US3584036A - Preparation of alpha-monochloro acids - Google Patents

Abstract

ALKANEMONOCARBOXYLIC ACIDS AND CYCLOALKANECARBOXYLIC ACIDS ARE CHLORINATED IN THE PRESENCE OF A CHLORINATION CATALYST TO OBTAIN HIGH YIELDS OF THE CORRESPONGING ALPHAMONOCHLORO ACID WHEN THE REACTION IS CARRIED OUT AT 145200*C.

Description

United States Patent PREPARATION OF ALPHA-MONOCHLORO ACIDS Arthur R. Sexton and John C. Little, Midland, Mich., as-

signors to The Dow Chemical Company, Midland, Mich.

No Drawing. Continuation-impart of application Ser. No. 346,400, Feb. 21, 1964. This application June 19, 1967, Ser. No. 647,181

Int. Cl. C07c 61/08 US. Cl. 260-514 6 Claims ABSTRACT OF THE DISCLOSURE Alkanemonocarboxylic acids and cycloalkanecarboxylic acids are chlorinated in the presence of a chlorination catalyst to obtain high yields of the corresponding alphamonochloro acid when the reaction is carried out at 145- 200 C.

This is a continuation-in-part of copending application Ser. No. 346,400 filed Feb. 21, 1964, now abandoned.

BACKGROUND OF THE INVENTION The present invention relates to an improved chlorination process which provides unexpectedly high yields of certain alpha-monochloroalkanecarboxylic acids alpha-monochloro-cycloalkanecarboxylic acids at high levels of conversion.

The uncatalyzed chlorination of alkanemonocarboxylic acids and cycloalkanemonocarboxylic acids produces mixtures of randomly chlorinated acids from which it is impossible to separate a good yield of the alpha-chloro isomer. It is known that alkanecarboxylic acids can be chlorinated in the presence of various acidic inorganic catalysts to obtain predominantly the alpha-chloro derivative. An acyl halide forms part of the catalyst system and is apparently an essential component. This may be added separately or formed in situ from the unchlorinated acid reactant. Known inorganic acid catalysts include the halides, oxyhalides, oxygen acids, and oxides of phosphorus, arsenic, antimony, sulfur, selenium, and tellurium; the halides of tin, iron, and aluminum; the halooxygen acids of phosphorus and sulfur; and the essential equivalents of these, for example, elemental phosphorus plus iodine, iron filings, and the like. This process is recommended to be carried out at 50-140 C., preferably at 90-100 C.

Similarly, it is known that acids such as cyclohexanecarboxylic acid can be chlorinated at about the same temperature and in the presence of the same kind of catalyst to obtain improved yields of the alphachloro derivatives.

Both of the above known procedures provide somewhat improved yields of the desired alpha-monochlorinated products. For example, very high yields of alpha-chloropropionic acid are thereby obtained. Somewhat lower yields of alpha-chloro higher aliphatic acids are found. It had been thought that such processes also provided high yields of the alpha-chloro acid when cyclohexanecarboxylic acid was chlorinated. However, more recent work using modern analytical techniques has indicated that the actual yields of a-chloro isomers when these processes are applied to such acids are substantially lower than previously thought and that appreciable quantities of the undesirable randomly chlorinated isomers are in fact present in the chlorinated products.

SUMMARY OF THE INVENTION It has now been found that a near quantitative yield of the alpha-chloro acid is obtained when an alkanemonocarboxylic acid or a cycloalkanemonocarboxylic acid as defined below is chlorinated in the liquid phase in the presence of an inorganic acid catalyst as described above and- 3,584,036 Patented June 8, 1971 DETAILED DESCRIPTION The present improved process is applicable to making the alpha-monochloro derivatives of alkanecarboxylic acids of 4-18 carbon atoms, particularly those having the general formula wherein R is an alkyl radical of 1-16 carbon atoms and R is hydrogen or an alkyl radical of 1-8 carbon atoms. Acids of the above formula where R is primary alkyl of 2-16 carbon atoms and R is hydrogen are preferred reactauts.

