FORM2
THE PATENT ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. TITLE OF THE INVENTION
"EFFICIENT PROCESS FOR PREPARING COUMARIN"
2. APPLICANT
NAME : OMKAR SPECIALITY CHEMICALS LTD.
NATIONALITY : INDIAN
ADDRESS : Unit III, B-34, M.I.D.C. Badlapur (East)
Dist-Thane, Pin-421503,
Maharashtra, India.
The following specification particularly describes the invention and the manner in which it is to be performed.

EFFICIENT PROCESS FOR PREPARING COUMARIN
FIELD OF INVENTION:
The present invention relates to an efficient process for preparing coumarin. More particularly it provides coumarin with good yield and good purity.
BACKGROUND OF INVENTION:
In the existing system as given in United States Patent Application Number 2204008, wherein, the said invention relates to an improved process for preparing coumarin from salicylaldehyde, sodium acetate and acetic anhydride by adding catalyst in the reaction mixture. This invention was an improvement in the old and simple process of condensing salicylaldehyde with acetic anhydride by refluxing at 135°C - 155°C in presence of sodium acetate. The old process has disadvantage of formation of tars, resins etc. from which the product isolation is cumbersome task. Also, the best possible yield reported by this method is 38% only.
Thus, the improved method claimed in US patent '408 suggested use of catalyst consisting of an oxide or a salt of one of the metals of group seven or eight of the periodic system. Further in order to increase the yield such condensation was carried out by first heating at 120°-160° C for 2-4 hours and then increasing the temperature gradually to 170°-190°C, and maintained at this temperature for 2-6 hours. However, the yield could not reach beyond 75%. Present invention provides an efficient process which provides coumarin with good purity and good yield.
SUMMARY OF INVENTION:
Present invention provides a process for preparing coumarin comprising introducing the mixture of salicylaldehyde, sodium acetate in acetic acid and acetic anhydride in a reactor maintained at the temperature range of 235°C to 245°C, collecting portion of hot liquid containing coumarin expelling out from the top of the reactor and re-circulating the remaining portion of expellant inside the reactor from its bottom; simultaneously introducing in the reactor the mixture of

salicylaldehyde, sodium acetate in acetic acid and acetic anhydride to compensate void created by collection of liquid portion
Coumarin is isolated from the liquid portion by distillation under vacuum at 135°C to 180°C. Optionally, it can be further purified by recrystallization in methanol and water.
BRIEF DESCRIPTION OF THE DRAWINGS:
Figure 1: IR of coumarin obtained by process of this invention
Figure 2: Depicts GC chromatogram showing purity of coumarin obtained in example 1. Figure 3: Depicts GC chromatogram showing purity of coumarin obtained in example 2. Figure 4: Depicts HPLC chromatogram showing purity of coumarin obtained in example 3.
DETAIL DESCRIPTION OF INVENTION:
The efficient process for producing coumarin with good yield and in good purity in accordance with the present invention comprises heating together the raw materials salicylaldehyde, sodium acetate in acetic acid and acetic anhydride at 235°C to 245°C. At this temperature the hot liquid is produced which contain coumarin. In fact at this temperature part of raw materials start getting vaporized and some part of gaseous un-reacted raw materials start merging within this hot liquid. This temperature is advantage as the maximum extents of raw materials undergoes reaction to contribute towards coumarin and remaining quantities get vaporized, thus produce very minimum byproducts, if any. However, at this temperature the hot materials inside the reactor try to expel out from the reactor. Their forceful entrapment in the reactor in order to achieve the maximum conversion of reactants to coumarin results in charring of materials. Also, it can burst the reactor. To avoid the charring, bursting and also to increase efficiency of process, the material is taken out to withdraw some portion containing coumarin and rest is kept circulated in the reactor.
In preferred embodiment of the invention, the raw materials mixture of salicylaldehyde, sodium acetate in acetic acid and acetic anhydride is introduced in a reactor maintained at the temperature range of 235°C to 245°C. Portion of hot liquid containing coumarin expelling out from the top of the reactor is collected in collection pot and remaining portion of expellant is re-

