Aluminium chlorid

Prepared by the dehydration of benzamide. Hydrolysed by dilute acids and alkalis to benzoic acid. Good solvent. benzopheDone,C]3HioO,PhC(0)Ph. Colourless rhombic prisms, m.p. 49 C, b.p. 306°C. Characteristic smell. It is prepared by the action of benzoyl chloride upon benzene in the presence of aluminium chloride (Friedel-Crafts reaction) or by the oxidation of di-phenylmethane. It is much used in perfumery. Forms a kelyl with sodium. 

Both these molecules exist in the gaseous state and both are trigonal planar as indicated by reference to Table 2.8. However, in each, a further covalent bond can be formed, in which both electrons of the shared pair are provided by one atom, not one from each as in normal covalent bonding. For example, monomeric aluminium chloride and ammonia form a stable compound ... 

This compound, which contains atoms arranged tetrahedrally around the boron atom, can readily be isolated from a mixture of dimethyl ether and boron trichloride. On occasions a chlorine atom, in spite of its high election affinity, will donate an electron pair, an example being found in the dimerisation of gaseous monomeric aluminium chloride to give the more stable Al2Clg in which each aluminium has a tetrahedral configuration ... 

Metals in higher oxidation states form halides which are essentially covalent, for example AICI3, SnCl, FeClj when these compounds dissolve in water they do so by a strongly exothermic process. Indeed it is perhaps incorrect to think of this only as a dissolution process, since it is more like a chemical reaction—but to differentiate for a particular substance is not easy, as we shall see. The steps involved in the case of aluminium chloride can be represented as... 

Aluminium also has a strong tendency to achieve a noble gas configuration by electron pair acceptance as shown in dimeric aluminium chloride. 

Diborane has a qeometric structure similar to that of dimeric aluminium chloride, namely... 

When lithium hydride is allowed to react with aluminium chloride in ether solution, two reactions occur ... 

Both boron and aluminium chlorides can be prepared by the direct combination of the elements. Boron trichloride can also be prepared by passing chlorine gas over a strongly heated mixture of boron trioxide and carbon. Like boron trifluoride, this is a covalent compound and a gas at ordinary temperature and pressure (boiling point 285 K). It reacts vigorously with water, the mechanism probably involving initial co-ordination of a water molecule (p, 152). and hydrochloric acid is obtained ... 

It forms an ion BCI4 only under special circumstances, and never in aqueous solutions (cf. BF3). Like the trifluoride, it is an electron pair acceptor, but the adducts formed tend to decompose more readily. Unlike the corresponding aluminium chloride, boron trichloride exists only as the monomer. 

Aluminium chloride can be prepared not only by the direct combination of the elements but also by the passage of dry hydrogen chloride over heated aluminium ... 

Pure anhydrous aluminium chloride is a white solid at room temperature. It is composed of double molecules in which a chlorine atom attached to one aluminium atom donates a pair of electrons to the neighbouring aluminium atom thus giving each aluminium the electronic configuration of a noble gas. By doing so each aluminium takes up an approximately tetrahedral arrangement (p. 41). It is not surprising that electron pair donors are able to split the dimer to form adducts, and ether, for example, forms the adduct. 

Aluminium chloride is used extensively in organic chemistry as a catalyst, for example in the Friedel-Crafts reaction ... 

QHe + C2H5" C,H5C2H5 + and then hydrogen chloride and aluminium chloride are formed ... 

Describe the laboratory preparation, from aluminium, of (a) anhydrous aluminium chloride, (b) potassium aluminium sulphate dodecahydrate. 

The solid anhydrous halides of some of the transition metals are often intermediate in character between ionic and covalent their structures are complicated by (a) the tendency of the central metal ion to coordinate the halide ions around it, to form an essentially covalent complex, (b) the tendency of halide ions to bridge, or link, two metal ions, again tending to covalency (cf. aluminium chloride, p. 153 and iron(III) chloride, p. 394). 

TTie true ketones, in which the >CO group is in the side chain, the most common examples being acetophenone or methyl phenyl ketone, C HjCOCH, and benzophenone or diphenyl ketone, C HjCOC(Hj. These ketones are usually prepared by a modification of the Friedel-Crafts reaction, an aromatic hydrocarbon being treated with an acyl chloride (either aliphatic or aromatic) in the presence of aluminium chloride. Thus benzene reacts with acetyl chloride... 

Required Aluminium chloride, 30 g. benzene, 75 ml. acetyl chloride, 20 ml. 

Required Aluminium chloride, 3 g. benzene, 7 5 mi. acetyl chloride, 2 ml. 

Place in a 25 or 50 ml. round-bottomed flask, 3 g. of finely powdered anhydrous aluminium chloride and 7 5 ml. of dry benzene. Fit the flask with a reflux water-condenser. Place the flask in a cold water-... 

