CHAPTER

Literature

Survey
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1.1 INTRODUCTION

Benzyl alcohol (also known as α-cresol) is an aromatic alcohol with the formula

C6H5CH2OH. The IUPAC name of this compound is phenyl methanol. At room

temperature, benzyl alcohol exists as a colourless liquid that has a mildly aromatic smell.

When this aromatic alcohol is deprotonated, the resulting anion is called a benzylate. Benzyl

alcohol is a colourless liquid with a faint aromatic scent. Its polarity, low toxicity, and low

vapour pressure make it a useful solvent. Benzyl alcohol has modest water solubility (4

g/100 mL), and alcohol and diethyl ether are miscible. The anion formed by alcohol group

deprotonation is called benzylate, or benzyl oxide.

This compound is not very soluble in water. However, it forms miscible mixtures with

diethyl ether and other alcohols. Many plants are known to naturally produce C 6H5CH2OH.

The essential oils extracted from jasmine, ylang-ylang, and hyacinth contain some amount of

benzyl alcohol.

IUPAC Name: Phenyl methanol

Synonyms:
 Phenyl carbinol
 Benzene methanol
 Hydroxy toluene
 Benzene carbinal
 Alpha-toluenol
 Phenyl methyl alcohol

Chemical Formula: C7H8O

Molecular Weight: 108.14 g/mol

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Appearance – Colourless liquid

Natural Occurrence: Benzyl alcohol produced naturally, and it is commonly found in

fruits and teas. It is present also in a variety of essential oils like jasmine, hyacinth, and

ylang-ylang. It is also contained in the castoreum of the beaver's castor sacs.

Structure of Benzyl Alcohol

This compound consists of a hydroxyl group attached to a methyl group, which is in turn

attached to an aromatic ring. The structure of a C6H5CH2OH molecule is illustrated below.

The pi electrons in the benzene ring are delocalized due to resonance. Essentially, the

structure of a benzyl alcohol molecule is that of a toluene molecule in which one of the

hydrogen atoms has been replaced by a hydroxyl group.

Benzyl alcohol is a precursor to the drug thalidomide and is used as a reactant in chemical

synthesis. Benzyl alcohol serves as a chiral auxiliary in asymmetric synthesis, particularly

for the conversion of aldehydes to acids.

The conversion of the carbonyl group to alcohol can be accomplished through a

hydroxylation reaction, for example in the presence of rhodium hydroxide on alumina, using

N-bromosuccinimide to promote the transformation. The product formed is the benzyl

alcohol of α- or β-configuration, depending on the chiral auxiliary used. Other chiral

auxiliary compounds commonly used in the aldehyde-alcohol condensation include α-

phenyl-γ-butyrolactone, α-benzoyloxyazetidine, 1-benzyl-2-azetidine carboxylic acid, and γ-

butyrolactone. The reaction is applicable to the condensation of other aldehydes, including

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aldehydes containing enantioenriched or racemic carbon-carbon double bonds and with

carbonyl groups other than carboxyl.

Oligomerization and Polymerization

Benzyl alcohol, either in its aldehyde or hydrate form, is able to oligomerize in the presence

of excess hydrogen halides, for example, HF, to form dibenzyl ethers. Reactions are

catalyzed by a palladium or platinum complex, and the selectivity of oligomerization is

governed by the nature of the anion. Benzyl alcohol forms homopolymers in anhydrous

solvents such as benzene, and poly (2-methylbutanal) has been prepared. The monomer has

been used in solution polymerization to form poly benzyl ethers.

Benzyl alcohol can form hydrogen-bonded aggregates in the solid state, with hydroxyl

groups arranged to provide intermolecular hydrogen bonds. Oligomers have been prepared

by the condensation of benzyl alcohol and water. The oligomerization takes place by either

mechanism involving carboxylate anions or by the addition of hydrogen halides.

Benzyl alcohol polymerization with ethylene leads to polyethylene. The polymerization of

ethylene on a small scale using benzyl alcohol as a catalyst was discovered by M. O. Wallin

and J. W. Adams, in their study on polymers produced by olefins. This is a chain-growth

polymerization and is thought to be initiated by the formation of active cationic centers such

as carbocations, or by a radical mechanism. Polyethylene can be prepared by polymerizing

ethylene and benzyl alcohol, and a range of polyethylenes can be prepared by changing the

monomer ratio. Benzyl alcohol polymerization is a homogeneous catalytic process, as the

catalyst is soluble in the reaction mixture. The main advantage of benzyl alcohol

polymerization is that it is a non-migrating polymerization, which leads to a polymer with

greater purity than polymers prepared by free-radical polymerization.

