Full Text
CHEMISTRY
Academician I. L. Knunyants, N. D. Kuleshova, and M. G. Lin’kova
ON THE STRUCTURE OF THE ADDITION PRODUCTS OF ALKYLSULFENYL CHLORIDES TO UNSATURATED ACIDS
The ease of isomerization of α-haloid-β-(alkylthio)-substituted propionic acids into β-haloid-α-alkylthio derivatives under the action of nucleophilic reagents ($^{1}$), and in some cases already upon heating ($^{2}$),
\[ \mathrm{RSCH_2CHClCOOR'} \ \xrightleftharpoons[\ ]{\Delta}\ \mathrm{CH_2ClCH(SR)COOR'} \]
makes it difficult to determine the structure of compounds obtained by addition of alkylsulfenyl chlorides to acrylic systems.
Nevertheless, we have recently shown that ethylsulfenyl chloride adds to acrylonitrile with formation of the nitrile of β-chloro-α-(ethylthio)propionic acid ($^{3}$)
\[ \mathrm{CH_2{=}CHCN \ \xrightarrow{C_2H_5SCl}\ CH_2ClCH(SC_2H_5)CN.} \]
The mode of addition of alkylsulfenyl chlorides to α,β-unsaturated acids and their esters remained open.
By the interaction of alkylsulfenyl chlorides with acrylic acid, its homologs (methacrylic, dimethylacrylic, and crotonic acids), and also their esters, we obtained a series of β-chloro-α-(alkylthio) derivatives of propionic acid (see Table 1), the structure of which was established by comparing the reaction of methyl β-chloro-α-(ethylthio)isobutyrate I with ethyl β,β-dimethyl-β-chloro-α-(ethylthio)propionate
Table 1
| Substance | Yield, % | B.p., °C/mm | $d^{20}_{4}$ | $n^{20}_{D}$ | MR found | MR calc. | Found, % C | Found, % H | Calculated, % C | Calculated, % H |
|---|---|---|---|---|---|---|---|---|---|---|
| β-Chloro-α-(alkylthio) derivatives of propionic acid | ||||||||||
| $\mathrm{ClCH_2{-}C(SC_2H_5)CH_3COOCH_3}$ (I) | 86 | 96—97°/8 | 1,1511 | 1,4848 | 48,91 | 49,02 | 42,31 | 6,59 | 42,74 | 6,60 |
| $\mathrm{CH_3CHClCH(SC_2H_5)COOCH_3}$ | 100 | 98—100°/10 | 1,138 | 1,4800 | 49,05 | 49,02 | 42,61 | 6,65 | 42,74 | 6,60 |
| $\mathrm{ClCH_2CH(SC_2H_5)COOCH_3}$ ($^{4}$) | 72 | 93—94°/10 | 1,175 | 1,4850 | 44,51 | 44,43 | ||||
| $\mathrm{(CH_3)_2CClCH(SC_2H_5)COOC_2H_5}$ (II) | 77 | 112—113°/10 | 1,076 | 1,4733 | 58,46 | 58,29 | ||||
| $\mathrm{CH_2ClCH(SC_2H_5)COOH}$ | 53,5 | 98—100°/0,004 | 1,247 | 1,5071 | 40,19 | 39,66 | 36,25 | 5,23 | 35,61 | 5,34 |
| $\mathrm{CH_2ClC(SC_2H_5)CH_3COOH}$ (III) | 81 | 115—120°/0,004 | 1,204 | 1,5020 | 43,89 | 44,28 | 39,39 | 5,85 | 39,45 | 6,02 |
