US2578647A - Method of preparing esters of 1, 2, 4-butanetriol - Google Patents

Description

, Patented Dec. 11, 1 951 METHOD OF PREPARING ESTERS OF 1,2,4-BUTANETRIOL Charles H. Stiteler, Hillsdale, and Pliny 0. Tawney, Passaic, N. J., assignors to United States Rubber Company, New York, N. Y., a corporation of New Jersey No Drawing. Application October 18, 1950, Serial No. 190,870

This inventionrelates to a new and highly advantageous process of making esters of 1,2,4- butanetriol. More particularly it relates to such a process wherein the starting materials are allyl alcohol or an allyl ester of an aliphatic saturated C1 to C4. monocarboxylic acid, concentrated sulfuric acid in catalytic amount, formaldehyde, and an aliphatic saturated C1 to C4 monocarboxylic acid. Still more particularly, it relates to such a process wherein an anhydride of an aliphatic saturated C2 to C4 monocarboxylic acid is also incorporated in the reaction mixture as a reagent.

The aforementioned esters of 1,2,4-butanetriol formed in accordance with the present invention are extremely valuable chemicals because they can be readily isolated from the resulting reaction mixture and converted to 1,2,4-butanetriol by hydrolyzing or alcoholizing by standard methods well known to'the art. The chemical, 1,2,4- butanetriol, is useful as a substitute for glycerol, especially in the makingof polyester resins by reaction with polybasic acids. Thus the present invention provides a new and extremely advantageous route to 1,2,4-butanetriol. The process of the invention has the further advantages that the raw materials are relatively inexpensive, the

process is easily carried out and the equipment requirements are simple.

Heretofore many methods of making 1,2,4- butanetriol have been proposed. However, the only method having any possible commercial application is that devised by Reppe in which acetylene is catalytically combined with formaldehyde under pressure to form butynediol which ishydrated and then hydrogenated under pressure to form 1,2,4-butanetriol. The first step is dangerous due to the explosive reactivity of acetylene under pressure and both the first and third steps require expensive equipment because of the high pressures involved. In contrast, the process of the present invention is simple, safe, and easily adaptable to large scale operation in standard equipment at atmospheric pressure. The raw materials required are all cheap and readily available.

We have discovered that 1,2,4-butanetriol esters can be made simply by heating a mixture of allyl alcohol, oran aliphatic saturated C1 to C4 monocarboxylic acid ester thereof, formaldehyde, concentrated sulfuric acid, and an aliphatic saturated Cl. to C4 monocarboxylic acid. The reaction product formed isbelieved to be chiefly 1,2,4-

butanetriol tri-ester. This tri-ester is preferably isolated from'the reaction mixture in any suitable manner and is alcoholized or hydrolyzed by any standard method to 1,2,4-butanetriol.

We have further discovered that the process outlined above can be greatly improved by carrying out the reaction in the presence of an anhydride of an aliphatic saturated C2 to C4 mono carboxylic acid, thus increasing the yield con 8 Claims. (01. 260-491) siderably. We believe that the better yields of the product obtained when such an anhydride is employed are largely attributable to the reaction of the anhydride with the water formed in the main reaction, thereby preventing the reaction from becoming slow and incomplete because of the accumulation of water formed in the esterification.

The aliphatic saturated monocarboxylic acid which is referred to herein is most preferably acetic acid. However, the allyl ester, the ester of 1,2,4-butanetriol formed as product and the anhydride can be derived from any of the C1 to C4 fatty acids, namely formic, acetic, propionic, n-butyric and isobutyric, except, of course, that formic anhydride does not exist.

In the preferred practice of our invention, wherein allyl acetate, acetic acid and acetic anhydride are employed, the reaction is represented as follows:

The reaction of our invention is carried out at a temperature ranging from 40 C. to 100 C., the preferred temperature range being from 55 C. to C. We find that below 40 C. the reaction is too slow to be practical, while above C. the reaction often becomes too vigorous to control or objectionable amounts of undesirable by-products are formed.

Since the reaction is highly exothermic, suitable precautions, usually involving use of adequate cooling means, should be taken to keep it under control.

