United States Patent Office Patented May 8, 1956 2 Tentials

2,744,929 United States Patent Office Patented May 8, 1956 2 tentials. For purposes of simplification, the invention will be described in more detail with reference to the use 2,744,929 of selenium dioxide, the preferred catalyst, although by adjustment of conditions, tellurium dioxide can be used PRODUCTION OF UNTERATED CARBOXYLIC 5 instead. It is desirable, in order to supress by-product forma Curtis W. Smith and Roy T. Holm, Berkeley, Calif., as: tion, to maintain in the reaction mixture at all times at signors to Shell. Development Company, Emeryville, least an equivalent amount of aldehyde to oxidizing Calif., a corporation of Delaware agent, and preferably a stoichiometric excess of aldehyde No Drawing. Application September 26, 1952, groups to oxidizing agent. Where further oxidation of Serial No. 311,802 the initially formed unsaturated carboxylic acid is not undesirable, as, for example, in the conversion of unsat 19 Claims. (CI. 260-530) urated aldehydes to hydroxy-unsaturated carboxylic acids by oxidation of a chain carbon atom, generally a carbon This invention relates to the oxidation of unsaturated atom alpha to a carbon atom to which the multiple carbon aldehydes. It deals with a new method of carrying out to-carbon linkage is attached as well as the aldehyde such oxidation selectively to produce the corresponding group or groups present, it is, of course, feasible to em. unsaturated carboxylic acids in high yields. ploy in the reaction higher ratios of oxidizing agent to The oxidation of saturated aldehydes to the correspond unsaturated aldehyde than are required for oxidizing alde ing saturated carboxylic acids is a well known reaction 20 hyde groups only. In the preferred modification of the which is carried out commercially on a large scale, espe invention, namely, oxidation of unsaturated aldehydes, to cially for the production of acetic acid. No such suc the corresponding unsaturated carboxylic acids, about cess has been achieved heretofore, however, in the oxida 0.5 to about 1 equivalent of peroxide is used, as a general tion of unsaturated aldehydes. Due to their great tend rule, per equivalent of aldehyde in the unsaturated alde ency to undergo side reactions during oxidation, unsat 25 hyde being oxidized. Lower proportions are operative urated aldehydes give only poor yields of desirable acids but there is usually no advantage to be gained from their under the usual conditions of reaction. Some unsaturat use. Excess peroxide is preferably avoided in the pre ed acid can be obtained by oxidizing unsaturated alde ferred method of operation because it not only tends to hydes with hydrogen peroxide according to Staudinger cause undesirable side reactions, as previously indicated, patent-U. S. 2,377,584 but large amounts of dihydroxy 30 but also is generally uneconomical since it is difficult to aldehyde are simultaneously produced in the patented recover for reuse in the process after completion of the process. As a result, expensive indirect methods of pro reaction. Either aqueous or anhydrous peroxide solu duction have been generally necessary for the synthesis tions can be used for the reaction, but with aqueous per of unsaturated carboxylic acids. oxide the yields are generally higher with the more con It is an object of the present invention to overcome centrated solutions and it is preferred in the case of the foregoing disadvantages of prior methods of produc- - aqueous hydrogen peroxide, for example, to use solu ing unsaturated carboxylic acids from aldehydes. An tions of at least 30%, more preferably at least 50%, by important object is to provide an efficient, commercially weight, concentration. Aqueous hydrogen peroxide of attractive method for converting unsaturated aldehydes about 85%–93% concentration gives about the same to the corresponding unsaturated carboxylic acids by re results in the reaction as anhydrous peroxide. action with peroxides with reduced production of by The amount of selenium or tellurium dioxide or mix products. A special object of the invention is to produce tures thereof used in the reaction can be varied widely high yields of alpha,beta-olefinic carboxylic acids by re although as a rule it is desirable to use at least 0.2%, acting alpha,beta-olefinic aldehydes with hydrogen per and more preferably at least 2%, based upon the weight oxide. Another special object is to provide an advan 45 of unsaturated aldehyde present. Amounts greater than tageous method for recovery of the catalyst used in oxidiz about 25% seem to give no advantage over smaller ing aldehydes. Still another object of the invention is amounts and increase the problem of catalyst recovery. the provision of a method of oxidizing unsaturated al Temperatures within a range of about 20° C. to about dehydes in which the product is recovered in the form 100° C. are suitable for the reaction which is usually sub of an ester of the corresponding acid. Further objects and 50 stantially complete in three hours or less at the preferred advantages of the new method will