Parabanic Acid Research Articles

Reaction products of parabanic acid and alkylene carbonates as components of polyurethane foams

AbstractEsteramidoimidotetraols are obtained by reacting 8‐ and 12‐molar excess of ethylene carbonate or propylene carbonate with parabanic acid. The parabanic acid ring undergoes opening, and linear polymeric products are formed. The products can conveniently be used as polyols for polyurethane foams. The results of a study on thermal stability and on compressive strength of foams prepared from these tetraols, measured before and after thermal treatment, are reported. Copyright © 2007 Society of Chemical Industry

An Unprecedented Study of the Rearrangement of 5,5‐Diazidobarbituric Acids under Various Conditions.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

An Unprecedented Study of the Rearrangement of 5,5-Diazidobarbituric Acids under Various Conditions

The unexpected parabanic acid derivatives 6a,b were obtained via unprecedented rearrangement of 5,5-diazidobarbituric acids 2a,b upon stirring in water at 50-60°C. Themolysis of diazides 2a,b in benzyl alcohol at 120–130°C afforded the tetrazole derivative 11 and/or benzyl allophanate 14.

Kinetics and mechanism of formation of polymeric products during the hydroxyalkylation of parabanic acid with oxiranes

AbstractThe kinetics of the reaction between N‐(2‐hydroxyalkyl) hydroparabanates (HAHP) and N,N′‐bis(2‐hydroxyalkyl) parabanates (HAP) with ethylene and propylene oxides were studied. The addition of oxiranes to imide function of HAHP led to the formation of HAP. Further reaction of HAP with oxiranes resulted in trioxoimidazolidine ring opening and polymeric products. The kinetics of the system was studied in detail. Based on the final kinetic equations, the mechanism of the reactions was postulated. The temperature dependences of kinetic parameters and analytical data provided experimental evidences supporting the mechanism. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 399–406, 2006

A preliminary study of polyureas and poly(parabanic acid)s incorporating furan rings

Novel furanic polyureas were synthesised by solution polycondensation reactions between difuranic diamines and aliphatic diisocyanates and then converted to the corresponding poly(parabanic acid)s by heterocyclisation with oxalyl chloride. These condensation reactions and chemical modifications were first studied with model compounds. The polymers were characterised by FTIR and 1H-NMR spectroscopy and inherent viscosity.

Hydroxyalkylation of parabanic acid. III. Polymers from parabanic acid and ethylene carbonate

AbstractThe influence of initial molar ratio of reagents, amount of catalyst, and temperature of reaction between parabanic acid and ethylene carbonate on structure of product was studied. The reaction led to the opening of the trioxoimidazolidine ring, resulting in formation of thermally resistant linear polymeric products constructed of urea and oxoamidoester subunits linked via imide bond. The percentage of side products was estimated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1443–1449, 2006

Advanced Oxidation of Caffeine in Water: On-Line and Real-Time Monitoring by Electrospray Ionization Mass Spectrometry

High performance liquid chromatography (HPLC), ultraviolet spectroscopy (UV), and total organic carbon (TOC) analyses show that caffeine is quickly and completely degraded underthe oxidative conditions of the UV/H2O2,TiO2/ UV, and Fenton systems but that the organic carbon content of the solution decreases much more slowly. Continuous on-line and real-time monitoring by electrospray ionization mass (ESI-MS) and tandem mass spectrometric experiments (ESI-MS/MS) as well as high accuracy MS measurements and gas chromatography-mass spectrometry analysis show that caffeine is first oxidized to N-dimethylparabanic acid likely via initial OH insertion to the C4=C8 caffeine double bond. A second degradation intermediate, di(N-hidroxymethyl)parabanic acid, has been identified by ESI-MS and characterized by ESI-MS/MS and high accuracy mass measurements. This polar and likely relatively unstable compound, which is not detected by off-line GC-MS analysis, is likely formed via further oxidation of N-dimethylparabanic acid at both of its N-methyl groups and constitutes an unprecedented intermediate in the degradation of caffeine.

