US2811538A - Preparation of organic acids by the - Google Patents

Description

United States PatentO PREPARATION OF ORGANIC ACIDS BY THE CAUSTIC FUSION OF v.CYANOHYDRIN Edward F. Riener, Haddonfield, N. J., assig nor toRohm &'Haas Company, Philadelphia," Pa.,a corporation ofgDelaware N0 Drawing. Applicationlune 29, 19 55, 1

Serial N0. 518,982

7 Claims. c1.z60, 406

This invention relates to the preparation of -organic acids. It relates to the preparation'of'dicarboxylic acids and'monocarboxylic acids. l

The object of this invention is to provide an economical and commerciallypracticable method of manufacturing monobasic and dibasic organic acids} This and other "objects are accomplished by the process of this invention which comprises reacting molten caustic alkali at a temperaturefrom abOut'ZOO C. to about 400 C. with a saturated aliphatic acid which contains l6 to 22 carbon atoms, or withan ester of such an acid, said acid also containing vicinal cyano-hydroxy substituents.

Thus the invention comprises subjectingtocaustic fusion an ,acid, or an ester thereof, which acid contains 16jto 22 carbon atoms and also contains in the acid chain a group of thestructure, v

(IJN (I)H The cyano-hydroxy. derivatives of a given acid or ester split inlessentiallythe same way, when fused with caustic, toyield mixtures of essentially the same monocarboxylic and dicarboxylic acids. V

The cyano-hydroxy acids and esters which are emif ployed in this process are the subject of another application for Letters Patent, Serial No. 518,983, filed June 29, 1955. They are prepared by reacting an epoxidized aliphatic acid containing 16 to 22 carbon atoms, or an ester thereof, with Theiacids which are-subjected to caustic fusion by the process of this invention are, therefore, the cyano-hydroxy derivatives .,of palmitic, margaric, stearic, nondecoic, ara- "chi dic,. eicosic' and behenic acids, of which substituted stearic acid is the preferred species.

. The instant invention also embraces the caustic fusion of the esters of the above-described cyano-hydroxy acids as well asof the acids, per se. The operable esters are those of the acids and monohydric or polyhydric alcohols which are typified by the following: methyl, ethyl, iso- 'propy1, n-butyl, sec-butyl, tert-butyl, tert-amyl, n-octyl, Z-ethylhexyl, lauryl, octadecyl, cyclohexyl and benzyl alcohols; ethylene glycol, 1,2-propylene glycol, 2-ethylhexandiol-l,3, butandiol-1,3,-butandiol-l,4, dodecandiol- 1,l2; diethylene glycol; glycerol; pentaerythritol; and the isomers and homologues of the above. Since the alcohol portions of the esters do. not contribute anything to the formation of acids and are actually destroyed during the caustic fusion, itis preferredto employ the cheapest and most' re'adily available 'esterso fthe substituted acids.

These are the lower alkyl esters, namely "the methyl, ethyl,

propyl, and butyl esters of the acids and also the natural- 1y occurring esters. The cyano-hydroxy glyceridicesters, namely the substitutednaturaloilsand fats, areincluded in this last category and they are typified by. the following cyano-hydroxylated materials: tallow and soybean, corn, cottonseed, safilower, sunflower, sesame, poppy'seed,,wal-I nut, peanut, linseed, perilla and sardine oils.

In the preferred .embodi ent of the process, of this in: vention, the cyano-hydroxy derivative is added to the liquid caustic reactant at a temperature from about 200 C. to about 400 C. It is much preferred to employ temperatures from about; 310 C. to about 340 C. Alternatively, the caustic and the ester or acid can be mixed and heated together; or the caustic can be added to the heated acid or ester. The addition of water aids in the melting or fusionof the caustic, especially at the lower operating temperatures. As a matter of fact, ordinary commercial grades of sodium and potassium hydroxides contain some'water which aids in the fusion of these materials. The important consideration is that the reaction mixture of caustic and the acid or ester be fluid at the temperature of reaction. Obviously the reaction can be carried out at superatmospheric temperatures as well as at atmospheric pressure. I p

