Chapter 3 Friedel-Crafts alkylation of Phenol using …...Craft in 1877 to attach substituent to an aromatic ring. There are two main types of Friedel-Craft reactions: alkylation reaction

CChhaapptteerr 33 ______________________

Friedel-Crafts alkylation of Phenol using Ionic Liquid as Catalyst

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3.1 Introduction

Phenol was discovered in 1834 by Friedlieb Ferdinand Runge who extracted it from coal tar.

Coal tar remained the primary source until the development of the petrochemical industry.

The antiseptic properties of phenol were used by Sir Joseph Lister (1827–1912) in his

pioneering technique of antiseptic surgery. Lister decided that the wounds themselves had to

be thoroughly cleaned. He then covered the wounds with a piece of rag or lint covered in

phenol, or carbolic acid as he called it. The skin irritation caused by continual exposure to

phenol eventually led to the substitution of aseptic (germ-free) techniques in surgery. Phenol

is the active ingredient in some oral analgesics such as Chloraseptic spray and Carmex.

Phenol is also known as carbolic acid and phenic acid, it is an organic compound with

molecular formula C6H5OH. It is white crystalline solid at room temperature. The molecule

consist of phenyl (-C6H5) bonded to hydroxyl group (-OH) it is mildly acidic, but requires

careful handling due to its propensity to cause burns.

Phenol is appreciably soluble in water, with about 8.3 g dissolving in 100 ml water.

Homogeneous mixture of phenol and water at phenol to water at various mass ratios is

possible. The sodium salt of phenol, sodium phenoxide is far more water soluble. It is slightly

acidic , the phenol molecules have weak tendencies to lose the H+ ion from the hydroxyl

group, resulting in the highly water soluble phenolate anion C6H5O- also called phenoxide

.Compared to aliphatic alcohols, phenol is about 1 million times more acidic , although it is

still considered a weak acid. It reacts completely with aqueous NaOH to lose H+, whereas

most alcohols react only partially. Phenols are less acidic than carboxylic acids, and even

carbonic acid.

The major uses of phenol, consuming two third of its production, involve its conversion to

plastic or related materials. Condensation with acetone gives bisphenol-A, a key precursor to

polycarbonate and epoxide resins. Condensation of phenol, alkylphenols or diphenols with

formaldehyde gives phenolic resins, a famous example is Bakelite. Hydrogenation of phenol

gives cylohexanone, a precursor to nylon. Manfred Weber et al. (2004) shows that non ionic

detergents are produced by alkylation of phenol to give the alkylphenols e.g. nonylphenol,

which are then subjected to ethoxylation. Phenol is also used versatile precursor to a large

collection of drugs, many herbicides and pharmaceutical drugs.

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The alkylation of phenol with olefins in the presence of acid catalyst to produce alkylphenols

has been subjected of investigation for long because of its fundamental and industrial

importance. The para alkylphenol isomer imparts improved performance properties to the

class of metallic detergents used in lubricating oils, known as Phenates.

Both heterogeneous and homogenous catalysts have been used for the alkylation of phenols.

Heterogeneous catalyst such as macro porous cation exchange resins (Amberlyst-15) are

preferred to homogenous acid catalyst since they can be easily separated from the reactant

product mixture and also eliminate undesirable side reactions.

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3.2 What is Friedel–Crafts alkylation?

The Friedel-Crafts reactions are a set of reactions developed by Charles Friedel and James

Craft in 1877 to attach substituent to an aromatic ring. There are two main types of Friedel-

Craft reactions: alkylation reaction and acylation reaction, both processing by electrophilic

substitution.

The Friedel-Crafts alkylation involves the electrophilic substitution of alkyl groups on

aromatic rings when arenes are treated with alkyl halide in presence of Lewis acids. The

alkenes or alcohol can also be used to alkylate aromatic rings under these reaction conditions.

This reaction is catalyzed by Lewis acid like anhydrous AlCl3, FeX3, ZnCl2, BF3 etc. it is a

reversible reaction and hence dealkylation is also possible under the same conditions. It fails

when benzene ring contains a more powerful electronegative group than halogen e.g. nitro

group. The aryl halide cannot be used to instead of alkyl halides.

Despite more than 120 years of history, the Friedel-Crafts alkylation and acylation reactions

are still in the forefront of organic synthesis research. Vast numbers of new catalysts have

been developed, including metal halides, triflates by Olah et al. (2003). In the meantime, our

awareness of the need for environmentally caring chemical production initiated efforts in

green chemistry. Unfortunately, many of the traditional Friedel-Crafts catalysts (e.g. AlCl3,

BF3, FeCl3 and many others) do not fulfill the current requirements of environmental

protection and safety standards. As a possible solution, considerable efforts were devoted to

the application of solid acid catalysts in Friedel-Crafts reactions again by Olah et al. (1985).

The most common solid acids are: zeolites, clays, cationic resin, sulphonic acids, metal, and

heteropolyacids. The fundamental concept is to identify new, stable and recyclable catalysts

as replacements for the conventional liquid acids, and ultimately develop environmentally

safe industrial processes.

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3.2.1 The general reaction scheme

+ R-X

AlCl3 reflux

R

+ HX

Benzene alkylhalide

alkylbenzene

haloa cid

Figure 3.1: Reaction scheme of alkylation benzene.

Benzene reacts with alkyl halide at Room Temperature. The mechanism of reaction as follow

1) Formation of carbonium ion.

2) Carbonium ion acts as electrophile and attacks the Benzene ring to form the arenium

ion.

3) The arenium ion then starts loosing proton to generate alkyl benzene.

This reaction has one big disadvantage, namely that the product is more nucleophilic than the

reactant due to the electron donating alkyl-chain. Therefore, another hydrogen atom is

substituted with an alkyl-chain, which leads to over alkylation of the molecule.

The alkylation reaction of phenol with tert-butyl alcohol (TBA) is of both industrial

importance and academic relevance. Alkylation of phenol with tert-butyl alcohol yields

butylated phenols which use as raw materials in the production of antioxidants, phenolic

resins, agrochemicals, rubber chemicals, printing ink, varnish, surface coatings, fungicides,

ultraviolet absorbers petroleum additives and heat stabilizers for polymeric materials. 2-tert-

butylphenol is an intermediate for pesticides, fragrances and other products, whereas 4-tert-

butylphenol is used to make phosphate esters, fragrances, oil�eld chemicals and demulsi��

2,4-Di-tert-butylphenol is an intermediate for antioxidants and 2,6-di-tert-butylphenol is used

as an antioxidant intermediate and in pharmaceuticals was described by Yadav et al. (2002).

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3.3 Conventional process used

Both homogenous and heterogeneous catalysts have been reported in the tert-butylation of

phenol which include Lewis acid, AlCl3 and BF3 was used by Kirk et al. (2005), Bronsted

acids such as H3PO3,H2SO4, HF and HClO3, Cation exchanged resins, zeolites, mesoporous

materials, heteropolyacids, super critical and near critical water have been studied. The major

draw backs of liquid acid catalysts include their hazardous, corrosive nature and tedious

work-up involved in the separation of these catalysts from the reaction mixture. The solid

acid catalysts whose reaction was carried at temperature ranges from 120 – 150oC have the

problem of rapid deactivation due to coke formation, due to pore blocking and also spent

catalyst disposal problems. The Cation-exchange resins show good performance but are

thermally unstable and fouling of resin is still a major issueAlkylphenols of greatest

commercial importance have alkyl groups ranging in size from one to twelve carbons. The

direct use of alkylphenols is limited to a few minor applications such as epoxy-curing catalyst

and biocides. The vast majority of alkylphenols are used to synthesize derivatives which have

applications ranging from surfactants to pharmaceuticals.

