United States Patent [191 ‘[11] 3,772,157 Horsley v[451 Nov. 13, 1973

[54] PURIFICATION OF Z-CHLOROALKANOIC Society, 1952, Wash.,'D.C., pg. 38, 40, 41. ACIDS BY AZEOTROPIC DISTILLATION Technique of Organic Chemistry, Vol. IV, (1951) Dis [75] Inventor: Lee H. Horsley, Midland, Mich. tillation: Weissberger, lnterscience Publ., N.Y., pg. [73] Assignee: The Dow Chemical Company, 356-371. Midland, Mich. [22] Filed: Dec. 10, 1971 Primary Examiner—Wilbur L. Bascomb, Jr. Att0rney-—William M. Yates et al. [211 Appl. No.: 206,861

[52] US. Cl ...... 203/52, 203/63, 203/67, [57] ABSTRACT 203/68, 203/69, 203/70, 203/56, 203/82, 260/539 R, 260/539 A Monochloroacetic acid can be separated efficiently [51] Int. CL... C07c 53/16, B0ld 3/36, C070 53/32 from dichloroacetic acid and 2-chloropropionic acid [58] Field of Search ...... 203/63, 67, 68, 69, can be separated from 2,2-dichloropropionic acid by 203/70, 56, 52, 82; 260/539 A, 539 R adding an azeotrope-forming agent to such a mixture and distilling off the monochloro acid azeotrope. Aze [56] References Cited otrope formers have a boiling point of about UNITED STATES PATENTS l45°-240°C and are , halogenated hy drocarbons, and ethers. 2,809,214 10/1957 Haimsohn ...... 260/539 A 2,790,828 4/1957 l-laimsohn ...... 260/539 A OTHER PUBLlCATlONS 11 Claims, No Drawings l-lorsley, L. H.: Azeotropic Data, American Chemical 3,772,157 1 2 PURIFICATION OF Z-CHLOROALKANOIC ACIDS to the chlorinated acid mixture is ‘not a critical factor, BY AZEOTROPIC DISTILLATION for any significant amount will distill from the mixture as its azeotrope with the monochloro acid and so effect BACKGROUND OF THE INVENTION a separation to the extent that it is present. Preferably, This invention relates to a new chemical process and 5 enough azeotrope-former is used to separate essentially it concerns particularly a process for separating chloro all of the monochloro acid. A smaller'amount will re acetic acid and 2-chloropropionic acid from their mix sult in incomplete recovery of the monochloro acid tures with the corresponding dichlorinated acids by az while an excess requires unnecessary distillation to re eotropic distillation. move it. The chlorinated lower aliphatic acids are made by The distillation pressure is also not a critical condi well known direct chlorination processes which yield as tion. Preferably, the distillation is run at a pressure be the crude product, the desired chlorinated acid mixed tween about 10 mm. Hg and atmospheric pressure for with small but appreciable quantities of under reasons of distillate condensation ef?ciency at lower chlorinated material and the over-chlorinated com pressures and increasing corrosion of equipment and pound, depending upon the degree of chlorination In thermal decomposition of products at higher pressures. the chlorination of propionic acid to make 2,2 The distillation pressure is advantageously varied ac dichloropropionic acid, an effective grass-killer, for ex cording to the particular system involved, since the ample, the product is contaminated with a significant concentration of monochloro acid in the azeotrope in amount of the monochloro acid. Since these two acids creases somewhat with increasing pressure. have very close boiling points, puri?cation by simple 20 The classes of azeotrope-forming compounds suit distillation is impossible and an expensive recrystalli able for use in this process can be divided into a num zation procedure must be resorted to if a pure product ber of groups and subgroups. Thus, aliphatic, cycloali is desired. phatic, and aromatic hydrocarbons having normal boil Similarly, when acetic acid is chlorinated to make ing points within the de?ned range are operable. The monochloroacetic acid, a useful intermediate in the 25 aliphatic hydrocarbons can be de?ned further as satu production of glycine, 2,4-dichlorophenoxyacetic acid, rated, ole?nic, and acetylenic aliphatic hydrocarbons. and other such compounds, a signi?cant amount of di These can be branched or straight chain compounds. chloroacetic acid is also formed. Since the monochloro Examples of these