Patented Aug. 29, 1939 2,170,825 UNITED STATES 2,170,825PATENT OFFICE PROPONCACD SYNTHESS Donald J. Loder, Wilmington, Del, assignor to E. I. du Pont de Nenours is mington, Del, a corporation ofCompany, Delaware Wi No Drawing. Application January 27, 1938, Serial No. 18,226 8. Claims. (C. 260-532) This invention relates to an improved, process for the preparation of propionic acid and its ethyl chloride, and the like, may likewise be used, esters and particularly to the preparation of pro although due to its availability, low cost, and pionic acid by the interaction of ethanol and car adaptability I prefer to employ ethanol as the bon monoxide in the presence of boron fluoride major raw material. . as the catalyst. An aqueous solution of borontrifluoride is pre An object of the invention is to provide a ferred as the catalyst, which may be made in var 5 process for the preparation of propionic acid in , ious ways such, for example, as by the solution exceedingly high yields from ethanol and carbon of boron trifluoride in water; by the interaction O monoxide. A further object of the invention is of anhydrous hydrogen fluoride with boric oxide to provide a process for preparing propionic acid or boric anhydride; or, if desired, by the intro O and its ethyl ester from ethanol and carbon mon duction of boron trifluoride as a gas directly into oxide in the presence of such proportions of water the mixture of water, ethanol, ether and/or ester and boron trifluoride that substantially 100% prior to or during the reaction. Other boron flu 15 conversion of the ethanol to acid and/or ester oride compounds may be employed which contain is obtained. Yet another object of the invention , boron, fluorine and water such, for example, as 15 is to provide operating conditions for the afore aqueous solutions of dihydroxyfluoboric acid, mentioned process under which substantially no borofluohydric acid, and, in general, the oxygen undesirable by-products are formed during the ated acids obtained from mixtures of hydrogen reaction. Other objects of the invention will fluoride and the boric acids. hereinafter appear. Aqueous solutions of boron trifluoride, as well I have found that propionic acid and its ethyl as the other enumerated catalysts are preferably 20 ester can be prepared in exceptionally high yields used alone, although agents may be added to pro from carbon monoxide and ethanol, providing mote the activity of these catalysts, if desired, 25 boron fluoride is employed as the catalyst in the . . such as freehydrofluoric acid, powdered nickel, presence of suitable amounts of water and under nickel oxides, or other powdered metals or metal 25 the proper temperature conditions. Generally, oxides. Generally, however, I have found it pref it may be stated that my improved process in erable to use aqueous boron trifluoride alone, for volves carrying out the propionic acid synthesis it is not only easily prepared but is such a power 30 by correlation of boron trifluoride concentration, ful catalyst that further modification by the ad water concentration and temperature in order dition of other substances is not ordinarily nec that the reaction is effected rapidly and without essary. , 30 the formation of condensation products hereto A careful study of the ethanol-carbon mon- ; fore invariably encountered when ethanol or oxide to propionic acid reaction has revealed that 35 other higher alcohols have been condensed with it is desirable to have present sufficient water to carbon monoxide, particularly in the presence of inhibit the formation of by-products and tars, boron halogen-containing catalysts. and I have determined that it is advantageous 35 The ethanol-carbon monoxide reaction to to. have at least A mol of water present per mol of ethanol, and preferably 1 to 3 mols of water 40 whichbe expressed this invention as follows: is particularly directed may. ' per mol of the alcohol. nounced effect of raisingpl. conversion Water has to propionicthe pro acid from 50-70% when no water is present, to In accordance with the particular operating con 90-100% when there are one or more mols of ditions, it will be found that in some instances water. The boron trifluoride should be present 45 propionic acid may not be formed as the acid, but for optimum operating conditions in the ratio may be produced as the ester by condensation of from 1 to 4 mols per mol of the ethanol and preferably between 2 and 3 mols of boron fluo process,of the acid as indicated with the below: ethyl alcohol. used in the ride per mol of ethanol, and, for some purposes, solutions saturated with borontrifluoride may be 50 used. These concentrations of water and boron The ethanol used may be replaced, if desired, trifluoride appear to be unique for the synthesis 50 wholly or partly by diethyl ether or esters of pro of propionic acid and give exceptionally high pionic acid, principally ethyl propionate. Fur yields if temperature conditions are properly thermore, compounds which decompose upon hy controlled. These conditions can advantageously be used also in the reaction of carbon monoxide 5R drolysis to give ethanol such, for example, as with alcohols such as propanol, normal and iso 2,170,825. 