The use of alkylphenols in the production of both polymer additives and monomers for

engineering plastics is expected to show above average growth as plastics continue to replace

traditional building materials.

Physical properties of alkylphenols are comparable to phenols. The properties are strongly

influenced by the type of alkyl substituents and its position on the ring. Para-alkylphenols

have higher melting point and boiling point than the corresponding ortho-isomers. The

melting point of para-alkylphenols goes through a maximum for tert-butyl and then decrease.

An alkene stream consisting of a mixture of isomers produces an alkylphenol that has a

depressed melting point. As the carbon chain of the alkyl group surpasses 20, the resulting

phenols take on a waxy form. Alkylphenols, especially when did-and tri substituted, tend to

super cool. Alkylphenols show the same sensitivity to oxidation that of phenol. The solubility

of alkylphenols in water falls off precipitously as the number of carbons attached to the ring

increases. They are generally soluble in common organic solvents; acetone, alcohols,

hydrocarbons, toluene. Solubility in alcohols or heptanes follows the generalization that “like

dissolves like”. More polar alkylphenol has greater solubility in alcohols, but not in aliphatic

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hydrocarbon; likewise with cresol and xylenols. The solubility of an alkylphenol in

hydrocarbon solvent increases as the number of carbon atoms in the alkyl chain increases.

Alkyl groups in the ortho position affects the environment, around the hydroxyl group; the

larger the group the greater the effect. Intermolecular hydrogen bonding decreases with the

introduction of a tert-butyl group ortho to the hydroxyl, reducing the atmospheric by about

20o C. substitution of the second ortho position with a tert-butyl group effectively precludes

any hydrogen bonding. The impact of ortho alkyl substituents on hydrogen bonding can be

advantageously applied to the analysis and separation of alkylphenols. A mixture of ortho and

para isomers is separated effectively using normal phase chromatography

There is a health benefit associated with hindering hydrogen bonding. Alkylphenols as a class

are generally regarded as corrosive health hazards, but this corrosivity is eliminated when the

hydroxyl group is flanked by bulky substituents in the ortho position. In fact, hindered

phenols are utilised as antioxidants in plastics with FDA (Food and Drug Administration)

approval for indirect food contact.

p-tert-butyl phenol (PTBP) or 4-(1, 1-dimethyl-ethyl) phenol is produced from the alkylation

of phenol with isobutylene under acid catalysis. Isobutylene is commercially produced mostly

from the dehydration of tert -butyl alcohol or from the cracking of methyl tert-butyl ether

(MTBE). The principal products of this alkylation are 2-tert-butylphenol, 4-tert-butylphenol,

2,4-di-tert-butylphenol, and minor amounts of 2,4,6-tri-tert-butyl-phenol and 4-tert-

octylphenol. 4-tert-Butylphenol is available in a technical grade which is used in the

production of phenolic resins. A high purity grades are available for the production of

glycidyl ethers and for the chain termination of polycarbonates. 4-tert-Butylphenol is

available as a �� -aged in paper or plastic bags (25 kg net weight), and as a

molten material in tank wagon and railcar quantities.

Phenolic resin applications account for 60–70% of all 4-tert butyl phenol consumed

worldwide. These resins are used in a wide range of applications which include paints,

coating resins, and printing inks. 4-tert-Butylphenol novolak resins react with ethylene oxide

to form oil�eld demulsi��re converted into phosphate esters for use as hydraulic ��

and synthetic lubricants.4-tert-Butylphenol resoles react with alkaline-earth metal hydroxides

to produce metal resinates. Resinates are combined with a rubber component to give an

adhesive. Other uses of 4-tert-butylphenol include the chain termination of poly carbonates

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where its use in the place of phenol gives a polycarbonate with better heat distortion

characteristics and improved process ability for injection grade material

The primary use for 2,4-di-tert-butylphenol is in the production of substituted triaryl

phosphites. 2,4-di-tert-butylphenol reacts with phosphorus trichloride typically using a

trialkylamine or quaternary ammonium salt as the catalyst. Hydrogen chloride were formed

and either complexed with the amine or liberated as free hydrogen chloride gas forming the

phosphite ester, tris(2,4-di-tertbutylphenyl) phosphite. The phosphite-based on 2,4-di-tert-

butylphenol is a solid and very hydrolytically stable. Because of this hydrolytic stability it has

replaced the use of tris(4-nonylphenyl) phosphite and other less stable phosphites in poly

ole�� -oxidant based on 2,4-di-tert-

butylphenol is the diphosphite derived from pentaerythritol, bis(2,4-di-tert-butylphenyl)

pentaerythrityl diphosphite. It too is widely used in polyole��

where high performance is required. 2,4-Di-tert-butylphenol is also used in the production of

a benzotriazole-based UV stabilizer.

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3.4 Advantages and Disadvantages / Limitations

3.4.1 Advantages of Friedel–Crafts alkylation

The industry of polymers is constantly finding new uses for existing materials. Joseph et al.

(1981) invented carbocationic polymerization provides a unique opportunity to prepare tailor

made polymers. By using this variety of polymers can be prepared with desired molecular

weight, molecular weight distribution, polymer composition and molecular architecture.

These properties can be varied by modification of the concentration of reactants.

Jimenez et al. studied the synthesis of alkyl-aryl by a modified Friedel-Crafts alkylation; they

study the influence of the concentration of the reactants on the physical properties and

structure of the prepolymer and on the kinetics of polymerization, chemical properties, and

low degree of polymerization. This prepolymer can be low cost plasticizer. The prepolymer

has good chemical stability and low toxicity.

The single great advantages of Friedel-Craft systems over those of Bronsted acids is their

ability to prolong the lifetime of the kinetic chain and thus renders propagation to high

molecular weights possible. Friedel-Crafts acids are capable of coordinatively complexing

conjugate bases of Bronsted acids and thus lead to remarkably stable counter anions. Mixture

of Bronsted acids with Friedel-Crafts acids, therefore are among the strongest acids known

and have found use as most effective initiators of carbocationic polymerization.

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3.4.2 Limitation of Friedel-Crafts reaction

1. The reaction works only with benzene or activated benzene derivatives. It will not

occur if the benzene ring is deactivated.

2. The reaction works only

3. Because of the intermediate formation of carbocations, product mixtures might be

obtained, due to rearrangements of the carbocations.

4. The Friedel-Crafts reaction often leads to the introduction of more than one alkyl

group in the molecule. The reason for such undesired polyalkylation is as follows:

Upon introduction of one alkyl group, the resultant compound becomes more

activated than the starting material and actually reacts faster with the electrophile,

leading to the almost inevitable second alkylation.

5. This limitation can be avoided in particular cases, if benzene (or the benzene

derivative) is used in very large excess. Such approach is of course not always

practical, due to availability of the particular benzene derivative.

6. Limitations 3) and 4) are successfully addressed by the related process of Friedel-

Crafts acylation.

