US2370577A - Process for the production of trichloro acids - Google Patents

Description

Patented Feb. 27, 1945 PROCESS FOR THE PRODUCTION OF TRICHLORO ACIDS Ralph E. Plump, Haddonfleld, N. J., .assignor to The Pennsylvania Salt Manufacturing Company, Philadelphia, Pa., a corporation of Pennsylvania No Drawing. Application May 27, 1943, Serial No. 488,738

16 Claims. (01. 260-530) The present invention relates to a process for the production of trichloroacids of the type represented by trichloroacetic acid, 2,2,3 trichloropropicnic acid, and 2,2,3 trichlorobutyric acid from trichlcroaldehydes, and more particularly it relates to a method by which chloroacids of the stated type may be easily and economically prepared by the oxidation of their corresponding chloroaldehydes by means of a chlorate.

In 1885, Seubert reported (Berichte 18, p. 3336) that chloral hydrate (trichlorcacetaldehyde hydrate) would react with dry, solid potassium chlorate to yield a mixture of various products, including some trichloroacetic acid, the salt thereof, chloroform, phosgene, carbon dioxide, chlorine, hexachloroethane and the like. He concluded that, while the yield was not as expected, the method could be used for preparetion of small quantities of a well-crystallizable mixture of trichloroacetic acid and its potassium salt. In addition to the unsatisfactory reaction obtained, the procedure reported by Seubert was hazardous due to the explosive tendency thereof.

In industrial practice, concentrated or fuming nitric acid has been employed in the oxidation of trichloroaldehydes to form thecorresponding acid, the work of Seubert not having found application, apparently because of the unsatisfactory nature of the reaction. The use of concentrated or fuming nitric acid makes the process relatively expensive, due to the cost of the acid. In addition, the reaction must be carried out in specialized, non-corrosive equipment, and provision must be made for the disposal of the fumes of nitrogen dioxide evolved. It is apparent, therefore, that the method used industrially at the present time in the preparation of the trichloroacids leaves much to be desired.

One object of the present invention is to provide a process by which satisfactory yields of a trichloroacid of the type stated may be easily and economically produced from the corresponding trichloroaldehyde by the use of a cheap oxidizing agent, which is substantially consumed by the reducing action of the trichloroaldehyde, leaving only a neutral residual inorganic chloride to be eliminated from the trichloroacid.

A further object of the present invention is to provide a process for the production of a trichloroacid which may be conducted in non-specialized equipment and which presents only a very slight fume disposal problem.

Still another object of the present invention is to provide a process for the oxidation of a trichloroaldehyde to the corresponding trichloroacid by means of a chlorate, which process may be conducted without hazard to produce a satisfactory yield of a good technical grade of the trichloroacid.

Other objects will be apparent from a consideration of this specification and the claims.

In accordance with the present invention, the trichloroaldehyde to be oxidized is reacted, in the presence of water, with a chlorate in a safe, efiicient, and direct operation, without resort to involved and expensive methods of separation, to produce a good yield of a suitably pure trichloroacid.

As above pointed out, the process is applicable for the production of trichloroacids of the type represented by trichloroacetic acid, 2,2,3,trichloropropionic acid, and 2,2,3,trichlorobutyric acid from the corresponding trichloroaldehydes. These acids and the corresponding aldehydes may be represented by the formulae R-CClz-COOH and'R-CClz-CHO respectively, where R is selected from the group consisting of Cl, CH2C1, and CH3-CHCl--. Thus. where R is chlorine, the chloroacid and the chloroaldehyde are trichloroacetic acid and trichloroacetaldehyde (chloral); where R is a CH2C1 group, the chloroacid and the chloroaldehyde are 2,2,3,trichloropropionic acid and 2,2,3,trichloropropanal-l (propyl chloral); and where R is a CH3'CHCl-- group, the chloroacid and chloroaldehyde are 2,2,3,trichlorobutyric acid and 2,2,3,- trichlorobutanal-l (butyl chloral). In most in stances, the use of a hydrate of the trichloroaldehyde will be found to be advantageous, but, if desired, the anhydrous aldehyde may be used in the process. Herein, unless otherwise specified, the term trichloroaldehyde includes the hydrate thereof.

