The Art of Perfumery, and Methods of Obtaining the Odors of Plants

Stoltze has recommended a method by which all the acid can be removed from the benzoin:--The resin is to be dissolved in spirit, to which is to be added a watery solution of carbonate of soda, decomposed previously by alcohol. The spirit is to be removed by distillation, and the remaining watery solution, from which the resin has been separated by filtration, treated with dilute sulphuric acid, to precipitate the benzoic acid. This method gives the greatest quantity of acid, but is attended with a sacrifice of time and alcohol, which renders it in an economical point of view inferior to the above process of Scheele. It is so far valuable, that the total acid contents of the resin can be determined by it. Dr. Gregory considers the following process for obtaining benzoic acid the most productive. Dissolve benzoin in strong alcohol, by the aid of heat, and add to the solution, whilst hot, hydrochloric acid, in sufficient quantity to precipitate the resin. When the mixture is distilled, the benzoic acid passes over in the form of benzoic ether. Distillation must be continued as long as any ether passes over. Water added towards the end of the operation will facilitate the expulsion of the ether from the retort. When the ether ceases to pass over, the hot water in the retort is filtered, which deposits benzoic acid on cooling. The benzoic ether and all the distilled liquids are now treated with caustic potash until the ether is decomposed, and the solution is heated to boiling, and super-saturated with hydrochloric acid, which afterwards, on cooling, deposits, in crystals, benzoic acid.