Potassium benzilate

If water is excluded this potassium salt can be isolated in the form of orange-yellow crystals which, with benzil, yield the red solution sensitive to the action of air. The solution probably contains the potassium-benzil radicle which is also obtained by the addition of metallic potassium to benzil (Beckmann and Paul,2 Schlenk 3) ... 

Experiment.1—Benzil (5 g.) is heated for ten minutes to boiling on the wateT bath with 15 c.c. of alcohol and a solution of 5 g. of potassium hydroxide in 10 c.c. of water. After cooling, the suspension of potassium benzilate crystals is filtered as dry as possible by suction, and the salt, after being washed with a little alcohol, is dissolved in 20-30 c.c. of cold water. The solution is filtered and dilute sulphuric acid is added, at the boiling point, to the clear filtrate. The free acid is precipitated partly in the form of crystals. It is separated by filtration with suction while hot and washed with hot water. It can then be recrystallised at once from a large volume of hot water or, after drying, from benzene. Yield about 4 g. 

The amount of alcohol and the concentration is such that the maximum amount of potassium benzilate will crystallize out. 

If more alcohol is used in proportion to the water, a large amount of potassium salt crystallizes during the heating and this is objectionable, while less alcohol holds in solution a considerable amount of potassium benzilate and thus decreases the yield. 

A detailed Organic Synthesis procedure is available for the conversion of benzil into benzilic acid. It is advantageous to isolate the acid as its potassium salt, for this enables the removal of the more soluble potassium benzoate, which results from a competitive cleavage reaction. Benzilic acid is then obtained in 77-79% yield by acidifying an aqueous solution of potassium benzilate. Since benzil is usually obtained by the oxidation of benzoin, both this conversion and rearrangement can be performed in tandem by using alkaline sodium bromate. Thus, benzilic acid is obtained in 84-90% yield from benzaldehyde via benzoin. 

According to Gattermann and Wieland,88c solutions of benzil (5 g) in ethanol (15 ml) and of potassium hydroxide (5 g) in water (10 ml) are mixed and heated under reflux on a water-bath for 10 min. When the solution has cooled, the crystal mass of potassium benzilate is filtered off with good suction, washed with ethanol, and dissolved in water (20-30 ml). After filtration, the benzilic acid (4 g) is precipitated from the boiling aqueous solution by dilute sulfuric acid. 

The driving force for the reaction is provided by the formation of a stable carboxy-late salt (potassium benzilate). Once this salt is produced, acidification yields benzilic acid. The reaction can generally be used to convert aromatic a-diketones to aromatic a-hydroxyacids. Other compounds, however, also will undergo benzilic acid-type of rearrangement (see questions). 

C13H25NO6, Methyl 8-t-butoxy-6-hydroxy-7-nitrooctanoate, 45B, 12 Ci3H2s02f Tridecanoic acid (A form), 46B, 13 CmHiiK03, Potassium benzilate, 44B, 112 CiuHi3NO, N,N-Diphenylacetamide, 33B, 9 Ci4Hift03, Kavaic acid, 40B, 13... 

When benzii is heated with potassium hydroxide solution, it undergoes a molecular rearrangement with the formation of the potassium salt of benzilic acid, or diphenyl lycollic acid ... 

To obtain the free acid, dissolve the potassium salt in 50 ml. of cold water, filter the solution if a small undissolved residue remains, and then boil the clear solution gently whilst dilute sulphuric acid is added until the separation of the acid is complete. Cool the solution and filter off the pale orange-coloured crystals of the benzilic acid wash the crystals on the filter with some hot distilled water, drain well, and then dry in a desiccator. Yield of crude acid, 4 g. Recrystallise from benzene (about 50 ml.) to which a small quantity of animal charcoal has been added, filtering the boiling solution through a preheated funnel fitted w ith a fluted filter-paper, as the benzilic acid readily crystallises as the solution cools alternatively, recrystallise from much hot water. The benzilic acid is obtained as colourless crystals, m.p. 150°. 

Benzil (and other a-diketones Ar—CO—CO—Ar) upon refluxing with aqueous-alcoholic potassium hydroxide undergo the beozilic acid rearrangement. Thus benzil is converted into a salt of benzilic acid ... 

