US2662924A

US2662924A - Dehydrochlorination of polychlorocyclohexanes

Info

Publication number: US2662924A
Application number: US259281A
Authority: US
Inventors: David D Humphreys
Original assignee: Ethyl Corp
Current assignee: Ethyl Corp
Priority date: 1951-11-30
Filing date: 1951-11-30
Publication date: 1953-12-15
Anticipated expiration: 1970-12-15
Also published as: GB720129A; FR1068108A

Description

Patented Dec. 1 5, 1953 DEHYDROCHLORINATION F POLY- CHLOROCYCLOHEXANES David D. Humphreys, Baton Rouge, La., assignor to Ethyl Corporation, New York, N. Y., a corporation of Delaware No Drawing. Application November Serial No. 259,281

5 Claims. (01. 260-648) This invention relates to the dehydrochlorination of organic chlorine compounds and more particularly to a new and improved catalytic method for the dehydrochlorination of benzene hexachloride and similar compounds, characterized by an unusual and novel distribution of products.

The dehydrochlorination of benzene hexachloride has been traditionally carried out by thermal treatment at temperatures in the vicinity of 275-500" (3., usually in the presence of a catalyst, such as iron or ferric chloride. This is a suitable method for the preparation of trichlorobenzene, particularly when an outlet for the nongamma isomers of benzene hexachloride is thereby provided. However, this procedure is inefiicient in that large quantities of 1,2,3-trichlorobenzene, for which there exists no market outlet, are produced along with the desired 1,2,4-isomer. The 1,3,5-isomer is produced only in negligible amounts. The dehydrochlorination product, therefore, must be either purified by a difficult and costly fractionation operation or the crude mixture must be sold at a reduced premium. Another disadvantage of this method is that considerable carbonization of organic material takes place in the reaction zone. The carbonaceous material thereby formed is deleterious to the process in that it tends to foul process equipment, it represents a loss of potential yield of dehydrohalogenation product, and it adversely affects the reaction rate and the efficiency of the catalyst employed. The above method of dehydrochlorination of benzene hexachloride is also deficient in that the reaction sequence cannot be stopped at any of the intermediate products, but always proceeds to completion, with the formation of trichlorobenzenes. Thus, valuable chemical intermediates and biocides present in the reaction mixture such as 2,3,4,5,6-pentachlorocyclohexene-l are not recovered but are converted to the completely aromatized end-products.

Another method used for the dehydrochlorination of benzene hexachloride consists of heating the benzene hexachloride with a solution of alkali, such as sodium hydroxide or potassium hydroxide. This procedure is extremely inefiicient in that the valuable hydrogen chloride produced in the dehydrochlorination is converted by the action of the alkali into relatively valueless sodium chloride or potassium hydroxide, respectively.

In the formation of benzene hexachloride by additive chlorination of benzene, varying amounts of monochlorobenzene hexachloride and dichlo- 2 robenzene hexachloride are Thelddehydrochlorination normally formed. wou ead to the formation of valuable ucts, such as tetra h prodmbenzenec lorobenzenes and pentach1o-- A principal object of my invention is to provide a new and improved meth g f o r tii e dehydrochlorination of polychlorocyclohexanes Another ob ect is to provide a catalytic process for produc1ng a mixture, of trichlorobenzene in l,2,4-tr1chlorobenzene predominates over agfiieviighlorobenzene to a degree not heretofore Another object is to provide a metho drochlorinating benzene hexachloride v v e ar y a preponderant amount of 1,2,4-trichlorobenzene together with 2,3,4,5,6-pentach10r0cyc10hexene-1 is formed. Another object is to provide a prac ticable means of producing 2,3,4,5,6-pentach1orocyclohexene-l by the dehydrochlorination of benzene hexachloride. Still another object is to provide a method for increasing the rate of dehydrochlorination of benzene hexachloride. A further ob ect is to provide a method for the dehydrochlorlnation of benzene hexachloride in which hydrogen chloride in high purity is produced as one of the products. Still another obiggrioscfi provide a practicable means for the deorma ion of anIdIpctachlorocyclohexari f ave discovered that polychloroc clohex such as benzene hexachloride, can be readily a i iil ei iiciently catalytically dehydrochlorinated at a high reaction velocity to yield mixtures of isomeric polychlorobenzenes by contacting the polychlorocyclohexane;with a selective, highly specific catalyst, as described hereafter. In the case of benzene hexachloride, the proportion of" l, 2,4-trichlorobenzene in the product is markedly higher than has been obtained heretofore. Moreover, my invention can be carried out so, that under certain conditions substantial quanti ties of polychlorocyclohexenes are obtained. The

