Phosphorylation of model lignin compounds
Abstract Generated abstract
This study examines phosphorylation reactions of lignin model compounds as a means of clarifying transformations that may occur in lignin structural units and identifying features associated with insecticidal activity. Guaiacol, ethyl vanillate, and 1-(4-hydroxy-3-methoxyphenyl)propanol-1 were reacted with O-methyl-O-ethyl chlorothiophosphate to synthesize corresponding thiophosphate derivatives, including products formed by esterification of either the aliphatic or phenolic hydroxyl group in the guaiacylpropanol model. The synthesized compounds were characterized by yield, decomposition or boiling behavior, sulfur content, refractive index, density where available, and biological tests. The results indicate that the obtained thiophosphates show insecticidal activity, that a propyl substituent on the aromatic ring reduces this activity, and that phosphorylation of the aliphatic hydroxyl group gives the more active guaiacylpropanol derivative.
Full Text
PHOSPHORYLATION OF MODEL LIGNIN COMPOUNDS
Communication 1. Synthesis of Thiophosphates
L. A. PERSHINA, G. G. LYKHINA, V. N. SHVACHEVA
(Presented by the scientific seminar of the Faculty of Chemical Technology)
According to current concepts, lignin is a polydisperse, amorphous, natural polymer of irregular structure, whose principal structural elements are phenylpropane units. However, lignin cannot be regarded as a constitutionally defined compound formed as a result of the polymerization of uniform structural units. At least three aromatic monomers form its main skeleton: dehydroconiferyl alcohol, pinoresinol, and the β-coniferyl ether of guaiacylglycerol. Variants of bonds are: phenyl–coumaran, β–aryl, and β–aryl ether. Considering that up to 60 phenylpropane residues enter into the lignin macromolecule, the structure of lignin is very complex. Therefore, in studying the chemical transformations of lignin, compounds are widely used that model individual structural elements of lignin containing various functional groups.
To study the phosphorylation reaction of lignin with acid chlorides of O,O-dialkylthiophosphoric acids, we selected as model compounds guaiacol, ethyl vanillate, and 1-(4-hydroxy-3-methoxyphenyl)propanol-1.
Comparison of the behavior of model compounds and lignin during phosphorylation makes it possible to understand the processes occurring in individual structures of the lignin macromolecule, and also to identify the groupings of atoms responsible for insecticidal activity.
The aim of the present work was to obtain O-methyl-O-ethyl thiophosphates of the above-listed model lignin compounds and to study their insecticidal activity.
In the case of 1-(4-hydroxy-3-methoxyphenyl)-propanol-1, two thiophosphates were obtained: by esterification of the hydroxyl group in the α-position of the side chain and in the benzene ring.
Testing of insecticidal activity, carried out at Tomsk State University, showed that the thiophosphates obtained possess insecticidal action. The presence of a propyl radical in the benzene ring significantly reduces the insecticidal properties. Of the thiophosphates of guaiacyl-propanol-1, the most active preparation is the one with the phosphorylated aliphatic hydroxyl group.
O-Methyl-O-ethyl thiophosphates of model lignin compounds
Table 1
| No. | Substance | Yield, % of theoretical | Boiling temperature, °C | Sulfur, % found | Sulfur, % calculated | \(n_D^{20}\) | \(d^{20}\) | Insecticidal activity: paramecia, after min | Insecticidal activity: 100% death of flies, after min |
|---|---|---|---|---|---|---|---|---|---|
| 1 | 2-Methoxyphenyl \(O\)-methyl \(O\)-ethyl thiophosphate; structure shown as an aromatic ring bearing \(OCH_3\) and \(O\!-\!P(=S)(OCH_3)(OC_2H_5)\) substituents | 45.0 | 152–155 \((1–2\ \mathrm{mm\ Hg})\) | 12.2 | 12.16 | 1.522 | 1.217 | 10 | 20 |
| 2 | Ethyl ester of a methoxy-substituted aromatic \(O\)-methyl \(O\)-ethyl thiophosphate; structure shown as an aromatic ring bearing \(OCH_3\), \(H_5C_2O–C(=O)\), and \(O\!-\!P(=S)(OCH_3)(OC_2H_5)\) substituents | 85.4 | Decomposes at 110 \((25\ \mathrm{mm\ Hg})\) | 9.4 | 9.5 | 1.502 | 1.137 | 17 | 40 |
| 3 | Model lignin compound bearing a methoxyphenolic ring and an \(O\!-\!P(=S)(OCH_3)(OC_2H_5)\) thiophosphate group; structure shown with \(HO\), \(H_3CO\), and a side chain \(CH–CH–CH_3\) | 60.0 | Decomposes at 158–160 \((8–10\ \mathrm{mm\ Hg})\) | 9.8 | 10.0 | — | — | 30 | 120 |
| 4 | Model lignin compound bearing a methoxyphenolic aromatic ring and an \(O\!-\!P(=S)(OCH_3)(OC_2H_5)\) thiophosphate group; structure shown with a side chain \(H_3C–H_2C–(O)_nH\) [[unclear: exact side-chain notation]] | 65.0 | Decomposes at 160–165 \((8–10\ \mathrm{mm\ Hg})\) | 9.6 | 10.0 | — | — | — | — |
Experimental Part
Starting reagents.
