EP0000414B1

EP0000414B1 - Process for halogenating carboxylate compounds

Info

Publication number: EP0000414B1
Application number: EP78200077A
Authority: EP
Inventors: Robert James Crawford
Original assignee: Procter and Gamble Co
Current assignee: Procter and Gamble Co
Priority date: 1977-07-12
Filing date: 1978-07-03
Publication date: 1982-07-14
Also published as: CA1119156A; EP0000414A1; US4148811A; JPS5439013A; EP0057291A3; IT7850224A0; JPS623136B2; EP0057291A2; IT1105085B

Description

The present invention relates to processes for halogenating carboxylic acids, acid halides and acid anhydrides at the α-carbon atom in the presence of a cyanoquinodimethane compound.
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.
Some regioselectivity in halogenation reactions has been achieved heretofore. For example, the treatment of aliphatic carboxylic acids having at least one a-hydrogen atom with halogens such as bromine or chlorine in the presence of a phosphorus halide catalyst comprises the well-known Hell-Volhard-Zelinsky preparation of a-halo acids. However, chlorination reactions carried out according to the HVZ procedure are not regiospecific and mixtures of chlorinated products are typically secured.
For the most part, the HVZ halogenation is used to brominate carboxylic acids and salts and is, therefore, expensive as compared with the corresponding chlorination reaction.
By the present invention, it has been discovered that cyanoquinodimethane compounds can be used in the a-halogenation of carboxylic acids and salts, carboxylic acid anhydrides and carboxylic acid halides. The resulting a-halogenated products are useful as lubricant additives and as intermediates for the production of lubricants, and as surfactants and surfactant intermediates.

RELATED REFERENCES

The general topic of the directive effect of the carboxyl group on the chlorination of aliphatic systems is treated by Little, Sexton, et al., Journal of the American Chemical Society 91 7098, (1969). See also, U.S. Patent 3,584,036 to Sexton, et al., which relates to a-chlorination reactions.
Other publications relating to regiospecific halogenation reactions include: Y. Ogata, et al., J. O_rg. Chem., 40, 2960 (1975); Y. Ogata, et al., Tetrahedron, 26, 5929 (1970); Y. Ogata, et al., Nippon Kagaku Kaishi, 1517 (1975) [Chem. Abstr. 83, 178239 (1975)]; Y. Ogata, et al., Japanese Patent 75-135024; Y. Ogata, et al., Japanese Patent 74-24913; A. F. Young, U.S. Patent 3,634,504; D. N. Harpp, et al., J. Org. Chem., 40, 3420 (1975); and H. Haschke, German Patent 2,440,213.
While the foregoing references relate to various means for achieving the regiospecific halogenation of organic compounds, especially carboxylic acids, the present invention employs an entirely new catalyst for this purpose. This invention also provides higher yields of the desired monochlorinated product, and in shorter times, than do the art-disclosed processes. Moreover, the process herein is especially suitable for a-halogenating both short chain and the longer-chain fatty acids, i.e., those in the chain length range above about C₁₀ which are especially useful as detersive surfactants. In this regard, the present invention provides a marked improvement over the process disclosed in U.S. 3,584,036, cited above.
In addition to the foregoing, U.S. Patent 3,988,369 to Pearson, October 26, 1976, teaches a process for halogenating organic compounds in the presence of a trialkyl phosphate.

SUMMARY OF THE INVENTION

The present invention encompasses a process for halogenating carboxylic acids and salts, acid anhydrides and acid halides (all hereinafter "carboxylate compounds") having at least one reactive alpha hydrogen substituent, comprising contacting said carboxylate compound with a halogen (especially chlorine) or halogen source in the presence of an effective amount of a cyanoquinodimethane compound and acidic auxiliary agent, as described more fully hereinafter.
A representation of the reaction of the present process with organic acids is as follows:
where R and R' are hydrocarbyl or hydrogen, as described more fully hereinafter.