production of cyclic olefins under conditions;

which permit them to be isolated before beingfurther dehydrochlorinated is an important feature of my invention.

By benzene hexachloride I mean either a total. stereoisomeric mixture of 1,2,3,4,5,6-hexachloro-- cyclohexanes, such as is produced in the additive" chlorination of benzene (hereafter designed as:

.crude benzene hexachloride), or any of the in-- dividual 1,2,3,4,5,6-hexachlorocyclohexane stereo-- isomers or any mixture of two or more of the-- stereoisomeric l,2,3,4,5,6 hexachlorocyclohexanes, including'amixture such as that arising:

of these compounds" amples herein.

3 when the gamma isomer has been removed from a total stereoisomeric mixture.

The catalysts which are suitable for use in my process comprise organic sulfonic acids.

When I contact benzene hexachloride as herein defined at a temperature of at least 180 C. with catalytic quantities of one of the specific and selective catalysts described above, I smoothly produce mixtures of 1,2,4-trichlorobenzene and 1,2,3-trichlorobenzene inwhich-tharatio of the commercially important lfzflieisomer ,to 1,2,3-isomer is as high as 175 per cent of the ratio obtained when old methodsare used. Whenbenzene hexachloride is dehydrochlorinated=bynther mal treatment in the absence of a. catalyst the dehydrochlorination rates are greatly .depressedbelow those in my process. I obtain equally advantageous results with other polychlorocyclohexanes, as enumerated herein.

Example 1 illustrates one manner in which my inventi n inla practiced andalso points out the advantages .andbenefits .oimc'xinvention. .All part and p r en a es :are 'by weight i all ex- Example I :.'Io arreaction wessel equipped with a mechanical agitator, a temperature measuring device and a packed distillation column was charged 100 .parts :by weight: of crude bcnzene hexachloride and one part1by weight o'i =p-toluenesulfonic acid. :To the :top .of the=packed idistlllingcolumn was connected a condenser, a variable take-ofi'distilling head containing 'a-.temperature measuring device, a distillate -co'oler, and=a rtared hydrogen 5 chloride absorber containing sodium hydroxide solution.

The reaction wessel was heated by controlled external means, and the agitator: was started as -soon-as the charge was *fluid enough'tobe-stirred. The reaotion-wasmonsideredto havestarted when "hydrogen chloride fumes were observed. -A-fter a substantial reflux in -the distillation column wasestablishedjdistillate was taken off at a rate =suffioient to maintain the reactor temperatureat 300-350 during 'the --maj or part of =the run.

"The rateof dehydroohlorination was=determined by periodio-wei ghing of theamount of hydrogen chloride absorbed hy the sodium hydroxide in the hydrogen chloride absorber. reaction tima thatiis, .the time -required for evolution of per cent of the theoretical amount of hydrogen chloride or complete conversion of 'the benzenehexachloride -to *trichlorobenzene,

was used as-the criterion for velocityof the -de- 4 The 50=per cent 4 lenesulfonic acid, 2-naphthalenesulfonic acid, 1,4-naphthalenedisulfonic acid, toluene-w-sulfonic acid, taurine, 3-aminopropane-1-sulfonic acid, decanesulfonic acid, isethionic acid and others thereof, sulfoacetic acid, ethane-1,2-disulfonic acid, anthraquinone-l-sulfonic acid, mbenzenedisulfonic acid, .ethylbenzene-p-sulfonic acid, 2-chlorotoluene-5-sulfonic acid, mahogany ,acids and the like are used in place of p-toluenesulfonic acid equally beneficial results are obtained. Many of these compounds are not easily obtainable as the free acid, but are obtained in the formof metal or amine salts. The salts are of equal applicability in my invention, since under my reaction conditions they are converted to {the free acids. Among the catalysts herein described, I prefer to use lower arylsulfonic acids such as benzenesulfonic acid and p-toluenesulfonic'aoid since these catalysts are the most economical.

