632

PAROXYBENZOIC ACID-SALICIN-PHILLYRIN.

5

Paroxybenzoic Acid (H¤‚Í ̧Ð ̧Н,) is the name given to an acid metameric with the salicylic, which crystallizes in delicate long needles, and furnishes a sparingly soluble salt with copper. The cadmium salt crystallizes readily in rhombohedra, and its salts with lead and silver are also characteristic.

Paroxybenzoic acid is produced by various reactions, such as that of fused potash upon tyrosin (1618) and upon carthamin, and of hydriodic upon anisic acid. Indeed, anisic acid may be viewed as methyl-paroxybenzoic acid [H‚¤,H1(ЄH ̧)→]·

(1461) SALICIN (Є13H187, or C26H18011=286); Fusing pt. 248° (120° C.).—This substance has been made the subject of a series of interesting researches by Piria (Ann. de Chimie, II. Ixix. 281, and III. xiv. 257). Salicin is contained in the bark of most of the willows, and confers upon them their peculiar bitterness. It is procured by adding to an aqueous infusion of the bark, hydrated oxide of lead, and boiling, by which the tannin and colouring matters are removed, and then on filtering and evaporating the liquid, the salicin is obtained in crystals. It is soluble in five or six parts of cold water, and is still more readily dissolved by alcohol. These solutions exert a left-handed rotatory action upon a ray of polarized light. A solution of salicin is not precipitated by infusion of gelatin, nor by one of tannin, but with an ammoniacal solution of acetate of lead it yields a precipitate consisting of H1Pb. When salicin is moistened with strong sulphuric acid it acquires a deep red colour, and a compound acid is formed which has been termed sulpho-rufic acid.

When salicin is boiled for a few minutes with dilute sulphuric or hydrochloric acid a remarkable change occurs; grape sugar is found in the solution, and on neutralizing the acid, the liquid strikes a very intense blue with the ferric salts, owing to the presence of saligenin (E,HO).* On agitating the solution with ether, the saligenin is separated, and may be obtained on evaporation crystallized in pearly tables, which fuse at 18c° (82° C.) (p. 292). A similar transformation is effected when salicin is

34

8

* Phillyrin (2 €27H4011, 3 H2O) is the name given to a crystallizable substance contained in the bark of the Phillyrea, which splits, when boiled with acids, into grape sugar and a resinous substance; and which when submitted to lactic fermentation yields phillygenin and sugar, phillygenin containing the elements of 3 atoms of saligenin (Bertagnini).

DERIVATIVES OF SALICIN.

633

allowed to stand for some time after mixture with a solution of synaptase (note, p. 598). The change which occurs may be thus represented :

By heating saligenin carefully in closed vessels, an atom of water is expelled, and a resinous body named saliretin (¤‚H ̧Ð) remains. The same effect is produced by boiling salicin or saligenin for some time with a dilute acid; the solution becomes turbid and deposits the resin, which is insoluble in water, but soluble in alcohol, ether, and concentrated acetic acid. It acquires a red colour when moistened with oil of vitriol.

When salicin is heated to 248° (120°C.) it fuses, and at a higher temperature is completely decomposed. If heated with caustic potash it is also decomposed, and potassic oxalate and salicylate are formed. Concentrated nitric acid converts salicin into oxalic and carbazotic acids. If salicin be boiled with sulphuric acid and peroxide of manganese, formic acid is the principal product. But the most interesting transformation of which it is susceptible is that produced by chromic acid :-if 1 part of salicin be mixed with part of potassic dichromate, 1 of sulphuric acid, and 20 parts of water, on the application of a gentle heat formic and carbonic acids are produced, whilst a fragrant oily liquid distils over with the vapour of water, and condenses in the receiver; it has exactly the odour of the meadow-sweet or the heliotrope, and analysis has proved it to have the same composition (EH) as the essential oil of these plants. Both saligenin and saliretin also yield oil of spirea when treated with the dichromate and sulphuric acid, the change effected being simply one of oxidation :

16

13 15 3

Chlorine produces three different substitution-products with salicin; viz., H1,C107; €13H18C1,,; and HCl,,. When digested with synaptase they each furnish a corresponding chlorinated form of saligenin (see table, p. 627), and if boiled with dilute acids each yields a corresponding chlorinated form of saliretin.

634

HELICIN-HELICOIDIN-NATURE OF SALICIN.

2

Helicin (4 €13H1607, 3 H2→).—When one part of salicin is digested without the application of heat in ten parts of nitric acid of sp. gr. 1160 for twenty-four hours, it becomes gradually dissolved, and loses 2 atoms of hydrogen; the solution acquires a yellow colour, and crystals of helicin are deposited: the mother liquor must be removed by submitting the crystals to pressure in linen, after which they must be washed with cold water and with ether, which leaves them in a state of purity. Helicin crystallizes in small delicate colourless needles, which are very soluble in boiling water and in alcohol, but not in ether. It has a bitterish taste; when heated to 212° it loses its water of crystallization; it fuses at 347° (175° C.), and is gradually decomposed, becoming converted into an insoluble resinoid mass. Under the influence of alkalies, or of synaptase, helicin assimilates the elements of water and is converted into oil of spiræa, and glucose :

Dilute nitric acid also decomposes helicin, and liberates oil of spiræa. When boiled with dilute nitric acid, nitrosalicylic and oxalic acids are formed.