DETAILED DESCRIPTION OF THE INVENTION

The present invention encompasses a process for halogenating carboxylate compounds. The carboxylate compounds used herein are characterized by at least one reactive α-hydrogen substituent, which is displaced by a halogen atom during the process. In the practice of the invention, the carboxylic acids and salts, acid chlorides, or carboxylic acid anhydrides are contacted with a halogen or halogen source in the presence of an effective amount of a cyanoquinodimethane material and ah acidic auxiliary agent.
By "halogenating" herein is meant displacing an a-hydrogen substituent 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 carboxylate compounds and, on an industrial scale, is especially useful for chlorination reactions.
By "carboxylate compound" herein is meant carboxylic acids (and salts), carboxylic acid halides and carboxylic acid anhydrides.
By "effective amount" herein is meant an amount of the cyanoquinodimethane material and auxiliary agent sufficient to direct the halogenation reaction regiospecifically such that it occurs almost exclusively at the a-hydrogen substituent of the carboxylate compound.
The cyanoquinodimethane materials and acidic auxiliary agents are described in more detail hereinafter.
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 a-halogenation of the carboxylate compounds. 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 carboxylate compounds which are α-halogenated in the manner of this invention comprise carboxylic acids and carboxylic acid-derived materials. These carboxylate compounds are the free acids and salts, the acid anydrides and the acid halides.
The present process can be used to a-halogenate carboxylate compounds, especially carboxylic acids, comprising from 2 to 30 carbon atoms. (Of course, for the corresponding symmetrical carboxylic acid anhydride, equivalent compounds will comprise from 4 to 60 total carbon atoms). The process herein is especially useful for α-halogenating the C₃ to C₁₈ carboxylic acids. However, for halogenating. the shorter members in this class, other art-disclosed processes are adequate, albeit sub-optimal. The special economic advantages of the present process are particularly noteworthy when α-halogenating, especially a-chlorinating, the C₆‾C₁₈ carboxylate materials for which the art-disclosed processes yield mixed results. Accordingly, the present process is especially useful for α-halogenating, especially a-chlorinating, carboxylate materials based on 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 well-known organic halogenating agents such as N-chlorosuccinimide (NCS) and N-bromosuccinimide (NBS).
The cyanoquinodimethane materials used herein are all members of the well-known class of compounds which have recently been the subject of intensive study as electrically-conductive organic solids. Reviews of these materials, methods of preparation and a list of references to additional compounds and preparative methods appear in the articles by Wheland and Gillson, Journal of the American Chemical Society, 98, 3916 (1976) and Wheland and Martin, J. Org. Chem., 40, 3101 (1975).
In general, the cyanoquinodimethanes useful herein are characterized by the moiety:
where R can be H or one or more substituent groups, e.g., halogen, alkoxyl, alkyl, thioalkyl, and CN. See Wheland and Martin, above.
The tetracyanoquinodimethane (TCNQ) compounds preferred for use herein are of the formula (R as above):
Other specific examples of cyanoquinodimethanes useful herein include hexacyanobutadiene (HCBD) and tetracyanonaphoquinodimethane (TNAP), represented by the following formulas

TCNQ, TNAP and HCBD are prepared by techniques known in the literature. (While HCBD is not, in the most formal sense, a quinone structure, its extended conjugated system of electrons is "quinone-like". Accordingly, HCBD is considered a cyanoquinodimethane in the present invention).

Auxiliary agents

The auxiliary agents used in the practice of this invention include many of the common acidic materials known in the art for use in halogenation reactions. Such acidic materials include both Lewis acids and inorganic protonic acids which are of considerably greater acid strength than hydrocarbyl carboxylic acids. Typical examples of such acidic auxiliary agents include acetyl chloride, PBr₃, PCI₃, thionyl chloride, sulfuryl chloride, oxalyl chloride, PCI_S, phosgene, fluorosulfonic acid, chlorosulfonic acid, and trifluoromethanesulfonic acid. The most highly preferred auxiliary agent herein is chlorosulfonic acid.
It is to be understood that carboxylic acid halides (especially acid chlorides) are operative in the practice of this invention as auxiliary agents when α-halogenating carboxylic acids or anhydrides thereof. However, carboxylic acid halides can themselves be halogenated if they contain an a-hydrogen substituent. The α-halogenation of carboxylic acid halides is carried out in the presence of a more acidic auxiliary agent such as CIS0₃H, or PCI₃, and the cyanoquinodimethane material. This is not a preferred halogenation method, inasmuch as it requires the separate preparation of a stoichiometric amount of acid chloride, which is thereafter a-halogenated.
The most preferred catalyst system herein comprises a mixture of TCNQ and chlorosulfonic acid. Various ratios of these materials can be employed, but a 1:5-1:50 mole ratio of TCNQ:CIS0₃H is convenient.
The most preferred halogenation reagent herein comprises gaseous chlorine and the aforesaid mixture of TCNQ and chlorosulfonic acid. Of course, the chlorine in this reagent is replenished as it is exhausted during the reaction. Replenishment of the chlorine is most conveniently carried out by bubbling gaseous chlorine into the reaction mixture.
The halogenation reaction of this invention is carried out by contacting the carboxylate compound with the halogen or halogen source in the presence of a cyanoquinodimethane material and acidic auxiliary agent at a temperature of 70°C, 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 150°C to 250°C. When halogen sources such as the N-halosuccinimides are used, temperatures of 70°C-250°C are operative and convenient. Bromination 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 carboxylate compounds are liquids and are quite convenient to use in that state without additional solvents.
Typical use concentrations of the cyanoquinodimethanes relative to the carboxylate compounds are 0.01-10.0 mole percent, preferably 0.05-5.0 mole percent, most preferably 0.05-0.5 mole percent.
Typical use concentrations of the acidic auxiliary agents relative to the carboxylate compounds are 0.1-10 mole percent, preferably 1-5 mole percent.
The following examples illustrate the practice of this invention but are not intended to be limiting thereof. Percentage yields are in parentheses.