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The mechanism of polymerization is thought to be initiated by a nucleophilic attack of the

alcohol onto a carbon atom of the growing chain, which in turn triggers more chain growth.

The polymer chains terminate with alcohol groups which can undergo further cyclization

reactions to form cyclohexylidene ketals or benzofuranones. Polyethylene formed by this

method is linear, having short polymer chains. Linear polyethylenes produced by this

mechanism are normally called poly(ethylene-co-1-hexene) (PE-1-hexene), as the hexene is

incorporated into the chain.

In addition to the main chain, terminal hydroxyl groups are also produced, and these undergo

cyclization reactions to form the cyclohexylidene ketals or benzofuranones. The degree of

cyclization can be controlled by the ratio of ethylene and alcohol in the feed.

Ethylene polymerization can be performed at lower temperatures (25-55 °C) compared with

typical Ziegler–Natta, and metallocene catalysts (160-350 °C), which makes it advantageous

in commercial operations. It can also be run at a lower pressure than metallocene and

Ziegler–Natta catalysts, at atmospheric pressure.

The mechanism of initiation and propagation in benzyl alcohol polymerization is still not

entirely clear. It is thought to be initiated by heterolytic cleavage of the benzyl group,

followed by cyclization to form an open-chain species. This is followed by recombination to

form a propagating polyethylene chain. This chain may be terminated by a different type of

initiation, which is thought to be the formation of a cyclic ketal, which undergoes ring

opening to form a linear polyethylene. However, many possible mechanisms are possible,

and further study is required.

It was found that for certain reactions, such as the polymerization of benzyl alcohol, the

addition of methyl bromide results in a higher initial conversion rate. This is likely due to the
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methyl bromide reacting with the alkoxy groups of the benzyl alcohol to form alkyl bromide

species.

Properties of Benzyl Alcohol-C6H5CH2OH

Chemical Data
Benzyl Alcohol C6H5CH2OH

Molar Mass 108.14 grams per mole

Density 1.044 grams per cubic centimetre

Melting Point 257.9 K (-15.2oC)

Boiling Point 478.4 K (205.3oC)

Odor : Slightly aromatic

Dipole moment- 1.67 D

Flash Point: 93.6°C

Lower Explosive Limit (LEL): 1.3 %

Upper Explosive Limit (UEL): 13 %

Autoignition Temperature: 436°C

Vapor Pressure: 0.1 mmHg at 20°C ; 1 mmHg at 58°C

Acidity(pka) – 15.40

Vapor Density (Relative to Air): 3.72 - Heavier than air; will sink

Specific Gravity: 1.05 - Denser than water; will sink

Boiling Point: 205°C at 760 mmHg

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Molecular Weight: 108.13

Water Solubility: 10 to 50 mg/mL at 21°C

Lethal Dose or Concentration:

LD50 (median dose) - 1250mg/kg (rat, oral)

Solubility in water and other solvent :

 It is soluble in water (3.50 g/100 mL (20 °C); 4.29 g/100 mL (25 °C))

 It is soluble in benzene, methanol, ether, acetone, chloroform, ethanol.

Physical Properties

 Under standard conditions, benzyl alcohol is a colourless, slightly aromatic liquid.

 This compound is soluble in several organic solvents such as benzene, methanol,

acetone, and ether.

Chemical Properties

 The reaction between carboxylic acids and benzyl alcohol leads to the formation of

esters. This interacts with carboxylic acids to form esters just like most alcohols. Benzyl

esters are common protecting groups in organic synthesis because they can be extracted

by mild hydrogenolysis.

 This compound undergoes a Ritter reaction with acrylonitrile to yield N-benzyl

acrylamide.

 When deprotonated, C6H5CH2OH yields a benzylate anion.

Preparation Methods

Benzyl Alcohol Production Process:

Benzyl alcohol is manufactured industrially from toluene via hydrolyzed benzyl chloride.
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C6H5CH2Cl+H2O → C6H5CH2OH+HCl

Another route involves benzaldehyde hydrogenation, a by-product of the toluene to benzoic

acid oxidation.

Benzyl alcohol is currently produced mainly by a chemical synthetic method from benzyl

chloride and sodium hydroxide. In the case of a chemical synthetic method, benzyl chloride

(synthetic benzyl chloride) is prepared by a Grignard reaction and then benzyl alcohol is

obtained from the synthetic benzyl chloride through reduction, hydrolysis, and

dehydrogenation.

