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 substitution by an NO2 group takes place in the aromatic residue, giving a mixed nitric nitrobenzoic ester. The analysis of the products points to the entrance of 1 NO2 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 C12 unit formula.
In analysing these products we have employed the Dumas method for total nitrogen. For the O.NO2 groups we have found the nitrometer and the Schloesing methods to give concordant results. For the NO2 groups it was thought that Limpricht's method, based upon reduction with stannous chloride in acid solution (HCl), would be available. The quantitative results, however, were only approximate, owing to the difficulty of confining the reduction to the NO2 groups of the nitrobenzoyl residue. By reduction with ammonium sulphide the O.NO2 groups were entirely removed as in the case of the cellulose nitrates; the NO2 was reduced to NH2 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 C12 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 analytical 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 dinitrobenzoate | Trinitrate dinitrobenzoate | ||
| Total | Nitrogen | 7.84 | 8.97 | 7.99 | 9.24 |
| O.NO2 | " | 5.00 | 5.45 | 4.00 | 5.54 |
| NO2 | " (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 C12 formula, was prepared and analysed with the following results:
| Calc. for Mononitrate tetranitrobenzoate | |||
| Total | Nitrogen | 6.76 | 7.25 |
| O.NO2 | " | 1.30 | 1.45 |
| NO2 | " (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 C12 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.