PHOSPHORYLATION OF MODEL LIGNIN COMPOUNDS. COMMUNICATION 5. INTERACTION OF O-METHYL-O-ETHYL CHLOROTHIOPHOSPHATE WITH AROMATIC ALCOHOLS AND PHENOL ALCOHOLS

G. G. Lykhina, L. A. Pershina

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

The lignin macromolecule contains both phenolic and alcoholic hydroxyl groups. To select conditions for the phosphorylation only of the alcoholic groups of lignin, we investigated the conditions of interaction of O-methyl-O-ethyl chlorothiophosphate with model compounds containing both phenolic and alcoholic hydroxyl groups. The preparation of such thiophosphates has not been described in the literature.

It is known that, in the phosphorylation of hydroxyl-containing compounds, the role of the base is reduced either to activation of the phosphorylating reagent or to absorption of the alkyl halides formed. In this case inorganic bases can only absorb the hydrogen halide evolved, whereas organic bases can perform both roles.

The phosphorylation of aromatic alcohols and phenol alcohols with O-methyl-O-ethyl chlorothiophosphate was carried out by us in anhydrous solvents in the presence either of pyridine or of anhydrous potassium carbonate. Table 1 gives the results of the synthesis of O-methyl-O-ethyl thiophosphates of aromatic alcohols.

The alcoholic hydroxyl groups of model lignin compounds do not interact with O-methyl-O-ethyl chlorothiophosphate in the presence of anhydrous potassium carbonate in organic solvents. Consequently, for phosphorylation of the alcoholic hydroxyl groups of model lignin compounds it is necessary both to activate the phosphorylating reagent and to absorb the hydrogen halide formed. In this reaction pyridine performs this role. The formation of a reactive complex of O,O-dialkyl chlorothiophosphate with tertiary amines is indicated by Toy and Beck [1].

Phenylpropyl alcohols with a hydroxyl group in the α- and γ-positions are not phosphorylated. The presence in the benzene ring of —OH and —OCH₃ groups in the n-position promotes phosphorylation of hydroxyl groups located in the α- and γ-positions of the propane side chain. Moreover, guaiacyl derivatives are somewhat more reactive than the corresponding veratryl derivatives. A double bond in the side chain substantially lowers the reactivity of hydroxyl groups in the γ-position—the yield of coniferyl alcohol thiophosphate is only 20%. The thiophosphates of model lignin compounds first obtained by us were tested in the laboratory of the Department of Invertebrate Animals of Tomsk University as contact insecticides on houseflies. It appears to us that testing these compounds will help reveal new insecticides, as well as groupings of ato-

Table 1

Phosphorylation of model lignin compounds by hydroxyl groups

groups in phosphorylated lignins responsible for insecticidal activity.

Introduction of an O-methyl-O-ethylthiophosphoric acid residue in place of a hydrogen atom into hydroxyl groups of both phenolic and aliphatic character imparts insecticidal activity to the compounds. The synthesized O-methyl-O-ethylthiophosphates of lignin model compounds possess weak insecticidal action.

Experimental Part

Starting reagents:

O-methyl-O-ethyl chlorothiophosphate was obtained from the Shchelkovo Chemical Plant. The technical product was purified by repeated distillation under vacuum. The freshly distilled product with \(T_{\text{bp}}\) \(96—102^\circ\text{C}\) (26—27 mm Hg) contains, %: S 17.9; Cl 19.9. Calculated for \(\mathrm{C_3H_8O_2P(S)Cl}\), %: S 18.2; Cl 20.3. \(n_D^{20}\) 1.4740.

Pyridine was preliminarily distilled over KOH.

Potassium carbonate—“ch. d. a.” grade.

Organic solvents—chemically pure, dehydrated.

1-Phenylpropanol-1 was obtained by the method [2] through the interaction of benzaldehyde with magnesium ethyl bromide. \(T_{\text{bp}}\) \(108—110^\circ\text{C}\) (15 mm Hg). Found, %: OH 12.63; calculated for \(\mathrm{C_9H_{12}O}\), %: OH 12.5.

1-Phenylpropanol-3 was synthesized from styrene and formaldehyde by the method of Schreiner and Ruby [3]. \(T_{\text{bp}}\) \(120^\circ\text{C}\) (8 mm Hg). Found, %: OH 12.4; calculated for \(\mathrm{C_9H_{12}O}\), %: OH 12.5.