Although any chlorate, preferably a water-soluble chlorate, may be employed as the oxidizing .agent, sodium chlorate, due to its cheapness, is

advantageously used. Examples of other ch10- rates applicable for use are potassium chlorate, caesium chlorate, lithium chlorate, calcium chlorate, and the like.

In the preferred embodiment of the present invention, the chlorate is present in the amount required by the following equation:

that is, A; mol of chlorate per mol of trichloroaldehyde. An excess of chlorate, for example, up to about 10% or more, may be employed, but since an excess represents a loss of material and no advantage is agained, the chlorate is advantageously present in an approximately stoichiometric proportion. The excess chlorate, if present, may be subsequently destroyed by further processing, for example, by steaming in the presence of acid and the chloride ions. Since any unreacted trichloroaldehyde (hydrate). may be easily separated from the trichloroacid produced in the process, less than the stoichiometric amount of chlorate may be used, but this is also of no advantage.

As previously stated, in accordance with the process of the present invention, the reaction between the trichloroaldehyde and the chlorate is conducted in the presence of water. The presence of the water assures the conversion of the trichloroaldehyde directly into the chloroacid and the formation of phosgene, chloroform, and other undesired products isminimized. Yields of the trichloroacid of 60 mol per cent. based on the chloroaldehyde, and greater have been obtained. In addition, the water serves as a temperature moderating means. and consequently, as a guarantee of safety. For instance, should the heat of the reaction proceed beyond the control of ordinary cooling appliances, the presence of an appreciable quantity of water in the reaction mixture immediately functions in maintaining the temperature of the mixture in the neighborhood of 100 C. and no loss of reactants or of the trichloroacid occurs. The quantity of water required in practice is usually that required to render the reaction mixture of such consistency as to be capable of strong agitation at room temperature. The amount of water employed may vary over a wide range, and the use of an amount of water (by weight) equal to or double the weight of the trichloroaldehyde or trichloroaldehyde hydrate is preferred, although larger and smaller quantities may be used, for example, the water may correspond to one-half or less of the weight of the trichloroaldehyde or trichloroaldehyde hydrate. Usually, the amount of water employed will not be less than about one-third of the weight of the trichloroaldehyde or trichloroaldehyde hydrate, since, with relatively small amounts of water, the progress of the reaction is not as satisfactory, and a tendency for explosive action may be encountered.

Although the reaction will proceed in the absence of an acid, a more satisfactory reaction is obtained, and the reaction will be initiated at a lower temperature when an acid is present in the reaction mixture. The starting acid concentration may be high or low, and the acid employed may be organic or inorganic. A high concentration is about 1.5 normality equivalents and a low .concentration is about 0.05 normality equivalent, based on the trichloroaldehyde. The quantity of acid present may be about 0.1 to 0.3, molecular equivalent, based on the trichloroaldehyde. Usually, a pH of about 3 or 4 to less than 1 is employed. The use of the trichloroacid to be produced by the oxidation of the trichloroaldehyde is ideal, since isolation of the end product is then accomplished with a minimum of processing. Examples of other organic acids are oxalic, lactic, tartaric, and the like; and examples of inorganic acids are sulphuric, hydrochloric, nitric and phosphoric acids.

In converting the trichloroaldehyde to the chloroacid in accordance with the present invention, the trichloroaldehyde, the water, the acid (if the process is to be conducted in the presence thereof), and the chlorate are mixed in any desired manner; and the trichloroaldehyde is oxidized at a temperature at least suilicient to initiate the reaction. In the now preferred embodiment of the invention, the trichloroaldehyde is mixed with the water, and the mixture is acidifled. The mixture is then heated and the chlorate is added in fractions. for example. in porthe chlorate. The acid, if employed, may be fur-' nishedby acidifying either (or both) the trichloroaldehyde or the chlorate solution prior to mixing it with the other reactant. As a further optional procedure, the trichloroaldehyde and the chlorate may be dissolved in water, and the acid may be added slowly during the reaction.