Calculation of Attachment Energies and Relative Volume Growth Rates As an Aid to Polymorph Prediction

We calculate the morphologies of a number of the observed and hypothetical crystal structures of paracetamol, parabanic acid, and pyridine using the attachment energy model. We also estimate the relative growth volumes of the different polymorphs. This quantity is found to exhibit a large variation, which is generally well correlated with the attachment energy of the most dominant face of each polymorph, thus indicating how one face controls crystal growth. Such calculations suggest which thermodynamically feasible crystal structures could have a kinetic advantage in crystal growth. The application of the present results to polymorph prediction is discussed.

Investigating Unused Hydrogen Bond Acceptors Using Known and Hypothetical Crystal Polymorphism

The crystal structures found in a manual search for polymorphs are discussed in conjunction with low energy crystal structures found in a computational search for minima in the lattice energy, for barbituric acid, cyanuric acid, alloxan, parabanic acid, and urazole. Since all these molecules, with the exception of urazole, have crystal structures in which there are carbonyl groups not used in conventional hydrogen bonding, these results and the electrostatic properties of the molecules are used to interpret this unusual behavior. It appears that there is no great difference between the strengths of the various N-H donors and C=O acceptors within these molecules, and the observed crystal structures result from the compromise between the intermolecular interactions of the molecules.

High-pressure recrystallisation—a route to new polymorphs and solvates of acetamide and parabanic acid

Although the application of high pressure to organic compounds may favour thermodynamically the adoption of a new polymorphic form, for compounds with high melting points there is often a substantial kinetic barrier to be overcome before the molecules can rearrange. Hence pressure-induced phase changes are often very slow or may not occur at all. We have overcome this problem by growing single crystals from solution at high pressure. Using this technique we have prepared and structurally characterised for the first time a new polymorph of acetamide and a sesquihydrate of parabanic acid. We also report the results of a high-pressure powder neutron diffraction study on parabanic acid-d 2, which show that up to a pressure of 2.1 GPa direct compression does not induce a phase transition although several intermolecular interactions are substantially altered.

Study on reactions of 2-(dinitromethylene)-4,5-imidazolidinedione.

Some new reactions of 2-(dinitromethylene)-4,5-imidazolidinedione (1) with water, alcohols, carboxylic acids, and alkalis were discovered. By reaction of 1 with carboxylic acids, large particle size 1,1-diamino-2,2-dinitroethylene (2) was prepared. By reaction of 1 with methanol, the methanol adduct (4) was synthesized and characterized. By reaction of 1 with water, the synthetic pathway of 2-methylimidazole to 2 could be achieved in a continuous process. By reaction of 1 with KOH, 2 and potassium dinitromethane (6) could be formed at different temperature, respectively. Compounds 1 and 4 decomposed into parabanic acid (5), losing nitrogen oxides and carbon oxides. Some explosive properties of 1 were studied. The mechanisms of synthesis of 1, 2, and 5 are discussed.

(η 5-C 5H 5)Fe(CO) 2](Fp)-complexes of the parabanic acid mono- and dianion: synthesis, X-ray structures and reactivity of the heterocyclic ligand

[(η 5-C 5H 5)Fe(CO) 2](Fp)-complexes of the parabanic acid mono- and dianion have been synthesised in a photochemical reaction of FpI with parabanic acid and diisopropylamine in benzene. The former contains a reactive N(3)–H bond and can be readily thallated with TlOEt. Reaction of the thallated complex with Ph 3PAuCl, benzyl chloride and ethyl bromoacetate in DMF gave N(3)-aurated, N(3)-benzyl and N(3)-carboethoxymethyl complex, respectively. The structures of these complexes were confirmed by X-ray diffraction. The ester function in the N(3)-carboethoxymethyl complex was hydrolysed to afford air-stable, water-soluble acid, a potential metallocarbonyl labelling reagents for proteins.

