Researches on Cellulose Part 15

M. KRuGER (Inaug.-Diss., Gottingen, 1895).

~COMPARISON OF METHODS OF ESTIMATING FURFURAL AS HYDRAZONE AND PHLOROGLUCIDE.~

The author traces the development of processes of estimating furfural (1) by precipitation with ammonia (furfuramide), (2) by volumetric estimation with standardised phenylhydrazine, (3) by weighing the hydrazone.

In 1893 (Chem. Ztg. 17, 1745) Hotter described a method of quant.i.tative condensation with pyrogallol requiring a temperature of 100-110 for two hours. The insoluble product collected, washed, dried at 103, and weighed, gives a weight of 1.974 grm. per 1 grm. furfural.

Councler subst.i.tutes phloroglucinol for pyrogallol, with the advantage of doing away with the digestion at high temperature. (_Ibid._ 18, 966.) This process, requiring the presence of strong HCl, has the advantage of being applied directly to the acid distillate, in which form furfural is obtained as a product of condensation of pentoses, &c. A comparative investigation was made, precipitating furfural (a) as hydrazone in presence of acetic acid, and (b) as phloroglucide in presence of HCl (12 p.ct). In (a) by varying the weights of known quant.i.ties of furfural, and using the factor, hydrazone 0.516 [+ 0.0104] in calculating from the weights of precipitates obtained, the maximum variations from the theoretical number were +1.71 and -1.74. In (b) it was found necessary to vary the factor from 0.52 to 0.55 in calculating from phloroglucide to furfural. The greatest _total_ range of variation was found to be 2.5 p.ct. The phenol process is therefore equally accurate, has the advantages above noted, and, in addition, is less liable to error from the pressure in the distillates obtained from vegetable substances of volatile products, e.g. ketonic compounds, accompanying the furfural.

This method has been criticised by Helbel and Zeisel [Sitz.-ber, Wiener Akad. 1895, 104, ii. p. 335] on two grounds of error, viz. (1) the presence of diresorcinol in all ordinary preparations of phloroglucinol, and (2) changes in weight of the precipitate of phloroglucide on drying.

The process was carried out comparatively with ordinary preparations, and with specially pure preparations of the phenol. The quant.i.tative results were identical. The criticisms in question are therefore dismissed. Although the process is to be recommended for its simplicity and the satisfactory concordance of results it is to be noted that it rests upon an empirical basis, since the phloroglucide is not formed by the simple reaction 2 [C_{5}H_{4}O_{2} + C_{6}H_{6}O_{3}] - H_{2}O = C_{22}H_{18}O_{9}, but appears to have the composition C_{16}H_{12}O_{6}.

In part ii. of this paper the author discusses the question of the probable extent in the sense of diversity of const.i.tution of furfural-yielding const.i.tuents of plant-tissues. Glucoson was isolated from glucosazon, and found to yield 2.9-3.6 p.ct. furfural. Gluconic acid distilled with hydrochloric acid gave traces of furfural; so also with sulphuric acid and manganic oxide.

Starch was oxidised with permanganate, and a mixture of products obtained of which one gave a characteristic violet colouration with phloroglucol, with an absorption-band at the D line. On distilling with HCl furfural was obtained in some quant.i.ty. The product in question was found to be very sensitive to the action of bases, and was destroyed by the incidental operation of neutralising the mixture of oxidised products with calcium carbonate. It was found impossible to isolate the compound.

UNTERSUCHUNGEN UEBER DIE PENTOSANBESTIMMUNG MITTELST DER SALZSaURE-PHLORO-GLUCIN-METHODE.[8]

E. KRoBER (Journ. f. Landwirthschaft, 1901, 357).

~INVESTIGATION OF THE HYDROCHLORIC ACID-PHLOROGLUCINOL METHOD OF DETERMINING PENTOSANES.~

This paper is the most complete investigation yet published of the now well-known method of precipitating and estimating furfural in acid solution by means of the trihydric phenol. In the last section of the paper is contained the most important result, the proof that the insoluble phloroglucide is formed according to the reaction

C_{5}H_{4}O_{2} + C_{6}H_{6}O_{3} - 2H_{2}O = C_{11}H_{6}O_{3},

also, by varying the proportions of the pure reagents interacting, that the condensation takes place invariably according to this equation.

Incidentally the following points were also established:--The solubility of the phloroglucide, under the conditions of finally separating in a condition for drying and weighing, is 1 mgr. per 100 c.c. of total solution, made up of the original acid solution, in which the precipitation takes place, and the wash-water required to purify from the acid. The phloroglucide is hygroscopic, and must be weighed out of contact with the air. The presence of diresorcinol is without influence on the result, provided a sufficient excess of actual phloroglucinol is employed. Thus even with a preparation containing 30 p.ct. of its weight of diresorcinol the influence of the latter is eliminated, provided a weight be taken equal to twice that of the furfural to be precipitated.

The phenol must be perfectly dissolved by warming with dilute HCl (1.06 sp.gr.) before adding to the furfural solution. For collecting the precipitate of phloroglucide the author employs the Gooch crucible.

