The present invention provides a process for preparation of anisole.

BACKGROUND OF THE INVENTION
Aryl alkyl ethers such as anisole are very important industrial chemicals. Due to their fragrance, they can be used as additive in soap and detergent. These can also be used as intermediate in synthetic perfumes, dyestuff and insecticides. Anisole can also be used as gasoline additive instead of methyl tertiary butyl ether. In recent years, its demand is sharply increased in the market.
Sodium methyl sulfate, a major by-product formed in number of chemical processes is either discarded as a solid waste or is temporarily stored by many companies due to high disposal costs. There is need to evolve a strategy to efficiently utilize sodium methyl sulfate waste to curtail its disposal cost.
CN 107686441, CN 1036454C, US 2490842 disclose process for preparation of anisole by reacting phenol with sodium hydroxide followed by the reaction of corresponding sodium phenolate with dimethyl sulfate to give anisole. However low yield coupled with use of costly dimethyl sulfate and generation of large quantity of aqueous effluent makes the process less economical.
CN 107879902 discloses a method for preparing anisole by reacting aqueous phenoxide solution (prepared by dissolving phenol into a sodium hydroxide solution) with sodium methyl sulfate.
CN 103588625 discloses a method for preparing anisole by reacting sodium methyl sulfate with phenol under alkaline condition.
However, the reported processes are tedious for having multiple process operations, phenolic effluent load and suffers from low phenol to anisole conversion.
The present invention provides an alternate process with lesser number of unit operations, excellent yield, zero effluent discharge and more than 99% phenol to anisole conversion.

OBJECT OF THE INVENTION
The object of the present invention is to provide an alternative and cost-effective process for preparation of anisole.

SUMMARY OF THE INVENTION
In an aspect, the present invention provides a process for preparation of anisole,
comprising the steps of:
a) contacting phenol with a metal methyl sulfate in presence of an aqueous alkali hydroxide at a temperature of 80 to 115 °C to obtain a reaction mixture comprising anisole; and
b) isolating anisole from the reaction mixture of step a) by reactive distillation,
wherein reactive distillation is carried out by continuously separating anisole?water azeotrope from the reaction mass.
In another aspect, the present invention provides a process for preparation of anisole, comprising the steps of:
a) contacting phenol with a metal methyl sulfate in presence of an aqueous alkali hydroxide at a temperature of 80 to 115 °C to obtain a reaction mixture comprising anisole;
b) isolating anisole from the reaction mixture of step a) by reactive distillation;
c) neutralizing the remaining reaction mixture of step b) using a mineral acid; and
d) recovering metal sulfate from the neutralized mixture of step c),
wherein reactive distillation is carried out by continuously separating anisole?water azeotrope from the reaction mass.

DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a cost-effective and industrially applicable process for preparation of anisole.
As use herein, the term mineral acid refers to sulphuric acid.
As used herein, the alkali hydroxide refers to sodium hydroxide or potassium hydroxide.
As use herein, the metal methyl sulfate refers to sodium methyl sulfate or potassium methyl sulfate.
In an embodiment, the anisole is isolated using reactive distillation technique which means that as soon as anisole is formed it gets separated from the reaction mass by distilling it continuously as anisole-water azeotrope. This leads to an excellent conversion of phenol to anisole.
Reactive distillation enables the product to be isolated continuously as soon as it is formed, this aspect makes the process commercially efficient as less effort is required to isolate it from reactor and also reduces its exposure to the environment, thereby decreasing the degradation impurities.
In an embodiment of the present invention, the solution of alkali hydroxide has concentration of 5 to 48%, preferably 12-20-%.
In another embodiment, the addition of aqueous alkali solution is made in parts to enhance utilization of sodium methyl sulfate for anisole formation.
In a preferred embodiment, the reaction mixture is continuously and parallelly distilled to isolate anisole by reactive distillation during the part addition of aqueous alkali hydroxide at 80 to 115°C.
In an embodiment, the anisole is obtained with a yield of at least 95%. In another embodiment the anisole is obtained with a yield of 95 to 99.9%.
In an embodiment, the anisole is obtained with a purity of at least 98%. In another embodiment the anisole is obtained with a purity of 98 to 99.9%.
In an embodiment, the recovered metal sulfate has a purity of 98 to 99.5% and recovered methanol has a purity of 98 to 99.5%.
The recovered methanol can be recycled completely in the process and recovered metal sulfate has a good market for sale.
The present invention provides excellent yield of anisole, complete recovery and recycle of methanol and good quality sodium sulfate as by-product that makes the process very cost effective at commercial scale. The aqueous stream is recycled back in the process to make it a zero effluent discharge process.
In an embodiment, the metal methyl sulfate used in the process is generated as a by-product of a process utilizing dimethylsulfate.
As used herein, the term “isolating” refers to the method used to isolate the compound from the reaction mixture. The isolation is carried out using any of the process consisting of extraction, distillation, filtration, decantation, washing, dryings or combination thereof.
The completion of the reaction may be monitored by high pressure liquid chromatography (HPLC).
The phenol which is used herein as starting material can be prepared by any of the methods known in the art or can be obtained commercially.
Unless stated to the contrary, any of the words “comprising”, “comprises” and includes mean “including without limitation” and shall not be construed to limit any general statement that it follows to the specific or similar items or matters immediately following it.
Embodiments of the invention are not mutually exclusive but may be implemented in various combinations. The described embodiments of the invention and the disclosed examples are given for the purpose of illustration rather than limitation of the invention as set forth in the appended claims.
The following example is given by way of illustration and therefore should not be construed to limit the scope of the present invention.

