FIELD OF THE INVENTION:
The present invention relates to an improved process for the preparation of aromatic ketones. More particularly, the present invention relates to an improved process for the preparation of highly pure aromatic ketones by Friedel-Crafts acylation of alkanes using acetyl fluoride as an acylating agent in the presence of anhydrous hydrofluoric acid as the catalyst followed by monitoring the reaction in situ with FTIR real time probe.

BACKGROUND AND PRIOR ART OF THE INVENTION:
Aromatic ketones are valuable intermediates useful in the production of pharmaceutical compounds, cosmetics and in other applications. These types of ketones are usually prepared by the Friedel-Crafts acylation of an aromatic nucleus. However, in some cases these methodology does not produce the desired isomer, and more indirect methods must be employed. Further, 4’-isobutylacetophenone (4-IBAP) is an important intermediate for 2-(4-isobutylphenyl) propionic acid (trade name; ibuprofen), a well-known nonsteroidal anti-inflammatory, antipyretic and analgesic drug. Friedel-Crafts acylation is one of the most important methods for manufacturing acylated benzene derivatives. The reaction typically utilizes an acylating agent such as an acyl chloride, acyl fluoride, or acetic anhydride and an electrophilic catalyst such as aluminum chloride, boron trifluoride, or hydrogen fluoride.

The acetylation or alkylation of aromatic compounds in hydrogen fluoride is well known in the art. Since, typically, the aromatic compound reactant has a limited solubility in hydrogen fluoride, whereby the contact between the aromatic compound and the acylating or alkylating agent is restricted, the rate of reaction is reduced. In the past, due to the reduced rate of reaction, the acetylation or alkylation or aromatic compounds in hydrogen fluoride was carried out in a batch mode, typically in a continuously stirred batch reactor.

The ibuprofen manufacturing involves acylation of IBB to 4’-IBAP using Friedel’s Crafts catalyst i.e. AlCl3 in stoichiometric amounts or more, resulting in large amounts of aluminum trichloride hydrate waste going to landfills. Thus this process or step is highly polluting. See Cann and Connelly, Real World Cases in Green Chemistry, 2000, and references therein; The Presidential Green Chemistry Challenge Awards Program: Summary of 1997 Award Entries and Recipients, p. 2.
US5068448 discloses a continuous process for the production of 4'-isobutylacetophenone (4-IBAP) comprising feeding liquid hydrogen fluoride (HF) and an acetylating agent into an extractor-reactor to form a first, HF-rich phase containing the acetylating agent, feeding isobutyl benzene (IBB) to the extractor-reactor to form a second, IBB-rich phase which is contacted with said first, HF-rich phase in a manner such that the acetylating agent reacts with IBB to form 4-IBAP which is extracted into the first, HF-rich phase, and a light IBB-rich second phase containing the bulk of unreacted IBB, externally recycling said second, IBB-rich phase to the IBB feed point in combination with fresh IBB to make up for IBB consumed in the reaction and that and dissolved in the HF-rich phase, and withdrawing HF-rich phase containing 4-IBAP from the extractor-reactor.

WO2007044270 discloses a process to prepare acylated alkyl benzene compounds and derivatives thereof comprising acylating an alkyl benzene with an acylating agent at a temperature below about 0°C.

US5185469 discloses use of a continuous, multi-stage process for carrying out the acylation or alkylation reaction. In the multi-stage process, the continuous phase can be either the hydrogen-fluoride rich phase or the aromatic compound-rich phase. The movement of the continuous phase relative to the non-continuous (dispersed) phase can be countercurrent or co-current. The multi-stage process can be operated in a manner such that the aromatic compound feed to the reaction is entirely consumed or such that unreacted aromatic compound is recycled.

US4990681 discloses a method is provided for separating hydrogen fluoride (HF) from a mixture comprising HF complexed with an aromatic ketone in which the keto carbon atom is directly bonded to an aromatic ring carbon atom, e.g., 4-isobutylacetophenone, by adding a carboxylic acid anhydride, e.g., acetic anhydride, to the mixture while maintaining the mixture at conditions sufficient to sustain a reaction between the anhydride and the HF to form the corresponding acyl fluoride, e.g., acetyl fluoride, and carboxylic acid, e.g., acetic acid, and separating the acyl fluoride from the mixture.