When acid is present, the reaction is initiated by heating the mixture to a temperature of about 40 C. or higher. In the case trichloroacetaldehyde is used, a temperature of about 40 C. to C. is generally employed to initiate the reaction. In the case of 2,2,3 trichloropropanal-l, a temperature of about C. to C. is employed. while in the case oi 2,2,3 trichlorobutanal-l, a temperature of about C. is usually employed. In the absence of acid, the temperature employed to initiate the reaction will generally be substantially higher than the figures given. The reaction is exothermic, and by suitable (intermittent or continuous) cooling, the temperature is allowed to rise slowly to about C. by the time all of the chlorate has been added, and this temperature is maintained by external heating if necessary for about-thirty minutes to one hour-at the end of which period the reaction is complete. If no external cooling is employed during the main part of the reaction, the temperature rises to 98 C. to 102 C., and active ebullition occurs. This appears to have no deleterious efiect on the yield, but a more eflicient reflux system is required than when the reaction is moderated by external cooling.

The use of oxidation promotion catalysts, such as ammonium metavanadate and ceric sulphate, may be used to promote reaction at a lower temperature, and to be efiective these catalysts, if employed, need only be present in small amounts, for example, from about 0.05% to 0.5% based on the weight of the trichloroaldehyde or the trichloroaldehyde hydrate, although larger amountsmay be employed, if desired.

During the reaction, the use of strong agitation is recommended in order to provide intimate mixing of the reactants. For example, when the 2,2,3,trichlorobutanal-1 is oxidized to 2,2, 3,trichlorobutyric acid, the acid forms an oily layer in which the unreacted chloroaldehyde dissolves, thus removing it from the oxidizing action of the chlorate dissolved in the water layer. Hence, thorough mixing of these two layers causes the reaction to proceed smoothly to completion, provides better dissipation of heat generated by the reaction, greatly shortens the processing time required, and gives rise to a higher ratio of product to by-product.

The trichloroacid obtained as the result of the process may be isolated in any manner known to the art, for example, by extraction, salting out, fractional distillation, and the like. For example, when 2,2,3,trichlorobutyric acid is predish 8% 120 C., yielding 61.7

pared, the reaction mixture may be allowed to separate into two layers, and the oily layer at the bottom of the reaction vessel separated from the upper layer. Theseparated material may then be blown with steam to remove by-products and the small quantity of unreacted chloroaldehyde and to destroy any possible remaining traces of the chlorate. The oily layer may then be again separated from the water layer. This gives a good technical grade of product containing not less than 60% of the trichloroacid, the remainder being water and about 1.5% of inorganic chloride. This material may be readily concentrated by evaporation of the water to form a solid product of high technical purity. A chemically pure grade is obtained upon the distillation of the acid under reduced pressure.

By the use of thermo-regulators, the process of the present invention can be conducted in a semiautomatic or continuous manner.

The following examples are illustrative of the process of the present invention:

Example 1 Commercial butyl chloral hydrate (100 gm.) and 13.6 gm. of sodium chlorate were dissolved in 100 cc. of water at 70 C. and to this was added cc. of 12N aqueous sulphuric acid. The mixture was heated, and the reaction proceeded spontaneously at 73 C., and with cooling, the temperature was held between 75 C. and 85 C. After 20 minutes, the main reaction was substantially complete, the mixture was then raised temporarily to 100 C., the product layer was then separated and dried in an open dish on a steam bath for 2 hours. 61 gm. of solid 2,2,3,trichlorobu'tyric acid was obtained. About 2 additional gm. of product remained dissolved in the water layer.

Example 2 The foregoing experiment was repeated but without external cooling. Reaction began at 72 C. and with active agitation, the temperature reached 102 C., where it held constant for about 5 minutes, after which it fell, and at 25C. the lower layer was separated and heated in an open grams of solid 2,2, trichlorobutyric acid on coo Example 3 Pure chloral hydrate (16.5 'gm.. 0.1 mol) was treated in a solution consisting of 16.5 co. 0!

