Ketones bisulphite addition compounds

Certain ketones give bisulphite addition compounds. 

Bisulphite compounds of aldehydes and ketones. These substances are decomposed by dilute acids into the corresponding aldehydes or ketones with the liberation of sulphur dioxide. The aldehyde or ketone may be isolated by steam distillation or by extraction with ether. Owing to the highly reactive character of aldehydes, the bisulphite addition compounds are best decomposed with saturated sodium bicarbonate solution so um carbonate solution is generally employed for the bisulphite compounds of ketones. 

Aldehydes and Ketones. The best derivative from which an aldehyde can be recovered readily is its bisulphite addition compound, the main disadvantage being the lack of a sharp melting point. The aldehyde (sometimes in ethanol) is shaken with a cold saturated solution of sodium bisulphite until no more solid adduct separates. The adduct is filtered off, washed with a little water, then alcohol. A better reagent is freshly prepared saturated aqueous sodium bisulphite solution to which 75% ethanol is added to near-saturation. (Water may have to be added dropwise to render this solution clear.) With this reagent the aldehyde need not be dissolved separately in alcohol and the adduct is finally washed with alcohol. The aldehyde is recovered by dissolving the adduct in the least volume of water and adding an equivalent quantity of sodium carbonate (not sodium hydroxide) or concentrated hydrochloric acid to react with the bisulphite, followed by steam distillation or solvent extraction. 

Ketones. Ketones are more stable to oxidation than aldehydes and can be purified from oxidisable impurities by refluxing with potassium permanganate until the colour persists, followed by shaking with sodium carbonate (to remove acidic impurities) and distilling. Traces of water can be removed with type 4A Linde molecular sieves. Ketones which are solids can be purified by crystallisation from alcohol, toluene, or petroleum ether, and are usually sufficiently volatile for sublimation in vacuum. Ketones can be further purified via their bisulphite, semicarbazone or oxime derivatives (see p. 51). The bisulphite addition compounds are formed only by aldehydes and methyl ketones but they are readily hydrolysed in dilute acid or alkali. 

Aldehydes and simple ketones react with a saturated solution of sodium metabisulphite to yield crystalline bisulphite-addition compounds ... 

Aldehydes, ketones, alcohols Anion Ketones and aldehydes held as bisulphite addition compounds. Eluted with hot water and NaCl respectively. 

The student should note that ketones in class (1), t.c., those having the >CO group in the side chain, will form additive compounds with sodium bisulphite only if this >CO group is not directly joined to the benzene ring acetophenone therefore will not form such compounds, whereas benzyl methyl ketone, CaHsCHjCOCH, will do so. Many quinones, particularly ortho quinones such as phenanthraquinone, form additive compounds with sodium bisulphite. 

The aromatic halogenated ketones, unlike those of the aliphatic series, are quite stable compounds. Another difference is that the aromatic derivatives, although they contain a carbonyl group, form no additive compounds with bisulphite. ... 

For a given carbonyl compound, K will be influenced by the size of the nucleophile thus the value of K for addition of the very bulky bisulphite anion (S2O320, p. 213) to (MeCH2)2C=0 is only 4 x 10-4, compared with K = 38 for addition of HCN (above) to the very similar ketone, MeCH2COMe. The value of K is also influenced by the nature of the atom in the nucleophile that attacks the carbonyl carbon atom, and of the bond that is thereby formed as is observed in the following sequence for reaction with the same carbonyl compound ... 

Remarks on Sections 6 and 7.-—The method here described for the synthesis of cyanohydrins—treatment of the bisulphite compound of the aldehyde with potassium cyanide—cannot be used in all cases. Concentrated solutions of hydrocyanic acid or anhydrous hydrogen cyanide are often used. The general method for the synthesis of a-amino-acids, the nitriles of which are formed by the union of ammonium cyanide with aldehydes or ketones (Strecker), is to be contrasted with that for the synthesis of a-hydroxy acids. For additional amino-acid syntheses see Chap. VII. 2, p. 276. 

A carbonyl compound (an aldehyde or a ketone) can be separated from its admixture with non-carbonyl compounds by shaking the mixture with a saturated solution of sodium bisulphite. This treatment yields a crystalline addition bisulphite derivative of the carbonyl compound ... 

Acetone (CH 3 CO.CH 3 ), or dimethyl ketone, is formed when iso-propyl alcohol is oxidised with potassium bichromate and sulphuric. It is also produced in eonsiderable quantities during the dry distillation of wood, and many other organie compounds. Cmde wood spirit, which has been freed from acetic acid, consists in the main of a mixture of acetone and methyl- alcohol. The two substances may be roughly separated by the addition of ealeium chloride, whieh eombines with the methyl-alcohol. On subsequent distillation crude aeetone passes over, and may be purified by conversion into the bisulphite compound. 

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