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3.5 Literature Survey

Zhang et al. (1998) has carried out the alkylation reaction of phenol with TBA by zeolite beta

as a catalyst. The reaction was carried out in the tubular down flow stainless steel reactor (i.d.

4mm). 95.5% conversion of phenol and 76.38% selectivity of p-TBP were obtained at 418 K,

higher ��

Zhang et al. (2001) has carried out the alkylation reaction of phenol with TBA by Zeolite

(HY) as catalyst. The reaction was carried out in tubular down flow stainless steel reactor

(i.d. 4mm). The maximum conversion of phenol and selectivity of 2,4-DTBP was obtained at

418 K, low space velocity (0.42 – 1.66), higher reactant molar ratio and strong acidic sites on

the zeolite (HY).

Yadav et al. (2002) has carried out the alkylation reaction of phenol with MTBE by Dodeca-

tungstophosphoric acid (DTP)/K-10. The reaction was carried out in 100 cm3 autoclave at a

pressure of 200 psi. 68% conversion of phenol and 38% selectivity of o-TBP were obtained

at 150oC, 1000 r.p.m., and 1:2 molar ratio of phenol: MTBE and 0.04 g/cm3 catalyst loading.

The kinetic of reaction was also studied and reaction was found to be second order.

Sakthivel et al. (2002) has studied the alkylation of phenol with TBA using H-GaMCM-41

molecular sieve with different Si:Ga ratio. The reaction was carried out in fixed bed reactor

using 750 mg of H-GaMCM-41 catalyst. Before reaction, the catalyst was activated at 773K

in flowing air for 8hrs, followed by cooling to reaction temperature (448 K) under nitrogen

atmosphere. After 1 hr, the reaction mixture with desire (molar) ratio and weight hour space

velocity (WHSV) was fed into reactor using a liquid injection pump (sigma motor) with

nitrogen as carrier gas. The maximum conversion of phenol (37%) and selectivity of p-TBP

(84.6%) was obtained at 448 K, 4.8 hr-1 WHSV and 1:2 molar ratio of TBA to Phenol. The

catalyst show higher phenol conversion and p-TBP selectivity over Al- and Fe- analogue of

H-MCM -41.

Shen et al. (2003) has studied the alkylation of phenol with TBA by 1-butyl-3-

methylimidazoliumhexaflorophosphate [BMIM] [PF6]. The reaction was carried out in the

sealed tubes. The maximum conversion of phenol and selectivity of 2,4-DTBP was obtained

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at temperature of 60oC, 1:2 molar ratio of reactant phenol:TBA, 0.5 mmol ionic liquid per

mole of phenol.

Ojha et al. (2005) has studied the alkylation of phenol by TBA using Zeolite catalyst

obtained from hydrothermal treatment of fly ash. The reaction was carried out in 500ml batch

reactor. 27% conversion of phenol and 95.75% selectivity of p-TBP were obtained. The

kinetic modelling of reaction was done and reaction was found to be surface reaction

controlled.

Gui et al. (2005) has studied the alkylation of phenol with TBA by using SO3H

functionalized ionic liquid. The reaction was carried out in 20 ml autoclave with glass tube

inside equipped with magnetic stirring at autogenously pressure. 80.4% conversion of phenol

and 60.2% selectivity of 2,4-DTBP was obtained at 70oC, 1:2 molar ratio of phenol to TBA

and 15 mmol ionic liquid per 10 mmol phenols.

Kurian et al. (2006) has studied the alkylation of phenol by TBA using transition metal

exchange pillared montmorillonites as a catalyst. 54% conversion of phenol and 96.4%

selectivity of p-TBP were obtained at 200oC, 1:3 molar ratio of phenol to TBA and space

velocity of 2.6 hr-1.

Duan et al. (2006) has studied the alkylation of phenol by TBA using 2-methylpyridinium

trifloromethanesulphonate. The reaction was carried out in 90ml autoclave with glass tubes

inside, equipped with magnetic stirrer. 94% conversion of phenol and 83% selectivity of 2,4

DTBP was obtained at a 100oC, 1:2 molar ratio of phenol to TBA and 1:2 molar ratio of

Phenol to ionic liquid.

Shon et al. (2007) has studied the alkylation of phenol by TBA using mesoporous solid

materials, SBA-15, functionalized with strong (-SO3H), moderate (-PO3H2) and weak (-

COOH) acid group. The phenol conversion was in the order of SBA-15-SO3H>SBA-15-

PO3H2>SBA-15-COOH. The selectivity of ether product is more at lower reaction

temperature and SBA-15-COOH having weak acidic sites, 2-TBP at moderate temperature

over SBA-15-PO3H having medium acidic strength, 4-TBP and 2,4 DTBP at relatively high

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temperature over SBA-15-SO3H having strong acid strength. The selectivity also affected

due to molar ratio of reactant.

Ghiaci et al. (2010) has studied the alkylation of phenol by TBA using Al-MCM-41

containing 5-36% H3PO4 as catalyst. The reaction was carried out in Pyrex reactor (i.d. 8

mm). The maximum conversion of phenol and selectivity of 2, 4-DTBP was obtained using

30 wt% H3PO4/ Al-MCM-41(0.5 gm) catalyst at a temperature of 463oK and 2:1 molar ratio

of TBA to Phenol.

Ma et al. (2010) has studied the alkylation of phenol by TBA using aluminium containing

mesoporous Al/SBA-15 catalyst which is prepared by post synthesis method and direct

synthesis method. Post synthesis method gives good activity of catalyst compared to direct

synthesis method. The reaction was carried in the tubular reactor at atmosphere pressure. The

89.17% conversion of phenol and 60.77% selectivity of p-TBP were obtained at 5 molar ratio

of TBA to phenol, 2.5 hr-1 space velocity, 0.05 gm catalyst and 190oC temperature. The

activity of catalyst remains almost constant up to four runs.

Bhatt et al. (2011) Friedel–Crafts alkylation reactions such as tert-butylation, iso-propylation

and sec-butylation of phenol have been carried out over 12-tungstophosphoricacid supported

onto neutral alumina under mild conditions by varying different parameters. The supported

catalysts were characterized by various physicochemical techniques such as FT-IR, TGA, and

XPS analysis. The catalyst shows significantly high conversion and selectivity towards the

important products. The catalysts were efficiently regenerated followed by a simple workup

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3.6 Ionic Liquid as catalyst

Molecular catalysis is widely used in chemical industry as for example in oxidation,

metathesis, hydroformylation and carbonylation, hydrocyanation, oligomerisation. Some of

these reactions have no heterogeneous counterpart (hydroformylation, hydrocyanation.).

However despite its well-established advantages such as, at least theoretically, using a single-

site well-defined catalyst, high selectivity and activity compared to heterogeneous catalysis, it

suffers from a serious drawback, the separation and recycling of the catalyst. Catalyst

recovery in an active form suitable for recycling is generally not feasible and the products

may be contaminated with catalyst residues. This is all the more important as molecular

catalysts tend to become more structurally sophisticated. This situation often leads to

expensive purification procedures which disagree with the development of more

sustainable processes. Therefore, there is a need for systems that can combine the advantages

of homogeneous catalysis with straightforward separation, recovery and reuse of the catalyst.

