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PENTOSE REACTIONS. 209
HC—CH
II II
from this its aldehyde, the furfurol HC C.CHO. The furfurol pass-
O
ing over, on distilling with hydrochloric acid, can be detected by the aid
of aniline-acetate or xylidine acetate paper, which is colored a beautiful
red by furfurol. In the quantitative estimation we can use the method
suggested by Tollens, which consists in converting the furfurol in the
distillate into phloroglucide by means of phloroglucin and weighing (see
Tollens and Krober, Grund, Bendix and Ebstein), or according to
Jolles l
by bisulphite and retitrating with iodine solution. In using
these methods it must be borne in mind that glucuronic-acid compounds
also yield furfurol under the same conditions. The two following pentose
reactions, as suggested by Tollens, are especially applicable.
The orcin-hydrochloric acid test. Mix with the solution or the substance
introduced into water an equal volume of concentrated hydrochloric acid, add
some orcin in substance, and heat. In the presence of pentoses the solution
becomes reddish-blue, then bluish-green, and on spectroscopic examination an
absorption-band is observed between C and D. If it is cooled and shaken with
amyl alcohol, a bluish-green solution which shows the same band is obtained.
The phloroglucin-hydrochloric acid test. This test is performed in the
same manner as the above, using phloroglucin instead of orcin. The solution
becomes cherry-red on heating and then becomes cloudy and hence a shaking out
with amyl alcohol is very necessary. The red amyl-alcohol solution shows an
absorption-band between D and E. The orcin test is better for several reasons
than the phloroglucin test (Salkowski and Neuberg 2
). In regard to the use
of these tests in urine examination see Chapter XIV.
Many modifications of these tests have been suggested. Brat 3
performs
the crcin reaction by the addition of NaCl and heating to only 90-95°. Bial 4
uses a hydrochloric acid containing ferric chloride for the orcin test and claims
to get a greater delicacy. On too strong and too long heating (l§-2 minutes),
when using this modification, a confusion with sugars of the six carbon series may
occur (Bial, van Leersum). 5
According to R. Adler and 0. Adler the phlo-
roglucin and orcin tests can be made with glacial acetic acid and a few drops
hydrochloric acid instead of with the hydrochloric acid alone. These investigators
also use a mixture of equal volumes of aniline and glacial acetic acid as a reagent
for pentoses. On the addition of a little pentose to the boiling mixture a beautiful
red color of furfurol-aniline acetate is obtained. A. Neumann 6
performs the
orcin test with glacial acetic acid and adds concentrated sulphuric acid drop
by drop. On following the exact instructions not only do the pentoses give
this reaction, but also glucuronic acid, glucose, and fructose give characteristic
1
Bendix and Ebstein, 1. c, which contains the literature; Jolles, Ber. d. d. chem.
Gesellsch., 39 and Zeitschr. f. anal. Chem., 46.
2
Salkowski, Zeitschr. f. physiol. Chem., 27; Neuberg, ibid., 31.
3
Zeitschr. f. klin. Med., 47.
4
Deutsch. med. Wochenschr., 1902 and 1903, and Zeitschr. f. klin. Med., 50.
5
Bial, Zeitschr. f. klin. Med., 50; van Leersum, Hofmeister’s Beitrage, 5.
6
R. and O, Adler, Pfliiger’s Arch., 106; A. Neumann, Berl. klin. Wochenschr.,
1904.
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