US3415897A - Dehydrohalogenation of quaternary carbon atom-containing halogenated hydrocarbons - Google Patents

Description

United States Patent 3,415,897 DEHYDROHALOGENATION 0F QUATERNARY CARBON ATOM-CONTAINING HALOGENATED HYDROCARBONS Gary L. Gehrman, Homewood, and Byron W. Turnquest, Chicago, Ill., assignors to Sinclair Research Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed Aug. 3, 1966, Ser. No. 569,811 Claims. (Cl. 260-677) ABSTRACT OFTHE DISCLOSURE Quaternary carbon atom-containing halogenated hydrocarbons of the formula:

wherein R is an alkyl radical of up to 8 carbon atoms, the total carbon atoms in the three R groups being up to 18, R is a divalent hydrocarbon radical of 2 to 8 carbon atoms, and X is a halogen having an atomic weight of 35 to 127 (e.g. neohexyl chloride) are thermally dehydrohalogenated to the corresponding mono-olefins by first forming an intermediate complex of the halogenated hydrocarbon with collidine, followed by decomposing the intermediate complex to yield the corresponding quaternary carbon atom-containing mono-olefin. At least equimolar amounts of collidine are used, based on the amount of halogenated hydrocarbon feed.

The present invention relates to the production of substantially pure quaternary carbon atom-containing monoolefins by the dehydrohalogenation of quaternary carbon atom-containing halogenated hydrocarbons.

' Heretofore, methods for the production of quaternary carbon atom'containing olefins such as neohexene (3,3-dimethylbutene-l) by thermal dehydrohalogenation of the corresponding halogenated hydrocarbon, provide a reaction product that includes, in addition to the quaternary carbon atom-containing mono-olefin, certain side reaction products and hydrogen halide which can be removed by any of the known procedures of the art as, for instance, by fractional distillation. However, since side products formed in the dehydrohalogenation are tertiary olefins having boiling points close to that of the desired quaternary carbon atom-containing mono-olefin, removal of these side products by straight fractionation is difficult and requires high efficiency and costly fractionation equipment.

A process for the dehydrohalogenation of quaternary carbon-containing alkyl halides to the corresponding quaternary carbon-containing monoolefins has now been discovered which not only provides the desired product in essentially pure form but in yields of at least 85 mole percent and even greater than 90 mole percent. In accordanee with the present invention, a quaternary carboncontaining alkyl halide feed is thermally dehydrohalogenated in the presence of collidine, in a particular manner, employing two different ranges of reaction temperatures. We have found that the neoalkyl halide feed of the invention reacts with collidine under select temperatures, i.e., about 300 to 370 F. to form an intermediate complex with collidine, and that the intermediate complex com pletely decomposes when subjected to a heat treatment at elevated temperatures below the decomposition temperature of collidine, usually at least 440 F. up to 500 F., to provide the desired quaternary carbon-containing monoolefin and collidine hydrohalide, At least a molar equiv- Patented Dec. 10, 1968 alent, preferably a molar excess, of collidine is reacted with the neoalkyl halide feed. In general, a mole ratio of collidine to neoalkyl halide feed of about 1 to 20, preferably about 1 to 5 moles of collidine per mole of neoalkyl halide is employed at a temperature of about 300 to 370 F. for a time sufficient to form the intermediate complex, and the intermediate complex is subjected to heat treatment at a temperature of about 440 to 500 F. while recovering the corresponding quaternary carbon-containingmono-olefin and collidine hydrohalide. The reaction time of the neoalkyl halide feed and collidine will vary according to the particular temperature selected but is that sufficient to form the intermediate complex. In most instances, the reaction time is at least about 2 hours, preferably at least about 5 hours. Normally, heating the reactants from ambient temperature to 400 F. in a batch system gives suflicient time to form the intermediate in the low temperature phase. In a flow system, however, where the reactor is held at approximately 400 F., little or no intermediate formation or dehydrohalogenation takes place unless a low temperature zone has been included.