However, in the case of a chemical synthetic method, a large amount of benzyl chloride,

which is a material that is difficult to handle, is used and, as a result, the problem of

secondary pollution is caused. An alternative to the chemical synthetic method is a

biological method.

The use of sodium hydroxide in the hydrolysis of benzyl chloride yields benzyl alcohol and

sodium chloride as the products. The chemical equation for this reaction is given by:

NaOH + C6H5CH2Cl → NaCl + C6H5CH2OH

An alternate method of preparing this compound involves the Grignard reaction between

formaldehyde (H-CHO) and phenyl magnesium bromide (Ph-Mg-Br).

Hydrolysis of benzyl chloride

The most common industrial method, this process uses alkaline saponifying agents to

combine with the hydrogen chloride that is formed.

The reaction is

C6H5CH2Cl + H2O → C6H5CH2OH + HCl.

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Hydrogenation of benzaldehyde :

This method uses benzaldehyde, a by-product of the oxidation of toluene to benzoic acid.

Microorganisms :

Microorganisms like the fungus Rhodotorula muciluginosa can be used to convert

benzaldehyde to benzyl alcohol. Engineered microorganisms can also be used to produce

benzyl alcohol from glucose.

Other methods for producing benzyl alcohol :

 Grignard reaction of phenyl magnesium bromide ( C6H5MgBr) with formaldehyde

 Cannizzaro reaction of benzaldehyde

 Hydrolysis of a benzyl ester with water in the liquid phase

Benzyl alcohol is also found naturally in many foods and plants, including apricots, snap

beans, cocoa, cranberries, mushrooms, honey, jasmine, hyacinth, and ylang-ylang.

Benzyl Alcohol is Synthesised for Laboratory Use:

Benzyl alcohol is also produced by the Grignard reaction of phenyl magnesium bromide

(C6H5MgBr) with formaldehyde and the benzaldehyde Cannizzaro reaction. The latter also

gives benzoic acid, an example of a reaction by organic disproportion.

Applications of Benzyl Alcohol

This compound is widely used as a solvent for epoxy resin coatings, inks, and paints. Some

other applications of benzyl alcohol are listed below.

 C6H5CH2OH is a precursor to several esters.

 Used in Pain management.

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 Used in Rubber Dyes..

 A solution of benzyl alcohol with a concentration of 10% can be used as a local

anaesthetic and also as an antimicrobial agent.

 This compound is a component of the fluid mixtures used in electronic cigarettes (it

enhances the flavour).

 Benzyl alcohol can serve as a dielectric solvent for the reconfiguration of some

nanowires via dielectrophoresis.

Known as Phenylethanol, is the simplest aromatic alcohol and is the primary source of

phenyl in phenol-formaldehyde resin, the primary ingredient of the lacquer industry. It is

also the most commonly used material in microencapsulation.

Benzyl alcohol is used in many chemical reactions, such as hydrogenation to produce aniline

or as a chiral auxiliary ligand for palladium complexes. It is a very important product for the

plastics industry, and for many other industries including the manufacture of caprolactam,

phenylethylamine, and phenyl methanol.

Benzyl alcohol is used as a standard in the testing of wines, in particular for the evaluation of

residual sugar in Madeira wine.

 Benzyl alcohol is used as a common solvent for the decoration of tints, waxes, shellacs,

oils, lacquers, and epoxy resin.

 Benzyl alcohol is used in intravenous medicines, cosmetics, and topical products as a

bacteriostatic preservative at low concentrations.

 5% solution of benzyl alcohol for the treatment of head lice in people 6 months of age

and older.

 It affects the spirals of the louse, preventing them from closing.

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 These then become clogged with water or mineral oil or other matter and cause

asphyxiation to cause the insect to die.

 Benzyl alcohol is commonly used as the active ingredient in lotion products containing 5

percent benzyl alcohol for curing lice infestations.

 It is used to determine the presence of contaminants and the quality of quartz.

Is benzyl alcohol acid or base?

The family of organic compounds known as benzyl alcohols contains benzyl alcohol, also

known as alpha-toluenol or benzene methanol. Chemical compounds forming the

substructure of phenyl methanol are these. Benzyl alcohol is a (based on its pKa) highly mild

simple (essentially neutral) compound.

Uses in health care

Benzyl alcohol is used as a bacteriostatic preservative at low concentration in intravenous

medications, cosmetics, and topical drugs. 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.

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. It affects the louse's spiracles, preventing them from

closing. These then become clogged with water or mineral oil or other matter and cause the

insect to die from asphyxiation.

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Benzyl alcohol is used effectively for treating lice infestations as the active ingredient in

lotion shampoo with 5% benzyl alcohol.

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.