This situation is common to enzymatic, organometallic and organo catalysis. Different

approaches have been employed to achieve this goal. The catalyst can be immobilized or

contained in either a ‘‘solid matrix’’ or in a ‘‘liquid phase’’ which forms a different

immiscible phase with the reaction products. If gaseous reagents are present, triphasic or

multiphase mixtures may be encountered. But in the latter case, the key issue is the suitable

choice of the catalyst liquid phase. Baker et al. (2006) developed many alternatives for non-

conventional solvents which make it possible to take advantage of molecular engineering to

tailor polarity, viscosity, thermal stability and solubilising power. Without being complete,

one can cite perfluorinated solvents, supercritical fluids and non aqueous ionic liquids.

ILs has been used in various immobilization strategies: as ‘‘liquid supports’’ in multiphase

catalysis or in heterogeneous systems (SILP). In these different uses, ILs has played specific

and different roles. In this part of the review, we will describe the different strategies and

concepts of IL use in catalytic applications, bearing in mind the possibility of applying these

processes in a continuous mode on an industrial scale.

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Ionic Liquids (ILs) have attracted rising interest in the last decades with a diversified range of

applications. The types of ionic liquid available have also been extended to include new

families and generations of ionic liquids with more specific and targeted properties. This

expanding interest has led to a number of reviews on their physicochemical properties, the

design of new families of ionic liquids, the chemical engineering and the wide range of

arrangements in which ILs have been utilized and pilot or industrial developments.

In addition to the fact that they are now commercially available, there is a better

understanding of ionic liquids as chemical reagents along with their physical properties as

well as application as engineering fluids. Consequently, ionic liquids have been used more

widely and efficiently, with better control over the process. Smiglak et al. (2007) introduce

the structural functionalities on the cationic or anionic part which makes it possible to

design new ILs with targeted properties. More recently, ILs appear to be the use in

increasingly diverse applications such as sensors, fuel cells, batteries, capacitors, thermal

fluids, plasticizers, lubricants, ionogels, extractants and solvents in analysis, synthesis,

catalysis and separation, to name just a few. Some new applications, such as energetic

compounds or pharmaceutical ILs, are still emerging. ILs can be used as more than just an

alternative ‘‘green’’ solvents. They differ from molecular solvents by their unique ionic

character and their ‘‘structure and organization’’ which can lead to specific effects. They

are tunable, can used for multipurpose materials.

Diversity is a key word for all IL, diversity of anion-cation combinations, diversity of

modes of preparation, modes of purification and nature of impurities (quality), diversity of

properties, diversity of mode of use, diversity of applications. So it is difficult to make

generalisations about their physical properties or their use. The contribution ILs make to

homogeneous catalysis has more to do with the enhancement of catalytic performances

(activity, selectivity or new chemistry) and the possibility of catalyst separation and

recycling. They can also act as solvents, as multifunctional compounds like solvents and

ligands, solvents and catalysts, stabilising agents for the catalysts or intermediates.

The performance of an IL will strongly depend on the technology in which it is implemented.

They can be utilised in many different ways: homogeneous, multiphase, heterogeneous, in

bio transformations or in organocatalysis. They play a specific role in all these approaches.

New families of ILs with various other cations have been developed these last decades. ILs is

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not trivial. They are generally composed of asymmetric and flexible ions, with components

of highly different sizes and shapes, and involve different types of dominant interactions.

Theoretical treatment and interpretations are complicated. However, it is important to have a

better understanding of neat IL’s properties, and their properties and interactions with other

species such as molecular species or metal complexes to better understand their role in

catalysis.

Chaippe et al. (2009) explains the polarity is one of the most important properties for

characterising the solvent effect in chemical reactions. It is also the property which has

probably been the most widely discussed in the case of ILs. There is no single parameter and

direct measurement that can characterize IL polarity. According to Reichardt (2005) and

Bright et al. (2006) explains, solvatochromic dyes can be used to determine empirical

polarity parameters but these parameters (Kamlet-Taft equation) are probably not truly

independent on the probe molecule used. The difficulty in the case of ILs is to find a suitable

soluble probe which measures the polarity parameters as independently as possible of the

other influences of the solvent.

ILs has relatively moderate surface tensions compared to organic solvents observed by

Martino et al. (2006). For industrial implementation, some IL properties must be investigated

under real process conditions. Wasserscheid et al. (2007) examined compressibility of IL

under long-term conditions and under high pressure. They can be compared to conventional

solvents as shown in Fig.3.2; it gives a tentative qualitative description of ILs compared to

alternative solvents, in terms of polarity and volatility.

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Fig 3.2: Typical polarity and volatility characteristic of alternative solvents. Olivier et al.

(2010)

In homogeneous catalysis, the catalyst separation and recycling is an important issue. The

recycling can be operated by chemical transformation or by direct distillation, depending on

the catalyst and its stability. Its recycling can also be performed using a biphasic liquid/liquid

system. Initially developed for the aqueous biphasic system, this concept was further

extended to other media than water including ILs. Most organic substrates generally do not

have sufficient solubility in the catalyst phase, particularly in water, to give practical reaction

rates in catalytic applications, or in many cases there are incompatibilities between the

catalyst and the solvent. ILs offers an attractive option to improve the reactant’s solubility in

the catalyst phase. In addition, it is often possible to find a biphasic IL/organic system for

which the catalyst is dissolved and immobilized in the IL. The ideal situation is obtained

when the IL displays partial miscibility with the substrates and when the products have

negligible miscibility with the IL (Fig. 3.3). Separation is then obtained by decantation which

simplifies the process scheme and limits the risks of catalyst decomposition during

distillation. This option can also provide opportunities for new chemistry, for example, by

shifting equilibrium through in situ extraction or by improving selectivity for primary

reaction products when there is a preferential solubility of one reactant in the catalyst phase

and then in situ extraction of reaction intermediates in the other phase. This can be a way to

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operate separative catalysis and process intensification. This improvement of selectivity has

been exemplified for transformations where consecutive reactions such as olefin

oligomerisation or selective diene hydrogenation need to be avoided.

Fig 3.3: The IL-liquid/liquid-biphasic concept (M = monomer, M-M = dimer, M-M-

M=trimer

ILs proved to be very complex solvents. They can solvate polar and non-polar species,

they can behave as polar or non-polar solvents. Besides their ‘‘chemical’’

characteristics, their physical properties such as an elevated viscosity can affect the

diffusion and reduce reaction rates. The solubility of gas or the selective solubilisation

of reactants relative to the products can also change the reaction selectivity. The

formation of primary reaction products can be favoured by their selective extraction

from the IL catalytic phase in an organic upper phase. It is then difficult to rationalize

the IL effects on chemical and catalytic reactions. Solvation properties, interactions

with solutes, substrates, transition states, metal complexes, reactants, their cohesive

pressure, their degree of organisation and their viscosity are all to be considered when

ILs are used as solvents. To date, the ILs’ effects have been best described and

rationalized on chemical reactions rather than on catalytic reactions involving

transition metal complexes. In some cases, the generation of the active catalyst has

been dependent on the nature of the ILs. ILs can inhibit or promote the formation of

the active species. They can also dramatically affect the outcome of reactions was

explained by Earle et al. (2004).

