Benzyl chloride
Encyclopedia
Benzyl chloride, or α-chlorotoluene, is an organic compound
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...

 with the formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....

 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
Toluene
Toluene, formerly known as toluol, is a clear, water-insoluble liquid with the typical smell of paint thinners. It is a mono-substituted benzene derivative, i.e., one in which a single hydrogen atom from the benzene molecule has been replaced by a univalent group, in this case CH3.It is an aromatic...

 with chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...

:
C6H5CH3 + Cl2 → C6H5CH2Cl + HCl

In this way, approximately 100,000 tonnes are produced annually. The reaction proceeds via free radical
Free radical halogenation
In organic chemistry, free-radical halogenation is a type of halogenation. This chemical reaction is typical of alkanes and alkyl-substituted aromatics under application of heat or UV light. The reaction is used for the industrial synthesis of chloroform , dichloromethane , and hexachlorobutadiene...

, involving the intermediacy of the chlorine atoms. Side products of the reaction include benzal chloride
Benzal chloride
Benzal chloride is an organic compound with the formula C6H5CHCl2. This colourless liquid is a lachrymator and is used as a building block in organic synthesis....

 and benzotrichloride
Benzotrichloride
Benzotrichloride, also known as trichlorotoluene is an organic compound with the formula C6H5CCl3. It is principally used as an intermediate in the preparation of other chemical products such as dyes.-Production and uses:...

.

Other methods exist, such as the Blanc chloromethylation
Blanc chloromethylation
The Blanc chloromethylation is the chemical reaction of aromatic rings with formaldehyde and hydrogen chloride catalyzed by zinc chloride to form chloromethyl arenes.-References:# Gustave Louis Blanc Bull. Soc. Chim. France 1923, 33, 313....

 of benzene
Benzene
Benzene is an organic chemical compound. It is composed of 6 carbon atoms in a ring, with 1 hydrogen atom attached to each carbon atom, with the molecular formula C6H6....

. Benzyl chloride was first prepared from treatment of benzyl alcohol
Benzyl alcohol
Benzyl alcohol is an organic compound with the formula C6H5CH2OH. The benzyl group is often abbreviated "Bn", 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...

 with hydrochloric acid
Hydrochloric acid
Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....

.

Uses and reactions

Industrially, benzyl chloride is the precursor to benzyl esters which are used as plasticizer
Plasticizer
Plasticizers or dispersants are additives that increase the plasticity or fluidity of the material to which they are added; these include plastics, cement, concrete, wallboard, and clay. Although the same compounds are often used for both plastics and concretes the desired effects and results are...

, flavorants, and perfumes. Phenylacetic acid
Phenylacetic acid
Phenylacetic acid is an organic compound containing a phenyl functional group and a carboxylic acid functional group. It is a white solid with a disagreeable odor...

, a precursor to pharmaceuticals, arises via benzyl cyanide, which is generated by treatment of benzyl chloride with sodium cyanide. Quaternary ammonium salts, used as surfactant
Surfactant
Surfactants are compounds that lower the surface tension of a liquid, the interfacial tension between two liquids, or that between a liquid and a solid...

s, are readily formed by alkylation of tertiary amines with benzyl chloride.

In organic synthesis
Organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...

, benzyl chloride is used for the introduction of the benzyl
Benzyl
In organic chemistry, benzyl is the term used to describe the substituent or molecular fragment possessing the structure C6H5CH2-. Benzyl features a benzene ring attached to a CH2 group.-Nomenclature:...

 protecting group
Protecting group
A protecting group or protective group is introduced into a molecule by chemical modification of a functional group in order to obtain chemoselectivity in a subsequent chemical reaction...

 for alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....

s, yielding the corresponding benzyl ether, and carboxylic acid
Carboxylic acid
Carboxylic acids are organic acids characterized by the presence of at least one carboxyl group. The general formula of a carboxylic acid is R-COOH, where R is some monovalent functional group...

s, yielding the corresponding benzyl ester. Benzoic acid
Benzoic acid
Benzoic acid , C7H6O2 , is a colorless crystalline solid and the simplest aromatic carboxylic acid. The name derived from gum benzoin, which was for a long time the only source for benzoic acid. Its salts are used as a food preservative and benzoic acid is an important precursor for the synthesis...

 (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
DEA list of chemicals
The United States Drug Enforcement Administration maintains lists regarding not only the classification of illicit drugs . It also maintains List I of chemicals and List II of chemicals, which contain chemicals which are used to manufacture the controlled substances/illicit drugs...

 drug precursor chemical by the US Drug Enforcement Administration
Drug Enforcement Administration
The Drug Enforcement Administration is a federal law enforcement agency under the United States Department of Justice, tasked with combating drug smuggling and use within the United States...

.

Benzyl chloride also reacts readily with metallic magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...

 to produce a Grignard Reagent. It is preferable over benzyl bromide
Benzyl bromide
Benzyl bromide, or α-bromotoluene, is an organic compound consisting of a benzene ring substituted with a bromomethyl group. It can be prepared by the bromination of toluene at room temperature in air, using manganese oxide as a heterogeneous catalyst...

 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
Bibenzyl
Bibenzyl is an aromatic chemical compound that can be considered a derivative of ethane in which one phenyl group is attached to each carbon atom....

.

Safety

Benzyl chloride is an alkylating agent. Indicative of its high reactivity (relative to alkyl chlorides), benzyl chloride reacts with water in a hydrolysis
Hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...

 reaction to form benzyl alcohol
Benzyl alcohol
Benzyl alcohol is an organic compound with the formula C6H5CH2OH. The benzyl group is often abbreviated "Bn", 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...

 and hydrochloric acid
Hydrochloric acid
Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....

. Since benzyl chloride is quite volatile
Volatility (chemistry)
In chemistry and physics, volatility is the tendency of a substance to vaporize. Volatility is directly related to a substance's vapor pressure. At a given temperature, a substance with higher vapor pressure vaporizes more readily than a substance with a lower vapor pressure.The term is primarily...

 at room temperature, it can easily reach the mucous membranes where the hydrolysis takes place with production of hydrochloric acid
Hydrochloric acid
Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....

. This explains why benzyl chloride is a lachrymator
Lachrymatory agent
Tear gas, formally known as a lachrymatory agent or lachrymator , is a non-lethal chemical weapon that stimulates the corneal nerves in the eyes to cause tears, pain, and even blindness...

 and has been used as a war gas
Chemical warfare
Chemical warfare involves using the toxic properties of chemical substances as weapons. This type of warfare is distinct from Nuclear warfare and Biological warfare, which together make up NBC, the military acronym for Nuclear, Biological, and Chemical...

. It is also very irritating to the skin.
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