CAFFE′INE. C8H10N4O2. Syn. Caffe′ina, Théine, Guaranine. A peculiar nitrogenised principle, discovered by Robiquet in coffee. It is, moreover, the essential principle of tea, of Paraguay tea, and of Guarana, infusions of which are used as beverages in different parts of the world. The proportion of caffeine to the pound was found by Liebig to be as stated below in the six descriptions of coffee named:—
| Martinique | 32 | grains. |
| Alexandrian | 22 | ” |
| Java | 22 | ” |
| Mocha | 20 | ” |
| Cayenne | 19 | ” |
| St Dominique | 16 | ” |
In Hyson tea it exists in the proportion of from 2·5 to 3·4 per cent.; and in gunpowder tea from 2·2 to 4·1. In Paraguay tea, or maté as it is called in Brazil, and in Guarana, it exists in the proportion of ·13 per cent.
Prep. 1. Coarsely powdered raw or unroasted coffee is boiled in water, and subacetate of lead added to the filtered decoction to throw down the extractive and colouring matter;
the excess of lead is next precipitated with sulphuretted hydrogen, and the liquid filtered and evaporated by a gentle heat; the residuum is dissolved in boiling water, the solution agitated with freshly burnt animal charcoal, filtered, evaporated, and crystallised. By redissolving the product in hot alcohol, it may be obtained in white, shining, silky filaments, as the solution cools.
2. (H. J. Versman.) Quick-lime, 2 lbs.; water, q. s. to form a hydrate; raw coffee (bruised), 10 lbs.; mix, put it into a displacement apparatus, and cause alcohol of 80% to percolate through the mixture, until the fluid obtained no longer contains caffeine; the mass in the percolator is then roughly ground to powder, mixed with a fresh quantity of quick-lime, and the process of percolation repeated with fresh alcohol, as before. The spirit is next distilled from the mixed tinctures in a retort, and the residuum washed with a little warm water to remove the oil; the evaporation is then gently conducted until a crystalline mass is obtained, which is further freed from adhering oil by pressure between folds of blotting paper. It is purified by redissolving it in boiling water or hot alcohol, &c., as before.
3. (A. Vogel.) An extract of powdered coffee is made with commercial benzol; this being distilled off, leaves an oil and caffeine behind; the oil is then removed by a little ether or by hot water, from which latter liquid the alkaloid crystallises on cooling.
4. From a hot infusion of tea-leaves by treatment with subacetate of lead and sulphuretted hydrogen, as in process 1 (above).
5. (F. V. Greene.) Powdered guarana is intimately mixed with three times its weight of finely divided litharge, and the mixture boiled in distilled water, the ebullition being continued until, on allowing the temperature to fall below the boiling point, the insoluble portion is found to subside rapidly, leaving the supernatant liquid clear, bright, and without colour. The quantity of distilled water required will be found to be about a pint for every fifteen grams of the guarana used in the experiment, and as the boiling has to be continued for several hours before the desired and all essential separation mentioned above takes place, water must be added from time to time to supply the place of that lost by evaporation. When cool, the clear liquid is decanted upon a filter, and when it has passed through, which it will be found to do with facility, the precipitate is to be transferred to the filter, and washed with boiling water, the washing to be continued as long as yellowish precipitates are produced with either phosphomolybdic acid solution, auric, or platinic chloride. A stream of sulphuretted hydrogen gas is now passed through the filtrate to remove the small quantity of lead that has been dissolved, and the sulphide thus formed separated by filtration. The solution is evaporated on a water bath to expel the excess of sulphuretted hydrogen, filtered to remove a trace of sulphur, finally evaporated to the crystallising point, and the caffeine which crystallises out in cooling removed from the mother liquor and pressed between folds of bibulous paper. After being thus treated the crystals will be found to be perfectly white. On diluting the mother liquor with distilled water, filtering, and evaporating, a second crop of crystals are obtained, which are also perfectly white, after being pressed as above. The crystals are now dissolved in boiling dilute alcohol, filtered, and the solution set aside to crystallise by spontaneous evaporation. The resulting crystals of caffeine are perfectly pure and colourless.
6. (O. Caillol and P. Cazeneuve.) The following is a process for the rapid preparation of caffeine:—Black tea is thoroughly softened with four times its weight of hot water; a quantity of calcium hydrate equal to that of tea used is then added, and the whole evaporated on a water-bath to perfect dryness. The dry residue is exhausted with chloroform in a displacement apparatus, and the chloroform recovered from the percolate by distillation. The residue left in the retort is a mixture of caffeine and a resinous substance containing chlorophyll. On treating it with hot water, filtering and evaporating the filtrate on a water bath, the caffeine is obtained in perfectly white crystals.