US2373956A - Rearrangement of unsaturated aliphatic alcohols - Google Patents

Description

Patented Apr. 17, 1945 v i p v UNITED STATES PATENT [or-Flor.

' REARRANGEMENT OF UN SATUKAT-ED AIJPHATIC ALCOHOLS George. W. Hearne, Berkeley,vv and. Donald- S. La France,Walnut Creek, Calih, assignors to Shell Development Cnmpany, San Francisco, 'Calif., a corporation of Delaware No Drawing; .Application.August .29,' 1940-,

Serial No. 35.4,?7-06 4 Claims. (01. 260 -642) Thi invention relates. to aproces for the re-v meric primary alcohol or to a different isomeric arrangement of unsaturated alcohols and relates secondary alcohol. 1 more particularly to a processior rearranging The aliphatic unsaturated alcohols which aliphatic allyl type unsaturated primary alco-V may be rearranged or isomerized in accordance hols to aliphatic allyl type unsaturated second- 5 with the process of theinvention are characterary alcohols and for rearranging aliphatic allyl ized by possessing, at least four carbon atoms type unsaturated secondary alcohols to-aliphatic in a chain two of which are joined by an oleflnic allyl type unsaturated primary alcohols; linkage and one of which is a saturated primary The allylic or three-carbon type'ofxrearrangeor secondary carbon atom bearing a hydroxy ment of aliphatic. allyl type unsaturated alcohols group and directlylinkedto one. of the unsatsuch as crotyl alcohol, methyl vinyl carbinol and uratedcarbon atoms oi the 'olefinic' linkage. the like, has heretofore been considered ex- Such unsaturated alcohols are for'purposes oi tremely diflicult if not impossible. In the proconvenience designated herein and in the apduction of these alcohols and products derived pended claims as allyl type alcohols," since they therefrom, there is great need for economical contain thegrouping and efficient process for the conversion of a primary-alcohol tothesecondaryalcohol isomer, a secondary alcohol totheprimary alcohol iso mer or asecondary alcohol to a secondary which. is characteristic of allyl alcohol andits homologuesr cohol isomer. This 1s particularly so where a o process for the productionof the unsaturated 2 The anyl type Saturated alcohols to'whmh alcohol results in a product'ccmprising a mixture g ig m applllcable may be represented of several isomers. Thus,- crotyl chloride and e genera ormu methyl vinyl carbinyl chloride,- the principal RC.H=$ CHOH R2 products of the high temperature chlor-substi- R1 tion of normal butylenes, rearrange on distilla wherein R,',,R1 and R2 may represent hydrogen, tion at atmospheric pressure, or during hyalkyl. radical or substituted alkyl radicals but drolysis,sothat a mixtureof the corresponding wherein at least R or R2 represents analkyl or isomeric alcohols is always, obtained. In order substituted alkyl' radical. The alkyl radicals to produce substa tia y only the primary o whichR. R1 and R2 may. represent are, for exonly the secondary alcohol, some method for ample, methyl, ethyl, propyl, isopropyl', butyl,

their controlled and eflicient rearrangement is isobutyl; tertiary butyl, amyl, hexyl, etc. Repnecessary. Such a methodis provided. by the resentative substituted alkyl radicals...which R, .present invention. A R1 and R2 may represent are the above-listed It is an object of the present invention to proalkyl radicals and their homologues wherein one vide a novel, efiicient and economical process for or more, hydrogen atoms'has been substitutedby effecting the allylic rearrangement of an aliphatic a suitable organic or inorganic substituent such allyl type unsaturated primary or secondary -alcoas the halogen atoms, the hydroxy group, the carhol to an isomeric.aliphaticallyl.type unsaturated boxy group, the alkoxy groups and the like.

.primaryor secondary alcohol. The treatment 40 Specificv allyl type unsaturated primary and of a primary unsaturated .alcoholpof. the class to secondary alcohols; to. whichthe processot the which the invention is applicable results in invention is applicable are, among others, the its rearrangement to the corresponding; isomeric following:

unsaturated secondary alcohol. Dependingupon and their homologues and suitable substitutionthe structure of theparticular. alcohol treated, products H the treatment .of an. unsaturated secondary al.- In. accordance with .the processof theinvencohol may result in its rearrangement. toanisoe tion the aliphatic unsaturatedalcohol tobe rearranged i heated in the presence of a suitable acidic rearranging medium while maintaining the hydrogen ion concentration of the rearranging medium within a prescribed optimum range. Suitable rearranging media consist of dilute solutions of a reagent capable of supplying a sufficiently high hydrogen ion concentration in a solvent having a high di-electric constant, for

example, dilute aqueous solutions of inorganic acid such as sulfuric acid, hydrochloric acid, phosphoric acid, etc. 1

It has been found that by correlation of the concentration of the hydrogen ions in the rearranging medium the reaction temperature and the time of contact of the alcohol with the rearranging medium, undesirable side reactions can be reduced to a minimum and the desired isomeric alcohol prepared with excellent yields. The invention i described in detail with respect to its application to the preparation of crotyl alcohol from methyl vinyl carbinol and the preparation of methyl vinyl oarbinol and the alcohol. It is to be understood, however, that the invention is not limited to the rearrangement of these specific unsaturated alcohols, but is applicable to all unsaturated primary and secondary alcohols of the class herein defined.

