US2876258A - Preparation of olefinically-unsaturated organic acids - Google Patents

Description

IPLR'EIPARATION F OLEFINICALLY-UNSATU- RATED ORGANIC ACIDS W. Va., assignors to Union Carbide Corporation, a corporation of New York No Drawing. Application March 21, 1957 Serial No. 647,481

12 Claims. (Cl. 260 526) This invention is directed to a process for the production of olefinically-unsaturated organic acids. More particularly, this invention is directed to the pyrolysis of epsilon-caprolactones to produce the olefinically-unsaturated acids and has for an object the provision of a process for manufacturing olefinically-unsaturated acids of a predetermined type. More specifically, it is an object of this invention to provide a process for the production of delta-olefinically-unsaturated organic acids from the corresponding epsilon-caprolactones, and in the case of epsilon-alkyl-epsilon-caprolactones, epsilon-olefinicallyunsaturated organic acids. A particular object of the invention is to provide a process for the; production of delta-hexenoic acid to the substantial exclusion of gammahexenoic acid which comprises pyrolyzing epsiloncaprolactone.

Heretofore, according to customary practices, the

methods of producing olefinically-unsaturated acids from lactones involve the hydrolysis of the lactone to the corresponding hydroxy acids followed by dehydration to provide the corresponding unsaturated acids usually as a mixture of isomers. Random distribution of isomers occurs and it is impossible, from a practical standpoint, to isolate the respective isomers.

. By virture of the process of this invention, random distribution of isomers is substantially avoided and olefinically-unsaturated acids of a desired type can now be produced with greater selectivity and ease.

Quite unexpectedly it has been discovered that epsiloncaprolactones can be cracked under pyrolysis conditions whereas the corresponding deltaand gamma-lactones cannot. This is indeed surprising in view of the fact vthat S-mernbered rings have substantially the same degree of strain as the 7-membered rings, yet when the gammalactones are subjected to pyrolysis conditions they do not crack. Normally, it would be expected that the epsilonc aprolactones would be similar in reactivity to the gammaand delta-lactones. p

f It has been discovered that epsilon-caprolactones can bepyrolyzedto specific unsaturated acids to the substant-ial exclusion of undesirable mixtures of isomer which are normally to be expected under conditions involving hydrolysis and dehydration of the epsiloncaprolactone as discussed, supra. As used herein the term substantial exclusion? is intended to mean the production of a reaction mixture containing the desired isomer in predominating amounts and the undesired isomer in amounts of the order of less than ten percent by weight of the total contained unsaturated acids.

: The process of this invention is directed to the preparation of 'olefinically-unsaturated acids from epsiloncaprolactones corresponding to the general formula:

United States Patent Patented Mar. 3, 1959 ice wherein, R, R R and Y represent hydrogen atoms and lower alkyl groups containing from 1 through 8 carbon Epsilon-caprolactone Gamma-isopropyl-epsilon-caprolactone Alpha-methyl-epsilon-caprolactone Beta-methyl-epsilon-caprolactone Gamma-methyl-epsilon-caprolactone Delta-methyl-epsilon-caprolactone Epsilon-methyl-epsilon-caprolactone Alpha-ethyl-cpsilon-caprolactone Beta-ethyl-epsilon-caprolactone Gamrna-ethyl-epsilon-caprolactone Delta-ethyl-epsilon-caprolactone Epsilon-ethyl-epsilon-caprolactone Alpha,beta-dirnethyl-epsilon-caprolactone Alpha,gamma-dimethyl-epsilon-caprolactone Alpha,delta-dimethyl-epsilon caprolactone Alpha,epsilon-dimethyl-epsilon-caprolactone Beta,gamma-dimethyl-epsilon-caprolactone Betta,delta-dirnethyl-epsilon-caprolactone Beta,epsilon-dimethyl-epsilon-caprolactone Gamma,delta.dimethyl-epsilon-caprolactone Gamma epsilon-dimethyl-epsilon-caprolactone Delta-epsilon-dimethyl-epsilon-carprolactone Beta,beta,delta-trimethyl-epsilon-caprolactone Alpha,beta,gamma-trimethyl-epsilon-caprolactone Alpha,beta,delta-trimethyl-epsilon-caprolactone Alpha,beta,epsilon-trimethyl-epsilon-caprolactone Beta,gamma,delta-trimethyl-epsilon-caprolactone Beta,gamma,epsilon-trirnethyl-epsilon-caprolactone Gamma,delta,epsilon-trimethyl-epsilon-caprolactone Alpha,ethyl-beta-methyl-epsilon-caprolactone A!pha-cthyl-gamma-methyl-epsilon-caprolactone Alpha-ethyl-delta-methyl-epsilon-caprolactone Alpha-ethyl-epsilon-methyl-epsilon-caprolactone Beta-ethyl-alpha-methyl-epsilon-caprolactone Beta-ethyl-gamma-methyl-epsilon-caprolactone Beta-ethyl-delta-methyl-epsilon-caprolactone Beta-ethyl-epsilon-metbyl-epsilon-caprolactone Gamma-ethyl-alpha-methyl-epsilon-caprolactone Gamma-ethyl-beta-methyl-epsilon-caprolactone Gamma-ethyl-delta-methyl-epsilon-caprolactone Gamma-ethyl-epsiion-methyl-epsilon-caprolactone Delta-ethyl-alpha-methyl-epsilon-caprolactone Delta-ethyl-beta-methyl-epsilon-caprolactone Delta-ethyl-gamma-methyl-epsilon-caprolact0ne Delta-ethyl-epsilon-methyl-epsilon-caprolactone Epsilon-ethyl-alpha-methyl-epsilon-caprolactone EpsiIon-ethyl-beta-methyl-epsilon-caprolactone Epsilon-ethyl-gamma-methyl-epsilon-caprolactone Epsilon-ethyl-delta-methyl-epsilon-caprolactone Alpha,alpha-dimethyl-epsilon-caprolactone Beta-beta-dirnethyl-epsilon-caprolactone Gamma,gamma-dimethyl-epsilon-caprolactone' Alpha,alpha,delta-trimethyl-epsilon-caprolactone Beta,beta,gamma-trimethyl-epsilon-caprolactone Gam ma, gamma,epsilon-trimethyl-epsilon-caprolactone Beta,beta-dimethyl-gamma-ethyl-epsilon-caprolactone As used herein the term pyrolyzing is intended to mean cracking or the epsilon-caprolactones or heating to a temperature sufiici'ently high to crack the epsilon-captolactones and includes conditions of temperature of from, at, or above the boiling point of the selected caprolactone starting material to. about 800 C. More particularly, the pyrolysis conditions of this invention involve temperatures of the order of from about 400 C. to about 600 -C.' at normal atmospheric pressures.

