Glucosazone

Now since the configuration of carbon atoms 3, 4 and 5 of glucose and fructose art identical, it folhjws that glucosazone and fructosazone are identical in all respects. The osazone is formed however more rapidly from fructose than from glucose, and this difference in rate of formation may be used to distinguish the two sugars, provided the reactions are carried out under strictly parallel conditions (pp. 138, 338). 

Both maltose and lactose, being reducing sugars, give osazones which differ from one another and from glucosazone in crystalline form. Sucrose (G-r-r-F), having no potential aldehyde or ketone grouping, does not form an osazone. 

Glucosazone is only slightly soluble in boiling ethanol or methylated spirit for recrystallisation therefore it is sufficient to place about 0 5 g. of the crude material in a 150 ml. flask fitted... 

Then filter the remainder of the product at the pump, drain and dry. The glucosazone is thus obtained as bright yellow crystals, m.p. 204° with decomposition. 

Osazone formation. The preparation of glucosazone has already been given (p. 137). It may be carried out on a small scale by either of the following methods, according as (a) the phenyl hydrazine base, or (Z>) one of its salts, is used. 

Hydrolysis by acids. Sucrose is readily hydrolysed by dilute acids. Dissolve 0 5 g. of sucrose in 5 ml. of water, add 2 ml. of dil. H2SO4 and heat in a boiling water-bath for 5 minutes. Cool and show that the solution has reducing properties, and will form glucosazone. Note that the excess of acid must be neutralised before carrying out the reduction tests. 

Osazone formation. Forms an osazone, m.p. 206 (see however footnote, p. 140) this osazone, unlike glucosazone, is soluble in hot water. See p. 139 for preparation. Examine the crystals under the microscope and note the sheaves of plates, not needles (Fig. 63(B),... 

Hydrolysis by acids. Place 15 ml. of starch solution in a boiling-tube, add I ml. of cone. HCl, mix well and place in a boiling water-bath for 20 minutes. Cool and add 2 drops of iodine solution to i ml. of the solution no blue coloration is produced. On the remainder, perform tests for glucose in particular show that glucosazone can be formed. Neutralise the excess of acid before carrying out these tests. (Note that a more concentrated acid is required to hydrolyse starch than to hydrolyse the disaccharides, such as sucrose.)... 

At the end of 30 minutes treat the mixture in A as follows Dissolve 8 ml. of glacial acetic acid in 10 ml. of water, add 4 ml. of phenylhydra-zine and mix well in order to obtain a clear solution. Add this to the solution in A and mix thoroughly a slightly cloudy solution may be obtained, but this will clear on heating. Place the mixture in a boiling water-bath and note the formation of j ellow crystals of glucosazone after about 15 minutes. At the end of about i hour, cool, filter off the precipitate and identify as directed on p. 139. 

At the end of about an hour,f filter the solution and tfansfer 20 ml. of the clear filtrate to a boiling-tube. Dissolve 2 5 ml. of phenylhydrazine in 3 ml. of glacial acetic acid diluted with 3 ml. of water, and add this solution to that in the boiling-tube. Mix well and place the tube in a boiling water-bath. After about 15 minutes, crystals of glucosazone begin to separate. At the end of about i hour, filter off the precipitate and identify (p. 319). 

Phenylhydrazinc, as hydrochloride solution plus sodium acetate, reacts with polyhydroxy aldehydes or ketones yielding osazones or diphenyl-hydrazones, yellow solids, of definite melting point and utilized in identification of sugars, e.g.. phenyl-d-glucosazone. CH OH (CHOH), C (NNHC6H5)CH (NNHCftH,) plus aniline C6H5NH plus NH,... 

Many of the simpler sugars react after this manner, forming osazones, which have characteristic appearances under the microscope, and are of special value for identification purposes. (J. C. S., 125, 222.) Preparation 249.—Glucosazone. 

Several mechanisms34 have been proposed for this reaction. That of Weygand,36 in which an Amadori rearrangement is proposed, has considerable merit.37 Illustrations of unusual osazone formation are described by Bonner and Drisko.38 When phenyl /S-D-xylopyranosyl sulfone (XXII) or /J-D-glucopyranosyl sulfone (XXIV) is oxidized by periodic acid, a dialdehyde oxidation product (XXIII or XXV), which is susceptible toward further oxidation, is obtained. The reaction of XXIII or XXV with phenylhydrazine yields glyoxal phenylosazone and benzenesulfinic acid. Surprisingly, both XXII and XXIII react with phenylhydrazine to form D-xylosazone and D-glucosazone, respectively. 

Very little conclusive evidence for the position of the methyl group in 2-methyl-D-mannose is available. Pacsu and Trister4 showed that the sugar reacted with phenylhydrazine in the cold to give a phenylhydrazone but not a phenylosazone. More drastic conditions were required to form the phenylosazone, during which reaction the methyl group was lost with the formation of D-glucosazone. 

The structure of this sugar was established as follows (a) reaction with phenylhydrazine yielded 4-methyl-D-glucosazone 11 (b) oxidation (HOBr) yielded a methylmannonolactone, which exhibited the properties that are characteristic of 8-lactones.7... 

Watters, Hockett and Hudson1 have prepared a non-crystalline monomethylmannose which forms an osazone with the same properties as those of 6-methyl-n-glucosazone. The synthesis was achieved by methylation of methyl 2,3,4-triacetyl-a-D-mannopyranoside, followed by hydrolysis. Schmidt and Heiss,13 studying the epimerization of 6-methyl-D-gluconic acid, have claimed to have isolated the phenyl-hydrazide of 6-methyl-n-mannonic acid. 

---