Aluminum chloride, dissolution water

To a flame-dried, three-neck, 1-1 flask were added, in order, p-xylene (107 g, 1.0 mol), phosphorus trichloride (412 g, 3.0 mol), and anhydrous aluminum chloride (160 g, 1.2 mol). The reaction mixture was slowly heated to reflux with stirring. After 2.5 h at reflux, the reaction was allowed to cool to room temperature and the volatile components distilled at reduced pressure. The residual oil was slowly added to cold water (1 1) with stirring, and a white solid formed. The solid was removed by filtration, washed with water, and air dried. The solid was suspended in water (1 1) to which was added 50% sodium hydroxide solution (90 ml) to cause dissolution. The solution was saturated with carbon dioxide and filtered through Celite . The basic solution was washed with methylene chloride (200 ml) and acidified with concentrated hydrochloric acid (200 ml). The white solid that separated was isolated by extraction with methylene chloride (3 x 250 ml). The extracts were dried over magnesium sulfate, filtered, and evaporated under reduced pressure to give the pure 2,5-dimethylbenzenephosphinic acid (99 g, 60%) as an oil, which slowly crystallized to a solid of mp 77-79°C. 

Typical procedure. Symmetrical diaryl ketone [946] In a 100-mL round-bottomed flask with a side-arm, oxalyl chloride (1.05 mL, 12 mmol) was added dropwise over a period of 5 min to a solution of p-xylene (1.23 mL, 10 mmol) in dichloromethane (50 mL) at 5 °C. Aluminum chloride (1.33 g, 10 mmol) was then added portion-wise over 5 min to give a yellow suspension. The reaction mixture was allowed to warm to room temperature and stirred for 1 h, during which time dissolution of the solid and gas evolution were observed. A second equivalent of p-xylene (1.23 mL, 10 mmol) was then added dropwise over a period of 5 min, and the reaction mixture was stirred for 13 h at room temperature. It was then chilled in an ice/ water bath, and water (25 mL) was added dropwise over a period of 10 min. The layers were separated, and the aqueous layer was extracted twice with dichloro-... 

In near-neutral and deaerated solutions, the oxide film on anodized aluminum is stable and protective in distilled water and chloride solutions, as well as in solutions of inhibitive anions. Thus the inhibition of aluminum corrosion by anions differs from that of iron or zinc in that the presence of dissolved oxygen in the solution is not necessary to stabilize the oxide film. In corrosion inhibition by chromate ions, their interaction with the oxide film on aluminum has been shown to result in the formation of an outer layer of the film that is more protective due to its high electronic resistance and low dissolution rate. Chromate ions were also found to prevent the uptake and penetration of chloride ions into the aluminum oxide film. 

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