Online Encyclopedia

Search over 40,000 articles from the original, classic Encyclopedia Britannica, 11th Edition.

ALKALOID

Online Encyclopedia
Originally appearing in Volume V01, Page 686 of the 1911 Encyclopedia Britannica.
» Make a correction to this article.
» Add information or comments to this article.
Spread the word: del.icio.us del.icio.us it!

ALKALOID , in See also:

chemistry, a See also:term originally applied to any organic See also:base, i.e. a nitrogenous substance which forms salts with acids; now, however, it is usual to restrict the term to bases of See also:vegetable origin and characterized by remarkable toxicological effects. Such bases occur almost exclusively in the See also:dicotyledons, generally in See also:combination with malic, citric, tartaric or similar plant-acids. They may be extracted by exhausting the plant-tissues with a dilute See also:acid, and precipitating the bases with potash, soda, See also:lime or See also:magnesia. The separation of the mixed bases so obtained is effected by repeated fractional See also:crystallization, or by taking See also:advantage of certain properties of the constituents. A chemical See also:classification of alkaloids is difficult on See also:account of their complex constitution. I. A. Wyschnegradsky, and after-wards W. Konigs, expressed the See also:opinion that the alkaloids were derivatives of See also:pyridine or See also:quinoline. This view has been fairly well supported by later discoveries; but, in addition to pyridine and quinoline nuclei, alkaloids derived from isoquinoline are known. The purely dhemical literature on the alkaloids is especially voluminous; and from the assiduity with which the constitutions of these substances have been and are still being attacked, we may conclude that their See also:synthesis is but a question of See also:time. See also:Piperine, See also:conine, atropine, belladonine, See also:cocaine, hyoscyamine and See also:nicotine have been already synthesized; the constitution of several others requires See also:confirmation, while there remain many important alkaloids—quinine, See also:morphine, See also:strychnine, &c.—whose constitution remains unknown.

The following classification is See also:

simple and convenient; the See also:list of alkaloids makes no pretence at being exhaustive. (r) Pyridine See also:group. Piperine; conine; trigonelline; arecaidine; guvacine; See also:pilocarpine; See also:cytisine; nicotine; sparteine. (2) See also:Tropine group. Alkaloids characterized by containing the tropine (q.v.) See also:nucleus. Atropine; cocaine; hygrine; See also:ecgonine; pelletierine. (3) Quinoline group. The alkaloids of the quina-barks: See also:quinine, &c.; the strychnos bases: strychnine, See also:brucine; and the See also:veratrum alkaloids: veratrine, cevadine, &c. (4) Isoquinoline group. ,The See also:opium alkaloids: morphine, codeine, thebaine, papaverine, narcotine, narceine, &c.; and the complicated substances See also:hydrastine and See also:berberine. In addition to the above See also:series there are a considerable number of compounds derived from See also:purin which are by some writers classed with the alkaloids. These are treated in the See also:article PURIN.

There are also reasons for including such compounds as muscarine, choline, neurine and betaine in this group. The greater number of these substances are of considerable medicinal value; this aspect is treated generally in the article See also:

PHARMACOLOGY. Reference should also be made to the articles on the individual alkaloids for further details as to their medicinal and chemical properties. The chemistry of the alkaloids is treated in detail by See also:Arne Pictet in his La Constitution chimique See also:des alcaloides vegelaux (See also:Paris, 1897); enlarged and translated by H. C. See also:Biddle with the See also:title The Vegetable Alkaloids (New See also:York, 1904); and by J. W. See also:Bruhl, E. Hjelt, and O. Aschan: See also:Die Pflanzen-Alkaloide (1900). A pamphlet, Die Alkaloidchemie in den Jahren 1900-1904, by See also:Julius See also:Schmidt, may also be consulted.

End of Article: ALKALOID

Additional information and Comments

There are no comments yet for this article.
» Add information or comments to this article.
Please link directly to this article:
Highlight the code below, right click, and select "copy." Then paste it into your website, email, or other HTML.
Site content, images, and layout Copyright © 2006 - Net Industries, worldwide.
Do not copy, download, transfer, or otherwise replicate the site content in whole or in part.

Links to articles and home page are always encouraged.

[back]
ALKALINE EARTHS 		[next]
ALKAN, CHARLES HENRI VALENTIN MORHANGE (1813-1888)

Site © 2006 - Net Industries