1-Guaiacylpropanol-1 was obtained by the method [4], \(T_{\text{mp}}\) \(85—86^\circ\text{C}\) (from benzene). Found, %: OH 18.65; \(\mathrm{OCH_3}\) 16.95. Calculated for \(\mathrm{C_{10}H_{14}O_3}\), %: OH 18.65; \(\mathrm{OCH_3}\) 17.0.

1-Guaiacylpropenol-3 was synthesized from ferulic acid by the method [5]. A fraction with \(T_{\text{bp}}\) \(170^\circ\text{C}\) (2 mm Hg) was used; found, %: OH 18.55; \(\mathrm{OCH_3}\) 16.9; calculated for \(\mathrm{C_{10}H_{14}O_3}\), %: OH 18.65; \(\mathrm{OCH_3}\) 17.0. \(n_D^{20}\) 1.5516.

1-Guaiacyl-1-propanol-3 was obtained by the method [6]. \(T_{\text{mp}}\) \(72^\circ\text{C}\) (from petroleum ether). Found, %: OH 18.8; \(\mathrm{OCH_3}\) 17.15. Calculated for \(\mathrm{C_{10}H_{12}O_3}\), %: OH 18.9; \(\mathrm{OCH_3}\) 17.25.

1-Veratrylpropanol-1 was obtained by the method [4]. We recommend carrying out the decomposition of the organomagnesium compound with a 2% solution of sulfuric acid or a saturated solution of ammonium chloride to avoid dehydration. A fraction with \(T_{\text{bp}}\) \(148^\circ\text{C}\) (2 mm Hg) was used. Found: OH 8.5%; calculated for \(\mathrm{C_{11}H_{16}O_3}\): OH 8.65%, \(n_D^{20}\) 1.5520. 1-Veratrylpropanol-3 was obtained by reduction of the ethyl ester of 1-(3,4-dimethoxyphenyl)propionic acid with lithium aluminum hydride under the conditions of Chuksanova, Sergeeva, Shorygina [5]. \(T_{\text{bp}}\) \(171^\circ\text{C}\) (2 mm Hg). Found: OH 8.5%. Calculated for \(\mathrm{C_{11}H_{16}O_3}\): OH 8.65%.

Preparation of Thiophosphates

Into a three-necked flask equipped with a reflux condenser, stirrer, and dropping funnel were placed 0.02 mole of the starting aromatic alcohol, 25 ml of solvent, and 0.02 mole of pyridine. The contents of the flask were heated to the boiling temperature of the solvent, and then 0.02 mole of O-methyl-O-ethyl chlorothiophosphate was added dropwise with stirring. After being kept for a certain period of time with stirring and at the boiling temperature of the solvent, the reaction mass was cooled and poured into ice water. The mixture was extracted twice with benzene. The benzene extracts were washed

with water, dried over ignited sodium sulfate, and passed twice through a chromatographic column with aluminum oxide. The benzene was distilled off under vacuum; oily transparent products of a slightly yellowish color remained in the flask. When an attempt was made to distill them under vacuum, they rapidly decomposed in the temperature range 140–165°C (1–5 mm Hg).

Conclusions

1. Six O-methyl-O-ethyl thiophosphates of lignin model compounds not described in the literature have been synthesized.

2. It has been shown that, in an organic-solvent medium, in the presence of pyridine, only the alcoholic hydroxyl groups of phenolic alcohols react with O-methyl-O-ethyl chlorothiophosphate.

3. Aromatic alcohols do not react with O-methyl-O-ethyl chlorothiophosphate in anhydrous organic solvents in the presence of potassium carbonate.

4. The presence of —OH and —OCH₃ groups in the benzene ring in the p-position promotes phosphorylation of hydroxyl groups located at the α- and γ-carbon atoms of the side propyl chain.

5. The thiophosphates obtained possess weak insecticidal activity.

LITERATURE

1. A. Toy, T. Beck, J. Am. Chem. Soc., 72, 3191, (1950).
2. R. Grignard, C., 623, 1901.
3. R. Schrainer, F. Ryubi. Syntheses of Organic Preparations. Coll. 5, 83, Moscow, IL, 1954.
4. M. Kulka, H. Hibbert, J. Am. Chem. Soc., 65, 1180, (1943).
5. A. A. Chuksanova, L. L. Sergeeva, N. N. Shorygina. Izv. AN SSSR, Chemical Series, No. 12, 2219 (1959), No. 7, 1254, (1964).
6. C. F. Allen, R. John, J. R. Byers, J. Am. Chem. Soc., 71, 2684, (1949).