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Synthesis of 3,5-Dimethoxy-4-Hydroxypropenylbenzene

"Syringylpropenylbenzene"

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1,3-dimethoxy-2-hydroxybenzene

A flask containing 126 parts of pyrogallol is connected to a reflux condensor. Methyl Bromide is passed into the flask by a glass tube ending in a capillary and passing through the condensor near the bottom of the flask until the air displaced. A solution of sodium methylate (prepared by dissolving 57.5parts of sodium in 640 parts of absolute methanol) is run into the flask together with a continuous stream of methyl bromide continued until the reaction nearly neutral. The gas is rapidly absorbed and sodium bromide separates. The 1,3-dimethoxy-2-hydroxybenzene is isolated as follows: Water is added until the sodium bromide dissolves and is separated off. The methanol is evaporated and the residue is steam distilled. Any 1,2,3-trimethoxybenzene (keep!) present passes over with the product in the steam. The residue is acidified and extracted with ether. The ether solution is evaporated and the resulting oil is fractionated under reduced pressure. The pure 1,3-dimethoxy-2-hydroxybenzene is obtained as white crystals that have; MP: 55-56C. JACS 39, 1433 (1917)

2-allyloxy-1,3-dimethoxybenzene

A mixture of 154 parts of 1,3-dimethoxy-2-hydroxybenzene, 133 parts of allyl bromide and 180 parts of anhydrous potassium carbonate in 400 parts of dry acetone were heated to reflux with occasional shaking for 8 hours. The solvent was removed by distillation and the residue was diluted with water and extracted, thereafter, with ether. The ether was washed with dilute sodium hydroxide solution, then with water. The resulting solution was then dried with CaCl2 and distilled under reduced pressure on the steam bath to remove ether and excess allyl bromide. The residual liquid was distilled under high vacuum and the product was obtained as an almost colorless oil. The 2-allyloxy-1,3-dimethoxybenzene distilled had; BP: 102C/2mmHg, 130C/9mmHg. Refract. Index: nD22= 1.5300. Yield: 184parts (95%).

3,5-dimethoxy-4-hydroxyallylbenzene

2-allyloxy-1,3-dimethoxybenzene (104parts) was boiled under reflux at 75mmHg pressure for 1 hour and was then distilled under reduced pressure. 3,5-dimethoxy-4-hydroxyallylbenzene was obtained as a colorless oil having; BP: 123-125C/2mmHg, nD21=1.5478, Yeild: 147parts or 90%

3,5-dimethoxy-4-hydroxypropenylbenzene (potassium salt)

A mixture of 100parts of 3,5-dimethoxyhydroxyallylbenzene, 50 parts of potassium hydroxide and 200 parts of water was placed into a flask connected to a distillation assembly and heated to boiling. The clear solution soon became thick with precipitate. When the temperature reached 110C it had set almost solid. At this point 450 parts of aniline were added and the mixture was distilled again. After about 100 parts of the distillate were collected, the solution became very thick with precipitate. This precipitate was removed and the temperature began to rise: about 150 parts of distillate had been collected at this point. The distillation was continued until approximately 100 parts of aniline were collected and the temperature of boiling was 178-180C. The hot mixture was allowed to cool and a mixture of aniline and the potassium salt of 3,5-dimethoxy-4-hydroxypropenylbenzene solidified.

3,5-dimethoxy-4-hydroxypropenylbenzene

The solid mass was dissolved in water and extracted with ether. The alkaline aqueous layer was acidified with dilute HCl acid. The oil which separated was extracted with ether and the ether solution was washed with dilute hydrochloric acid, the was washed with water and then dried. The ether was removed under reduced pressure and the residue was distilled under high vacuum. 3,5-dimethoxy-4-hydroxypropenylbenzene came over as 93 parts of an colorless oil at 107-108C/0.05mmHg, nD27=1.541