EXAMPLE
Example: 1- Water (850 g) was added to a 3000 ml stainless steel reactor at 25–35°C. Aqueous sodium hydroxide (48%, 292 g) and phenol (282 g) were added to the reactor and stirred for 30 minutes. Sodium methyl sulfate (483 g) was added and reaction mass was heated to 100-110oC. Mixture-1 containing anisole and water (550 g) was collected continuously by reactive distillation (gas phase temperature of 90-100°C) in 3–4 hours. Aqueous solution of sodium hydroxide (250g; 20%) was added to the reactor. Reactive distillation was continued to collect another 300g of distillate (mixture-2) containing anisole and water.
To the remaining reaction mass, sulphuric acid (160g, 37.5%) was added and heated to collect another distillate (120 g) containing very little anisole (<0.5% w/w), phenol (<0.5% w/w) and water. The phenol content in the reaction mass remained below 10 ppm.
This distillate material was recycled in next batch as a source of water for next reaction to provide anisole in a yield of 98% and of purity 98.5%.
The remaining residue was cooled to 25 to 35°C and methanol (1000 g) was added to precipitate out sodium sulfate. The mass was filtered to get crude sodium sulfate and filtrate called mother liquor. Crude sodium sulfate was further washed twice with methanol (200g) then dried under vacuum at 80–140oC to get sodium sulfate (99.5% pure, yield 99%; with respect to sodium methyl sulfate). Methanol layer was recycled in next reaction.
To the combined mixture 1 and 2 containing anisole and water, sodium hydroxide solution (48%, 50g) was added, stirred for 30 min and the layers were separated to obtain pure anisole (yield 99%; purity: 99.8%).
The aqueous wash layer was recycled in next batch as a sodium hydroxide solution to give anisole of purity 99.5% in a yield of 99%.
From mother liquor (which is mixture of mainly water and methanol), methanol was recovered and recycled, remaining aqueous residue was recycled to make sodium hydroxide solution for next reaction.

WE CLAIM:

1. A process for preparation of anisole, comprising the steps of:
a) contacting phenol with a metal methyl sulfate in presence of an aqueous alkali hydroxide at a temperature of 80 to 115°C to obtain a reaction mixture comprising anisole; and
b) isolating anisole from the reaction mixture of step a) by reactive distillation.
2. The process as claimed in claim 1, wherein the process further comprises the steps of:
c) neutralizing the remaining reaction mixture of step b) using a mineral acid; and
d) recovering metal sulfate from the neutralized mixture of step c).
3. The process as claimed in claim 1, wherein the alkali hydroxide is selected from sodium hydroxide and potassium hydroxide.
4. The process as claimed in claim 1, wherein the metal methyl sulfate is selected from sodium methyl sulfate and potassium methyl sulfate.
5. The process as claimed in claim 1, wherein the anisole is obtained with a purity of at least 98%.
6. The process as claimed in claim 2, wherein the recovered metal sulfate has a purity of at least 98%.
7. The process as claimed in claim 1, wherein the aqueous alkali hydroxide is used in a concentration of 5 to 48%.
8. The process as claimed in claim 1, wherein the reaction mixture is continuously and parallelly distilled to isolate anisole by reactive distillation during part addition of aqueous alkali hydroxide at 80 to 115°C.