Authors:J. Madarász, G. Pokol, C. Novák, H. Moselhy, and S. Gál
Residual differences after model fitting were investigated in both isothermal and non-isothermal kinetics in order to make
numerical comparisons between several models and various parameter-estimating methods. Data from two independent experimental
series were evaluated.
A large data set, collected earlier under isothermal conditions from decompositions and hydrothermal reactions of aluminium
hydroxides and oxides, was processed first. It showed that mechanical activation of the starting gibbsite affected reactivity
of samples in several subsequent reactions for all model equations tried. The relative residual deviation concept is introduced,
and statistics were applied to find a model that fits a certain reaction in most of the cases.
In the second study, the sulphate decomposition step of aluminium sulphate octadecahydrate was investigated. TG curves were
measured using a constant heating rate. Dynamic models were fitted by three mathematical methods, including a new general
purpose one. Fitting ability of the methods with various complexity were compared on the basis of residual deviations obtained
after integration of the model equations. As well as evaluating the best fit, this new parameter-estimating method provides
a statistical analysis of the reliability of the whole model fitting process.
Authors:Cs. Novák, A. Végh, S. Marokházi, G. Pokol, and L. Szente
Racemic free mandelic acid and its methyl, ethyl, isoamyl and benzyl esters were found to form inclusion complexes with all
the three studied natural cyclodextrins proved by thermoanalytical results. Differences between the solid state stability
of guests were detected mainly by evolved gas analysis. Even signs of an eventual optical resolution by molecular inclusion
were observed in several cases, but still not sufficiently proven. Due to the rather high volatility and low melting points
of the majority of guest substances DSC technique was found to be suitable for studying the cyclodextrin complexes of mandelic
Authors:D. Kozma, Klára Tomor, C. Novák, G. Pokol, and E. Fogassy
Racemic malic acid (I) was resolved by R-α-phenylethylamine(II). The S-(−)-I.R-(+)-II diastereoisomer was in excess in the precipitated salt. DSC curves and X-ray powder diffractograms proved that the diastereoisomeric salt mixture precipitated during the resolution was isomorphous with the optically pure S-(−)-I.R-(+)-II salt. The diastereoisomeric salt mixture containing the R-(−)-I.R-(+)-II salt in abundance bound crystal solvate (water or methanol) when produced by the total evaporation of the mother liquor, while the optically pure R-(−)-I.R-(+)-II salt crystallized without solvate. It is generally assumed that solid solution formation takes place when the two diastereoisomers are alike and the high similarity results in less efficient enantiomer separation.
Authors:D. Kozma, C. Novák, G. Pokol, and E. Fogassy
The products obtained in the optical resolution of the N-methylamphetamine by the Pope-Peachy method, using half equivalent R, R-tartaric acid and half equivalent hydrochloric acid in absolute ethanol were investigated by thermoanalytical methods. The DSC measurements of the precipitated salts provide sufficient information for following the progress of the resolution. In this way, the results of the resolution can be estimated with the precision of about 5% optical purity.
Authors:D. Kozma, L. Poszáváca, Mária Ács, G. Pokol, and E. Fogassy
The diastereoisomeric salt pair formed between α-phenyl-ethyl-amine and R-1-phenylethylsuccinamic acid were investigated by
physico-chemical methods. Melting and solubility phase diagrams were determined, the coincidence of the eutectic points of
the two phase diagrams were demonstrated. The large difference in physico-chemical properties of the salt pair explains the
efficient enantiomer separation.
Authors:R. Illés, Cs. Kassai, G. Pokol, E. Fogassy, and D. Kozma
The enantioselectivity of the diastereomeric supramolecular compound (SMC) formation between O,O'-dibenzoyl-(2R,3R)-tartaric
acid (DBTA) and chiral secondary alcohols was investigated. On the basis of TG measurements the DBTA:chiral alcohol molar
ratio in the SMC-s is nearly 1:1. Among the investigated complexes the most stable SMC is trans-2-iodo-cyclohexanol-DBTA. The SMC forming capability and the enantioselectivity depends on the space filling of the alcohol
side chain or ring. In the case of trans-2-halogen-cyclohexanols a relationship can be observed between the thermal stability of the SMC-s and the enantioselectivity
of SMC forming.
