Chemistry

A. S. ONISHCHENKO and N. I. ARONOVA

cis- and trans-1-Halobutadienes and Their Relation to Diene Synthesis

(Presented by Academician B. A. Kazanskii, January 8, 1960)

In a number of papers \((^{1-4})\) it was reported that 1-chlorobutadiene-1,3 does not enter into diene synthesis. This behavior was explained by the stabilizing influence of the chlorine atom at \(C_1\) in the intermediate carbonium system (I), which, because of this, is incapable of ring closure \((^5)\).

\[ \begin{array}{cccccc} \text{(I)} & \text{(II)} & \text{(IIa)} & \text{(III)} & \text{(IIIa)} & \text{(IV)} \end{array} \]

However, the ability of 1-substituted butadienes to undergo diene-synthesis reactions also depends on their geometrical isomerism. It is known that the cis-isomers \((\mathrm{II},\ R = \mathrm{CH_3},\ \mathrm{C_6H_5},\ \mathrm{CN}\ \text{etc.})\), whose structure hinders their conversion into the cisoid conformation \((\mathrm{IIa})\), do not enter into this addition reaction, whereas the trans-dienes \((\mathrm{III})\), for which facile conversion into the cisoid conformation \((\mathrm{IIIa})\) required for diene synthesis may take place, give normal adducts in good yield \((^{6-11})\). From the fact that 1-chloro-2-methyl- \((^{12,13})\), 1-chloro-3-methyl- \((^{14})\), and 1,4-dichlorobutadienes \((^{15})\) react readily with maleic anhydride, it must likewise be concluded that these dienes are trans-isomers. Until now nothing has been known about the geometrical isomerism of 1-halobutadienes, and it could only be assumed that their trans-isomers \((\mathrm{III},\ R = \mathrm{Cl},\ \mathrm{Br})\) should enter into the diene-synthesis reaction, whereas the cis-isomers \((\mathrm{II},\ R = \mathrm{Cl},\ \mathrm{Br})\) would not be capable of this reaction.

We have established that 1-chlorobutadiene, obtained by dehydrochlorination of 1,4-dichlorobutene-2 \((^{2,3,16})\), is a mixture of cis- and trans-isomers in a ratio of approximately \(9:1\), which cannot be separated on a column at 25 theoretical plates. On interaction of this mixture with maleic anhydride \((50–55^\circ,\ 12\ \text{hr})\), a normal diene-synthesis product is formed in up to 10% yield; its structure was proved by dehydrogenation to phthalic anhydride. This fact undoubtedly shows that the initial mixture contains about 10% trans-1-chlorobutadiene, which forms the adduct. The cis-isomer remaining after isolation of the adduct, in accordance with its configuration, is in fact incapable of entering into diene synthesis. However, in the presence of iodine, cis-1-chlorobutadiene is converted comparatively readily into the trans-isomer, giving an equilibrium mixture of cis- and trans-forms, similarly to what occurs in the case of cis-piperylene \((^{17})\). As a result, when a mixture of cis-1-chlorobutadiene with maleic anhydride is heated in the presence of iodine, gradual formation of the adduct corresponding to the trans-isomer takes place, the yield of which may reach 80%. Such conversion of cis-1-chlorobutadiene into the trans-form also occurs at room temperature, but the reaction rate is then low. Were ...

the Raman spectra of cis- and mixtures of cis- and trans-isomers of 1-chlorobutadiene-1,3 were recorded and studied \((^{18})\). Similarly, 1-bromobutadiene-1,3, obtained by dehydrobromination of 1,4-dibromobutene-2 \((^{3,19})\), is a mixture of cis- and trans-isomers \((II+III,\ R = \mathrm{Br})\) in a ratio of approximately \(14:1\), which was proved by condensation of the trans-isomer with maleic anhydride and isolation of the cis-isomer. Under the influence of iodine, cis-1-bromobutadiene is also isomerized to the trans-form, which gives an adduct with maleic anhydride that, already under the experimental conditions \((\sim 70^\circ,\ 100\ \text{hr})\), splits off hydrogen bromide and adds a new molecule of maleic anhydride, giving a bis-anhydride of composition \(\mathrm{C}_{12}\mathrm{H}_8\mathrm{O}_6\).

Experimental Part

1-Chlorobutadiene-1,3 \((II+III,\ R = \mathrm{Cl})\), obtained from 1,4-dichlorobutene, had the following constants: b.p. \(66—67^\circ\) at \(760\ \mathrm{mm}\), \(n_D^{20}\) 1.4712; \(d_4^{20}\) 0.9537. \(MR\) found 25.93. \(\mathrm{C}_4\mathrm{H}_5\mathrm{Cl},\ \mathrm{F}_2\), calculated 24.61. \(\lambda = 232,\ \varepsilon = 17400\).

Anhydride of 3-chloro-\(\Delta^4\)-cyclohexene-1,2-dicarboxylic acid \((IV,\ R = \mathrm{Cl})\). A mixture of 88.5 g (1 mole) of 1-chlorobutadiene and 33 g (0.3 mole) of maleic anhydride (+ hydroquinone) was left overnight at room temperature and then heated for 12 hr at \(50—55^\circ\). The crystalline reaction product that separated was filtered off; 18.3 g (\(\sim 10\%\)) of anhydride (IV) was obtained, which after recrystallization from a mixture of benzene with acetone had m.p. \(130—131^\circ\).

\[ \begin{gathered} \text{Found \%: C 51.42; H 3.78; Cl 19.24}\\ \mathrm{C}_8\mathrm{H}_7\mathrm{O}_3\mathrm{Cl}.\ \text{Calculated \%: C 51.48; H 3.78; Cl 19.01.} \end{gathered} \]

