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Tautomerization, salicylic acid

The photophysics of solid salicylic acid (SA) has been studied by using steady-state and time-resolved spectroscopic techniques [207,208], Dimers of SA form in two possible structures (59 and 60) due to fast ground-state double proton transfer. Dual fluorescence is observed at 380 nm and 440 nm, which are ascribable to the excited-state double proton transfer between different dimeric structures of SA. The enol form is more stable in the ground state. However, in the excited singlet state, the keto form has a lower potential energy [207], This excited enol-keto tautomerism has a barrier height of -1250 cm as is calculated from the dependence of dual fluorescence on excitation wavelength in the... [Pg.620]

Sulfasalazine (5-[4-[(2pyridylideneamino)sulfonyl]phenyldiazenyl]salicylic acid) (40) was first isolated in triclinic form and it was shown by X-ray analysis that the molecule is present in the amide tautomeric form 40c (2001ACX435). Later it was isolated in monoclinic form, and this form was shown by X-ray analysis to exist in the imino form 40d (Scheme 31) (2005AXCo226). [Pg.230]

In the Kolbe reaction, phenoxide ion reacts with CO2 to produce salicylic acid through a mechanism in which the phenoxide ion reacts like an enolate anion attacking the electrophilic carbon of CO2, followed by loss of a proton and keto-enol tautomerization to give the salicylate anion. [Pg.938]

The vast majority of papers devoted to tautomerization dynamics deal with ESIPT reactions. Since Weller s suggestion that the large Stokes shift he measured for salicyhc acid fluorescence was caused by rapid proton transfer in the excited state [62], and the development of techniques to study this on a femtosecond timescale, the field has blossomed. Most of the 2000 papers on tautomerization dynamics is on ESIPT, from both an experimental and a theoretical point of view. The number of compounds exhibiting ESIPT is far too large to discuss here. It ranges from molecules as simple as malonaldehyde to systems as complicated as 3-hydroxyflavone or 2-(2 -hydroxyphenyl)benzothiazole. In particular, substituted salicylic acids and ortho-hydroxybenzaldehydes have attracted much attention from both experimentalists and theoreticians. Weller s idea is depicted in Figure 1.10. [Pg.15]

The dashed arrow indicates the excited-state proton transfer. There are a few cases of dual emission from both the normal (E) and tautomeric (T) forms. Salicylic acid is not one of them in most solvents. [Pg.16]

Photochemically Liduced Tautomerism of Salicylic Acid and Its Related Derivatives... [Pg.1357]

Bisht, P.B., Petek, H., Yoshihara, K., and Nagashima, U., Excited state enol-keto tautomerization in salicylic acid a supersonic free jet study, J. Chem. Phys., 103, 5290,1995. [Pg.1385]

Sulfasalazine,5- 4- [(2-pyridylideneamino)sulfonyl] -phenyldiazenyl salicylic acid, a derivative of 5-aminosalicylic acid and sulfapyridine, is a pharmaceutical compound used in the treatment of inflammatory bowel disorders and rheumatoid arthritis [90]. It was shown that the sulfasalazine can be obtained in two crystal forms, as a monoclinic or as a triclinic form. These forms differ not only in the spatial arrangement of the molecules but also in their tautomeric form (Scheme... [Pg.311]

Similar azomethine ylides 48 are involved as key intermediates in the racemi-zation of optically active a-amino acids in the presence of a catalytic amount of aldehyde (83JOC843). Grigg confirmed this mechanism (83TL4457) and carried out the reactions of optically pure a-amino acids with salicyl- or o-methoxybenzaldehyde and maleic anhydride or N-phenylmaleimide in acetic acid. Cycloadducts of N-unsubstituted azomethine ylides 48 with dipolaropbiles were obtained only as racemates. These results indicate that the a-amino acids first produced the corresponding imine carboxylic acids with the retention of optical activity but these then undergo a tautomeric equilibration with N-protonated azomethine ylides 48 losing their optical purity. The ylides 48 were captured by several dipolaropbiles as racemic cycloadducts. As the imines of a-amino acids usually suffer spontaneous decarboxylation (as will be discussed later in Section (II,E), the formation of... [Pg.252]


See other pages where Tautomerization, salicylic acid is mentioned: [Pg.215]    [Pg.21]    [Pg.123]    [Pg.13]    [Pg.49]    [Pg.1358]    [Pg.312]    [Pg.195]    [Pg.78]   


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