Although the oxides or hydroxides of lithium and of the alkaline earthmetals can be used, it is much preferred to employ sodium hydroxide or potassium hydroxide or mixtures of the two for the sake of economy and efiiciency. It is also recommended that an inert liquid such as mineral oil or white oil be present during the caustic fusion reaction. Such a material, although not essential, serves as a flux and greatly facilitates the stirring and mixing of the reactants. I V After the caustic fusion the scission products are sep* arated. By the preferred procedure, thecooled reaction mixture, which is usually a soap-like mass is treatedwith water in order to dissolve the salts or soaps of the organic acids which have formed. If an organic solvent such as mineral oil has been employed, it is best removed by extraction with a low-boiling organic liquid such as diethyl ether or petroleum ether which is later separated from the high-boiling solvent by distillation. The aqueous solution is then acidified with a strong mineral acid, such as hydrochloric acid or sulfuric acid; and the free organic acids which are thus formed are next removed by extrac tion with an organic solvent, such as diethyl ether. The organic solvent is stripped off and a mixture of monobasic and polybasic acids is thereby obtained. When it is desired to separate the monobasic and dibasic acids, the mixture is dissolved in a dilute solution of a caustic alkali, preferably sodium hydroxide, in an amount sufficient to convert the organic acids to soluble salts. The resultant aqueous solution of salts is mixed with an organic solvent, preferably an inert hydrocarbon such as octane, and the mixture is again acidified with a strong mineral acid to a pH Which is no lower thanabout 5.5. As a result, salts of the monobasic organic acids are converted to the acids per se; and these acids are simultaneously extracted by the organic solvent. After removal of the organic solution, the organic monobasicacids areobtained by distillation of the solvent. The aqueous solution is then further acidified to a pH of about 1.5 to 2 and is also preferably cooled to about 5 C. The dibasic acids which then precipitate are filtered off and are washed with water and later dried. This procedure for separating monobasic and dibasic acidsisreferred to herein as ?the pH method." As an alternative method, a mixture of all of the salts resulting from a caustic fusion can, itself, be treateddirectly by thepH method of acidulation as a simpler and faster methodof separating and isolating the resultant mixture of monobasic acids on the onehand and the mixture of dibasicacids on theother. Obviously this asngc'ssalternative" procedure eliminates a precipitation step and the redissolving step.

The instant process for making monobasic and dibasic acids from cyano-hydroxy acids"and esters is very-'etli ciefitbecause' the number-of scissionproducts isunusually low. Furthermore, .the'processfhas'the advantage of producing 'a'higher'rati'on of dibasic acids to m'onob'asic acids than do 'those processes which utilize other derivatives of acids and l esters.

The following examples; in which all parts are by weight, serve 'to' illustrate theprocess ofthis invention:

Example 1 A-mixture of 56'parts'of potassium hydroxide, 40 parts of sodium hydroxide and 120 parts of mineral oil was placed in a reactorequipped with an attachable cover, thermometer, stirrer, and an inlet tube for liquids. The stirred mixturewas-heated-to320 and was held at 320 to 325 C. while to it was added slowly and; uniformly over a period of approximately one hour 68 parts ofa mixture 9,10 and 10,9-cyanohydroxystearic acid. (The latter had been made by the reaction of sodium cyanide and epoxystearic acid in methanol.) After addition was complete, the stirred reaction mixture was held at 320 to 325 C. for an additional hour. The mass was allowed to cool and was then added to 800 parts of water. The mineral oil was separated and the aqueous phase was extracted with diethyl ether to remove all of the mineral oil. The aqueous phase was then acidified to a pH of 1.5 and the precipitated mixture of acids was extracted by means of diethyl ether. The separated ether solution was evaporated and a yield of 67 parts of a mixture of acids having a neutral equivalent of 126 was obtained. (A neutral equivalent, obtained by titrating a known quantity of an acid or mixture of acids with standard alkali is a measure of the average molecular weight of the acid for each mole of carboxyl group in the acid or mixture of acids.)

The monobasic and diabasic acids were then separated as follows: The mixture of acids was dissolved in an aqueous solution of sodium hydroxide. To the resultant solution wasadded 100 parts of octane. This mixture was agitated and heated to 80 C. at which point a 50% aqueous solution of sulfuric acid was slowly added until the-aqueous phase had a pH of 5.9. The organic and aqueous phases were separated. The octane was removed by distillation and a mixture of monobasic acids was obtained as a residue. The aqueous phase was then further acidified to a pH of 1.5 and chilled to 5 C. The precipitated mixture of dibasic acids was filtered off, washed and dried. The product amounted to 2416 parts, had a neutral equivalent of 102 andcontained azelaic and sebacic acids in essentially equimolar amounts.

This procedure was repeated'many times at varying temperatures as low as 200 C. and using various grades of cyanohydroxystearic acidderived from-varying grades of oleic acid. In all instances the ratio of dibasic acids-to monobasic acids was of the order of at least 1 to 2; and in most instances it approached 1 to 1.

The procedure which has been exemplified above is used inthe caustic fusion of the cyanohydroxy. derivatives of all the aliphatic acids containing 16 to 22 carbon atoms, and also the esters thereof. Obviously, the scission products which are obtained vary depending on the length of the chain of the particular aliphatic acid and also on the positionof the cyano and hydroxyl groups in the acid chains. Furthermore, a mixture of position isomers (e. g., the 9,10- and 10,9-isomers) is invariably obtained in the preparation of the cyanohydroxyacids and esters and this also gives rise to a mixture of scission products. Consequently, in every. case during fusion, a mixture ofthe salts of both monobasicand dibasic acids is inVariableob tained. The monobasic .anddibasicacids are. readily separated by. the so-called pH method described. above. The individual acids can be isolated by chromatography;

althoughinmany industrial applications-for example in the formation resinsthe mixtures of dibasic acids and mixtures of monobasic acids can be used just about as satisfactorily as the individual acids in the mixtures; and consequently the isolation ofthe individual acids is not always necessary.

As' stated above, naturally occurring fats and oils represent-a preferred source of the cyanohydroxy compounds which are converted by the instant process into valuable monobasic and dibasic saturated aliphatic acids. The following examples are typical of the results obtained by the fusion of cyanohydrins obtained from natural fats and oils.

Example 2 A stirred mixture of 73 parts of sodium hydroxide and parts of mineral oil was heated to 275 C. and to it was added, over a period of an hour, 93 parts of methyl cyanohydroxy--"rapeseedate (i. e., the methyl ester of the cyanohydroxy acids of rapeseed oil containing 3.4% nitrogen) The mixture was heated at 275 C. for an additional half-hour after which it was treated in themanner described in Example 1. The yield was 87 parts of a mixtureof monobasic and dibasic acids-having a neutral equivalent of 142. The acids were isolated by the pH method described above and a yield of- 19.3 parts of dibasic acids having a neutral equivalent of 108 was obtained.

The same procedure was employed in the preparation of monobasic and dibasic acids from the caustic fusion of the methyl ester of the cyanohydroxy fatty acids of tallow (containing 1.8% nitrogen). Thus, 69.5 parts of this ester was added dropwise over a period of an hour to a stirred mixture of 56 parts of potassium hydroxide, 40 parts of sodium hydroxide and 120 parts of mineral oil which was held at 255 C. Heating was continued for an additional half-hour. A total of 73 parts of a mixture of acids having a neutral equivalent of 198 wasobtained of which 13.4 parts were dibasic acids having a neutral equivalent of 101.

