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31.
V. V. Brei 《Theoretical and Experimental Chemistry》2009,45(3):186-188
The feasibility of using the equation log k = const – αH
0s was examined for solid acid catalysts. Data for the thermoprogrammed dealkylation of cumene showed that the temperature dependence
of the strength of the acid sites of the catalyst H
0s(T) should be considered in calculating the coefficient α. In this case, α→1.
Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 45, No. 3, pp. 173-175, May-June, 2009. 相似文献
32.
David J. Heldebrant Dr. Clement R. Yonker Dr. Philip G. Jessop Dr. Lam Phan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(31):7619-7627
CO2‐binding organic liquids (CO2BOLs) are mixtures of a base (typically an amidine or guanidine) and an alcohol, and have been shown to reversibly capture and release CO2 with low reaction energies and high gravimetric CO2 capacity. We now report the ability of such liquid blends to chemically bind and release other acid gases such as CS2, COS, and SO2 analogously to CO2. These systems bind with sulfur‐containing acid gases to form colored ionic liquids with new O‐alkylxanthate, O‐alkylthiocarbonyl, and O‐alkylsulfite anions. The capture and thermal stripping of each acid gas from these systems and their applicability towards flue gas desulfurization is discussed. 相似文献
33.
Evidence for ion–ion interactions between peptides and anions (HSO4− or ClO4−) derived from high‐acidity acids 下载免费PDF全文
Xiaohua Liu Jean‐Claude Tabet Richard B. Cole 《Journal of mass spectrometry : JMS》2014,49(6):490-497
The existence of gas‐phase electrostatic ion–ion interactions between protonated sites on peptides ([Glu] Fibrinopeptide B, Angiotensin I and [Asn1, Val5]‐Angiotensin II) and attaching anions (ClO4? and HSO4?) derived from strong inorganic acids has been confirmed by CID MS/MS. Evidence for ion–ion interactions comes especially from the product ions formed during the first dissociation step, where, in addition to the expected loss of the anion or neutral acid, other product ions are also observed that require covalent bond cleavage (i.e. H2O loss when several carboxylate groups are present, or NH3 loss when only one carboxylate group is present). For [[Glu] Fibrinopeptide B + HSO4]?, under CID, H2O water loss was found to require less energy than H2SO4 departure. This indicates that the interaction between HSO4? and the peptide is stronger than the covalent bond holding the hydroxyl group, and must be an ion–ion interaction. The strength and stability of this type of ion‐pairing interaction are highly dependent on the accessibility of additional mobile charges to the site. Positive mobile charges such as protons from the peptide can be transferred to the attaching anion to possibly form a neutral that may depart from the complex. Alternatively, an ion–ion interaction can be disrupted by a competing proximal additional negatively charged site of the peptide that can potentially form a salt bridge with the positively charged site and thereby facilitate the attaching anion's departure. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
34.
Vasant R Choudhary Chinta Sivadinarayana Kshudiram Mantri 《Journal of Chemical Sciences》1999,111(5):669-676
The acidity and initial and time-on-stream activity in propane aromatization (at 550°C, space velocity of 3100 cm3g−1
(zeolite)h−1) of Ga-impregnated H-ZSM-5 zeolite without or with binders (50 wt%), such as silica, alumina and kaolin, have been investigated.
Both the acidity and catalytic activity of the zeolite are influenced by the presence of binder in the catalyst, depending
upon the binder. The influence is found to be lowest for alumina and highest for kaolin. Among the binders, alumina is the
most preferred binder for the zeolite catalyst. 相似文献
35.
R. V. Linko V. A. Soldatkina B. E. Zaitsev M. A. Ryabov V. I. Sokol 《Russian Chemical Bulletin》1999,48(6):1095-1099
Phenanthrenequinone monoxime and its mono-, di-, and trinitro derivatives were synthesized. The acidity constants and their
variation with the number and position of nitro groups were determined. The electronic and IR spectra of the nitro compounds
were studied. The bands in the electronic spectra were assigned based on quantum-chemical calculations in the Pariser—Parr—Pople
approximation. Correlations between the pK
a values and some calculated characteristics of the compounds under study were found.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1106–1110, June, 1999. 相似文献
36.
Jorge Antonio Guerrero‐Álvarez Wendy Paloma Mas‐Ku Cesar Garcías‐Morales Armando Ariza‐Castolo 《Magnetic resonance in chemistry : MRC》2010,48(5):356-361
The relative acidities of the cis and trans isomers of a series of 1,5‐oxazaspiro[5.5]undecane derivatives were determined by measuring ΔpK in acid‐base titrations followed by 1 H NMR. Relative structural stabilities were determined by measuring substituent chemical shift and γ‐gauche effects in 13C, 15N, and 17O NMR. Crystallographic characterization of a model spiro[5.5]undecane is presented to support the basicity in solid state. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
37.