various groups are , unde and dichloro acids have boiling points only 5° apart, a cane, , dodecene, tetradecene, undecyne, iso simple distillation will not provide enough separation 30 propylcyclohexane, cyclooctane, dicyclopentane, cy and recrystallization is necessary to obtain a puri?ed mene, butylbenzene, naphthalene, and decahydro product. Substantial underchlorination will essentially naphthalene. For obvious reasons, inert, normally liq eliminate the dichlorinated product, but this procedure uid hydrocarbons are preferred and hydrocarbons con involves the distillation of an economically impractical 35 taining no aliphatic unsaturation are more desirable amount of unreacted acetic acid. than their unsaturated analogs. It is known that chloroacetic acid forms lower boiling Similarly, the class of halogenated hydrocarbons in azeotropes with a number of dissimilar kinds of com cludes halogenated aliphatic hydrocarbons, haloge pounds such as o-bromotoluene, decane, cymene, and nated cycloaliphatic hydrocarbons, and halogenated others. It is also known that dichloroacetic acid forms aromatic hydrocarbons. In the same way, the halogen lower boiling azeotropes with some of the same com atom or atoms present can be one or more of the com pounds and would generally be expected to form azeo mon halogens, ?uorine, bromine, chlorine, and iodine. tropes with the others. Such, in fact, has been found to Some examples of this class are bromobenzene, o be the case. The same situation exists with 2 chloropropionic acid and 2,2-dichloropropionic acid. dichlorobenzene, benzyl chloride, difluorotetra 45 bromoethane, and tetrachloroethane. In both cases, the respective azeotropes have about as The class of ethers includes dialkyl close boiling points as do the monochloro and dichloro ethers and alkyl aryl ethers, these being the only com acids themselves. Therefore, azeotropic distillation ap monly available ethers within the speci?ed boilng point pears to offer no better chance for effective separation of these acids than distillation of the mixed acids alone. range. Examples are diamyl ether, phenetole, dime 50 thoxybenzene, ethyl octyl ether, anisole, and other SUMMARY OF THE INVENTION such ethers. It has now been found quite unexpectedly that both Of particular interest and advantage in the present chloroacetic acid and 2-chloropropionic acid can be process are the saturated aliphatic hydrocarbons. separated efficiently from their mixtures with the cor These are not only stable and unreactive compounds, responding dichlorinated acids by adding to those mix but they also have the property of mutual insolubility tures an azeotrope-forming compound and distilling its with the monochloro acids at ambient and moderate azeotrope with the monochloro acid from the resulting temperatures so that the distilled and condensed azeo mixtures. Operable azeotrope-forming compounds trope separates into two liquid phases, thereby greatly facilitating the separation of the pure monochloro acid. have a boiling point at atmospheric pressure of about 60 l45°—240°C, preferably about l70°—220°C, and are by A particularly useful and readily available member of drocarbons, halogenated hydrocarbons, and hydrocar this class is a paraf?nic hydrocarbon fraction having a bon ethers. A mixture of related compounds such as a boiling range of approximately l70°—220°C and con saturated aliphatic hydrocarbon fraction having a boil sisting essentially of , undecanes, dodecanes, ing range of about l70°—220°C is a preferred example. and tridecanes. The azeotropes of other compounds 65 listed above can be conveniently separated by addition DETAILED DESCRIPTION of water, whereupon an aqueous monochloro acid The quantity of azeotrope-forming compound added phase separates, or, in the case of chloroacetic acid, 3,772,157 3 sufficient cooling of the azeotrope will cause the sepa 300 130 26 ration of the solid acid. 100 112 3b This process can be operated either as a batch pro ‘200 13!) ill 745 llili #lll cess or continuously. In the batchwise operation of the lOU 1'30 48. 