DESC:Field of the invention
The present invention relates to the development of continuous process for the highly selective preparation of para-tert-butyl toluene from the toluene and iso-butelene under mild reaction condition.
Background of the invention
The alkylations of aromatic hydrocarbons to corresponding alkylated-aromatic products are applied on a large scale and has great importance in the chemical industry. The alkylations processes are generally carried out by the reaction of aromatic hydrocarbons with olefins or alcohols in suitable solvents to corresponding alkylated-aromatic products with varied conversion and selectivity. Among the processes established for the alkylated aromatic products, p-xylene, p-diisopropylbenzene, p-ethyltoluene, p-dietylbenzene, and p- or-cymenes, p-tert-butyltoluene is very important product in fine chemical and petrochemical industries. p-tert butyl toluene is an intermediate for the p-tertiary butyl benzaldehyde, p-tertiary butylbenzoic acid and p-tertiary butyl methylbenzoate used in the synthesis of fine chemicals. p-tert butyltoluene is produced by tert-butylation of toluene in the liquid phase in presence of different catalysts such as sulphuric acid, activated clays or silica- alumina and H-MOR, H-Y and H-BEA zeolite catalysts at different temperature.
The formation of isomers of tert-butyl toluenes by the catalytic alkylation of toluene with butylating agents such as isobutylene, diisobutylene, MTBE or tert-butyl alcohol has been reported by several groups till date. In some cases, these processes have been effective to afford high conversion, but produce mixtures of the meta and para isomers. The conversion of toluene to desired p-tert butyl toluene depends on the controlled operating conditions including selection of right catalysts with suitable tert-butylating agents. The difficulties of adequate reaction control and the nature of the catalyst frequently render low conversion and or high ratio of meta to para isomers and hence un-economical for the commercial utilization.
The present invention relates to the development of continuous process for the highly selective preparation of para-tert-butyl toluene from the toluene and isobutelene under mild reaction condition.
Alkylations of toluene are carried out in presence of different catalytic systems involving homogeneous and heterogeneous catalysts, different butylating agents under different optimized reaction conditions. Some important references on alkylation of toluene under homogeneous and heterogeneous catalytic conditions are given below:

Reference may be made to the publications, Indian Journal of Chemistry, Section B: Organic Chemistry Including Medicinal Chemistry, 33B(11), 1053-61; 1994 wherein alkylation of benzene, toluene and xylene isomers with C-2, C-3 and C-4 aliphatic alcohols on TiO2-SiO2-Al2O3 and MoO3-SiO2-Al2O3 is reported by Sabu, K. R. et al. The inherent disadvantages are low selectivity and yield of desired alkylated product.

Reference may be made to the publications, Applied Catalysis, A: General, 257(1), 49-55; 2004
wherein Mravec, Dusan et al reported Tert-butylation of toluene over zeolite catalysts by tert- butyl alcohol however, the selectivity of desired alkylated product is poor.

Reference may be made to the publication, Journal of Molecular Catalysis A: Chemical, 223(1-2), 305-311; 2004 wherein regioselective butylation of toluene on mordenite catalysts: influence of acidity is studied by Peter, Sebastian C. et al. 67% selectivity with other isomers are reported in the gas phase alkylation reactions.

Reference may be made to the publication, Applied Catalysis, A: General, 286(1), 44-51; 2005 wherein novel route to produce 4-t-butyltoluene by t-butylation of toluene with t-butylalcohol over mesoporous Al-MCM-41 molecular sieves is reported by Selvaraj, M. et al. The conversion of the toluene is 85% with selectivity 80% for toluene and 5% for other isomers are reported.

Reference may be made to the publications, ChemPhysChem, 6(3), 466-472; 2005 wherein pressure effects on Friedel-Crafts alkylation reactions in supercritical difluoromethane is studied by Abbott, Andrew P. et al. The effect of pressure on the selectivity and conversion of the desired para isomer of the alkylated product is studied.

Reference may be made to the publication, Shiyou Huagong, 35(1), 79-83; 2006 wherein alkylation of toluene with tert-butyl alcohol over H type mordenite catalyst is reported by Zhou, Zhiwei et al. The alkylation is carried out in presence of cyclohexane solvent and effect of solvent on the selectivity and conversion is studied.