The reaction temperatures employed in the dehydrohalogenation process of the invention are extremely important in obtaining yields of the desired products in excess of mole percent. For example, if the neoalkyl halides feed and the collidine are subjected initially to too high a temperature (i.e., beyond about 370 F.) the intermediate will not form. Likewise, if the high temperature second stage of the invention (i.e., beyond about 440 F.) is not included, the intermediate complex formed in the first stage will not properly decompose into the desired product resulting in considerable yield loss. Moreover, complete decomposition of the intermediate is desired not only to obtain the high yield reaction but also for the recovery of collidine. If the high temperature stage of the invention is not included in the process, the collidine hydrohalide forms an agglomerate with the undecomposed intermediate and is recovered as rather large spheres, approximately 2 to 5 mm. in diameter. When the high temperature second stage of the invention is employed in the process, the resulting collidine hydrohalide is, in contrast, in the form of minute crystalline needles. The resulting size and form of the collidine hydrohalide product is of importance when recovering collidine by regeneration from its hydrohalide salt with anhydrous ammonia. The minute crystalline needles from the high temperature reaction respond very well to ammonia treatment whereas the spheres of collidine hydrohalide resulting from a reaction in which the second stage high temperature treatment was not included do not react readily with anhydrous ammonia and collidine recovery is very difficult.

The halogenated hydrocarbon feed subjected to the dehydrohalogenation of the present invention may be rep resented by the general formula:

wherein R is an aliphatic monovalent hydrocarbon radical such as a lower alkyl, including cycloallkyl, of up to 8 carbons, the total carbon atoms in all Rs being up to 18, preferably up to 12, and R may be branched or substituted with noninterfering groups; R is a divalent aliphatic hydrocarbon radical, e.g., alkylene, of 2 to 8 carbons, preferably 2 to 4 carbon atoms; and X is a halogen atom having an atomic weight of 35 to 127. Preferably, the halogen is substituted on a carbon atom beta to the neo-carbon atom. It is particularly preferred that the beta carbon atom be at an end of the carbon chain. Suitable feeds include, for instance, 1-chloro-3,3-dimethylbutane; 1-chloro-3,3-dimethylpentane; 2hloro-4,4-dimethylpentane, etc.

The following examples are included to further illustrate the process of the present invention:

EXAMPLE 1 8.4 moles of collidine and 7 moles of neohexyl chloride (1.2:1 mole ratio) were charged to a one gallon glasslined stirred autoclave. The temperature was maintained at 330 F. After 8 hours low-boiling products were discharged overhead through a water-cooled condenser into Dry Ice traps. A 10 mole percent yield of neohexene was obtained. Reactor residue contained only collidine, neohexyl chloride and a small amount of collidine hydrochloride.

EXAMPLE 2 12.8 moles of collidine and 10.7 moles of neohexyl chloride (1.2:1 mole ratio) were charged to the autoclave described in Example 1. Temperature was maintained at 350 F. After 7 hours low-boiling products were discharged overhead through a water-cooled condenser into Dry Ice traps. 15 mole percent neohexene was obtained. The reactor residue contained collidine, neohexyl chloride and an insoluble tar-like material mixed with the collidine hydrochloride.

EXAMPLE 3 The liquid phase was decanted from the reactor residue from Example 2. The remaining solid phase was treated with acetone. The tar was very soluble and crystals of collidine hydrochloride were removed by filtration. The solvent and residual collidine and neohexyl chloride were removed by vacuum distillation. The remaining tar was submitted for carbon, hydrogen and chlorine analysis. The results of the analysis listed in Table I indicate that the I By difierence.

A sample of the intermediate was heated in a distillation apparatus at atmospheric pressure. It partially decomposed at 405 F. to yield 28 wt. percent neohexene, 15 wt. percent neohexyl-chloride, collidine hydrochloride and higher boiling material.

EXAMPLE 4 12.8 moles of collidine and 10.7 moles of neohexyl chloride (1.211 mole ratio) were charged to the autoclave described in Example 1. Temperature was maintained at 390405 F. Low-boiling products were discharged overhead throughout the experiment at a rate sufficient to maintain reactor pressure at 100 p.s.i.g. After 6 hours the pressure dropped and remained below 100 p.s.i.g. indicating the reaction was complete. Low boiling products were discharged overhead through a water cooled condenser into Dry Ice traps. Neohexene was obtained in 85 mole percent yield. The reactor residue contained collidine, neohexyl chloride and collidine hydrochloride mixed with a small amount of the tar-like intermediate.