| $\mathrm{CH_2ClCH(SCH_3)COOH}$ (IV) | 42,7 | 73—75,5 * | 31,16 | 4,35 | 31,06 | 4,53 | ||||
| $\mathrm{CH_2ClC(SCH_3)CH_3COOH}$ | 81,3 | 72—74 * | 35,82 | 5,20 | 35,61 | 5,34 | ||||
| $\mathrm{CH_3CHClCH(SC_2H_5)COOH}$ | 54,8 | 85—86 * | 39,18 | 5,77 | 39,45 | 6,02 | ||||
| Acid chlorides of β-chloro-α-(alkylthio)propionic acids | ||||||||||
| $\begin{array}{c}\mathrm{CH_2{-}C{-}COCl}\\[-2pt]\vert\ \ \ \diagup\!\!\mathrm{CH_3}\\[-2pt]\mathrm{Cl}\ \ \ \diagdown\!\!\mathrm{SC_2H_5}\end{array}$ | 70 | 109—110°/5—6 | 1,5097 | 35,18 | 4,74 | 35,80 | 4,97 | |||
| $\begin{array}{c}\mathrm{CH_2{-}C{-}COCl}\\[-2pt]\vert\ \ \ \diagup\!\!\mathrm{CH_3}\\[-2pt]\mathrm{Cl}\ \ \ \diagdown\!\!\mathrm{SCH_3}\end{array}$ | 85 | 82,5—83,5°/9 | 1,301 | 1,5100 | 42,98 | 43,00 | 31,45 | 4,39 | 32,08 | 4,27 |
| $\begin{array}{c}\mathrm{CH_2{-}CH{-}COCl}\\[-2pt]\vert\ \ \ \vert\\[-2pt]\mathrm{Cl}\ \ \ \mathrm{SC_2H_5}\end{array}$ | 40,2 | 79—80°/3 | 1,306 | 1,5165 | 42,95 | 43,00 | 31,41 | 4,07 | 32,08 | 4,27 |
* Melting points are given.
acids II and β-chloro-α-(ethylthio)isobutyric acid III with β-chloro-α-(methylthio)propionic acid IV.
Thus, upon the action of two moles of 2 N NaOH in methanol on I and II under identical conditions, β-methoxy-α-(ethylthio)isobutyric acid (V) and β,β-dimethyl-α-(ethylthio)acrylic acid (VI) were isolated:
\[ \mathrm{ClCH_2CCH_3(SC_2H_5)COOCH_3} \ \xrightarrow[\mathrm{CH_3OH}]{2\mathrm{NaOH}}\ \begin{matrix} \mathrm{CH_2 - CCH_3 - COOH}\\ \big| \qquad \big|\\ \mathrm{OCH_3}\quad \mathrm{SC_2H_5} \end{matrix} \qquad \begin{matrix} \mathrm{(I)}\\[2.5em] \mathrm{(V)} \end{matrix} \]
\[ \begin{matrix} \mathrm{CH_3}\\ \diagdown\\[-0.4em] \mathrm{C - CH - COOC_2H_5}\\ \diagup\ \big|\quad \big|\\[-0.2em] \mathrm{CH_3}\quad \mathrm{Cl}\quad \mathrm{SC_2H_5} \end{matrix} \ \xrightarrow[\mathrm{CH_3OH}]{2\mathrm{NaOH}}\ \begin{matrix} \mathrm{CH_3}\\ \diagdown\\[-0.4em] \mathrm{C = C - COOH}\\ \diagup\quad \big|\\[-0.2em] \mathrm{CH_3}\quad \mathrm{SC_2H_5} \end{matrix} \qquad \mathrm{(II)} \qquad \mathrm{(VI)} \]
Upon the action of triethylamine on II in ethereal solution, with elimination of hydrogen chloride, the ethyl ester of β,β-dimethyl-(α-ethylthio)acrylic acid is formed \((^3)\). Under these conditions I remains unchanged.
