Dehydration Products Research Articles

Efficient conversion of cellulose to lactic acid over yttrium modified siliceous Beta zeolites

The selective one-pot synthesis of lactic acid (LA) from cellulose, and further the raw biomass, on heterogeneous catalysts is the key point for the development of biorefinery technology. Herein, we reported an yttrium (Y) modified siliceous Beta zeolites catalyst via two-step post-synthesis for highly efficient conversion of cellulose to LA. Under condition of 220 °C and 2 MPa N2, the cellulose could be transformed to LA with a yield of 49.2 % within 30 min, and the substrate can be extended to various raw biomass. It was demonstrated that the dealumination and modification of Y can efficiently modulate the acidity on the surface of zeolite. The dehydration products HMF and other derivatives were suppressed, and the yield of LA was correlated in line with the acid amount, which were attributed to the increased Lewis acidity originated by Y incorporation. These results contribute to the development of the green and efficient synthesis of bio-chemicals.

Carbamoyl Functionalized Bent para-Phenylenes via an Unexpected Reaction of the Burgess Reagent with α-Ketols.

The attempted dehydration of macrocyclic α-ketols with the Burgess reagent has resulted in the unexpected synthesis of carbamoylated, bent para-phenylene units. The same reaction with an acyclic analogue affords the intended dehydration product, indicating that the change in reactivity is conformationally controlled and a result of the bifunctional nature of the Burgess reagent.

High-pressure vibrational spectra of humite-group minerals: Fluorine effect on thermodynamic properties and hydrogen bonds

The humite-group minerals could be potential water carriers as the dehydration products of serpentine in subduction slabs. Fluorine is an important element incorporated into the crystal structures through the substitution mechanism of OH− = F−, and has significant impacts on the thermodynamic properties. We conducted in situ high-pressure Raman and Fourier transform infrared (FTIR) measurements on natural F-bearing clinohumite, humite and norbergite samples, up to approximately 19GPa. The isothermal mode Grüneisen and intrinsic anharmonic parameters were calculated for both the lattice and OH-stretching modes, and the anharmonic contribution to the heat capacities was further evaluated for these hydrous phases. As compared with the OH-clinohumite sample, the anharmonic contribution is larger in magnitude for the F-bearing clinohumite, while such anharmonic contributions are even more significant in the humite and norbergite samples with higher fluorine concentrations. Both the Raman and FTIR spectra indicate that the OH-stretching modes above 3450 cm−1, which are controlled by the neighboring HH, systematically show positive pressure dependences. On the other hand, the OH bands below 3450 cm−1 shift to lower frequencies at elevated pressure, due to F− or Ti4+ substitutions. The F− substitution of OH− group could alleviate local HH repulsion effect, and create new H sites with shorter hydrogen bond lengths. These hydrogen bond would get shorter (negative pressure dependences), and are likely to participate in the hydrogen bond symmetrization at high pressure.

Statistical approaches in the analysis of in situ thermo‐Raman spectroscopic data for gypsum as a basis for studying dehydration and phase transformations in crystalline hydrates

AbstractThe study of a gypsum single crystal was carried out using in situ thermo‐Raman spectroscopy in the temperature range of 80–870 K. The conventional peak fitting approach was used to qualitatively determine the temperature ranges of gypsum dehydration and phase transitions. The dependence of the intermediate products of gypsum dehydration on the measurement conditions and the state of sample was confirmed. A detailed analysis of the temperature behavior of ν1(SO4) in a single crystal indicated the coexistence of CaSO4·2H2O + γCaSO4 (380–440 K) and γ‐CaSO4 + β‐CaSO4 (680–740 K) phases, which was explained by the reaction front movement in a solid. For the first time, an approach based on statistical algorithms was applied for processing datasets of experimental temperature‐dependent spectra of crystalline hydrates, including the calculation of the Pearson's r coefficient, skewness, ∆corr parameter, based on the autocorrelation function. The use of statistical methods for individual spectral regions made it possible to reveal the temperature differences in the pretransition regions for individual modes or their groups. In particular, the region of ν2(SO4) symmetric bending vibrations of sulfate ions was found sensitive to dehydration and accompanying phase transition at 410 K, beginning at lower temperatures (380 K) as compared with other regions, which is associated with the lack of the hydrogen bond influence on sulfate ions after the loss of water. Thus, statistical approaches are a source of additional information to clarify the quantitative indicators of the observed effects. The use of statistics is promising in the study of multistage processes of dehydration and phase transformations in crystalline hydrates in cases where peak fitting is inconvenient.

