US2430016A

US2430016A - Production of haloprenes

Info

Publication number: US2430016A
Application number: US695052A
Authority: US
Inventors: George W Hearne; France Donald S La
Original assignee: Shell Development Co
Current assignee: Shell Development Co
Priority date: 1946-09-05
Filing date: 1946-09-05
Publication date: 1947-11-04
Anticipated expiration: 1964-11-04

Description

the 1,2-dihalo-3-butenes.

Patented Nov. 4, 1947 PRODUCTION OF HALQPRENES George W. Hearne,

El Cerrito, and Donald S. La France, Richmond, CaliL,

assignors to Shell Development Company, San Francisco, Calif., a corporation of Delaware No Drawing. Application September 5, 1946, Serial No. 695,052

16 Claims. (01. 260-655) 1 This invention relates to a practical and economical method for producing 2-halo-1,3-butadienes, referred to hereinafter as the haloprenes by analogy with chloroprene (2-chlorobutadiene- 1,3) which is the most important, commercially,

of this class of compounds due to the fact that chloroprene is the essential component of neoprene rubber.

In the past acetylene has been the only source of commercial chloroprene and a complicated procedure, involving the intermediate production of vinyl acetylene, has been necessary in chloroprene manufacture. This has made chloroprene a relatively expensive compound and has materially restricted the use of neoprene in spite of its many special advantages over other types of synthetic rubber. The present invention is of particular value in that it provides a simple and efficient process which is especially well adapted to the large scale production of chloroprene from a cheap starting material, namely, 1,2-dichlorobutene-3, which may be readily obtained by chlorinating butadiene.

The invention is not limited to the production of chloroprene, however, and an important object is the'provision of a relatively simple and direct method for the production of haloprenes from Another object is to provide an economically practical method of converting 1,2-dihalo-3-butenes to haloprenes which can readily be carried out continuously on a largescale. A special object isto produce haloprenes, particularly chloroprene, in high yields from 1,2- dihalo-3-butenes. Further objects and advantages of the invention will be apparent from the following description of the new process.

According to the invention, haloprenes are produced by .treating a 1,2-dihalobutene-3 with an aqueous solution of an alkali at a temperature at least equal to the boiling temperature of the haloprene under the reaction conditions and separating the haloprene produced from the reaction mixture. This method of operation has several important advantages over other methods for converting a 1,2-dihalobutene-3 to a haloprene. In this connection it must be noted that, although high temperature pyrolysis of other dichlorbutenes such as 2,3-dichlorbutene-l, does produce chloroprene the pyrolysis of either 1,2-dichlorbutene-3 or 1,4-dichlorbutene-2 forms l-chlorbutadiene-l,3 instead of 2-chlorbutadiene-l,3 (chloroprene). In order to produce chloroprene, it has been proposed to treat 1,2-dichlorbutene-3 with solid caustic alkali. This is described in Carothers patentU. S. 2,038,538. In accordance with one of the embodiments of the present invention it has been found that yields greatly exceeding those obtainable by the previously proposed method may be attained by employing an aqueous solution of an alkali, such as sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, etc. According to this process, the 1,2-dichlorbutene-3 to be dehydrochlorinated is introduced into a. solution of the alkali, such as a 10% aqueous sodium hydroxide solution, preferably with stirring or agitation.-

The solution is maintained above the boiling point of chloroprene (i. e., about 60- C.) and preferably at the boiling point of the alkali solution. The reaction producedchloroprene which vaporizes due to the elevated temperature employed.

In order to avoid undesirable side reactions, the chloroprene should be removed substantially as rapidly as formed. The dehydrochlorination can also be effected with aqueous sodium carbonate or calcium hydroxide at about their boiling points. what slower than when efiected with aqueous sodium hydroxide. Also, possibly due to the longer contact period at the relatively high temperatures, some of the chloroprene was found to be polymerized during the treatment with aqueous solutions of alkalies other than the alkali metal hydroxides.

