石灰石/石膏法烟气脱氟反应的动力学研究

对石灰石/石膏湿法烟气脱氟反应过程进行了描述,建立了基于双膜理论的CaCO3 HF反应动力学模型,并对模型进行了计算和分析,考察了反应温度、反应时间、HF气相分压、Ca/F摩尔比等因素对反应的影响。结果表明,CaCO3颗粒的转化率和脱氟率随着反应温度、反应时间、HF气相分压的增加而增加,Ca/F摩尔比对脱氟率有重要影响,双膜理论模型可较好地描述石灰石/石膏湿法脱氟反应的动力学行为。研究结果对于典型的湿法烟气脱硫技术的气态氟化物的脱除机理研究和为开发统一的燃煤污染物控制技术具有指导意义。     

Kinetochromic spectrophotometry-I Determination of fluoride by catalysis of the zirconium-xylenol orange reaction

The reaction between slightly aged solutions of zirconyl chloride and Xylenol Orange is catalysed by the presence of substoi-chiometric amounts of fluoride, phosphate, arsenate, sulphate, citrate or oxalate. The reaction provides a method for determining fluoride in amounts from 0.5 to 5 mug in a final volume of 100 ml. This kineto-chromic reaction provides an effective molar absorptivity of 2.0 x 10(5) for the fluoride ion. The colour reaches maximal development within 90 min and remains stable thereafter for 60 min, when measured against a reaction system blank containing no fluoride. Because of its substoichiometric nature the reaction may not be used for the determination of large amounts of fluoride.     

Effects of ion-pairing and hydration on the SNAr reaction of the F- with p-chlorobenzonitrile in aprotic solvents

Theoretical ab initio calculations including liquid phase optimizations were used to investigate the S(N)Ar reaction of the fluoride ion with p-chlorobenzonitrile in dimethyl sulfoxide solution. The effect of the counter ion and hydration of the fluoride ion with one water molecule was analyzed. The calculations indicate that the gas-phase S(N)Ar reaction is more favorable than the corresponding S(N)2 reactions involving fluoride ion and 2-chlorobutane. However, the substantially higher solvent effect on the S(N)Ar reaction makes the nucleophilic substitution on the aromatic ring less favorable than the aliphatic reaction in the liquid phase. For the anhydrous tetrabutylammonium fluoride system, the theoretical free energy barrier of 22.1 kcal mol(-1) is close to the experimental one of 24.4 kcal mol(-1). The smaller tetramethylammonium cation strongly associates with the fluoride ion and increases the barrier by 5 kcal mol(-1). Similarly, just one water molecule hydrating the fluoride ion has the same effect. An analysis of the reaction involving the ion pair and the free anion in different polarity media predicts an unexpected behavior and indicates there is an ideal solvent polarity for each counter ion.     

Autoinductive exponential signal amplification: a diagnostic probe for direct detection of fluoride

A new example of an exponential signal amplification strategy for the direct detection of fluoride is demonstrated. The amplification occurred through reaction of fluoride with a responsive chromogenic probe. The probe activity is based on a unique dendritic chain reaction that generates a fluoride anion, which is the analyte of interest, during the disassembly pathway of the dendritic probe. This autoinductive amplification mechanism may be applied for detection of other analytes by coupling activity of a modified probe with that of the fluoride amplifier.     

A catalytic-kinetic method for the determination of traces of fluoride in biological material

A catalytic-kinetic method for the determination of nanogram amounts of fluoride, based on its inhibiting action on the catalyst in the zirconium-catalyzed reaction between perborate and iodide, is described. The rate measurements are accomplished very simply by using a Landolt reaction system with a biamperometric detection of the induction period. The standard deviation in the working range 19–190 ng of fluoride (1–10 nmol) is ± 2 ng. The method can be made specific by combining it with a separation of the fluoride by microdiffusion. This has been demonstrated by analyzing biological material and comparing the results with the fluoride contents obtained with other methods.     

