Benzyl chloride

Description

Benzyl chloride is an effective electrophile used in organic chemistry for introducing benzyl groups. Benzyl chloride can be used for the benzyl protection of amines and alcohols, however this is more commonly performed with benzyl bromide.

Description

Benzyl chloride is a colorless to slight yellowliquid with a strong, unpleasant, irritating odor. The odorthreshold is 0.05 ppm. Molecular weight = 126.6;Specific gravity (H2O:1) = 1.10; Boiling point = 179.4℃;Freezing/Melting point = -43℃; Vapor pressure =1 mmHg at 20℃; Flash point = 67℃ (cc); Autoignitiontemperature = 585℃. Flammable Limits in Air:LEL =5 1.1%; UEL=14.0%.Hazard Identification(based on NFPA-704 M Rating System): Health 3,Flammability 2, Reactivity 1. Practically insoluble in water;solubility=0.05%.

Chemical properties

Benzyl chloride is a colorless to s lightly yellow liquid with a strong, unpleasant, irritating odor. The Odor Threshold is 0.05 ppm.The stabilized form of benzyl chloride contains a fixed amount of a sodium carbonate solution or propylene oxide.

Physical properties

Colorless to pale yellowish-brown liquid with a pungent, aromatic, irritating odor. Odor threshold concentration is 47 ppbv (Leonardos et al., 1969). Katz and Talbert (1930) reported an experimental detection odor threshold concentration of 210 μg/m3 (41 ppbv). The solubility of benzyl chloride in water is 0.33 g/L at 4°C, 0.49 g/L at 20°C, and 0.55 g/L at 30°C. It is freely soluble in chloroform, acetone, acetic acid esters, diethyl ether, and ethyl alcohol.

The Uses of Benzyl chloride

Benzyl chloride is used to manufacture benzyl Compounds, dyes, artificial resins, tanning agents, pharmaceuticals, plasticizers, synthetic tannins, perfumes, lubricants, and quaternary ammonium compounds. It is also an intermediate in preparing phenylacetic acid (precursor to phamaceuticals). Benzyl chloride has been used as an irritant gas in chemical warfare.

Definition

ChEBI: Benzyl chloride is a member of the class of benzyl chlorides that is toluene substituted on the alpha-carbon with chlorine.

Preparation

Benzyl chloride is the starting material for a large number of industrial syntheses. The first preparation of it involved not the chlorination of toluene, however, but the reaction of benzyl alcohol with hydrochloric acid (S. Cannizzaro, 1853). Today, most side-chain chlorination of toluene to produce benzyl chloride. Dibenzyl ether is formed as a byproduct in the alkaline hydrolysis of benzyl chloride to benzyl alcohol. This ether can be re-converted to benzyl chloride by cleavage with hydrogen chloride at a temperature below 100°C.

Production Methods

Benzyl chloride can be synthesized by chloromethylation of benzene in the presence of a catalyst (ZnCl2) or by treatment of benzyl alcohol with SO2Cl2. Commercially it is produced by chlorination of boiling toluene in the presence of light.

What are the applications of Application

Benzyl chloride is used mainly to produce plasticizers (e.g., benzyl butyl phthalate), benzyl alcohol, and phenylacetic acid via benzyl cyanide (used in the production of synthetic penicillin). On a smaller scale, it is used to produce quaternary ammonium salts (for disinfectants and phase-transfer catalysts), benzyl esters (benzyl benzoate and benzyl acetate for the flavors and perfumes industry), dyes of the triphenylmethane series, dibenzyl disulfide (antioxidant for lubricants), benzylphenol, and benzylamines.

Reactions

Benzyl chloride can be oxidized to benzoic acid or benzaldehyde, or substituted to give the halogenated, sulfonated or nitrated product.With NH3 it yields mono-, di- or tribenzyl amine. With alcohols in base the benzylalkyl ether is formed. With phenols either the phenolic or nuclear hydrogens can react to give benzylaryl ether or benzylated phenols. Reaction with NaCN gives benzyl cyanide (phenylacetonitrile); with aliphatic primary amines the product is the N-alkylbenzylamine, and with aromatic primary amines N-benzylaniline is formed. Benzyl chloride is converted to butyl benzyl phthalate plasticizer and other chemicals.

Synthesis Reference(s)

The Journal of Organic Chemistry, 29, p. 3692, 1964 DOI: 10.1021/jo01035a504
Synthetic Communications, 16, p. 1173, 1986 DOI: 10.1080/00397918608056363
Tetrahedron Letters, 29, p. 5783, 1988 DOI: 10.1016/S0040-4039(00)82191-7

General Description

Benzyl chloride appears as a colorless liquid with an irritating odor. Toxic by inhalation and skin absorption. Flash point 153°F. Slightly soluble in water. Corrosive to metals and tissue. A lachrymator. Density 9.2 lb /gal.

