无机化学课件：16 Non-Aqueous Solvents

1、Non-Aqueous SolventsWhy non-aqueousSome reagents may react with H2ONon-polar molecules are insoluble in watereg:dichloromethane, hexane, toluene and ethers such as diethyl ether, tetrahydrofuran, and diglymeionic liquidsInorganic non-aqueous solventliquid ammonia, NH3liquid sulfur dioxide, SO2sulfur

2、yl chloride, SO2Cl2sulfuryl chloride fluoride, SO2ClFphosphoryl chloride, POCl3dinitrogen tetroxide, N2O4antimony trichloride, SbCl3bromine pentafluoride, BrF5hydrogen fluoride, HFpure sulphuric acid and other inorganic acidsnon-aqueous solvents categoriesprotic solvents (e.g. HF, H2SO4, MeOH);aprot

3、ic solvents (e.g. N2O4, BrF3);coordinating solvents (e.g. MeCN, Et2O, Me2CO).A protic solvent undergoes self-ionization to provide protons which are solvated, If it undergoes self-ionization.an aprotic solvent does so without the formation of protons.Limitations of non-aqueous solventsmany are highl

4、y reactivequantitative data are scarcequalitativeion-association (in solvents of relative permittivity lower than that of water) data are difficult to interpretno integrated treatment of inorganic chemistry in non-aqueous solvents is yet possibleRelative Permittivity相对介电常数dielectric constant,the for

5、ce is reduced by an amount that depends upon the relative permittivity of the material.In a vacuumAbsolute permittivity of a material =orQP neutralizes part of the charge on each plateRelative PermittivityIn a fluid with dielectric constant r, the force on Q2 is reduced by the factor 1/ r compared w

6、ith the force in vacuum.Since intermolecular forces are electrical, the dielectric constant r of a solvent affects equilibrium constants and reaction rate constants.The deviation of r from 1 is due to two effectsthe induced polarization and the orientation of the permanent dipole moments. r increase

7、s as the molecular polarizability a increasesr increases as the molecular electric dipole moment m increases. Using the Boltzmann distribution law to describe the orientations of the dipoles in the applied electric fieldNonaqueous acid-base chemistry The acid-base reactions in non-aqueous solvents a

8、re typically described by means of the solvent-system definition, although the regular Brnsted-Lowry theory may be applied for the protic solvents, which possess a hydrogen atom that can dissociate. solvent-system Acid-Base definitionacids are the compounds that increase the concentration of the sol

9、vonium (positive) ionsbases are the compounds that result in the increase of the solvate (negative) ions, where solvonium and solvate are the ions found in the pure solvent in equilibrium with its neutral moleculesprotic solvents autodissociation2NH3 NH4+ (ammonium) + NH2 (amide)3HF H2F+ + HF2- (hyd

10、rogen difluoride) 2H2SO4 H3SO4+ + HSO4-aprotic solvents autodissociationN2O4 NO+ (nitrosonium) + NO3 (nitrate) 2SbCl3 SbCl2+ (dichloroantimonium) + SbCl4- (tetrachloroantimonate) POCl3 POCl2+ + POCl4-Acid-Base ReactionNaNH2 is a base and NH4Cl is an acid in liquid ammonia, they react, producing the

11、salt and the solvent:NaNH2 + NH4Cl 2NH3 + NaClaprotic example,NaNO3 + NOCl N2O4 + NaClLimiting acids and limiting bases The limiting acid in a given solvent is the solvonium ion, such as H3O+ (hydronium) ion in water. An acid which has more of a tendency to donate a hydrogen ion than the limiting ac

12、id will be a strong acid in the solvent considered, and will exist mostly or entirely in its dissociated form. The limiting base in a given solvent is the solvate ion, such as OH (hydroxide) ion, in water. A base which has more affinity for protons than the limiting base cannot exist in solution, as

13、 it will react with the solvent.Noble gas chemistry The reactions of the compounds containing xenon are mostly conducted in hydrogen fluoride or bromine pentafluoride, Sulphuric solvents are also used sometimes, in particular sulfuryl chloride fluoride for strong oxidants.which dissolve readily both

14、 xenon difluorides and its multiple derivatives, Extreme oxidants Sulfuryl chloride fluoride is the solvent of choice for many reactions that deal with extreme oxidants. For example, it can be used to generate and study free carbocations and arenium ions (cyclohexadienyl cation that appears as a rea