Spinifex‐like textured metaperidotites from the Higo Metamorphic Rocks, Japan, a possible high‐pressure dehydration product of antigorite serpentinite

AbstractSpinifex‐like textured metaperidotites from the Higo Metamorphic Rocks (HMR), west‐central Kyushu, Japan, may be formed by high‐pressure dehydration of antigorite, and may indicate deep subduction of serpentinite reaching a pressure–temperature condition of 1.6 GPa and 740–750 °C. Three rock types have been identified based on mineral assemblage and rock texture: Type I (L) consisting of medium‐grained (1–5 cm long) olivine + enstatite + chromite ±tremolite with secondary talc and anthophyllite that occurs in low‐grade metamorphic rocks of the biotite zone, Type I (H) of coarse‐grained (up to 10 cm long) olivine + enstatite (with clinoenstatite lamella) + chromite ±tremolite with secondary talc that occurs in high‐grade metamorphic rocks of the garnet‐cordierite zone, and Type II composed of Al‐spinel + chlorite + olivine + apatite + ilmenite with minor sodic gedrite in the garnet‐cordierite zone together with Type I (H). Olivines in all rock types are mostly serpentinized during exhumation. The chromite‐olivine thermometer gives 560–690 °C for Type I (L) rocks, and the spinel‐olivine thermometer gives 610–740 °C for Type II rocks. The peak metamorphic pressure will be higher than 1.6 GPa based on the location of the experimentally determined invariant point (P = 1.6 GPa and T = 670 °C) of antigorite + forsterite + enstatite + talc + H2O. This estimate is consistent with the occurrence of chlorite in Type II rocks, which is stable up to 890 °C at 2.0 GPa. The spinifex‐like textured metaperidotites occur as small bodies in the low P/T type gneisses, implying tectonic juxtaposition of them probably during exhumation of the HMR. Recent findings of medium pressure (0.9–1.2 GPa) granulites and gneisses from the HMR may indicate that the HMR has a deep root into the wedge mantle from which the spinifex‐like textured metaperidotites have derived.

Effect of the cerium modification on acid–base properties of Mg–Al hydrotalcite-derived oxide system and catalytic performance in ethanol conversion

The prospects of using cerium as a modifying additive of Mg–Al hydrotalcite-derived oxide system have been estimated by low-temperature nitrogen ad(de)sorption, X-ray diffraction, scanning electron microscopy, 1H and 27Al solid-state nuclear magnetic resonance (NMR), X-ray photoelectron and UV–Vis diffuse reflectance spectroscopy techniques. The effect of such tuning of structural-textural characteristics and acid–base properties of the surface on its catalytic performance in ethanol conversion has been studied. Solid-state NMR spectroscopic study of the probe molecule adsorption and temperature-programmed desorption of NH3 and CO2 with mass-spectrometry control are used to determine the nature and strength distribution of acidic and basic sites of Mg–Al(–Ce) oxide systems. It has been found that the selectivity towards 1-butanol up to 68.1% (548 K) is achieved in ethanol conversion over Mg–Al–Ce sample at time-on-stream ≤ 2 h. At higher time-on-stream, the specific rates of the target product (1-butanol) formation are comparable for both modified and un-modified catalysts, but the products distribution differs. Cerium modification of Mg–Al oxide catalyst leads to increase in specific rate of acetaldehyde formation due to increase in the number of basic sites and their surface density. Wherein, the rate of ethanol dehydration products (ethylene and diethyl ether) is reduced, apparently, due to decrease in a number of Lewis acidic sites formed by Al3+ cations octahedrally coordinated to oxygen.

