Full resolution (JPEG) - On this page / på denna sida - III. The Carbohydrates - 1. Monosaccharides - Pentoses (C5H10O5)
<< prev. page << föreg. sida << >> nästa sida >> next page >>
Below is the raw OCR text
from the above scanned image.
Do you see an error? Proofread the page now!
Här nedan syns maskintolkade texten från faksimilbilden ovan.
Ser du något fel? Korrekturläs sidan nu!
This page has never been proofread. / Denna sida har aldrig korrekturlästs.
210 THE CARBOHYDRATES.
colored solutions with special absorption-bands which can be made use of in
identifying the various sugars. Fr. Sachs has tested Bial’s test and has given
special precautions to prevent confusion with glucuronic acid. Jolles * pre-
cipitates (from urine) the pentoses as osazones, distills the precipitate with
hydrochloric acid, and tests the distillate with Bial’s reagent.
In performing the above two tests for pentose it must be borne in mind that
glucuronic acid gives the same reactions and also that the colors alone are not
sufficient. The spectroscopic examination must therefore never be omitted.
Both tests are to be considered as tests of detection rather than definite pentose
reactions, and therefore for a positive detection of pentoses we must prepare also
the osazones or other compounds.
Arabinoses. The pentose isolated by Neuberg from human urine
is r-arabinose. It can be isolated from the urine as the diphenylhydra-
zone, from which the arabinose can be separated by splitting with for-
maldehyde. The inactive r-arabinose seems to be the pentose regularly
occurring in pentosuria and thus far, in only one case, has /-arabinose
been found. /-Arabinose is said to pass into the urine after partaking of
certain fruits, such as plums, in large amounts (C. Barszczewski 2
).
The r-arabinose is crystalline, has a sweetish taste, and melts at
163-164° C. Its diphenylhydrazone, which, according to Neuberg
and Wohlgemuth,3
can be used in its quantitative estimation, melts
at 206° C, is insoluble in cold water and alcohol, but readily soluble
in pyridine. The osazone melts at 166-168° C.
The dextrorotatory /-arabinose is obtained by boiling gum arabic or
cherry gum with dilute sulphuric acid. The d-arabinose has been pre-
pared synthetically. The phenylosazone of /-arabinose melts at 160°.
The /-arabinose which crystallizes in plates or prisms melts at about
164°. The specific rotation is (a) D = +104.5°.
Xyloses. The /-xylose occurs extensively in the plant kingdom and
is prepared from wood-gum by the action of dilute acid. Xylose is
crystalline, melts at 150-153° C, dissolves very readily in water but
with difficulty in alcohol, is faintly dextrorotatory, (a) D = +18.1°, and
gives a phenylosazone which melts at 155-158° C, and according to
Tollens and Muther a diphenylhydrazone which melts at 107-108°.
According to Bertrand xylose can be transformed into xylonic acid,
CH2(OH)[CH(OH)]3COOH, by bromine-water and the brom-cadmium
compound or the brucine salt (Neuberg) of this acid is well suited for
the detection and isolation of /-xylose. On oxidation with nitric acid
the optically inactive trioxyglutaric acid, with a melting-point of 152° C.
is obtained.
1
Fr. Sachs, Biochem. Zeitschr., 1 and 2; Jolles, ibid., 2, Centralbl. f. inn. Med.,
1907. and Zeitschr. f. anal. Chem., 46.
2
Neuberg, Ber. d. d. chem. Gesellsch., 33; Barszczewski, Maly’s Jahrsb., 27, 733.
•Zeitschr. f. physiol. Chem., 35.
<< prev. page << föreg. sida << >> nästa sida >> next page >>