As indicated above, we have found that the failure to attain completion of the reaction can be prevented by the use of a C2 to C4 acid anhydride. Preferably the amount of anhydride used is sufiicient to react with all of the water liberated during the reaction. The use of acid anhydride is by far the most practical, most convenient and most eificacious method of giving high yields. However, this end can be accomplished to some extent by other much less preferable means, e. g., by increasing the amount of concentrated sulfuric acid relative to the allyl alcohol or allyl ester. However, this increases the cost and also increases the magnitude of the waste disposal problem. Alternatively, the amount of saturated C1 to C4 monocarboxylic acid can be increased relative to the allyl alcohol or allyl ester, thus to some extent accomplishing the desired end by merely diluting the water formed. However, this greatly increases the cost and is not nearly as efiective as the use of the anhydride.

The organic reagents employed should be essentially anhydrous. Essentially anhydrous formaldehyde is available as, paraformaldehyde or trioxymethylene. The use of formaldehyde in the forms just mentioned is greatly to be preferred over the use of pure anhydrous formaldehyde itself which, being gaseous is extremely diflicult to handle.

The sulfuric acid employed. should .behighly concentrated, i. e., should not-contain more than 5 weight percent of water. Preferably it does not contain more than 2% ofewater,

The reaction should be carried out in such a manner that there is no substantial access of extraneous moisture to ;the reaction mixture.

The ester of 1,2,4-butanetriol .is preferably made by either of two procedures which differ from each other onlyin the order to which the reagents aremixed. In one method the sulfuric acid and the Organic acid anhydride are added, either simultaneously or successively, gradually to a previously formed mixture of the allylester (which can be charged into the reactor as such or can be made in situ; e. g., from allyl alcohol and an acid anhydride), the aliphatic monocarboxylic acid and formaldehyde. The second method comprises adding a solution of the allyl ester in the organic acid anhydride gradually to a previously formed mixture of the aliphatic-C1 to C4 monocarboxylic acid, formaldehyde and sulfuric acid.

The time required to effect the intermixture of the reagents is not critical except that it should be sufiicientlylong to ensure that the temperature is kept from exceeding 100 C., and preferably from exceeding 85 C., and that regions of local overheating are avoided. The mixing time obviously depends upon a combination of factors including stirring rate, shape of the containing vessel, size of batch, and rate of removal of heat. After the mixing is complete and exothermic evolution of heat has substantially ceased, the

mixture should be heated at fromAO .to 100? C.,

and preferably from to.-85 C., fora period of time sufficient to effect .substantiallycomplete reaction. Theheating time required after mixing is complete varies somewhatwithsizeof batch and average temperature -maintained within the ranges given-above but usuallyis several hours. Generallyspeaking,- times rangingfrom 6 to 20 .hours, including the timerequired for initial mixing, are sufficient to effect substantially complete reaction.

Organic acids and anhydrides of organic acids containing more than four carbon atoms per molecule, 1. e.,' higher than butyric, cannot be used inthe practice of our invention because they are not sufficiently miscible with sulfuric acid. The reagents used in our invention form a completely homogeneous single phase reaction mixture.

In any particular reaction contemplatedbythe present invention, the allyl ester and the anhydride need not be derivedfrom the sameacid as that used as reagent. For example, allyl formate can be treated withacetic acid and formaldehyde in the presence of sulfuric acid,and in the presence or absence of propionic anhydride. However, as a practical matter itis usually more .convenient to use anyone organic acid with the corresponding allyl ester, and the corresponding anhydride if anhydride is used, the particular acid chosen depending upon economic conditions. At present, acetic acidv and its derivatives are less expensive on a molar basis than the other organic acids contemplated by ,the invention.

Therefore, the invention is hereafter exemplified ,using acetic acid and its derivatives.

The reaction conditions and the results obtained will naturally vary with the choice of organic acid, allyl ester and organic anhydride, but such variations will not exceed in magnitude those caused by varying other factors, e. g., by changing the size of the batch.

-Optimum-results are obtained when the molar ratio of formaldehyde to allyl alcohol or ester thereof is substantially 2:1, 1. e. from 1.9:1 to 2.1:1. The yield of desired ester of 1,2,4-butanetriol is reduced if this molar ratio is increased ,to 3 1 or reduced to 1:1.

The molar ratieof theanhydride to the allyl alcohol or ester is preferably at least 1:1. The

yield is substantially reduced if this ratio is re- "anhydride is omitted altogether.