Example I

Preparation of 2-Chlorostearic Acid

A 1-liter five-neck round bottom flask is placed in an efficient fume hood and is fitted with a mechanical stirrer, thermometer, Dry Ice condenser, and two fritted gas dispersion tubes (opposite necks). The two dispersion tubes are connected via PVC tubing to a T-connector, the third arm of which is connected to a chlorine gas source containing an in-line flowmeter capable of reading 200-1000 ml/min.
The dispersion tubes are removed temporarily, and the flask is charged with 569.0 g (2.0 moles) of powdered stearic acid. The stearic acid is melted by warming the flask with a heating mantle while stirring at low speed. When the acid has melted (temperature approximately 80°C), 1.65 g (0.008 mole) of TCNQ (Aldrich Chemical Co.) is added. The chlorine gas flow to the dispersion tubes is started and set at a rate of 250 ml/min. Chlorosulfonic acid, 4.0 ml (0.063 mole) is pipetted rapidly into the flask (temp. _<90°C) and the dispersion tubes are immediately fitted to the flask so that the chlorine is evolved well beneath the surface of the liquid. The stirrer is adjusted to a high speed setting, and the solution is heated as rapidly as possible to 150°C. (Immediately prior to the addition of chlorosulfonic acid, full line voltage is applied to the heating mantle. When the solution temperature reaches 130°C, the voltage is cut to 0, allowing the temperature to coast to 150°C}, During the heating period, the Dry Ice condenser is filled with a Dry Ice-alcohol slurry. When the temperature reaches 148°C, the chlorine flow rate is increased to 1000 ml/min. This point is considered time 0 for purposes of timing the reaction.
Throughout the reaction, the solution temperature is maintained at 150±3°C by careful adjustment of the current to the heating mantle. Since the reaction is mildly exothermic, this temperature is usually maintained during the first half hour with no current applied to the mantle. During the second half hour, the cooling effect of condensing chlorine necessitates constant monitoring of the solution temperature and mantle setting. At 65 minutes reaction time, the chlorine flow rate is reduced to 250 ml/min. At 75 min., the heating mantle is removed and is replaced by an ice bath, and the dispersion tubes and condenser are removed. When the solution temperature reaches 80-90°C, the entire reaction mixture is poured into 1500 ml of acetonitrile. The resulting mixture is warmed on a steam bath until a clear, yellow, homogeneous solution is obtained. The solution is placed in an ice bath and stirred or swirled vigorously to effect crystallization of the product. After standing at 0°C overnight; the product is collected by suction filtration, washed thoroughly with cold acetonitrile, and vacuum dried to afford 535.5 g (84%) of 2-chlorostearic acid, M.P. 63.5-64°C.
As an optional modification of the foregoing procedure, an additional 0.8 portion of TCNQ can be added at 50 min. reaction time. This serves to prevent the formation of minor by-products that result if the reaction is allowed to run beyond the time when starting material is consumed. With this modification, the yield of recrystallized 2-chlorostearic acid is increased to 89%.
The process of Example I is carried out with lauric acid, myristic acid, palmitic acid, and commercial tallow fatty acids, i.e:, mixtures of lauric, myristic, palmitic and stearic acids, respectively. High yields (ca. 90%) of the a-chlorinated acids are secured in each instance.
The process of Example I is carried out using the following acidic auxiliary agents in place of the chloro- sulfonic acid: PBr₃; PCI₃; PCI₅; acetyl chloride; thionyl chloride; sulfuryl chloride; oxalyl chloride; phosgene; fluorosulfonic acid; chlorosulfonic acid; stearoyl chloride; and trifluoromethane sulfonic acid. In each instance, excellent yields of pure 2-chlorostearic acid are secured.
The process of Example I is carried out using HCBD and TNAP, respectively, as the cyanoquinodimethane agent (0.008 moles). In each instance, good yields of the desired 2-chlorostearic acid are secured.
The process of Example I is repeated using acetic, propionic, butyric, pelargonic, pentadecanoic, margaric, arachidic, behenic, tricosanoic, and cerotic acids, respectively, and their respective anhydrides, and the α-chlorinated products are secured.

