Researches on Cellulose Part 3

_Structureless celluloses_ of the 'normal' type, and insoluble therefore in alkaline lye, treated under similar conditions to those described above for the fibrous celluloses, yield a higher proportion of dibenzoate. The following determinations were made with the cellulose (hydrate) regenerated from the sulphocarbonate:--

Mol. proportions of reagents Yield Dibenzoate p.ct.

C_{6}H_{10}O_{5} : 2NaOH : 2BzCl 145 34.7 [Caustic soda at 10 per cent. NaOH]

C_{6}H_{10}O_{5} : 4NaOH : 2BzCl 162 62.7 [Caustic soda at 20 per cent. NaOH]

_Limit of reaction._--The cellulose in this form having shown itself more reactive, it was taken as the basis for determining the maximum proportion of OH groups yielding to this later reaction. The systematic investigations of Skraup [Monatsh. 10, 389] have determined that as regards the interacting groups the molecular proportions 1 OH : 7 NaOH : 5 BzCl, ensure complete or maximum esterification. The maximum of OH groups in cellulose being 4, the reagents were taken in the proportion C_{6}H_{10}O_{5} : 4 [7 NaOH : 5 BzCl]. The yield of crude product, after purifying as far as possible from the excess of benzoic acid, was 240 p.ct. [calculated for dibenzoate 227 p.ct.]. On further investigating the crude product by treatment with solvents, it was found to have still retained benzoic acid. There was also present a proportion of only partially attacked cellulose (mon.o.benzoate). The soluble benzoate amounted to 90 p.ct. of the product. It may be generally concluded that the dibenzoate represents the normal maximum but that with the hydrated and partly hydrolysed cellulose molecule, as obtained by regeneration from the sulphocarbonate, other OH groups may react, but they are only a fractional proportion in relation to the unit group C_{6}H_{10}O_{5}. In this respect again there is a close parallelism between the sulphocarbonate and benzoyl-ester reactions.

_The dibenzoate_, even when prepared from the fibrous celluloses, is devoid of structure, and its presence in admixture with the fibrous mon.o.benzoate is at once recognised as it const.i.tutes a structureless incrustation. Under the microscope its presence in however minute proportion is readily observed. As stated it is soluble in certain of the ordinary solvents of the cellulose esters, e.g. chloroform, acetic acid, nitrobenzene, pyridine, and phenol. It is not soluble in ether or alcohol.

_Hygroscopic moisture of benzoates._--The crude mon.o.benzoate retains 5.0-5.5 p.ct. moisture in the air-dry condition. After removal of the residual cellulose this is reduced to 3.3 p.ct. under ordinary atmospheric conditions. The purified dibenzoates retain 1.6 p.ct. under similar conditions.

_a.n.a.lysis of benzoates._--On saponification of these esters with alcoholic sodium hydrate, anomalous results are obtained. The acid numbers, determined by t.i.tration in the usual way, are 10-20 p.ct. in excess of the theoretical, the difference increasing with the time of boiling. Similarly the residual cellulose shows a deficiency of 5-9 p.ct.

It is by no means improbable that in the original ester reaction there is a const.i.tutional change in the cellulose molecule causing it to break down in part under the hydrolysing treatment with formation of acid products. This point is under investigation. Normal results as regards acid numbers, on the other hand, are obtained by saponification with sodium ethylate in the cold, the product being digested with the half-saturated solution for 12 hours in a closed flask.

The following results with specimens of mono- and dibenzoate, purified, as far as possible, may be cited:

Combustion results Saponification results Calc. C_{6}H_{5}.COOH Calc. Cellulose Calc.

Mon.o.benzoate C 56.60 58.65} H 5.06 5.26} 46.0 45.9 58.0 60.8

Dibenzoate C 63.10 64.86} H 3.40 4.86} 65.5 66.6 34.3 40.3

The divergence of the numbers, especially for the dibenzoate, in the case of the hydrogen, and yield of cellulose on hydrolysis are noteworthy. They confirm the probability of the occurrence of secondary changes in the ester reactions.

