Barbituric acid, structure

Barbituric acid, structure, 55, 133 Barbituric acid, and /V-alkyl, bromination, 58, 306... 

Ultraviolet speotroscopic studies with 5,5-disubstituted barbituric acids (44) indicated that in aqueous solutions, the dominant forms are either the dioxo tautomeric form (i.e., monolaotam in alkaline medium) or the trioxo tautomerio form (barbituric acid structure in acid medium). The acidity of barbiturates in aqueous solution depends on the number of substituents attached to barbituric acid. The 5,5-disubstituted barbituric acids, 5,5-disubstituted thiobarbituric acids, and 1,5,5-trisubstituted barbituric acids are relatively weak acids, and salts of these barbiturates are easily formed by treatment with bases. The pKa of 5,5-disubstituted barbituric acids ranges from 7.1 to 8.1 (44). The 5,5-disubstituted barbiturio aoids can undergo a second ionization, having pKa values in the range of 11.7 to 1 2.7. The alkali metal salts of the barbiturates coupled with their highly lipophilic character will cause chemical incompatibility reactions (precipitation) when these compounds are mixed with acid salts of weakly basic amines. 

R. Prankerd, Some physical factors and drug activity— Physical properties and biological activity in certain barbituric acid structures. University of Otago, Dunedin, NZ, Master of Pharmacy Thesis, 1977. 

Potentiometric H2O Baird DR, Barbituric acids Structure-reactivity, a quantitative... 

The structure of barbituric acid was the subject of disagreement for many years, but since 195 2 (52BSB44) the trioxo formulation (57 R = H) has been accepted generally, along with the fact that barbituric acid loses a proton, first from carbon (anion) and subsequently from nitrogen (dianion). Barbital (5,5-diethylbarbituric acid) adopts a similar trioxo form (57 R = Et) (69AX(B)1978). 

Barbituric acid — see also Pyrimidine-2,4,6-trione, perhydro-acidic pK, 3, 60 bromination, 3, 70 fluorination, 3, 70 structure, 3, 68 tautomerism, 2, 27 in thermography, 1, 392 Barbituric acid, iV-alkyl-chlorination, 3, 70 Barbituric acid, 5-aminomethylene-synthesis, 3, 524 Barbituric acid, 5-arylidene-pyridopyrimidines from, 3, 227 Barbituric acid, 1,3-dicyclohexyl-synthesis, 3, 113 Barbituric acid, 2-thio-sensitizing dye... 

Early investigators adduced various kinds of chemical evidence in support of a monohydroxy-dioxo structure for barbituric acid (112) (a) reaction with diazomethane afforded a mono-O-methyl deriva- iye,i59,i6o barbituric acid and its 5-alkyl derivatives are much stronger acids than the 5,5-dialkyl derivatives, and (c) the 5-bromo and 5,5-dibromo derivatives have different chemical properties. - The early physical evidence also appeared to substantiate the monoenol structure, this formulation having been suggested for barbituric acid in 1926 on the basis of its ultraviolet spectrum and again in 1934, In the 1940 s, ultraviolet spectroscopic studies led to the suggestion of other monohydroxy and dihydroxy structures for barbituric acid, whereas its monoanion was assigned structure 113 (a clear distinction between ionization and tautomerism was not made in these papers). 

Barbituric acid can be considered as a cyclized malonic acid diamide (malonyl-urea). It is therefore a cyclic diketone that may be classified, in the sense of the compounds discussed in Section 12.6, as a coupling component with a methylene group activated by two carbonyl groups in the a- and a -positions. The reaction with arenediazonium salts was studied by Nesynov and Besprozvannaya (1971). These authors obtained coupling products (in good yield) that they considered to be arylhydrazones. Coupling with 4-(phenylazo)benzenediazonium chloride was studied by Chandra and Thosh (1991). The lH NMR spectra of these compounds are consistent with the arylhydrazone structure 12.68. 

An experimental study of barbituric acid found one new polymorph where molecules in the asymmetric unit adopted two different conformations [10]. The conformational aspect was investigated through the use of ab initio calculations, which permitted the deduction that the new form found would have a lower lattice energy than would the known form. It was also found that many hypothetical structures characterized by a variety of hydrogen-bonding structures were possible, and so the combined theoretical and experimental studies indicated that a search for additional polymorphs might yield new crystal structures. 

These dyes are invariably monoazo compounds with the reactive system attached to the diazo component, owing to the ready availability of monosulphonated phenylenediamine intermediates. Pyrazolone couplers are most commonly used, as in structure 7.82 (where Z is the reactive grouping), and this is particularly the case for greenish yellow vinylsulphone dyes. Catalytic wet fading by phthalocyanine or triphenodioxazine blues is a characteristic weakness of azopyrazolone yellows (section 3.3.4). Pyridones (7.83), barbituric acid (7.84) and acetoacetarylide (7.85 Ar = aryl) coupling components are also represented in this sector, with the same type of diazo component to carry the reactive function. 

Aminoanthraquinone is diazotized advantageously with nitrosylsulfuric acid after being dissolved in sulfuric acid. Coupling the diazo compound onto barbituric acid, for instance, affords a yellow pigment [3] with the structure 79 ... 

