US Patent 1643804
Process of Manufacturing Vanillin
Abstract:
The oxidation of iso-eugenol (from reacting Eugenol from cloves with KOH and then acidification) with a nitrocompound in amine solvent under basic conditions caused by the addition of excess hydroxides
Example 1:
Oil of cloves (essentially Eugenol) is heated with KOH around 200*C to form the potassium salt of of iso-eugenol. This mixture is then dissolved in an excess of aniline. The dissolving of the solid mass into the aniline is greatly accelerated by using moist aniline, such as aniline that has stood overnight in contact with water. When using absolutely dry aniline the solution is not complete after heating the mix at 165-170*C for 6 hours. If, however, moist aniline is used, the solution is completed in about 3 hours by keeping the mixture at about 100*C. A large excess of aniline may be used for this operation.
When the solid mass has entirely entered in solution into aniline, a good way of operating is to then add a strong solution of sodium hydroxide in water and then distill off a great deal of the excess of aniline used. A satisfactory way of doing this is to raise the temperature of the mixture to about 125*C and introduce a jet of steam over the top surface of the mixture. The steam is then condensed. This is similar to regular steam distillation, however, the steam does not need to be introduced to the bottom of the boiling flask for effectiveness.
When the greater portion of the excess aniline has distilled over, the mass, while still hot and before it has a chance to solidify, is drawn off into a covered apparatus having an efficient stirrer and containing an excess of cold nitrobenzol. Ortho-nitrotoluol may also be used.
If, after stirring the mixture thoroughly, the mass so obtained is set aside and let stand for several days at RT it will be found that the iso-eugenol has converted to vanillin and part of the nitrobenzol has been transformed (reduced) to azo-benzol.
If, on the contrary, the mixture is heated to about 115*C while the stirrer is still in operation, the reaction will take place rather suddenly and violently. Again iso-eugenol will become vanillin with the concurrent reduction of the nitrobenzol to azobenzol.
Then, keep the above mixture at 100*C for 2 hours, when the reaction will be practically complete and direct steam distillation may be used. The excess aniline and nitrobenzol will come over. If it should happen that the reaction was not complete, the reaction will continue during the steam distillation. The distillate obtained will contain about equal parts of aniline and nitrobenzol.
When all these compounds have come over, and the mass is still near 80*C is drawn off into an open settling kettle. Enough water is added to ensure complete solution of the alkali compound with vanillin, and the mass is then cooled down. The azo-benzol, which is insoluble in water, will settle to the bottom. The supernatant liquor is decanted, making sure that it does not contain any azobenzol. The aqueous solution is concentrated and cooled down and the alkali salt of vanillin will crystallize out as reddish-brown crystals. On filtration of these crystals, and treating them with sulfuric acid, crude vanillin is obtained. The mother liquors are in turn treated with sulphuric acid and worked up to recover additional vanillin.
In a regular run and using oil of cloves containing ~85% of Eugenol, the yields of pure vanillin melting at 81.75*C to 82*C will be around 71.5% Azobenzol is produced in approx. the same proportion as vanillin (by mass).
Notes:
Temperatures in the first step should reach 205*C, but no higher than 210*C.
Air should be excluded from the mixture being heated in the first step.