Synthesis and properties of template-free mesoporous alumina and its application in gas phase dehydration of glycerol

Mesoporous alumina was prepared by varying the crystallization time and acid concentration and evaluated in the glycerol dehydration. The samples were characterized by X-ray diffractometry (XRD), specific surface area (SBET), NH3-Temperature-programmed desorption (NH3-TPD), and Temperature-programmed Oxidation (TPO). The gas phase dehydration of glycerol was performed in a fixed-bed quartz tubular reactor at 500 °C using a 10% glycerol aqueous solution. The specific surface area, the crystallinity and the acidic properties of the samples were dependent on both the crystallization time and the acid concentration. The catalytic properties are related to the specific surface area and acidic characteristics. Samples with higher crystallization time showed lower surface area and lower amount of acid sites. Samples with the highest acid concentration solution had the higher surface area. Conversions of glycerol above 92% were obtained for all samples. The selectivity for dehydration products was strongly related to the amount and strength of acid sites.

The influence of H/D kinetic isotope effect on radiation-induced transformations of hydroxyl-containing compounds in aqueous solutions

Vicinal diols and its derivatives can be exploited as model compounds for the investigation of radiation-induced free-radical transformations of hydroxyl-containing biomolecules such as carbohydrates, phospholipids, ribonucleotides, amino acids, and peptides. In this paper, for the first time, the prospects of isotope reinforcement approach in inhibiting free-radical transformations of hydroxyl-containing compounds in aqueous solutions are investigated on the example of radiolysis of 1,2-propanediol and 1,2-propanediol-2-d1 aqueous solutions. At an absorbed dose rate of 0.110 ± 0.003 Gy·s−1 a profound kinetic isotope effect (KIE) is observed for the non-branched chain formation of acetone, which is a final dehydration product of predominant carbon-centred radicals CH3·C(OH)CH2OH. In 0.1 and 1 M deaerated solutions at pH 7.00 ± 0.01, the values of KIE are 8.9 ± 1.7 and 15.3 ± 3.1, respectively. A rationale for the fact that a strong KIE takes place only in the case of chain processes, which may occur during free-radical transformations of vicinal diols, is also provided herein based on the results of 2-propanol and 2-propanol-2-d1 indirect radiolysis. Lastly, the lack of KIE is shown in the case of 2-butanone formation from 2,3-butanediol or 2,3-butanediol-2,3-d2. This indicates that the type (primary, secondary) of the β-carbonyl radicals formed as a result of CH3·C(OH)CH(OH)R (R = H, CH3) dehydration determines the manifestation of the effect.

Influence of water re-curing on microstructure of heat-damaged cement mortar characterized by low-field NMR and MIP

Water re-curing has been recognized as a potential method to recover the mechanical strength and durability of heat-damaged cement-based materials, which benefits from the improvement of its microstructure due to the rehydration and carbonation of dehydration products. In this contribution, the influence of water re-curing on the microstructure of heat-damaged cement mortar was evaluated by combining Mercury Intrusion Porosimetry (MIP) with low-field Nuclear Magnetic Resonance (LF-NMR). The heat-damaged cement mortar specimens were prepared through exposing to a series of ascending temperatures (105 °C, 200 °C, 400 °C, 600 °C, 800 °C). First, the influence of water re-curing on the porosity and pore size of the heat-damaged cement mortar was analysed with the results of MIP tests. Then, the microstructural evolution of the heat-damaged cement mortar was monitored by means of LF-NMR in the process of water re-curing. At last, a conversion of T2 spectra into pore size distribution (PSD) curves was performed. Causes for the difference in the PSD curves determined by LF-NMR and MIP were discussed. Results demonstrated that LF-NMR was a powerful tool to follow the microstructural evolution of heat-damaged mortar specimens during water re-curing. When combined with MIP tests, the LF-NMR technique can provide quantitative information with respect to the evolution of PSD in a nondestructive way. Capillary pores can be segmented into smaller pores due to the filling of products generated by the rehydration of dehydrated products. The microdamage was partially healed after 10.5 days of water re-curing. The original exposure temperature has a noteworthy impact on the recovery rate and level of the heat-damaged mortar during water re-curing.

