3,576,860 United States Patent Office Patented Apr. 27, 1971 2 3,576,860 Further objects, aspects and advantages of the inven PREPARATION OF CHLOROACETYL CHLORIDE . tion will be apparent from the description which follows. Dimitri A. Zazaris, Belleville, Ill., assignor to Chlorination of acetic acid alone in the absence of a Monsanto Company, St. Louis, Mo. catalyst by prior art processes usually requires relatively No Drawing. Filed Dec. 20, 1967, Ser. No. 691,975 5 high temperatures, 110 to 120° C., in order for the re Int, C. C07c53/20 action to occur. Temperature in this range, however, re U.S. C. 260-539 9 Claims Sult in a high yield of dichloroacetic acid. In order to re duce the reaction temperature, acetic anhydride, acetyl chloride, inorganic salts or combination of the three have ABSTRACT OF THE DISCLOSURE O been added to the acetic acid. Reaction ompositions of 85 weight percent acetic anhydride and 15 weight percent Chlorination of acetic anhydride and acetic anhydride acetic acid have been utilized. In the chlorination of this acetic acid mixtures in the presence of lithium chloride to mixture, the product obtained was predominantly mono yield a mixture of monochloroacetyl chloride and mono chloroacetic acid. This is contrary to what would be ex chloroacetic acid having a small concentration of the poly pected since theoretically acetic anhydride should give 1 chlorinated derivatives. mole of acid and 1 mole of acid halide per mole of an hydride. The use of many inorganic salts did not mate rially change this result. Many of the present commercial herbicides, such as the It has previously been determined that the low yield of chloroacetamides and "2,4-D,' utilize a monochloroacetyl 20 monochloroacetyl chloride is due to the interactions of chloride or monochloroacetic acid as an intermediate. the acid chloride and any free acid, resulting in the for Inclusion of the polychlorinated acids or acid chlorides in mation of predominantly the monochloroacetic acid. the intermediate, yields a product which has decreased When acetic anhydride alone is chlorinated, the product biological activity and different physical properties which contains more chloro acids than chloro acid halides and interfere in the formulation of the herbicide. The mono 25 the concentration of dichlorinated derivatives is higher chloroacetic acid and monochloroacetyl chloride should, than when a mixture with acetic acid is chlorinated. These therefore, have a minimum of the polychlorinated deriva side reactions are disadvantageous if the product desired tives, which should not exceed about 2%, in order to is the acid halide. obtain maximum biological activity and ease of formula It has now been found that the introduction of lithium tion. 30 chloride alone or in combination with hydrogen chlo Separation of the monochloro acids and acid chlorides ride to a reaction mixture containing 0 to about 17 per from the polychlorinated derivatives by conventional cent of acetic acid and about 83 to 100 percent of ace means is an expensive and difficult operation due to the tic anhydride yields a mixture of monochloroacetic acid close similarities in physical properties. As an alternate, and monochloroacetyl chloride, which contains less than the preparation of monochloroacetic acid and acid chlo 35 1.5 percent of the dichloro derivative in the acid halide, rides was modified to decrease the amount of the poly in a weight ratio which approaches theory (1.19 for ace chlorinated derivatives formed to an acceptable level. tic anhydride and 0.89 for the 83/17 mixture). In the prior art, acetic anhydride and/or acetyl chlo In the chlorination of acetic anhydride or acetic acid ride have been added to catalyze the chlorination of acetic acetic anhydride mixtures, it is generally held that many acid and partially suppresses the formation of the poly 40 different reactions are occurring simultaneously, but not chlorinated derivatives. The chlorination of acetic anhy in the same degree or rate, among which are: dride alone results in the formation of a large concentra tion (9 to 11%) of the polychlorinated derivatives. The (1) CHCsoO -- Cl2 --> Cicirc-soO addition of inorganic salts also only partially suppresses / M the formation of the polychlorinated derivatives, even in 45 CH3C=O CH3CO the presence of acetic anhydride. These modifications of the chlorination reaction do not reduce the concentration of polychlorinated derivatives to -- CHit-Cl -- CCH3COOH an acceptable level unless the reaction is stopped when CH3C=O O only approximately 80 to 85% of the acetic acid-acetic anhydride has been converted. This requires the separa (2) o -- HCl -- CH3COOH -- OH, -ci tion and recycling of a large amount of unreacted start CH3C=O ing material. 