Ifhe amount of sulfuric acid present needs to be only that required to catalyze the reaction. Greater amounts can be used but offer no advantage. The amount of sulfuric acid is usually such as to give a molar ratio thereof to allyl alcohol or ester of about 0.511, typically, from 0.4:1 to 0.6:1.

The molar ratio of organic acid to allyl alcohol or ester can be varied Widely without decreasing the yield provided that the ratio of the sum of the molar equivalents of acyl groups supplied by the organic acid itself and the anhydride to the allyl alcohol or ester is substantially greater than 2:1, preferably at least 2.5:1. --There is no equivalents of the acetyl radical.

In the discussionherein of the amount of the acid and anhydride relative to the allylcompound, -it should also be borne'in mind that the equivalents of acylgroups supplied thereby do not include the anhydride required to form the corresponding allyl ester-when allyl alcohol-is used as a reagent.

The preferred molar ratios of reagents is substantially as follows:

.Before converting theintermediate esterto the corresponding ,butanetriol it isadvisable to .remove most of the acid and anhydride. The anhydride andorganicacid are removed by distillation, preferably in vacuo. The sulfuric acid is neutralized with an alkalimetal or. alkaline earth ,metal base or carbonate.

The sulfate salt so formed is essentially insoluble in the non-aqueous solution and is .conveniently filtered off,.al-

though distillation may take place without filtra- 0 tion. This neutralization and removal. of the sulfate may be carried out before or after the distillationstep. However, there is less risk of undesirable reaction. between the vproduct and hot concentrated sulfuric acid if. the neutralization and filtrationvprecede allor a substantialpart of the distillation.

The residue after removal of substantially all of theacid andanhydride may be subjectedto alcoholysis or hydrolysisby any standard means, or itmay be runner distilled in high vacuum to separate the ester. The distilled ester is chiefly 1,2,4-butanetriester. However, physical constants of the distillate indicate that it contains a small amount of a diflicultly separable impurity which may be a diester of 1,2,4-butanetriol. As this impurity is either very small in amount or is converted to 1,2,4-butanetriol in the second stage of the reaction its presence may be ignored. The distillation of the ester is carried out in order to effect an improvement in the purity of the 1,2,4- butanetriol.

Hydrolysis or alcoholysis may be effected in the presence of either acidic or alkaline catalysts in any usual way, acidic catalysts being preferable with alcoholysis. The butanetriol is isolated by distillation. Alcoholysis is preferable when the butanetriol is to be used in anhydrous condition.

The following working examples illustrate the invention more fully. All parts are by weight.

Example 1 A mixture of 1000 parts (10 mols) of allyl acetate, 2400 parts (40 mols) of acetic acid and 600 parts (20 mols) of paraformaldehyde is heated at 70 C. with stirring. During 2.5 hours 510 parts (5 mols) of 98% sulfuric acid are added while maintaining the temperature at 70-75 by heating or cooling. Then 1020 parts mols) of acetic anhydride are added during an hour longer, the temperature being held constant at about 70 by cooling. The solution is heated at 70-75 with stirring for 10 hours additional, and then allowed to cool somewhat before neutralizing the sulfuric acid with 530 parts (5 mols) of anhydrous sodium carbonate. is filtered and washed with acetic acid recovered from a previous batch. The filtrate is distilled in vacuo to yield 1190 parts of a fraction boiling at 127-133 C. at 2 mm. Hg and having a refractive index (n of 1.4370. This fraction is chiefly the triacetate of 1,2,4-butanetriol.

If the acetic anhydride is omitted the yield is reduced, and the fraction boiling over the same temperature range is less pure, as shown by a refractive index (71, of 1.443.

Example 2 A mixture of 712 parts of the acetate of hutanetriol made as in Example 1 and boiling at 127-133 at 2 mm. Hg (made in the presence of acetic anhydride), 1080 parts of synthetic methanol and 1.0 part of concentrated sulfuric acid is heated under a fractionating column packed with glass helices, at first with total reflux and then with partial take-off, the distillation temperature being held below C. until the methyl acetatemethanol azeotrope is gone. The residueis neutralized with sodium carbonate and distilled in vacuo to give 304 parts of 1,2,4-butanetriol boiling at 126-131 C. at 1 mm., (14 1.186, 11 1.476.