Helicoidin [(H34→14)2 3 H2O=(Є13H18079€13H1607)2 3 H2O] is a crystalline compound which is the result of the imperfect oxidation of salicin. It is prepared in the same manner as helicin, but the specific gravity of the nitric acid employed must not exceed 109. The circumstances necessary to ensure its production are, however, not accurately known.

Both chlorine and bromine form compounds with helicin, in which 1 atom of hydrogen is displaced by an atom of chlorine or of bromine, the formula of chlorohelicin being Є11CIO: it is decomposed by synaptase into glucose and salicyl chloride.

Nature of Salicin.-The foregoing observations and experiments appear to lead definitely to the conclusion that salicin must be regarded as a colligated body derived from saligenin and grape sugar. Saligenin is a substance which readily undergoes transformations by chemical agents, being converted by sulphuric acid. into a peculiar red compound, by nitric acid into carbazotic acid, and by other oxidizing agents into oil of spiræa. When salicin is submitted to the action of chemical agents, the saligenin is the constituent which is first affected if these agents act with moderate intensity; whilst the sugar either remains in combination with the modified saligenin, as in the various forms of chlorosalicin, or it is set at liberty. If the reaction be more violent, the

POPULIN- -COUMARIN.

635

elements of the sugar also take part in the changes which are effected for example, when salicin is oxidized by chromic acid, the saligenin yields the oil of spiræa, and the sugar produces formic acid.

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(1462) Populin [Є20H2O, 2 H2O].-This compound may be regarded as salicin, in which one atom of hydrogen has been displaced by benzoyl. It is found in the bark and the leaves of the aspen (Populus tremula), and probably also in other varieties of the poplar. It is extracted by a process similar to that employed for salicin. Populin requires about 70 parts of boiling water for its solution, and 2000 parts of cold water: it is freely soluble in boiling alcohol. When crystallized from a hot aqueous solution it forms colourless, silky, extremely delicate needles, which have a sweetish taste resembling that of liquorice; these crystals, if heated to 212°, lose 2 H2O; at a higher temperature they are decomposed, benzoic acid being amongst the products. When boiled with baryta water for a few minutes, a clear solution is obtained, and on separating the excess of baryta by means of a current of carbonic acid, the solution is found to contain salicin and baric benzoate ::

Populin.

2

When boiled with dilute acids, populin assimilates the elements of water, and is decomposed into a mixture of benzoic acid, saliretin, and glucose:

Synaptase is without action upon populin; concentrated nitric acid converts it into a mixture of nitrobenzoic, carbazotic, and oxalic acids; dilute nitric acid converts it into benzoyl-helicin, €13H15(ЄH.). A mixture of potassic dichromate and sulphuric acid liberates oil of spiræa from populin in abundance.

6

(1463) Coumarin (E,HO2 =148); Fusing pt. 122° (50° C.); Boiling pt. 518° (270° C.).-This substance is found in the Tonka bean (Coumaroma odorata), in the common melilot, in the sweetscented vernal grass, to which much of the fragrance of hay is owing, and in several other sweet-scented plants. Coumarin is most easily extracted from the Tonka bean by digesting the powdered seeds in alcohol; on evaporating the alcoholic solution, crystals of coumarin are obtained, and may be purified by digestion with animal charcoal, and by recrystallization. Coumarin

636

COUMARIC ACID-ANISIC SERIES.

1

assumes the form of colourless rectangular plates, or of rhombic prisms with slightly rounded faces. It may be distilled unaltered. Its vapour has an agreeable aromatic odour. It has a burning taste, and is but slightly soluble in cold water, though it is freely dissolved by boiling water; the solution on cooling deposits coumarin in silky needles. Dilute acids dissolve it without alteration. Concentrated nitric acid converts it at first into nitrocoumarin [Є,H,(NO),], but by prolonged boiling it transforms it into carbazotic acid. Substitution-compounds containing chlorine and bromine may also be formed from it. One of its most singular compounds is obtained by heating coumarin with a solution of antimonic chloride in hydrochloric acid: gas is evolved, and as the liquid cools, a canary-yellow precipitate (Є,н ̧Ð ̧‚SbCl ̧?) is deposited in crystals.

When coumarin is boiled with a concentrated solution of caustic potash it assimilates the elements of water, and is converted into potassic coumarate :—

Coumaric acid may be obtained from this salt crystallized in brilliant transparent plates, by decomposing a hot solution of the coumarate by hydrochloric acid. Coumaric acid fuses at about 374° (190° C.); at a higher temperature it is decomposed, yielding a crystalline sublimate, and an oil which combines with potash, and reddens the ferric salts.

When coumaric acid is fused with caustic potash, it is decomposed into potassic acetate and salicylate (Chiozza), whilst hydrogen escapes :

(1464) The essential oils furnished by the seeds of Pimpinella anisum, or common anise, of the Anethum fœniculum, or fennel, of the Illicium anisatum, or star anise, and of the Artemisia dracunculus, or tarragon, are closely allied to each other; they vary in odour, but all consist of two portions, one of which is a hydrocarbon isomeric with oil of turpentine, and the other is a solid crystalline oxidized compound (EH), which is convertible by oxidation into anisyl hydride (E,H,O,H).