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3.7 Experimental Data

3.7.1 Material and Reagents

Crystalline phenol and diethyl ether were purchased from S. D. fine-chem. Limited,

Mumbai. Tertiary butyl alcohol was purchased from Central Drug House (P) LTD,

New Delhi. 1, 4-butanesultone and p-toluenesulphonic acid were purchased from

Merck India Ltd. (Mumbai, Maharashtra, India), while triethylamine was purchased

from Thomas Baker (chemicals) Pvt. Ltd. The ionic liquid [BMIM] [HSO4], [BMIM]

[PTSA], and [TTDP] [HSO4] used in reaction were synthesised in lab. All other

chemicals were obtained from reputed firms. They were used without further

purification.

3.7.2 Synthesis of Ionic Liquid

3.7.2.1 1-butyl 3-methylimidazolium para-toluenesulphonic acid ([BMIM]+[PTSA-])

1-Butyl 3-methylimidazolium chloride (1.74 g, 0.01 mol) was placed in a two necked flask

with stirrer and was cooled to 00C. Then 5ml of water was added to it and para-

toluenesulphonic acid (1.90 g, 0.01 mol) was added slowly under stirring. The mixture was

stirred for 2 h, and the water was removed on a rota-evaporator at 600C to obtain a green

colour liquid as the procedure explain by Joseph et al. (2005).

Figure 3.4 structure of [BMIM] [PTSA]

115

3.7.2.2 1-Butyl 3-Methyl imidazolium hydrogen sulphate (BMIM [HSO4]).

[BMIM][Cl] (25gm) and KHSO4 (19.48gm) was added in 1:1 proportion and methanol was

used as a solvent (20 ml) in three necked stirred reactor. The mixture was stirred for 30 hrs at

650 rpm. After that the precipitate of KCL formed was filtered and dried in rota-evaporator at

600C, for 2hrs as explained by Joseph et al. (2005).

Figure 3.5 Structure of [BMIM] [HSO4]

3.7.2.3 Trihexyl (tetradecyl) phosphonium hydrogen sulphate. [TTDP][HSO4]

By combining trihexyl(tetradecyl)phosphonium chloride (0.66 kg, 1.26 mol, Cytec

Industries) and sulphuric acid (0.2348gm) in the presence of an excess of sodium hydroxide

(40% w/w in water, 0.24 kg, 2.43 mol) an water. This mixture was heated to 55 °C with

vigorous agitation for 4 h, and washed three times with water to remove sodium chloride.

Vacuum stripping at 135 °C to remove any residual water gave the product, an orange/brown

liquid, in 95% isolated yield (0.93 kg, 1.20 mol, chloride content 0.082% w/w by titration

with AgNO3) followed the procedure as stated by Bradaric et al. (2002).

Figure 3.6 Structure of [TTDP] [HSO4].

116

3.7.2.4. 1-Ethyl-3-methylimidazolium ethyl sulphate [EMIM] [EtSO4]

Diethyl sulphate (29 ml, 0.221 mol) was added drop wise to a solution of 1-methylimidazole

(18.146 g, 0.221 mol) in toluene (100 ml) cooled in an ice-bath under nitrogen at a rate to

maintain the reaction temperature below 40 °C. Formation of the IL product was immediate

and caused the initially clear solution to become opaque, followed by biphasic separation of

the toluene solution and formation of a denser IL phase. After addition of the diethyl

sulphate, the reaction mixture was stirred at room temperature for 1 h. The upper, organic

phase was decanted and the lower, IL phase was washed with toluene (50 ml), dried with

heating at 75 °C under reduced pressure to remove residual organic solvents, and finally in

vacuum to yield the resulting 1-ethyl-3-methylimidazolium ethyl sulphate IL as a colourless

hydroscopic liquid, free from starting materials.

N+

N

CH3

CH3

S

O

O

OOH

CH3

Figure 3.7 Structure of [EMIM] [EtSO4]

117

3.7.3 Experimental set-up

The reactions were carried out in three necks round bottom flask with magnetic needle. The

overall capacity of round bottom flask was 25 ml. It was provided with condenser and

temperature thermometer to measure the temperature. The Revolution per minute and

temperature of reaction mixture in round bottom flask was controlled by Digital magnetic

stirrer. The following figure 3.8 shows the assembly of reaction set up.

Figure 3.8 Experimental setup

3.7.4 Experimental Procedure

1. The required amount of ionic liquid is weight and added in 25 ml three necked Round

bottom flask.

2. Required volume of phenol and tertiary butyl alcohol is added to Round bottom flask

containing ionic liquid.

3. The reaction mixture is heated to 80oC with continuous stirring for 8 hr.

118

4. Reaction Sample is collected at 2 hr interval.

5. The Sample is analysed using gas chromatography.

3.7.5 Analysis

The analysis is done using gas chromatography with SE 30 Column. The method used as

shown in figure 3.9

Figure 3.9 Temperature program for analysis of reaction mixture.

119

3.7.6 Mechanism of the Reaction Schematic representation of the reaction

Alkylation reaction of phenol with tert-butyl alcohol

Figure 3.10: Alkylation reaction of phenol with Tertiary butyl alcohol

Figure (3.10) shows the alkylation reaction of phenol with Tertiary butyl alcohol. The

products of the reaction are ortho-tertiary butyl alcohol, para-tertiary butyl alcohol, 2,4-

Ditertiary butyl alcohol and water. The above mentioned products formed in the presence of

(1-(4-sulphonic acid) butyl triethylammonium p-toluene sulphonic acid [EMIM][EtSO4] as a

catalyst. While reaction doesn’t takes place in the presence of 1-butyl3-methylimidazolium

para-toluenesulphonic acid ([BMIM]+[PTSA-]), 1-Butyl 3-methylimidazolium hydrogen

sulphate (BMIM [HSO4]) and Trihexyl (tetradecyl)phosphonium hydrogen sulphate.

120

3.7.7 Resonance structure of alkylated product

Figure 3.11: Resonance structure of phenol at ortho, meta and para attack

Figure 3.11 shows the resonance structure of phenol at ortho, meta and para attack. When the

electrophile attack the ortho or para position the positive charge at carbon atom is neutralized

by OH group, thus preferred product forms. When it attack the Meta position of phenol the

positive charge does not neutralized by OH group thus prevent the formation of meta

product. So presence of OH group prefers the formation of ortho and para products while

prevent the formation of meta products.

121

3.7.8 Mechanism of alkylation reaction using ionic liquid as a catalyst:

Step 1: Ionic liquid donates its proton to tertiary butyl to form tertiary butyl cation with the

removal of water molecule.

Step 2: This cation attack the various position of Phenol ring to form products.

Step 3: Hydrogen gets released when cation attacks phenol ring at various positions which

again combine with ionic liquid.

122

[IL]: Ionic liquid.

123

3.8 Results and Discussion

The alkylation reaction of phenol with tertiary butyl alcohol was studied using four different

ionic liquids. Different ionic liquid were 1- butyl 3-methylimidazolium para-toluenesulphonic

acid ([BMIM]+PTSA-), 1-Butyl 3-Methyl Imidazolium hydrogen sulphate (BMIM [HSO4]),

and Trihexyl(tetradecyl) phosphonium hydrogen sulphate. [TTDP][HSO4], and (1-(4-

sulphonic acid) butyl triethylammonium p-toluene sulphonic acid [EMIM][EtSO4]. The

reaction was studied at parameters mentioned in Table 3.1. No conversion of phenol was

obtained when 1- butyl 3-methylimidazolium para-toluenesulphonic acid ([BMIM] [PTSA],

1-Butyl 3-Methyl Imidazolium hydrogen sulphate [BMIM] [HSO4] and Trihexyl(tetradecyl)

phosphonium hydrogen sulphate.[TTDP][HSO4] ionic liquids were used as catalyst. While

(1-(4-sulphonic acid) butyl triethylammonium p-toluene sulphonic acid [EMIM][EtSO4]

gave good conversion so all further experiments were carried out using this ionic liquid only.