Guaiacol was a reagent of “pure” grade.
Esterification of vanillic acid with ethyl alcohol was carried out under the conditions of [1]. 1-(4-Hydroxy-3-methoxyphenyl)-propanol-1 was obtained by the method of [2]; m.p. 85–86°C (from benzene).
Analyses: found, %: OH 18.60; OCH$_3$ 16.95.
Calculated, %: OH 18.65; OCH$_3$ 17.00.
Synthesis of thiophosphates.
O-Methyl-O-ethyl chlorothiophosphates of guaiacol and of the ethyl ester of vanillic acid were obtained by the method [3] proposed for the preparation of LeBaycid.
Esterification of 1-(4-hydroxy-3-methoxyphenyl)-propanol-1 was carried out by two methods:
- Under conditions of interaction of O-methyl-O-ethyl chlorothiophosphate with the aliphatic hydroxyl group.
Into a three-necked flask equipped with a dropping funnel, reflux condenser, and stirrer were introduced 3.64 g (0.02 mole) of 1-(4-hydroxy-3-methoxyphenyl)-propanol-1, 15 ml of acetone, and 1.6 g of pyridine. The contents of the flask were heated to the boiling point of acetone, and, with the stirrer operating, 3.49 g (0.02 mole) of O-methyl-O-ethyl chlorothiophosphate was gradually added over 30 min. The reaction mixture was kept at 65–70°C for 3 h, then cooled, poured onto ice, and rapidly extracted with benzene. The benzene solution was dried over Na$_2$SO$_4$ and passed twice through a chromatographic column with Al$_2$O$_3$, $h = 10$ cm.
Benzene and the unreacted starting substances were distilled off under vacuum; an oily product remained at the bottom of the flask, decomposing at 158–160°C.
- Under conditions of esterification of the phenolic hydroxyl group:
$$ 4\ \text{g}\ (0.02\ \text{mole})\ (\mathrm{NaO})(\mathrm{OCH_3})\ \mathrm{C_6H_3CH(OH)CH_2CH_3}, $$
obtained in absolute methyl alcohol by the action of sodium methylate in an equimolecular amount, was introduced into a three-necked flask equipped with a dropping funnel, reflux condenser, and stirrer. Then 15 ml of toluene was added. The contents of the flask were heated to 70–75°C, and, with the stirrer operating, 3.5 g (0.02 mole) of O-methyl-O-ethyl chlorothiophosphate was introduced over 30 min. The reaction mixture was kept at this temperature for 4 h and cooled. The precipitated NaCl was filtered off and washed with toluene; the yield was 99% of theoretical. The toluene solution was dried over Na$_2$SO$_4$ and passed twice through a chromatographic column with Al$_2$O$_3$. The toluene was distilled off under vacuum; the reaction product was obtained as a colorless oil decomposing at 160–165°C.
The characteristics of the thiophosphates obtained are given in Table 1.
LITERATURE
- Beilsteins Handbuch der Organischen Chemie, X, 392, 1932.
- Ph. C. Roberti, R. F. Iork, W. S. Mac Gregor. J. Am. Chem. Soc., 72, 5760, 1950.
- G. Schrader. New Organophosphorus Insecticides, “Mir,” Moscow, p. 337, 1965.