DESC:FIELD OF THE INVENTION
The present invention relates to a continuous process for the preparation of phenyl alkyl ketone particularly m-(trifluoromethyl) acetophenone.

BACKGROUND OF THE INVENTION
m-(trifluoromethyl)acetophenone is an important intermediate in medicines, pesticides, and dyes. m-(trifluoromethyl)acetophenone is conventionally prepared by using batch processes. These known batch processes are unsatisfactory for economic, ecological and safety reasons.
Accordingly, there is a substantial need to overcome the batch processes to avoid its disadvantages.

DESCRIPTION OF THE INVENTION
The present invention provides a continuous process for the preparation of m-trifluoromethyl acetophenone comprising the steps of diazotization, coupling and hydrolysis.
The process comprises the steps of adding m-trifluoromethylaniline in a range of 17 moles -17.5 moles, sulphuric acid in a range of 30 moles -30.5 moles, sodium nitrite in a range of 18 moles -18.5 moles, continuously at a temperature in the range of 0°-5°C to form diazonium salt with continuous overflow followed by continuous coupling of overflowing diazonium salt with controlled addition of acetaldoxime in a range of 21 moles -21.5 moles, mixture of CuSO4 in a range of 1 mole -1.5 moles, water in a range of 162 moles -162.5 moles and acetic acid in a range of 5 moles -5.6 moles, along with toluene in a range of 7 moles -7.5 moles, with an adjusted pH to form m-(trifluoromethyl) acetophenone oxime with continuous overflow. The organic layer containing m-(trifluoromethyl) acetophenone oxime is continuous hydrolysed in the presence of an acid 33 moles -33.5 moles, to obtain m-trifluoromethyl acetophenone. The temperature for hydrolysis was maintained in the range of 65-70°C.
The pH is adjusted to 3-4.5 with continuous addition of sodium hydroxide in the process. Hydrolysis is carried out preferably in the presence of hydrochloric acid.
According to the present invention problems posed by batch scale diazotization can be overcome by employing continuous process wherein an aromatic amine is continuously diazotized, coupled and hydrolyzed in a continuous-stirred tank reactor (CSTR) with control of temperature throughout the reaction mixture. The steps of the process are continuous in nature, this makes the process simple and easy to perform and obviates high costs.

EXAMPLE
The invention is illustrated by the following non-limiting example:
Process for the preparation of 3’-(Trifluoromethyl) acetophenone:
Stage I: Preparation of 3'-(Trifluoromethyl) acetophenone oxime:
2802 gm of m-trifluoromethylaniline (99.5%), 21400 gm of dilute sulphuric acid (14%) were fed into a CSTR (R1) followed by addition of 694 gm of toluene and 3198 gm of sodium nitrite (40%) solution to prepare 28096 gm of diazo solution. The temperature was maintained at 0°- 3°C.
A second CSTR (R2) was provided for coupling reaction with points for addition of diazo solution, toluene, copper sulphate, water, acetic acid, acetaldoxime and NaOH.
In the second coupling reactor (R2), addition of 28096 gm of the diazo solution was started through overflow along with the addition of 3717 gm of NaOH (30%) to maintain the pH at 3.5 to 4.5. The temperature was maintained at 0-3°C. After 40 minutes, 2479 gm of 50% acetaldoxime, mixture of 262 gm of copper sulphate, 2926 gm of water and 339 gm of acetic acid solution along with 9299 gm of toluene was added in the coupling reactor maintaining pH at 3.5 to 4.0. using 3717 gm of NaOH (30%) solution and temperature at 0°-3°C. The coupling mass formed was continuously collected in another reactor and heated to 25°-30°C under stirring. Thereafter, the aqueous and organic layer were separated, and the lower aqueous layer was sent to Effluent Treatment Plant. The top organic layer (13502 gm) contained 3'-(trifluoromethyl) acetophenone oxime, which was confirmed by Gas Chromatography analysis. The organic layer was subjected to continuous hydrolysis.
Stage II: Preparation of 3'-(Trifluoromethyl) acetophenone
Two reactors (R3 and R4) were arranged for carrying out hydrolysis of 3'-(trifluoromethyl) acetophenone oxime. The second hydrolysis reactor (R4) was arranged to receive the overflow of the first hydrolysis reactor (R3). The organic layer from Stage I (13502gm) and 4077 gm of HCl (30%) were fed into R3 and R4 up to overflow volume and the temperature was maintained up to 70°C for 3 hours.
After completion of the reaction, while ensuring the content of 3'-(trifluoromethyl) acetophenone oxime was less than 1%, the flow rate of coupling mass was adjusted. After hydrolysis, the continuous overflow of hydrolysis mass was collected in another reactor, followed by separation of organic and aqueous phase. The crude organic mass (12787gm) was washed with 2944 gm of 3% sodium bicarbonate solution. The final organic phase was subjected to recovery of toluene (8743gm) and 3'-(Trifluoromethyl) acetophenone (2277gm) was isolated from the organic phase by vacuum distillation. Yield of 3'-(Trifluoromethyl) acetophenone was 67%.

The foregoing description of the invention has been set merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to person skilled in the art, the invention should be construed to include everything within the scope of the disclosure.

,CLAIMS:

1. A process for preparing m-trifluoromethyl acetophenone, the process comprising:
continuous addition of m-trifluoromethylaniline, sulphuric acid and sodium nitrite at a temperature in the range of 0°-5°C to form diazonium salt having continuous overflow;
continuous coupling of overflowing diazonium salt with controlled addition of acetaldoxime, mixture of CuSO4, water and acetic acid along with toluene with a pH maintained at 3-4.5 to form m-(trifluoromethyl) acetophenone oxime with continuous overflow followed by separation of organic layer; and
continuous hydrolysis of the organic layer using an acid to obtain m-trifluoromethyl acetophenone.
2. The process as claimed in claim 1, wherein the pH is maintained by adding sodium hydroxide.
3. The process as claimed in claim 1, wherein the acid is hydrochloric acid.