β-Chloro-α-(ethylthio)isobutyric acid III, with an aqueous solution of potassium bicarbonate, forms β-hydroxy-α-(ethylthio)isobutyric acid (VII):
\[ \begin{matrix} \mathrm{CH_2 - CCH_3 - COOH}\\ \big|\qquad \big|\\ \mathrm{Cl}\quad \mathrm{SC_2H_5} \end{matrix} \ \xrightarrow[\mathrm{KHCO_3}]{\mathrm{H_2O}}\ \begin{matrix} \mathrm{CH_2 - CCH_3 - COOH}\\ \big|\qquad \big|\\ \mathrm{OH}\quad \mathrm{SC_2H_5} \end{matrix} \qquad \mathrm{(III)} \qquad \mathrm{(VII)} \]
β-Chloro-α-(methylthio)propionic acid IV, under the same conditions or with triethylamine in chloroform solution, forms the unstable α-methylthioacrylic acid (VIII).
Both from acid VIII and from the mother liquor, 2,4-dinitrophenylhydrazone of pyruvic acid was isolated:
\[ \begin{matrix} \mathrm{CH_2 - CH - COOH}\\ \big|\quad \big|\\ \mathrm{Cl}\quad \mathrm{SCH_3} \end{matrix} \ \xrightarrow[\mathrm{KHCO_2}]{\mathrm{H_2O}}\ \begin{matrix} \mathrm{CH_2 = C - COOH}\\ \big|\\ \mathrm{SCH_3} \end{matrix} \ \rightarrow\ \begin{matrix} \mathrm{CH_2 = C - COOH}\\ \big|\\ \mathrm{OH} \end{matrix} \ \rightarrow\ \mathrm{CH_3 - COCOOH} \qquad \mathrm{(IV)} \qquad \mathrm{(VIII)} \]
These properties confirm that alkylsulfenyl chlorides add to methacrylic and dimethylacrylic acids and to their esters in accordance with the polarity of the reagents:
\[ \begin{matrix} & \curvearrowright & \curvearrowright \mathrm{O}\\[-0.2em] \mathrm{>C^{\delta+}=C-C\!\left<} \end{matrix} \ +\ \mathrm{R-S^{\delta+}-Cl^{\delta-}} \ \rightarrow\ \begin{matrix} \mathrm{>C-C-C\!\left<}\\ \big|\quad \big|\quad \big\|\\ \mathrm{Cl}\quad \mathrm{SR}\quad \mathrm{O}\\ && \mathrm{OX} \end{matrix} \]
From β-chloro-α-(alkylthio)propionic acids, the corresponding acid chlorides were obtained with thionyl chloride (see Table 1).
On the basis of literature data \((^{1,2,6})\), isomerization upon heating with thionyl chloride of β-halo-α-(alkylthio) derivatives of propionic acid into α-halo-β-(alkylthio)-substituted compounds should not occur. Confirmation of the structure of the acid chlorides as β-halo-α-(alkylthio) derivatives of propionic acid is also provided by formation, with \(\mathrm{Na_2S}\), of β-propiothiolactones \((^7)\):
\[ \begin{matrix} & \mathrm{SR}\\[-0.2em] & \big|\\ \mathrm{>C-C}\\ \big|\quad \big|\\ \mathrm{X}\quad \mathrm{COCl} \end{matrix} \ +\ \mathrm{Na_2S} \ \rightarrow\ \begin{matrix} & \mathrm{SR}\\[-0.2em] & \big|\\ \mathrm{>C-C}\\ \big|\quad \big|\\ \mathrm{S-CO} \end{matrix} \]
Thus, alkylsulfenyl chlorides add to unsaturated esters and acids in the same order as to nitriles, namely with the formation of β-halo-α-(alkylthio) derivatives.
Experimental Part
General method for preparing β-chloro-α-alkylthiopropionic acids and their derivatives. To acrylic acid, its derivatives, or homologs in ether or chloroform solution, 1 : 3, an equivalent amount of alkylsulfenyl chloride in the same solvent and ratio was added with cooling by ice water. The addition proceeds with noticeable heating and is completed rapidly. After removal of the solvent in vacuo, β-chloro-α-(alkylthio)propionic acids or their derivatives were obtained; for purification these were distilled in vacuo or crystallized. The yields were almost quantitative.