2 sure increased during heating to between 500 and butanol, and, generally speaking, all alcohols 900 atmospheres. The temperature was main higher than methanol, for the preparation of tained within the indicated range for 37 minutes higher organic acids. and whenever the gas absorption caused the pres For improved operation I have found that when sure to fall to 800 atmospheres the pressure was the above concentration of water and boron tri raised again to 900 atmospheres by introducing fluoride are employed the synthesis should pref Carbon monoxide from high pressure storage. At erably be carried out at temperatures below 180° the end of the 37-minute reaction period, gas C. down to approximately 125° C. with preferred absorption substantially ceased. The autoclave temperatures ranging between 135 and 165° C. was cooled and 775 parts of product discharged. 0. The pressure should likewise be maintained, for Upon analysis the product was found to contain 16 optimum results, above 25 atmospheres and pref a yield based on reactants used of 6.6% of ethyl erably between 500 and 1000 atmospheres. propionate and 85% of propionic acid. The carbon monoxide used may be obtained Eacample 3 from various commercial sources such, for ex 5 ample, as from water gas, producer gas, coke The process of Example 2 was repeated using a 15 oven gas and the like, but to obtain products with charge containing 624 parts of a molal mixture the highest degree of purity it is preferable to of 1 part diethyl ether, 4.6 parts of water and 4 remove from such commercial gases objectionable parts of boron trifluoride. The temperature was raised in 45 minutes to from 150 to 160° C. and 20 constituents.Furthermore, inert gases may be present in the maintained in this range for 60 minutes with a 20 carbon monoxide used and they are, in some in pressure between 800 and 900 atmospheres. 732 stances, desirable. Nitrogen, for example, has, parts of product were discharged which, upon it appears, little deleterious effect on the reaction analysis, gave a yield of 92% propionic acid. or yield and, in fact, it may be used advanta 25 geously in order to aid in the agitation of the Eacample 4 25 reactants, particularly if the carbon monoxide is The process of Example 2 was repeated with to be bubbled through them. Other strictly inert a charge containing 764 parts of a molal mixture gases will usually act similarly to nitrogen. containing 1 part of ethanol, 1.8 parts of water While the above description has been directed and 2.7 parts of boron trifluoride. These re 30 particularly to the reaction of carbon monoxide actants were raised within 32 minutes to a tem 30 with ethanol, diethyl ether, and/or ethyl pro perature ranging between 144 and 158° C. and pionate, I have found that generally the higher maintained at that temperature for approximate alcohols will react similarly to give higher acids. ly 60 minutes. The pressure, during this reac Normal and isopropyl alcohol will give isobutyric tion, was held between 250 and 300 atmospheres. 35 acid; normal butyl alcohol will give methyl ethyl 816 parts of product were discharged which, upon acetic acid; isobutyl alcohol will give trimethyl analysis, gave a yield of 70% propionic acid. acetic acid and the higher alcohols, correspond-, Eaconple 5 'ing higher acids. When carrying Out my proceSS with the higher alcohols, I have found it to be The process of Example 2 was repeated with a generally true that best results are realized when charge of 684 parts of a mixture containing, On 40 a molal basis, 1 part of ethanol, 1.8 parts of Water, the reaction is conducted at temperatures below and 2.4 parts of boron trifluoride. This mixture 180° C. down to 125° C. and preferably between was raised to a temperature between 135 and 150 135The and more 165° detailedC. practice of the invention is C. in 26 minutes, maintained at that temperature illustrated by the following examples in which for 39 minutes, during which a pressure was held 45. parts are given by weight unless otherwise stated. between 800 and 900 atmospheres. 