Reference may be made to the publication, Journal of Molecular Catalysis A: Chemical, 265(1-2), 109-116; 2007 reported by Pai, Shivanand et al in butylation of toluene: Influence of zeolite structure and acidity on 4-tert-butyltoluene selectivity.
Reference may be made to the publication, Indian Journal of Chemistry, Section A: Inorganic, Bio-inorganic, Physical, Theoretical & Analytical Chemistry, 47A(2), 181-185; 2008 by Yu, Weihua et al in synthesis and characterization of Al-HMS catalysts and their application for t-butylation of toluene. The report discloses the synthesis of Al-HMS catalyst its reactivity at 175-1850C in decane solvent however, the conversion and selectivity towards para isomers of alkylated product was moderate.

Reference may be made to the publication, Industrial & Engineering Chemistry Research, 49(5), 2091-2095; 2010 wherein alkylation of toluene with t-butyl alcohol over zeolite catalysts is reported Dong, Hong-jun and Shi, Li. The report discloses the conversion of toluene was 38% and selectivity of desired isomer was 78%.

Reference may be made to the publication, Turkish Journal of Chemistry, 34(6), 875-885; 2010 where in vapor phase alkylation of toluene using various alcohols over H3PO4/MCM-41 catalyst: influence of reaction parameters on selectivity and conversion is reported by Abbaspourrad, Alireza et al. The process used H3PO4 impregnated Al-MCM-41 molecular sieve catalyst for the alkylation of toluene to obtain 73% para isomer and 27 % other isomers of alkylated products.

Reference may be made to the publication, Journal of Chemistry, 9(4), 1875-1884; 2012 wherein investigation of Friedel-Crafts alkylation in the presence of supported sulfonic acid on silica gel is studied by Kiasat, A. R. et al. The process involves preparation of cellulose sulfonic acid supported on silica gel as catalyst for the alkylation of toluene at high temperature to produce para isomer in 87% selectivity.

Reference may be made to the publication, Canadian Journal of Chemistry, 91(12), 1262-1265; 2013by Mack, Ryan et al in indium(III) triflate - a catalyst for greener aromatic alkylation reactions. Though the catalyst used in the alkylation is recoverable and reusable, the yield and selectivity of the desired alkylated product is low.

In addition to above references, Chinese authors have reported alkylation reaction of substituted aromatics, however high temperature, low conversion, and low selectivity of desired para isomers are the inherent disadvantage of the processes. Therefore, a need for a process for the preparation of selective para isomer of butylated toluene without using solvent or additive.
Object of the Invention
The main object of the present invention is to provide a continuous alkylation of toluene using isobutelene as a butylating agent in the presence of catalyst.

Another object of the present invention is to provide a process for the preparation of para-tert- butyl toluene (henceforth PTBT) with very high selectivity and high conversion.

Another object of the present invention is to provide a process for the preparation of PTBT using toluene as a substrate, sulphuric acid as a catalyst and commercially available isobutelene as a butylating agent.

Another object of the present invention is to provide a process for the preparation of PTBT using toluene as a substrate, sulphuric acid as a catalyst and commercially available isobutelene as a butylating agent without using any solvent media.

Another object of the present invention is to provide a process for the preparation of PTBT using toluene as a substrate, sulphuric acid as a catalyst and commercially available isobutelene as a butylating agent at 15-300C temperature.

Still another object of the present invention is to purify the target product, PTBT by continuous distillation method to obtain pure and selective PTBT.

A continuous process for selective preparation of para-tert-butyl toluene, which comprises of alkylation of toluene using isobutelene gas as a alkylating agent in the presence 98% H2SO4 at temperature ranges between 15-30 degree C for period of 1.5 h under vigorous stirring condition and separation of product from the crude mixture. The process claimed above used inexpensive acid and the process offers high conversion and exclusive selectivity of para isomers.
The process as claimed in claim 1, wherein the catalyst is 2.5-5.0 weight % with addition rate of 0.3- 0.5 gm/h.
The process wherein isobutelene gas was bubbled at the rate of 4.0- 6.0 gm/h.
The process wherein the temperature was maintained at 24-26 degree C for 1.0- 2.0 h.
The process wherein vigorous stirring (500-700 rpm) is needed to mix the heterogeneous system properly.
The process wherein the para isomer is formed selectively and distilled out from crude mixture by distillation method.
The process wherein unreacted toluene is recycled.
The process wherein catalyst is recovered and recycled after proper treatment.