be apparent from the temperature range of about 35° C. to 50° C. Either following description of the invention. , . normal, superatmospheric or subatmospheric pressure It has been found that unsaturated aldehydes can be can be used. selectively oxidized at the aldehyde group to produce As previously indicated, it is preferable that the process high yields of unsaturated carboxylic acids, by carrying 55 be carried out in a liquid medium in the presence of an out the reaction, in the presence of selenium or tellurium organic diluent which is a solvent for the unsaturated dioxide, with an oxidizing agent having an oxidation carboxylic acid produced and preferably also dissolves potential greater than ... that of said dioxide, preferably a the unsaturated aldehyde which is being oxidized. Wa peroxide oxidizing agent. This is quite surprising since ter, although it may be present in controlled limited not only do such oxidizing agents, particularly peroxides, 60 amounts without interfering with the success of the proc tend to attack unsaturated linkages leading to polymeriza- - ess, does not serve as a suitable solvent-diluent in the tion or oxidation but also these dioxides are known to process when monomeric unsaturated carboxylic acids oxidize carbonylic compounds at other points in the are the desired product. While it is preferable that the molecule in preference to the carbonyl group. Further chosen organic solvent-diluent be substantially inert under more, selenium dioxide alone oxidizes alcohols to alde 65 the reaction conditions, this is not always essential pro hydes but stops cleanly there without forming carboxylic vided the reaction which the solvent-diluent undergoes acids. It was most unexpected, therefore, to find that is not undesirable. A number of different types of or unsaturated aldehydes as a class can be successfully ganic compounds have been found to be suitable as sol oxidized to unsaturated carboxylic acids by means of vent-diluents in the new reaction. Alcohols, preferably selenium or tellurium dioxide catalyst and oxidizing agents alcohols of three to ten carbon atoms per molecule, are having oxidation potentials greater than that of the dioxide especially useful. The tertiary alcohols such as tertiary used, particularly peroxides having such oxidation po butyl and tertiary amyl alcohols, dimethyl propyl car 2,744,929 3. A. binol, methyl diethyl carbinol, 1-methylcyclohexanol, di within the range of about 30° C. to about 60° C. After methyl phenyl carbinol, and the like have the advantage completion of the oxidation, as can be established by of being quite inert to esterification in the process as nor titration of samples from the reactor to determine when mally carried out to produce free unsaturated carboxylic the formation of acid is complete, the unsaturated car acids. However, primary and secondary alcohols have boxylic acid produced can be recovered by distilling the been found to be also suitable in the process. Examples reaction mixture or the mixture can be worked up in of such alcohols which have been found to be satisfactory other suitable ways to obtain the desired final product. are, for instance, methyl, ethyl, normal- and iso-propyl, The process can be carried out continuously by introduc normal-, iso- and secondary-butyl, and the corresponding ing the oxidizing agent, preferably a peroxide, at spaced anyl and hexyl alcohols, 2-ethyl hexanol, lauryl alcohol, O points along the path of flow of a solution of the start cyclohexanol, 3-methylcyclohexanol, benzyl alcohol, fur ing unsaturated aldehyde and selenium dioxide in the furyl alcohol, and tetrahydrofurfuryl alcohol. Instead chosen solvent-diluent as the solution is passed through of monohydroxy alcohols, polyhydroxy alcohols may be a tubular reactor, reaction tower, or a plurality of reac used, suitable examples being butylene glycol, pentanediol tors in series, or other suitable form of apparatus in which 12, hexanediol-1,2,2-methylpentanediol-2,4, cyclohexane 5 proper temperatures and flow rates are maintained as diol-1,2, catechol, etc. Substituted alcohols can like previously indicated. Still other reaction methods can wise, be used in the process. The polyalkylene, particu be used for carrying out the reaction. larly polyethylene, glycols, preferably those containing Where the unsaturated carboxylic acid produced is in two to eight alkylene glycol units per molecule, and the tended as an intermediate for further synthesis, it is hydroxyethers of polyhydric alcohols such, for example, often advantageous to use the solution of unsaturated as ethylene glycol mono-secondary butyl ether, propylene acid in the chosen solvent-diluent for this purpose di glycol mono-ethyl ether, diethylene glycol mono-isopropy rectly without isolating the acid from the mixture. Thus, ether and glycerol dimethyl ether, are examples of solvent when the unsaturated carboxylic acid is to be esterified diluents which are successful. Non-hydroxy ethers are with a saturated alcohol, such alcohol can be used as the also effective solvent-diluents in the new process.

Load more