The improved process is similarly adapted to making the alpha-monochloro derivatives of cycloalkanemonocarboxylic acids of 5-7 carbon atoms such as cyclobutanecarboxylic acid, cyclopentanecarboxylic acid, and cyclohexanecarboxylic acid. Acids of the first defined class include butyric acid, hexanoic acid, octanoic acid, lauric acid, and stearic acid.

Catalysts which can be employed in the present improved process are those previously known for the general reaction as defined above. These may be used in combination with an acyl halide or carboxylic acid anhydride as taught by the prior art, either such a derivative of another carboxylic acid or, preferably, the halide or anhydride of the acid being chlorinated. The quantity of inorganic catalyst is not critical so long as it is at least a catalytically effective amount. Catalyst concentrations of 0.1-5 percent by weight of carboxylic acid are suitable and 0.5-2 percent is preferred.

The reaction can be carried out using any of a number of known chlorinating agents, for example, chlorine, N- chlorosuccinimide, N-chlorourea, phosphorus pentachloride, sulfuryl chloride, or the like. Gaseous chlorine is preferred as a convenient and economical reagent and for the simplified separation procedures required to obtain a pure product.

The quantity of chlorinating agent is not a critical limitation in the process for, as shown in prior art processes, an amount considerably less than or in excess of that theoretically needed to monochlorinate all of the carboxylic acid can be used successfully. Preferably, no more than about 130 percent of the theoretical quantity is used in order to avoid excessive formation of polychlorinated acid. Best yields of the alpha-monochloro acid are obtained using -120 percent of the theoretical proportion of chlorinating agent.

The liquid phase in which the acid is chlorinated may consist essentially of the liquid carboxylic acid or a solvent suitable for this kind of chlorination reaction may be included. Chlorinated or nitro-substituted aromatic or aliphatic hydrocarbons such as tetrachloroethane, dichlorobenzene, nitrobenzene, and trichlorobenzene can be used as solvents. Where the normal boiling point of the solvents is below the reaction temperature, the reaction must be run under superatmospheric pressures. Operation in the absence of a solvent is preferred.

In a preferred mode of operation of this improved process, chlorine is bubbled through a mole of molten carboxylic acid containing 0.5-2% by weight of phosphorus trichloride until 0.8-1.2 moles of chlorine have been reacted as measured by the gain in weight of the reaction mixture, the temperature of the mixture being maintained throughout at 155-l95 C. The crude reaction mixture thereby obtained consists essentially of the alpha-monochlorocarboxylic acid and a minor proportion of unreacted acid, together with catalyst residues and other chlorinated acids which are usually present in amounts of the order of tenths of a percent by weight. Further purification, where desirable, can be accomplished by known means, for example, crystallization, distillation, or chromatographic absorption.

The major present use for alpha-monochlorocarboxylic acids of the classes described is as chemical intermediates and the reaction products obtained from the claimed process are ordinarily of sufficiently high purity to be used directly for such purpose with no intermediate purification or with only a flash distillation to remove the traces of catalyst residues and polychlorinated byproducts. Since randomly chlorinated carboxylic acid isomers are not readily separated and are also relatively easily dehydrohalogenated, the advantage of the present process in providing a product which can be used in this fashion without need for fractional distillation or other extended purification procedure is apparent. The importance of the high conversions and, particularly, the high yields which are characteristic of the claimed process is thereby emphasized.

The new process and its advantages and differences from the known methods are illustrated by the examples which follow.

EXAMPLE 1 A cylindrical reactor equipped with a perforated ring sparger at the bottom, reflux condenser, and temperature regulating and measuring means was charged with 353 g. of butyric acid and 11 g. of phosphorus trichloride. This mixture was reacted with 319 g. of chlorine introduced through the sparger at ISO-180 C. over a period of 8 hours. The organic product contained 92.2 percent by weight of 2-chlorobutyric acid, 2.3 percent of 2,2-dichlorobutyric acid, 2.1 percent of unreacted butyric acid, and the remainder was other chlorinated products.

