PROCESS FOR ALPHA HALOGENATING ALKYL CARBOXYLIC ACIDS AND CATALYST COMPOSITION FOR USE THEREIN

Abstract: Alpha-halogenation of C₈ to C₃₀ carboxylic acids is carried out using a halogen source in the presence of a catalyst system comprising a free radical inhibitor, a strong acid and an organic acid anhydride.

Description: HALOGENATION PROCESS AND CATALYST SYSTEM FOR USE zw FIELD OF THE INVEMTION The present invention relates to compositions and processes for halogenating C8 to C30 carboxylic acids at the alpha carbon atom. BACKGROUND OF THE INVENTION The halogenation of organic compounds at a specific carbon atom (i.e., regiospecifically) is difficult, especially on an industrial scale. In general, halogenation reactions tend to occur to some extent at all available carbon-hydrogen linkages in the molecule undergoing halogenation. A successful process for achieving alpha-halo genation of carboxylic acids is described in U.S. Pat. No. 4,148,811, Crawford, issued April 10, 1979. In that process, the reaction is carried out using a halogen source in the presence of a catalyst system comprising a cyanoquinone free radical inhibitor and an acidic material, preferably chlorosulfonic acid. Yields of 80-90% of the alpha-halogenated carboxylic acid are achieved with the Crawford process. Other references relating to alpha-halogenation of carboxylic acids (or their anhydrides or acid halides) are the following. U.S. Pat. Nos. 3,751,461, Dhingra, issued August 7, 1973; 3,671,584, Schlecht, issued June 20, 1972; 4,007,222, Haschke et al., issued February 8, 1977; 3,584,036, Sexton, issued June 8, 1971; 3,634,504, Young, issued January 11, 1972; Harpp et al., J. Org. Chem., Vol. 40, No. 23,3420 (1975); Ogata et al., J. Org. Chem., Vol. 45, No. 14, 2831 (1980); Ogata et al., Can. J. Chem., Vol. 55, 1268 (1977); Ogata et al., Organic Synthesis, Vol. 59, 20 (1979); Ogata et al., Bull. Chem. Soc. Jap., Vol. 52, 255 (1979); Little et al., J. Am. Chem. Soc., Vol. 91, No. 25, 7098 (1969); ogata et al., J. Org. Chem., Vol. 40,. No. 20, 2960 (1975); Ogata et al., Nip. Kag. Kai, Vol. 9, 1517 (1975); Ogata et al., Jap. Pat. No. 135,024, October 25, 1975; Ogata et al., Tetrahedron, Vol. 26, 5929 (1970). The alpha-halogenated carboxylic acids are useful in the production of lubricants and as surfactants and surfactant intermediates. SUMMARY OF THE INVENTION The present invention constitutes an improvement over the process of Crawford U.S. Pat. No. 4,148,811 in that higher yields are obtained. In accordance with the present invention the alpha-halogenation of a C8 to C30 carboxylic acid is carried out with a halogen source in the presence of a catalyst system comprising a free radical inhibitor, a strong acid and an organic acid anhydride. A representation of the reaction of the present invention is as follows: EMI2.1 <tb> <SEP> Strong <SEP> Acid <tb> <SEP> R' <SEP> Free <SEP> Radical <tb> R <SEP> - <SEP> C <SEP> - <SEP> COOH <SEP> + <SEP> Halogen <SEP> Inhibitor <SEP> > <SEP> R <SEP> - <SEP> C <SEP> - <SEP> COOH <tb> I <SEP> OrganicAcid > <SEP> I <tb> <SEP> H <SEP> Anhydride <SEP> Halide <tb> where R is a hydrocarbyl group and R' is hydrogen or a hydrocarbyl.group, the sum of the carbon atoms in R and R' being from 6 to 28. DETAILED DSSCRIPTION OF THE; INVENTION The present invention encompasses a process for halogenating carboxylic acids which have at least one hydrogen atom on the carbon atom adjacent to the carboxylate group. The hydrogen atom is displaced by a halogen atom during the process. In the practice of the invention, the carboxylic acid is contacted with halogen or a halogen source in the presence of an effective amount of a catalyst system comprising a free radical inhibitor, a strong acid and an organic acid anhydride. By "halogenating" herein is meant displacing an alpha-hydrogen with halogens other than fluorine. As is well known, fluorination reactions are carried out under special conditions and are therefore not contemplated in the practice of this invention. The present process is particularly useful for chlorinating or brominating carboxylic acids, and on an industrial scale, is especially useful for chlorination reactions. By an "effective amount" herein is meant an amount of the free radical inhibitor, strong acid and anhydride sufficient to direct the halogenation reaction regiospecifically such that it occurs almost exclusively at the alpha-hydrogen substituent of the carboxylic acid. By "comprising" herein is meant