§ 353. The salts of morphine are for the most part crystalline, and are all bitter, neutral, and poisonous. They are insoluble in amylic alcohol, ether, chloroform, benzene, or petroleum ether.
Morphine meconate is one of the most soluble of the morphine salts; it is freely soluble in water. Of all salts this is most suitable for subcutaneous injection; it is the form in which the alkaloid exists in opium.
Morphine hydrochlorate (C17H19NO3HCl) crystallises in silky fibres; it is readily soluble in alcohol, and is soluble in cold, more freely in boiling water. The purest morphine hydrochlorate is colourless, but that which is most frequently met with in commerce is fawn or buff-coloured.
Morphine acetate is a crystallisable salt, soluble in water or alcohol; it is in part decomposed by boiling the aqueous solution, some of the acetic acid escaping.
Morphine Tartrates.—These are readily soluble salts, and it is important to note that the morphine might escape detection, if the expert trusted alone to the usual test of an alkaloidal salt giving a precipitate when the solution is alkalised by the fixed or volatile alkalies; for the tartrates of morphine do not give this reaction, nor do they give any precipitate with calcic chloride. By adding a solution of potassium acetate in spirit, and also alcohol and a little acetic acid to the concentrated solution, the tartrate is decomposed, and acid tartrate of potassium is precipitated in the insoluble form; the morphine in the form of acetate remains in solution, and then gives the usual reactions.
The solubility of morphine salts in water and alcohol has been investigated by Mr. J. U. Lloyd. His results are as follows:—
| Morphine Acetate. | ||
| 11 | ·70 | parts of water by weight at 15·0° dissolve 1 part of morphine acetate. |
| 61 | ·5 | parts of water by weight at 100° dissolve 1 part of morphine acetate. |
| 68 | ·30 | parts of alcohol by weight (·820 specific gravity) at 15·0° dissolve 1 part of morphine acetate. |
| 13 | ·30 | parts of alcohol by weight (·820 specific gravity) at 100° dissolve 1 part of morphine acetate. |
| Morphine Hydrochlorate. | ||
| 23 | ·40 | parts of water dissolve at 15° 1 morphine hydrochlorate. |
| ·51 | part of water dissolves at 100° 1 morphine hydrochlorate. | |
| 62 | ·70 | parts of alcohol (·820 specific gravity) dissolve at 15° 1 morphine hydrochlorate. |
| 30 | ·80 | parts of alcohol (·820 specific gravity) dissolve at 100° 1 morphine hydrochlorate. |
| Morphine Sulphate. | ||
| 21 | ·60 | parts of water at 15° dissolve 1 morphine sulphate. |
| ·75 | part of water at 100° dissolves 1 morphine sulphate. | |
| 701 | ·5 | parts of alcohol (·820) at 15° dissolve 1 morphine sulphate. |
| 144 | ·00 | parts of alcohol (·820) at 100° dissolve 1 morphine sulphate. |
§ 354. Constitution of Morphine.—The chief facts bearing on the constitution of morphine are as follows:—
It certainly contains two hydroxyl groups, because by the action of acetic anhydride, acetyl morphine and diacetyl morphine, C17H18(CH3CO)NO3 and C17H17(CH3CO)2NO3 are produced. The formation of the monomethyl ether of morphine (codeine), C17H17(OH)(OCH3)NO, is also a testimony to the existence of hydroxyl groups. One of the hydroxyl groups has phenolic functions, the other alcoholic functions. By suitable oxidation morphine yields trinitrophenol (picric acid), and by fusion with an alkali, protocatechuic acid; both of these reactions suggest a benzene ring. On distilling with zinc dust phenanthrene, pyridine, pyrrol, trimethylamine, and ammonia are formed; evidence of a pyridine nucleus. If morphine is mixed with 10 to 15 times its weight of a 20 per cent. solution of potash, and heated at 180° for from four to six hours, air being excluded, a phenol-like compound is formed, and a volatile amine, ethylmethylamine (the amine boils at 34° to 35°, and its hydrochloride melts at 133°). This reaction is interpreted by Z. H. Skrauk[378] and L. Wiegmann to indicate that the nitrogen is directly connected with two alkyl groups—that is, ethyl and methyl.