Etherification of glycerol with tert-butyl alcohol catalysed by ion-exchange resins

The reaction of glycerol with tert-butyl alcohol in the liquid phase on acid Amberlyst-type ion-exchange resins was studied. The influence of temperature, mole ratio n(TBA)/n(G), water and swelling of gel, and macroreticular type of polymer catalysts on etherification reaction was investigated. The most favourable reaction temperature is 75°C. The conversion of glycerol and yield of glycerol tert-butyl ethers has increased with the mole ratio n(TBA)/n(G). Dry form of macroreticular catalysts provided the best results. Etherification reaction of glycerol with isobutylene in non-aqueous conditions gives the highest yield of desired ethers. The influence of water was studied. The gel forms of ion-exchange resins have very low catalytic activity. It can be concluded that water has an inhibition effect on ion-exchange resins. By comparing the gel and macroreticular forms of Amberlyst ion-exchange resins it can be concluded that very acid forms of macroreticular ion-exchange resins with a high degree of crosslinking are more active catalysts for the studied reaction due to their pores which are sufficiently large so that the voluminous tert-butyl ethers of glycerol can be formed. It was estimated that tert-butyl alcohol as tert-butylation agent is not suitable for etherification of glycerol with the formation of di-and triethers.     

Real-time monitoring of the UV-induced formation of quantum dots on a milliliter,microliter, and nanoliter scale

Microchimica Acta - The authors report on a systematic study on the low-cost, low-temperature, and fast synthesis of water soluble quantum dots (QDs) stabilized by mercaptosuccinic acid by UV...     

Structural and Spectroscopic Properties of Benzoylpyridine-Based Hydrazones

Photochromic hydrazones are attracting the attention in the field of photochromic systems especially due to their P-type character. To understand the structural features and their correlation with the spectroscopic data, UV-Vis, vibrational and ellipsometry spectroscopic techniques are employed with the support of density functional theory (DFT) calculations to three hydrazone derivatives based on benzoylpyridine. Interestingly, analysis of the structure shows the presence of two distinct rotamers around the pyridine ring with different energy and the well-defined conjugation path that changes due to E to Z isomerization especially in the hydrazone −C=N−NH part of the skeleton. IR and Raman spectra are analyzed, showing a higher selectivity in the Z form; moreover, the comparison with the normal modes proves the effect of the reaction on the backbone structure. The experimental results are in good agreement with the theoretical predictions, especially in the case of the Raman spectrum. The molecular polarization also changes from E to Z forms as predicted by DFT calculations. Spectroscopic ellipsometry on thin films of TOPAS doped with 10 %wt of the dimethylamino hydrazone derivative is used to prove such change at the molecular level. A modulation of the refractive index is observed, and it is correlated with the concentration of the active moiety and the calculated electronic polarizabilities.     

Fuels obtained by thermal cracking of individual and mixed polymers

Utilization of oils/waxes obtained from thermal cracking of individual LDPE (low density polyethylene), HDPE (high density polyethylene), LLDPE (linear low density polyethylene), PP (polypropylene), or cracking of mixed polymers PP/LDPE (1: 1 mass ratio), HDPE/LDPE/PP (1: 1: 1 mass ratio), HDPE/LDPE/LLDPE/PP (1: 1: 1: 1 mass ratio) for the production of automotive gasolines and diesel fuels is overviewed. Thermal cracking was carried out in a batch reactor at 450°C in the presence of nitrogen. The principal process products, gaseous and liquid hydrocarbon fractions, are similar to the refinery cracking products. Liquid cracking products are unstable due to the olefins content and their chemical composition and their properties strongly depend on the feed composition. Naphtha and diesel fractions were hydrogenated over a Pd/C catalyst. Bromine numbers of hydrogenated fractions decreased to values from 0.02 g to 6.9 g of Br₂ per 100 g of the sample. Research octane numbers (RON) before the hydrogenation of naphtha fractions were in the range from 80.5 to 93.4. After the hydrogenation of naphtha fractions, RON decreased to values from 61.0 to 93.6. Diesel indexes (DI) for diesel fractions were in the range from 73.7 to 75.6. After the hydrogenation of diesel fractions, DI increased up to 104.9.     

Bestimmung eines Gemisches aus prim?rem und sekund?rem 4-Brom-benzylamin durch Spektroskopie im nahen IR

Zusammenfassung Eine Methode zur Bestimmung des Gemischs von prim. und sek. 4-Brom-benzylamin in Benzol durch Spektroskopie im nahen IR wird vorgeschlagen. Für die Bestimmung des prim. 4-Brom-benzylamins wurde das kombinierte Absorptionsband bei =2022,3 nm und für die sek. Verbindung die Absorption bei 1529,3 nm nach Korrektur für das prim. Amin benutzt. Modellgemische wurden mit einer durchschnittlichen Abweichung für das prim. Amin von – 2,45% und für das sek. Amin von + 1,08% analysiert.

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Determination of a mixture of primary and secondary 4-bromobenzylamine by spectroscopy in near infra-red

For the determination of prim. and sec. 4-bromobenzylamine in mixture the absorption maximum was used of the combined band at =2022,3 nm and that of the first overtone of the NH-stretching of the absorption band for the prim. and sec. amine at =1529,3 nm. From the absorption at =2022,3 nm the amount of the prim. amine and from the absorption at =1529,3 nm, after correction for the prim. compound, the concentration for the sec. amine was determined. All measurements were carried out in benzene. The method was developed with the aim to determine 4-bromobenzylamine in the hydrogenation mixture after hydrogenation of 4-bromobenzonitrile. In the analysis of model mixtures the mean error of the determination was – 2.45% for the prim. and + 1.08% for the sec. amine.

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Für die technische Zusammenarbeit danken wir Frau Jaroslava Krídlova.     

Aggregation behavior of novel hyaluronan derivatives—a fluorescence probe study

Aggregation properties of hydrophobized hyaluronan with different molecular weights and degrees of substitution were studied using pyrene and perylene as fluorescence probes. Both probes in contrast to native biopolymer confirmed aggregation of modified hyaluronan. The critical aggregation concentration (cac) was determined by the pyrene I₁/I₃ and perylene fluorescence intensity method. The cac value varied both with the molecular weight and the degree of substitution and was between 0.610 and 0.003 g·L^?1. Pyrene polarity scale confirmed formation of hydrophobic domains.