chloride is prepared industrially by the gas-phase photochemical reaction of toluene with chlorine:[1]
- C6H5CH3 + Cl2 → C6H5CH2Cl + HCl
In this way, approximately 100,000 tonnes are produced annually. The reaction proceeds via free radical, involving the intermediacy of the chlorine atoms.[2] Side products of the reaction include benzal chloride and benzotrichloride.
Other methods exist, such as the Blanc chloromethylation of benzene. Benzyl chloride was first prepared from treatment of benzyl alcohol with hydrochloric acid.
Uses and reactions
Industrially, benzyl chloride is the precursor to benzyl esters which are used as plasticizer, flavorants, and perfumes. Phenylacetic acid, a precursor to pharmaceuticals, arises via benzyl cyanide, which is generated by treatment of benzyl chloride with sodium cyanide. Quaternary ammonium salts, used as surfactants, are readily formed by alkylation of tertiary amines with benzyl chloride.[1]
In organic synthesis, benzyl chloride is used for the introduction of the benzyl protecting group for alcohols, yielding the corresponding benzyl ether, and carboxylic acids, yielding the corresponding benzyl ester. Benzoic acid (C6H5COOH) can be prepared by oxidation of benzyl chloride in the presence of alkaline KMnO4
C6H5CH2Cl + 2 KOH + 2 [O] → C6H5COOK + KCl + H2O
It may be used in the synthesis of amphetamine-class drugs, and for this reason sales of benzyl chloride are monitored as a List II drug precursor chemical by the US Drug Enforcement Administration.
Benzyl chloride also reacts readily with metallic magnesium to produce a Grignard Reagent.[3] It is preferable over benzyl bromide for the preparation of benzylic Grignard reagent, since the reaction of the bromide with magnesium tends to form the Wurtz-coupling product 1,2-diphenylethane.
Safety
Benzyl chloride is an alkylating agent. Indicative of its high reactivity (relative to alkyl chlorides), benzyl chloride reacts with water in a hydrolysis reaction to form benzyl alcohol and hydrochloric acid. Since benzyl chloride is quite volatile at room temperature, it can easily reach the mucous membranes where the hydrolysis takes place with production of hydrochloric acid. This explains why benzyl chloride is a lachrymator and has been used as a war gas. It is also very irritating to the skin.
References
- ^ a b M. Rossberg et al. “Chlorinated Hydrocarbons” in Ullmann’s Encyclopedia of Industrial Chemistry 2006, Wiley-VCH, Weinheim. doi:10.1002/14356007.a06_233.pub2
- ^ Furniss, B. S.; Hannaford, A. J.; Smith, P. W. G.; Tatchell, A. R. (1989), Vogel's Textbook of Practical Organic Chemistry (5th ed.), Harlow: Longman, p. 864, ISBN 0-582-46236-3.
- ^ Henry Gilman and W. E. Catlin (1941). "n-Propylbenzene". Organic Syntheses; Collected Volumes, vol. 1, p. 471.
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