The Friedel-Crafts Reaction, in which an aromatic hydrocarbon reacts with an alkyl halide under the influence of aluminium chloride ... 

METHYLACETOPHENONE. Required Toluene, 250 ml. acetyl chloride, 35 ml. aluminium chloride, 40 g. 

By treatment with anhydrous aluminium chloride (Holmes and Beeman, 1934). Ordinary commercial, water-white benzene contains about 0 05 per cent, of thiophene. It is first dried with anhydrous calcium chloride. One litre of the dry crude benzene is shaken vigorously (preferably in a mechanical shaking machine) with 12 g. of anhydrous aluminium chloride for half an hour the temperature should preferably be 25-35°. The benzene is then decanted from the red liquid formed, washed with 10 per cent, sodium hydroxide solution (to remove soluble sulphur compounds), then with water, and finally dried over anhydrous calcium chloride. It is then distilled and the fraction, b.p. 79-5-80-5°, is collected. The latter is again vigorously shaken with 24 g. of anhydrous aluminium chloride for 30 minutes, decanted from the red liquid, washed with 10 per cent, sodium hydroxide solution, water, dried, and distilled. The resulting benzene is free from thiophene. 

Friedel and Crafts reaction. alkyl halide condenses with an aromatic hydrocarbon in the presence of anhydrous aluminium chloride to yield, in the first instance, a hydrocarbon in accordance with the following scheme —... 

The ketones are readily prepared, for example, acetophenone from benzene, acetyl chloride (or acetic anhydride) and aluminium chloride by the Friedel and Crafts reaction ethyl benzyl ketones by passing a mixture of phenylacetic acid and propionic acid over thoria at 450° and n-propyl- p-phenylethylketone by circulating a mixture of hydrocinnamic acid and n-butyric acid over thoria (for further details, see under Aromatic Ketones, Sections IV,136, IV,137 and IV,141). 

The yield of iso-propylbenzene is influenced considerably by the quality of the anhydrous aluminium chloride employed. It Is recommended that a good grade of technical material be purchase in small bottles containing not more than 100 g. each undue exposure to the atmosphere, which results in some hydrolysis, is thus avoided. Sealed bottles containing the reagent sometimes have a high internal pressure they should be wrapped in a dry cloth and opened with care. 

The apparatus required is similar to that described for Diphenylmelhane (Section IV,4). Place a mixture of 200 g. (230 ml.) of dry benzene and 40 g. (26 ml.) of dry chloroform (1) in the flask, and add 35 g. of anhydrous aluminium chloride in portions of about 6 g. at intervals of 5 minutes with constant shaking. The reaction sets in upon the addition of the aluminium chloride and the liquid boils with the evolution of hydrogen chloride. Complete the reaction by refluxing for 30 minutes on a water bath. When cold, pour the contents of the flask very cautiously on to 250 g. of crushed ice and 10 ml. of concentrated hydrochloric acid. Separate the upper benzene layer, dry it with anhydrous calcium chloride or magnesium sulphate, and remove the benzene in a 100 ml. Claisen flask (see Fig. II, 13, 4) at atmospheric pressure. Distil the remaining oil under reduced pressure use the apparatus shown in Fig. 11,19, 1, and collect the fraction b.p. 190-215°/10 mm. separately. This is crude triphenylmethane and solidifies on cooling. Recrystallise it from about four times its weight of ethyl alcohol (2) the triphenylmethane separates in needles and melts at 92°. The yield is 30 g. 

Aroylbenzoic acids. Aromatic hydrocarbons condense with phthalic anhydride in the presence of anhydrous aluminium chloride producing aroylbenzoic acids in good yields ... 

Place a mixture of 1 0 g. of the hydrocarbon, 10 ml. of dry methylene chloride or ethylene dichloride or syw.-tetrachloroethane, 2 5 g. of powdered anhydrous aluminium chloride and 1-2 g. of pure phthalic anhydride in a 50 ml. round-bottomed flask fitted with a short reflux condenser. Heat on a water bath for 30 minutes (or until no more hydrogen chloride fumes are evolved), and then cool in ice. Add 10 ml. of concentrated hydrochloric acid cautiously and shake the flask gently for 5 min utes. Filter oflf the solid at the pump and wash it with 10-15 ml. of cold water. Boil the resulting crude aroylbenzoic acid with 10 ml. of 2 -5N sodium carbonate solution and 0 2 g. of decolourising carbon for 5 minutes, and filter the hot solution. Cool, add about 10 g. of crushed ice and acidify... 

By the rearrangement of an ester of a phenol in the presence of aluminium chloride (Fries reaction), phenolic ketones are produced ... 

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