Aldehyde bisulphite compounds

Sodium hyposulphite (hydrosulphite) is converted by aldehydes into aldehyde bisulphite compound and aldehyde sulphoxylate ... 

Alkali bisulphite compound of (a) aldehyde, (b) ketone Sulphonic acids. 

About 0-1 per cent, of hydroquinone should be added as a stabiliser since n-hexaldehyde exhibits a great tendency to polymerise. To obtain perfectly pure n-/iexaldehyde, treat the 21 g. of the product with a solution of 42 g. of sodium bisulphite in 125 ml. of water and shake much bisulphite derivative will separate. Steam distil the suspension of the bisulphite compound until about 50 ml. of distillate have been collected this will remove any non-aldehydic impurities together with a little aldehyde. Cool the residual aldehyde bisulphite solution to 40-50 , and add slowly a solution of 32 g. of sodium bicarbonate in 80 ml. of water, and remove the free aldehyde by steam distillation. Separate the upper layer of n-hexaldehyde, wash it with a little water, dry with anhydrous magnesium sulphate and distil the pure aldehyde passes over at 128-128-5°. 

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. 

Separations based upon differences in the chemical properties of the components. Thus a mixture of toluene and anihne may be separated by extraction with dilute hydrochloric acid the aniline passes into the aqueous layer in the form of the salt, anihne hydrochloride, and may be recovered by neutralisation. Similarly, a mixture of phenol and toluene may be separated by treatment with dilute sodium hydroxide. The above examples are, of comse, simple apphcations of the fact that the various components fah into different solubihty groups (compare Section XI,5). Another example is the separation of a mixture of di-n-butyl ether and chlorobenzene concentrated sulphuric acid dissolves only the w-butyl other and it may be recovered from solution by dilution with water. With some classes of compounds, e.g., unsaturated compounds, concentrated sulphuric acid leads to polymerisation, sulphona-tion, etc., so that the original component cannot be recovered unchanged this solvent, therefore, possesses hmited apphcation. Phenols may be separated from acids (for example, o-cresol from benzoic acid) by a dilute solution of sodium bicarbonate the weakly acidic phenols (and also enols) are not converted into salts by this reagent and may be removed by ether extraction or by other means the acids pass into solution as the sodium salts and may be recovered after acidification. Aldehydes, e.g., benzaldehyde, may be separated from liquid hydrocarbons and other neutral, water-insoluble hquid compounds by shaking with a solution of sodium bisulphite the aldehyde forms a sohd bisulphite compound, which may be filtered off and decomposed with dilute acid or with sodium bicarbonate solution in order to recover the aldehyde. 

Sulphate sulphite or sulphide may indicate a sulphate, sulphonate, mercaptan, or bisulphite compound of an aldehyde or ketone. 

Aldehydes are usually most easily separated from the essential oils in which they occur, by means of acid sodium sulphite. The oil—or the suitable fraction thereof— is well shaken for a time varying according to the nature of the aldehyde, with an equal volume of a saturated solution of sodium bisulphite, with a little ether added, in order to hinder the non-aldehydic portion of the oil from becoming occluded in the crystals of the bisulphite compound of the aldehyde. These crystals are separated and washed well with ether They are then decomposed by warming with a solution of sodium carbonate, and the regenerated aldehyde is extracted by means of ether. 

Cinnamic aldehyde, C HgO, is the principal odorous constituent of dnnamon and cassia oils, and is manufactured to a considerable extent, artificially. It can be extracted from the oils in which it occurs by means of sodium bisulphite, the sodium bisulphite compound being decomposed with dilute sulphuric acid, and distilled in a current of steam. The preparation of artificial cinnamic aldehyde, which is used in perfumery as a substitute for the natural oils, is usually carried out. by a condensation of benzaldehyde and acetaldehyde, according to the following reaction —... 

There is a solid aubepine met with in commerce, which appears usually to be the sodium bisulphite compound of anisic aldehyde. 