EXAMPLE 914 pounds of collidine and 455 pounds of neohexyl chloride (2:1 mole ratio) were charged to a 200 gallon glass-lined stirred autoclave. Temperature was raised to 370 F. at which point neohexene was produced at a rapid rate and was discharged overhead through an efficient water cooled column at a rate sufficient to maintain a reactor pressure of 50 p.s.i.g. The temperature of the reactor was raised to 410 F. as the rate of neohexene coming overhead decreased. The reaction yielded 268 pounds (85.5 mole percent) of neohexene. Plugging was encountered when an attempt was made to discharge the reactor residue through the 1 inch bottom draw of the autoclave. The plugging was caused by the solid phase which consisted of spheres, 2-5 millimeters in diameter, of collidine hydrochloride and the agglutinant intermediate EXAMPLE 6 1,030 pounds of collidine and 345 pounds of neohexyl chloride (3:1 mole ratio) was charged to the 200 gallon autoclave. The operating procedure was the same as that described in Example 5 with the exception that the final reactor temperature was 444 F. The reaction yielded 212 pounds (89.5 mole percent) of neohexene. The tarlike intermediate was absent and no plugging was encountered upon discharge of the reactor residue. The collidine hydrochloride was obtained as fine crystals slurried with the liquid phase remaining in the reactor.

EXAMPLE 7 795 pounds of collidine and 663 pounds of neohexyl chloride (1.221 mole ratio) were charged to the 200 gallon autoclave. The operating procedure was the same as that described in Example 5 with the exception that the final reactor temperature was 485 F. The reaction yielded 428 pounds (93 mole percent) of neohexene. The reactor residue was the same as that described in Example 6. No plugging problem was encountered.

EXAMPLE 8 Collidine and neohexyl chloride were fed continuously at a 3 to 1 mole ratio to the 200 gallon autoclave at a temperature of 400 F. The pressure was changed to obtain the best possible purity of neohexene in the overhead without losing too much neohexene in the bottoms. Approximately 4 wt. percent neohexene was the least concentration in the bottoms at any pressure. The yield was low due to the slow reaction rate under these conditions.

It is claimed:

1. A process for the production of substantially pure quaternary carbon atom-containing mono-olefins which comprises thermally dehydrohalogenating in the presence of collidine, a halogenated hydrocarbon having the general formula:

wherein R is an alkyl radical of up to 8 carbon atoms, the total carbon atoms in the three R groups being up to 18; R is a divalent aliphatic hydrocarbon radical of 2 to 8 carbon atoms; and X is a halogen having an atomic weight of 35 to 127, said collidine being present in at least equimolar amounts based on the amount of halogenated hydrocarbon, at a temperature of about 300 to 370 F., for a time sufiicient to form an intermediate complex of collidine and said halogenated hydrocarbon and decomposing the intermediate complex to provide said quaternary carbon atom-containing mono-olefin.

2. The process of claim 1 wherein the halogenated hydrocarbon is a neoalkyl chloride.

3. The process of claim 2 wherein the neoalkyl chloride is neohexyl chloride.

4. The process of claim 1 wherein the decomposition is conducted at a temperature of at least about 440 F.

5. The process of claim 4 wherein about 1 to 20 moles of collidine are present, based on the amount of halogen- References Cited ated hydrocarbon.

6. The process of claim 5 wherein R is alkylene and UNITED STATES PATENTS X is substituted on a carbon atom which is beta to the 3,227,770 1/1966 Burk et a1 260677 neo carbon atom 5 3,227,766 1/ 1966 Kruse et a1 260 677 7. The process of claim 6 wherein the carbon atom beta to the neo-carbon atom is at the end of the carbon OTHER REFERENCES chain. Brewster & McEwe n, Organic Chemistry, third edi- 8. The process of claim 7 wherein about 1 to 5 moles tion, 1964, p. 740. of collidine are present, based on the amount of halogen- 10 ated hydrocarbor E. Primary EXLZHHIZEI.

9. The process of claim 3 wherein about 1 to 5 moles of L MYERS, Assistant Examinel. collidine are present, based on the amount of halogenated Ydrocarbon. US. Cl. X.R.

10. The process of claim 9 wherein the decomposition 15 260 683 15 is conducted at a temperature of about 440 F. to 500 F.