Description of the Invention
Accordingly, the present invention provides a process for the preparation of para-tert-butyl toluene, an important intermediate product to produce 4-tert-butylbenzoic acid and 4-t-butylbenzaldehyde; they are especially used in perfumery and in the fields of plastics and resins wherein the said process comprises reacting toluene with bubbling of isobutelene gas in presence of catalytic amount of sulphuric acid at temperature ranges between 15-30oC, separating the catalyst and recovering the product by conventional distillation method.
In an embodiment of the present invention sulphruirc acid is used as the catalyst.
In an embodiment of the present invention the concentration of sulphuric acid 80 to 95%.
In an embodiment of the present invention the isobutelene is used as an alkylating agent.
In still another embodiment of the present invention is effected at a temperature in the range of 15- 30 oC.
In an another embodiment of the present invention the catalyst is separated by gravity decantation from the reaction mixture and the product is separated by conventional distillation method.

Scientific Explanation
The Bronsted acid catalysed alkylation reaction generally affords ortho, meta and para substituted alkylated products. The selectivity of the alkylated product towards para position is highly important in view of industrial application of para- alkylated products in various fields. The temperature, addition of catalyst to maintain the specific ratio between starting material and catalyst and stirring speed of agitator are important criteria in alkylation reactions. These parameters have been optimised under continuous alkylation reaction and achieved selectively para substituted alkylated product.
The following example is given by way of illustration of the present invention and therefore should not be construed to limit the scope of the invention.

EXAMPLE 1
Alkylation of toluene
The reactor was continuously charged with toluene at a rate of 5gm/h and sulphuric acid (98%) (2.5% by wt. w. r. t toluene) at 0.416gm/h at 15-30 oC. Isobutelene gas was bubbled through the mixture of toluene and sulphuric acid continuously at same temperature. The reaction is exothermic in nature and the temperature was controlled using chiller in such way that the reaction temperature does not exceed to 24-26 oC. The rate of addition of toluene and sulphuric acid was carefully controlled to get the conversion of toluene into desired para alkylated product to 50% with 70% selectivity. The produced para alkylated product and waste sulphuric acid was continuously collected in the separate receivers. The pure para alkylated product was distilled out to get pure PTBT. The aqueous layer is checked for acidity and the water removed to get the acidity similar to fresh sulphuric acid for recycle.
EXAMPLE 2
Alkylation of toluene
The raw materials toluene and sulphuric acid were continuously charged into the reactor with at a rate of 5gm/h and 0.083 gm/h (5% by wt. w. r. t toluene). Isobutelene gas was bubbled through the mixture of toluene and sulphuric acid continuously at same temperature. The reaction temperature was controlled using chiller in such way that the reaction temperature does not exceed to 24-26 oC. The rate of addition of toluene and sulphuric acid was carefully controlled to get the conversion of toluene into desired para alkylated product to 80% with 99% selectivity. The produced para alkylated product was distilled out to get pure PTBT.
EXAMPLE 3
Alkylation of toluene
The reactor was continuously charged with toluene and sulphuric acid with the quantities mentioned in example 2. at 30-33 oC. The isobutelene gas was bubbled through the mixture of toluene and sulphuric acid continuously at same temperature. The reaction is exothermic in nature and the temperature was controlled using chiller in such way that the reaction temperature does not exceed to 35oC. The rate of addition of toluene and sulphuric acid was carefully controlled to get the conversion of toluene into desired para alkylated product to 32% with 99% selectivity. The produced para alkylated product and waste sulphuric acid was continuously collected in the separate receivers. The pure para alkylated product was distilled out to get pure PTBT.
EXAMPLE 4
Alkylation of toluene using recovered sulphuric acid.
The reactor was continuously charged with toluene and sulphuric acid recycled without any treatment with the quantities mentioned in example 2. at 15-30 oC. The isobutelene gas was bubbled through the mixture of toluene and sulphuric acid continuously at same temperature. The reaction is exothermic in nature and the temperature was controlled using chiller in such way that the reaction temperature does not exceed to 24-26 oC. The rate of addition of toluene and sulphuric acid was carefully controlled to get the conversion of toluene into desired para alkylated product to 9% with 62% selectivity. The produced para alkylated product and waste sulphuric acid was continuously collected in the separate receivers. The pure para alkylated product was distilled out to get pure PTBT.
EXAMPLE 5
Alkylation of toluene at 40°C
The reactor was continuously charged with toluene and sulphuric acid with the quantities mentioned in example 2. at 40-43oC. The isobutelene gas was bubbled through the mixture of toluene and sulphuric acid continuously at same temperature. The reaction is exothermic in nature and the temperature was controlled using chiller in such way that the reaction temperature does not exceed to 43oC. The rate of addition of toluene and sulphuric acid was carefully controlled to get the conversion of toluene into desired para alkylated product to 40% with 75% selectivity. The produced para alkylated product and waste sulphuric acid was continuously collected in the separate receivers. The pure para alkylated product was distilled out to get pure PTBT.