Example II

α-Halogenation of Acid Halides and Anhydrides

Following the procedure of Example I, stearoyl chloride is reacted with chlorine in the presence of CIS0₃H and TCNQ. The product is distilled to provide substantially pure 2-chlorostearoyl chloride.
The foregoing reaction is repeated using stearic anhydride and the α-chlorinated anhydride is secured.
In a modification of the process of Example li, the chlorine.gas is replaced by liquid bromine and the corresponding α-brominated compound is secured.

Example III

Mixtures especially adapted for use in the α-halogenation of carboxylate compounds are as follows:
The foregoing mixtures are typically used at concentrations of 0.01%-10% of the carboxylate compound being halogenated and the reaction proceeds substantially exclusively at the α-CH group.

Example IV

The process of the present invention can be carried out using free halogens in the manner described hereinbefore. Organic halogenating agents such as N-chlorosuccinimide can also be employed, as follows.
Into a 50 ml 3-neck round bottom flask fitted with a condenser, thermometer, and magnetic stirrer were placed 11.4 g (0.04 mole) stearic acid, 8.0 g (0.06 mole) N-chlorosuccinimide, 0.1 ml (0.0015 mole) chlorosulfonic acid, and 0.04 g (0.0002 mole) TCNQ. The flask was placed in a heating bath set at 150°C. The mixture was stirred during heating, and a homogeneous liquid phase was formed. The solution temperature continued to rise above that of the heating bath, and a sudden exothermic reaction occurred in which the reaction temperature increased to ca. 220°C. The reaction mixture was cooled and dissolved in chloroform, and the resulting solution was washed thoroughly with dilute aqueous sodium chloride solution. After drying and removal of the chloroform, the residue was recrystallized from acetonitrile to afford 8.9 g (70%) of 2-chlorostearic acid which was equivalent in purity to the product of Example I.

Example V

Following the procedures of Examples I and II herein, carboxylate compounds are a-chlorinated, α-brominated and a-iodinated in the presence of the following mixtures of substituted TCNQ and acidic auxiliary agents:
The foregoing mixtures are typically used at concentrations of 0.01%-10.0% of the carboxylate compound being halogenated and the reaction proceeds substantially exclusively at the a-CH group to provide the α-halogenated carboxylate compound.
As can be seen from the foregoing, the present process provides an improved means for carrying out a-halogenations, especially a-chlorinations, of carboxylate compounds, especially carboxylic acids. By the present invention, the use of cyanoquinodimethane materials substantially improves yields of a-chlorinated products and greatly decreases side-reactions which have heretofore led to undesirable byproduct formation. TCNQ, HCBD, TNAP and derivatives thereof are available by art-disclosed processes for use in the present invention.

Claims

1. A process for replacing an a-hydrogen substituent of carboxylate compounds with halogen in the presence of a catalyst characterized in, that one contacts the carboxylic acids, carboxylic acid salts, carboxylic acid anhydrides or carboxylic acid halides at a temperature of 70°C or greater with a halogen or halogen source other than fluorine or a fluorine source in the presence of an effective amount of: a cyanoquinodimethane having the moiety

where R is H or one or more substituents; or hexacyanobutadiene (HCBD); and an acidic auxiliary agent.

2. A process according to Claim 1 wherein the cyanoquinodimethane material is selected from tetracyanoquinodimethane (TNCQ), HCBD, and tetracyanonaphthoquinodimethane (TNAP), and derivatives thereof, and the auxiliary agent is a Lewis acid or an inorganic protonic acid.

₁3. A process according to Claim 1 wherein the cyanoquinodimethane material is a member selected from TCNQ, HCBD, and TNAP, and derivatives thereof, and the auxiliary agent is a member selected from PCI₃, PCig, PBr₃, thionyl chloride, sulfuryl chloride, oxalyl chloride, acetyl chloride, phosgene, fluorosulfonic acid, chlorosulfonic acid, and trifluoromethanesulfonic acid.

4. A process according to Claim 1 wherein the halogen or halogen source is a chlorinating or brominating agent.

5. A process according to Claim 4 wherein the halogen source is a member selected from N-chlorosuccinimide and N-bromosuccinimide, and wherein the process is carried out at a temperature within the range from 70°C to 250°C.

6. A process according to Claim 1 wherein the carboxylate compound is a carboxylic acid which comprises from 2 to 30 carbon atoms.

7. A process according to Claim 6 wherein the carboxylic acid is selected from lauric acid, myristic acid, palmitic acid, stearic acid, and mixtures thereof.

8. A process according to Claims 1 and 6 for chlorinating carboxylic acids on the a-carbon, comprising contacting said carboxylic acid with chlorine at a temperature within the range from 150°C to 250°C in the presence of an effective amount of a catalyst system comprising TCNQ, or derivatives thereof, and chlorosulfonic acid, wherein the mole ratio of the TCNQ or the TCNQ-derivative:CISO₃H is in the range of 1:5 to 1:50.