PHOSPHORYLATION OF MODEL LIGNIN COMPOUNDS.

COMMUNICATION 3. INTERACTION OF DIMETHYL PHOSPHITE

WITH AROMATIC ALCOHOLS

V. P. VASIL’EVA, L. A. PERSHINA

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

The transesterification reaction of dialkyl and diaryl phosphites is successfully used for the synthesis of phosphorus-containing celluloses [1], phenol-formaldehyde resins [2], polyvinyl alcohol [3], and lignin [4]. In the latter work it was shown that the interaction of dimethyl phosphite with lignin proceeds through its addition to the carbonyl groups of lignin and transesterification with aliphatic hydroxyl groups.

In the present work, the relative reactivity of aromatic alcohols, which model the principal structural elements of the lignin macromolecule, in their interaction with dimethyl phosphite has been determined. The data obtained make it possible to draw interesting conclusions about the reactivity of the aliphatic hydroxyl groups of the lignin macromolecule.

Table 1 gives the quantities of the starting substances and of the methanol evolved when the reaction was carried out for three hours at

Table 1

Interaction of dimethyl phosphite with model lignin compounds containing hydroxyl groups

at a temperature of 150°C, one hour at 160°C, and one hour at 180°C. Figure 1 shows the dependence of the yield of methyl alcohol on time.

Phenolic alcohols of the guaiacylpropyl and syringyl series prove to be less reactive than their phenylpropyl analogues. Judging by the amount of methyl alcohol evolved, ethylguaiacylcarbinol is half as reactive as ethylphenylcarbinol. Under these conditions, coniferyl alcohol and guaiacol do not at all

Fig. 1. Dependence of the yield of methyl alcohol on time during the interaction of dimethyl phosphite with aromatic alcohols: 1—phenylpropanol-3; 2—phenylpropanol-1; 3—1-veratrylpropanol-1; 4—phenylethanol; 5—1-guaiacylpropanol-1; 6—1-veratrylpropanol-3; 7—benzyl alcohol; 8—1-guaiacylpropanol-3.

interact with dimethyl phosphite; 1-guaiacylpropan-3-ol and 1-veratrylpropan-3-ol are distinguished by low reactivity.

Thus, the hydroxyl group in the α-position in model lignin compounds, upon interaction with dimethyl phosphite, is more reactive than the hydroxyl group in the γ-position.

Alcohols of the veratryl series are more reactive than those of the guaiacyl series. Possibly, the presence of an OH group or an OCH₃ group in the p-position of the benzene ring has an effect. This influence can be estimated quantitatively by comparing the values of σ-constants, proportional to the charges induced by hydroxyl and methoxyl groups in the p-position: $\sigma_{\mathrm{OH}}=-0.37$; $\sigma_{\mathrm{OCH_3}}=-0.268$.

Experimental Part

Starting Reagents

1. Dimethyl phosphite, obtained at the Volgograd Chemical Combine, was distilled under vacuum, $t_{\mathrm{bp}}=56^\circ$ (10 mm Hg); $n_D^{20}=1.403$.

2. Benzyl alcohol was distilled under vacuum, $t_{\mathrm{bp}}=84^\circ$ (16 mm Hg); $n_D^{20}=1.5405$.

3. 1-Phenylethan-2-ol was obtained by the method of [5], $t_{\mathrm{bp}}=219$—$220^\circ$; $n_D^{20}=1.5295$.

4. 1-Phenylpropan-1-ol was obtained by the interaction of benzaldehyde with magnesium ethyl bromide [6], $t_{\mathrm{bp}}=108^\circ$ (10 mm Hg).

5. 1-Phenylpropan-3-ol was obtained by the method of [7], $t_{\mathrm{bp}}=120$—$121^\circ$ (8 mm Hg), $n_D^{20}=1.5268$.