Effect of the synthesis conditions of Ce0.9Gd0.1O1.95 powder on its morphology and characteristics of the oxygen ion-conducting ceramics obtained by spark plasma sintering

In this work, Ce0.9Gd0.1O1.95(10GDC) powders were synthesized by thermal decomposition of oxalate precursor crystals Ce1.8Gd0.2(C2O4)3·10H2O having a plate shape. The morphology of the oxide was found to be strongly influenced by the dehydration conditions of the precursor crystals. Dehydration in air at 125 °C led to the formation of the product in a pseudomorph form, retaining the shape of the precursor crystals and showing only slight dimensional changes. The formation of a pseudomorph was accompanied by a loss of crystallinity. When dehydration occurred at an increased water vapor pressure at the same temperature, a crystalline product formed having a significantly altered morphology. Unlike dehydration in air, after which the crystals retained their shape, an intensive shattering of the crystals occurred upon dehydration at an increased water vapor pressure. Structural transformations during dehydration were shown to determine the product morphology. The 10GDC powders with different textural characteristics were obtained by oxidative thermolysis (at 300 °C) of dehydration products. The oxide powders were sintered by spark plasma sintering at a temperature of 1100 °C and a pressure of 40 MPa. The microstructure, relative densities, and conductivities of the ceramic samples obtained from powders of two different morphologies were compared. The sintered ceramic samples had comparable grain size (<1 μm); however, the material obtained from the crystalline product of dehydration showed a higher relative density. The ionic conductivity of the ceramic material obtained using the crystalline product of dehydration was almost one order of magnitude higher than that of the sintered material obtained from the poorly crystallized product of dehydration.

Synthesis and Analgesic Activity of N,6-Diaryl-4-hydroxy-4-methyl-2-oxocyclohexane-1-carboxamides and Their Dehydration Products

A series of new N,6-diaryl-4-hydroxy-4-methyl-2-oxocyclohexane-1-carboxamides was obtained through the reaction of N-arylamides of acetoacetic acid with benzalacetone and 4-chlorobenzalacetone under basic conditions (KOH) in methanol at room temperature. Increasing of the amount of potassium hydroxide used in the reaction led to the formation of dehydration products, namely N,6-diaryl-4-methyl-2-oxocyclohex-3-ene-1-carboxamides. The latter were also formed by using unsubstituted acetoacetamide and N-methylacetoacetamide. The synthesized compounds were tested for analgesic activity.

Improvement of Fire Resistance of Polymeric Materials at their Filling with Aluminosilicates

Effect of content of synthetic aluminosilicates in medium-density polyethylene on the fire hazard characteristics and mechanical properties of compositions is investigated. It has been shown that during decomposition of the filler with the release of water, its effectiveness depends not only on the endothermic effect of decomposition and the content of dehydration products, but also on the correspondence of temperature of the dehydration of the filler and the temperature of intensive decomposition of the polymer. Regardless of the type of fillers, an increase in their content in polymer composite material helps to reduce combustibility. It has been shown that compositions based on epoxy oligomers or medium-density polyethylene and synthetic zeolite have properties of self-extinguish and fairly high physical and mechanical characteristics. It is shown that epoxy polymer composite material with the content of inorganic fillers 40-70 wt.% can be used for sealing building structures and other products operating at elevated temperatures, as well as in a mode where the fire resistance and heat resistance of the sealing compound are decisive. A number of efficiency of flame-suppressing of fillers is presented. Formulations of compositions based on epoxy oligomers or medium-density polyethylene whith synthetic zeolite having an optimal ratio of fire hazard and mechanical properties and not having toxic or carcinogenic effects when heated are recommended.

