GB2165536A

GB2165536A - The preparation of piperonal

Info

Publication number: GB2165536A
Application number: GB08426112A
Authority: GB
Inventors: James Peter Millington; David Anthony Hughes
Original assignee: Electricity Council
Current assignee: Electricity Council
Priority date: 1984-10-16
Filing date: 1984-10-16
Publication date: 1986-04-16
Also published as: GB2165536B; GB8426112D0

Abstract

A process for the preparation of piperonal comprises oxidising 4-methyl-methyl-dioxylbenzene with ceric sulphate to produce the desired piperonal.

Description

SPECIFICATION A process for the preparation of piperonal A naturally occurring perfumery additive piperonal (also known as 1, 3-benzodioxole 5-carboxaldehyde or 3, 4-methylenedioxybenyaldehyde, or heliotropin) is obtained synthetically by the oxidation of the essential oil sassafras. Several synthetic routes have been disclosed in the literature, see for example J.

Org.Chem. 26,4814, 1961 and Bull.Soc.Chim. France 1964, 1892, but none of these have met with any commercial success.

This present invention is concerned with the preparation of piperonal by a novel synthetic route from a relatively accessible starting material in a single step using an oxidising agent which is preferably generated electrochemically. The starting material for the process of this invention is 4-methylmethylene-dioxybenzene. This starting material has been found previously to be extremely resistant to oxidation and attempts to convert it to piperonal using powerful oxidising agents such as chromic acid and manganese dioxide have failed.

We have now discovered surprisingly that the relatively mild oxidising agent ceric sulphate is able to convert 4-methyl-methylene-dioxybenzene into piperonal in good yield.

Accordingly, the present invention comprises oxidising 4-methyl-methylene-dioxybenzene with ceric sulphate to produce the desired piperonal.

The 4-methyl-methylene-dioxybenzene is conveniently prepared from the coal tar derived product 3,4-dihydroxy toluene and this may be reacted with a disubstituted methane derivative in a conventional elimination reaction to produce 4-methylmethylene-dioxybenzene. The disubstituted methane may be dichloromethane, dibromomethane or di-iodomethane, with the products of elimination being hydrogen chloride, hydrogen bromide and hydrogen iodide, respectively. The preferred disubstituted methane is dichloromethane.

In order to produce the desired piperonal, 4methyl-methylene-dioxybenzene is preferably reacted with electrochemically generated ceric sulphate in a well stirred reaction vessel at room temperature. The ceric sulphate is preferably prepared by oxidising a solution of cerous sulphate in aqueous sulphuric acid, for example using cerous sulphate at 0.1 M in 5% H2SO4, in a suitable electrochemical cell. The electrochemical cell for use in generating the ceric sulphate has separate anode and cathode compartment and desirably the same electrolyte is circulated through each side of the cell to minimise the effect of migration of cerium through the membrane which divides the anode from the cathode compartment. It will be appreciated that only the anolyte is used as the oxidising solution.The membrane separating the anode and cathode compartments may be any semipermeable membrane which is resistant to the electrolyte, including any microporous or woven plastic or any ion selective membrane which has the appropriate resistance to the electrolyte. Preferably the cell is divided using a cation selective membrane based on polyfluoroethers which contains also sulphonic acid groups.

The anode material may be a noble metal coated onto titanium, such as platinum or platinum/irridium, or ruthenium dioxide or the anode material may be anodised lead or a lead alloy or lead coated mild steel or lead dioxide deposited onto titanium.

The preferred material being lead coated mild steel.

The cathode may be constructed from mild steel, nickel, lead, titanium or stanless steel, with the latter being the preferred material. To achieve high current efficiencies at high current densities in this dilute electrolyte it is desirable that a cell, where high mass transport to the anode surface may be achieved, is used. Such a cell is described in our European Patent Specification No 0064417.

In addition to piperonal having a use in perfumery, it also has applications in medicine, suntan preparations, mosquito repellant, a laboratory reagent and as a flavouring; it is to be understood that the present invention also includes compositions for these various purposes which include a minor proportion of piperonal which has been prepared by the process of this invention.