The gas‐phase acidities (GA) of various aryl‐substituted fluoroalkanes, XC6H4CH(R1)R2, were calculated at the B3LYP/6‐311 + G(d,p)//B3LYP/6‐311 + G(d,p). The acidity values of alkanes having a common substituent X varied significantly with the change of R1 and R2. Their changes in acidity of 1 and 2 having two strong electron‐withdrawing groups (CF3 or C2F5) at the deprotonation site and 8 , 9 , 10 , 11 having no fluorine atom at β‐position were linearly correlated with the corrected number of fluorine atoms contained in the fluorinated alkyl group (R2 > 0.999). On the other hand, the GA values of β‐fluorine substituted alkanes ( 3 , 4 , 5 , 6 , 7 ) deviated in a stronger acid direction from the line. The enhanced acidity was attributed to the additional stabilization of the conjugate anion caused by the β‐fluorine negative hyperconjugation. The magnitude of β‐fluorine negative hyperconjugation of the fluorinated alkyl group (ΔGoβ‐F) given by the deviations from the line decreased with increasing electron‐withdrawing ability of substituent X on the benzene ring, indicating that β‐fluorine negative hyperconjugation competes with the electronic effect of the substituent X. The GAel values obtained by subtraction ΔGoβ‐F from the apparent GA value were successfully correlated in terms of the Yukawa–Tsuno equation. The obtained ρel and r?el values were linearly related to the GAel value of the respective phenyl‐substituted fluoroalkanes, supporting our previous conclusion that the ρ and r? values for the substituent effect caused by the electronic effects of the substituent on the acidity are determined by the thermodynamic stability of the parent ion (ring substituent = H). Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
38.
Prof. Dr. Samih A. Halawy Dr. Ahmed I. Osman Dr. Adel Abdelkader Mahmoud Nasr Prof. Dr. David W. Rooney 《ChemistryOpen》2022,11(3):e202200021
Measuring the Lewis-acidic surface sites in catalysis is problematic when the material‘s surface area is very low (SBET ≤1 m2 ⋅ g−1). For the first time, a quantitative assessment of total acidic surface sites of very small surface area catalysts (MoO3 as pure and mixed with 5–30 % CdO (wt/wt), as well as CdO for comparison) was performed using a smart new probe molecule, tetrahydrofuran (THF). The results were nearly identical compared to using another commonly used probe molecule, pyridine. This audition is based on the limited values of the surface area of these samples that likely require a relatively moderate basic molecule as THF with pKb=16.08, rather than strong basic molecules such as NH3 (pKb=4.75) or pyridine (pKb=8.77). We propose mechanisms for the interaction of vapour phase molecules of THF with the Lewis-cationic Mo and Cd atoms of these catalysts. Besides, dehydration of isopropyl alcohol was used as a probe reaction to investigate the catalytic activity of these catalysts to further support our findings in the case of THF in a temperature range of 175–300 °C. A good agreement between the obtained data of sample MoO3-10 % CdO, which is characterised by the highest surface area value, the population of Lewis-acidic sites and % selectivity of propylene at all the applied reaction temperatures was found. 相似文献
39.
调节待测体系的pH值是配位滴定中一种重要的选择性滴定手段。采用CTE1.0程序计算了不同酸度条件下的终点误差,同时用配位滴定法测定了模拟样品和市售药品中的锌含量。计算结果和实测结果均表明,在不含钙离子的待测体系中,测定锌离子含量的合适酸度条件为pH=6;在钙、锌混合离子溶液中,测定锌含量的合适酸度条件为pH=5。平行测定实验的相对标准误差为1.63%,加标回收率为99.1%-101.8%。 相似文献
40.
改性Y型分子筛对硫醇硫醚的吸附脱除研究 《燃料化学学报》2017,45(12):1467-1472
通过液相离子交换法制备了Cu(I)Y、Ni Y、Ce Y分子筛,以XRD、低温N2吸附-脱附、NH3-TPD、吡啶红外Py-FTIR等方法对其进行物性表征。利用固定床技术、WK-2D微库伦仪及硫化学发光检测GC-SCD色谱评价了改性分子筛对于硫含量300μg/g模拟油(含硫化合物二丙硫醚、环己硫醇和1-庚硫醇与壬烷配制)及HDS汽油的吸附脱硫性能。结果表明,吸附剂对模拟油和HDS燃料油品中硫醇硫醚具有吸附效果,且改性后的分子筛在吸附脱硫过程中,强的B酸对于吸附脱硫有负作用,会使油品中硫醇硫醚发生催化反应,聚合的大分子硫化物遮盖及阻塞吸附活性位点,从而使吸附剂不能够完全地吸附硫化物,造成吸附硫容较小,而弱L酸无催化活性对吸附脱硫有正面影响。 相似文献