Page:1902 Encyclopædia Britannica - Volume 26 - AUS-CHI.pdf/777

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CHEMISTRY 721 activity. The formation of optically-active nitrogen com- nating between these two formulae, as well as in proving pounds foreseen by Le Bel and established by Pope and the correctness of the formula commonly assigned to Peachey, and the still more recent discovery of such com- glucose. The method he adopted consisted in, as it were, pounds derived from the metal tin and from sulphur by attaching a label to the CO group, and subsequently these latter chemists (Proc. Chem. Soc. 1900, p. 42; determining the position of the label. The label used was Trans. Chem. Soc. 1900, p. 1072), have afforded proof that carboxyl, C02H, the group characteristic of acids, which the doctrine of asymmetry may be extended to elements was attached by affixing hydrogen cyanide to the CO other than carbon, and it may be confidently expected that group and then hydrolysing the cyanogen group :— these are not the only cases in which it will be found to be /OH applicable. The extraordinary value of the doctrine of asym: CO + H.CN = C metry will be appreciated when its application to compounds X

CN such as those of the sugar group—which are all optically.OH active—is understood, especially when it is borne in mind ,OH

C(

2 + OH., = : C that prior to the introduction of the theory it was h-NR, X CN impossible to explain in any satisfactory manner several C02H cases of isomerism occurring in this group, and this too at To determine the position of the carboxyl group the acids a time when the number of compounds included in the were then reduced, i.e., the OH groups were displaced by group was far smaller than is now the case. hydrogen by means of hydrogen iodide, and they were thus Among the many investigations into minute structure converted into acids of the acetic series of the formula carried out in recent years, none ranks higher in import- CrHu02 (heptylic acids). The acid from glucose proved ance or is more full of interest than that of to be the normal acid, and that from fructose butylmethylGlucoses ^lsc^er on fhe sugars, in the course of which acetic acid, proving that the CO group in glucose was at he has been led not only to synthesize glucose, the end of the chain, but that it formed, as it were, the but also to prepare a large number of new isomeric hexoses, second link in fructose :— and to place their constitution beyond all doubt with the CH2(OH) ch3 CH3 aid of the van’t Hoff-Le Bel theory. As a monument of CH(OH) CH CH 2 2 experimental skill the inquiry stands unrivalled, and no CH(OH) CH2 CH2 better illustration can be given of the perfection to which CH(OH) CH2 CH2 analytic and synthetic methods have been carried by CH(OH) CH2 CH.C02H organic chemists. The carbohydrates—a class of comCH (OH) ch .co h CH 2 2 2 3 pounds of supreme importance on account of the part they Mannitol. Normal heptylic Butylmethylplay as structural and food materials in the economy of acid. acetic acid. plants and animals—stand in close genetic relationship, E. Fischer’s entry on the scene dates from the year 1884, and glucose (dextrose) being the end term of the series, and when he made the all-important discovery of phenylhydrthe product into which most of the more complex members azine, C6H5.NH.NH2 or Ph.NH.NH2. Although of the group are resolved by hydrolysis, has long attracted not the Rosetta stone which enabled him to Fischer’s the attention of chemists. At an early date it was dis- decipher the minute structure of glucose researcbescovered that both glucose and fructose (Isevulose)—the two and its congeners, this compound made possible for isomeric hexoses of the formula C6H1206 which are formed the first time the separation and identification of such on hydrolysing cane sugar—are derivatives of the paraffin compounds. Its use and value depend on the fact that hydrocarbon normal hexane, Cf)Hu, in which the six keto-compounds generally are converted by it into hydrcarbon atoms are known to be arranged just as the links azones, which are usually well-defined crystalline subare in a simple branchless chain. Both yield mannitol, stances : — C(.H140)J, a well-known natural product, on reduction.

CO + Ph.NH.NHo = : C.N.NHPh + OH.,.

Mannitol is proved to be a hexhydric alcohol, C6H8(OH)6, by its conversion into a hexanitrate, and as it is a In the case of the hexoses, which are readily oxidized, the highly stable compound (alcohols containing several action, however, usually proceeds a stage farther, an hydroxyl groups attached to one carbon atom being osazone being formed by the oxidation, at the expense of the unstable), there can be no doubt that the six atoms of phenylhydrazine, of the “ alcohol ” group contiguous to the oxygen which it contains, and which were originally hydrazo-group, and the action on the new keto-compound present in the hexoses, are each separately associated with thus produced of another molecule of phenylhydrazine; a carbon atom. When mannitol is distilled with a solution thus:— CH2(OH) CH2(OH) of hydrogen iodide, it is converted into hexylic iodide, CH2(OH) CH(OH) CH(OH) C0,H13I, which on further reduction yields the hydrocarbon, CH(OH) CH(OH) normal hexane. Glucose behaves as an aldehyde on CH(OH) CH(OH) CH(OH) oxidation, being converted into mbnobasic gluconic acid, OH(OH) CH(Ofl) GO so that one of the oxygen atoms is present as COH; C:N.NHPli C:N.NHPh CH:N.NHPh consequently its formula may be written :— CHO CH:KNHPh II. III. CH2(OH).CH(OH).CH(OH).CH(OH).CH(OH).COH. The first of these formula? represents the intermediate The behaviour of fructose, on the other hand, is that of a ketone rather than that of an aldehyde ; but two ketoses can product formed from glucosehydrazone; Ho. II., that derived in like manner from fructosehydrazone; Ho. III. be derived from an alcohol such as mannitol represents glucosazone, the final product whether glucose Mannitol, CH2(OH).CH(OH).CH(OH).CH(OH).CH(OH).CH2(OH) or fructose be used. The production of one and the same CHo(OH).CH(OH).CH(OH).CH(OH).CO.CH2(OH) Ketoses, CH substance from the two hexoses is a result of peculiar 2(OH).CH(OH).CH(OH).CO.CH(OH).CH2(OH) It was not until 1885 that Kiliani succeeded in discrimi- importance as bearing on their structure, for it will be obvious that it affords the proof that a greater part—the 1 For a full discussion of the doctrine and its consequences see four upper tiers, as it were—of their molecules is identi-’ ▼an’t Hoff’s Arrangement of Atoms in Space. English translation by cally constituted. Eiloart (Longmans, Green, and Co.). On reference to the formula of glucose, it will be noticed S. II.— 91 1