2 o It is, therefore, an object of this invention to provide a O O ClCH2C novel synthetic process for the preparation of monochlo 55 N HCl roacetic acid and monochloroacetyl chloride which elimi (3) CH3C-OH -- ClCH2C Cl-) yo - nates the above disadvantages. CH3C=O It is another object of this invention to provide a proc ClCHCOOH ess for preparing monochloroacetic acid and monochloro -- acetyl chloride having less than 4.0 and 1.5 weight per 60 cent of dichloroacetic acid or dichloroacetyl chloride in CH,8-ci the acid and acid chloride fractions, respectively. It is a further object of this invention to provide a proc g ess for preparing monochloroacetic acid and the mono (4) CH3C Cl -- Cl2 ---> ClCHCCl chloroacetyl chloride in which at least 95% of the start 65 O O O ing compound is converted to the desired monochloro derivative. (5) ClCH2C-Cl -- CH3COOH -- ClCH2COH -- CHC-Cl It is a still further object of this invention to provide (6) CH3COOH + Cl2 - ClCH2COOH -- HCl a process for the preparation of monochloroacetic acid As can be seen from Reactions 1, 3 and 5, the forma and monochloroacetyl chloride from acetic anhydride in 70 tion of monochloroacetic acid is favored over the forma which the weight ratio of monochloroacetyl chloride to tion of monochloroacetyl chloride, and thus more acid monochloroacetic acid approaches the theoretical 119:100. is formed than acid halide. 3,576,860 3 4 In accordance with the present invention, the chloride In a suitable vessel, equipped with a temperature ion probably interacts with the monochloric anhydride measuring means, a reflux condenser, an off-gas outlet (Equations 1 and 3) to give the products monochloroacetyl fitted with a reflux condenser, and a chlorine sparger con chloride and acetic acid. The formation of the acid halide nected to a gas measuring means, was added the acetic is thus favored and the acid halide/acid weight ratio ap anhydride or acetic anhydride-acetic acid mixture and proaches theory. the required amount of lithium chloride, and the batch In the prior art, chlorination reactions were terminated heated to about 90° C. Chlorine was introduced into the after about 80 to 85% of the reaction mixture was con mixture at a slow rate for the first 1/2 hours. During this verted to the chlorinated product in order to reduce the induction period, only small amounts of chlorine were quantity of dichlorinated compounds. The unreacted acid absorbed and the reaction mixture attained the typical or anhydride thus had to be separated from the reaction l O yellowish-green coloration of chlorine. After the reac medium. In the present invention, chlorination of the tion was initiated, the coloration disappeared and the reaction composition to a conversion of at least 95% is chlorine was absorbed as it was added. The chlorine rate possible without any material increase in dichloro forma was increased and adjusted to provide a reaction time of tion. In actual practice, quantitative conversions have 5 about 8 to 9 hours. The temperature was controlled with been obtained. in the approximate range of 80 to 90° C. during the Reaction temperature for the procedure of the present reaction time. Chlorine addition was discontinued when invention is in the approximate range of 70 to 100° C., the off-gas attained the chlorine coloration. The specific with the preferred temperature range being about 80 to gravity of the mixture at this period was approximately 90° C. Temperatures outside this range can be utilized 20 1.3607 at 75° C. but lead to an increase in dichlorinated derivatives at the The results obtained from this procedure using various higher temperature and longer reaction times and increase mixtures of acetic anhydride and acetic acid and various in dichlorinated products at lower temperatures. amounts of lithium chloride is reported in Table I. Chlorine is initially introduced into the reaction mix It will be noted that in some runs hydrogen chloride ture, during the induction period, at a relatively slow rate. 25 is added as a co-catalyst. The use of hydrogen chloride re During this period of the reaction, the mixture attains the duces the induction time from about 1/2 hours to about coloration of chlorine. After the reaction has started, this 15 minutes. Hydrogen chloride, when utilized, is added to coloration will disappear. The chlorine rate is then in the reaction mixture prior to the chlorine addition. Hy creased and adjusted to a rate that will provide complete drogen chloride is added to the reaction medium in an chlorination in about 8 to 9 hours. Completion of chlori 30 amount up to about 15 percent by weight of the reaction nation is evidenced by the presence of free chlorine in medium with the optimum amount being about 5 to 10 the off gas. percent. The procedure with hydrogen chloride is as provi The amount of lithium chloride added to the reaction ously described with the exception that the induction mixture is in the range of about 0.1 to 2.5 percent by period is reduced to about 15 minutes.