15、ctive intermediate in electrophilic aromatic substitution)Super Acid, Magic Acid & Super BaseHOS(O)2FSbF5 + HOS(O)2FLi(n-C4H9)The Hard/Soft Acid/Base (HSAB) PrincipleHSAB is an extremely useful qualitative theory that enables predictions of what adducts will form in a complex mixture of potential Le

16、wis acids and basesHard acidsLow electronegativity (c) of the acidic atom. A value in the range 0.7-1.6 is typical of hard acids;Relatively small size;Relatively high charge ( 3+).(s,f blocks, left side of d block in higher OSs)Hard basesVery high c of the donor atom (in the range 3.4-4);Relatively

17、small size of the donor atom.Soft bases intermediate to high c (2.1-3.0)large size, leading to polarizabilitySoft acids intermediate to high c (1.9-2.5);large size;low charge (1+, 2+)AcidsBaseshardsofthardsoftHydroniumH+MercuryCH3Hg+, Hg2+, Hg22+HydroxideOH-HydrideH-Alkali metalsLi+,Na+,K+PlatinumPt

18、2+AlkoxideRO-ThiolateRS-TitaniumTi4+PalladiumPd2+HalogensF-,Cl-HalogensI-ChromiumCr3+,Cr6+SilverAg+AmmoniaNH3PhosphinePR3Boron trifluorideBF3boraneBH3CarboxylateCH3COO-ThiocyanateSCN-CarbocationR3C+P-chloranilCarbonateCO32-carbon monoxideCObulk MetalsM0HydrazineN2H4BenzeneC6H6GoldAu+Hard and soft ac

19、ids and basesIn most acid-base interaction, the combination of HOMO-LUMO forms the NEW HOMO-LUMO of the productsA base has a pair of electrons in HOMO of suitable symmetry to interact with LUMO of the acidHSAB InteractionHard acids tend to bind to hard bases.Soft acids tend to bind to soft bases.Fun

20、damentals. The basic premise of Hard/Soft Acid/Base Theory is very simple: Hard acids prefer hard bases; soft acids prefer soft bases.Hard acidbase interactions are predominantly electrostatic; soft acidbase interactions are predominantly covalentEstimation of HOMO & LUMO EnergyEHOMO = -IELUMO = -AA

21、bsolute Hardness & Absolute ElectronegativityILs are materials composed solely of anions and cations.Molecular solvents are composed of neutral species benzene, propylene carbonate, waterIonic LiquidsCation StructuresInorganic Organic BR4- Sulfonate -O-(SO2R) PR6- Imide -N-(SO2R)2 Methide -C-(SO2R)3

22、 Anion StructuresR = halide, perfluoroalkyl and other electron withdrawing alkyl or aryl substituentsIonic liquids:Polarity (adjustable) Very low vapor pressureLiquid ranges ( 300 C)Solubility of gases & a wide range of compoundsImmiscibility with solventsHydrophilicity/lipophilicity (adjustable)Aci

23、dity (adjustable)Electrolyte Storage: 150oC for 2 hrIonic Liquid1M TEABF4/PCSupercritical FluidsBeyond the Critical PointSLGSupercritical Fluid (SF)PTTcpcIf TTc, gas can not be liquefied at any pressurecritical temperature of gasBeyond the Critical PointSLGPTTcpcGLGLTTcTTcTTcSupercritical Fluids Hav

24、e Unusual Properties1. Densities are variable (like a gas)2. Good solvents (like a liquid)3. Viscosities are low (like a gas)Density of a SFr, g/mL01p, atm0400ideal gas lawpredictionactualpcnV=PRTOther Applications of SFs1. De-caffeination of coffee, teaThe old way:acetone, benzene, ethanol, freons,

25、 pentane, hexane, CCl4, CHCl3, CH2Cl2Other Applications of SFs1. De-caffeination of coffee, teaThe modern way:(a) extract caffeine using SF CO2(b) contact CO2 with water(c) discard water, recycle CO2 Comparisons of acidity and basicity between solvents There exists a large corpus of data concerning acid strengths in aqueous solution (pKa values), and it is tempting to transfer this to other solvents. Such comparisons are, however, fraught with danger, as they only consider the effect of solvation on the stability of the hydrogen ion, while neglecting its effects on the stabilit