氟-铁恒电位配位滴定法测定铁离子研究

以氟离子溶液作滴定剂,氟离子选择性电极作指示电极,在pH=1.5的条件下,对恒电位配位滴定法测定铁离子进行了研究。对pH=1.5的条件下使用氟离子选择性电极的可行性,氟-铁的反应速率及电极的响应速率进行了讨论。     

Why does fluoride anion accelerate transmetalation between vinylsilane and palladium(II)-vinyl complex? Theoretical study

Transmetalation between palladium(II)-vinyl complex and vinylsilane was theoretically investigated with the DFT and MP2 to MP4 methods to clarify the reaction mechanism and the reasons why fluoride anion accelerates the Pd-catalyzed cross-coupling reaction between vinyl iodide and vinylsilane. This transmetalation occurs with a very large activation barrier (45.8 kcal/mol) and a very large endothermicity (25.6 kcal/mol) in the absence of fluoride anion, where the potential energy change resulting from the solvation effect is evident. This is consistent with the experimental fact that this cross-coupling reaction does not proceed well in the absence of fluoride anion. The effects of fluoride anion were investigated in three possible reaction courses. In the first course, fluorovinylsilicate anion is formed before the transmetalation, and it reacts with the palladium(II)-vinyl complex. In the second course, an iodo ligand is substituted for fluoride anion, and then the transmetalation occurs between the palladium(II)-fluoro-vinyl complex and vinylsilane. In the third course, fluoride anion attacks the Si center of vinylsilane in the transition state of the transmetalation between the palladium(II)-iodo-vinyl complex and vinylsilane. Our theoretical calculation suggests that fluorovinylsilicate anion is not formed in the case of trimethylvinylsilane. In the second and third cases, the transmetalation occurs with a moderate activation barrier (E(a)) and a considerably large exothermicity (E(exo)): E(a) = 25.3 kcal/mol and E(exo) = 5.7 kcal/mol in the second course, and E(a) = 12.7 kcal/mol and E(exo) = 24.8 kcal/mol in the third course, indicating that fluoride anion accelerates the transmetalation via the second and third reaction courses. The acceleration of transmetalation by fluoride anion is clearly interpreted in terms of the formation of a very strong Si-F bond and the stabilization of the transition state by the hypervalent Si center, which is induced by the fluoride anion. Our computational results show that hydroxide anion accelerates the transmetalation in a manner similar to that observed with fluoride anion. From these results, we predict that the electronegative anion accelerates this transmetalation because the electronegative group forms a strong covalent bond with the silyl group and facilitates the formation of the hypervalent Si center in the transition state.     

Novel fluorogenic probe for fluoride ion based on the fluoride-induced cleavage of tert-butyldimethylsilyl ether

A highly sensitive and selective fluorogenic probe for fluoride ion, 4-methylumbelliferyl tert-butyldimethylsilyl ether (4-MUTBS), was designed and synthesized. 4-MUTBS was a weakly fluorescent compound and was synthesized via the one-step reaction of 4-MU with tert-butyldimethylsilyl chloride. Upon incubation with fluoride ion in acetone-water solution (7:3, v/v), the Si-O bond of 4-MUTBS was cleaved and highly fluorescent 4-methylumbelliferone (4-MU) was released, hence leading to the fluorescence increase of the reaction solution. The fluorescence increase is linearly with fluoride concentration in the range 50-8000 nmol l(-1) with a detection limit of 19 nmol l(-1) (3sigma). Because of the high affinity of silicon toward fluoride ion, the proposed probe shows excellent selectivity toward fluoride ion over other anions. The method has been successfully applied to the fluoride determination in toothpaste and tap water samples.     

Reactions of nitro alcohols with n,n-diethyl-1,1,2,3,3,3-hexafluoropropylamine

Fluorination of nitro alcohols with N,N-diethyl-1,1,2,3,3,3-hexafluoropropylamine (PPDA) was investigated. 3-Nitrobenzyl fluoride (II) was obtained from the reaction of PPDA and 3-nitrobenzyl alcohol (I) (yield 66%). The reaction of 2-methyl-2-nitro-1-propanol (IV) with PPDA given 2-methyl-2-nitropropyl 2,3,3,3-tetrafluoropropionate (V). reduction of 3-nitrobenzyl fluoride (II) with lithium aluminium hydride gave the corresponding amino compound, 3-aminobenzyl fluoride (VI) in poor yield.     

