Patent GB-290649-A (GB)
IPC: F22B7/20
Filed: 1928-01-26
Abstract: 290,649. Riedel Akt.-Ges., J. D. May 20, 1927, [Convention date]. Addition to 285,451. Aromatic aldehydes.- o- and p-Propenyloxybenzenes are oxidized to the corresponding aldehydes by means of aromatic nitro compounds in excess, for example, nitrotoluene. The process may be used in the preparation of vanillin as in mixtures of simple 1-propenyl-3: 4-pyrocatechin ethers only those are oxidized which contain a free hydroxyl radicle in the para position to the propenyl group. Thus, for example, a mixture of isomeric propenylmonomethylpyrocatechin ethers prepared according to Specification 285,156 can be decomposed directly by oxidation of the alkali salts into a mixture of vanillin and iso-chavibetol, the vanillin being subsequently extracted or it is possible to subject, after separation of the main quantity of the isochavibetol, the filtrate thereof to oxidation; this filtrate contains in addition to iso-eugenol and small quantities of iso-chavibetol other isomeric propenylpyrocatechin ethers one of which is converted to vanillin and the other to a great extent into iso-chavibetol. If the mixture of the alkali salts of the two propenylmonoalkyloxymethylpyrocatechin ethers produced in the decomposition of iso-safrol or camphor oils be oxidized by nitro compounds, then methylated and finally heated with dilute acids, there results an easily separable mixture of iso-vanillin and isoeugenol. The iso-eugenol may be converted into vanillin by the process of the parent Specification. Pure p-oxy-m-ethoxybenzaldehyde can be obtained in the same way from a mixture of isomeric ethyl ethers, described in Specification 284,199. In examples, (1) Safrol is heated under pressure with methyl alcoholic potash and the product treated with dimethyl sulphate and saponified, whereby a mixture of monomethyl ethers of 1-propenyl-3 : 4-pyrocatechin is obtained. The mixture is rubbed up with caustic soda and the resulting salt is oxidized with nitrobenzene acidified and extracted with bisulphite solution. Decomposition of the bisulphite compound gives vanillin. The oxidation may also be carried out after the separation of not only the iso-chavibetol but also of the main portion of the iso-eugenol as the sodium salt. (2) Safrol is treated with methyl alcoholic potash, and the two methoxymethyl ethers of propenylpyrocatechin are rubbed up with caustic soda and oxidized as in the example given in the parent Specification by nitro-benzene. The solution is neutralized and treated with dimethyl sulphate; and the methyl ethers are saponified and shaken out with bisulphite solution. By decomposing the bisulphite solution iso-vanillin is obtained. Sodium iso-eugenolate is obtained from the remaining ethereal solution and decomposed to isoeugenol which is oxidized as described in the parent Specification. (3) A mixture of ethyl ethers of propenylpyrocatechin obtained according to Specification 285,156 is freed from the main portion of the para ethyl ether, rubbed up with caustic soda and oxidized with nitrobenzene. The product is worked up as in the previous example, the meta ethyl ether of protocatechuic aldehyde and the para ethyl ether of 1-propenyl-3, 4-pyrocatechin being obtained. Specification 309,929 also is referred to.