The present invention relates to an improved process for alkylation of phenols.
Particularly, this invention relates to an improved process for alkylation of phenol and substituted phenols with methyl tertiary butyl ether (MTBE) in presence of a catalyst. More specifically the present invention relates to an improved process for preparing alkyl phenols by alkylation phenol and substituted phenols with MTBE to produce t-butyl phenols using cation-exchange resin as catalyst.
Alkylation of phenols is industrially important reaction leading to various alkyl phenols, which are valuable industrial chemicals find use as precursors in a variety of industries. Among the alkyl phenols, tert-butylated phenols are most valuable. 4-tert-butyl phenol is used in making fragrances, oil field chemicals, demulsifiers and resins. 2-tert-butyl phenol is an intermediate for pesticides, resins and fragrances etc. Di-alkylated phenol such as 2,4-di-tert butyl phenol and 2,6-di-tert butyl phenol are used as antioxidants, and pharmaceutical intermediates. Tertiary butylated methyl phenols such as 2,6-di-tert-butyl 4-methyl phenol is used as antioxidants in fuels, lubricating oils, food products and pharmaceuticals.
Tertiary butyl phenols are generally manufactured by alkylation of phenol with pure isobutylene or C4 fraction from naphtha/gas cracker or catalytic Cracking operation in a petroleum refinery.
A variety of alkylating agents are known to be used, but typically olefins, alkyl halides and alcohols are used.
The alkylation reaction of phenol with isobutylene is carried out in presence of liquid acid catalyst such as H2SO4, H3PO4 and BF3. The alkylation reaction with these acidic catalysts gives, depending upon the reaction conditions such as temperature, purity of isobutylene, pressure, phenol to isobutylene ratio and type of acidic catalyst, various alkylated products including mono and polyalkylated products. The liquid acids catalysts are highly corrosive, pullulating, hazardous to handle and gives lower selectivities of desired alkyl phenol product. Further there are problems associated

with handling of pure isobutylene and mixed C4-streams from safety angle, particularly for small capacity production capacities. Therefore, it is advantageous to perform the alkylation reaction using tertiary-butyl alcohol, isobutyl alcohol or MTBE, which can be dehydrated/ cracked separately or in situ generating isobutylene which reacts with phenol to form alkyl phenol. When alcohol is used as a source of isobutylene, water is formed as by-product which is required to be removed simultaneously using azeotropic solvent such as benzene, toluene or xylenes. Removal water improves the activity of the catalyst.
Recently MTBE has been used to produce isobutylene, by cracking either separately or in situ, which is used to alkylate phenols to produce alkyl phenols.
When alkylation is conducted with alcohols use of catalysts other than liquid acids such as ion exchange resins, zeolites, acidic days etc. is also known in the prior art.
In alkylation of phenols with MTBE catalysts such as H2SO4, ZrCl4, perchloric acid have been reported to be used. These catalysts based on liquid acids are hazardous and pullulating.
For heteropoly acids, zeolites, clays including sulphated zirconia have also been reported in the alkylation of phenols with MTBE.
For alkylation of phenols using clays, zeolite based catalyst reaction temperature of 150° or more is needed below which the reaction rate is slow.
In view of the problems of pollution, handling, safety in handling liquid acid catalysts and isobutylene and slow reaction rate, at lower temperature, with clay or zeolite catalysts there is a need to develop an improved process, for producing alkyl phenols by alkylation phenols and substituted phenols using MTBE as alkylation agent, which can be operated at low to moderate temperature and ecofriendly.

The main object of the present invention is to provide an improved process for alkylation of phenols
Another object of the present invention is to provide a process by reacting phenol and substituted phenols with methyl tertiary butyl ether (MTBE) as alkylation agent.
Still another objective of the present invention is to overcome the above disadvantages to provide a method of to prepare alkyl phenols by reaction of phenol or substituted phenols which can be operated at low to moderate temperatures with a non-polluting active catalyst and the overall process is ecofriendly.
The present invention relates to a new and improved process for producing alkyl phenol and substituted alkyl phenols by reacting phenol or substituted phenols with methyl tertiary butyl ether in presence of a catalyst. To overcome the disadvantages related to the known methods some modifications of the known methods have been devised. Such modifications include use of sulfonated styrene-divinyl benzene copolymers cation exchange resins as catalyst for the alkylation of phenols to alkyl phenols with methyl tertiary butyl ether as alkylating agent.
It has now been discovered that phenol or substituted phenols can be alkylated with isobutylene to produce in good yield into tertiary alkyl phenols under particularly mild conditions with respect to temperature, pressure and corrosion by using cation exchange resin as catalyst and MTBE as alkylating agent.
During the investigations, the authors have found that alkyl phenols are produced by the reaction of isobutylene produced in situ from MTBE cracking. The cracking of MTBE to isobutylene and its reaction with phenol occur simultaneously in presence of cation exchange resin catalyst at mild temperature. Methanol which is formed as a byproduct acts as a co-solvent in the reaction and is recovered from the main products by distillation.