circulated inside the reactor from its bottom. This collection and re-circulation can be simply achieved through an external tube connecting the top and bottom of reactor and having mean for collection of portion of liquid. Thus, materials get advantage of motion and charring is avoided. Also, thermosiphon effect is sufficient to keep the liquid moving from top to bottom. Simultaneously the mixture of salicylaldehyde, sodium acetate in acetic acid and acetic anhydride is introduced in reactor to compensate the void created by collection of liquid portion. In addition to this, when hot liquid leave the reactor and come outside in tube then due to temperature drop outside the reactor, the gaseous un-reacted raw materials may get condensed in tube itself and enter in reactor in their liquid form which results in spending more time inside reactor compared to the time which they would have spend being in gaseous phase. Ultimately it enhances the yield. Additionally the yield can be further be improved by artificially condensing these gaseous un-reacted raw materials in tube. A condenser or cooling jacket can be suitable employed for this purpose. Vacuum distillation at 135°C to 180°C of collected liquid portion give coumarin yield around 98%. The purity is more than 99%. Optionally, it can be further purified by recrystallization in methanol and water.
The reactor and the tube are made up of material which can withstand heat. Suitably steel and more advantageously stainless steel is used for this purpose.
Hereinafter the present invention is particularly described in following examples. Although the present invention has been described and illustrated with a reference to specific examples, it is understood that modifications and variations of composition and procedure are contemplated within the scope of the appended claims.
Example 1
250 liters from mixture of salicylaldehyde (1800kg), Sodium acetate (9.52 kg in 28.56 ltrs acetic acid) and Acetic Anhydride (1800kg), was introduced in a stainless steel reactor maintained at 235°C to 245°C. Immediately started the partial collection and remaining re-circulation of expelling hot liquid through stainless steel tube. The remaining mixture of raw materials was simultaneously introduced at the flow rate of 100 lit/hr till consumption of total quantity. The collected liquid product was vacuum distilled at 135°C to 180°C to obtain coumarin in following yield and purity. No charring occurred.

Yield: 99.05% GC Purity: 99.78%
Example 2
250 liters from mixture of salicylaldehyde (1600kg), sodium acetate in acetic acid (8.46 kg in 25.39 ltrs acetic acid) and acetic anhydride (1600kg) was introduced in a stainless steel reactor maintained at 235°C to 245°C. Immediately started the partial collection and remaining recirculation of expelling hot liquid through stainless steel tube. The remaining mixture of raw materials was simultaneously introduced at the flow rate of 100 lit/hr till consumption of total quantity.
The collected liquid product was vacuum distilled at 135°C to 180°C to obtain coumarin in following yield and purity. No charring occurred. Yield: 98.09% GC Purity: 99.99%
Example 3
100 kg of crude product of example 1 was taken in stainless steel reactor and added 96 kg methanol and 104 kg water. The mixture was heated till clear liquid obtained. Then allowed to stand for 1 hour followed by gradually cooling to 28°C to 26°C. After centrifugation and drying material of 100.00 % purity was obtained.

We claim:
1. A process for preparing coumarin comprising introducing the mixture of salicylaldehyde, sodium acetate in acetic acid and acetic anhydride in a reactor maintained at the temperature range of 235°C to 245°C, collecting portion of hot liquid containing coumarin expelling out from the top of the reactor and re-circulating the remaining portion of expellant inside the reactor from its bottom; simultaneously introducing in the reactor the mixture of salicylaldehyde, sodium acetate in acetic acid and acetic anhydride to compensate void created by collection of liquid portion
2. The process of claim 1, wherein the coumarin is isolated from hot liquid by distillation under vacuum at 135°C to 180°C.
3. The process of claim 1, wherein the collection and re-circulation is achieved through an external tube connected to the top and bottom of said reactor for re-circulation of expellant and having mean for collection of portion of hot liquid.
4. The process of claim 3, wherein the tube optionally comprises condenser or cooling jacket.
5. The process of claim 1 and 3, wherein the reactor and tube is made up of stainless steel.
6. The process of claim 2 further comprises optional purification of coumarin by
recrystallization in methanol and water.