Hydroxyalkylation of parabanic acid. II. Reactions of parabanic acid with oxiranes

Reactions of parabanic acid with ethylene oxide, propylene oxide, or glycerin epichlorohydrin were studied at the initial molar ratios of reagent ranging from 1: 1 to 1: 8. The effects of catalyst presence and temperature on the course of reaction were analyzed. The conditions were established at which the parabanic acid ring was preserved and those at which it opened to form polymeric products.

Oxidative adsorption and hydrogen-mediated desorption of parabanic acid on Pt(111) electrodes

The adsorption properties of parabanic acid (PBA) on Pt(111) electrodes are described. The process takes place with charge transfer at potentials higher than 0.175 V. The PBA adlayer is particularly stable against oxidation or CO adsorption but is desorbed upon hydrogen adsorption. Comparison between voltammetric charges and charge displacement experiments, carried out at low potentials, enables the estimation of the PBA contribution to the overall voltammetric charge. Spectroelectroelectrochemical experiments suggest that PBA adsorption takes place through one of its nitrogen atoms, after breaking of the corresponding NH bond. The kinetics of the PBA adlayer desorption takes place through an instantaneous nucleation and growth mechanism, linked to the adsorption of hydrogen atoms.

A computational and experimental search for polymorphs of parabanic acid – a salutary tale leading to the crystal structure of oxo-ureido-acetic acid methyl esterElectronic supplementary information (ESI) available: crystal structures of the 16 lattice energy minima in Table 2, in the space group setting used in the minimisation. See http://www.rsc.org/suppdata/ce/b2/b211784c/

A computational search to predict the crystal structure of parabanic acid produced the known P21/c crystal structure as the global minimum in the lattice energy. However, there are many hypothetical structures only 2–6 kJ mol−1 less stable than the known form, which are within the energy range of possible polymorphism and have reasonable mechanical properties and relative growth rates. The harmonic intermolecular frequencies and the attachment energy estimate of relative growth rates suggest that the known polymorph is thermodynamically and kinetically favoured, but the possibility of other polymorphs cannot be excluded. A simultaneous experimental search for new polymorphs found crystals with a new morphology and X-ray powder pattern when a solution of parabanic acid in methanol was left to evaporate. Eventually, the structure was shown by single crystal X-ray diffraction to be that of oxo-ureido-acetic acid methyl ester. Thus, under the conditions of recrystallisation from methanol, parabanic acid had undergone a previously unreported ring-opening reaction, and had not crystallised as a new polymorph as had seemed likely prior to single crystal characterisation. The combination of the experimental and theoretical studies indicates that new polymorphs of parabanic acid are unlikely to be found readily.

Towards a realistic model for the quantitative evaluation of intermolecular potentials and for the rationalization of organic crystal structures. Part II. Crystal energy landscapesFor Part I, see ref. 4.Electronic Supplementary Information (ESI) is available: the crystallographic coordinates of all the crystal stuctures considered and the SCDS-Pixel input and output files have been deposited. See http://www.rsc.org/suppdata/ce/b3/b311836c/

Many crystal structures were generated by a computer predictor for naphthalene, naphthoquinone, 1,2-dichlorobenzene, 2,3-dimethylbenzoic acid, parabanic acid and pyridine, and the lattice energies were then calculated by standard atom–atom potentials, by point-charge models, and by the SCDS-Pixel method. Using results from the latter approach, the relative importance of coulombic, polarization, dispersion and repulsion energies in crystals is discussed in relationship with the chemical characteristics of the constituent molecule, with crystal density, and with some key crystal structural factors like interplanar angles and some intermolecular distances believed to be indicators of crystal stabilization. In general, intermolecular interactions are better discussed when considering the electron density of large molecular moieties or of entire molecules, than when considering atom–atom distances. Significant comparisons between atom–atom energies and the more accurate Pixel energies are presented. The performance of the Pixel-SCDS method in ranking crystal energies against experimental structures, in the so-called crystal structure prediction exercise, is comparable to, and sometimes better than that of atom–atom force fields.