It has been proposed in Lange patent-U. S. 2,180,115 to use anhydrous solutions of alkalies, particularly alcoholic alkali, for the production of chloroprene from 1,2-dichlorbutene-3, but this method also is less advantageous than the process of the present invention. By the use of aqueous solutions of alkali, not only may increased yield of the desired haloprenes be obtained, but also the economy and ease of operation are improved, particularly with respect to the recovery of the products which are substantially insoluble in water and boil at temperatures sufliciently different from that of water so that they are easily separated without resort to the elaborate procedures which are necessary when organic solvents are used.

As previously indicated, the preferred aqueous alkali solutions for use in the process are solutions of alkali metal hydroxides, sodium. and potassium hydroxides being particularly suitable because of their low cost. However, equally satisfactory results can be obtained with aqueous-ammonium, lithium or rubidium hydroxides lnstead of the alkali metal hydroxides,tl 1e corresponding carbonates such, for example, as

s dium carbonate, potassiumcarbonat'e, nd the' The reactions are, however, some-' DIOCESS.

like may be used. Aqueous solutions of the alkaline earth metal hydroxides such as magnesium, calcium, strontium and barium hydroxides may also be used with good results for the dehydrohalogenation of 1,2-dihalo-3-butenes according to the invention. Regardless of the particular aqueous alkali chosen, it is advantageous to maintain the concentration of alkali in the solution between about 1% and about 30%, preferably between about and about 15%, by weight. The desired concentration may be conveniently maintained by continuously or intermittently adding make-up alkali to the solution. The addition may be made directly to the reactor or a part of the solution may be Withdrawn and alkali added before recycling the solution to the reactor. In either case it may be desirable to continuously or intermittently discard a part of the solution or remove therefrom the chlorides formed in the reaction in order to prevent an excessive accumulation of such materials in the system.

As a rule, it is desirable to employ such a volume of aqueous alkali in the reaction as will insure the presence of a substantial stoichiometric excess'of alkali based on the 1,2-dihalobutene-3 to be dehydrohalogenated. Very large excesses may be used, the only limit being those imposed by the volume of solution involved which, of course, should not be so great as to unduly burden the reaction system.

With any of the previously described aqueous alkali solutions, the reaction may be carried out at a temperature at least equal to the boiling temperature of the haloprene or haloprenes being produced. An upper temperature limit is the boiling temperature of the aqueous alkali solution used. For ease of control, the dehydrohalogenation is preferably carried out at the boiling temperature of the aqueous alkali under the reaction conditions because this temperature can readily be maintained with minimum attention from the operator. However, lower temperatureswhich are sufficient to vaporize the haloprene have been found to be effective in the When Operating as preferred at the normal boiling point of the aqueous alkali solution, it is desirable to condense the. distillate from the reaction and return the aqueous layer of the condensate to the reaction, preferably as reflux.

The process is particularly adapted for continuous operation, but may also be carried out 'batchwise or intermittently; Normal pressures may be maintained advantageously but higher or lower pressures are also suitable. Still other variations in the process may be made without departing from the invention.

The following example is presented to illustrate a preferred method for the production of g. high'yields of chloroprene from butadiene using the process of the invention:

. Example I Butadiene-1,3 and chlorine were separately preheated to a temperature of about 150 C., and were then intimatelycommingled in a molal ratio of about 4 to 1. The mixture was then conveyed through a reaction chamber filled with carbon chips and maintained at a temperature of between about 150 C. and 190 0., the rate of passage of the gaseous mixture being such that 1.26 gm. of chlorine were introduced into the chamber per minute. The reaction products showed that yield of 1,2-dichlorbutene-3 and ,4- dichlorobutene-2 was about 70 mol per cent based l,2,3,4-Tetrachlorbutane on the chlorine applied, the exact composition of the product being:

Yield in mol per cent of Reaction product chlorine applied Monochlor-diolefin 1,2-Dichlorbutene-3. 1,4-Dichlorbutene-2.

Polymer The 1,2-dichloride obtained directly by the chlowater continuously by fractionation.

rination of the butadiene and that obtained by the catalytic allylic rearrangement were then slowly added to a boiling 10% sodium hydroxide solution. The mixture was maintained in a state of agitation, and the chloroprene formed as the result of this reaction was distilled off substantially as rapidly as it was formed. It was found that about 94% of the dichloride was converted to chloroprene, or approximately a yield of 65.8% based on the butadiene treated.

