松香中枞酸型树脂酸的MNDO研究

应用半经验MNDO量子化学计算方法确定了松香中4种枞酸型树脂酸的优化几何构型及相对能量，据此对该类树脂酸分子的构象及相对稳定性作了分析与预测，并与已知的实验结果作了对比。     

Novel skeletal rearrangements of a diterpene derived from deltaline

Treatment of imines 5 and 7, both prepared from the C₁₉-diterpenoid alkaloid deltaline (1), with NaNO₂–HCl resulted in the formation of diterpene 6 with an eight-membered ring through a sequence of denitrogenation and enlargement of ring B. In addition, two unusual skeletal rearrangements of diterpene 6 were also observed, leading to two structurally novel products 8 and 10. The structures of compounds 8 and 10 were confirmed by their X-ray crystallographic analyses and 2D NMR data.     

Distribution coefficients for twelve elements in oxalic acid medium on a strong anion-exchange resin

The distribution coefficients were determined for twelve elements, namely As(III), Ce(III), Cr(III), Co(II), Cu(II), In(III), Lu(III), Mn(II), Hg(II), Mo(VI), Sc(III) and Zn(II), on a strong base anion exchanger in pure oxalic acid solutions. The K_D curves are given. A scheme was developed for the chromatographic separation of five elements, namely As(III), Mn(II), Co(II), Zn(II) and Cu(II). Ce(III) can be separated from Lu(III).     

On the electrochemical behaviour of pyruvic and lactic acids at a platinized platinum electrode in acid medium

The electrochemical oxidation of pyruvic and lactic acids at a platinized platinum electrode has been studied in acidic (M H₂SO₄) medium. The oxidation process takes place at potentials more positive than 900–1000 mV (on RHE scale). The final products are acetic acid and CO₂. Unambiguous polarization measurements could be carried out only in the case of preoxidized surfaces. For the interpretation of the phenomena observed, a mechanism involving reactions of organic species with electrochemically formed OH radicals is proposed.Studying the reduction of pyruvic acid, it has been stated that, similar to the behaviour of simple aliphatic ketones, the conversion of the

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group into -CH₂- occurs to a significant extent.     

Electrochemical reduction of isonicotinic amide in a strong acid medium

Isonicotinic amide was studied by dc and DP polarography and linear sweep cyclic voltammetry in a strong acid medium (pH < 3). Tafel slopes and reaction orders were obtained at potentials corresponding to the foot of the polarographic wave.In a very strong acidic medium the process occurs through the formation of a protonated gem-hydroxylamine which is transformed into the aldehyde via a substitution by water, which is the rate-determining step. For 0 < pH < 3, the gem-hydroxylamine formed after two reversible electron transfers can eliminate an ammonia molecule in two ways: (a) proton-catalysed substitution by water followed by the formation of a hydrated aldehyde; and (b) non-catalysed elimination to form the free aldehyde. The limiting current of the wave is partially controlled by these concurrent chemical reactions and. consequently, the process appears as ECE.     

Uptake of actinides by sulphonated phosphinic acid resin from acid medium

The removal of uranium and americium from nitric acid solutions by sulphonated phosphinic acid resin has been investigated. The capacity of the sulphonated resin exceeds the capacities of phosphinic acid resin and commercial cation exchange resin. Other advantages of the sulphonated resin for uranium and americium removal include reduced sensitivity to acidity and inert salt concentration.     

Hydroxamic acids as weak base indicators: protonation in strong acid media.

The protonation equilibria of N-phenylbenzohydroxamic, benzohydroxamic, salicylhydroxamic, and N-p-tolylcinnamohydroxamic acids have been studied at 25 degrees C in concentrated sulfuric, hydrochloric, and perchloric acid media; the UV-vis spectral measurements were analyzed using the Hammett equation and the Bunnett-Olsen and excess acidity methods. The medium effects observed in the UV spectral curves were corrected with the Cox-Yates and vector analysis methods. The H(A) acidity function based on benzamides provided the best results. The range of variation of the solvation coefficient m is similar to that of amides, this indicating similar solvation requirements for amides and hydroxamic acids. For the same substrate, the observed variations of pK(BH)(+) with the mineral acid used was justified by formation of solvent-separated ion pairs; for the same mineral acid, the observed changes in pK(BH)(+) can be explained by the solvation of BH(+). The change of the pK(BH)(+) values was in reasonably good agreement with the sequence of the catalytic efficiency of the mineral acids used, HCl > H(2)SO(4) > HClO(4).     

NKC-9大孔强酸性树脂富集硫脲金

酸性硫脲溶液浸金是近年来湿法冶金的一个研究热点[1],主要集中在金的浸出过程。而对于浸出液中硫脲金的富集与分离,已通过电解法、还原法、炭吸附和溶剂萃取等[2 4]方法进行了研究,但存在问题很多,如电解法要求金浓度比较高,炭吸附中炭易破碎,溶剂萃取法的萃取量低等。离子交换法富集分离硫脲金是一种非常有前途的方法[5 6]。我们研究了以功能基为 SO3H的NKC 9大孔强酸性苯乙烯系阳离子交换树脂为吸附剂,以有机和无机混合溶剂为洗脱液,对硫脲金的吸附与洗脱进行了系统的研究,得到了有意义的研究成果。1　实验部分1 1　仪器与试剂WF…     

Extent of exchange of bromine-82 with bromamine-T in strong acid medium

The extent of exchange of bromine-82 with bromamine-T in strong acid medium is low due to the formation of at lower acid concentrations and bromine at higher acidities. formation occurs over a narrow acid concentration range and is less stable than .     

