BETAINE, a crystalline substance, called also acetobetaine, lycine and oxyneurine, discovered in the sugar-beet by C. Scheibler in 1869. It occurs in cotton seed, in barley and wheat shoots, in vetch and in many other plants often associated with choline. It is also found in cuttlefish and crayfish and in mussels, etc.
Betaine is obtained synthetically by oxidizing choline (0. Liebreich, 1869), or by heating glycine (aminoacetic acid) with methyl iodide and alkali (P. Griess, 1875), and its hydrochloride is synthesised by heating together trimethylamine and chloroace tic acid (Liebreich). The free hydrated base, which is the methyl hydroxide of dimethylglycine, crystal lizes from alcohol in deliquescent crystals readily soluble in water. On heating it readily loses water, passing into an internal anhy dride (I.), which has the characteristic betaine structure and is the prototype of many more complex betaines.
Formula I. represents the chemical structure hitherto ascribed to betaine in which quinquevalent nitrogen and bivalent oxygen are united by a non-polar or covalent linking, but it has also been suggested by Paul Pfeiffer (1922) that this anhydride formation is due to a polar or electrovalent association of the two atoms as indicated by formula II. According to this hypothesis betaine contains two ions of opposite sign (positive quaternary ammonium ion and negative carboxylate ion) bound together by a methylene group.
The term betaine is also employed generically to designate a large group of substances having the foregoing chemical struc ture. Several of these betaines are obtainable from natural sources, two examples of which are given.
Nicotinic acid (pyridine-3-carboxylic acid), derivable from the tobacco alkaloid, crystallizes in needles and melts at 23 2 ° C. It is soluble in hot water and in alcohol, but not in ether. It may be converted by the successive action on its alkali salt of methyl iodide and moist silver oxide into a betaine which is identical with the alkaloid trigonelline (III.) discovered by E. Jahns (1885 ) in the seeds of fenugreek (Trigonella foenum graecum) .
•y-Butyrobetaine (IV.), obtained by Taheda (191 o) from dog's urine after phosphorus poisoning, is probably identical with one of Brieger's ptomaines or putrefaction bases; it was first syn thesised by Willstatter 0902).
Closely related to betaine are the bases, choline, neurine and muscarine. Choline (bilineurine), which was first isolated by A. Strecker in 1862, is found in the bile, in brain substance, and in yolk of egg in the form of lecithin, a complex ester of glycerin with phosphoric acid and the fatty acids. It is also found in combination with sinapic acid in sinapin, the glucoside obtained from white mustard, and can be obtained from this glucoside by hydrolysis with baryta water. Synthetically prepared by the action of trimethylamine on an aqueous solution of ethylene oxide (A. Wurtz, 1868), it forms deliquescent non poisonous crystals of strongly alkaline reaction, and absorbs car bon dioxide from the air.
Neurine, trimethylvinylammonium hydroxide, : CH•N a very poisonous, crystalline ptomaine base produced by the putrefaction of albumin, may be prepared by the action of moist silver oxide on ethylene dibromide and trimethylamine.
Muscarine, an exceedingly poisonous substance found in many fungi, may be obtained synthetically by oxidizing choline with dilute nitric acid (0. Schmiedeberg, 1876). Its constitution is generally represented as CH (OH) The name muscarine is also given to an oxazine colouring matter.
See G. Barger, The Simpler Natural Bases (i914) ; P. Pfeiffer, "On the theory of Betaines," Berichte der deutschen chemischen Gesellschaft (1922).