Although only a 65.8% yield was recovered, this yield is far greater than that heretofore obtainable by operating according to the known processes. Also, the above yield could be further increased by employing efficient recovery systems. This is due to 'the fact that it was noticed that relatively large handling losses were produced in the above-described process, particularly in the recovery of the unsaturated dihalides produced during the vapor phase halogenation of the diene. This loss, if recovered by properly designed means, would further increase the actual yield of the final product.

The following example shows the advantage, particularly with respect to yield of chloroprene, obtainable by the process of the invention compared with methods using solid alkalies or alcoholic alkali solutions.

Example II 1,2-dichlobutene-3 was fed at a, liquid hourly space velocity of 0.165 into a boiling 10% aqueous. sodium hydroxide solution. The mixture was maintained in a state of agitation and the chloroprene formed was removed as an azeotrope with It was found that the conversion to chloroprene was equal to about 86%, based on the 1,2-dichlorbutene-3 introduced, and that the yield of chloroprene was equal to about 96% as calculated on the dichlorbutene consumed.

When 1,2-dichlorbutene-3 was treated with solid sodium hydroxide in the proportions of 210 grams of sodium hydroxide to 106 grams of the dichlorbutene, using a temperature of about C., and distilling off and analyzing the overhead vapors from the reaction, it was found that the yield of chloroprene was equal to only about 65% based on the 1,2-dichlorbutene-3 consumed.

In another run 1,2-dichlorbutene-3 was mixed with a Z-normal alcoholic potassium hydroxide solution, and the mixture was then subjected to a'distillation under a subatmospheric pressure. An analysis of the reaction products showed that chloroprene was thus produced in a yield of 67%,

based on the amount of the dichlorbutene introduced into the reaction zone.

Other haloprenes may be produced in the same way as shown by the following examples:

Example III Example IV 1,2-dichlorbutene-3 was slowly added to a refluxing saturated lime'solution and the chlordprene distilled off as fast as formed. The conversion based on the 1,2-dichlorbutene-3 consumed was about '71 Example V Using a sodium carbonate solution of concentration in place of the lime solution of Example IV, a fair conversion to chloroprene, based on the 1,2-dichlorbutene-3 consumed, was obtained.

It will be seen that the process of the invention is capable of wide variation, not only with respect to 'the 1,2-dihalo-3-butenes whichm'ay be .reacted and the aqueou alkali solutions which may be used, but also in regard to the method of operation and the conditions under which the reaction may be carried out. Thus, for example, it is often advantageous, particularly when using aqueous alkalies in the form of the carbonates or alkaline earth metal hydroxides, to carry out the reaction in the presence of a polymerization inhibitor such, for instance, as catechol, p-tertiary butyl phenol, hydroquinone, or the like. Also, in the production of iodoprene from a 1-halo-2-iod0- butene-3, a reduced pressure of the order of about 500 mm. Hg or less is advantageous. Still other variations may be made in the invention which is not limited to the details disclosed by way of example nor by any theory proposed in explanathan the boiling temperature of chloroprene, and

distilling chloroprene from the reaction mixture substantiallyas soon as it is formed therein.

4. A process for the conversion of 1,2-dichlorbutene-3 to chloroprene which comprises treating the 1,2-dichlorbutene-3 with an aqueous sodium hydroxide solution at about the boiling temperature of the sodium hydroxide solution, and distilling chloroprene from the reaction mixture substantially as soon as it is formed therein.

5. A process for the conversion of 1,2-dichlor- I butene-3 to chloroprene which comprises treating tion of the improved results which are achieved.

This application is a continuation-in-part of copending application Serial No. 429,390, filed February 3, 1942, and of copending application Serial No. 303,098, filed November 6, 1937, of which said application Serial No. 429,390'is a division.