Extent of exchange of36Cl with CAB in strong acid medium

Aqueous chloramine-B /C₆H₅SO₂NCl Na/ solution is known to contain species like RNCl^–, RNHCl, RNCl₂, RN⁺H₂Cl, HOCl and H²⁺OCl where R=C₆H₅SO₂. The exchange studies between³⁶Cl and CAB carried out in various media by ion-exchange method indicated that there is no exchange in solution at pH7. As the pH is decreased below 7, the extent of exchange increases reaching a maximum at pH 3. 3. The exchange decreases as the acidity is increased between pH 3.3 and 1N and again the exchange increases beyong 1N. The observed increase in exchange in strong acid medium is due to the evolution of chlorine.     

Oxidation with permanganate in strong alkaline medium. Oxidation of pyruvic and lactic acids

The reaction of permanganate ion with pyruvic acid and lactic acid has been studied in aqueous solutions containing 0.10–2.0 mol dm^?3 alkali. In this range of HO^? concentration the reaction is followed slowly by the reduction of manganate, thus, the above process can be studied separately. In the case of lactic acid (LA), the reactive species is alkoxy anion, and the deprotonation constant could be calculated from the kinetic data. A mechanism based on electron abstraction from the alkoxy anion has been proposed. In the case of pyruvic acid (PA) oxidation may proceed with participation of enolate anion, or hydrate anion, or an adduct. These three possibilities have been investigated. © John Wiley & Sons, Inc.     

Kinetics and molecular orbital calculations of desulfonation of strong acid cation-exchange resin

This paper deals with the desulfonation properties of some strong acid cation-exchange resins. The sulfate concentration in solution is continuously increased when a strong acid cation-exchange resin is mixed with water. The leaching of sulfate results from the desulfonation of the fixed group, and the amount of leached sulfate depends on the counter ion charge, the crosslinking degree and the exchanger matrix. The effects of the counter ion charge on the desulfonation rate suggested that the counter ion induces the nucleophilic attack of a water molecule on the sulfo group. This interpretation was supported by semiempirical molecular orbital calculations for the C₆H₅SO₃⁻M^m+ (M^m+ = Na⁺, Mg²⁺ and Al³⁺) systems, and the transition state of the Na⁺ system was successfully predicted by DFT calculations. The crosslinking degree influenced the desulfonation rate, which can be related to the decreasing hydration number of each counter ion in the resin phase with the increasing crosslinking degree. Furthermore, different exchanger matrices produced the differences in the rates, which may be derived from the electron-density donation from the exchanger matrix to the sulfo group. The desulfonation is governed by the electron-density of the sulfur atom and the water activity in the solid phase.     

Quantitative determination of diterpene acids in garden sage leaves

A procedure is developed for the quantitative determination of diterpene acids in garden sage leaves by UV spectrophotometry at the wavelength 285 nm. The target group of compounds was selectively extracted by petroleum ether 40/70. It was shown that the completeness of extraction is determined mainly by the number of portions of the pure solvent: at the optimum ratio of the mass of the weighed portion to the volume of solvent 1 g/200 mL, double extraction is sufficient. The duration of each extraction is 20 min. The procedure was used in the analysis of samples of garden sage leaves from various producers. It was found that the concentration of diterpene acids in samples varied from 2.1 to 3.6 wt % (in terms of carnosic acid). The error of a single determination of the sum of diterpene acids in garden sage leaves is ±2.38% (P = 0.95).     

Differentiating diterpene resin acids using ToF‐SIMS and principal component analysis: new tools for assessing the geochemistry of amber

Amber is a polymerized plant resin having remarkable preservation potential in the geological record. Numerous analytical techniques have been applied to the study of amber organic chemistry in order to extract paleobotanical information. However, only exploratory work has been conducted using time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS), despite its immense potential due to the high mass resolution and range that can be analyzed concurrently. Detailed assessments of ion fragmentation patterns are prerequisite, given that amber is comprised of a challenging range of terpenoids, carboxylic acids, alcohols, and associated esters. In recent work, we demonstrated the applicability and efficiency of ToF‐SIMS as a tool to investigate amber chemical composition. However, only two diterpene resin acid standards were considered in this preliminary study, namely abietic acid and communic acid. We now extend this work by documenting the ToF‐SIMS spectra of ten additional diterpene resin acids and ask whether ToF‐SIMS analysis can distinguish subtle differences within a larger set of diterpenoids. Both positive and negative ToF‐SIMS spectra were produced, although negative polarity appears particularly promising for differentiating diterpene resin acids. Principal component analysis (PCA) was used to distill the data and verified that purified diterpenes have distinct ToF‐SIMS spectra that can be applied to amber chemotaxonomy as well as to the analysis of modern resins of known botanical origin. While this work is pertinent to the study of the composition and histories of ambers, the mass spectra of the 12 diterpene standards could prove valuable to any system where diterpenoid chemistry plays a role. Copyright © 2014 John Wiley & Sons, Ltd.     

Thermal behaviour of citric acid and isomeric aconitic acids

Thermal decomposition of citric acid, trans- and cis-aconitic acid has been studied using the TG-MS, TG-FTIR and DSC techniques. The measurements were carried out in an argon atmosphere over a temperature range of 293–673 K. The influence of the acid structures and configurational geometry on stability of the transition products and pathways of thermal transformations of the studied compounds studied is discussed.