EXAMPLE 2 By the procedure of Example 1, a mixture of 70 g. of hexanoic acid and 1.53 g. of P001 was reacted with 53 g. of chlorine at 175 C. in 3 hours. The organic reaction product contained 94.5 percent by weight of 2-chlorohexanoic acid with the remainder being other chlorinated products. This represented a yield of 94.5 percent of the alpha-chloro acid based on 100% conversion.

When the above procedure is repeated excepting for holding the temperature below 150, the yield is reduced to 25-70%.

EXAMPLES 3-9 Using the apparatus and general procedure of Example 1, hexanoic acid was reacted with about 1.1 mole equivalents of chlorine with various catalysts and temperatures as noted. Yields listed are of 2-chloro-hexanoic acid and are calculated as in previous examples. Reaction times were 3-5 hours.

Temp Percent Percent Ex-. Catalyst conversion yield 4 P+I2 175 88 90 5 PzO5+HCL 175 85 U2 6 Hexanoyl chl0ride+HzSO4 125 77 35 7.. Same 150 78 72 8 Same 175 00 94 9 None 175 61 50 Examples 6-8 show the increased conversion and yield of alpha-chloro acid as the temperature is increased to the preferred range.

EXAMPLE 10 To a 50 ml. tapered flask equipped with condenser and sparger and immersed in an oil bath maintained at 175 C. there was added 5.0 g. of cyclobutanecarboxylic acid and 0.45 g. of phosphorus trichloride. With the contents of the flask held at 175 C. by the oil bath, 1.8 g. of chlorine was added through the sparger over a period of 2.3 hours. Analysis of the organic reaction product showed it to consist of 39.8 percent by weight of l-chlorocyclobutanecarboxylic acid, and 3.3 percent of other chlorinated acids, the balance being cyclobutanecarboxylic acid. The yield of tat-chlorinated acid was 92 percent based on the cyclobutanecarboxylic acid disappearing.

EXAMPLES l 1-l7 A glass reactor flask equipped with stirrer, condenser, sparger, and means for controlling and measuring temperature was charged with 256 g. of cyclohexanecarboxylic acid and 8 g. of phosphorus trichloride. The temperature of the mixture was adjusted to about 100 C. and 142 g. of chlorine was introduced through the sparger over a period of about 6 hours at 97101 C. Analysis of the organic portion of the reaction mixture showed it to contain 29 weight percent of unreacted cyclohexanecarboxylic acid, 12 percent of 1-chlorocyclohexanecarboxylic acid, 50 percent of isomeric monochlorocyclohexanecarboxylic acids, and the remainder was polychlorinated products. The yield of 1-ch1orocyclohexanecarboxylic acid was 18 percent based on the cyclohexanecarboxylic acid which was actually reacted.

Using essentially the same procedure except for immaterial variations in catalyst concentration as noted, chlorinations were carried out at various temperatures with the same proportion of reactants. The results are summarized in the following table wherein the listed yields are of 1-chlorocyclohexanecanboxylic acid.

TABLE Temp., Wt. percent Percent Percent Example 0. P013 conversion yield EXAMPLES 18-20 Cyclohexanecarboxylic acid was reacted with chlorine at a constant temperature of 170 C. and with various proportions of PCl under conditions otherwise as described in Example 12. The yield of the 1-chloro acid was found to be little affected by the changes in catalyst concentration as shown below, but the color of the product increased somewhat with the concentration of catalyst.

Wt. percent PCI 0.6, 1.0, 2.0. Percent yield: 99, 98.5, 96.5.

6 4. The process of claim 1 wherein the acid is cyclo- References Cited hexanecarboxyhc acid.

5. The process of claim 1 wherein the chlorinating agent UNITED STATES PATENTS is chlorine. 3,052,716 9/1962 Jason et al 260514 6. The process of claim 1 wherein the chlorination 5 catalyst is a. halide, oxyhalide, oxygen acid, or oxide of CHARLES B. PARKER, Primary Examiner phosphorus, arsenic, antimony, sulfur, selenium, or tellurium; a halide of tin, iron or aluminum; a halooxygen acid KILLOS Asslstant Exammer of phosphorus or sulfur; phosphorus plus iodine; or a US. Cl. X.R.

combination thereof. 10 260-413, 539