“FTIR Spectroscopy with In Situ Reaction Monitoring” discloses suitable for a wide range of chemistries, ReactIR in situ Fourier Transform Infrared (FTIR) Spectroscopy provides real-time monitoring of key reaction species, and how they change during the course of the reaction. Designed to follow reaction progression, ReactIR Attenuated Total Reflection (ATR) provides specific information about reaction initiation, conversion, intermediates and endpoint.

“Using FT-IR for In-Situ monitoring of Polyurethane synthesis” by ABB Measurement and Analytics - Analytical Measurement Products discloses Fourier transform infrared spectroscopy (FTIR) is a measurement technique which generates an infrared spectrum of emission, absorption, Raman scattering or photoconductivity of a liquid, solid or gas.
An FTIR spectrometer is capable of collecting spectral data in a broad spectral range at the same time - this makes it preferable to dispersive spectrometers for many applications, as they can only determine intensity across a narrow range of wavelengths at a given time. The name Fourier transform infrared spectroscopy stems from the fact that a Fourier transform is needed to produce the actual spectrum from the raw data before it can be analyzed.

“Chemical composition monitoring using an In-Situ Infrared Probe” by Walter M. Doyle discloses a new approach to process analysis utilizing an infrared probe which can be immersed within a volume of liquid chemical. Based on the internal reflectance principle, the immersion probe can be coupled to a process FTIR spectrometer to provide essentially real-time analysis of either batch or continuous reactions. After describing the design of the probe, the paper presents the results of a series of laboratory scale experiments in which a small version of the immersion probe was used to monitor various polymerization reactions.

“Real time In-Situ monitoring of Organic reactions using an FTIR Fiber Optic System” discloses the use of the FTIR as a reaction monitor can aid in recognizing formation of intermediates as well as in determining depletion of reactants and formation of products. In most cases, it is not feasible to remove aliquots of a reaction mixture for measurement with traditional IR accessories such as liquid cells. The use of a Fiber Optic Probe system allows real-time monitoring of the reaction in the reaction vessel.

WO1993010875 discloses the process comprises contacting water in the mixture with an acyl fluoride, and carboxylic anhydride, or both to form the corresponding carboxylic acid of the anhydride, and separating HF from the carboxylic acid. For a mixture containing HF and acyl fluoride, the mixt, is heated under conditions to form an azeotropic mixture of HF and acyl fluoride and an anhydrous vapour enriched in HF, and the vapour enriched in HF is separated from the liquid mixture.

EP215351 discloses title compounds are prepared by reacting aromatic hydrocarbons with AcF in the presence of anhydrous HF at 0-70 °C/= 2 kg/cm2-gage. A stainless steel packed column containing a top reflux apparatus and bottom reboiler was fed 22 mol/h Ac2O and 21.0 mol/h HF. The reactor was operated at < 1.0 kg/cm2-gage and heated such that the head temperature was ~35 °C, and AcF was distilled out of the head at 21 mol/h, and a liquid mixture comprising 21 mol AcOH and 1 mol Ac2O was withdrawn every hour from the bottom. Another reactor was charged with PhOMe, AcF, and HF so that the AcF/PhOMe molar ratio was 0.95 and the HF/AcF molar ratio was 20, and the temperature was maintained at 25 °C for 2 h producing an acetylation yield (relative to PhOMe) of 89%, consisting of 97% 4-MeOC6H4Ac.

JP2005060337 discloses a method for producing aromatic ketones which comprises reacting an aromatic compound with an acylating agent in the presence of a Bronsted acid. For example, heptanoic acid was reacted with p-xylene in the presence of HN(SO2CF3)2 to give 1-(2,5-dimethylphenyl)-1-heptanone (82%). This process reduces byproduct production and environment pollution.

WO2017079718 discloses provides methods that include acylating an aromatic containing compound by reacting the aromatic containing compound with an anhydride containing compound to form an acylated aromatic containing compound. For example, furan was reacted with lauric acid in hexane in the presence of trifluoroacetic anhydride and H-BEA catalyst to provide 2-dodecanoylfuran, which was hydrogenated in hexane in the presence of copper chromite to give 2-dodecylfuran. 2-Dodecylfuran was sulfonated and neutralized to make sodium 2-dodecylfuran-5-sulfonate.