Table 3.1: Parameter studied at atmosphere pressure with their range for phenol reactions.

Sr. No. Parameters Range

1 Revolution per minute 300 – 800 rpm

2 Reaction Temperature 333 – 373oK

3 Change of Concentration of Reactant. 1:1 – 1:4a

4 Catalyst loading 1:0.2 – 1:1.5b

a: ratio of moles of Phenol to TBA.

b: ratio of moles of Phenol to ILs.

124

3.8.1 Effect of speed of agitation

3.8.1.1 Conversion of Phenol.

Figure 3.12: Effect of Speed of agitation on the conversion (Condition: 80oC, Phenol/TBA 1:2 mol/mol, Catalyst loading Phenol/ILs 1:0.5 mol/mol, 8 hr)

The reaction was carried out at temperature of 80oC, 1:2 molar ratio of phenol to Tertiary

butyl alcohol and 1:0.5 molar ratio catalyst loading of phenol to Ionic liquid [EMIM][EtSO4].

The Speed of agitation was changed from 200rpm to 1000rpm. Figure 3.12 shows the effect

of revolution per minute on the conversion of phenol. It is clear that the maximum conversion

of phenol obtained at 800 rpm which are 85.2% remains constant for further increase up to

1000 rpm. Which depicts that after 800rpm reaction is independent of mass transfer

coefficient. Hence 800rpm is considered to be constant revolution per minute of all

experiments carried out.

0

20

40

60

80

100

0 200 400 600 800 1000 1200

% C

onve

rsio

n

Speed of agitation (rev/min)

125

3.8.1.2 Selectivity of products

� Selectivity of o-TBP

Figure 3.13: Effect of Speed of agitation on selectivity of o-TBP

Figure 3.13 illustrates the effect of speed of agitation on the selectivity of o-TBP. The

reaction was carried out at temperature of 80oC, 1:2 molar ratio of phenol to Tertiary butyl

alcohol and 1:0.5 catalyst loading of phenol to Ionic liquid [EMIM][EtSO4]. The revolution

per minute was increased from 200 to 800. From the figure it is clear that with increase in

time, the selectivity of o-TBP decreases. Selectivity of o-TBP decreases due to Di-alkylation

of o-TBP and due to enhance in mass transfer with decrease in revolution per minute was.

The maximum selectivity of o-TBP obtained at 800 rpm, which is 65.23%.

0

10

20

30

40

50

60

70

0 1 2 3 4 5 6

% C

onve

rsio

n

Time (hr)

200

400

600

800

126

3.8.1.3 Selectivity of p –TBP

0

5

10

15

20

25

30

0 2 4 6 8

% C

onve

rsio

n

Time (hr)

200400600800

Figure 3.14 Effect of speed of agitation on selectivity of p –TBP

Figure 3.14 depicts the effect of revolution per minute on the selectivity of p-TBP. The


alcohol and 1:1 catalyst loading of phenol to Ionic liquid [EMIM][EtSO4]. The revolution per

minute increased from 200 to 800. From the figure 3.8.3 it can be seen that the selectivity of

p-TBP is decrease with respect to time at all the RPM. The minimum and maximum

selectivity of p-TBP at 800 rpm and 200 rpm is 27.23% and 12.21% respectively. The

selectivity of p-TBP decreases due to dialkylation, which causes conversion of p-TBP to 2,4-

DTBP.

127

3.8.1.4 Selectivity of 2, 4-DTBP

0

20

40

60

80

0 2 4 6 8

% C

onve

rsio

n

Time (hr)

200

400

600

800

Figure 3.15: Effect of speed of agitation on selectivity of 2, 4-DTBP.

Figure 3.15 shows the effect of speed of agitation on the selectivity of 2,4 DTBP. The


alcohol and 1:0.5 catalyst loading of phenol to Ionic liquid [EMIM][EtSO4]. The revolution

per minute was increased from 200 to 800. From the figure it is clear that selectivity of 2, 4

DTBP increases with time. In initial hours of reaction the concentration of 2,4-DTBP is

almost similar. This is observed because the mono product gets converted to di product as

soon it forms. The maximum selectivity of 2,4 DTBP obtained at 800 rpm while minimum

selectivity obtained at 200 rpm after 8hrs. The maximum selectivity after 8 hr is 56.77%

while minimum selectivity is 35.80%.

128

Conclusion

From the experiment conducted, 800 rpm considered as optimum speed of agitation because

of following reasons

1) Highest conversion of phenol obtained

2) High selectivity of 2,4 DTBP

3) High Di-alkylation

4) Low selectivity of o-TBP and p-TBP.

129

3.8.2 Effect of Reaction Temperature

3.8.2.1 Conversion of Reactant

0

20

40

60

80

0 2 4 6 8

Con

vers

ion

of P

heno

l %

Time (hr)

50

60

70

80

90

Figure 3.16 Effect of reaction temperature on the conversion of phenol.

The Figure 3.16 shows the effect of Temperature on the conversion of phenol. The reaction

was carried out at Revolution per minute of 200 rpm, 1:2 molar ratio of phenol to Tertiary

butyl alcohol and 1:0.5 catalyst loading of phenol to Ionic liquid [EMIM][EtSO4]. The

reaction temperature was varied from 50oC to 90oC. The conversion continuously increases

up to 8 hr, after that rate of conversion decreases. The maximum conversion obtained after 8

hr at 80oC. While the least conversion obtained after 8 hr at 50oC. From the graph it is clear

that the conversion at temperature 70oC and 90oC is approximately same, while at 90oC least

conversion of phenol obtained due to vaporisation of TBA after 80oC.

130

3.8.2.2 Selectivity of o-TBP

0

10

20

30

0 2 4 6 8 10

% S

elec

tivity

Time (hr)

50

60

70

80

90

Figure 3.17 Effect of reaction temperature on the selectivity of o-TBP.

Figure 3.17 illustrates the effect of reaction temperature on the selectivity of o-TBP. The

reaction was carried out at Revolution per minute of 800 rpm, 1:2 molar ratio of phenol to

Tertiary butyl alcohol and 1:0.5 catalyst loading of phenol to Ionic liquid [EMIM][EtSO4].

The reaction temperature was varied from 50oC to 90oC. Fig. 3.8.6 shows that increase in

temperature results in decrease in the selectivity of the o-TBP. The selectivity of o-TBP after

8 hr found to be maximum at 80oC while minimum at 50oC. The selectivity of o-TBP is less,

due to Di-alkylation. The maximum selectivity of o-TBP is 32.34%.

131

3.8.2.3 Selectivity of p-TBP

0

5

10

15

20

25

30

0 2 4 6 8

% S

elct

ivity

Time (hr)

50

60

70

80

90

Figure 3.18: Effect of reaction temperature on the selectivity of p-TBP

Figure 3.18 depicts the effect of reaction temperature on the selectivity of p-TBP. The



The reaction temperature was varied from 50oC to 90oC. It is observed from the figure that

selectivity of o-TBP at 80oC is maximum where as for higher temperature the conversion

decreases due to loss of TBA. The maximum selectivity of p-TBP after 8 hr is 23.32%.