5 preferred separation of monochloroacetic acid from n-Tridecane‘. 1C0 ‘\ 125 l HO. 7 . n-Undeennv. 50 102 .‘lll dichloroacetic acid using an aliphatic hydrocarbon D0, . . . _ ...... t . . . . t .. 0 ...... I00 117 40 such as undecane, for example, the distilled azeotrope 170.... , n-Dodecanv. I01] 125 55 D0...... _ ...... iu'l‘i'irlnemiv. llltl 122i 7‘3 separates into two layers and the heavy chloroacetic 2»<'l1loror>ropioni<'maid. . .. lt-llPCiLllt' , 100 103 '1! acid layer is drawn off for a ?nishing distillation to re "l,Q-tlltjlllOl'Olll’ODltllll0 at-irl. _. . . . .do. . H10 105'» iii move any remaining undecane or traces of acetic acid 1 ‘Value calculated from vapor pressure-tampvruturv curve. if present. The condenser and separator are maintained Saturated aliphatic hydrocarbons are preferred azeo at about 60° slighty above to keep the chloroacetic acid tropic agents because. they are immiscible with the layer from solidifying. The light, undecane layer is re monochlorinated acids and this makes possible an easy turned to the still if more is needed. When all of the separation of azeotropic agent from the chlorinated chloroacetic acid has been separated, the light layer is acid in a two phase distillate. The approximate critical withdrawn until all undecane is removed from the still solution temperatures of some of these systems are pot, leaving dichloroacetic acid as the residue. listed in Table 2.. Equal volumes of the two components Continuous operation is preferred for commercial were used in these determinations. practice. In this type of operation, using the system above, the chloroacetic acid — dichloroacetic acid 20 TABLE 2 mixture plus undecane can be fed into a fractional dis System Solution Temperature, “C tillation column at about its midpoint and the chloro n-Undecane-Chloroacctic Acid 169 acetic acid — undecane azeotrope distillate is con n-‘Chloroacetic Acid 175 n-Undecane-Dichloroacetic Acid 24 densed as a two phase liquid into a heated liquid sepa— n-Dodecane~Dichloroacetic Acid 35 rator from which most of the heavy layer passes to a 25 finishing column for removal of remaining undecane EXAMPLES l—9 and any acetic acid present. Pure chloroacetic acid is The efficiency of various azeotropic agents was de drawn off from the bottom of the ?nishing column. termined by distillinga small sample from monochloro Some of the heavy layer in the separator is fed as acetic acid containing a minor proportion of a dichlo needed into the top of the main distillation column as roacetic acid, then adding azeotropic agent to the dis re?ux. The light (undecane) layer from the separator tillation ?ask and distilling a second sample. Analysis plus undecane from the finishing column is also fed into of the two distillate samples and the still residue the top of the main column while pure dichloroacetic showed the measure of improvement in separation af acid is drawn off from the bottom of the main column, forded by the particular azeotropic agent. A 1A inch by conditions in this column being maintained such that 35 12 inch Vigreux column was used for these distillations the undecane inventory remains principally in the which were run under reduced pressure. Analysis was upper part. When equilibrium has been established, by vapor phase chromatography. The results obtained only small amounts of undecane need be added to the are listed in Table 3. Each group of experiments was mixed chlorinate acid feed from time to time as run using the same monochloroacetic -— dichloroacetic makeup to replace mechanical losses. The system thus 40 acid mixture. The variations in residue analysis within operates with an essentially constant inventory of unde each group indicate experimental variation in analyses. cane while the effluent products are substantially pure chloroacetic acid and substantially pure dichloroacetic TABLE 3 acid, any trichloroacetic acid remaining with the latter Wt. pervvnl 45 ilii-lilorozu'vtii- ‘\Wl'l 1 product. Buildup of lights such as acetic acid in such a Azuotrnpiv lllil‘lll Pressure,mitt. ll: W»lll

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