Benzyl chloride

Benzyl chloride, or α-chlorotoluene, is an organic compound with the formula C6H5CH2Cl. This colorless liquid is a reactive organochlorine compound that is a widely used chemical building block.

Not to be confused with benzoyl chloride.
Benzyl chloride
Benzyl chloride
Names
Preferred IUPAC name
(Chloromethyl)benzene
Other names
α-Chlorotoluene
Benzyl chloride
Identifiers
3D model (JSmol)
Abbreviations BnCl
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.002.594
EC Number
  • 202-853-6
KEGG
UNII
Properties
C7H7Cl
Molar mass 126.58 g·mol−1
Appearance Colorless to slightly yellow liquid
Odor Pungent, aromatic[1]
Density 1.100 g/cm3
Melting point −39 °C (−38 °F; 234 K)
Boiling point 179 °C (354 °F; 452 K)
very slightly soluble (0.05% at 20 °C)[1]
Solubility soluble in ethanol, ethyl ether, chloroform, CCl4
miscible in organic solvents
Vapor pressure 1 mmHg (20 °C)[1]
-81.98·10−6 cm3/mol
1.5415 (15 °C)
Hazards
Safety data sheet External MSDS
NFPA 704 (fire diamond)
Flammability code 2: Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Flash point between 38 and 93 °C (100 and 200 °F). E.g. diesel fuelHealth code 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasReactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g. calciumSpecial hazards (white): no code
2
3
1
Flash point 67 °C (153 °F; 340 K)
585 °C (1,085 °F; 858 K)
Explosive limits ≥1.1%[1]
Lethal dose or concentration (LD, LC):
1231 mg/kg (rat, oral)
150 ppm (rat, 2 hr)
80 ppm (mouse, 2 hr)[2]
380 ppm (dog, 8 hr)[2]
NIOSH (US health exposure limits):
PEL (Permissible)
 TWA 1 ppm (5 mg/m3)[1]
REL (Recommended)
 C 1 ppm (5 mg/m3) [15-minute][1]
IDLH (Immediate danger)
 10 ppm[1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Preparation

Benzyl chloride is prepared industrially by the gas-phase photochemical reaction of toluene with chlorine:[3]

C6H5CH3 + Cl2 → C6H5CH2Cl + HCl

In this way, approximately 100,000 tonnes are produced annually. The reaction proceeds by the free radical process, involving the intermediacy of free chlorine atoms.[4] Side products of the reaction include benzal chloride and benzotrichloride.

Other methods of production 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 plasticizers, flavorants, and perfumes. Phenylacetic acid, a precursor to pharmaceuticals, is produced from benzyl cyanide, which in turn 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.[3]

Benzyl ethers are often derived from benzyl chloride. Benzyl chloride reacts with aqueous sodium hydroxide to give dibenzyl ether. In organic synthesis, benzyl chloride is used to introduce the benzyl protecting group in reaction with alcohols, yielding the corresponding benzyl ether, carboxylic acids, and 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

Benzyl chloride 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.[5] It is preferable over benzyl bromide for the preparation of this 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. In contact with mucous membranes, hydrolysis produces hydrochloric acid. Thus, benzyl chloride is a lachrymator and has been used in chemical warfare. It is also very irritating to the skin.

It is classified as an extremely hazardous substance in the United States as defined in Section 302 of the U.S. Emergency Planning and Community Right-to-Know Act (42 U.S.C. 11002), and is subject to strict reporting requirements by facilities which produce, store, or use it in significant quantities.[6]

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See also

References
  1. NIOSH Pocket Guide to Chemical Hazards. "#0053". National Institute for Occupational Safety and Health (NIOSH).
  2. "Benzyl chloride". Immediately Dangerous to Life and Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  3. "Chlorinated Hydrocarbons". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a06_233.pub2.
  4. 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
  5. Henry Gilman and W. E. Catlin (1941). "n-Propylbenzene". Organic Syntheses.; Collective Volume, 1, p. 471
  6. "40 C.F.R.: Appendix A to Part 355—The List of Extremely Hazardous Substances and Their Threshold Planning Quantities" (PDF) (July 1, 2008 ed.). Government Printing Office. Archived from the original (PDF) on February 25, 2012. Retrieved October 29, 2011. Cite journal requires |journal= (help)
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