The invention will now be illustrated by the following example: A solution of ceric sulphate (0.125M) in sulphuric acid (5%) was prepared by electrolysing a solution of cerous sulphate in the anode compartment of a DEM cell (as described in our European Patent Specification No. 0064417 at a currrent of 75A (1500A/m2) for 38 minutes, equivalent to a current efficiency of 70%.

The cell was constructed from a lead anode, a cation selective membrane as cell divider, and a stainless steel cathode. The catholyte solution was of identical composition to the anolyte. The oxidising solution (the anolyte) was reacted with 4-methyl-methylenedioxy-benzene (50g) in a well stirred round bottomed flask at ambient temperature, for 5 minutes.

The mixture was then extracted with three portions of diethyl-ether (500ml) and the extracts combined and dried over anhydrous sodium sulphate. Upon evaporation the ether solution yielded an oil (52g) which on analysis was shown to contain unchanged starting material (26g) and piperonal (26g). The piperonal yield was 83% based on the ceric sulphate used and 90% based on the starting material consumed.

1. A process for the preparation of piperonal which comprises oxidising 4-methyl-methylenedioxybenzene with ceric sulphate to produce the desired piperonal.

2. A process as claimed in Claim 1, wherein the ceric sulphate is produced using ceric sulphate which oxidising agent has been generated electrochemically.

3. A process as claimed in Claim 1 or Claim 2, wherein the 4-methyl-methylene-dioxybenzene is produced by reacting 3,4-dihydroxy toluene with a disubstituted methane.

4. A process as claimed in Claim 3, wherein the disubstituted methane is dichloromethane, dibro

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION A process for the preparation of piperonal A naturally occurring perfumery additive piperonal (also known as 1, 3-benzodioxole 5-carboxaldehyde or 3, 4-methylenedioxybenyaldehyde, or heliotropin) is obtained synthetically by the oxidation of the essential oil sassafras. Several synthetic routes have been disclosed in the literature, see for example J. Org.Chem. 26,4814, 1961 and Bull.Soc.Chim. France 1964, 1892, but none of these have met with any commercial success. This present invention is concerned with the preparation of piperonal by a novel synthetic route from a relatively accessible starting material in a single step using an oxidising agent which is preferably generated electrochemically. The starting material for the process of this invention is 4-methylmethylene-dioxybenzene. This starting material has been found previously to be extremely resistant to oxidation and attempts to convert it to piperonal using powerful oxidising agents such as chromic acid and manganese dioxide have failed. We have now discovered surprisingly that the relatively mild oxidising agent ceric sulphate is able to convert 4-methyl-methylene-dioxybenzene into piperonal in good yield. Accordingly, the present invention comprises oxidising 4-methyl-methylene-dioxybenzene with ceric sulphate to produce the desired piperonal. The 4-methyl-methylene-dioxybenzene is conveniently prepared from the coal tar derived product 3,4-dihydroxy toluene and this may be reacted with a disubstituted methane derivative in a conventional elimination reaction to produce 4-methylmethylene-dioxybenzene. The disubstituted methane may be dichloromethane, dibromomethane or di-iodomethane, with the products of elimination being hydrogen chloride, hydrogen bromide and hydrogen iodide, respectively. The preferred disubstituted methane is dichloromethane. In order to produce the desired piperonal, 4methyl-methylene-dioxybenzene is preferably reacted with electrochemically generated ceric sulphate in a well stirred reaction vessel at room temperature. The ceric sulphate is preferably prepared by oxidising a solution of cerous sulphate in aqueous sulphuric acid, for example using cerous sulphate at 0.1 M in 5% H2SO4, in a suitable electrochemical cell. The electrochemical cell for use in generating the ceric sulphate has separate anode and cathode compartment and desirably the same electrolyte is circulated through each side of the cell to minimise the effect of migration of cerium through the membrane which divides the anode from the cathode compartment. It will be appreciated that only the anolyte is used as the oxidising solution.The membrane separating the anode and cathode compartments may be any semipermeable membrane which is resistant to the electrolyte, including any microporous or woven plastic or any ion selective membrane which has the appropriate resistance to the electrolyte. Preferably the cell is divided using a cation selective membrane based on polyfluoroethers which contains also sulphonic acid groups. The anode material may be a noble metal coated onto titanium, such as platinum or platinum/irridium, or ruthenium dioxide or the anode material may be anodised lead or a lead alloy or lead coated mild steel or lead dioxide deposited onto titanium. The preferred material being lead coated mild steel. The cathode may be constructed from mild steel, nickel, lead, titanium or stanless steel, with the latter being the preferred material. To achieve high current efficiencies at high current densities in this dilute electrolyte it is desirable that a cell, where high mass transport to the anode surface may be achieved, is used. Such a cell is described in our European Patent Specification No 0064417. In addition to piperonal having a use in perfumery, it also has applications in medicine, suntan preparations, mosquito repellant, a laboratory reagent and as a flavouring; it is to be understood that the present invention also includes compositions for these various purposes which include a minor proportion of piperonal which has been prepared by the process of this invention. The invention will now be illustrated by the following example: A solution of ceric sulphate (0.125M) in sulphuric acid (5%) was prepared by electrolysing a solution of cerous sulphate in the anode compartment of a DEM cell (as described in our European Patent Specification No. 0064417 at a currrent of 75A (1500A/m2) for 38 minutes, equivalent to a current efficiency of 70%. The cell was constructed from a lead anode, a cation selective membrane as cell divider, and a stainless steel cathode. The catholyte solution was of identical composition to the anolyte. The oxidising solution (the anolyte) was reacted with 4-methyl-methylenedioxy-benzene (50g) in a well stirred round bottomed flask at ambient temperature, for 5 minutes. The mixture was then extracted with three portions of diethyl-ether (500ml) and the extracts combined and dried over anhydrous sodium sulphate. Upon evaporation the ether solution yielded an oil (52g) which on analysis was shown to contain unchanged starting material (26g) and piperonal (26g). The piperonal yield was 83% based on the ceric sulphate used and 90% based on the starting material consumed. CLAIMS