Fusion of the adduct with sulfur \((\sim 230^\circ)\) until the evolution of hydrogen sulfide ceased led to the formation of phthalic anhydride with m.p. \(130—131^\circ\), identical with an authentic sample.

cis-1-Chlorobutadiene-1,3 \((II,\ R = \mathrm{Cl})\). To the diene remaining after removal of the adduct, 5 g of maleic anhydride was added and the solution was heated at \(50—55^\circ\) for another 12 hr. No further formation of adduct was observed. The unreacted cis-1-chlorobutadiene was distilled on a column of 25 theoretical plates. 68 g (\(\sim 78\%\)) of pure cis-diene (II) was obtained; b.p. \(66.8—67^\circ\), \(n_D^{20}\) 1.4703; \(d_4^{20}\) 0.9553. \(MR\) found 25.86. \(\mathrm{C}_4\mathrm{H}_5\mathrm{Cl},\ \mathrm{F}_2\), calculated 24.61; \(\lambda = 232,\ \varepsilon = 17400\).

\[ \begin{gathered} \text{Found \%: C 54.31; H 5.74; Cl 40.05}\\ \mathrm{C}_4\mathrm{H}_5\mathrm{Cl}.\ \text{Calculated \%: C 54.26; H 5.70; Cl 40.05.} \end{gathered} \]

Isomerization of cis-1-chlorobutadiene (II) to the trans-isomer (III). 50 g of the pure cis-isomer, 1 g of iodine, and 50 ml of dry toluene were heated in an ampoule at \(100^\circ\) for 20 hr. After removal of the iodine with sodium thiosulfate, the mixture of isomers was distilled on a column (25 theoretical plates):

To 5 ml of dry toluene were added 3.7 g of the 3rd fraction of the diene and 1 g of maleic anhydride (+ hydroquinone), after which the mixture was heated in an ampoule at \(60^\circ\) for 6 hr. 0.7 g of crystalline adduct (IV) was obtained, identical with that described above, with m.p. \(130^\circ\).

Condensation of a mixture of cis- and trans-1-chlorobutadienes with maleic anhydride in the presence of iodine.
a) To a solution of 3.7 g of the original mixture of isomers of 1-chlorobutadiene and 4 g of maleic anhydride in 20 ml of benzene, 2% iodine and a small amount of

amount of hydroquinone, and the mixture was heated for 24 hours on a boiling water bath in a sealed ampoule. 5 g of adduct (IV) with m.p. 130° was obtained.

b) 1.7 g (0.02 mole) of 1-chlorobutadiene, 1.9 g (0.02 mole) of maleic anhydride, 2% iodine, and traces of hydroquinone were added to 10 ml of dry benzene, and this mixture was left in a sealed ampoule at room temperature for 6 months. The crystalline adduct that separated was isolated; 2.8 g (80%) of the above-described adduct (IV), m.p. 130.5°, was obtained.

1-Bromobutadiene-1,3 (II + III, R = —Br), obtained from 1,4-dibromobutene-2 (m.p. 53°), had the following constants: b.p. 47—48.2° at 161 mm, \(n_D^{20}\) 1.5112, \(d_4^{20}\) 1.3777. \(MR_D\) found 28.78. For \(\mathrm{C_4H_5Br, F_2}\), calculated 27.5.

Anhydride of 3-bromo-\(\Delta^4\)-cyclohexene-1,2-dicarboxylic acid (IV, R = Br). A mixture of 56 g of the starting 1-bromobutadiene (II + III) and 5 g of maleic anhydride in the presence of hydroquinone was left at 25—30° for 5 days. The crystalline reaction product that separated was isolated; 7 g (~7%) of adduct (IV), with m.p. 107—109° with decomposition (from benzene), was obtained.

Found, %: C 41.62; H 3.09; Br 34.16
\(\mathrm{C_8H_7O_3Br}\). Calculated, %: C 41.58; H 3.05; Br 34.16.

Fusion of this adduct with sulfur at 230—235° until evolution of hydrogen sulfide ceased led to phthalic anhydride with m.p. 130°, which gave no depression with an authentic sample.

cis-1-Bromobutadiene-1,3 (II, R = Br). The liquid mixture remaining after separation of the adduct was distilled with a dephlegmator, and after repeated distillation over sodium pure cis-1-bromobutadiene-1,3 (II) was obtained, with b.p. 47—48° at 161 mm; \(n_D^{20}\) 1.5100, \(d_4^{20}\) 1.3878. \(MR_D\) found 28.68; for \(\mathrm{C_4H_5Br, F}\) calculated 27.50.

Found, %: C 36.32; H 3.84; Br 59.36
\(\mathrm{C_4H_5Br}\). Calculated, %: C 36.12; H 3.78; Br 60.09

Condensation of a mixture of cis- and trans-1-bromobutadienes with maleic anhydride in the presence of iodine. A mixture of 22 g (0.17 mole) of the starting 1-bromobutadiene, 18.6 g (0.17 mole) of maleic anhydride, and 0.4 g of iodine in 50 ml of dry benzene was heated in a sealed ampoule for 100 hours at 70°. 8.3 g of crystalline (crude) product was obtained, yield 37%. The substance is difficultly soluble in acetone and acetic anhydride and is a bis-anhydride of composition \(\mathrm{C_{12}H_8O_6}\), with m.p. 364°.

Found, %: C 58.20; H 3.46
\(\mathrm{C_{12}H_8O_6}\). Calculated, %: C 58.07; H 3.25

It is hydrolyzed by alkali as the anhydride of a tetrabasic acid.

Zelinsky Institute of Organic Chemistry
Academy of Sciences of the USSR

Received
2 I 1960

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