Heterogeneous Catalytic Conversion of Sugars Into 2,5-Furandicarboxylic Acid.

Achieving the goal of living in a sustainable and greener society, will need the chemical industry to move away from petroleum-based refineries to bio-refineries. This aim can be achieved by using biomass as the feedstock to produce platform chemicals. A platform chemical, 2,5-furandicarboxylic acid (FDCA) has gained much attention in recent years because of its chemical attributes as it can be used to produce green polymers such polyethylene 2,5-furandicarboxylate (PEF) that is an alternative to polyethylene terephthalate (PET) produced from fossil fuel. Typically, 5-(hydroxymethyl)furfural (HMF), an intermediate product of the acid dehydration of sugars, can be used as a precursor for the production of FDCA, and this transformation reaction has been extensively studied using both homogeneous and heterogeneous catalysts in different reaction media such as basic, neutral, and acidic media. In addition to the use of catalysts, conversion of HMF to FDCA occurs in the presence of oxidants such as air, O2, H2O2, and t-BuOOH. Among them, O2 has been the preferred oxidant due to its low cost and availability. However, due to the low stability of HMF and high processing cost to convert HMF to FDCA, researchers are studying the direct conversion of carbohydrates and biomass using both a single- and multi-phase approach for FDCA production. As there are issues arising from FDCA purification, much attention is now being paid to produce FDCA derivatives such as 2, 5-furandicarboxylic acid dimethyl ester (FDCDM) to circumvent these problems. Despite these technical barriers, what is pivotal to achieve in a cost-effective manner high yields of FDCA and derivatives, is the design of highly efficient, stable, and selective multi-functional catalysts. In this review, we summarize in detail the advances in the reaction chemistry, catalysts, and operating conditions for FDCA production from sugars and carbohydrates.

Conformational Change Initiates Dehydration in Fluconazole Monohydrate

Experimental and computational techniques have been used in combination to monitor the dehydration process of fluconazole monohydrate (MH), thus unveiling the dehydration mechanism at the molecular level. Experimentally, dehydration was observed to start at around 55 °C and be complete around 100 °C, with the metastable Pbca, Z′ = 1 polymorph (AH-C) as the sole product of dehydration (as determined by in situ hot-stage PXRD). Conformational and structural changes were identified as key in the initiation and progression of the dehydration process. Thermal expansion is most significant along the c axis, with molecular dynamics (MD) simulations and experimental observations identifying that water migrates through the MH crystal lattice within the plane perpendicular to that direction. Water was found to migrate within the (001) plane along both the a and b axis directions. The MD simulations revealed that water was not able to migrate within the lattice at room temperature. Migration at 70 °C (343 K) was plausible, but only after the hydroxyl group underwent a conformational change. The conformational change, around the hydroxyl group, is key to both the weakening of the fluconazole–water hydrogen bonding, found in the MH structure, and the promotion of the fluconazole–fluconazole hydrogen bonding, required for the formation of polymorph AH-C.

Wettability of welded wood-joints investigated by the Wilhelmy method: part 2. Effect of wollastonite additive

AbstractThe effect of wollastonite on the wetting properties of welded Scots pine-joints was studied using the multicycle Wilhelmy plate method and by observation of the chemical composition of the welded joints. Welding pine with wollastonite for 5 s resulted in a decrease in the water uptake and the swelling, and an increase in the contact angle of the welded joint compared to welded wood without wollastonite. High-performance liquid chromatography and gas chromatography/mass spectrometry showed the presence of dehydration products such as furfural, 5-hydroxymethylfurfural, and levoglucosan in methanol extracts from welded joints of specimens welded with and without wollastonite. Phenols were also found by analysis using the Folin-Ciocalteu method and High-performance liquid chromatography. The importance of such compounds in relation to the wetting properties of the welded joint is discussed.

