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Unusual mineralized and silicified carbonate-rich geodes were found hosted in Lower Triassic red mudstones in Central Spain. From their borders to their centres, the geodes display (a) a millimetric carbonate crust, (b) a quartz rim, (c) massive dolomite, (d) gold-bearing iron-rich infills (hematite laths and goethite with up to 7000 ppm of gold) and (e) calcite cements that sometimes seal the central hollow. Textural evidence indicates that the geodes were originally anhydrite, which was subsequently replaced by quartz and dolomite. The resultant porosity from this replacement, or by later dissolution, has been filled by epithermal gold-bearing iron-oxide hydroxides, romanechite and calcite. (Beta)(super 13)C values indicate the participation of meteoric waters in an environment which was characterized by both a sub-desert climate and a temperate-tropical climate. Oxygen signatures reflect very variable temperatures for all minerals, with the exception of calcite, which appears to have precipitated at < 38 degrees C. Iron-oxide temperature values can reach up to 85 degrees C (epithermal stage). The mineralogical assemblages of these unusual geodes denote early diagenetic replacement followed by the epithermal activity. This mineralization is linked to the Late Hercynian, calc-alkaline volcanism of Central Spain (the Hiendelaencina mining district).

A study seeks to analyze the activation of either anomer of S-phenyl 2,3-di-O-benzyl-4,6-O-benzylidene-1-deoxy-1-thia-D-glucopyranoside with triflic anhydride in dichloromethane at -78 degrees Celsius in the presence of 2,6-di-tert-butyl-4-methylpyridine. The addition of alcohols results in the formation of alpha-glucosides with high selectivity attributes. Low-temperature nuclear magnetic resonance analysis reinforces the hypothesis that glucosyl triflate is created at the initial phase of the reaction.

The existence of a second intermediate in the reaction catalyzed by dethiobiotin synthetase, has been postulated in earlier studies. This second intermediate has been characterized as a mixed carbamic-phosphoric anhydride formed when carbamate is phosphorylated by ATP. Further analysis of the second intermediate showed typical reactions expected from a mixed anhydride such as hydrolysis to DAPA, CO2, and Pi under acidic conditions and cyclization to DTB and Pi under basic conditions.

Dimethyl salts produced from the reaction of triflic anhydride and dimethyl sulfide were utilized for the oxidation of unsaturated and saturated ones to carbonyl compounds. The reaction process involving the dialkyl(trifluomethanesulfonyl)sulfonium salts and aqueous sodium acetate results in the formation of corresponding soulfoxides without sulfone formation. Furthermore, the synthetic process was sensitive to steric and electronic factors.

The decomposition of tert-butylsulfenyl tert-butylsulfinyl thioanhydride is a first order reaction resulting in the formation of 1:1:1 mixture of di-tert-butyl tetrasulfide, a thioanhydride and di-tert-butyl thiosulfinate. The reaction takes place in the presence of radical inhibitor and is very much affected by heat. During the decomposition rearrangement also takes place. The stability of linear sulfenyl sulfinyl thioanydrides increases with the increase in degree of substitution.

Hydrolysis of substituted cinnamoyl-L, beta-phenyllactate esters catalyzed by carboxypeptidase A proceeds through the formation of an anhydride intermediate, which is unaffected by substituents. Absence of changes in absorption between pH values of 7.5 and 9.5 during hydrolysis of one of the 4-substituted cinnamoyl esters indicates that the intermediate is intact and discounts the mechanism that considers hydrolysis of the anhydride intermediate.

Imidazo(1,2-c)pyrimidin-3-one compounds are produced by the cyclodehydration of 5-(carboxymethy)amino-substituted pyrimidines using acid anhydrides. X-ray crystal structure studies reveal the bicyclic type A(super-1) mesoionic-like structures of the compounds. These compounds possess a combination structure of a valence tautomer and a resonance hybrid and are mesoionic. Substituted alkyl halides, under basic reaction conditions, alkylate the position N-1, where the compound has no blocking group.

Reaction of Re207 with carboxylic anhydrides (RCO)20 in tetrahydrofuran or acetonitrile solution yields two different structural types of perrhenic anhydrides. The complexes of RC(O)-O-ReO3.2L are produced by strong electron withdrawing groups. Mixed anhydrides are formed by the anhydrides of perrhenic acids which are also subjected to alkylation.

The factors that influence the conformation of anhydrides were studied. UV-VIS spectral analysis of anhydrides was done in benzene and THF and structures were determined using X-ray crytallography. Anhydrides with small substituents preferred the syn- or the anti-conformation of the carbonyl groups. Dihedral angles were found to increase while minimum energies were similar. Results showed that the gas phase structure became more twisted as a result of increased steric demands. These changes caused significant alterations in the reduction potential and UV-VIS spectra.

An economical and practical method for the synthesis of imide derivatives under mild conditions based on the utilization of inexpensive and readily available reagents. The synthetic approach involved the reaction of a anhydride with an appropriately substituted amine to form an amic acid. The corresponding amide derivative was then formed by the in situ cyclization of the intermediate amic acid in the presence of Lewis acid and hexamethyldisilazane.

A simple one-spot synthesis method facilitates the preparation of the N-acyloxazolidinone and sultam derivatives in high yields under mild conditions. It is seen that acyloxazolidinones with additional functional groups can be made in mild reaction conditions. The formation of lithium-initiated imide is discussed.

Different possible pathways of the aminolysis reaction of succinic anhydride are examined by applying high level electronic structure theory. The results have shown that the most favorable pathway of the reaction is through the bifunctional acid catalyzed stepwise mechanism and the presence of the aprotic solvent benzene has lowered all energy barriers.

The triethylammonium salt of a carboxylic acid reacts with one-sixth equivalent of triphosgene to give a symmetric anhydride for the corresponding acid. It is a one-pot reaction and is complete in minutes at ice-water temperature. The reaction is carried out under natural conditions and does not use toxic reagents. This method is applicable to both electron-rich and electron-deficient carboxylic acids.

Reply to the comment on kinetics of diels-alder reaction of maleic anhydride and isoprene in supercritical CO2 is presented. It is concluded that the apparent rate constant observed in the experiments in the multiphase region is larger than the true rate constant in the supercritical phase measured at very low mole fractions of the reactants.

A comment is presented to correct an analysis of data in the Ph.D. thesis of G.C. Alexander reported by Glebov et al. The comment is also forwarded with detailed study and observation to improve the understanding of the kinetics reaction in the model.

The conclusion that peroxyacetic nitric anhydride (PAN) and peroxyisobutyric nitric anhydride (PiBN) coelute in the chromatographic system used in the study is questionable. In addition, PiBN cannot be considered an interference in the analysis of PAN using gas electron chromatography with electron capture detection. More solid and convincing evidence should be presented to prove the coelution of PiBN and PAN.