CHEMISTRY

A. I. TITOV

NITROSOCHLORINATION OF OLEFINS AND THEIR DERIVATIVES BY AN IONIC MECHANISM

ANOMALOUS ADDITION TO CHLOROETHYLENES

(Presented by Academician M. M. Shemyakin, October 9, 1962)

Nitrosation as substitution is realized for very active forms of unsaturated compounds, for example for enolate ions, similar to ArO⁻:

\[ \mathrm{RCH{=}CR{-}O^-} \]

We also observed rapid nitrosation of mercury derivatives

\[ \mathrm{RCH{=}CH{-}HgX}, \]

similar to the reactions of \(\mathrm{Ar{-}HgX}\). However, for olefins themselves, under the action of nitrosating agents \(\mathrm{NOX}\), the formation of addition products

\[ \mathrm{O{=}N{-}CR_2{-}CR_2{-}X} \]

is characteristic.

According to the theory developed in 1941–1945 \((^{1-3})\), the most active nitrosating agent is the nitrosyl cation

\[ \mathrm{O{=}N^+}, \]

owing to its maximal electrophilicity and coordination unsaturation and, consequently, its ability to form transition complexes through interaction with mobile and spatially accessible \(p\)- or \(\pi\)-electrons, for example, respectively, of amines \(\mathrm{R_2NH}\) and olefins

\[ \mathrm{R_2C{=}CR_2}. \]

In particular, the preparation of nitrates

\[ \mathrm{ON{-}CR_2{-}CR_2{-}ONO_2} \]

by the action of a solution of \(\mathrm{N_2O_4}\) in conc. \(\mathrm{HNO_3}\) was considered as conjugate addition of \(\mathrm{ON^+}\) and \(\mathrm{NO_3^-}\) to the \(\pi\)-bond of olefins \((^{2,3})\).

The formation of nitrosochlorides

\[ \mathrm{ON{-}CR_2{-}CR_2{-}Cl} \]

with the less active

\[ \mathrm{O{=}N^{+\delta}{-}Cl} \]

proceeds readily only with reactive olefins. Nitrosochlorination of ethylene and, as a rule, of haloethylenes was not successful \((^{4-6})\). For example, after prolonged standing (3–15 days at 20°) of mixtures of \(\mathrm{NOCl}\) with chloro- and fluoroethylenes in sealed tubes, nitrochlorides \((^{4,5})\)

\[ \mathrm{O_2N{-}CR_2{-}CR_2{-}Cl} \]

were obtained along with other products; the authors believe these arose as a result of oxidation of nitrosochlorides by \(\mathrm{NOCl}\), and only in the case of 1,2-fluorochloroethylene was \(\mathrm{CHFCl{-}CCl{=}NOH}\) isolated. In our opinion, the reaction is complicated by the equilibrium \((^7)\)

\[ \mathrm{2NOCl \rightleftarrows Cl_2 + 2NO}\quad (0.5\%), \]

and, consequently, by chlorination of haloolefins and interaction of \(\mathrm{NO}\) with nitroso compounds \((^8)\), which should lead to initiation of radical reactions \(\mathrm{NO_2\cdot}\), \(\mathrm{NO_3\cdot}\), and \(\mathrm{Cl\cdot}\).

In accordance with the general theory of nitration—nitrosation, for the smooth and rapid preparation of nitrosochlorides of haloethylenes we successfully applied the action of solutions of halides of the type \(\mathrm{AlCl_3}\) in excess nitrosyl chloride at low temperatures. As has been known since 1938–1948 \((^7)\), these aprotic acids form with \(\mathrm{NOCl}\) complexes of the type

\[ \mathrm{[AlCl_4]^-\,NO^+}, \]

which strongly dissociate into the ions

\[ \mathrm{O{=}N^+} \]

and

\[ \mathrm{AlCl_4^-}, \]

where the latter, or more probably the solvate

\[ \mathrm{AlCl_4^- \rightarrow NO{-}Cl}, \]

serves as a donor of chloride ions. The conjugate addition of \(\mathrm{NO^+}\) and \(\mathrm{Cl^-}\) may be represented by the scheme in which the arc denotes the \(\pi\)-bond and the dotted lines the distribution of \(\pi\)-electron density in transition complex I:

\[ \mathrm{ O{=}N^+ + \left( \begin{matrix} CR_2\\ CR_2 \end{matrix} \right) \rightarrow O{=}N^+ \begin{matrix} CR_2\\[-2pt] \vdots\\[-2pt] CR_2 \end{matrix} \ \xrightarrow[\ -\,NO^+\!\cdot AlCl_4^-\ ]{\ Cl^-\ \ \ NO\!\cdot AlCl_4^-\ } \ O{=}N{-}CR_2{-} \begin{matrix} \\[-8pt] R_2C{-}Cl \end{matrix} } \tag{1} \]

\[ \mathrm{(I)} \]

Similarly, we succeeded in carrying out the addition of $\mathrm{SOCl^+}$, $\mathrm{SO_2Cl^+}$, $\mathrm{PCl_2^+}$ and $\mathrm{Cl^-}$ to olefins and vinyl chloride by means of solutions of $\mathrm{AlCl_3}$ in $\mathrm{SOCl_2}$, $\mathrm{SO_2Cl_2}$, $\mathrm{PCl_3}$, which serves as additional confirmation of the ionic mechanism of our method of nitrosochlorination.