JP2004292365 discloses preparation of aromatic ketones by acylation of aromatic compounds with carboxylic acids in the presence of catalytic amount of Lewis acid catalysts of MXm-Ln [wherein, M is a metal ion selected from Bi, Ga, In, Hf and rare earth element; X is a bis(perfluoroalkanesulfonyl)amide anion; L is a neutral molecule capable of coordinating with M; m is the valence of the metallic M; and n is an integer of 0-10]. Thus, p-xylene was treated with hexanoic acid and Bi[N(SO2CF3)2]3 in a sealed reactor at 180 °C for 45 h to give 67% 1-(2,5-dimethylphenyl)-1-hexanone.

Article titled “Synthesis of dodecylbenzene by Friedel-Crafts acylation reaction” by Hu, Shuaishuai et al. published in Jingxi Shiyou Huagong (2008), 25(3), 46-49 reports a method for the synthesis of the title compound. [i.e., detergent alkylate no. 2, dodecyl benzene, lauryl benzene, Nalkylene]. Dodecyl benzene was prepared by lauroyl chlorination, Friedel-Crafts acylation and Huang Minglong deoxidation, followed by purification by vacuum distillation and recrystallization procedures. Lauroyl chloride was first prepared from dodecanoic acid and thionyl chloride. A reaction of lauroyl chloride, aluminum chloride and benzene at 80 °C for 9 h gave 1-phenyl-1-dodecanone. A Huang Minglong reduction of that ketone was carried out using hydrazine hydrate. After vacuum distillation and recrystallization, the yield of the target product was 59.2%. The product structure was determined by NMR.

Article titled “Aluminum dodecatungstophosphate (AlPW12O40) as a non-hygroscopic Lewis acid catalyst for the efficient Friedel-Crafts acylation of aromatic compounds under solvent-less conditions” by Firouzabadi, Habib published in Tetrahedron (2004), 60(48), 10843-10850 reports stable and non-hygroscopic aluminum dodecatungstophosphate (AlPW12O40), which was prepared easily from cheap and commercially available compounds was found to be an effective catalyst for Friedel-Crafts acylation reactions using carboxylic acids, acetic anhydride, and benzoyl chloride in the absence of solvent under mild reaction conditions.

The inherent disadvantages in the use of conventional Lewis acid metal halides for Friedel-Crafts acylation are that it is non-regenerable and requires more than stoichiometric amounts because of complex formation of the catalyst with the carbonyl product formed. Work-up to decompose the resultant intermediate complex by hydrolysis forms a large amount of waste product and separation is lengthy and expensive. Further, Higher reaction temperature exerts very high pressure on the reaction system. This is hazardous in case of highly corrosive and hazardous reaction conditions.

Therefore there is a need for a process for the preparation of aromatic ketones which is simple to operate and can be carried out in a media which are not toxic and corrosive. Moreover the catalyst should be simple to separate and reusable. Accordingly, the present inventors developed a highly efficient process technology for the production of aromatic ketones which makes possible the achievement of the additional advantages over the prior art processes being practiced industrially.

OBJECTIVE OF THE INVENTION:
The main objective of the present invention is to provide an improved process for the preparation of highly pure aromatic ketones by Friedel-Crafts acylation of alkane using acetyl fluoride as an acylating agent in the presence of anhydrous hydrofluoric acid as the catalyst followed by monitoring the reaction in situ with FTIR real time probe.

SUMMARY OF THE INVENTION:
Accordingly, the present invention provides an improved process for the preparation of highly pure aromatic ketones comprising the steps of:
a) charging the reactor with alkane and dispersant followed by addition of catalyst along with acylating agent;
b) heating the reaction mixture of step (a) at the temperature ranging from 30 oC to 170 oC for the time period ranging from 15 to 20 minutes under continuous stirring followed by monitoring the reaction in situ with FTIR real time probe to afford aromatic ketones.

In preferred embodiment, said alkane is selected from isobutyl benzene, toluene, ethyl benzene or n-butyl benzene.

In another preferred embodiment, said dispersant is selected from stearic acid, lauric acid, neodecanoic acid, behenic acid or oleic acid.

In still another preferred embodiment, said catalyst is hydrogen fluoride (HF).

In yet another preferred embodiment, said acylating agent is acetylfluoride (AcF).

In still yet another preferred embodiment, said aromatic ketone is selected from 4’-isobutylacetophenone (4’-IBAP), methyl acetophenone or n-butyl phenyl acetophenone.

In still yet another preferred embodiment, purity of said 4’-isobutylacetophenone is in the range of 97 to 99.6%.

In still yet another preferred embodiment, said process provides selectivity towards desired ketone is in the range of 93% to 95%.