Phenylbenzoyldiazomethane may be prepared by the oxidation of benzil-monohydrazone with mercuric oxide in the presence of dry etber as a solvent Tbe addition of a little alcoholic potassium hydroxide serves to catalyse the reaction ... 

The caustic potash is melted with a small quantity of water in a siheror nickel crucible. The temperature of the mass is brought to 150, and the finely powdered benzil added. The benzil melts, and the mixture shortly changes to a solid mass of potassium ben/ilatc. The cooled melt is dissolved in water, and the alkaline solution acidified with hydrochloric acid, which precipitates the benzilic acid. The crystalline mass, which contains small quantities of benzoic acid, is separated from the mother-liquor and washed with cold water. It is then transferred to a porcelain basin, dissolved in hot water, and the solution boiled until the smell of bcn/oic acid has gone. On cooling, benzilic acid crystallises out, and is purified by a second crystallisation from hot water. 

A mixture containing 8 g (0.06 mol) of N-methyl-3-chloro-piperidine and 13.6 g (0.06 mol) of benzilic acid in 50 cc of anhydrous isopropyl alcohol was refluxed for 3 days the isopropyl alcohol was removed by distillation in vacuo, the residue treated with dilute aqueous hydrochloric acid and the aqueous acid mixture extracted repeatedly with ether. The aqueous phase was separated, made strongly alkaline with 20% aqueous sodium hydroxide and extracted with ether. The ether extracts were dried with potassium carbonate and distilled the product was collected at 175° to 176°C (0.03 mm), yield 11.5 g (59%). The ester base thus prepared was then dissolved in 75 cc of isopropyl alcohol and 3.4 g (0.037 mol) methyl bromide added. The reaction mixture was allowed to stand at 30°C for 2 days and the product isolated by filtration, yield, 13 g (87%), MP 228° to 229°C dec. 

Treatment of the derivatives of 7-azalumazines, 514, with alcoholic sodium hydroxide caused a benzilic acid type of rearrangement via 515, followed by decarboxylation and oxidation by air or potassium permanga-... 

In a 500-cc. round-bottomed flask, 21 g. (0.1 mole) of benzil (Org. Syn. Coll. Vol. 1, 1941, 87) and 21 g. (0.1 mole) of dibenzyl ketone (Note 1) are dissolved in 150 cc. of hot alcohol. The flask is fitted with a reflux condenser, the temperature of the solution is raised nearly to the boiling point, and a solution of 3 g. of potassium hydroxide in 15 cc. of alcohol is added slowly in two portions through the condenser. When the frothing has subsided the mixture is refluxed for fifteen minutes and then cooled to 0°. The dark crystalline product is filtered with suction and washed with three 10-cc. portions of 95 per cent alcohol. The product melts at 218-220° and weighs 35-37 g. (91-96 per cent of the theoretical amount) (Note 2). 

Many oxidizing agents have been used, especially copper sulfate and other cupric salts. Potassium dichromate in acetic acid and manganese dioxide are good oxidants for benzil bis(phenylhydrazone). Nitrous acid has been used for the osazones of acetylated sugars and for phenylglyoxal bis(phenylhydrazone). ... 

Phenanthrenequinone has been prepared by treatment of phe-nanthrene with chromic acid in acetic acid 5 potassium dichromate in sulfuric acid 3-6 hydrogen peroxide in acetic acid 6 7 and selenium dioxide above 250°.8 It can also be prepared from benzil with aluminum chloride at 120° 9 and from biphenyl-2,2 -dialdehyde with potassium cyanide.10... 

Dufraisse announced that 138 was formed when an alkaline solution of hydroxyindanone 185 is treated with air or oxygen up to 80% 138 could be obtained in this way. This observation can be explained either by oxidation of an enolate ion to an oxiranol, with subsequent rearrangement, or by oxidative cleavage of the enolate ion to a benzilic acid (186), which after ring closure will lose CO2 and HjO to give 138 (Scheme 8). Compound 138 is also formed when n-benzoylbenzil (187) is treated with potassium hydroxide in ethanol a benzilic acid rearrangement may be the first step of the sequence. 

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