water, 5 gm. of concentrated sulphuric acid and 0.016 gm. of ammonium metavanadate, at 50' (3., with 1.75 gm. of solid sodium chlorate (0.016 mol) and the temperature was maintained at 50' C.- 55" C. in a cooling bath. After 20 minutes, this first portion of sodium chlorate appeared to be exhausted and second portion (1.75 gm.) was added. The temperature was again maintained at 50 C.-55 C. After a second reaction period of 20 minutes, an extra 0.3 gm. of sodium chlorate were added, and the mixture was then heated at 60 C. for 10 minutes. Preceding and at this point, there was a small amount of chlorine generated, but no detectable chloroform or phosgene was observed. Finally, in order to destroy any excess chlorate, 3 cc. of concentrated hydrochloric acid were added, and the mixture distilled to its volume. Then an equal volume of concentrated hydrochloric acid was added, and the reaction product was extracted with carbon tetrachloride. on completely evaporating the carbon tetrachloride, 11 gm. (67% yield) of solid trichloroacetic acid were obtained.

Example 4 Crude 'propyl chloral hydrate (trichloropropenal-1) (17.8 gm., 0.1 mol) was dissolved in 18 cc. of water and 1 cc. of concentrated hydrochloric acid. The mixture was heated to 65 Qand 1.75 gm. (0.016 mol) of solid sodium chlorate were added, and the temperature was maintained at 65-67 C. for 15 minutes when the reaction was observed to be slowing down. A second portion (1.75 gm.) of sodium chlorate was then added, and the temperature was maintained at 70 C. ,for 25 minutes. Finally, after standing 1.5 hours, the reaction mixture was evaporated in an open dish on the steam bath for 50 minutes when 1.9 gm. of sodium chloride and about 12 gm. of solid 2,2,3 trlchloropropionic acid were obtained. The acid pressed out on a porous plate melted at Example 5 Example 6 Commercial butyl chloral hydrate (5 lbs.) and 2 lbs. of technical 2,2,3 trichlorobutyric acid were heated to 70 C. in about 5 liters of aqueous liquor remaining from a previous batch with active agitation and were then treated with 400 gm. of sodium chlorate in 3 equal portions. After add ing the first portion, the temperature was held at 70-75 C. by a stream of water directed against the reaction flask. After one-half hour, the

second portion was added, and the temperature was held at '7280 C. After another one-half hour, the last portion was added, the temperature this time being held at 7785 C., and finally'by means of external heating, the reaction mixture was heated to 99 C. On cooling to 70 (2., four and one-half pounds of technical 2,2,3 trichlorobutyric acid were obtained, exclusive of the two pounds added at the start.

7 Example 7 Thirty pounds of commercial butyl chloral hydrate and 200 cc. concentrated hydrochloric acid were heated to 70 C. in 24 pounds of water in a 50 liter reaction vessel fitted with a good agitator. Six one-pound portions of sodium chlorate were added at one-half hour intervals under the following temperature conditions: the first 2 lbs. at 70-75 C., the second 2 lbs. at 75-80 C., the fifth lb. at 80-85 C., and the last 1b. at -90 0., after which the temperature was raised to C. and maintained at this point by external heating for 1 hour. On cooling to 70 C., the product layer was separated and blown with steam which eliminated at small portion of unreacted butyl chloral hydrate and 2.82 pounds of crude 1,1,1,2, tetrachloropropane, a useful byproduct. A determination of anhydrous 2,2,3, trichlorobutyric acid indicated a conversion of butyl chloral to the acid equivalent to 79% of I the theoretical.

' Example 8 Commercial butyl chloral hydrate (30 lbs.) in 15 liters of water was heated and treated with 6 pounds of sodium chlorate dissolved in enough water to make a saturated solution. Reaction under these conditions, when only slight acidity exists, due to prolonged storage of the aldehyde, began at about 80 C., but thereafter was selfsustaining with the regulated addition of the chlorate solution. After a total reaction time of about 3 hours, in the neighborhood of 85 0.,

separation of the 2,2,3, trichlorobutyric acid in the usual way indicated about 80% conversion. Example 9 Commercial butyl chloral. hydrate (30 lbs.) in about 15 liters of water containing 500 cc. of concentrated nitric acid, was heated to, 70 C. and treated with 6 lbs. of sodium chlorate dissolved in enough water to make a saturated solution. External cooling was employedand the rate of addition of the chlorate solution was ad-- justed so that the main part of the reaction proceeded at 80 C.-85 C. Evolution of chlorine was very slight and after 3 hours reaction time, separation of 2,2,3, trichlorobutyric acid in the usual way indicated about 80% conversion. A second run using only 250 cc. of concentrated nitric acid gave the same results.