In contrast to related reactions, in particular nitrofluorination ($^9$), in the nitrosochlorination of chloroethylenes an anomalous orientation of $\mathrm{NO^+}$ and $\mathrm{Cl^-}$ was observed. Thus, in the reaction with vinylidene chloride $\mathrm{CH_2=CCl_2}$, 1,1,2-trichloro-1-nitrosoethane, $\mathrm{ON{-}CCl_2{-}CH_2{-}Cl}$, was obtained. We believe that the cause of this deviation from Markovnikov’s rule is the conjugation effect of the halide and the nitroso group according to the scheme

\[ \mathrm{Cl{-}CR_2{-}N{=}O}. \]

This effect, according to our observations, is strongly manifested in the high mobility of chlorine in gem-chloronitroso compounds, for example in the reaction with $\mathrm{Ag^+}$, in the ease of their conversion with $\mathrm{OH^-}$ into $\mathrm{R_2C{=}NOOH}$ and $\mathrm{Cl^-}$, with $\mathrm{N_2H_4}$ into $\mathrm{R_2C{=}NOH}$ (see below), and in similar transformations, as well as in the comparative difficulty of their oxidation and isomerization into the oxime form. According to this hypothesis, the mechanism of anomalous nitrosochlorination, for example of 1-chloroethene, should be expressed as follows:

\[ \mathrm{ O{=}N^+ + \begin{pmatrix} CH_2\\ CHCl \end{pmatrix} \rightarrow ON{-} \begin{matrix} CH_2^{+\delta}\\ |\\ CH{-}Cl \end{matrix} \ \xrightarrow[\ -\,NO^+\!\cdot AlCl_4^-\ ]{\ Cl{-}NO\!\cdot AlCl_4^-\ } ON{-}CH(Cl){-}CH_2Cl } \tag{2} \]

The tendency toward strengthening of the conjugation shown in the complex with $\mathrm{NO^+}$ leads to addition of the chloride ion to carbon 2. In a similar way one may represent the slow nitrosochlorination of $\mathrm{O{=}N^{+\delta}{-}Cl}$, as a donor of $\mathrm{NO^+}$ and $\mathrm{Cl^-}$, all the more so since its ability to form complexes through interaction with $\pi$-electrons is known ($^3$).

Nitrosochlorination was most vigorously activated by $\mathrm{AlCl_3}$; $\mathrm{FeCl_3}$, $\mathrm{SbCl_5}$, and $\mathrm{SnCl_4}$ were also used successfully. Additions of $\mathrm{ZnCl_2}$ acted considerably more weakly owing to the smaller polarization of $\mathrm{NOCl}$ in the adduct

\[ \mathrm{O{=}N{-}Cl \longrightarrow ZnCl_2}. \]

Activation by $\mathrm{AlCl_3}$ and $\mathrm{FeCl_3}$ had, to one degree or another, a catalytic character owing to dissociation of their complexes with nitroso chlorides. Under the action of $\mathrm{NO^+BF_4^-}$ on $\mathrm{CH_2{=}CCl_2}$ and of $\mathrm{NO^+}$ on $\mathrm{C_2F_4}$ in HF ($^9$), nitrofluorination of haloethylenes was observed.

By our method of nitrosochlorination, vinylidene chloride gave 1,1,2-trichloro-1-nitrosoethane $\mathrm{CH_2Cl{-}CCl_2{-}NO}$; trichloroethylene gave 1,1,2,2-tetrachloro-1-nitrosoethane $\mathrm{CHCl_2{-}CCl_2{-}NO}$; 1,2-dichloroethylene gave the acid chloride of dichloroacetohydroxamic acid $\mathrm{CHCl_2{-}CCl{=}NOH}$ (the oxime form of nitroso chloride); vinyl chloride gave $\mathrm{CH_2Cl{-}CCl{=}NOH}$. Nitrosochlorination of ethylene initially gave 1,2-nitrosochloroethane $\mathrm{CH_2Cl{-}CH_2{-}NO}$, which, through chlorination of its oxime form, was converted into $\mathrm{CH_2Cl{-}CCl_2{-}NO}$; the same compound is formed on chlorination of $\mathrm{CH_2Cl{-}CCl{=}NOH}$. Thus, $\mathrm{CH_2Cl{-}CCl_2{-}NO}$ can be obtained both directly from $\mathrm{CH_2{=}CCl_2}$ and from $\mathrm{CH_2{=}CHCl}$ or $\mathrm{CH_2{=}CH_2}$. Photochemical nitrosochlorination of vinylidene chloride with $\mathrm{NOCl}$ in a stream of $\mathrm{NO}$, initiated by $\mathrm{Cl\cdot}$ through photolysis of $\mathrm{O{=}N{-}Cl}$, also gave $\mathrm{CH_2Cl{-}CCl_2{-}NO}$,