We claim
1. A continuous process for selective preparation of para-tert-butyl toluene, which comprises of alkylation of toluene using isobutelene gas as a alkylating agent in the presence 98% H2SO4 at temperature ranges between 15-30 degree C for period of 1.5 h under vigorous stirring condition and separation of product from the crude mixture. The process claimed above used inexpensive acid and the process offers high conversion and exclusive selectivity of para isomers.
2. The process as claimed in claim 1, wherein the catalyst is 2.5-5.0 weight % with addition rate of 0.3- 0.5 gm/h.
3. The process as claimed in claim 1 to 2 wherein isobutelene gas was bubbled at the rate of 4.0- 6.0 gm/h.
4. The process as claimed in claim 1 to 3 wherein the temperature was maintained at 24-26 degree C for 1.0- 2.0 h.
5. The process as claimed in claim 1 to 4 wherein vigorous stirring (500-700 rpm) is needed to mix the heterogeneous system properly.
6. The process as claimed in claim 1 to 5 wherein the para isomer is formed selectively and distilled out from crude mixture by distillation method.
7. The process as claimed in claim 1 to 6 wherein unreacted toluene is recycled.
8. The process as claimed in claim 1 to 7 wherein catalyst is recovered and recycled after proper treatment.
DATED THIS DAY OF 2016
SCIENTIST
IPU,CSIR
Council of Scientific and Industrial Research

Abstract
A Continuous Process for Highly Selective Preparation of para-tert-Butyl Toluene

The present invention relates to the continuous process for the highly selective preparation of para-tert-butyl toluene from toluene and isobutelene under mild reaction conditions. A continuous process for selective preparation of para-tert-butyl toluene, which comprises of alkylation of toluene using isobutelene gas as a alkylating agent in the presence 98% H2SO4 at temperature ranges between 15-30 degree C for period of 1.5 h under vigorous stirring condition and separation of product from the crude mixture. The process claimed above used inexpensive acid and the process offers high conversion and exclusive selectivity of para isomers.

,CLAIMS:We claim
1. A continuous process for selective preparation of para-tert-butyl toluene, which comprises of alkylation of toluene using isobutelene gas as a alkylating agent in the presence 98% H2SO4 at temperature ranges between 15-30 degree C for period of 1.5 h under vigorous stirring condition and separation of product from the crude mixture. The process claimed above used inexpensive acid and the process offers high conversion and exclusive selectivity of para isomers.
2. The process as claimed in claim 1, wherein the catalyst is 2.5-5.0 weight % with addition rate of 0.3- 0.5 gm/h.
3. The process as claimed in claim 1 to 2 wherein isobutelene gas was bubbled at the rate of 4.0- 6.0 gm/h.
4. The process as claimed in claim 1 to 3 wherein the temperature was maintained at 24-26 degree C for 1.0- 2.0 h.
5. The process as claimed in claim 1 to 4 wherein vigorous stirring (500-700 rpm) is needed to mix the heterogeneous system properly.
6. The process as claimed in claim 1 to 5 wherein the para isomer is formed selectively and distilled out from crude mixture by distillation method.
7. The process as claimed in claim 1 to 6 wherein unreacted toluene is recycled.
8. The process as claimed in claim 1 to 7 wherein catalyst is recovered and recycled after proper treatment.
DATED THIS DAY OF 2016
SCIENTIST
IPU,CSIR
Council of Scientific and Industrial Research