Betaine forms

Azolecarboxylic acids can be quite strongly acidic. Thus l,2,5-thiadiazole-3,4-dicar-boxylic acid has first and second values of 1.6 and 4.1, respectively <68AHC(9)107). The acidic strengths of the oxazolecarboxylic acids are in the order 2>5>4, in agreement with the electron distribution within the oxazole ring <74AHC( 17)99). Azolecarboxylic acids are amino acids and can exist partly in the zwitterionic, or betaine, form e.g. 394). 

If a sample contains groups that can take up or lose a proton, (N//, COO//), then one must expect the pH and the concentration to affect the chemical shift when the experiment is carried out in an acidic or alkaline medium to facilitate dissolution. The pH may affect the chemical shift of more distant, nonpolar groups, as shown by the amino acid alanine (38) in neutral (betaine form 38a) or alkaline solution (anion 38b). The dependence of shift on pH follows the path of titration curves it is possible to read off the pK value of the equilibrium from the point of inflection... 

UV spectrum changes dramatically. The salt causes maxima at 251 (4.16), 286 (4.16), 387 (3.56), and 473 (3.37) nm. NMR data for a sample in CF3COOD were presented. It is interesting to note that the nonmethylated derivatives of 130 and 131 are present in solution above pH 6.5 as betaines, forming a protonated pyridine ring and an olate group (91MI3). 

Betaines formed in this way can then be converted to the alkene, and this is one reason why betaine intermediates were long accepted in the Wittig reaction. 

All studied model compounds can distinctly be divided into three groups (Table VII). The first group is composed of substances in which the sulfur, selenium or cyclopentadienyl anion acts as an anionic center. They exist only in open betaine forms, and their PES do not contain local minima corresponding to cyclic isomers. The second group contains compounds with arsonium cationic and oxide anionic centers and silicon and germanium betaines with arsonium and amide centers. They exist as cyclic isomers and their PES have no local minima corresponding to the open forms. Finally, the third group consists of six studied compounds with phosphonium cationic and oxide or amide anionic centers and arsonium-imide betaine. Their PES have minima for both cyclic and open forms separated by low barriers. 

Note b, only the betaine form is present on PES c, only the cyclic form is present on PES b + c, both betaine and cyclic forms are possible. 

Of the four possible azaquinolizinium systems, only the 1-aza- (pyrido[l,2-a]pyrimidin-5-ium, 234), the 2-aza- (pyrido[l,2-a]pyrazin-5-ium, 235) and the 4-aza- (pyrido[l,2- ]pyridazin-9-ium, 237) quir olizinium systems are known in at least a betaine form. No example of the fully aromatic 3-azaquinoIizinium system (pyrido[l,2-c]pyrimidin-9-ium, 236) has been found. 

Betaine(Trimethyl Glycine Trimethyl Glycocoll or Trimethyl Amino-Acetic Acid), (CH3)aIsI.CHg.CO.O or (CH3)3fo.CH2.CO.O mw 117.15, N 11.96%, OB to COz-184.4%. Prisms(from ale), mp 293°(decomp) sol in w in ale insol in ether occurs in plants (usually together with choline) and in some sea animals. Can be prepd by methylation of amino-acetic acid or by other methods. Betaine has been used in org synthesis to render various compds water-soluble. For instance, Girard s reagent(which is a deriv of betaine) is used to prepare water-sol derivs of insol ketones and aIdehydes(Ref 2,p 510) Betaine forms additive compds with acids and salts, some of them explosive (See below)... 

Figure 6.12. Bleaching curves of betaine form of selected DHIs in a PTU matrix (c = 4.97 x 10 7...

The reaction of tosyl isocyanate with 2-methyl- 1-dimethylaminopropene yields the betaine 330. In contrast, the betaine formed from the less basic enamine 331, derived from TV-methylaniline, adds a further molecule of the isocyanate to afford the hex-ahydropyrimidinedione 332 (equation 134)163. 

Ethyl 2-pyridylacetate reacts with diethyl ethoxymethylene malonate to give cyclic compound 64, which, on refluxing in hydrochloric acid, affords 4-quinolizone (65) (51JA3681). The 40% contribution of the betaine form 66 to the resonance hybrid was estimated on the basis of the H-NMR spectrum of 65 (73JOC4391). 

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