Verfolgung der Verbrennungsreaktionen exothermer Massen auf Basis von Aluminium,Fluoriden und Kaliumnitrat mit Differentialthermoanalyse

DTA was applied to investigate the course of combustion of exothermic mixtures composed of aluminium, fluorides and potassium nitrate, and the results obtained were compared with the simultaneous results of X-ray investigations. The combustion of exothermic mixtures composed of aluminium, fluorides and potassium nitrate is similar to the combustion of mixtures where the potassium nitrate is substituted by sodium nitrate. Two exothermic reactions occur: between 400 and 520?, and between 800 and 1130?, in mixtures with sodium fluoride and between 450? and 650? and 850 and 1130? in mixtures with calcium fluoride. The reaction in the lower temperature range initiates the combustion of the mixture. In sodium fluoride mixtures this reaction takes place at lower temperature and seems to be more intense, since these mixtures inflame earlier than those with calcium fluoride. The reaction in the higher temperature range, which occurs at approximately the same temperature in the two cases, liberates the main part of the useful heat of the exothermic mixtures.     

The reaction of 1,2-diiodo-tetrafluoroethane with sulfur trioxide

As an extension of our studies on the reaction of I(CF₂CF₂)_nI (n = 2 and 3) with sulfur trioxide¹⁾, the reaction of 1,2-diiodo-tetrafluoroethane with sulfur trioxide was studied.1,2-Diiodo-tetrafluoroethane was reacted with an excess of sulfur trioxide at reaction temperature ranging from 0°C to 115°C.The products were not the expected iododifluoroacetyl fluoride and/ or oxalyl fluoride, but thermally stable derivatives with polysulfate structures.These derivaties could be converted nearly quantitatively into iododifluoroacetyl fluoride and ethyl iododifluoroacetate by potassium fluoride and by ethanol, respectively.The possible structures of these derivatives will be discussed based on these results and ¹⁹F-NMR studies.     

Direct fluorination of aryl oxygen compounds

A study has been made of the reaction of aryl oxygen compounds with elemental fluorine in hydrogen fluoride and acetonitrile. Hydrogen fluoride acted as a good solvent in the reaction of salicylic acid, salicylaldehyde and phenyl salicylate. Salicylalcohol gave a mixture of fluorination and oxidation products. Diphenyl derivatives were also fluorinated and gave mainly monofluoro compounds.     

The preparation of organomagnesium fluorides by organometallic exchange reactions

The preparation of alkyl- and aryl-magnesium fluorides by the reaction of dialkyl- and diaryl-magnesium compounds with fluorinating agents, such as BF₃ etherate, SiF₄, Bu₃SnF, Ph₃SiF and Et₂AlF in tetrahydrofuran were studied. Methyl-, ethyl-, and phenyl-magnesium fluoride were prepared in high yield by the reactions of dimethyl-, diethyl-, and diphenyl-magnesium with boron trifluoride diethyl etherate in tetrahydrofuran. Methylmagnesium fluoride was prepared in quantitative yield by the reaction of dimethylmagnesium with silicon tetrafluoride in tetrahydrofuran and butylmagnesium fluoride was prepared in quantitative yield by the reaction of tributyltin fluoride in THF with dibutylmagnesium. Other combinations of R₂Mg compounds and fluorinating agents resulted in the formation of less pure products.     

