Vol. 20 No. 4 (2022)

Aim. To share our experience when working with the Pd-catalyzed hydrogenation and discuss reactions occurred contrary to our expectations, as well as express our vision of the causes for such an unusual reactivity.
Results and discussion. Catalysis is a key technology and among the central themes of both petrochemical and fine chemical industries. Although extremely useful and reliable, it can sometimes astonish researchers. The paper discusses 17 intriguing cases of the catalytic hydrogenation and hydrogenolysis reactions from our practice in the High-pressure Synthesis Laboratory (Enamine Ltd.). All examples presented are characterized by peculiar performance of commercially sourced heterogeneous palladium-containing catalysts (Pd/C or Pd(OH)₂). Thus, some cases were characterized by reduced activity of the catalyst (or even its complete loss), meaning that reaction conditions found before to be suitable for reduction appeared to be “broken”, and we had to search for a new, often harsher reaction setup. Curiously, it is a matter of classical Pd-catalyzed hydrogenations of N⁺–O^– and C=C fragments. Apparently, these results indicate the heterogeneity of commercially available catalysts and are related to their fine internal structure, in particular the surface morphology. Another interesting issue the article deals with is chemoselectivity of the catalytic hydrogenation. Sometimes some reactions led to astonishing results going across theoretical views and expectations. Saturation of benzene rings instead of (or accompanying) debenzylation, breaking of the common order of hydrogenation for compounds containing several aromatic parts with different resonance energies, irreproducible experiment, obtaining of different products under the same conditions, uncommon results of Pd-catalyzed reactions is the list of interesting results, which we observed and discussed in the article. Analyzing the information available in the literature and considering all the results gathered we tend to believe that the presence of impurities of noble metals (Rh, Ru, Pt) in the catalysts used to be a possible reason for these strange findings. The study supports the general idea that commercial palladium catalysts differ in efficiency, resulting in significant differences in selectivity, reaction time, and yields. Elucidating the regularities behind such empirical results is undoubtedly an interesting area of research in the field of catalysis.
Experimental part. All starting compounds exposed to hydrogenation were synthesized in Enamine Ltd. and had purity of not less than 95 %. The palladium-containing catalysts used in the experiment were purchased from 6 commercial sources within 2011 – 2022. The structure and purity of the compounds synthesized were characterized by ¹H NMR spectroscopy, liquid chromatography coupled with the mass spectrometry method, elemental analysis. Chromatographic experiments revealed the purity of all compounds obtained being not less than 95 %.
Conclusions. In the paper we have summarized our experience with the Pd-catalyzed hydrogenation and presented cases of unusual reactivity or unexpected outcomes of the reactions encountered in our practice. In general, complications we faced were of three types: (1) irreproducibility of the procedures most likely as the result of a changeable activity of the catalysts; (2) chemoselectivity issues when two or multireducible functional groups were present in the substrate; (3) undesirable Pd-catalyzed defunctionalization reactions. In turn, these complications led to increase in production costs, loss of time and resources. Therefore, because of this variability in the efficiency of Pd catalysts, far more efforts are required to find out the key differences between commercial sources of Pd catalysts, as well as to create protocols clearly defining the catalytic activity of each batch of the catalyst allowing to identify high-quality catalysts immediately prior to the use without wasting precious time and synthetic materials.

Aim. To summarize and analyze literature data on the polymethine dyes containing the 2,2-difluoro-1,3,2-dioxaborine ring.
Results and discussion. Boron difluoride complex of β-diketone (2,2-difluoro-1,3,2-dioxaborine, F2DB) is a unique structural motif endowing organic compounds with prominent physicochemical properties, such as a strong fluorescence and high mo-lar attenuation coefficients. Incorporation of the F2DB core into a polymethine chromophore either as an end-group or as an integral part of the polymethine chain allows obtaining dyes with exceptional characteristics, highly appealing for design of up-to-date functional materials. This review focuses on the synthesis and spectral properties of the F2DB-containing polymethines along with the latest advancement in the synthesis of highly fluorescent polyanionic polymethines. A brief discussion of the effects of the structural modification of the π-conjugated system on the photophysical properties of dyes is included.
Conclusions. The literature on the F2DB-containing polymethines demonstrates a high potential of the F2DB core for the development of strongly fluorescent and intensely absorbing dyes.

Aim. To study the component composition of free and total monosaccharides in the raw material of Cetraria islandica (L.) Ach. harvested in Ukraine.
Materials and methods. The component composition of free and total monosaccharides in the raw material was determined by gas chromatography with mass-spectrometric detection (GC-MS).
Results and discussion. Among the free monosaccharides, the presence of D-perseitol, (6.99 mg g^–1) and D-mannitol (1.12 mg g^–1) was determined. Among the total monosaccharides, the content of D-glucose (203.64 mg g^–1) prevailed. D-mannose (53.74 mg g^–1), D-galactose (51.71 mg g^–1), D-xylose (0.83 mg g^–1) and L-rhamnose (0.53 mg g^–1) were found in lower quantities, as well as polyatomic alcohols – D-dulcitol (8.46 mg g^–1) and D-mannitol (3.10 mg g^–1).
Conclusions. For the first time, the component composition of free and total monosaccharides in the raw material of C. islandica harvested in Ukraine has been determined. The results obtained will be used as a component of the comprehensive systematic study of the raw material of C. islandica harvested in Ukraine.

Aim. To highlight the results of the research conducted in 2020 – 2021 aiming at studying the  ffect of multi-depth and multifraction sowing of the  hybrid corn seeds of the DMS Sticker mid-early maturity group on the yield when grown in the conditions of the Northern Steppe of Ukraine and determine the economic efficiency of the approaches.
Materials and methods. Winter wheat was a predecessor crop in the study. Tillage methods and  related conditions are described in the article. Herbicides were used to protect against weeds. Sowing was carried out in the third decade of April at a soil temperature of +8 – 10 ºС. The experiment considered 2 factors, namely the depth of sowing seeds and the size of the seed fraction. The results obtained were processed using measurement, mathematical and statistical methods of research, as well as calculation and comparison approaches.
Results and discussion. On average, depending on the factors studied, the height of the plants varied significantly, as a rule, the tallest plants were obtained from large seeds, which had the highest mass of 1000 seeds. Thus, in particular, on average over two years of research, the height of the plants was 250.4 cm when the weight of 1000 seeds was 255 g, and the seeds were wrapped by 4 – 5 cm; when the weight of 1000 seeds was 300 g, the height was 251.1 cm, while with the weight of 350 g it was 258.3 cm; with the wrapping depth of 7 – 8 cm the height was 252.1 cm, 255.8 and 268.5 cm, and with the wrapping depth of 10 – 11 cm it was 257.6 cm, 261.8 and 266.1 cm.
Conclusions. The use of the large seed fraction provided an increase in the yield of the DMS Sticker corn hybrid by 1.09 – 1.79 t ha^-1 compared to the use of the small seed fraction and was 8.70 t ha^-1. When using the large seed fraction and the wrapping depth of 10 – 11 cm, the cost of production was 56,550 UAH ha^-1. The cost price of 1 ton of production was the lowest and amounted to UAH 2,247.1, the conditional net profit was the highest – 37,000 UAH ha^-1, and the level of profitability was 189.3 %.