6. Guaiacol was recrystallized from water, $t_{\mathrm{m}}=28^\circ$.

7. 1-(4-Hydroxy-3-methoxyphenyl)propan-1-ol was obtained by the action on vanillin of magnesium ethyl bromide [8], $t_{\mathrm{m}}=83^\circ$.

8. 1-(3,4-Dimethoxyphenyl)propan-1-ol was synthesized from veratric aldehyde and magnesium ethyl bromide under the conditions for obtaining 1-(4-hydroxy-3-methoxyphenyl)propan-1-ol [8], $t_{\mathrm{bp}}=150^\circ$ (5 mm Hg), $n_D^{20}=1.5520$.

9. 1-(4-Hydroxy-3-methoxyphenyl)propan-3-ol was obtained from ferulic acid according to the procedure [9], $t_{\mathrm{bp}}=165^\circ$ (5 mm Hg), $n_D^{20}=1.5516$.

10. 1-(3,4-Dimethoxyphenyl)propan-3-ol was synthesized from methylated ferulic acid according to a scheme analogous to the preparation of 1-(4-hydroxy-3-methoxyphenyl)propan-3-ol [9], $t_{\mathrm{bp}}=171^\circ$ (1 mm Hg).

11. 1-(4-Hydroxy-3-methoxyphenyl)prop-1-en-3-ol was obtained by the method [10, 11], $t_{\mathrm{m}}=72^\circ$.

Phosphorylation

A weighed portion of the alcohol (0.75 M) and dimethyl phosphite (0.25 M) are placed in a distillation flask and heated in a helium atmosphere, first at $t=150^\circ\mathrm{C}$ for 3 h, then for 1 h at $t=160^\circ\mathrm{C}$ and for one hour at $t=180^\circ\mathrm{C}$, with distillation of methyl alcohol, which is weighed periodically.

Methyl alcohol was identified by fuchsine-sulfurous acid, $n_D^{20}=1.3284$.

Conclusions

1. In terms of the rate of interaction with dimethyl phosphite, aromatic alcohols are arranged in the following series: phenylpropan-3-ol, phenylpropan-1-ol, 1-veratrylpropan-1-ol, phenylethanol, 1-guaiacyl-1-propanol, 1-veratrylpropan-3-ol, benzyl, 1-guaiacylpropan-3-ol.

2. Phenol alcohols and alcohols of the guaiacylpropyl and veratrylpropyl-

... series are less reactive than their phenylpropyl analogues.

1. Alcohols of the veratryl series are more reactive than those of the guaiacyl series.

2. Hydroxyl groups in the $\alpha$-position in model lignin compounds, upon interaction with dimethyl phosphite, are more reactive than hydroxyl groups in the $\gamma$-position.

REFERENCES

1. E. E. Nifant’ev. Uspekhi khimii, 34, 2206 (1965).

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

3. E. E. Nifant’ev. In: Research in the Chemistry and Technology of Fertilizers, Pesticides, and Salts, 63, Nauka, Moscow, 1966.

4. L. A. Perishina, Yu. S. Pilipchuk, V. I. Shufledovich. Sb. Khimiya drevesiny, Riga, No. 4, 1969.

5. B. V. Tronov, V. P. Lopatinskii, V. A. Levin. Izv. TPI, 196, 121 (1969).

6. Grignard, C., 623, 1901.

7. R. Shriner, F. Ruby. Syntheses of Organic Preparations, Collection 5, 83, Inostrannaya Literatura, Moscow, 1954.

8. Ph. C. Roberti, R. F. Jork, W. S. Macgregor. J. Am. Chem. Soc., 72, 5760, 1950.

9. A. A. Chuksanova, L. L. Sergeeva, N. N. Shorygina. Izv. AN SSSR, ser. khim., 12, 2219 (1957); 7, 1254 (1964).

10. C. F. Allen, R. John, J. R. Beyers. J. Am. Chem. Soc., 71, 2683, 1949.

11. J. A. Pearl. J. Org. Chem., 24, 736, 1959.