ABBREVIATION:
FTIR: Fourier transform infrared spectroscopy
4’-IBAP: 4’-isobutylacetophenone
HOR: Hot oil return
HOS: Hot oil supply
BRR: Brine refrigeration return
BRS: Brines refrigeration supply
RTD: Resistance temperature detector
HF: Hydrogen Fluoride
IBB: Isobutylbenzene
ATR: Attenuated Total Reflection
AcF: Acetylfluoride
AcOH: Acetic Acid
Ac2O: Acetic anhydride
PhOMe: Phenyl Methoxide
HN(SO2CF3)2: Bis(trifluoromethylsulfonyl)imide
PFA: Perfluoroalkoxy
CAPEX: Capital expenditure

BRIEF DESCRIPTION OF THE DRAWINGS:

Figure 1: PFA lined SS304 stirred tank jacketed reactor with FTIR probe

DETAILED DESCRIPTION0 OF THE INVENTION

The invention will now be described in detail in connection with certain preferred and optional embodiments, so that various aspects thereof may be more fully understood and appreciated.

The present invention provides an improved highly efficient process for the preparation of highly pure aromatic ketones which makes possible the achievement of the additional advantages over the process being practiced industrially.

In an embodiment, the present invention provides an improved process for the preparation of highly pure aromatic ketones comprising the steps of:
a) charging the reactor with alkane and dispersant followed by addition of catalyst along with acylating agent;
b) heating the reaction mixture of step (a) at the temperature ranging from 30o to 170oC for the time period ranging from 15 to 20 minutes under continuous stirring followed by monitoring the reaction in situ with FTIR real time probe to afford aromatic ketones.

In preferred embodiment, said alkane is selected from isobutyl benzene, toluene, ethyl benzene or n-butyl benzene.

In another preferred embodiment, said dispersant is selected from stearic acid, lauric acid, neodecanoic acid, behenic acid or oleic acid.

These dispersing agents are used in very small amount, helped to carry out reaction at very mild conditions.

In still another preferred embodiment, said catalyst is hydrogen fluoride (HF).

In yet another preferred embodiment, said acylating agent is acetyl fluoride (AcF).

In still yet another preferred embodiment, said aromatic ketone is selected from 4’-isobutylacetophenone (4’-IBAP), methyl acetophenone or n-butyl phenyl acetophenone.

In still yet another preferred embodiment, purity of said 4’-isobutylacetophenone is in the range of 97 to 99.6%.

Thus, the purity of isobutyl acetophenone is useful in ibuprofen manufacturing industry on large scale. The product isobutyl acetophenone does not contain any fluoride contamination.

In yet still another preferred embodiment, said process provides selectivity to the desired ketone is in the range of 93% to 95%.

The reaction conditions are very mild, the reaction temperature is ambient temperature, very low reaction time; due to lower reaction temperature the reaction pressure is low. At the end of reaction, the IBAP-HF complex is thermally cleaved by heating complex at 160 to 170oC, this avoids use of acetic anhydride for releasing complex also the acetic acid formation is avoided, which reduces the corrosion of process equipment.

The anhydrous hydrofluoric acid is used as the catalyst and is recovered completely at the end of reaction; the process does not produce any kind of aqueous effluent. Also the byproduct acetic acid is recovered with highest purity.

The reaction is monitored using FTIR probe and this is done continuously using on-line measurement probe. Figure 1 shows a) PFA lined SS304 stirred tank jacketed reactor b) column c) reactor valve d) pressure gauge e) RTD f) motor g) FTIR probe h) heating and cooling arrangement i) FTIR data longer system. This helped to monitor and control reaction on a continuous basis. This could avoid taking sample out of highly hazardous reaction material. All the reactant species like isobutyl benzene concentration, acetyl fluoride concentration, and isobutyl acetophenone concentration could be monitored with the help of FTIR probe, thus it helped to maintain the constant reactant molar ratios and constant rate of reaction / formation of product.

In one embodiment, the main reactor is fitted FTIR real time reaction monitoring probe was inserted through the bottom of reactor and is dipping in reaction mixture all the time. The FTIR probe is DiComp probe (Mettler-Toledo make) and was also equipped with RTD for temperature sensing. The FTIR probe had the mid absorption IR band 650 to 4000 cm-1. The FTIR probe was pre-calibrated for starting material isobutyl benzene etc. The reaction was performed with the continuous monitoring with the help of FTIR probe and it was observed that the reaction between acetyl fluoride and isobutyl benzene in presence of HF was instantaneous. The product i.e. 4’-IBAP got released after recovery of HF-excess acetyl fluoride mixture and post only thermal treatment of isobutyl benzene- acetyl fluoride complex.