Air & Water Reactions

A lachrymator. Slightly soluble in water.

Reactivity Profile

Halogenated aliphatic compounds, such as Benzyl chloride, are moderately or very reactive. Reactivity generally decreases with increased degree of substitution of halogen for hydrogen atoms. Materials in this group are incompatible with strong oxidizing and reducing agents. Also, they are incompatible with many amines, nitrides, azo/diazo compounds, alkali metals, and epoxides.

Hazard

Highly toxic, intense eye and skin irritant. A lachrymator. Upper respiratory tract irritant. Prob- able carcinogen.

Health Hazard

Benzyl chloride is a corrosive liquid. Con tact with the eyes can cause corneal injury.Exposure to its vapors can produce intenseirritation of the eyes, nose, and throat. Highconcentrations may cause lung edema anddepression of the central nervous system.Flury and Zernik (1931) stated that exposureto 16 ppm for 1 minute was intolerable tohumans. The LC50 values for a 2-hour expo sure in mice and rats are 80 and 150 ppm,respectively. The subcutaneous LD50 valuein rats is 1000 mg/kg (NIOSH 1986).
Benzyl chloride tested positive to thehistidine reversion–Ames test for mutagenic ity. Subcutaneous administration of this com pound in laboratory animals caused tumors atthe site of application.

Health effects

A concentration of 16 ppm of benzyl chloride in air is reported to be intolerable to humans within 1 min. The compound is a potent lachrymator, strongly irritating to the eyes, nose, and throat and capable of causing lung edema.

Fire Hazard

Benzyl chloride burns but does not ignite readily. Benzyl chloride may ignite combustibles. When heated to decomposition, Benzyl chloride emits toxic and corrosive fumes. Some organic chlorides decompose to yield phosgene. Incompatible with active metals such as copper, aluminum, magnesium, iron, zinc, and tin and keep from strong oxidizing agents. Avoid contact with acids or acid fumes. Keep separate from oxidizing materials. May become unstable at elevated temperatures and pressures; may react with water resulting in some nonviolent release of energy. Polymerizes with evolution of heat and hydrogen chloride when in contact with all common metals except nickel and lead.

Toxicology

The acute oral toxicity (LD50) of benzyl chloride in rats is 1231 mg/kg and in mice 1624 mg/kg. The subcutaneous LD50 (in rats) of benzyl chloride in oil solution is 1000 mg/kg. Exposure of rats and mice to benzyl chloride concentrations of 100 –1000 mg/m3 for 2 h caused irritation of the mucous membranes and conjunctivitis, vol. 11. Benzyl chloride is a strong skin-sensitizing agent for guinea pigs . Benzyl chloride acts weakly mutagenic in validated test systems. Subcutaneous injection of weekly doses of 80 mg/kg for 1 year followed by a post-observation period resulted in local sarcomas with lung metastases in rats. The mean induction time was 500 d. After dermal application of benzyl chloride, skin carcinomas were observed in mice.

Potential Exposure

Used as an intermediate and as an irritant gas in chemical warfare. In contrast to phenyl halides, benzyl halides are very reactive. Benzyl chloride is used in production of benzal chloride, benzyl alcohol, and benzaldehyde. Industrial usage includes the manufacture of benzyl compounds, cosmetics, dyes, plastics, synthetic tannins, perfumes and resins. It is used in the manufacture of many pharmaceuticals. Suggested uses of benzyl chloride include: the vulcanization of fluororubbers and the benzylation of phenol and its derivatives for the production of possible disinfectants.

First aid

If this chemical gets into the eyes, remove anycontact lenses at once and irrigate immediately for at least15 min, occasionally lifting upper and lower lids. Seekmedical attention immediately. If this chemical contactsthe skin, remove contaminated clothing and wash immediately with soap and water. Seek medical attention immediately. If this chemical has been inhaled, remove fromexposure, begin rescue breathing (using universal precautions, including resuscitation mask) if breathing hasstopped and CPR if heart action has stopped. Transferpromptly to a medical facility. When this chemical hasbeen swallowed, get medical attention. If victim is conscious,administer water or milk. Do not induce vomiting.Medical observation is recommended for 24
48 h afterbreathing overexposure, as pulmonary edema may bedelayed. As first aid for pulmonary edema, a doctor orauthorized paramedic may consider administering a corticosteroid spray.