132

3.8.2.4 Selectivity of 2, 4- DTBP

0

20

40

60

80

0 2 4 6 8 10

% S

elec

tivity

Time (hr)

50

60

70

80

90

Figure 3.19: Effect of reaction temperature on the selectivity of 2, 4- DTBP.

Figure 3.19 illustrate the effect of reaction temperature on the selectivity of 2, 4 DTBP. The



The reaction temperature was varied from 50oC to 90oC.From figure it is clear that the

maximum selectivity of 2,4 DTBP obtained at 50oC, while the selectivity of 70. 21% was

observed at 50oC temperature. At higher temperature dealkylation reaction is more favoured.

133

Conclusion

From the experimental data, 50oC considered as the optimum temperature for the system

because of the following reasons

1) Highest conversion to Phenol.

2) Highest selectivity of 2,4- DTBP

3) Highest dialkylation

134

3.8.3 Effect of change in concentration of Reactant.

3.8.3.1 Conversion of phenol

0

10

20

30

40

50

60

70

80

90

0 2 4 6 8 10

% S

elec

tivity

Time (hr)

phenol: TBA= 1:1

phenol: TBA= 1:2

phenol: TBA= 1:3

phenol: TBA= 1:4

Figure 3.20 Effect of reactant concentration on conversion of Phenol (Condition: 80oC, Catalyst loading Phenol/ILs 1:1 mol/mol, 8 hr)

Figure 3.20 shows the effect of reactant concentration on the conversion of phenol. The

reaction was carried out at Revolution per minute of 800 rpm, and 1:0.5 catalyst loading of

phenol to ionic liquid [EMIM][EtSO4]. The reactant molar ratio of phenol to tertiary butyl

alcohol was varied from 1:1 to 1:4. From the graph it is clear that as concentration of tertiary

butyl alcohol increases from 1:1 to 1:2, the conversion of phenol increases, but above it’s the

concentration continuously decreases due to dilution of catalyst. Thus the maximum

conversion of phenol obtained at 1:2 ratio phenol to tertiary butyl alcohol is 87.12%.

135


0

5

10

15

20

25

30

35

40

0 2 4 6 8 10

% S

elec

tivity

Time (hr)

phenol: TBA= 1:1

phenol: TBA= 1:2

phenol: TBA= 1:3

phenol: TBA= 1:4

Figure 3.21 Effect of reactant concentrations on the selectivity of o-TBP.

Figure 3.21 shows the effect of concentration of reactant concentration on the selectivity of o-

TBP. The reaction was carried out at Revolution per minute of 800 rpm, and 1:0.5 catalyst

loading of Phenol to Ionic liquid [EMIM][EtSO4]. The reactant molar ratio of Phenol to

tertiary butyl alcohol was varied from 1:1 to 1:4. For the entire molar ratio it is observed that,

selectivity of o-TBP decreases with the time. This is due to di-alkylation of o-TBP to 2, 4-

DTBP. The minimum selectivity of o-TBP observed at 1:4 molar ratio of Phenol to TBA,

while maximum selectivity observed at 1:2 molar ratios. The selectivity at molar ratio 1:4 and

1:3 is high in first two hours, but it decreases due to di-product formation.

136


0

5

10

15

20

25

0 2 4 6 8 10

% S

elec

tivity

Time (hr)

phenol: TBA= 1:1

phenol: TBA= 1:2

phenol: TBA= 1:3

phenol: TBA= 1:4

Figure 3.22 Effect of Reactant concentration on the selectivity of p-TBP.

The figure 3.22 shows the effect of reactant concentration on the selectivity of p-TBP. The

reaction was carried out at Revolution per minute of 800 rpm, and 1:0.5 catalyst loading of

phenol to Ionic liquid [EMIM][EtSO4]. The reactant molar ratio of phenol to tertiary butyl

alcohol was varied from 1:1 to 1:4. From the figure it is clear that the selectivity of p-TBP

continuously decreases with time at all the reactant concentration. It happens due to di-

alkylation of mono-products. Due to less formation of p-TBP compare to o-TBP its rate of

decrease in selectivity is less. The maximum selectivity of p-TBP is observed at 1:4 molar

ratio of phenol to TBA, while minimum selectivity observed at 1:1 molar ratio of phenol to

TBA.

137

3.8.3.4 Selectivity of 2, 4-DTBP

0

10

20

30

40

50

60

70

80

0 2 4 6 8 10

% S

elec

tivity

Time (hr)

phenol: TBA= 1:1

phenol : TBA = 1:2

phenol : TBA= 1:3

phenol: TBA= 1:4

Figure 3.23 Effect of Reactant Concentration on the selectivity of 2, 4-DTBP

Figure 3.23 illustrates the Effect of reactant concentration on the selectivity of 2,4-DTBP.

The reaction was carried out at Revolution per minute of 800 rpm and 1:0.5 catalyst loading

of phenol to Ionic liquid [EMIM][EtSO4]. The reactant molar ratio of phenol to tertiary butyl

alcohol was varied from 1:2 to 1:4. From the figure it is clear that selectivity of 2,4-DTBP

increases with time. The maximum selectivity of 2,4- DTBP obtained at 1:2 molar ratio of

phenol to TBA. While the minimum selectivity obtained at 1:1 molar ratio of phenol to TBA.

Above 1:2 molar ratios, the selectivity does not increase due to dilution of catalyst by TBA.

138

Conclusion

From the experiment conducted, 1:2 molar ratio of phenol to TBA considered as optimum

molar ratio because of following reasons

1) Highest conversion of phenol

2) Maximum formation of 2,4 DTBP

3) Highest dialkylation.

4) Minimum selectivity of o-TBP and p-TBP.

139

3.8.4 Effect of catalyst loading


0

5

10

15

20

25

30

35

0 2 4 6 8

% S

elec

tivity

Time (hr)

phenol: il = 1:0.2

phenol: il = 1: 0.5

phenol: il = 1: 1

phenol : il = 1:1.5

Figure 3.24: Effect of catalyst loading on the selectivity of o-TBP.

Figure 3.24 shows the effect of Catalyst loading on the selectivity of o-TBP. The reaction

was carried out at Revolution per minute of 800 rpm, 1:2 molar ratio of phenol to Tertiary

butyl alcohol and the temperature of 80oC. Catalyst loading of phenol to Ionic liquid

[EMIM][EtSO4] varied from 1:0.2 to 1:1.5 At all the catalyst loading selectivity of o-TBP

decreases with time. The maximum selectivity of o-TBP obtained at 1:0.2 molar ratio of

phenol to ionic liquid, causes dilution of catalyst. Weak acid favours the formation of o-TBP.

Thus selectivity is maximum at 1:0.2 molar ratio compare to other ratios. The minimum

selectivity of o-TBP obtained at 1:1.5 molar ratio of phenol to ionic liquid because of good

poly-alkylation of o-TBP.

140


0

2

4

6

8

10

12

14

0 2 4 6 8 10

% S

elec

tivity

Time (hr)

phenol : il =1: 0.2

phenol: il = 1: 0.5

phenol: il = 1: 1

phenol :il = 1: 1.5

Figure 3.25 Effect of catalyst loading on the selectivity of p-TBP.