Examples Following examples are given by way of illustration therefore should not be construed to limit the scope of the invention.

Example-1: Preparation of acetyl fluoride
The acetyl fluoride in hydrofluoric acid was generated by reaction between anhydrous HF and acetic anhydride. The reaction was carried out in 25-L nominal capacity PFA lined SS304 stirred tank jacketed reactor (Fig. 1). The reactor was supplied with cold oil and hot oil circulation for maintaining the process temperature (from 10 oC to 170 oC). The reactor was equipped with (made of SS316 material) brine cooled condenser and the mixture of anhydrous HF and acetyl fluoride was collected in a 25-L nominal capacity (made of SS304 material) storage vessel. The following procedure was employed for generating acetyl fluoride-HF mixture (acylation mixture). Initially the entire reaction section was evacuated by applying vacuum. Then to the main reactor, condenser and acetyl fluoride-HF mixture (acylation mixture) storage vessel was cooled by using circulating chilled brine at -10 oC.
HF gas was connected to storage vessel with the help of pressure cord (which was heated by using electrical heating tape). HF was allowed to condense in storage vessel at the rate of approximately 2 to 2.25 kg/h. During HF transfer the entire system was maintained under vacuum and the vent of system was completely kept closed. Initial pressure of storage vessel was 0.41 kg / cm2 (absolute). Around 12.3 kg of HF liquefied gas was collected in storage vessel within 5.5 hours. At the end of charging of HF the storage vessel pressure reached to 0.89 kg/cm2 (absolute). The anhydrous HF stored in storage vessel was charged to stirred tank reactor. The stirrer of the reactor was started. The initial pressure of the reactor was 0.41 kg / cm2 (absolute). Then to it 15.225 kg of acetic anhydride was charged in two hours under agitation under adiabatic and closed conditions. The acetic anhydride was charged with the help of pump. The reaction was mildly exothermic and at the end of reaction the temperature reached out to 53o C and pressure reached out 3.46 kg/cm2 (absolute). The reaction mixture was digested for 15 minutes and then the reactor vent valve going to condenser was opened slowly and the HF along with acetyl fluoride was allowed to vaporize and condense in the storage vessel. The reaction mixture was heated till the bottom temperature reached to 118 to 120o C and was maintained at this temperature for 30 minutes. The reaction mixture was cooled and removed, weighed 8.95 kg, the analysis showed it was acetic acid with traces of HF in it. This acetic acid was further distilled to recover pure acetic acid.

Example-2: Preparation of acetyl fluoride with continuous reaction monitoring
The similar reaction set-up as mentioned Example-1 was used except, the main reactor was fitted FTIR real time reaction monitoring probe was inserted through the bottom of reactor and was dipping in reaction mixture all the time. The FTIR probe was DiComp probe (Mettler-Toledo make) and was also equipped with RTD for temperature sensing. The FTIR probe had the mid absorption IR band 650 to 4000 cm-1. The FTIR probe was pre-calibrated for acetic anhydride and acetic acid mixture. The reaction was performed as mentioned under Example-1 with the continuous monitoring with the help of FTIR probe and it was observed that the reaction between acetic anhydride and HF was instantaneous without leaving any trace of acetic anhydride in the reaction medium and went to completion immediately.

Example-3: Preparation of 4’ IBAP with continuous reaction monitoring
The similar reaction set-up as mentioned Example-1 was used except, the main reactor was fitted FTIR real time reaction monitoring probe was inserted through the bottom of reactor and was dipping in reaction mixture all the time. The FTIR probe was DiComp probe (Mettler-Toledo make) and was also equipped with RTD for temperature sensing. The FTIR probe had the mid absorption IR band 650 to 4000 cm-1. The FTIR probe was pre-calibrated for starting material isobutyl benzene etc. The reaction was performed as mentioned under Example-3 with the continuous monitoring with the help of FTIR probe and it was observed that the reaction between acetyl fluoride and isobutyl benzene in presence of HF was instantaneous. The product i.e. 4’-IBAP was released after recovery of HF-excess acetyl fluoride mixture and post only thermal treatment of isobutyl benzene- acetyl fluoride complex.

