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218 THE CARBOHYDRATES.
Fructose does not reduce copper to the same extent as glucose.
Under similar conditions the reduction relationship is 100 : 92.08.
In detecting fructose and those varieties of sugar which yield fructose on
cleavage we make use of the following reaction, suggested by Seliwanoff which
consists in heating with hydrochloric acid and resorcinol. This depends upon
the formation of oxymethylfurfurol and is therefore obtained by all hexoses.
As the ketoses give about 20 per cent oxymethylfurfurol and the aldoses only
1 per cent the reaction is more readily obtained with the ketohexoses than with
the aldohexoses (v. Ekenstein and Blanksma, page 216). To a few cubic
centimeters of fuming hydrochloric acid add an equal volume of water and a small
quantity of the sugar solution or of the solid substance and a few crystals of
resorcinol, and apply heat. The liquid becomes a beautiful red, and gradually
a substance precipitates which is red in color and soluble in alcohol. According
to Ofnek 1
the mixture must not contain more than 12 per cent HC1, and the
boiling must not be continued longer than twenty seconds, if it is boiled for
a longer time and with more hydrochloric acid this reaction is also given with
the aldoses. R. and 0. Adler 2
perform the test with glacial acetic acid and a
drop of hydrochloric acid and some resorcinol, in which case a reaction with
aldoses is not obtained. Seliwanoff’s reaction, according to Rosin, 3
may
be made more delicate by a combination with the spectroscopic examination.
In regard to its use in urine examinations see Chapter XIV.
The naphtho-resorcinol reaction as suggested by B. Tollens and Rorive 4
can be carried out as follows: A few particles of the sugar and about the same
quantity of naphthoresorcinol are treated with about 10 cc. of a mixture of equal
volumes of water and concentrated hydrochloric acid of sp. gr. 1.19. This is
slowly heated to boiling over a low flame, and is continued for 1-3 minutes.
The fluid becomes more purple or violet than with Seliwanoff’s resorcin test.
The spectroscopic examination shows a faint band in the green.
According to Neuberg, 5
methylphenlhydrazine is an excellent substance
to use for the separation and detection of fructose, as it gives a characteristic
fructose methylphenylosazone. This osazone when recrystallized from alcohol
melts at 153°. It shows a dextrorotation of 1° 40’ when 0.2 gram of the osazone
is dissolved in 4 cc. pyridine and 6 cc. absolute alcohol.
Ofner has made objections to the use of methylphenylhydrazine in the detec-
tion of fructose. He has obtained the osazone from glucose and methylphenylhy-
drazine, although the osazone is formed much more quickly with fructose than
with glucose. Only when the separation of the osazone crystals with methyl-
phen}r
lhydrazine after the addition of acetic acid takes place within five hours
at ordinary temperatures is the presence of fructose positively proven (Ofner 6
).
The use of secondary asymmetric hydrazines as a general reagent for ketoses
and as a means of separation from aldoses is objected to by Ofner.
(/-Sorbinose (sorbin) is a ketose obtained from the juice of the berry of the
mountain ash under certain conditions. It is crystalline and levogyrate, and
is converted into c/-sorbite by reduction.
1
Monatshefte f. Chem., 25.
2
See footnote 6, p. 209.
3
Ber. d. d. chem. Gesellsch., 38.
* Ibid., 41, p. 1783 and Tollens, ibid., 41, p. 1788. See also Mandel and Neuberg,
Biochem. Zeitschr., 13.
1
Ibid., 35; also Neuberg and Strauss, ibid., 36.
6
Ibid., 37, and Zeitschr. f. physiol. Chem., 45.
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