Example 10 Butyl chloral hydrate (20 gm., 0.1 mol) after steam bath for 2 /2 hours at 95 C.-100 C. The

product layer was withdrawn and dried. This gave 12 gm. of solid 2,2,3, trichlorobutyric acid when cooled.

Considerable modification is possible in the amount of water and acid (if any) present, as

well as in the conditions under which the oxidation of the trichloroaldehyde to the trichloroacid is conducted, without departing from the essential features of the present invention.

1 claim:

1. The step in the process of preparing a trichloroacid of the formula RCClz-COOH where R is selected from the group consisting of 'Cl--, CH2C1, and CH3-CHCl--, which comprises oxi dizing in an aqueous medium the trichloroaldehyde corresponding to said acid with a chlorate at a temperature at least sufficient to initiate said oxidation reaction.

2. The process of claim 1 wherein the water is present in an amount from about, one-third to about twice the weight of the trichloroaldehyde.

3. The step in the process of preparing a trichloroacid of the formula RCCIa'COOH where R is selected from the group consisting of Cl--,

acid, water in an amount at 1am equal to onethird ofthe weight of the trichloroaidehyde. and

reaction mixture.

6. The process of preparing a trichloroacid oi the formula RCCla-COOH where R is selected from the group consisting of 01-, CH:'Cl-, and CHs-CHCl, which comprises forming a mixture of the trichloroaldehyde corresponding to said acid,,water in an amount from about one-third to about twice the weight at the trichloroaldehyde, acid in an amount suilicient to give a pH from about 4 to less than 1, and a water-soluble chlorate; agitating said mixture; oxidizing said aldehyde by said chlorate at a temperature within the range from about 40 C.'to 100 C., and separating the trichloroacid thus formed from the reaction mixture.

7. The process of claim 6 wherein there is present an oxidation promotion catalyst.

The mixture was a 10. The process of claim 6 'wherein 2,2,3,tri-

chloropropionic acid is formed by the oxidation of 2,2,3,trichloroproponal-'l.

11. The process of claim 6 wherein 2,2,3,tri-

chlorobutyric acid is formed by the oxidation of 2,2,3,trichlorobutanal-1.

12. The process of preparing a trichloroacid of the formula RCClz-COOH .where R is selected from the group consisting of Cl, CHzCl--, and CHa-CHCl-, which comprises mixing the trichlo- 4 roaldehyde corresponding to said acid with water and an acid to acidifythe mixture; heating said mixture in the range from about 40 C. to 100 0.; adding a water-soluble chlorate thereto;

maintaining said mixture at a temperature within said range to oxidize said aldehyde by said chlorate; and separatingthe trichloroacid thus formed from the reaction mixture.

13. The process of preparing a trichloroacid of the formula RCClz-COOH where R is selected from the group consisting of 01-, CHzCl-,' and CHa-CHC1--, which comprises mixing the trichloroaldehyde hydrate corresponding to said acid j with water from about one-third to twice the CH2C1, and CH3'CHCI, which comprises oxithe formula RCClz-COOH where R is selected from the group consisting of Cl--, CH2Cl--, and CHa-CHC1, which comprises forming a mixture of the trichloroaldehyde correspondingto said weight of the trichloroaldehyde hydrate, and acid in an amount sufilcient to give a pH from about 4 to less thanl; heating said mixture in the range from about 40 C. to C.; agitating said mixture; adding to said mixture over a period of time a water-soluble chlorate in substantially the stoichiometric proportion required to oxidize said aldehyde; maintaining the mixture at a temperature within said range to oxidize said aldehyde by said chlorate; and separating the trichloroacid thus formed from the reaction mixture.

14. The process of claim 13 wherein there is present an oxidation promotion catalyst.

15 The process of claim 13 wherein there is present ammonium metavanadate, as an oxidation promotion catalyst.

16. The process of claim 13 wherein the acid mixed with the trichloroaldehyde and water is a trichloroacid corresponding to that to be prepared.

was. PLUMP.