Example-4: Preparation of 4’ IBAP in the presence of dispersant
The similar reaction set-up as mentioned Example-1 was used. The reaction was performed as mentioned under Example-3. The main reactor was charged with 5 kg of isobutyl benzene and 25 gm of lauric acid, agitator was started and to it HF along with acetyl fluoride (as prepared in Example-1 and stored in storage vessel) was charged to the reaction mixture. The reaction mixture was heated and maintained at 30o C. The reaction temperature was maintained for 15 minutes at 30o C under continuous stirring. Meantime, the HF-acetyl fluoride storage vessel was cooled by supplying chilled brine at -10oC through jacket of the reactor. The reaction mixture after digestion for 15 minutes, the reactor vent valve going to condenser was opened slowly and the HF along with acetyl fluoride was allowed to vaporize and condense in the storage vessel. The recovered HF along with acetyl fluoride mixture was recycled in next batch. The reaction mixture was heated till the bottom temperature reached to 168 to 170o C and was maintained at this temperature for 15 minutes. The reaction mixture was cooled and removed, and weighed 6.33 kg. The reaction mixture was aqueous treated and was subjected to analysis showed the selectivity towards 4-IBAP as 95% and balance residue.

Example-5: Isolation and Purification of 4’ IBAP
The reaction mixture obtained from Example-3, 4 or 5 was mixed together and was washed with sodium bicarbonate solution. The washed crude mixture of 4-IBAP was charged to a 10-L capacity fractional distillation assembly equipped with 100 mm diameter X 1000 mm height packed distillation column, followed by condenser, twin receivers an vacuum pump. The distillation assembly was applied with 3 mm of Hg as the absolute vacuum. After initial removal of low boiling isobutyl benzene cut, main product (4-IBAP) cut was recovered when distillation still temperature was 110 oC, vapor top temperature was 86 oC, under reflux of 2:1, the 4-IBAP cut showed the purity as 4’-IBAP 99.48%, 3’-IBAP 0.38% as analyzed by GC. The other impurities like 2’-IBAP was less than 200 ppm. The fluoride contents in the distilled product were nil to traces.

Example-6: Preparation of methyl acetophenone
The similar reaction set-up as mentioned Example-3 was used. The reaction was performed as mentioned under Example-3. The main reactor was charged with 3.5 kg of toluene and 25 gm of lauric acid, agitator was started and to it HF along with acetyl fluoride (as prepared in Example-1 and stored in storage vessel) was charged to the reaction mixture. The reaction mixture was heated and maintained at 30 oC. The reaction temperature was maintained for 15 minutes at 30 oC under continuous stirring. Meantime, the HF-acetyl fluoride storage vessel was cooled by supplying chilled brine at -10 oC through jacket of the reactor. The reaction mixture after digestion for 15 minutes, the reactor vent valve going to condenser was opened slowly and the HF along with acetyl fluoride was allowed to vaporize and condense in the storage vessel. The recovered HF along with acetyl fluoride mixture was recycled in next batch. The reaction mixture was heated till the bottom temperature reached to 134 to 135 oC and was maintained at this temperature for 15 minutes. The reaction mixture was cooled and removed, and weighed 4.7 kg. The reaction mixture was aqueous treated and was subjected to analysis showed the conversion 75% and selectivity towards methyl acetophenone as 97% and balance residue.

Example-7: Preparation of 4-IBAP at high temperature and taking all the reactants together as disclosed in US5068448
The reaction was carried out in 25-L nominal capacity SS316 stirred tank jacketed reactor. The reactor was supplied with cold oil and hot oil circulation for maintaining the process temperature. The reactor was equipped with (made of SS316 material) brine cooled condenser. Then to the reactor 2880 gm of isobutyl benzene was charged and agitator was started. The reaction mass was cooled to 5 oC by circulating brine through the jacket of the reactor. Then to it 5200 gm of liquid anhydrous hydrogen fluoride (HF) was transferred under closed condition. The reaction mass was heated till 60 oC and at this temperature reaction pressure was 2.46 kg-g/cm2. Then to the reaction mass acetic anhydride liquid 2440 gm was charged with the help of metering pump within 60 minutes with the help of SSI make metering pump. The reaction mixture was further digested to 80 oC for four hours at pressure of 3.40 kg-g/cm2.
The reaction mixture after digestion, the reactor vent valve going to condenser was opened slowly and the HF along with acetyl fluoride was allowed to vaporize and condense in the storage vessel. The reaction mixture was heated till the bottom temperature reached to 140 to 150 oC and was maintained at this temperature for 30 minutes. The reaction mixture was cooled and removed, weighed 5.16 kg. The crude material after washing with water was made free of acetic acid gave 3.58 kg of crude material. The washed material was flash distilled gave 1.86 kg of distilled material containing 58% IBAP, 41.6% unconverted IBB and 0.49% others, 1.65 kg was found to be tarry residue, selectivity towards 4-IBAP 39.15% and balance residue. At higher reaction temperature higher amount of residue formation was observed.