_Action of nitrating acid upon the benzoates._--From the benzoates above described, mixed nitro-nitric esters are obtained by the action of the mixture of nitric and sulphuric acids. The residual OH groups of the cellulose are esterified and subst.i.tution by an NO_{2} group takes place in the aromatic residue, giving a mixed nitric nitrobenzoic ester. The a.n.a.lysis of the products points to the entrance of 1 NO_{2} group in the benzoyl residue in either case; in the cellulose residue 1 OH readily reacts. Higher degrees of nitration are attained by the process of solution in concentrated nitric acid and precipitation by pouring into sulphuric acid. In describing these mixed esters we shall find it necessary to adopt the C_{12} unit formula.

In a.n.a.lysing these products we have employed the Dumas method for _total nitrogen_. For the O.NO_{2} groups we have found the nitrometer and the Schloesing methods to give concordant results. For the NO_{2} groups it was thought that Limpricht's method, based upon reduction with stannous chloride in acid solution (HCl), would be available. The quant.i.tative results, however, were only approximate, owing to the difficulty of confining the reduction to the NO_{2} groups of the nitrobenzoyl residue. By reduction with ammonium sulphide the O.NO_{2} groups were entirely removed as in the case of the cellulose nitrates; the NO_{2} was reduced to NH_{2} and there resulted a cellulose amidobenzoate, which was diazotised and combined with amines and phenols to form yellow and red colouring matters, the reacting residue remaining more or less firmly combined with the cellulose.

_Cellulose dinitrate-dinitrobenzoate, and cellulose trinitrate-dinitrobenzoate._--On treating the fibrous benzoate--which is a dibenzoate on the C_{12} basis--with the acid mixture under the usual conditions, a yellowish product is obtained, with a yield of 140-142 p.ct. The nitrobenzoate is insoluble in ether alcohol, but is soluble in acetone, acetic acid, and nitrobenzene. In purifying the product the former solvent is used to remove any cellulose nitrates. To obtain the maximum combination with nitroxy-groups, the product was dissolved in concentrated nitric acid, and the solution poured into sulphuric acid.

The following a.n.a.lytical results were obtained (a) for the product obtained directly from the fibrous benzoate and purified as indicated, (b) for the product from the further treatment of (a) as described:

Found Calc. for (a) (b) Dinitrate Trinitrate dinitrobenzoate dinitrobenzoate Total Nitrogen 7.84 8.97 7.99 9.24 O.NO_{2} " 5.00 5.45 4.00 5.54 NO_{2} (Aromatic) 2.84 3.52 3.99 3.70

With the two benzoyl groups converted into nitro-benzoyl in each product, the limit of the ester reaction with the cellulose residue is reached at the third OH group.

The nitrogen in the amidobenzoate resulting from the reduction with ammonium sulphide was 4.5 p.ct.--as against 5.0 p.ct. calculated. The moisture retained by the fibrous nitrate--nitrobenzoate--in the air-dry state was found to be 1.97 p.ct.

The product from the structureless dibenzoate or tetrabenzoate on the C_{12} formula, was prepared and a.n.a.lysed with the following results:

Calc. for Mononitrate tetranitrobenzoate Total Nitrogen 6.76 7.25 O.NO_{2} " 1.30 1.45 NO_{2} " (Aromatic) 5.46 5.80

The results were confirmed by the yield of product, viz. 131 p.ct. as against the calculated 136 p.ct. They afford further evidence of the generally low limit of esterification of the cellulose molecule. From the formation of a 'normal' tetracetate--i.e. octacetate of the C_{12} unit--we conclude that 4/5 of the oxygen atoms are hydroxyl oxygen. Of the 8 OH groups five only react in the mixed esters described above, and six only in the case of the simple nitric esters. The ester reactions are probably not simple, but accompanied by secondary reactions within the cellulose molecule.

(p. 34) ~Cellulose Acetates.~--In the first edition (p. 35) we have committed ourselves to the statement that 'on boiling cotton with acetic anhydride and sodium acetate no reaction occurs.' This is erroneous. The error arises, however, from the somewhat vague statements of Schutzenberger's researches which are current in the text-books [e.g.

Beilstein, 1 ed. p. 586] together with the statement that reaction only occurs at elevated temperatures (180). As a matter of fact, reaction takes place at the boiling temperature of the anhydride. We have obtained the following results with bleached cotton:

Yield Calc. for Monoacetate C_{6}H_{7}O_{4}O.C_{2}H_{3}O

Ester reaction 121 p.ct. 125 p.ct.