that various other compatible materials may be present in the reaction mixtures during the halogenation reaction in such proportions as will not adversely affect the alpha-halogenation of the carboxylic acids. For example, various solvents and the like can optionally be present. The term "comprising" thus encompasses and includes the more restrictive terms consisting of" and "consisting essentially of" within its scope, so long as the processes and compositions of this invention include the specified ingredients, which are critical to the practice of the invention. All percentages herein are on a mole basis, unless otherwise specified. The carboxylic acids which are alphahalogenated in the manner of this invention comprise those having from 8 to 30 carbon atoms and having at least one hydrogen on the carbon atom which is adjacent to the carboxyl group. The preferred carboxylic acids for use in the present process are alkyl carboxylic acids having 8 to 18 carbon atoms (also called fatty acids). Accordingly, the present process is especially useful for alpha-halogenation (preferably alpha-chlorination) of carboxylic acids such as lauric acid, myristic acid, palmitic acid, stearic acid and mixtures thereof. The process of this invention is not limited with regard to the halogenation agent. Elemental halogens, liquid or gaseous, can be used. Chlorine gas is especially convenient, economical and preferred for use herein. Bromine can also be used, but is more expensive, as is iodine. Halogen sources other than elemental halogens can also be used. Such alternate halogen sources include, for example, well-known organic halogenating agents such as N-chlorosuccinimide (NCS) and N-bromosuccinimide (NBS). Free Radical Inhibitors A free radical inhibitor (also referred to in the art as "free radical scavenger") is an essential component of the catalyst system herein. The term "free radical inhibitor" is well known to those skilled in the art of organic reactions and many such materials are known. The following are exemplary. A. Cyanoquinones In general these compounds are characterized by the moiety EMI5.1 where R can be H or one or more substituent groups, e.g., halogen, alkoxyl, alkyl, thioalkyl, cyano, etc. See Wheland et al., J. Am. Chem. Soc. 98, 3916 (1976) and Wheland et al., J. Org. Chem. 40, 3101 (1975). The tetracyanoquinodimethane (TCNQ) compounds preferred for use herein are of the formula (R as above): EMI5.2 When R is hydrogen the compound is tetracyanoquinodimethane itself, which is the preferred free radical inhibitor herein. Other specific examples of cyanoquinones useful herein include hexacyanobutadiene (HCBD) and tetracyanonaphthoquinodimethane (TNAP), represented by the following formulas: EMI5.3 TCNQ, TNAP and lICBD are prepared by techniques known in the literature. (While HCBD is not, in the most formal sense, a cyanoquinone structure, its extended conjugated system of electrons is "quinone-like.ll Accordingly, HCBD is considered a cyanoquinone in the present invention.) See U.S. Pat. No. 4,148,811, noted above. B. Quinones These compounds contain the moiety EMI6.1 Examples of these compounds are benzoquinone, bromanil (tetrabromo-1,4-benzoquinone), chloranil (tetrachloro-1,4-benzoquinone), iodanil (tetraiodo-l, 4-benzoquinone), 2,3,5-trichloro-1,4-benzoquinone and di- tri- and tetra cyano-1,4-benzoquinone. C. Free radicals which are stable at room temperature (about 200C). These free radical compounds inhibit the formation of additional free radicals. An example of a stable free radical is diphenyl picrylhydrazil. The preferred free radical inhibitors herein are the cyanoquinones, especially tetracyanoquinodimethane (TCNQ). Other miscellaneous free radical inhibitors known to the art can also be used. Examples are elemental oxygen and m-dinitrobenzene. Acids The strong acids used in. the catalyst system in the process herein include any of those known to the art for use in organic halogenation reactions. Such acidic materials include both Lewis acids and organic and inorganic protonic acids which are of greater strength than the carboxylic acids which are to be alpha-halogenated in the process herein. Typical examples of such acids include trifluoroacetic acid, PBr3, PCl3, thionyl chloride, PC15, phosgene, fluoro sulfonic acid, chlorosulfonic acid, trifluoromethanesulfonic acid and sulfuric acid. The preferred acids are sulfuric acid and chlorosulfonic acid. The most preferred acid is sulfuric. Organic Acid