\[ \mathrm{CH_2{=}CCl_2 + Cl\cdot \rightarrow CH_2Cl{-}\dot{C}Cl_2 \xrightarrow{\ NO\ } CH_2Cl{-}CCl_2{-}NO,} \tag{3} \]

but in this case it was the product of normal addition by a radical mechanism.

Tetrachloroethylene did not undergo nitrosochlorination by the ionic mechanism owing to its increased electrophilicity and steric hindrance, but photochemical nitrosochlorination of $\mathrm{C_2Cl_4}$ according to an equation of type 3 proceeded rapidly on irradiation with a mercury lamp. In the seeming contra-

In this connection, tetrafluoroethylene, despite its gaseous state, reacted with \(\mathrm{NO^+AlCl_4^-}\) and gave a good yield of \(\mathrm{Cl—CF_2—CF_2—NO}\). The activity of \(\mathrm{C_2F_4}\) is due to the greater conjugation effect in the group \(\mathrm{F—C=C}\), of the type \(\overset{\downarrow}{\mathrm{F}}—\mathrm{C}=\mathrm{C}\), than in its chlorine analogue \(\mathrm{Cl—C=C}\), owing to the closeness of the sizes of the orbitals of C and F.

The conjugation of halides according to the scheme \(\mathrm{X—C=C}\) may be called a vicinal effect, while that considered in equation 2 may be called a geminal effect. From what has been said above it follows that in F atoms, in ionic nitrosochlorination, the vicinal effect predominates, whereas in Cl atoms the geminal effect does. In accordance with this conclusion, \(\mathrm{CF_2=CH_2}\), in contrast to \(\mathrm{CCl_2=CH_2}\), gave in this reaction \(\mathrm{CF_2Cl—CH=NOH}\), \(\mathrm{CHF=CHCl—CHFCl—CCl=NOH}\), \(\mathrm{CF_2=CFCl—CF_2Cl—CFCl—NO}\). The formation of \(\mathrm{Cl—HCCl—CCl_2—NO_2}\) from \(\mathrm{CHCl=CCl_2}\), \(\mathrm{Cl—CHF—CCl_2—NO_2}\) from \(\mathrm{CHF=CCl_2}\), and \(\mathrm{Cl—CF_2—CFCl—NO_2}\) from \(\mathrm{CF_2=CFCl}\) in slow reactions with \(\mathrm{NOCl}\) as such (see above), in the light of our data, can be rationally represented as occurring through oxidation of the corresponding nitrosochlorides. In prolonged nitrosochlorination of \(\mathrm{CF_2=CFCl}\) by means of \(\mathrm{NO^+AlCl_4^-}\), we also detected the formation of the nitrochloride along with the nitrosochloride, the principal reaction product. In a recent work \((^{10})\) on the nitrosochlorination of fluorochloroethylenes in the presence of \(\mathrm{FeCl_3}\) at \(45^\circ\) in a flow system, orientation in agreement with our hypothesis was also observed, although the authors themselves do not take into account the fundamental role of \(\mathrm{FeCl_3}\).

The addition of \(\mathrm{NO^+}\) and \(\mathrm{X^-}\) is accompanied by the formation of telomers \(\mathrm{ON—(—CR_2—CR_2—)_n—X}\), for example in the nitrosochlorination of \(\mathrm{CF_2=CFCl}\) by means of \(\mathrm{NO^+AlCl_4^-}\), with molecular weight \(\sim 500\). To nitrosohalogenation we can apply a number of conclusions drawn in discussing nitrofluorination \((^9)\). It is possible that nitrosohalogenation and nitrofluorination of electrophilic unsaturated compounds of the type \(\mathrm{X—C\equiv C—X}\) or \(\mathrm{(CF_3)_2C=CF_2}\) will also proceed by a mechanism of nucleophilic addition, for example through the action of \(\mathrm{NOF}\) and \(\mathrm{C(NO_2)_4}\) in the presence of \(\mathrm{NR_4^+F^-}\).

Judging from the chemical nature and electronic structure of the ring, cyclopropane compounds are also capable of adding \(\mathrm{NO^+}\) and \(\mathrm{Cl^-}\) with formation of 1,3-nitrosochlorides \((^{2,3})\).

