Interaction of Diethyl Chlorothiophosphate with Hydrolysis Lignin and Its Derivatives

L. A. Pershina, S. P. Zagrebelnyi

(Presented by Professor, Doctor of Chemical Sciences B. V. Tronov)

Very characteristic of lignin, isolated by the most diverse methods, are free hydroxyl groups capable of being methylated and acetylated. The amount of free hydroxyls varies somewhat depending on the methods of isolating the lignin.

Technical lignin from the Krasnoyarsk hydrolysis plant contains 5.2% hydroxyl groups; lignin from the Kansk hydrolysis plant, 3.8%.

According to literature data [1, 2], of the total amount of hydroxyl groups only a comparatively smaller part is phenolic; for lignin isolated with the aid of superconcentrated hydrochloric acid, 1.8% was found, and for sulfite lignin, 2.5% phenolic OH groups. The main part of the hydroxyls is contained in the side chains of lignin.

These aliphatic hydroxyl groups are, according to some data, partly secondary and partly tertiary.

The hydroxyl groups of lignin can form simple ethers; for example, with diazomethane the acidic hydroxyl groups are methylated; lignin extracted with alcohols in the presence of small amounts of anhydrous HCl is also considered by Brauns [1] to be etherified; esters are obtained under the action of acetic anhydride; N. Nikitin and T. Rudneva [3], under the action of monochloroacetic acid on lignin isolated by the hydrochloric-acid method, also obtained the corresponding ester.

In the present work we investigated the action of O,O-diethyl chlorothiophosphate on hydrolysis lignin and its chloro- and nitro-derivatives, and also on alkali-activated hydrolysis lignin, assuming that the hydroxyl groups of lignin and its derivatives can be esterified according to the following scheme:

$$ \begin{array}{c} S\\ \|\\ \text{Lignin}—OH + Cl—P—(OC_2H_5)_2 \longrightarrow HCl + \text{lignin}—\\ \qquad\qquad\qquad\qquad —O—P(OC_2H_5)_2\\ \qquad\qquad\qquad\qquad \|\\ \qquad\qquad\qquad\qquad S \end{array} $$

The products of the interaction of diethyl chlorothiophosphate and lignin were tested for insecticidal action, since it is known from the literature [4] that mixed esters of thiophosphoric acid are finding ever wider application as contact and systemic insecticides.

Experimental Part

Sulfuric-acid hydrolysis lignin, nitrolignin, chlorolignin, chloronitrolignin, and hydrolysis lignin activated with caustic soda at a ratio of 4 parts NaOH to 10 parts lignin, at 10–11 atm, for 4 hours, were subjected to interaction with diethyl chlorothiophosphate obtained by Fletcher’s method [5].

We carried out nitration of lignin under the conditions proposed by N. N. Shorygina and co-workers [6].

Chlorine derivatives of lignin were obtained by an electrochemical method. Chloronitrolignin was obtained from nitrolignin by passing chlorine through its aqueous suspension.

In the products obtained, nitrogen was determined by Kjeldahl’s method, chlorine by combustion in a bomb with metallic sodium, hydroxyl groups by Verley’s method, and carboxyl groups by titration. The analytical data are presented in Table 1.

Lignins and their derivatives were preliminarily treated with aqueous alkali, calculated according to the percentage content of hydroxyl groups, and then dried in a vacuum drying oven at 50°.

Course of the Synthesis

Into a round-bottom flask of 0.5 l capacity equipped with a reflux condenser, stirrer, and dropping funnel, lignin preliminarily treated with alkali was placed (amounts, see Table 1); 100 ml of dry toluene, 1–2 drops of pyridine, and then, in small portions, diethyl chlorothiophosphate were added. The reaction mixture was heated with stirring for two hours at the boiling temperature of toluene.

The precipitate was filtered off and washed several times with toluene until a negative reaction for the \(PO_4^{\prime\prime\prime}\) ion was obtained.

The results of analysis of the reaction products are given in Table 1.

Investigation of the Reaction Products

The products of the interaction of diethyl chlorothiophosphate with hydrolysis lignin and its derivatives were dissolved in water, alcohol, and benzene.

For this purpose, a weighed portion of the product (2–3 g) was placed in a weighed glass filter No. 2, washed with 100 ml of solvent, and the precipitate on the filter was dried and weighed. In the precipitates the percentage content of phosphorus and chlorine was determined. The analytical data for products treated with water, alcohol, and benzene, as well as the percentage solubility in these solvents, are given in Table 2.

On the basis of analysis of the reaction products treated with water, alcohol, and benzene, we can conclude that a chemical interaction takes place between lignin or its derivatives and diethyl chlorothiophosphate. Diethyl chlorothiophosphate dissolves well in alcohol and aromatic hydrocarbons, and if there had been no chemical interaction, the diethyl chlorothiophosphate would have been washed out by benzene; analysis of the products for phosphorus before and after treatment with benzene would have given identical results (Table 2).

From the amount of phosphorus and sulfur contained in the products obtained, it can be concluded that in the chemical interaction with diethyl chlorothiophosphate (in toluene, in the presence of pyri-

Table 1

Analysis data, in %

Table 2

lignin, when heated for two hours, not all hydroxyl groups enter into reaction, but only a small part of them—about 20%.

In preparations washed with water, negative results were obtained in the determination of chlorine.

Only sodium chloride can dissolve in water, but not diethyl chlorothiophosphate; consequently, the products studied do not contain diethyl chlorothiophosphate. Preparations washed with water and benzene, when tested for insecticidal activity, did not reduce their effectiveness in comparison with the starting preparations.

They were tested for insecticidal activity in the laboratory of invertebrate animals of Tomsk University under the supervision of Docent A. V. Kovalenok.

The contact action of the preparations was determined by applying them to a glass surface at the rate of 1 g/m². The surface of conical flasks of 150 ml capacity, into which flies were placed, was dusted. After 24 hours the percentage of dead flies was counted. The test data are given in Table 3.

Table 3

In comparison with O,O-diethyl-O-4-nitrophenyl-thiophosphate, the synthesized preparations are less toxic.

REFERENCES

1. G. Brants. J. Am. Ch. Soc., 61, 2120, 1939.
2. N. I. Nikitin. Chemistry of Wood. Publishing House of the Academy of Sciences of the USSR, 1954.
3. N. I. Nikitin, T. I. Rudneva, ZhPKh, 10, 1915, 1937.
4. N. I. Mel’nikov. Journal of General Chemistry, 22, 3, 253, 1952.
5. J. H. Fletcher, J. C. Hamilton, Hechenbleikner, E. J. Hoegberg, S. J. [unclear: name], and J. T. Cassaday, J. Am. Soc., 70, 3943, 1948.
6. N. N. Shorygina, T. V. Izumrudova. Report at the STC, journal Hydrolysis and Wood-Chemical Industry, No. 4, 1959.