Anhydrides The organic acid anhydrides used in the catalyst system in the process herein are organic compounds, which, upon reaction with water, yield an acid. Examples of these compounds are ketenes and carboxylic acid anhydrides. Ketenes contain the moiety = = C = 0 and carboxylic acid anhydrides contain the moiety EMI7.1 If desired the organic acid anhydride can be the ketene or carboxylic anhydride of the fatty acid which is being halogenated. Preferably the ketene or carboxylic anhydride is that of a C2 to C5 carboxylic acid. The preferred acid anhydride is acetic acid anhydride. The most preferred catalyst system herein is TCNQ:sulfuric acid: acetic anhydride. The free radical inhibitor, strong acid and organic acid anhydride can be used in various ratios in the catalyst system herein. Typically the molar ratio of free radical inhibitor:strong acid will be from 0.001:1 to 100:1 (preferably 0.10:1 to 1.0:1), and the molar ratio of free radical inhibitor:organic acid anhydride will be from 0.001:1 to 100:1 (preferably 0.01:1 to 0.1:1). The halogenation reaction of this invention is carried out by contacting the carboxylic acid with the halogen or halogen source in the presence of the free radical inhibitor/strong acid/organic acid anhydride catalyst at a temperature of 700C, or greater. Chlorination reactions using elemental chlorine as the halogen are carried out at temperatures above 130 C, preferably at temperatures within the range from 1450C to 2500C. When halogen sources such as the N-halosuccinimides are used, temperatures of 700C to 2000C are operative and convenient. Bromintion and iodination reactions are carried out under similar temperature conditions. The process herein can be carried out in the presence or absence of inert solvents. Preferably, the reaction is carried out without the use of solvents, and this is both convenient and economical on a commercial scale. Indeed, the use of solvents can lead to undesirable side reactions involving halogenation of many of the common hydrocarbon solvents. Under the reaction temperatures specified hereinabove, the carboxylic acids are liquids and are quite convenient to use in that state without additional solvents. Typically the catalyst system is used at a concentration such that the molar concentration of the free radical inhibitor is from 0.01 to 10.0 molar percent, preferably 0.05 to 5 and most preferably 0.05 to 0.5 molar percent, relative to the amount of carboxylic acid. The invention will be illustrated by the following nonlimiting example. EXAMPLE I Preparation of 2-Chlorostearic Acid A one-liter, three-necked round bottom reaction flask was mounted in a fume hood and placed in a 335 watt heating mantle. A mechanical stirrer, dry ice condenser and a fritted gas dispersion tube were fitted to the reaction flask. The temperature of the reaction flask was controlled by use of a Thrmo-Watch which maintains the function of a Jack-O-Matic, upon which the heating mantle was placed. The dispersion tube was connected to a chlorine source by PVC tubing and metered with an in line flowmeter having a range of 0.05 to 1 liter/min. The reaction vessel was initially charged with 1.0 mole of stearic acid (284.5 grams). The stearic acid was melted by raising the temperature to 80 C. At this time 0.005 mole TCNQ (1.02 grams) was added to the reaction vessel. Chlorine gas at a flow rate of 0.05 liter/min. was added to solubilize the TCNQ into the melted stearic acid. Acetic anhydride at a 0.06 molar level (6.125 grams) was then added to the reaction flask and the temperature was rapidly elevated to 1300C. Using a pipette, 0.016 mole sulfuric acid (1.6 grams) was then added to the reaction vessel. The temperature was then adjusted to 1500C and the chlorine flow rate was adjusted to 0.5 liter/min. This point was considered time zero for the beginning of the reaction. After 52 minutes of reaction time, the chlorine flow rate was readjusted to 0.05 liter/min. and the reaction mixture was slowly cooled under a head of chlorine gas to the product melting point (640C). After cooling, the reaction product was analyzed by gas chromatography as being 96.128 2chlorostearic acid, 2.71% 2,2-dichlorostearic acid, 0.42% free radical chlorination products, and 0.75% unreacted stearic acid. If the above reaction is carried out with fatty acids having alkyl chain lengths from 8 to 18 carbons, or combinations thereof, the corresponding 2chloroalkyl acids are produced in purities exceeding 95%.