4. A process as claimed in Claim 3, wherein the disubstituted methane is dichloromethane, dibro momethane or di-iodomethane.

5. A process as claimed in any one of the preceding claims, wherein the ceric sulphate is prepared by oxidising a solution of cerous sulphate in aqueous sulphuric acid in an electrochemical cell, which cell has a separate anode and cathode compartment and the same electrolyte is circulated through each side of the cell whereby the migration of cerium through the membrane is minimised.

6. A process as claimed in Claim 5, wherein the anode and cathode compartments are separated by a cation selective membrane.

7. A process as claimed in Claim 6, wherein the membrane comprises a polyfluoroether and contains sulphonic acid groups.

8. A process as claimed in any one of Claims 5 to 7, wherein the anode is a noble metal, coated onto titanium, ruthenium dioxide or anodised lead or a lead alloy or lead coated mild steel or lead dioxide deposited onto titanium.

9. A process as claimed in any of Claims 5 to 8 wherein, the cathode is mild steel, nickel, lead, titanium or stainless steel.

10. A process as claimed in any one of the preceding claims, wherein the ceric sulphate is generated in an electrochemcial cell as described in our European Patent Specification No 0064417.

11. A process as claimed in Claim 10, wherein the electrolyte is pumped through the cell at a rate of 10 to 50 cmisec.

12. A process as claimed in Claim 10 or Claim 11, wherein the cell is operated with a current density of from 1000 to 2000 A/m2.

13. A process as claimed in any one of Claims 5 to 12, wherein the cell is operated at a temperature of from 10 to 30 C.

14. A process as claimed in Claim 1 and substantially as hereinbefore described in the specific example.

15. Piperonal when produced by a process as claimed in any one of the preceding claims.

16. A composition of matter comprising a minor proportion of piperonal as claimed in Claim 15, especially a perfume, a suntan preparation, a mosquito repellant or an edible composition comprising the piperonal as a flavouring.