薄层色谱与红外光谱联用中新型固定相氟化钡的制备及应用

采用氟化钠与氯化钡反应制备了满足薄层色谱-红外光谱联用要求的氟化钡颗粒. 该方法虽然可以避免产生干扰红外光谱分析的碳酸钡杂质, 但氟化钡的产率偏低. 通过电感耦合等离子体(ICP)和X射线粉末衍射(XRD)分析证实, 氟化钠与氯化钡反应同时会生成氟氯化钡, 在沉淀洗涤过程中, 氟氯化钡的溶解会造成钡离子的流失和氟化钡产率的下降. 本文采用氟化钠溶液洗涤沉淀制备氟化钡, 可使氟氯化钡转化为氟化钡, 使氟化钡产率得到明显提高. 扫描电子显微镜和纳米粒度仪分析结果表明, 制备的氟化钡颗粒的粒径约为100 nm. 利用沉降挥发法制备了以氟化钡颗粒为固定相的薄层色谱板, 实验结果表明用该薄层色谱板可成功分离罗丹明B和孔雀石绿, 分离所得样品可被红外光谱检测且不受固定相的干扰.     

Substoichiometric precipitation of fluoride with lanthanum

The substoichiometric precipitation of fluoride with lanthanum was studied by using¹⁸F and¹⁴⁰La tracers and it was found that fluoride could be precipitated substoichiometrically with lanthanum and the reaction ratio between fluoride and lanthanum was 3∶1. The pH range at which fluoride can be separated substoichiometrically with lanthanum is between 2 and 8. Barium and indium interfere in the precipitation of fluoride, sodium, copper and manganese, however, not. Fluorosilicate can also be precipitated substoichiometrically by using lanthanum as a precipitant and the reaction ratio between fluorosilicate and lanthanum was 1∶2. This separation was applied for the determination of oxygen in silicon crystals. The concentration of oxygen measured in some silicon crystals was between 5 and 27 ppm and in good agreement with those by non-destructive method and infrared spectrophotometry.     

Etude de l'action de l'ion fluor sur la laquethorium-spadns

The reaction of fluoride with thorium—SPADNS lake was studied in detail with particular reference to the effects of pH and media. Two methods for the determination of microgram amounts of fluoride based on the reaction are described. The spectrophotometric method developed is more suitable for routine use, but the colorimetric titration method is less sensitive to the effect of large amounts of electrolyte.     

Highly selective fluoride sensing via chromogenic aggregation of a silyloxy-functionalized tetraphenylethylene (TPE) derivative

A silyloxy-functionalized tetraphenylethylene (TPE) derivative shows a remarkable change in the absorption spectrum on deprotection with fluoride ions. The reaction process is highly selective for fluoride and the resulting charge transfer band results in a bright green solution. A simple selective visual assay of aqueous fluoride ions was also obtained by the impregnation of cellulose strips with the TPE derivative.     

Perfluoroalkanosulfonyl fluoride-assisted Atherton–Todd-like reaction of diphenylphosphine oxide with alcohols under air generating diphenylphosphinate esters

An efficient method for the synthesis of diphenylphosphinate esters via the Atherton–Todd-like reaction of diphenylphosphine oxide with alcohols assisted by perfluoroalkanosulfonyl fluoride in the presence of triethylamine under air is achieved affording the corresponding diphenylphosphinate esters in moderate to good yields of 52–78%. The protocol features the use of non-toxic and stable perfluoroalkanosulfonyl fluoride and metal-free reaction conditions.     

Sulfuric acid breakdown of fluorite in the presence of silica

We study the reaction of CaF₂ with concentrated sulfuric acid in the presence of silica at 120 and 140°C using fluorite mineral, fluorite concentrate, and mica-fluorite ore samples. When steam is fed to the reaction mixture, fluorosilicic acid is formed and then distilled off, materially influencing the fluoride ion recovery. Addition of quartz makes the reaction to proceed in the kinetic area and increases the fluoride ion recovery, while the presence of mica-bound SiO₂ displaces the reaction to the diffusion area and decreases the fluoride ion recovery. We have found that rare alkali metals are concentrated as hexafluorosilicates in the insoluble residue during the sulfuric acid breakdown of fluorite in the presence of SiO₂.     

Pd-catalyzed C-h fluorination with nucleophilic fluoride

The palladium-catalyzed C-H fluorination of 8-methylquinoline derivatives with nucleophilic fluoride is reported. This transformation involves the use of AgF as the fluoride source in combination with a hypervalent iodine oxidant. Both the scope and mechanism of the reaction are discussed.