Acidic catalysts used in the prior art processes, need to be removed from the product by neutralization with an alkali and water washing cation exchange resin used in the present invention is non-polluting and may be separated from the reaction mixture by filtration and is recycled. The process of the present invention is ecofriendly as no alkali and water washing are required to remove the catalyst.
Accordingly the present invention provide an improved process for alkylation of phenol which comprises reacting phenol or substituted phenols or mixtures thereof with methyl tertiary butyl ether in presence of a cation exchange resin catalyst and a hydrocarbon solvent, wherein the concentration of cation exchange resin catalyst in the range of 2-20% weight percent of phenol or substituted phenol; phenol to methyl tertiary butyl ether molar ratio in the range of 0.1-3, hydrocarbon solvent to phenol ratio between 0.5-5 by weight at a temperature of between 40-150°C and reaction time for a period of 1-10 h, cooling the reaction mixture followed by filtering of the resin catalyst and purifying the alkyl phenols by distillation.
In an embodiment of the present invention the hydrocarbon solvent is selected from benzene, toluene or xylene preferable toluene.
In another embodiment of the present invention the ratio of hydrocarbon solvent to phenol is preferably between 1.0-4.0 by weight.
In yet another embodiment of the present invention the molar ratio of phenols to methyl tertiary butyl ether is in the range of 0.5-2.5.
In still another embodiment of the present invention the reaction temperature is in the range of 50-130°C.
In still another embodiment of the present invention the reaction time is in between 2-8 hour.

In still another embodiment of the present invention the catalyst is selected from microreticular or gel type or sulfonated divinyl benzene -styrene copolymer cation exchange resin.
In still another embodiment of the present invention the concentration of the catalyst used is in the range of 5-15 weight percent of phenol.
In the process of present invention the alkylated product is purified by removing the catalyst by filtration followed by fractional distillation.
It will be apparent from the foregoing that the present invention provides an improved process for alkylating phenols using cation exchange resin as catalyst and methyl tertiary butyl ether as alkylating agent at relatively mild temperature; the process is ecofriendly since hazardous acids are not used as catalyst and no effluent waste water streams are produced in the process.
The invention is further described by the following examples which are given only for the purpose of illustration and are not intended to limit the scope of the invention.
Example -1
Phenol (0.25 moles) and 0.25 moles of methyl tertiary butyl ether (MTBE) were mixed in 25 ml of toluene and charged into a stainless steel stirred reactor fitted with a condenser and heating/cooling arrangement. To this 3g of dried Amberlist-15 cation exchange resin was added. The reactor was closed. The temperature was maintained at 80±2 °C with help of an automatic controller system that controlled the outside heating of the reactor. After 2.5 hours the reaction mixture was cooled filtered and the liquid product was analyzed by gas liquid chromatography. The composition (wt%) of liquid obtained after removal of unreacted MTBE and by product methanol was as follows:
Phenol : 82.80
Monoalkylated phenols : 16.31

di-alkylated phenols : 0.43
Trialkylated phenols : 0.43
Others : 0.03
Example - 2
The procedure of example-1 was repeated except that the temperature was maintained at 120°C. The composition of liquid product obtained after removal of unreacted MTBE and byproduct methanol was as follows:
Phenol : 37.33
Monoalkylated phenols : 50.38
di-alkylated phenols : 12.29
Trialkylated phenols : traces
Example - 3
Procedure of example-1 was repeated except that in place of Amberlist -15 cation exchange resin, dried gel type cation exchage resin Tulsain-42 was taken and the temperature was maintained at 120°C. The liquid product obtained showed the following composition (wt%).
Phenol : 24.47
Monoalkylated phenols : 59.12
Di-alkylated phenols : 14.89
Trialkylated phenols : 1.52
Example - 4
Procedure of example-1 was repeated except that in place of Amberlist-15, 3g of dried zeolite (ZSM-5) powder was taken; temperature was maintained at 120°C. The liquid product obtained showed the following composition (wt%).
Phenol : 97.97
Monoalkylated phenols : 0.68
7

di-alkylated phenols : 0.23
Trialky lated phenols : 1.13
Example - 5
Procedure of example-1 was repeated except that in place of phenol, p-methyl phenol was taken and the temperature was maintained at 120°C. The composition (wt%) of the liquid product obtained after removal of resin, unreacted MTBE and byproduct methanol was as follows:
p-methyl phenol (p-cresol) : 31.40
monoalkylated p-cresol : 53.71
dialkylated p-cresol : 14.89

We Claim
1. An improved process for alkylation of phenol which comprises reacting phenol or
substituted phenols or mixtures thereof with methyl tertiary butyl ether in presence
of a cation exchange resin catalyst and a hydrocarbon solvent, wherein the
concentration of cation exchange resin catalyst in the range of 2-20% weight
percent of phenol or substituted phenol; phenol to methyl tertiary butyl ether molar
ratio in the range of 0.1-3, hydrocarbon solvent to phenol ratio between 0.5-5 by
weight at a temperature of between 40-150°C and reaction time for a period of 1-
10 h, cooling the reaction mixture followed by filtering of the resin catalyst and
purifying the alkyl phenols by distillation.
2. An improved process as claimed in claim 1 wherein the hydrocarbon solvent is
selected from benzene, toluene or xylene preferable toluene.
3. An improved process as claimed in claims 1 and 2 wherein the ratio of
hydrocarbon solvent to phenol is preferably between 1.0-4.0 by weight.
4. An improved process as claimed in claims 1 to 3 wherein the molar ratio of
phenols to methyl tertiary butyl ether is in the range of 0.5-2.5.
5. An improved process as claimed in claims 1 to 4 wherein the reaction temperature
is in the range of 50-130°C.

6. An improved process as claimed in claims 1 to 5 wherein the reaction time is in
between 2-8 hour.
7. An improved process as claimed in claims 1 to 6 wherein the catalyst is selected
from microreticular or gel type or sulfonated divinyl benzene -styrene copolymer
cation exchange resin.

8. An improved process as claimed in claims 1 to 7 wherein the concentration of the
catalyst used is in the range of 5-15 weight percent of phenol.
9. An improved process for alkylation of phenols substantially as herein described
with references to the examples.