β-Methoxy-α-(ethylthio)isobutyric acid V. To a solution of 15.7 g of I in 50 ml of methanol, 100 ml of a 2 N solution of NaOH in methanol was added dropwise. The reaction immediately becomes alkaline. On the following day the alcohol was evaporated, the residue was dissolved in water, and the unreacted starting material (0.6 g) was extracted with ether. After acidification of the aqueous layer, 7.5 g (52.5%) of VIII was obtained, b.p. 110—112°/0.004 mm; specific gravity 1.117; \(n_D^{20}\) 1.485; \(MR\) found 45.39, calculated 45.68.
Found, %: C 47.31; H 8.12; S 17.40
\(\mathrm{C_7H_{14}O_3S}\). Calculated, %: C 47.19; H 7.86; S 17.97
α-Ethylthio-β,β-dimethylacrylic acid VI. 0.08 mole of II was treated with 2 N NaOH in methanol under the conditions of the preceding experiment. However, until approximately one-half of the alcoholic alkali had been added, the reaction mixture remained neutral. After isolation, 33.7% of the ethyl ester of β,β-dimethylacrylic acid \((^8)\) was obtained, b.p. 91—93°/10 mm; specific gravity 1.028; \(n_D^{20}\) 1.4861; \(MR\) found 52.50; calculated 52.93, and 52.7% of VI, b.p. 95—96°/3 mm; specific gravity 1.077; \(n^{20}\) 1.4967; \(MR\) found 43.40; calculated 43.69.
β-Oxy-α-(ethylthio)isobutyric acid VII. 9.1 g of III in 200 ml of ether was shaken with water for 3 hours. No cleavage of ionic halide was observed. The ethereal solution was then treated with a 10% solution of potassium bicarbonate until alkaline. From the aqueous solutions, by acidification, VII was obtained, b.p. 135°/0.004 mm; specific gravity 1.172; \(n_D^{20}\) 1.4940; \(MR\) found 40.86; calculated 40.94. Molecular weight: found 165.2, calculated 164 (by titration).
Found, %: C 44.30; H 7.27; S 18.85
\(\mathrm{C_6H_{12}O_3S}\). Calculated, %: C 43.90; H 7.31; S 19.51
α-Methylthioacrylic acid VIII. 3 g of IV was treated with a 10% solution of potassium bicarbonate until alkaline reaction (\(\sim 2\) moles) and left for 2 hours at room temperature. After acidification of the aqueous solution with cooling, α-methylthioacrylic acid precipitated. The acid is soluble in water and readily soluble in alcohol and ether. M.p. 85—88° (from petroleum ether). From the aqueous solution, the 2,4-dinitrophenylhydrazone of pyruvic acid was isolated, m.p. 216° (from alcohol). A mixed sample with an authentic specimen gives no depression of the melting point.
Found, %: C 39.60; H 5.37; S 26.4
\(\mathrm{C_4H_6O_2S}\). Calculated, %: C 40.67; H 5.08; S 27.1
Institute of Organoelement Compounds
Academy of Sciences of the USSR
Received
25 VII 1960
References Cited
- K. D. Gundermann, Ann., 588, 167 (1954); 89, No. 5, 1263 (1956).
- K. D. Gundermann, Chem. Ber., 88, No. 9, 1432 (1955).
- M. G. Lin’kova, N. D. Patrina, I. L. Knunyants, DAN, 127, No. 4, 799 (1959).
- H. Brintzinger, M. Langheck, Chem. Ber., 87, No. 3, 325 (1954).
- I. L. Knunyants, M. G. Lin’kova, L. G. Ignatenok, Izv. AN SSSR, OKhN, 1955, No. 1, 54.
- R. C. Fuson, Ch. C. Price, D. M. Burness, J. Org. Chem., 11, No. 5, 475 (1946).
- M. G. Lin’kova, N. D. Patrina, I. L. Knunyants, DAN, 127, No. 3, 564 (1959).