Parabanic polymers obtained by the cyclocondensation reaction of polyureas containing 2,6-pyridyl structure

The polymers containing 1,3-imidazolidine-2,4,5-trione rings on the macromolecular backbone are known for a few years and named poly(parabanic acid)s. The paper presents some polymers and model compounds with urea and/or parabanic structures, as a result of the cyclocondensation reaction of the urea derivatives containing 2,6-pyridyl rest, with the oxalyl chloride. The 2,6-pyridyl radical has an acid acceptor character that determines an important distinct influence on the cyclocondensation reaction. The influence of the reaction conditions (temperature, time, beside of the presence or absence of pyridine (Py)) on the progress of the cyclocondensation was studied. The advance of the reaction was followed by IR spectra. The products were characterized by the elemental analysis, 1H NMR and IR spectra, solubilities and viscosity measurements. Thermal properties were determined by thermogravimetric analyses and differential scanning calorimetry. The analytical and spectral data demonstrated that, in absence of Py, the cyclocondensation performed almost completely only in the case of the aliphatic polyureas, while, in the same conditions, the aromatic polymers were only partly transformed. By using the Py as catalyst, both aromatic and aliphatic polyureas can be transformed into parabanic polymers at above 90% transformation degree (TD). A calculation method of the TD based on the IR spectroscopy was discussed.

Kinetics and mechanism of addition of parabanic acid (imidazolidine‐2,4,5‐trione) to oxiranes

AbstractThe results of studies on the kinetics of reaction of 1 mol of parabanic acid (imidazolidine‐2,4,5‐trione) with 1 mol of ethylene oxide (oxirane) or propylene oxide (2‐methyloxirane) carried out in the presence of triethylamine catalyst in dimethylsulfoxide solution are presented. A rate equation describing the reaction is presented and the mechanism proposed. The validity of the proposed mechanism is proved by instrumental analytical methods. The effect of temperature is also presented and the thermodynamic parameters of the reaction evaluated. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 35: 73–80, 2003

ChemInform Abstract: Synthesis, Selective Aldose Reductase Inhibitory Profile and Antihyperglycaemic Potential of Certain Parabanic Acid Derivatives.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Quantitative Cascade Condensations betweeno-Phenylenediamines and 1,2-Dicarbonyl Compounds without Production of Wastes

o-Phenylenediamines 1 underwent a series of cascade condensations with 1,2-dicarbonyl compounds to afford quantitative yields (eight cases) of heterocycles in solid-state syntheses that avoided waste formation. The products were produced in pure form and did not require purifying workup. The components were ball-milled in stoichiometric ratio, or in exceptional cases they were melted together and heated in the absence of solvents (some of them giving quantitative yields). Benzils and 2-hydroxy-1,4-naphthoquinone afforded quinoxaline derivatives 3 and 5, 2-oxoglutaric acid gave a 3-oxodihydroquinoxaline 7, and oxalic acid afforded the dihydroquinoxaline-2,3-dione 9. This last condensed with 1a in the melt, to afford a mixture of bis(benzimidazolyl) 10 and fluoflavin 11. Alloxane hydrate provided a 100% yield of the 3-oxodihydroquinoxaline-2-carbonylureas 15/16 at room temperature. Parabanic acid required a melt reaction providing a 78% yield of 3-oxodihydroquinoxalinyl-2-urea 22 and side products. Despite numerous reaction steps, most of these uncatalyzed stoichiometric reactions proceeded quantitatively in the solid state to give only one product (plus water), with unsurpassed atom economy. If catalysis with HCl was tried, the results were inferior. If melt reactions were required it appeared to be advantageous to have the products crystallize directly at the reaction temperature. The synthetic results have been interpreted mechanistically and compared to some similar solution reactions that do not exhibit the benefits of the solid-state techniques. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)