Comparison of structural, spectroscopic, theoretical and thermal properties of metal complexes (Zn(II), Mn(II), Cu(II), Ni(II) and Co(II)) of pyridazine-3-carboxylic acid and pyridazine-4-carboxylic acids

In our present work, we studied complexes of 3d-transition metals with pyridazine-3-carboxylic and pyridazine-4-carboxylic acids. The synthesis of manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II) complexes with pyridazinecarboxylic acids was performed. The effect of selected 3d-transition metal ions on the electronic system of ligands and the thermal properties of the complexes by the use of TG-FTIR were studied. The products of dehydration and decomposition processes of studied compounds were determined from the TG (thermogravimetric) and DSC (differential scanning calorimetry) curves. The crystal structures of manganese(II) pyridazine-3-carboxylate acid and pyridazine-4-carboxylate were analysed by the use of single-crystal X-ray analysis. The geometries, NBO atomic charges, energy of HOMO and LUMO orbitals were calculated in the B3LYP/6-311++G(d,p) level. The aromaticity of ligands and complexes were discussed on the basis of HOMA and Bird’s indices. The influence of the type of metal ion coordination and the location of the carboxylate anion in the pyridazine ring on the aromaticity of complexes were discussed. The comparison of the effect of metal ions on the electronic charge distribution and aromaticity of pyridazynecarboxylic and pyridinecarboxylic acids (i.e. nicotinic and picolinic acids) was done.

Effect of La promotion on Ni/Mg-Al hydrotalcite derived catalysts for glycerol steam reforming

Abstract The influence of lanthanum promotion on the physico-chemical properties and catalytic activity of Ni/Mg-Al catalysts in the glycerol steam reforming (GSR) reaction was studied. An Mg-Al and different Mg-Al-La supports with various molar ratios were synthesized using a co-precipitation technique. The calcined supports were then impregnated with 5 wt% Ni. After calcination at 600 °C, physico-chemical properties of the Ni-based catalysts were investigated by XRD, BET, H2-TPR, and CO2-TPD techniques. H2-TPR analyses showed that the quantity of lanthanum in the support composition influenced the reducibility of Ni species as well as their dispersion. CO2-TPD analyses showed that lanthanum addition improved catalyst basicity. The activity of all catalysts in the GSR reaction was tested (T = 400−700 °C, water/glycerol feed ratio 9:1, flow rate of 0.025 mL/min). The composition of the Ni/MAL0.4 (Ni/Mg6Al1.6La0.4; subscripted numbers indicate the molar ratio of each metal) catalyst provided a good metal-support interaction and Ni dispersion which translated to an overall superior performance in terms of hydrogen yields, glycerol conversion to gaseous products, and total glycerol conversions. TG-DSC analyses of the spent catalysts showed that the lanthanum quantity also influenced the quantity of coke deposition. The formation of encapsulating coke over all catalysts was linked to high concentrations of dehydration products observed in liquid product analysis. A stability test conducted at 600 °C for Ni/MAL0.4 revealed its deactivation due to encapsulating coke formation which resulted in active metal site blockage. With a reduced flow rate (0.008 mL/min), a different coke formation mechanism allowed the catalyst to last for 24 h.

Direct formation of LaFeO3/MCM−41 nanocomposite catalysts and their catalytic reactivity for conversion of isopropanol