The paper contains a large number of quant.i.tative results in proof of the various points established, and concludes with elaborate tables, giving the equivalents in the known pentoses and their anhydrides for any given weight of phloroglucide from 0.050 to 0.300 grm.

UEBER DEN PENTOSAN-GEHALT VERSCHIEDENER MATERIALIEN.

B. TOLLENS and H. GLAUBITZ (J. fur Landwirthschaft, 1897, 97).

~ON THE PENTOSANE CONSt.i.tUENTS OF FODDER-PLANTS AND MALT.~

(p. 171) (a) The authors have re-determined the yield of furfural from a large range of plant-products, using the phloroglucol method. The numbers approximate closely to those obtained by the hydrazone method.

The following may be cited as typical:

Substance Furfural p.ct.

Rye (Gottingen) 6.03 Wheat (square head) 4.75 Barley (peac.o.c.k) 4.33 Oats (Gottingen) 7.72 Maize (American) 3.17 Meadow hay 11.63 Bran (wheat) 13.06 Malt 6.07 Malt-sprouts 8.56 Sugar-beet (exhausted) 14.95

(b) A comparison of wheat with wheat bran, &c. was made by grinding in a mortar and 'bolting' the flour through a fine silk sieve. The results showed:

Furfural p.ct.

Original wheat 4.75 Fine flour 1.73 Bran (24 p.ct. of wheat) 11.25 Wheat-bran of commerce 13.06

It is evident that the pentosanes of wheat are localised in the more resistant tissues of the grain.

(c) An investigation of the products obtained in the a.n.a.lytical process for 'crude fibre' gave the following:

(1) In the case of brewers' grains:

100 grms. grains gave furfural = 29.43 pentosane --------------- 20 " crude fibre " = 2.52 Acid extract " = 22.76 Alkali " " = 1.20 Deficiency from total of original grains 2.95 -----

29.43

(2) In the case of meadow hay:

The crude fibre (30 p.ct.) obtained retained about one fourth (23.63 p.ct.) of the total original pentosanes.

(d) An investigation of barley-malt, malt-extract or wort, and finished beer showed the following: An increase of furfuroids in the process of malting, 100 pts. barley with 7.97 of 'pentosane' yielding 82 of malt with 11.18 p.ct. 'pentosane'; confirming the observations of Cross and Bevan (Ber. 28, 2604). Of the total furfuroids of malt about 1/4 are dissolved in the mas.h.i.+ng process. In a fermentation for lager beer it was found that about /10 of the total furfuroids of the malt finally survive in the beer; the yield of furfural being 2.92 p.ct. of the 'total solids' of the beer. In a 'Schlempe' or 'pot ale,' from a distillery using to 1 part malt 4 parts raw grain (rye), yield of furfural was 9 p.ct. of the total solids.

In a general review of the relations.h.i.+ps of this group of plant-products it is pointed out that they are largely digested by animals, and probably have an equal 'a.s.similation' value to starch. They resist alcoholic fermentation, and must consequently be taken into account as const.i.tuents of beers and wines.

UEBER DAS VERHALTEN DER PENTOSANE DER SAMEN BEIM KEIMEN.[9]

A. SCHoNE and B. TOLLENS (Jour. f. Landwirthschaft, 1901, 349).

~BEHAVIOUR OF PENTOSANES OF SEEDS IN GERMINATION.~

The authors have investigated the germination of barley, wheat, and peas, in absence of light, and generally with exclusion of a.s.similating activity, to determine whether the oxidation with attendant loss of weight, which is the main chemical feature of the germination proper, affects the pentosanes of the seeds. The following are typical of the quant.i.tative results obtained, which are stated in absolute weights, and not percentages.

_____________________________________________________________ Original seed Malt or Pentosane in germinated product _______________ A B A B ________ _______________ ____________________ _______ _______ Barley 500.00 434.88 39.58 40.38 " 500.00 442.26 40.52 41.17 Peas 300.00 286.60 15.25 15.97 ________ _______________ ____________________ _______ _______

The authors conclude generally that there is a slight absolute increase in the pentosanes, and that the pentosanes do not belong to those reserve materials which undergo destructive oxidation during germination.

In this they confirm the previously published results of De Chalmot, Cross and Bevan, and Gotze and Pfeiffer.

UEBER DEN GEHALT DER BAUMWOLLE AN PENTOSAN.

H. SURINGAR and B. TOLLENS (Ztschr. angew. Chem., 1897, I).

~PENTOSANE CONSt.i.tUENTS OF COTTON.~

(p. 290) It has been stated by Link and Voswinkel (Pharm. Centralhalle, 1893, 253), that raw cotton yields 'wood gum' as a product of hydrolysis. The authors were unable to obtain any pentoses as products of acid hydrolysis of raw cotton, and traces only of furfural-yielding carbohydrates. They conclude that raw cotton contains no appreciable quant.i.ty of pentosane.

FOOTNOTES:

[8] This paper appears during the printing of the author's original MS.