Toxicity

Benzyl chloride is used as a chemical intermediate in manufacturing certain dyes and pharmaceutical products and as a photographic developer. The acute (short-term) effects of benzyl chloride from inhalation exposure in humans consist of severe irritation of the upper respiratory tract, skin, eyes, and mucous membranes, and lung damage along with pulmonary edema (fluid in lungs). Exposure to high concentrations also causes effects on the central nervous system (CNS). Animal data indicate that long-term exposure to benzyl chloride by gavage (placing it experimentally in the stomachs of mice) increased the incidence of benign and malignant tumours at multiple sites and resulted in a significant increase in thyroid tumours in female rats. EPA has classified benzyl chloride as a Group B2, probable human carcinogen.

Carcinogenicity

Benzyl chloride caused genetic mutations and chromosome-damaging effects in a wide variety of in vitro assays; it was not mutagenic in vivo in the mouse micronucleus assay

Source

As of October 1996, benzyl chloride was listed for regulation but no MCLGs or MCLs have been proposed (U.S. EPA, 1996).
Reported as an impurity (≤ 0.05 wt %) in 98.5 wt % benzyl mercpatan (Chevron Phillips, April 2005).

Environmental Fate

Biological. When incubated with raw sewage and raw sewage acclimated with hydrocarbons, benzyl chloride degraded forming nonchlorinated products (Jacobson and Alexander, 1981).
Chemical/Physical. Anticipated products from the reaction of benzyl chloride with ozone or OH radicals in the atmosphere are chloromethyl phenols, benzaldehyde and chlorine radicals (Cupitt, 1980).
Slowly hydrolyzes in water forming HCl and benzyl alcohol. The estimated hydrolysis half-life in water at 25 °C and pH 7 is 15 h (Mabey and Mill, 1978). The hydrolysis rate constant for benzyl chloride at pH 7 and 59.2 °C was determined to be 0.0204/min, resulting in a half-life of 34 min (Ellington et al., 1986).
May polymerize in contact with metals except nickel and lead (NIOSH, 1997).
When heated to decomposition, hydrogen chloride gas may be released (CHRIS, 1984).

storage

Color Code—Blue: Health Hazard/Poison: Storein a secure poison location. This material should be storedin tightly closed containers in a cool, well-ventilated areaaway from sunlight, heat, moisture, active metals, oxidizers.Metal containers involving the transfer of this chemicalshould be grounded and bonded. Where possible, automatically pump liquid from drums or other storage containers toprocess containers. Drums must be equipped with selfclosing valves, pressure vacuum bungs, and flame arresters.Use only nonsparking tools and equipment, especially whenopening and closing containers of this chemical. Sources ofignition, such as smoking and open flames, are prohibitedwhere this chemical is used, handled, or stored in a mannerthat could create a potential fire or explosion hazard. A regulated, marked area should be established where this chemical is handled, used, or stored in compliance with OSHAStandard 1910.1045.

Shipping

UN1738 Benzyl chloride, Hazard class: 6.1; Labels: 6.1—Poisonous materials, 8—Corrosive material.

Purification Methods

Dry it with MgSO4 or CaSO4, or reflux it with fresh Ca turnings, then fractionally distil it under reduced pressure, collecting the middle fraction and storing it over CaH2 or P2O5. It has also been purified by passage through a column of alumina. Alternatively it is dried over MgSO4 and distilled in a vacuum. The middle fraction is degassed by several freeze-thaw cycles and then fractionated in an 'isolated fractionating column' (which has been evacuated and sealed off at ~10-6 mm) over a steam bath. The middle fraction is retained. The final samples are distilled in a vacuum from this sample and again retaining the middle fraction. The purity is >99.9% (no other peaks are visible by GLC, and the NMR spectrum is consistent with the structure. [Mohammed & Kosower J Am Chem Soc 93 1709 1971, Beilstein 5 IV 809.] IRRITANT and strongly LACHRYMATORY.

Incompatibilities

May form explosive mixture with air. Contact with water forms hydrogen chloride fumes. Strong oxidizers may cause fire and explosions. Unstabilized benzyl chloride undergoes polymerization with copper, aluminum, iron, zinc, magnesium, tin, and other common metals except lead and nickel, with the liberation of heat and hydrogen chloride gas. May accumulate static electrical charges, and may cause ignition of its vapors. Attacks some plastics and rubber. Thermal decomposition and polymerization reactions are inhibited, to a limited extent, by addition of triethylamine, propylene oxide, or sodium carbonate.

Waste Disposal

Incineration @ 816 C for 0.5 second minimum for primary combustion and 1204 C for 12.0 second for secondary combustion. Elemental chlorine formation may be alleviated by injection of steam or methane into the combustion process.