Authors:M. Zaharescu, A. Jitianu, A. Braileanu, J. Madarász, and G. Pokol
It is well known that SiO2 -based inorganic-organic hybrid materials present significant differences due to the organic moieties bound to the inorganic
network and to the preparation conditions.
In the present work the ageing effect on the thermal stability of the SiO2 -based inorganic-organic hybrid materials prepared using tetraethoxysilan (TEOS), triethoxymethylsilan (MTEOS), triethoxyvinylsilan
(VTEOS), tetramethoxysilan (TMOS), trimethoxymethylsilan (MTMOS) and trimethoxyvinylsilan (VTMOS) was studied.
TG/DTA-MS was used to study the decomposition process of the materials. The structural modifications of the materials during
ageing were studied using spectral methods.
The gels obtained starting with more reactive alkoxides, of methoxy-type, present more complex structures and are less stable
Authors:V. Leovac, R. Petković, A. Kovács, G. Pokol, and Katalin Szécsényi
Factors determining the complex formation reaction of copper(II), nickel(II) and cobalt(II) chloride and copper(II) bromide
with 3,5-dimethyl-1-(hydroxymethyl)-pyrazole (HL) has been studied. Depending on experimental conditions, complexes with different
composition were obtained: [CuCl2(dmp)]2 (I), [CuCl2(dmp)2]2 (II), [CoCl2(dmp)2] (III) (dmp=3,5-dimethylpyrazole), [CuBr(L)]2 (IV), [CoCl(L)(EtOH)]4 (V) and [NiCl(L)(EtOH)]4 (VI). The compounds were characterized by FTIR spectroscopy, solution conductivity and magnetic measurements. The crystal structure
of [CoCl(L)(EtOH)]4 has been determined by single crystal X-ray diffraction. The thermal decomposition of the compounds was studied and found
to be continuous for all of the compounds. The desolvation mechanism of [MCl(L)(EtOH)]4 (M=Co(II), Ni(II)) is explained on the basis of the route of complex formation of CoCl2 with HL.
Authors:J. Madarász, E. Beregi, J. Sztatisz, I. Földvári, and G. Pokol
Sintering processes in the Y2O3–Al2O3–B2 O3 system and its subsystems (Y2O3–B2O3 and Al2 O3–B2O3) have been investigated by using combined DTA and XRD measurements to get a better understanding of solid state chemical
changes resulting in the formation of yttrium aluminum borate (YAl3(BO3)4, YAB) phase and to study the possible role and contribution of various simple borates formed also in the former processes.
Two new exothermic heat effects of YBO3 formation have been detected by DTA in the Y2O3–B2O3 system between 720 and 980C. In the Al2O3–B2O3 system a new experimental XRD profile of Al4B2O9 was observed. Formation of these borates seems to promote the nucleation of double borate YAB below 1000C. Conversion of
Al4B2O9 to Al18B4 O33 was observed after a long term (10 h) sintering at 1050C. Similarly, an increased formation of YAB has been observed as
a product of the sintering reaction between YBO3 and Al18B4O33 at 1150C. The two latter single borates are found to be identical with the high temperature decomposition products of YAB.
Authors:J. Madarász, D. Kozma, G. Pokol, M. Ács, and E. Fogassy
Chiral drugs are generally resolved through formation of diastereoisomeric salts of different solubility. When the diastereoisomer
salts from a eutectic in the solid phase, a good estimate can be made for the efficiency of the resolution (S), through a calculation based on the eutectic composition (xeu). The eutectic composition can be computed from thermal data of a differential scanning calorimetric (DSC) measurement of
the diastereoisomeric salts .
In this work we investigated the influence of uncertainties of thermal data on the estimation of the efficiency of resolution
(S), spreading throughout the calculations involved. Performance of our error-estimating method is demonstrated on 6 diastereoisomer
salt pairs. The obtained deviations are close to the deviations of resolution experiments. Thus, it can be concluded that
the DSC measurements are useful means in predicting the efficiency of resolutions.