Example 4" The same procedure was followed-in the caustic fusion of a glyceridie ester; namely the cyanohydroxy derivative of tallow. Thus, .75 parts of that derivative yielded 755 parts of-a mixture-of acids having a neutral equivalent of 200, of which 13.6parts were dibasic acids having a-neutral equivalent of 101 and including azelaic and sebacic acids.

Essentially the same products were obtained by the fusion of the cyanohydroxy derivative of brown grease.

Similarly, the fusion of 77.5 parts of the cyanohydroxy acids of tallow gave rise-to 77 parts of a mixture of acids having a neutral equivalent of 178, of which 16.8 parts were dibasic acids having a neutral equivalent of 99.5.

I claim:

1. The process for preparing saturated aliphatic mono carboxylic and dicarboxylic acids which comprises reacting molten caustic alkali, at a temperature from about 200 C. to about 400 C., with a compound from the class consisting. of (a) saturated aliphatic acids containing 16 to 22 carbon atoms and (b) esters of said acids and saturated aliphatic alcohols containing 1 to 4 hydroxyl groups, said compound also containing in its acid chain a group having the formula OH CN (311 rcthereafter dissolving the resultant mixture of salts in water; and acidifying the resultant aqueous solution to precipitate said monocarboxylic and dicarboxylic acids, and isolating said acids.

2. The process for preparing saturatedaliphatic monocarboxylic and dicar'b'oxylic acids which comprises re- 'a'cting'molten caustic alkali, at a temperature from'aboitt 310 C. to about 340 C., with a saturated aliphatic acid containing 16 to 22 carbon atoms and also containing a cyano group and an hydroxyl group on vicinal carbon atoms; thereafter dissolving the resultant mixture of salts in water; and acidifying the resultant aqueous solution to precipitate said saturated aliphatic monocarboxylic and dicarboxylic acids and isolating said acids.

3. The process of claim 2 in which said acid is cyanohydroxystearic acid.

1. The process for preparing saturated aliphatic monocarboxylic and dicarboxylic acids which comprises rcacting molten caustic alkali, at a temperature from about 310 C. to about 340 C. with a lower alkyl ester of a saturated aliphatic acid which contains 16 to 22 carbon atoms and which also contains a cyano group and an hydroxyl group on vicinal carbon atoms; thereafter dissolving the resultant mixture of salts in water; and acidifying the resultant aqueous solution to precipitate said saturated aliphatic monocarboxylic and dicarboxylic acids and isolating said acids.

5. The process of claim 4 in which said ester is a lower alkyl ester of cyano-hydroxystearic acid.

6. The process for preparing saturated aliphatic monobasic and dibasic acids which comprises reacting molten caustic alkali, at a temperature from about 200 to about 400 C., with a glyceridic ester of a saturated aliphatic acid which contains 16 to 22 carbon atoms and which also contains a cyano and an hydroxyl group on vicinal carbon atoms; thereafter dissolving the resultant mixture of salts in water; and acidifying the resultant aqueous solution to precipitate said saturated aliphatic monocarboxylic and dicarboxylic acids and isolating said acids.

7. The process of claim 6 in which said glyceridic ester is a glyceridic ester of cyano-hydroxystearic acid.

Lane Ian. 1, 1952 Logan Ian. 13, 1953

Claims (1)

1. THE PROCESS FOR PREPARING SATURATED ALIPHATIC MONOCARBOXYLIC AND DICARBOXYLIC ACIDS WHICH COMPRISES REACTING MOLTEN CAUSTIC ALKALI, AT A TEMPERATURE FROM ABOUT 200*C. TO ABOUT 400*C., WITH A COMPOUND FROM THE CLASS CONSISTING OF (A) SATURATED ALIPHATIC ACIDS CONTAINING 16 TO 22 CARBON ATOMS AND (B) ESTERS OF SAID ACIDS AND SATURATED ALIPHATIC ALCOHOLS CONTAINING 1 TO 4 HYDROXYL GROUPS, SAID COMPOUND ALSO CONTAINING IN ITS ACID CHAIN A GROUP HAVING THE FORMULA