PHOSPHORYLATION OF LIGNINS WITH DIMETHYL PHOSPHITE

L. A. PERSHINA, V. P. VASIL’EVA, V. P. ZHUCHKOV

(Presented by the scientific seminar of the Faculty of Chemical Technology)

The introduction of phosphorus into the macromolecule of synthetic and natural polymers imparts to them a number of valuable properties: flame resistance, bactericidal activity, pesticidal and ion-exchange properties. In the phosphorylation of lignin with acid chlorides of phosphorus and thiophosphorus acids, products possessing insecticidal properties have been obtained [1].

Dialkyl phosphites, possessing high reactivity and ease of synthesis, are widely used for obtaining a variety of organophosphorus compounds. Studies by Petrov and Nifant’ev have shown that the transesterification reaction of dialkyl and diaryl phosphites can be successfully used for the synthesis of phosphorus-containing celluloses [2], phenol-formaldehyde resins possessing insecticidal action [3], and polyvinyl alcohol [4]; Nifant’ev and Fursenko [5], subjecting lignin to interaction with esters or amides of acids of trivalent phosphorus, introduced 8% phosphorus. The direction of the reactions was not investigated.

In the present work an attempt has been made to establish the direction of the reactions of the interaction of dimethyl phosphite with lignin.

Proceeding from the presence in lignin of reactive hydroxyl and carbonyl groups, several directions of this reaction should be anticipated: transesterification at hydroxyl groups, addition to carbonyl groups, and formation of phosphoric acid esters with quinone groups.

The change in the content of functional groups in phosphorylated lignins, given in Table 1, as well as the IR spectra (Fig. 1), make it possible to conclude that the interaction of dimethyl phosphite with lignins proceeds through carbonyl and aliphatic hydroxyl groups.

The interaction of dimethyl phosphite with lignin in the presence of metallic sodium proceeds at approximately the same rate as without it.

Experimental Part

Starting reagents

Dimethyl phosphite, obtained at the Volgograd Chemical Combine, was redistilled under vacuum. For the work a fraction with \(t_{\mathrm{boil}} = 56^\circ\mathrm{C}\) (10 mm Hg) was used; \(d_{0}^{20} 1.2004\); \(n_{D}^{20} 1.403\).

From the wood of Scots pine (Pinus silvestris) 108 years of age, lignins were isolated: dioxane lignin by the method of [6], copper-ammonia [7], and ultrasonic [8]. Technical hydrolysis lignin from the Krasnoyarsk plant was extracted with hot water in a Soxhlet apparatus with reverse-

Fig. 1. IR absorption spectra: a — hydrolysis lignin; b — phosphorylated hydrolysis lignin.

Vertical axis: transmittance, %.

…with a cold-water condenser for 3 hours. For 10 g, 500 ml of water was taken. It was dried to the air-dry state, ground in a ball mill, and screened through a sieve with an aperture diameter of 0.25 mm. The lignin was then extracted with an alcohol–benzene mixture (1 : 1) for 5 hours, washed with distilled water, and dried to the air-dry state.

Activated hydrolysis lignin was obtained by heating technical lignin with sodium hydroxide in an autoclave for 4 hours; the amount of sodium hydroxide was 20% of the weight of the lignin, the liquor ratio was 1 : 10, and the temperature was 180°C. Elemental and functional analyses of the initial lignins are given in Table 1.

Phosphorylation in an Excess of Dimethyl Phosphite

A weighed portion of lignin, a small piece of Na (0.002 g), and dimethyl phosphite were placed in a distillation apparatus. The reaction mixture was heated for 4 hours at 115°C. During the reaction, a slight vacuum was created in the apparatus and a stream of helium was passed through the reaction mixture, so that the methyl alcohol liberated during the reaction was removed.

Since ultrasonic dioxane lignin, activated lignin, and also the products of their phosphorylation dissolve well in dimethyl phosphite, the reaction mixture was poured dropwise into absolute diethyl ether. The precipitate that formed was filtered off, washed several times with ether, and dried over $P_2O_5$.

Copper–ammonia and hydrolysis lignins, as well as the products of their phosphorylation, did not dissolve in dimethyl phosphite; therefore the reaction mixture was filtered, and the precipitate was washed several times with ether. Elemental and functional analyses of the phosphorylated lignins are given in Table 1.

Phosphorylation in Benzene and Toluene

A weighed portion of hydrolysis lignin was placed in a flask with a reflux condenser, and dry benzene or toluene and dimethyl phosphite were added. The reaction mixture was heated at the boiling temperature of benzene or toluene for 4 hours. After this, the precipitate was filtered off, washed several times with ether and water, and dried over $P_2O_5$.

The effect of metallic sodium on the process of phosphorylation of hydrolysis lignin under different conditions is shown in Table 2.

IR spectra of hydrolysis lignin and of the product of its phosphorylation in toluene for 4 hours in the presence of metallic sodium were recorded on a UR-10 double-beam automatic spectrophotometer manufactured by “Veb Karl Zeiss,” GDR. The spectral slit width of the instrument was 4 cm$^{-1}$, the recording speed was 150, the recording time was 32, and the recording scale was 12. Amplifier data: gain, 5; frequency-pass bandwidth, 2; time constant, 1. The spectra were obtained for samples pressed with potassium bromide; concentration, 0.5%.

Conclusions

1. Preparations phosphorylated with dimethyl phosphite were obtained from dioxane lignin, copper–ammonia lignin, ultrasonic lignin, activated lignin, and hydrolysis lignin.

2. It was shown that the interaction of dimethyl phosphite with lignin proceeds through addition to carbonyl groups and transesterification at aliphatic hydroxyl groups.

Table 1

Changes in the content of functional groups of lignins upon interaction with dimethyl phosphite

Table 2

Effect of metallic sodium on the interaction of hydrolysis lignin with dimethyl phosphite

References

1. B. V. Tronov, L. A. Pershina, V. M. Morozova, A. V. Kovalenok, A. I. Galochkin. Journal of the Hydrolysis and Wood-Chemical Industry, 10, No. 5, 1961.

2. E. E. Nifant’ev. Advances in Chemistry, 34, 2206, (1965).

3. E. E. Nifant’ev, S. G. Fedorov. ZhPKh, 40, 1066, (1967).

4. N. M. Volchina, A. I. Meos, L. A. Vol’er, E. E. Nifant’ev. ZhPKh, 40, 209, (1967).

5. E. E. Nifant’ev, I. V. Fursenko. Author’s certificate No. 181108, application filed 13.01.65. Bulletin of Inventions, No. 9, 1966.

6. V. M. Reznikov, L. G. Matusevich, I. V. Sen’ko, G. V. Sukhaya. ZhPKh, 40, 1397, (1967).

7. Freudenberg, Engler, Flickinger, Sobek, Klink, Ber., 71, 1810, (1938).

8. L. A. Pershina, B. A. Yankovskii, Abstracts of Reports and Communications of the IX Mendeleev Congress, 128, No. 4, 1965.