The distillate from the steam distillation is twice shaken with not too much ether, and the ethereal extract, if necessary after concentration, is transferred to a wide-mouthed bottle, into which technical sodium bisulphite solution is poured in small portions with stirring (a glass rod is used) so that the aldehyde addition compound formed sets to a thick paste. The bottle is then stoppered and vigorously shaken the stopper is removed from time to time until all the benzaldehyde has entered into combination. (Odour ) The paste is now filtered with suction, and the solid on the funnel, after washing with ether, is at once decomposed by mixing it with an excess of sodium carbonate solution the liberated aldehyde is removed without delay by steam distillation. The distillate is extracted with ether, the extract is dried over a little calcium chloride, the ether is removed by distillation, and the benzaldehyde which remains is likewise distilled. Boiling point 179°. Yield 35-40 g. (70 per cent of the theoretical). 

The other reactions of the aldehydes, which are extraordinarily reactive substances, need only he mentioned here. Such reactions are reduction to alcohols, formation of hydrazones, oximes, semicarbazones, bisulphite compounds, acetals and cyanohydrins (by addition of hydrogen cyanide). 

Since the bisulphite compounds are decomposed into their constituents by wanning with sodium carbonate solution or with dilute acids, they are particularly useful for enabling aldehydes (and ketones) to be separated from mixtures with other substances. 

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. 

The distillate is at once extracted with ether and the extract, after having been separated from the water, is heated on the water bath until most of the ether has distilled. The residue, which contains unchanged phenol as well as the salicylaldehyde, is now vigorously shaken in a small glass-stoppered bottle with two volumes of concentrated commercial sodium bisulphite solution. A thick paste of the bisulphite compound of the aldehyde is formed. After this paste has stood for from half an hour to one hour the bisulphite compound is separated by filtration at the pump, pressed well on the filter funnel, and washed several times, first with alcohol and finally with ether, until completely free from adherent phenol. The crystals (small plates, iridescent like mother-of-pearl) are then decomposed with dilute sulphuric acid in a small round-bottomed flask whi( h is fitted with an air condenser and gently warmed on the water bath. After the liquid thus produced has cooled, the aldehyde which separates is extracted with ether and the ethereal solution is dried with anhydrous sodium sulphate. The pure aldehyde which remains when the ether is evaporated distils at 196°. The yield amounts to 10-12 g. 

Reaction XXXVIII. (c) Action of Hydrogen Cyanide on Aldehydes and Ketones and Hydrolysis of the Cyanohydrins so formed. (B., 14, 235 C. Z., (1896), 90 C., (1900), I., 402.)—As is explained under Reaction L, aliphatic and aromatic aldehydes and ketones or their bisulphite compounds react with hydrogen cyanide to form cyanohydrins (a-hydroxy-nitriles). These are readily hydrolysed to a-hydroxy-acids, for the preparation of which the above reaction is often directly used since the isolation of the nitrile is unnecessary. 

It is noteworthy that it is often preferable to use the bisulphite compound of the aldehyde rather than the aldehyde itself (see p. 156). The small quantity of ammonia used above to help the reaction may do so by the momentary formation of the ammonia compound of the aldehyde. 

Nascent hydrogen cyanide formed by the action of hydrochloric acid on potassium cyanide is usually employed except with sugars, where hydrocyanic acid and a little ammonia are used. The manner in which ammonia promotes the action, and the better results obtained by the use of the bisulphite compound of the aldehydes and potassium cyanide, have been dealt with under Reaction XXXVIII. (c). 

The action of hydrogen cyanide on the aldehyde itself, and the action of potassium cyanide on the bisulphite compound, are directly contrasted in the following preparation. 

Method II.—50 c.cs. (excess) of a saturated solution of sodium bisulphite are added to 15 gms. (1 mol.) of freshly distilled benzaldehyde in a beaker, and the whole stirred until the mass is semi-solid owing to the separation of the bisulphite compound of the aldehyde. The latter is filtered off at the pump, pressed, and washed with a little water and alcohol. It is then... 

Better results are here obtained by using the bisulphite compound of the aldehyde or ketone (cf. Reaction L. (a)). 

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