We claim as our invention:

1. A process for the conversion of 1,2-dichlorbutene-3 to chloroprene which comprises; introducing 1,2-dichlorbutene-3, at about the rate at which it is consumed by the reaction, into 'an aqueous sodium hydroxide solution which is agitated and maintained at about its boiling temper,- ature, and distilling chloroprene from the reaction mixture substantially as soon as it is formed therein.

2. A process for the conversion of 1,2-dichlorbutene-3 to chloroprene which comprises introducing 1,2-dichlorbutene-3 into an aqueous sodium hydroxide solution maintained at a tem-- perature greater than the boiling temperature of chloroprene, and distilling chloroprene from the the 1,2-dichlorbutene-3 with an aqueous sodium hydroxide solution at a temperature greater than the boiling temperature of chloroprene, and distilling chloroprene from the reaction mixture substantially as soon as it is formed therein.

6. A process for the conversion'of 1,2-dichlorbutene-3 to chloroprene which comprises treating the 1,2-dichlorbutene-3 with an aqueous sodium hydroxide solution at a temperature greater than the boiling temperature of chloroprene, and separating chloroprene from the reaction mixture.

7. A process for the conversion of 1,2-dichlorbutene-3 to chloroprene which comprises treating the 1,2-dichlorbutene-3 with an aqueous sodium hydroxide solution at a temperature at least equal to the boiling temperature of chloroprene, and separating chloroprene from the reaction mixture.

8. A process for the conversion of 1,2-dichlorbutene-3 to chloroprene which comprises treating the 1,2-dichlorbutene-3 with an aqueous solution of an alkali at a temperature at least equal to the boiling temperature of chloroprene, and separating chloroprene from the reaction mixture.

9. A process for the conversion of 1,2-dichlorbutene-3 to chloroprene which comprises treating the 1,2-dichlorbutene-3 with an aqueous potassium hydroxide solution at about the boiling temperature of the potassium hydroxide solution, and distilling chloroprene from the reaction mixture substantially as soon as it is formed therein.

10. A process for the conversion of 1,2-dichlorbutene-3 to chloroprene which comprises treating the 1,2-dichlorbutene-3 with an aqueous alkali metal hydroxide solution at about the boiling temperature of said aqueous solution, and distilling chloroprene from the reaction mixture substantially as soon as it is formed therein.

11. A process for the conversion of 1,2-dichlorbutane-3 to chloroprene which comprises treating reaction, into an aqueous sodium hydroxide solution which is agitated and maintained at about its boiling temperature, and distilling the Z-halobutadiene-1,3 produced from the-reaction mixture substantially as soon as it is formed.

13. A process for the conversion of a 1,2-dihalobutene-3 to a 2-halobutadiene-1,3 which comprises treating the 1,2-dihalobutene-3 with an aqueous solution 01' an alkali metal hydroxide at about the boiling temperature of said aqueous solution and distilling the 2-ha1obutadiene-'1,3 produced from the reaction mixture substantially as soon as it is formed.

14. A process for the conversion of a, 1,214.11-

halobutene-i; to a 2-ha1obutadiene-1,3 which comprises treating the 1,2-dihalobutene-3 with an aqueous solution of an alkali at a temperature at least equal to the boiling temperature of the 2-halobutadiene-1,3 which is produced and separating said 2-halobutadiene-L3 from the reaction mixture.

15. A process for the conversion of a 1,2-dihalobutene-3 to a 2-halobutadiene-1,3 which comprises treating a 1,2-dihalobutene-3 having a chlorine atom linked to the terminal carbon atom with an aqueous solution of an-alkali metal hydroxide at about the boiling temperature of said aqueous solution and distilling the 2-halobutadime-1,3 produced from the reaction mixture substantially as soon as it is formed.

16. A process for the conversion of a 1,2-diprises treating a 1,2-dihalobutene-3 having a bromine atom linked to the terminal carbon atom with an aqueous solution of an alkali at a temperature at least equal to the boiling temperature of the 2-halobutadiene-1,3 which is produced and separating said 2-halobutadiene-1,3 from the reaction mixture.

' GEORGE W. HEARNE.

DONALD S. LA FRANCE.

I REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,038,538 Carothers Apr. 28, 1936 2,180,115 Lange et al Nov. 14, 1939