Claims: CLAIMS 1. A process for alpha-halogenating alkyl carboxylic acids containing from 8 to 30 carbon atoms and having at least one reactive alpha-hydrogen substituent, comprising contacting said carboxylic acid with halogen or a halogen source in the presence of an effective amount of a catalyst system comprising: A. An acid having a greater acid strength than the alkyl carboxylic acids; B. A free radical inhibitor; and C. An organic acid anhydride. 2. A process according to Claim 1 wherein the alphahalogenation reaction is chlorination. 3. A process according to Claim 2 wherein the Component (B) free radical inhibitor is selected from cyanoquinones, quinones and free radicals which are stable at room temperature. 4. A process according to Claim 3 wherein the free radical inhibitor is a cyanoquinone of the formula EMI11.1 wherein R is a radical selected from hydrogen, halogen, alkoxyl, alkyl, thioalkyl and cyano. 5. A process according to Claim 3 wherein the free radical inhibitor is a quinone selected from tetrachloro-1,4benzoquinone, 2,3,5-trichloro-1,4-benzoquinone and di-, tri-, and tetra-cyano-1,4-benzoquinone. 6. A process according to any one of Claims 1-5 wherein the Component (A) strong acid is selected from trifluoroacetic acid, phosphorous trichloride, phosphorous tribromide, thionyl chloride, phosphorous pentachloride, phosgene, fluorosulfonic acid, chlorosulfonic acid, trifluoromethanesulfonic acid and sulfuric acid. 7. A process according to any one of Claims 1-6 wherein the Component (C) organic acid anhydride is selected from ketenes and carboxylic acid anhydrides having from 2 to 5 carbon atoms. 8. A process according to Claim 7 wherein the carboxylic acid is a C8 to C18 fatty acid, Component (A) is sulfuric acid, Component (B) is tetracyanoquinodimethane-and Component (C) is acetic anhydride and the halogen source is elemental chlorine. 9. A process according to any one of Claims 1-8 wherein the molar ratio of (B):(A) in the catalyst system is from 0.001:1 to 100:1, and the molar ratio of (B):(C) is from 0.001:1 to 100:1. 10. A process according to any one of Claims 1-9 wherein the catalyst system is used at a level wherein the molar concentration of Component (B) is from 0.05% to 5% based on the amount of carboxylic acid. 11. A process according to any one of Claims 1-10 wherein the reaction temperature is from 145"C to 2500C. 12. A catalyst composition for use in the process of any one of Claims 1-11 comprising: A. An acid having a greater acid strength than the C8 to C30 carboxylic acids; B. A free radical inhibitor; and C. An organic acid anhydride; wherein the molar ratio of (B):(A) is from 0.10:1 to 1.0:1 and the molar ratio of (B):(C) is from 0.01:1 to 0.1:1.

Inventors: GIBSON, MICHAEL STEVEN, HOWIE, JOHN KEENEY
Applicants: THE PROCTER & GAMBLE COMPANY
Application year: 1983
Main classification: C07C51
IPC codes: B01J31, C07C67, C07B61, C07C53, C07C51