Direct formation of 3–30% (w/w) LaFeO3/MCM−41, nanocomposite catalysts were performed by a sol−gel process, followed by calcination at 550 and 750 °C. The nanocomposites were characterized through different techniques including LAXRD, WAXRD, EDX, simultaneous TG−DTA, ATR−FTIR, nitrogen adsorption/desorption, and TEM. The nanocomposites featured high surface areas (up to 1000 m2/g) and enhanced thermal stability. The direct formation method led to nanodispersion and size confinement of LaFeO3 in MCM−41 mesopores. The nanocomposites showed very high catalytic activity for isopropanol conversion, whereas their parent materials (blank MCM-41 or bulk LaFeO3) were totally inactive under the same reaction conditions. Thus, nanocomposite catalysts with low loading ratios and low calcination temperature produced pure dehydration product (propene) with very high conversion and total selectivity. Nanocomposite catalysts with high loading ratios and high calcination temperature produced an appreciable amount of the dehydrogenation product (acetone) as well as the dehydration products. Moreover, high loading ratios at high reaction temperatures in air atmosphere led to the formation of oxidation products. The different reactivities of the nanocomposite catalysts were discussed and correlated to their nanostructure, in terms of enhancing of the mesoporous textures with surface acidity, oxidation ability and thermal stability.

Drying characteristics and optimization of ultrasound‐strengthened cold air drying combined with sequential far‐infrared radiation drying on potato

To improve the dehydration rate and product quality of potatoes, a new strategy utilizing ultrasound-strengthened cold air drying combined with sequential far-infrared radiation drying (UCAD-FIRD) was proposed. The results prove that UCAD greatly promotes dehydration speed, and stronger ultrasound power results in higher drying rate. Compared with UCAD process, UCAD-FIRD drastically shortens the required drying time. Potato slices dried by UCAD-FIRD retain more nutrients compared with those dried by UCAD alone, exhibited by lower color variations and a greater rehydration ratio. For example, total phenol content and Vitamin C content rise first and then, decline but still remain at a high level. The Gray Correlation Analysis is applied to obtain the best experimental group as follows: cold air temperature of 15°C, radiation temperature of 140°C, ultrasound power of 60 W. Therefore, the drying strategy of UCAD-FIRD can remarkably accelerate the drying rate and simultaneously improve the product quality. Practical applications Cold air drying (CAD) can well preserve the product quality due to low drying temperature. However, too long dehydration inevitably restricts its application, so some effective auxiliary measures can be applied to promote mass transfer in CAD to improve the dehydration process. In this study, we proposed a UCAD-FIRD drying strategy, in which contact ultrasound strengthening technology was applied in CAD to significantly accelerate the internal mass transfer of early drying process, subsequently, FIRD was applied to replace UCAD at a certain conversion point to further accelerate water removal in latter stage with lower moisture content. The UCAD-FIRD strategy could achieve both shorter dehydration time and better product quality, comparing with single CAD and UCAD. Therefore, UCAD-FIRD is a promising and practical drying strategy for fruits and vegetables which have great internal mass transfer resistance and thermo-sensitivity.

Analytical Control of Impurities and Active Ingredients in a (–)-Isopulegol Derivative with Highly Potent Analgesic Activity

An HPLC-UV procedure is proposed for identifying processing impurities and determining the contents of active ingredient in the drug substance of the promising non-narcotic analgesic (2R,4R,4aR,7R,8aR)- 4,7-dimethyl-2-(thiophen-2-yl)octahydro-2H-chromen-4-ol (1). Processing impurities including the starting reagents thiophene-2-carbaldehyde and (–)-isopulegol, a related stereoisomer of 1, and intermediates and dehydration products of 1 could be present as a result of the synthesis and isolation. The developed chromatography conditions could separate possible impurities and analyte 1 with the required resolution. The contents of the studied processing impurities were below the established detection limits of 0.056 μg/mL for thiophene-2-carbaldehyde; 0.32, (–)-isopulegol; 0.22, the stereoisomer; and 0.18, 0.22, and 0.37, for the dehydration products. The working range of concentrations for the procedure was 0.50 – 10 μg/mL. The recovery varied from 98.9 to 101.2% in the accuracy evaluation. The procedure was demonstrated to have sufficient accuracy. The average relative standard deviation in the intraday precision evaluation was 0.7%; in the interday precision assessment, 0.8%, which were below the acceptance criteria of 2.0 and 3.0%, respectively.