We give a description of several nitrosochlorination experiments.

1. Into a reactor containing a solution of 2 g of \(\mathrm{AlCl_3}\) in 10 ml of \(\mathrm{NOCl}\) at \(-20^\circ\), 25 g of \(\mathrm{CH_2=CCl_2}\) was added dropwise with stirring over 30 min; then, after standing for 1–2 hr, the contents were poured onto ice, the nitrosochloride was separated off and dried with \(\mathrm{CaCl_2}\). After distillation in vacuum, about 30 g of dark-blue \(\mathrm{CH_2Cl—CCl_2—NO}\) was obtained, b.p. \(36^\circ\) at 40 mm; \(d_4^{20}\) 1.489; \(n_D^{20}\) 1.4660; molecular weight 159.

Found, %: N 8.7; Cl 65.8

It, as well as \(\mathrm{CH_3—CCl_2—NO}\), immediately reacts with \(\mathrm{AgNO_3}\) in alcohol. On prolonged standing of the product in \(\mathrm{HNO_3}\) of specific gravity 1.5, it is converted into \(\mathrm{CH_2Cl—COOH}\), identified in the form of the anilide, m.p. \(133^\circ\).

1. Analogously, from 40 g of \(\mathrm{NOCl}\), 20 g of \(\mathrm{AlCl_3}\), and 40 g of \(\mathrm{CHCl=CCl_2}\), 23 g of tetrachloronitrosoethane was obtained, b.p. \(56^\circ\) at 40 mm.

Found, %: N 7.1; Cl 70.9

1. To a solution of 13.5 g of \(\mathrm{AlCl_3}\) in 40 g of \(\mathrm{NOCl}\) at \(-30^\circ\), about 50 g of liquid vinyl chloride is added, and after 4–5 hr it is poured onto ice; the oil is quickly separated, dried with \(\mathrm{MgSO_4}\), and distilled in vacuum. More than 30 g of the acid chloride of chloroacetohydroxamic acid, \(\mathrm{CH_2Cl—CCl=NOH}\), is obtained, b.p. \(78^\circ\) at 10 mm.

Found, %: N 11.2; Cl 55.1

In a mixture with water, the product gave a reaction for \(Cl^{-}\) and hydroxamic acid; in \(HNO_3\) it was rapidly converted into \(CH_2Cl—COOH\), and upon chlorination in 5% HCl at \(0^\circ\)—into \(CH_2Cl—CCl_2—NO\), described in experiment 1; it can be obtained in still better yield by chlorinating the mixture immediately after pouring it onto ice. Conversely, by adding \(CH_2Cl—CCl_2—NO\) at \(0^\circ\) to an aqueous hydrazine solution, \(CH_2Cl—CCl=NOH\) can be obtained in a yield \(>80\%\); \(CH_3—CCl_2—NO\) reacted analogously.

1. From 65 g of \(NOCl\), 13.5 g of \(AlCl_3\), and 60 g of 1,2-dichloroethylene under conditions similar to experiment 3, 31.2 g of \(CHCl_2—CCl=NOH\) were obtained, with b.p. \(86^\circ\) at 15 mm; \(d_4^{20}\) 1.597; \(n_D^{20}\) 1.5187.

Found, %: N 8.8; Cl 65.2

In \(HNO_3\) the product was converted into \(CHCl_2—COOH\), identified as the anilide with m.p. \(117^\circ\); upon chlorination, the resulting acid chloride of dichloroacetohydroxamic acid was converted into the tetrachloronitrosoethane of experiment 2.

1. Into a solution of 13.5 g of \(AlCl_3\) in 40 g of \(NOCl\), while cooling with solid \(CO_2\) and vigorously stirring in a shaker for 6 h, a slow stream of ethylene was passed. After pouring onto ice, about 10 g of an oil with the properties of \(\beta\)-chloroacetaldoxime were obtained; 7 g of this, for identification, were converted by chlorination, as in experiment 3, into \(CH_2Cl—CCl_2—NO\) in a yield of about 5 g.

2. Analogously, for 3 h, 6 l of \(C_2F_4\) were passed through, and then the temperature was raised to \(+5^\circ\). After washing, drying, and cooling the exit gases at \(-50^\circ\), about 30 g of a blue liquid were obtained, from which \(Cl—CF_2—CF_2—NO\), b.p. \(-5^\circ\), was isolated.

Found, %: F 44.5; Cl 21.6

The results of the iodometric determination of the ON group are close to theory.

In the experimental part of the study in 1950–1955, V. V. Smirnov, N. V. Shchitov, G. B. Petrova, and P. O. Gitel’ participated, and in the preparation of the article—F. L. Maklyaev, to whom I express my deep gratitude for this.

Received
5 X 1962

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