It has" been determined that the residence time for optimum conversion in the reaction zone of the heated selected epsilon-caprolactone is a function of the temperature of the reaction. It has been found that at the temperatures above specified, the reaction can be accomplished at a rate of from about 20 ml. per hour to about 1000 ml. per. hour in a heated zone one inch in diameter and, three feet long. atpractica'l efiiciencies of epsiloncaprolactonesto unsaturated acids. Expressed in terms of space velocity (liters/liter/hour) practical yields and conversions of epsilon-caprolactones are obtained at' space velocities of from 20. to 3000 approximately.

In carrying out the process of this invention an. epsiloncaprolactone, such as epsilon-caprolactone, is fed at a rate of from about 200 ml. per hour through a pyrolysis tube such as a stainless steel tube (1 inch by 36 inches.) preferably packed with Fiitros or glass beads to give an approximate free space of 70 percent at a temperature of 560 C. The efiiuent from the pyrolysis tube is analyzed for acid content.

The pyrolysis mixture maybe analyzed for acid by titration with base. Water and ice are usually added to the sample for analysis and the cold mixture is titrated quickly with 0.5 N sodium hydroxide or potassium hydroxide. Under these conditions the lactone ring is. not opened by the base.

Isolation of the unsaturated acids is simplified when a high conversion per pass is obtained since the starting lactone and the unsaturated acid usually boil fairly near each other. However, pyrolysis efficiencies are usually better, especially in the case of epsilon-caprolactone, if the conditions chosen are mild enough to avoid large amounts of gas formation during, the pyrolysis. The products may be isolated by the usual methods such as fractional distillation or extraction of the acid by means of sodium. bicarbonate or sodium carbonate at low temperatures from a solution of the reaction mixture in chloroform or some other water-insoluble solvent. The unused epsilon-caprolactone may then be recycled back to the pyrolysis tube.

Example I Epsilon-caprolactone (100 ml.) was fed at the rate of 200 ml./hr. through a stainless steel tube (1 inch by 36 inches) packed with Filtros which was heated to 440- 450 C. This corresponded to a space velocity of approximately 343. The effluent from the tube was condensed and titrated for acid. The efliuent was found to contain 5 percent S-hexenoic acid.

Example 11 Epsilon-caprolactone. was fed through the tube described in Example I at a rate of 280 nil/hr. at a temperature of 550 C; (space velocity equals 560). The tube effluent which condensed was titrated with base and was found to'contain 19 percent S-hexenoic acid.

Example III Titration'with base indicated. a purity of96 percent:.cal'- culated. as 6.-heptenoic. acid. An examination. of: theinirared spectrum of this product indicatedthat the double was" in the terminal'position. Very little ("estimated 5 percent) absorption characteristic of trans internal doublebonds' was observed.

Example I V The tube used in Examples I, II and III was coated on the inside with lsolute cement and after drying was packed with 5 mm. glass beads. Through this tube was passed 500 gramsofepsilon-caprolactone at a rate of 160 ml./hr. at an average temperature of 560 C. The space velocity was approximately 335. There wasobtained 475 grams. of tube condensate. Analysis indicated thatv the reaction mixture contained 17.4 percent. of 5.-hexenoic acid.