Example-8: Preparation of 4-IBAP at high temperature in presence of HF and AcF mixture as disclosed in US5068448
The reaction was carried out in 25-L nominal capacity SS316 stirred tank jacketed reactor. The reactor was supplied with cold oil and hot oil circulation for maintaining the process temperature. The reactor was equipped with (made of SS316 material) brine cooled condenser and the mixture of anhydrous HF and acetyl fluoride was prepared as mentioned under Example-1 was stored and used in this example. Initially the reactor was flushed with nitrogen and then was evacuated by applying vacuum. Then the condenser was cooled by using circulating chilled brine at -10 oC. The main reactor was charged with 5 kg of isobutyl benzene, agitator was started and to it HF along with acetyl fluoride (as prepared in Example-1 and stored in storage vessel) was charged to the isobutyl benzene. The reaction mixture was heated and maintained at 45 oC by supplying hot oil through the jacket of main reactor. The reaction temperature was maintained for 2 hours at 45 oC under continuous stirring. Meantime, the HF-acetyl fluoride storage vessel was cooled by supplying chilled brine at -10 oC through jacket of the reactor. The reaction mixture after digestion for 2 hours, the reactor vent valve going to condenser was opened slowly and the HF along with acetyl fluoride was allowed to vaporize and condense in the storage vessel. The recovered HF along with acetyl fluoride mixture was recycled in next batch. The reaction mixture was heated till the bottom temperature reached to 118 to 120 oC and was maintained at this temperature for 30 minutes. The reaction mixture was cooled and removed, and weighed 6.33 kg. The reaction mixture was aqueous treated and was subjected to analysis showed the results as 85.6% isobutyl benzene conversion, 11% isobutyl benzene, selectivity towards 4-IBAP 43% and balance residue. At higher reaction temperature higher amount of residue formation was observed.

Advantages of the invention:

1. Separation of acetyl fluoride synthesis from the main reaction section.
2. Use of catalytic amount of dispersants like stearic acid, lauric acid, oleic acid, neodecanoic acid, behenic acid etc.
3. Highly pure isobutyl acetophenone obtained
4. The reaction monitoring system and quantification is through online measurement with the help of FTIR probe.
5. Reactant species, molar concentration measurement through FTIR online measurement.
6. Nil to negligible effluents, very mild reaction conditions, normal material of construction for the commercial process and low CAPEX causes highly attractive commercial process are the other advantages of this process.
7. This process is used for acylation of other molecules such as toluene, isobutyl benzene, ethyl benzene, n-butyl benzene etc.

WE CLAIM:
1. An improved process for the preparation of aromatic ketones comprising the steps of:
a) charging the reactor with alkane and dispersant followed by addition of catalyst along with acylating agent;
b) heating the reaction mixture of step (a) at the temperature ranging from 30o to 170oC for the time period ranging from 15 to 20 minutes under continuous stirring followed by monitoring the reaction in situ with FTIR real time probe to afford aromatic ketones.
2. The process as claimed in claim 1, wherein said alkane is selected from isobutyl benzene, toluene, ethyl benzene and n-butyl benzene.
3. The process as claimed in claim 1, wherein said dispersant is selected from stearic acid, lauric acid, oleic acid, neodecanoic acid or behenic acid.
4. The process as claimed in claim 1, wherein said catalyst is hydrogen fluoride.
5. The process as claimed in claim 1, wherein said acylating agent is acetylfluoride.
6. The process as claimed in claim 1, wherein said aromatic ketone is selected from 4’-isobutylacetophenone , methyl acetophenone, or n-butyl phenyl acetophenone.
7. The process as claimed in claim 6, wherein purity of said 4’-isobutylacetophenone is in the range of 97 to 99.6%.
8. The process as claimed in claim 1, wherein said process provides selectivity towards said ketone is in the range of 93% to 95%.