This subsection examines the hydrolytic stability of cyclic structures containing a ureido link. Schematically, ring closure can be achieved by N-alkylation or by /V-acylation of the second N-atom of the ureido moiety. The former results in the formation of, e.g., hydantoins and dihydropyrimidines. The latter ring closure leads to, e.g., barbituric acids. Taken together, cyclic ureides can also be regarded as ring structures that contain an imido function with an adjacent N-atom. We begin our discussion with the five-membered hydantoins, to continue with six-membered structures, namely dihydropyrimidines, barbituric acids, and xanthines. 

Although uracil possesses a structure very similar to that of barbituric acid, it is a much weaker acid (pKa 9.38) [368]. Also unlike barbituric acid, it is not... 

Apart from tautomerism between identical structures, NMR can also be used to investigate tautomeric equilibria between states of different energy. Thus it can be shown that barbituric acid exists as a urea derivative and is only formally a pyrimidine derivative. 

Band structure cesium auride, 25 240-241 graphite-alkali metal compounds, 23 287 Band theory, for one-dimensional electrical Conductors, 26 237-241 Barbituric acid, 18 187 Barium... 

The C-13 magnetic resonance spectra of the naturally occurring uracils79-81 have been interpreted in terms of the diketo structures of the compounds. Similarly the triketo structure 36 has been found81 to predominate for 1 - (/3-D-ribofuranosyl) barbituric acid by a comparison of C-13 spectra of several model nucleosides. Also in the case of 6-hydroxycytidine the equilibrium lies 81 strongly toward the diketo form 37b in comparison with the lactim-lactam form 37a. Very recent N-14... 

Extended Adjacency Matrix-Kow Relationships Yang et al. [39] derived two descriptors, EAS and EAmax, from the extended adjacency (EA) matrix and demonstrated their correlation with log,0 ow for barbiturate acid derivatives with structures I and II ... 

Triaminopyrimidine and barbituric acid derivatives are complementary components presenting the required features, since they should be able to form two arrays of three hydrogen bonds with each other. However, as pointed out above, based solely on hydrogen bonding recognition, their association could yield either a linear or a macrocyclic supramolecular structure (Section 9.4.2 Figure 37). 

Fig. 46. X-Ray structure (left) of the cocrystal of the 1 1 species (right) formed by two complementary components derived from barbituric acid BA (A = ethyl) and 2,4,6-triamino-pyrimidine TAP (B = butyl) [9.119].

In the early days of chemistry, when few pure substances were known, newly discovered compounds were often given fanciful names—morphine, quicklime, muriatic add, and barbituric acid (named by its discoverer in honor of his friend Barbara)—to cite a few. Today, with more than 20 million pure compounds known, there would be chaos unless a systematic method for naming compounds were used. Every chemical compound must be given a name that not only defines it uniquely but also allows chemists (and computers) to know the compound s chemical structure. 

Keywords solid diazonium salt, barbituric acid, pyrazolinone, azocoupling, solid-solid reaction, hydrazono structure... 

The barbituric acid derivative 2 (0.50 mmol) was ground in an agate mortar. Solid diazonium salt 1 (0.50 mmol) was added and co-ground in 5 portions for 5 min, each. Most of the diazonium band at 2280 cm-1 had disappeared, but completion of the reaction was achieved by 24 h ultrasound application in a test tube. After neutralization (0.5 n NaOH, 20 mL), washings (H20) and drying, the quantitatively obtained products 3a-e assume the hydrazono structure. 

Figure 6. Structure of barbituric acid dyes based on DACMA.

Urea may be recognised as a structural feature in the triketo form disconnection then reveals diethyl malonate as the other reagent. The synthesis of barbituric acid is therefore effected (Expt 8.36) by condensation of diethyl malonate with urea in the presence of sodium ethoxide. Barbituric acid undergoes nitration in the 5-position on treatment with fuming nitric acid, and reduction of the nitro derivative (98) yields 5-aminobarbituric acid (99) (uramil). 

Therapeutic Function Sedative, Hypnotic Chemical Name Barbituric acid, 5,5-diallyl-Common Name Diallylbarbituric acid, Allobarbital, Diallymal Structural Formula ... 

The complex between melamine and cyanuric acid (1 1) was reported in the literature in the late 1970s, but it was only in the early 1990s that the contributions from Whitesides and the concept of self-assembly popularized these systems [45]. Whitesides and co-workers reported the formation of tapes (Fig. 11.11), crinkled tapes and cyclic hexamers (rosettes) formed between barbituric acid and N,N -bis(p-substituted phenyl)melamine [46], In this they effectively blocked one face of melamine and, by manipulating substituents at the para position, different structures were obtained. Whiteside s putative suggestion that melamine/cyanuric acid formed an extended array (Fig. 11.12) was confirmed recently by Rao et al. with the crystal structure [47]. Hamilton and coworkers reported the crystal structure of a 5-substituted isophthalic acid derivative, which forms a cyclic aggregate held together with six pairs of hydrogen bonds, which in a way resembles the trimesic acid (Fig. 11.13) [48]. 

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