Example V A sample of epsilon-caprolactone (200 grams) was passed through the tube used in Example IV at a temperature of 625 C. and a rate of mL/hr. (space velocity equals 223).. The tube effluent (127 grams) containing 32.6. percent 5-hexenoic acid as indicated by analysis.

Example VI A sample of epsilon-caprolactone (300 grams) was fed through the tube usedin Examples IV and V at a rateof 50 mL/hr; at a temperature of 575 C. (space velocity equals. 104). The tube efiiuenti (235 grams) contained 2617- percent S-hexenoic acid as indicated by analysis; The tube products from Examples IV, V and VI were composited and distilled under reduced. pressure. There was isolated S-hexenoic acid, boiiing at- 84 C. at 4mm. and having a refractive index of 1.4331.

Example VII A sample of 'epsilon-methyl-epsilon-caprolactone (585 grams)" was fed through the tube used in Examples IV, V and VI at ml./ hr. at a temperature of 535 C; (space velocity equals 277) The tube efiiuent (553 grams)- contained- 82.2 percent 6-heptenoic acid as indicated by analysis. Distillation of the reaction mixture gave the same product as obtained in Example Hi.

What is claimed is:

1. A process for the production of olefinically-unsaturated organic. acids which comprisespassing an epsiloncapro'lactone corresponding to the general formula:

wherein, R, R R andY represent hydrogen atoms and lower alkyl. groups containing from 1 through 8 carbon atoms, except that when R and R are both hydrogen; Y is hydrogen, at; a space velocity in the range of from about 20 liters/liter/hour to about 3000 liters/liter/hour through a heated reaction zone maintained at a temperature inthe range of from about 400 C. to about 600 C.

3. A process for the production of delta-hexenoic acid to the substantial exclusion of gamma-hexenoic acid which comprises passing epsilon-caprolactone at a space velocity in the range of from about 20 liters/liter/hour to about 3000 liters/liter/hour through a heated reaction zone maintained at a temperature in the range of from about 400 C. to about 600 C.

4. A process for the production of epsilon-unsaturated acids to the substantial exclusion of delta-unsaturated acids which comprises passing an epsilon-lower-alkylepsilon-caprolactone at a space velocity in the range of from about 20 liters/liter/hour to about 3000 liters/liter/ hour through a heated reaction zone maintained at a temperature in the range of from about 400 C. to about 600 C.

5. A process for the production of epsilon-unsaturated acids to the substantial exclusion of delta-unsaturated acids which comprises passing epsilon-methyl-epsiloncaprolactone at a space velocity in the range of from about 20 liters/liter/hour to about 3000 liters/liter/hour through a heated reaction zone maintained at a temperature in the range of from about 400 C. to about 600 C.

6. A process for the production of olefinically-unsaturated acids which comprises pyrolyzing an epsilon-methylepsilon-caprolactone.

7. A process for the production of an olefinically unsaturated organic acid which comprises pyrolizing an alkyl-epsilon-caprolactone.

8. A process for the production of olefinically-unsaturated organic acids which comprises heating an epsiloncaprolactone corresponding to the general formula:

RaYRRR ll'n'n'tl 0 wherein, R, R R and Y represent hydrogen atoms and lower alkyl groups containing from 1 through 8 carbon atoms, except that when R and R are both hydrogen, Y is hydrogen, at a temperature in the range of at or above the boiling point of said lactone to about 800 C.

9. A process for the production of olefinically-unsaturated organic acids which comprises pyrolyzing an epsilon-caprolactone corresponding to the general formula:

iii Milli wherein, R, R R and Y represent hydrogen atoms and lower alkyl groups containing from 1 through 8 carbon atoms, except that when R and R are both hydrogen, Y is hydrogen, to a temperature sufficiently high to crack the epsilon-caprolactone and produce an olefinically-unsaturated organic acid.

12. A process for the production of an olefinicallyunsaturated organic acid which comprises heating an epsilon-caprolactone corresponding to the general formula:

wherein, R, R, R, and Y represent hydrogen atoms and lower alkyl groups containing from 1 through 8 carbon atoms, except that when R and R are both hydrogen, Y is hydrogen, to a temperature sufficiently high to crack the epsilon-caprolactone to produce the olefinically-unsaturated acid.

References Cited in the tile of this patent Van Natta et al.: I. A. C. 8., vol. 56 (1934), page 455-7.

Brown et 9.1.: J. A. C. 8., vol. 66 (1944), page 839.

Claims (1)

1. A PROCESS FOR THE PRODUCTION OF OLEFINICALLY-UNSATURATED ORGANIC ACIDS WHICH COMPRISES PASSING AN EPSILONCAPROLACTONE CORRESPONDING TO THE GENERAL FORMULA: