Researches on Cellulose Part 9

The oxycellulose, after purification, dried at 110, gave the following a.n.a.lytical numbers:

C 43.64 43.78 43.32 43.13 H 6.17 6.21 5.98 6.08

Its compound with phenylhydrazine (_loc. cit._) gave the following a.n.a.lytical numbers:

N 0.78 0.96 0.84

(2) The reagents were as in (1), but the conditions varied by pa.s.sing a stream of carbonic acid gas through the solution contained in a flask, until Cl compounds ceased to be given off. The a.n.a.lysis of the purified oxycellulose gave C 43.53, H 6.13.

(3) The conditions were as in (2), but a much stronger hypochlorite solution--viz. 12B.--was employed. The yield of oxycellulose precipitated from solution in soda lye (10 p.ct. NaOH) was 45 p.ct.

There was only a slight residue of unattacked cellulose. The a.n.a.lytical numbers obtained were:

Oxycellulose C 43.31 43.74 43.69 " H 6.47 6.42 6.51 ________________________

Phenylhydrazine compound N 0.62 0.81

B. _Oxidation by permanganate_ (KMnO_{4}). (1) The cellulose 16 grms.

was treated with 1100 c.c. of a 1 p.ct. solution of KMnO_{4} in successive portions. The MnO_{2} was removed from time to time by digesting the product with a dilute sulphuric acid (10 p.ct.

H_{2}SO_{4}). The oxycellulose was purified as before, yield 40 p.ct.

a.n.a.lytical numbers:

Oxycellulose C 42.12 42.9 " H 6.20 6.11 ________________________

Phenylhydrazine compound N 1.35 1.08 1.21

(2) The cellulose (16 grms.) was digested 14 days with 2500 c.c. of 1 p.ct. KMnO_{4} solution. The purified oxycellulose was identical in all respects with the above: yield 40 p.ct. C 42.66, H 6.19.

(3) The cellulose (16 grms.) was heated in the water-bath with 1600 c.c.

of 15 p.ct. H_{2}SO_{4} to which were added 18 grms. KMnO_{4}. The yield and composition of the oxycellulose was identical with the above. It appears from these results that the oxidation with hypochlorites acids 1 atom of O to 4-6 of the unit groups C_{6}H_{10}O_{5}; and the oxidation with permanganate 2 atoms O per 4-6 units of C_{6}H_{10}O_{5}. The molecular proportion of N in the phenylhydrazine residue combining is fractional, representing 1 atom O, i.e. 1 CO group reacting per 4 C_{36}H_{60}O_{31} and 6 C_{24}H_{49}O_{21} respectively, a.s.suming the reaction to be a hydrazone reaction.

Further investigations of the oxycelluloses by treatment with (a) sodium amalgam, (b) bromine (water), and (c) dilute nitric acid at 110, led to no positive results.

By treatment with alcoholic soda (NaOH) the products were resolved into a soluble and insoluble portion, the properties of the latter being those of a cellulose (hydrate).

_Molecular weight of cellulose and oxycellulose._--The author endeavours to arrive at numbers expressing these relations by converting the substances into acetates by Schutzenberger's method, and observing the boiling-points of their solution in nitrobenzene.

FERMENTATION OF CELLULOSE

V. OMELIANSKI (Compt. Rend., 1897, 125, 1131-1133).

Pure paper was allowed to ferment in the presence of calcium carbonate at a temperature of 35 for 13 months. The products obtained from 3.4743 grams of paper were: acids of the acetic series, 2.2402 grams; carbonic anhydride, 0.9722 grams; and hydrogen, 0.0138 gram. The acids were chiefly acetic and butyric acid, the ratio of the former to the latter being 1.7 : 1. Small quant.i.ties of valeric acid, higher alcohols, and odorous products were formed.

The absence of methane from the products of fermentation is remarkable, but the formation of this gas seems to be due to a special organism readily distinguishable from the ferment that produces the fatty acids.

This organism is at present under investigation.

(p. 75) ~Const.i.tution of Cellulose.~--It may be fairly premised that the problem of the const.i.tution of cellulose cannot be solved independently of that of molecular aggregation. We find in effect that the structural properties of cellulose and its derivatives are directly connected with their const.i.tution. So far we have only a superficial perception of this correlation. We know that a fibrous cellulose treated with acids or alkalis in such a way that only hydrolytic changes can take place is converted into a variety of forms of very different structural characteristics, and these products, while still preserving the main chemical characteristics of the original, show when converted into derivatives by simple synthesis, _e.g._ esters and sulphocarbonates, a corresponding differentiation of the physical properties of these derivatives, from the normal standard, and therefore that the new reacting unit determines a new physical aggregate. Thus the sulphocarbonate of a 'hydrocellulose' is formed with lower proportions of alkaline hydrate and carbon disulphide, gives solutions of relatively low viscosity, and, when decomposed to give a film or thread of the regenerated cellulose, these are found to be deficient in strength and elasticity. Similarly with the acetate. The normal acetate gives solutions of high viscosity, films of considerable tenacity, and when those are saponified the cellulose is regenerated as an unbroken film.

The acetates of hydrolysed celluloses manifest a retrogradation in structural and physical properties, proportioned to the degree of hydrolysis of the original.

We may take this opportunity of pointing out that the celluloses not only suggest with some definiteness the connection of the structural properties of visible aggregates--that is, of matter in the ma.s.s--with the configuration of the chemical molecule or reacting unit, but supply unique material for the actual experimental investigation of the problems involved. Of all the 'organic' colloids cellulose is the only one which can be converted into a variety of derivative forms, from each of which a regular solid can be produced in continuous length and of any prescribed dimensions. Thus we can compare the structural properties of cellulose with those of its hydrates, nitrates, acetates, and benzoates, in terms of measurements of breaking strain, extensibility, elasticity.

Investigations in this field are being prosecuted, but the results are not as yet sufficiently elaborated for reduction to formulae. One striking general conclusion is, however, established, and that is that the structural properties of cellulose are but little affected by esterification and appear therefore to be a function of the special arrangement of the carbon atoms, i.e. of the molecular const.i.tution.

Also it is established that the molecular aggregate which const.i.tutes a cellulose is of a resistant type, and undoubtedly persists in the solutions of the compounds.

It may be urged that it is superfluous to import these questions of ma.s.s-aggregation into the problem of the chemical const.i.tution of cellulose. But we shall find that the point again arises in attempting to define the reacting unit, which is another term for the molecule. In the majority of cases we rely for this upon physical measurements; and in fact the purely chemical determination of such quant.i.ties is inferential. Attempts have been made to determine the molecular weights of the cellulose esters in solution, by observations of depression of solidifying and boiling-points. But the numbers have little value. The only other well-defined compound is the sulphocarbonate. It has been pointed out that, by successive precipitations of this compound, there occurs a continual aggregation of the cellulose with dissociation of the alkali and CS residues and it has been found impossible to a.s.sign a limit to the dissociation, i.e. to fix a point at which the transition from soluble sulphocarbonate to insoluble cellulose takes place.

On these grounds it will be seen we are reduced to a somewhat speculative treatment of the hypothetical ultimate unit group, which is taken as of C_{6} dimensions.

As there has been no addition of experimental facts directly contributing to the solution of the problem, the material available for a discussion of the probabilities remains very much as stated in the first edition, pp. 75-77. It is now generally admitted that the tetracetate _n_ [C_{6}H_{6}O.(OAc)_{4}] is a normal cellulose ester; therefore that four of the five O atoms are hydroxylic. The fifth is undoubtedly carbonyl oxygen. The reactions of cellulose certainly indicate that the CO- group is ketonic rather than aldehydic. Even when attacked by strong sulphuric acid the resolution proceeds some considerable way before products are obtained reducing Fehling's solution. This is not easily reconcilable with any polyaldose formula.

Nor is the resistance of cellulose to very severe alkaline treatments.

The probability may be noted here that under the action of the alkaline hydrates there occurs a change of configuration. Lobry de Bruyn's researches on the change of position of the typical CO- group of the simple hexoses, in presence of alkalis, point very definitely in this direction. It is probable that in the formation of alkali cellulose there is a const.i.tutional change of the cellulose, which may in effect be due to a migration of a CO- position within the unit group. Again also we have the interesting fact that structural changes accompany the chemical reaction. It is surprising that there should have been no investigation of these changes of external form and structure, otherwise than as ma.s.s effects. We cannot, therefore, say what may be the molecular interpretation of these effects. It has not yet been determined whether there are any intrinsic volume changes in the cellulose substance itself: and as regards what changes are determined in the reacting unit or molecule, we can only note a fruitful subject for future investigation. _A priori_ our views of the probable changes depend upon the a.s.sumed const.i.tution of the unit group. If of the ordinary carbohydrate type, formulated with an open chain, there is little to surmise beyond the change of position of a CO- group. But alternative formulae have been proposed. Thus the tetracetate is a derivative to be reckoned with in the problem. It is formed under conditions which preclude const.i.tutional changes within the unit groups.

The temperature of the main reaction is 30-40, the reagents are used but little in excess of the quant.i.tative proportions, and the yields are approximately quant.i.tative. If now the derivative is formed entirely without the hydrolysis the empirical formula C_{6}H_{6}O.(OAc)_{4} justifies a closed-ring formula for the original viz.

CO<[choh]_{4}>CH_{2}; and the preference for this formula depends upon the explanation it affords of the aggregation of the groups by way of CO-CH_{2} synthesis.

The exact relationship of the tetracetate to the original cellulose is somewhat difficult to determine. The starting-point is a cellulose hydrate, since it is the product obtained by decomposition of the sulphocarbonate. The degree of _hydrolysis_ attending the cycle of reactions is indicated by the formula 4 C_{6}H_{10}O_{5}.H_{2}O. It has been already shown that this degree of hydrolysis does not produce molecular disaggregation. If this hydrate survived the acetylation it would of course affect the empirical composition, i.e. chiefly the carbon percentage, of the product. It may be here pointed out that the extreme variation of the carbon in this group of carbohydrate esters is as between C_{14}H_{20}O_{10} (C = 48.3 p.ct.) and C_{14}H_{18}O_{9} (C = 50.8 p.ct.) i.e. a tetracetate of C_{6}H_{12}O_{6} and C_{6}H_{10}O_{5} respectively. In the fractional intermediate terms it is clear that we come within the range of ordinary experimental errors, and to solve this critical point by way of ultimate a.n.a.lysis must involve an extended series of a.n.a.lyses with precautions for specially minimising and quantifying the error. The determination of the acetyl by saponification is also subject to an error sufficiently large to preclude the results being applied to solve the point. While, therefore, we must defer the final statement as to whether the tetracetate is produced from or contains a partly hydrolysed cellulose molecule, it is clear that at least a large proportion of the unit groups must be acetylated in the proportion C_{6}H_{6}O.(OAc)_{4}.

It has been shown that by the method of Franchimont a higher proportion of acetyl groups can be introduced; but this result involves a destructive hydrolysis of the cellulose: the acetates are not derivatives of cellulose, but of products of hydrolytic decomposition.

It appears, therefore, that with the normal limit of acetylation at the tetracetate the aggregation of the unit groups must depend upon the CO- groups and a ring formula of the general form CO<[choh]_{4}>CH_{2} is consistent with the facts.

Vignon has proposed for cellulose the const.i.tutional formula

O------CH O [CHOH]_{3} / CH_{2}-CH/

with reference to the highest nitrate, and the decomposition of the nitrate by alkalis with formation of hydroxypyruvic acid. While these reactions afford no very sure ground for deductions as to const.i.tutional relationships, it certainly appears that, if the aldose view of the unit group is to be retained, this form of the anhydride contains suggestions of the general tendency of the celluloses on treatment with condensing acids to split off formic acid in relatively large quant.i.ty [Ber. 1895, 1940]; the condensation of the oxycelluloses to furfural; the non-formation of the normal hydroxy-dicarboxylic acids by nitric acid oxidations. Indirectly we may point out that any hypothesis which retains the polyaldose view of cellulose, and so fails to differentiate its const.i.tution from that of starch, has little promise of progress.

The above formula, moreover, concerns the a.s.sumed unit group, with no suggestion as to the mode of aggregation in the cellulose complex. Also there is no suggestion as to how far the formula is applicable to the celluloses considered as a group. In extending this view to the oxycelluloses, Vignon introduces the derived oxidised group

CHO.(CHOH)_{3}.CH . CO _O__

--of which one is apportioned to three or four groups of the cellulose previously formulated: these groups in condensed union together const.i.tute an oxycellulose.

These views are in agreement with the experimental results obtained by Faber and Tollens (p. 71). They regard the oxycelluloses as compounds of 'celloxin' C_{6}H_8{O}_{6} with 1-4 mols. unaltered cellulose; and the former they particularly refer to as a lactone of glycuronic acid. But on boiling with lime they obtain dioxybutyric and isosaccharinic acids; both of which are not very obviously related to the compounds formulated by Vignon. We revert with preference to a definitely ketonic formula, for which, moreover, some farther grounds remain to be mentioned. In the systematic investigation of the nitric esters of the carbohydrates (p.

41) Will and Lenze have definitely differentiated the ketoses from the aldoses, as showing an internal condensation accompanying the ester reaction. Not only are the OH groups taking part in the latter consequently less by two than in the corresponding aldoses, but the nitrates show a much increased stability. This would give a simple explanation of the well-known facts obtaining in the corresponding esters of the normal cellulose. We may note here that an important item in the quant.i.tative factors of the cellulose nitric ester reaction has been overlooked: that is, the yield calculated to the NO_{3} groups fixed. The theoretical yields for the higher nitrates are

Yield p.ct. N p.ct.

of cellulose of nitrate Pentanitrate 169 12.7 Hexanitrate 183 14.1

From such statistics as are recorded the yields are not in accordance with the above. There is a sensible deficiency. Thus Will and Lenze record a yield of 170 p.ct. for a product with 13.8 p.ct. N, indicating a deficiency of about 10 p.ct. As the by-products soluble in the acid mixture are extremely small, the deficiency represents approximately the water split off by an internal reaction. In this important point the celluloses behave as ketoses.

In the lignocelluloses the condensed const.i.tuents of the complex are of well-marked ketonic, i.e. quinonic, type. In 'nitrating' the lignocelluloses this phenomenon of internal condensation is much more p.r.o.nounced (see p. 131). As the reaction is mainly confined to the cellulose of the fibre, we have this additional evidence that the typical carbonyl is of ketonic function. It is still an open question whether the cellulose const.i.tuents of the lignocelluloses are progressively condensed--with progress of 'lignification'--to the unsaturated or lignone groups. There is much in favour of this view, the evidence being dealt with in the first edition, p. 180. The transition from a cellulose-ketone to the lignone-ketone involves a simple condensation without rearrangement; from which we may argue back to the greater probability of the ketonic structure of the cellulose. We must note, however, that the celluloses of the lignocelluloses are obtained as residues of various reactions, and are not h.o.m.ogeneous. They yield on boiling with condensing acids from 6 to 9 p.ct. furfural. It is usual to regard furfural as invariably produced from a pentose residue.

But this interpretation ignores a number of other probable sources of the aldehyde. It must be particularly remembered that laevulose is readily condensed (a) to a methylhydroxyfurfural

C_{6}H_{1}O_{6} - 3H_{2}O = C_{6}H_{6}O_{3} = C_{5}(OH).H_{2}.(CH_{3})O_{2}

and (b) by HBr, with further loss of OH, as under:

C_{6}H_{12}O_{6} - 4H_{2}O + HBr = C_{5}H_{3}(CH_{2}Br)O