Chapter 9

(a) Give four examples of non-aqueous solvents commonly used in organic chemistry, and give one example of a reaction that is carried out in each solvent. (b) Assess the relative importance of the use of aqueous and nonaqueous media in organic and inorganic general synthesis.

Explain what is meant by the relative permittivity of a solvent. What information does this property provide in terms of assisting you to choose a solvent for a given reaction?

Which of the following solvents are polar: (a) acetonitrile; (b) water; (c) acetic acid; (d) fluorosulfonic acid; (e) dichloromethane; (f) bromine trifluoride; (g) hexane; (h) THF; (i) DMF; (j) liquid sulfur dioxide; (k) benzene?

Discuss the following observations: (a) Zinc dissolves in a solution of sodium amide in liquid \(\mathrm{NH}_{3}\) with liberation of \(\mathrm{H}_{2} ;\) careful addition of ammonium iodide to the resulting solution produces a white precipitate which dissolves if an excess of ammonium iodide is added. (b) Addition of \(\mathrm{K}\) to \(\mathrm{H}_{2} \mathrm{O}\) results in a vigorous reaction; addition of K to liquid \(\mathrm{NH}_{3}\) gives a bright blue solution, which over a period of time liberates \(\mathrm{H}_{2}\)

Early in the study of chemical reactions in liquid \(\mathrm{NH}_{3},\) it was noted that nitrogen compounds behave in liquid \(\mathrm{NH}_{3}\) in a manner similar to analogous oxygen-containing species in water. For example, \(\mathrm{K}\left[\mathrm{NH}_{2}\right]\) has an analogue in \(\mathrm{K}[\mathrm{OH}],\) and \(\left[\mathrm{NH}_{4}\right] \mathrm{Cl}\) is analogous to \(\left[\mathrm{H}_{3} \mathrm{O}\right] \mathrm{Cl}\). What would be the corresponding compounds in the nitrogen system to the following from the oxygen system: (a) \(\mathrm{H}_{2} \mathrm{O}_{2}\) ; (c) \(\mathrm{HNO}_{3}\) (d) \(\mathrm{MeOH}\) (b) \(\mathrm{HgO}\) (e) \(\mathrm{H}_{2} \mathrm{CO}_{3}\) (f) \(\left[\mathrm{Cr}\left(\mathrm{OH}_{2}\right)_{6}\right] \mathrm{Cl}_{3} ?\)

Give an explanation for the following observations: \(\mathrm{AlF}_{3}\) has only a low solubility in liquid \(\mathrm{HF}\), but a combination of NaF and AlF \(_{3}\) leads to dissolution of the reagents; when \(\mathrm{BF}_{3}\) is added to the solution, a precipitate forms.

\(\mathrm{H}_{2} \mathrm{S}_{2} \mathrm{O}_{7}\) functions as a monobasic acid in \(\mathrm{H}_{2} \mathrm{SO}_{4}\). (a) Write an equation to show what happens when \(\mathrm{H}_{2} \mathrm{S}_{2} \mathrm{O}_{7}\) dissolves in \(\mathrm{H}_{2} \mathrm{SO}_{4}\). (b) Assess the strength of \(\mathrm{H}_{2} \mathrm{S}_{2} \mathrm{O}_{7}\) as an acid given that the ionization constant is \(1.4 \times 10^{-2}\)

Discuss the following observations: (a) The alkene \(\mathrm{Ph}_{2} \mathrm{C}=\mathrm{CH}_{2}\) forms a conducting solution in liquid HCl; when such a solution is titrated conductometrically with a solution of \(\mathrm{BCl}_{3}\) in liquid \(\mathrm{HCl}\), a sharp end- point is reached when the molar ratio of \(\mathrm{Ph}_{2} \mathrm{C}=\mathrm{CH}_{2}: \mathrm{BCl}_{3}\) is 1: 1 (b) For a solution of \(\mathrm{N}_{2} \mathrm{O}_{4}\) in \(\mathrm{H}_{2} \mathrm{SO}_{4},\) values of \(\nu=6\) and \(\gamma=3\) have been determined.

(a) Give three examples of commonly used ionic liquids. What general properties make ionic liquids attractive in 'green chemistry"? (b) Why are imidazolium salts not suitable as solvents to replace ethers in Grignard reactions? (c) In a metal chloride-based ionic liquid, reaction with water leads to metal oxochlorides and HCl. How can metal oxochlorides be removed?

An ionic liquid can be formed by adding \(\mathrm{ZnCl}_{2}\) to (2-chloroethyl)trimethylammonium chloride, XCl. When the ratio of \(\mathrm{ZnCl}_{2}: \mathrm{XCl}=2: 1,\) fast atom bombardment mass spectrometry shows the presence of \(\left[\mathrm{Zn}_{x} \mathrm{Cl}_{y}\right]^{z-}\) ions with \(m / z=171,307\) and \(443 .\) Suggest identities for these ions and write a series of equilibria to account for their formation.