In :order that the contrast between my inventionand prior means may be realized the ,fol- :lowing examplepresents results obtainedwhen powdered :iron is used ,as the catalyst.

Example .II

Using the same procedure as in Example I, a mixture-of parts of crude benzene .hexachloride and 3 partsof powdered ironwas heated-:to a

reactor temperaturecf 285-300 C. The '50 per lystthe 50 per cent reactiontime is-sloweddown to 63 minutes.

My invention maybe carried out aseithera batch-process or-a continuous process. .Onevaria- -tion ofbatch operation'has beendescribed inExample I, above.

In the continuous embodiment, which is the preferred embodimentof my invention, molten or solid polychlorocyclohexane is continuously charged to a-pot-type vessel or tube-type vessel containing a-chargeof catalyst or, alternatively, polychlorocyclohexane and catalyst can be charged to tllBW'QSSGl concurrently. Heat is applied to the vessel, and reaction products are continuously removed and recovered :from the reaction mixture by distillation and-subsequent condensation. Hydrogen chloride is continuously removed and collected in a hydrogen chloride scrubber. The mixture of products whichcomprisesthe distillateis resolved by fractional distillation or other means.

My-invention is operable over a'wide range or temperatures. Temperatures of at-least about 180 C. are preferably-employed. Generally, in order to avoid excessive losses o1 polychlorocyclo- 'hexane'by boiling, the temperature should be not higher'thanabout 350 C. 'In the preferred process applications of my invention, I remcvethe liquid products producedby continuous distillation from the reaction mixture. 'Since the boilmg point of 1,2,4-trichlorobenzene at normal pressure is about -213'C. and that of 1,2,3-trichlorobenzeneis about 219 C,, Ipref er to operate at atemperature of at least about 220 0.

My preferred range of temperature,therefore lies between about 220 C. and 350 C. h

The amount of catalyst employed can'be varied between a verylow percentage, such as aboutllOl per cent of the weight'of benzene hexachl oride to about lilper cent of the weight of benzene hexachloride. However, percentages greater than about 2 per cent of the weight of benzene hexachloride provide only minor additional benefits, so I prefer to use proportions of catalyst not greater than about 2 per cent of the weight of benzene hexachloride being reacted.

I claim: 1. A process. for the dehydrochlorination of a poiychlorocyclohexane comprising contacting said polychlorocyclohexane at an elevated ternperature with a catalytic amount of a sulfonic acid.

2. The process of claim 1 further defined in that the polychlorocyclohexane is benzene hexachloride.

3. A process for the dehydrochlorination of a polychlorocyclohexane comprising contacting said polychlorocyclohexane at a temperature of at least 180 C. with a minor quantity of sulfonic acid.

4.A process for the dehydrochlorination of a polychlorocyclohexane comprising contacting said polychlorocyclohexane at an elevated temperature with a sulfonic acid, the ratio of said polychlorocyclohexane to said sulfonic acid initiaily present being at least 9 to 1.

5, A process for the dehydrochlorination of a polychlorocyclohexane comprising contacting said polychlorocyclohexane at a temperature of 220-350 C. with an arylsulfonic acid.

DAVID D. HUMPHREYS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,872,700 Dreyfus M Aug. 23, 1932 2,042,223 Groll et a]. May 26, 1936 2,569,441 Alquist et a1 Oct. 2, 1951

Claims

1. A PROCESS FOR THE DEHYDROCHLORINATION OF A POLYCHLOROCYCLOHEXANE COMPRISING CONTACTING SAID POLYCHLOROCYCLOHEXANE AT AN ELEVATED TEMPERATURE WITH A CATALYTIC AMOUNT OF A SULFONIC ACID.