Figure 3.25 shows the effect of catalyst loading on the selectivity of p-TBP. The reaction was

carried out at Revolution per minute of 800 rpm, 1:2 molar ratio of phenol to Tertiary butyl

alcohol and the temperature of 80oC. Catalyst loading of phenol to Ionic liquid

[EMIM][EtSO4] varied from 1:0.2 to 1:1.5 From the Figure it is clear that the selectivity of p-

TBP slowly increases with time at all catalyst loading, due to Di-alkylation of p-TBP. The

selectivity of p-TBP is maximum at 1:0.2 molar ratio of phenol to TBA, while minimum at

1:1.5, since more the catalyst loading faster is the formation of di product from mono

products formed.

141

3.8.4.3 Selectivity of 2,4-DTBP

0

10

20

30

40

50

60

70

0 2 4 6 8 10

%Se

lect

ivity

Time (hr)

phenol :il = 1:0.2

phenol :il = 1:0.5

phenol :il = 1:1

phenol :il = 1:1.5

Figure 3.26 Effect of catalyst loading on selectivity of 2, 4-DTBP.

Figure 3.26 illustrates the effect of catalyst loading on the selectivity of 2, 4-DTBP. The


Tertiary butyl alcohol and the temperature of 80oC. Catalyst loading of phenol to Ionic liquid

[EMIM][EtSO4] varied from 1:0.2 to 1:1.5 Figure shows that with time the selectivity of 2,

4-DTBP increases. The maximum selectivity of 2,4 -DTBP obtained at 1:0.5 molar ratio of

phenol to ionic liquid, while the minimum selectivity obtained at 1:0.2 molar ratio of phenol

to ionic liquid.

142

Conclusion

From the experiment conducted, catalyst loading of 1:0.5 considered as optimum because of

following reasons

1) Higher conversion of phenol

2) Highest selectivity of 2,4 DTBP

3) Less formation of monoproducts

143

3.8.5 Catalyst reusability

In order to examine the recoverability and recyclability of the ionic liquid, after the reaction,

the ionic liquid was extracted with toluene and water then dried under vacuum for 5 h. After

vacuum drying, IL-1 was repeatedly used 4 times without signi��

conversion as well as desired product selectivity is also not been affected much, as shown in

Table 3.2

Experimental Conversion of Selectivity (%)run Phenol (%) 2-TBP 4-TBP 2,4-TBP

Fresh catalyst 87.1 27.79 16.9 70.29Recycle 1 86.39 26.99 15.16 70.84Recycle 2 85.29 25.69 15.11 70.13Recycle 3 85.12 25.91 15.41 71.66Recycle 4 83.67 23.57 13.91 67.5

Table 3.2 Catalyst reusability for Freidel Craft Reaction of Phenol

144

3.9 Kinetic of the reactions

Reversible reactions involved in the process are as follows:

Alkylation of phenol

1 2 4� �� k

P TBA TBP TBP

TBA isomerization

22 43

��k

TBA TBAk

Alkylation of 2TBA

42 2, 45

�� k

TBP TBP DTBPk

62 2,67

�� k

TBP TBP DTBPk

Alkylation of 4TBA

84 2,49

�� k

TBP TBP DTBPk

145

3.9.1 Rate of the reaction

Batch reaction kinetic model was developed based on the reaction mechanism

formulated from the product distribution for this reaction. The rated of formation

of products can be expressed as follows:

Rate of alkylation of phenol

��

��= ��

Rate of conversion of tert-butyl alcohol

��

��= �� + �� ,�� + �� ,��

� �� + �� ,��

Rate of formation of 2-TBP

��

��= �� + �� + �� ,��

+ �� ,��

Rate of formation of 4-TBP

��

��= �� + � � �� + �� ,��

Rate of formation of 2,4-DTBP

�� ,��

��= �� ,�� + �� ,��

Rate of formation of 2,6-DTBP

�� ,��

��= �� + �� + �� ,��

146

Rate of formation of Water

��

��= �� + �� ,�� + �� ,��

+ �� ,��

Where C is the concentration of respective components in mol/L, t is the batch reaction

time in seconds and k is the rate constant of respective reaction in L/mol s. Based on the

rate constant equations, rate constant have been calculated in stated table 3.3 which shows

that at reaction temperature 80oC has value of rate constant favorable for the formation of

products at optimum conditions of the reactions.

Table 3.3 Estimated Rate constant and Energy of Activation

temp oCK1 X 105 K2 X 1O4 K3 X 1O5 K4 X 1O5 K5 X 1O5 K6 X 1O5 K7X 1O5 K8X 1O5 K9X 1O5

90 1.02 0.98 1.11 0.83 0.4 8.23 22.81 5.56 0.8180 1.45 1.4 3.11 1.83 0.54 4.76 10.98 9.12 1.4570 1.6 1.75 3.89 2.34 1.13 2.1 4.12 19.34 1.6160 3.72 6.41 8.81 6.96 5.23 3.5 10.45 114.78 45.2150 4.12 7.24 10.45 5.98 5.01 14.2 155.23 160.23 68.56

Ea Kcal/mol 7.23 12.6 12.21 11.67 16.1 18.34 29.32

Rate Constant L/mol

147

3.9.2 Order of reaction.

Figure 3.27: Concentration v/s Time.

Sr. No. Phenol Concentration(mol/ml)

TBA Concentration,(mol/ ml) Slope = dy/dx

1) 0.00245 0.007742 0.0008822) 0.0021 0.007275 0.0007933) 0.00175 0.006809 0.0005934) 0.00135 0.006275 0.000423

Table 3.4: Rate at various concentration

Table 3.4 gives the rate at various concentration of phenol. The rate at various concentrationsis taken from figure 3.27

0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0 2 4 6 8 10

conc

entra

tion,

(mol

/ml)

Time, (hr)

148

Figure 3.28: In (-rA) v/s In (CA.CB)

For second order reactions

ln (-rA) = ln (CA.CB) +ln (k)

The reaction order is found to second order with rate constant 0.02686 lit/ (mol.sec). By

comparing equation of second order reaction and equation of trend line, the reaction is

pseudo second order with respect to phenol and Tertiary butyl alcohol.

y = 0.9457x + 3.291R² = 0.9842

-8

-7.8

-7.6

-7.4

-7.2

-7

-6.8

-6.6

-6.4

-6.2

-6-12 -11 -10 -9 -8

ln(-

rA)

ln(CA.CB)

149

3.10 Conclusions

1. Better selectivity of 2,4-DTBP is observed using laboratory synthesized IL 1-Ethyl-3-

methylimidazolium ethyl sulphate [EMIM] [EtSO4].

2. Reaction occurs at mild acidic condition and lower temperature at 80oC

3. Di-alkylated product i.e. 2,4-ditertbutylphenol is selectively formed in higher

concentration as compared to mono-products. And very negligible formation of 2,6-

ditertbutylphenl is observed.

4. Optimum condition is at 80oC, 1:2:0.5 molar ration of Phenol: TBA: IL, 8 hr.

5. Reaction is pseudo 2nd order with respect to phenol and TBA.

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Chapter 3 Friedel-Crafts alkylation of Phenol using …...Craft in 1877 to attach substituent to an aromatic ring. There are two main types of Friedel-Craft reactions: alkylation reaction