842 parts of There are, of course, many forms of the invention product was discharged which, upon analysis, other than these specific embodiments, gave a yield of approximately 98% propionic acid. 1. Eacample Eacample 6 50 The process of Example 2 was repeated with A silver-lined autoclave was charged with 806 a charge of 742 parts of a mixture, on a molal parts of a mixture containing, on a molal basis, basis, 1 part of ethanol, 0.07 part of diethyl 1 part of ethanol, 1.8 parts of water, and 2.8 parts ether, 1.8 parts of water and 2.86 parts of boron of boron trifluoride. The autoclave was heated trifluoride. This mixture was raised to a tem-, in a shaker machine to a temperature ranging perature between 141 and 151 C. in 31 minutes, 55 between 138 and 154 C. It was heated to reac maintained at temperature for 24 minutes and tion temperature within 28 minutes andThrough main during this period the pressure was held between tained at temperature for 20 minutes. 800 and 900 atmosphereS. 807 parts of product out the reaction a pressure of 800 to 900 atmos was discharged which, upon analysis, gave a 100% 60 pheres Was maintained by the periodic introduc yield of propionic acid. tion of carbon monoxide as it was absorbed. 871 The crude product from the synthesis contains parts of product was discharged which, upon water, borontrifluoride, propionic acid and, under analysis, gave a yield based upon reactants used certain operating conditions, ethyl propionate of 90% propionic acid and 10% ethyl propionate. and hydrocarbons. The recovery of the acid and 65 65 Ecample 2. ester from this crude product may be effected by first removing that portion of the boron fluor A silver-lined autoclave was evacuated and ide which is readily vaporized by merely heating Subsequently charged with 692 parts of a mix the product. As it is desirable to recover the ture containing, on a molal basis, i part of etha boron fluoride driven off during this stage of the 70 70 nol, 0.5 part of water and 1.5 parts of boron tri recovery, a packed tower, condenser and absorber fluoride. Compressed carbon monoxide was then for the boron fiuoride are provided, the latter admitted to raise the pressure to approximately containing preferably water. The residue from 300 atmospheres. With the tube agitated, the this step is steam distilled to recover the propi charge was then heated within 24 minutes to a onic acid and ester. The residual Water and 75 5. temperature between 140 and 152° C. The pres ... : ...... s, 1708as -3 processesboron fluoride described may bein treatedcepending in accordapplication with ser,the actant mixture substantially saturated with Nos. 54,329 and 54,351 for the recovery of the boron trifluoride. boron fluoride in substantially anhydrous form. 5.The proce of claim 1 conducted with a From a consideration of the above specification mola tatio of water to ethanol of greater than 1:1 whereiri.. the water-ethanol solution is sub it will be appreciated that many changes rainy be stantially saturated with boron trifluoride. ficingmade anyin the of thedetails advantages therein sivathereof without or departing seri 6. The process of claim 1 in which the ratio from the scope of the invention. of boron trifluoride to ethanol is more than 2 claim: - . ...' f mols of boron trifluoride per mol of ethanol. 7. The process which comprises producing ali 1. A process of producing proponic acid which phatic organic saturated monocarboxylic acids by O comprises reacting ethanol with carbon intinox the interaction of alcohols higher than methanol ide in the presence of boron fluoride and water, with carbon monoxide, using boron fluoride in as the catalyst, it a temperature between 125 C. the presence of water as the catalyst, at a tem and 180°C, and at a pressure in eices of 25 perature between 125° C. and 180° C., and pres atmospheres...... sures in excess of 25 atmospheres. S 2. Process of claim 1 conducted with a molat 8. A process for the preparation of propionic ratio of boron fluoride to ethanol of greater than acid whichi comprises absorbing carbon monoxide i:1. in a reaction mixture containing substantially 1 3. Process of claim 1 conducted with is total mol of ethanol, lbnols of water, and 2.8 mols ratio of boron Ruoride to ethahol of from 2 to 3 of boron trifluoride at a temperature between parts of boron fluoride to 1 part of ethanol. 135° C. and 165 C. and under a pressure between 4. The process of claim 1 conducted with a re 800 and 900 atmospheres. OONA to J. O.D.R.