{Cellulose 79.9 79.9 Saponification { {Acetic acid 29.9 29.4

This product is formed without apparent structural alteration of the fibre. It is entirely insoluble in all the ordinary solvents of the higher acetates. Moreover, it entirely resists the actions of the special solvents of cellulose--e.g. zinc chloride and cuprammonium. The compound is in other respects equally stable and inert. The hygroscopic moisture under ordinary atmospheric conditions is 3.2 p.ct.

_Tetracetate._--This product is now made on the manufacturing scale: it has yet to establish its industrial value.

NITRIRUNG VON KOHLENHYDRATEN.

W. WILL und P. LENZE (Berl. Ber., 1898, 68).

~NITRATES OF CARBOHYDRATES.~

(p. 38) The authors have studied the nitric esters of a typical series of the now well-defined carbohydrates--pentoses, hexoses, both aldoses and ketoses--bioses and trioses, the nitrates being prepared under conditions designed to produce the highest degree of esterification.

Starch, wood, gum, and cellulose were also included in the investigations. The products were a.n.a.lysed and their physical properties determined. They were more especially investigated in regard to temperatures of decomposition, which were found to lie considerably lower than that of the cellulose nitrates. They also show marked and variable instability at 50 C. A main purpose of the inquiry was to throw light upon a probable cause of the instability of the cellulose nitrates, viz. the presence of nitrates of hydrolysed products or carbohydrates of lower molecular weight.

The most important results are these:

_Monoses._--The _aldoses_ are fully esterified, in the pentoses 4 OH, in the hexoses 5 OH groups reacting. The pentose nitrates are comparatively stable at 50; the hexose nitrates on the other hand are extremely unstable, showing a loss of weight of 30-40 p.ct. when kept 24 hours at this temperature.

Xylose is differentiated by tending to pa.s.s into an anhydride form (C_{5}H_{10}O_{5}-H_{2}O) under this esterification. When treated in fact with the mixed acids, instead of by the process usually adopted by the authors of solution in nitric acid and subsequent addition of the sulphuric acid, it is converted into the dinitrate C_{5}H_{6}O_{2}.(NO_{3})_{2}.

_Ketoses_ (C_{6}).--These are sharply differentiated from the corresponding aldoses by giving _tri_nitrates C_{6}H_{7}O_{2}(NO_{3})_{3} instead of _penta_nitrates, the remaining OH groups probably undergoing internal condensation. The products are, moreover, _extremely stable_. It is also noteworthy that levulose gave this same product, the trinitrate of the anhydride (levulosan) by both methods of nitration (_supra_).

_The bisaccharides or bioses_ all give the octonitrates. The degree of instability is variable. Cane-sugar gives a very unstable nitrate. The lactose nitrate is more stable. Thus at 50 it loses only 0.7 p.ct. in weight in eight days; at 75 it loses 1 p.ct. in twenty-four hours, but with a rapid increase to 23 p.ct. in fifty-four hours. The maltose octonitrate melts (with decomposition) at a relatively high temperature, 163-164. At 50-75 it behaves much like the lactose nitrate.

_Trisaccharide._--Raffinose yielded the product

C_{18}H_{21}O_{5}.(NO_{3})_{11}.

_Starch_ yields the hexanitrate (C_{12}) by both methods of nitration.

The product has a high melting and decomposing point, viz. 184, and when thoroughly purified is quite stable. It is noted that a yield of 157 p.ct. of this nitrate was obtained, and under identical conditions cellulose yielded 170 p.ct.

_Wood gum_, from beech wood, gave a tetranitrate (C_{10} formula) insoluble in all the usual solvents for this group of esters.

The authors point out in conclusion that the conditions of instability and decomposition of the nitrates of the monose-triose series are exactly those noted with the cellulose nitrates as directly prepared and freed from residues of the nitrating acids. They also lay stress upon the superior stability of the nitrates of the anhydrides, especially of the ketoses.

NITRATED CARBOHYDRATES AS FOOD MATERIAL FOR MOULDS.

THOMAS BOKORNY (Chem. Zeit., 1896, 20, 985-986).

(p. 38) Cellulose trinitrate (nitrocellulose) will serve as a food supply for moulds when suspended in distilled water containing the requisite mineral matter and placed in the dark. The growth is rapid, and a considerable quant.i.ty of the vegetable growth acc.u.mulates round the ma.s.ses of cellulose nitrate, but no growth is observed if mineral matter is absent. Cellulose itself cannot act as a food supply, and it seems probable that if glycerol is present cellulose nitrate is no longer made use of.