A tri(pheny1urethane) derivative made from this 1,2,4-butanetriol as directed by Pariselle, Annales de Chimie (8), 24, 348, melts at 14.9-151 C. Pariselle reported a melting point of 149452 for the trl(phenylurethane) of 1,2,4-butanetriol.

Example 3 Allyl alcohol 580 parts (10 mols) is added slowly to 2040 parts (20 mols) of acetic anhydride under reflux and then is heated under reflux for an hour. After cooling, this solution is added during 3 hours to a stirred mixture of 1800 parts (30 mols) of acetic acid, 600 parts (20 mols) of paraformaldehyde and 510 parts (5 mols) of 98% sulfuric acid at -75 C. After the addition is complete the solution is stirred and heated at the The precipitate a claim and desire to protect by Letters Patent is:

1. The process of preparing an ester of 1,2,4- butanetriol with an aliphatic saturated monocarboxylic acid having not more than four carbon atoms per molecule which comprises heating a i mixture comprising an allyl compound selected from the group consisting of allyl alcohol and an ester of allyl alcohol with an aliphatic saturated monocarbcxylic acid having not more than four carbon atoms per molecule, concentrated sulfuric acid, formaldehyde, an aliphatic saturated monocarboxylic acid having not more than four carbon atoms per molecule, and an anhydride of an aliphatic saturated monocarboxylic acid having from two to four carbon atoms per molecule.

2. The process of claim 1 wherein the molar ratio of formaldehyde to said allyl compound is substantially 2:1 and wherein the ratio of the sum of the molar equivalents of said monocarboxylic acid and said anhydride to said allyl compound is substantially greater than 2:1, the molar equivalents supplied by said anhydride not includingthat required to form the corresponding allyl ester when said ally1 compound is allyl alcohol.

3. The process of claim 1 wherein the reagents are used in substantially the following molar proportions:

Allyl compound 1 Formaldehyde 2 Aliphatic monocarboxylic acid 4 Aliphatic monocarboxylic acid anhydride- 1 the specified molar proportion of said anhydride not including that required to form the corresponding allyl ester when said allyl compound is allyl alcohol.

4. The process of claim 1 wherein said sulfuric acid and said anhydride are added to a previously formed mixture of said ester of allyl alcohol, said aliphatic monocarboxylic acid, and formaldehyde.

5. The process of claim 1 wherein a solution of said ester of allyl alcohol in said anhydride is added to a previously formed mixture of said aliphatic monocarboxylic acid; formaldehyde, and sulfuric acid.

6. The process of claim 1 wherein the reaction is carried out at a temperature of from 40 C. to 100 C.

7. The process of preparing the tri-acetate of 1,2,4butanetriol which comprises heating at from 40 C. to 100 C. a mixture comprising allyl acetate, concentrated sulfuric acid, formaldehyde, acetic acid, and acetioanhydride.

8. The process of claim 7 wherein the reagents are used in substantially the following molar proportions:

Allyl acetate 1 Formaldehyde 2 Acetic acid 4 Acetic anhydride 1 CHARLES H. STITELER. PLINY O. 'IAWNEY.

No references cited.

Claims (1)

1. THE PROCESS OF PREPARING AN ESTER OF 1,2,4BUTANETRIOL WITH AN ALIPHATIC SATURATED MONOCARBOXYLIC ACID HAVING NOT MORE THAN FOUR CARBON ATOMS PER MOLECULE WHICH COMPRISES HEATING A MIXTURE COMPRISING AN ALLYL COMPOUND SELECTED FROM THE GROUP CONSISTING OF ALLYL ALCOHOL AND AN ESTER OF ALLYL ALCOHOL WITH AN ALIPHATIC SATURATED MONOCARBOXYLIC ACID HAVING NOT MORE THAN FOUR CABRON ATOMS PER MOLECULE, CONCENTRATED SULFURIC ACID, FORMALDEHYDE, AN ALIPHATIC SATURATED MONOCARBOXYLIC ACID HAVING NOT MORE THAN FOUR CARBON ATOMS PER MOLECULE, AND AN ANHYDRIDE OF AN ALIPHATIC SATURATED MONOCARBOXYLIC ACID HAVING FROM TWO TO FOUR CARBON ATOMS PER MOLECULE.