It has been found that crotyl alcohol can be rearranged to methyl vinyl carbinol and that methyl vinyl carbinol can be rearranged to crotyl alcohol as typified by the reversible equation:

with excellent yields and a minimum of undesirable side reaction by heating the alcohols at moderately elevated temperatures in a dilute aqueous acid solution and correlating the hydrogen ion concentration of the aqueous acid solution, and the time of contact of the alcohols with the acid solution.

The rearrangement of the alcohols is preferably efiected in an aqueous medium butother solvents having a di-electric constant substantially as high as that of water may be used as the solvent for the acid. By heating crotyl alcohol with a 1% aqueous solution of sulfuric acid atatmospheric pressure and at a temperature of about 92C., approximately equilibrium mixtures comprising about 70% methtyl vinyl carbinol and about 30% crotyl alcohol are obtained with a minimum formation of unsaturated ethers. The time of contact required to obtain a desired yield of isomeric alcohol may be substantially reduced by increasing the concentration of the acid in the rearranging medium. Increase in acid concentration, however, increases not only the rate of isomerization but undesired etherification, so that the use of acid solutions having a hydrogen ion concentration in excess of a well defined limited range will result in the formation of excessive undesirable reaction products. The use of even a trace of concentrated sulfuric acid as the rearranging medium results in the formation of products consisting of a mixture of unsaturated ethers with very little of the desired isomeric alcohol. On the other hand, aqueous solutions having too dilute a hydrogen ion concentration, for example, a 0.2% or less sulfuric acid solution, act extremely slowly producing but little of the desired isomeric alcohol. These extremely dilute solutions can, however, be used at higher temperatures and pressures. It is therefore essential that the hydrogen ion concentration of the rearranging'medium be controlled within a" well defined optimum range to obtain economically desirable yields of isomeric alcohols with a minimum of undesired reaction products.

In accordance with the process of the invention, the allyl type unsaturated alcohol to be rearranged is mixed with a suitable rearranging medium consisting of a dilute aqueous acid solution having a hydrogen ion concentration in terms of pH values of from 1.23 to,0.3. Although aqueous acid solutions having a hydrogen ion concentration as high as 0.3 in terms of pH values may suitably be used, it is preferred to carry out the process with aqueous acid solutions having a pH value in the range of 1.23 to 0.57 and still more preferably in the range of 0.95 to 0.75. For

example, an aqueous 0.5% to 4%, p eferably a 1% to 2.5%, sulfuric acid solution may be used.

Dilute aqueous sulfuric acid has been selected as a suitable rearranging medium in the description of the process of the invention. It is to be understood, however, that the invention is not limited to the use of this acid as a catalyst. Any suitable reagent capable of supplying a hydrogen ion concentration in terms of pH values of from about 1.23 to 0.3 in aqueous solution may be used. Inorganic acids, of which hydrochloric, hydrobromic, phosphoric, pyrophosphoric and dithionic are typical, may suitably be used in dilute aqueous solutions. Aqueous solutions or organic acids such as acetic acid, for example, work only slowly at atmospheric pressure but are more active, and may be used, if desired, at higher temperatures by working under superatmospheric pressures. Aqueous solutions of organic acids such as, for example, benzene sulfonic, naphthalene sulfonic, toluene sulfonic, their homologues and analogues may, however, suitably be used at atmospheric pressure. Good results have been obtained with theuse of a 5% aqueous ethyl sulfonic acid solution as the rearranging medium in the rearrangement of crotyl alcoholto methyl vinyl carbinol. Suitable catalysts may also comprise solutions or suspensions of acid-acting salts such as, for example, sodium bisulfate, sodium bromide, sodium chloride, etc, in dilute aqueous solutions of suitable acids. Although the ratioof aqueous acid solution to alcohol may vary within a Wide range within the scope of theinvention, it is preferred to use a large excess of the aqueous acid solution. Thus, the ratio of aqueous acid solution to alcohol may be about -1 to 15 parts, preferably 8 to 12 parts, by volume of aqueous acid solution to 1 part by volume of alcohol to be rearranged. If desired, greater proportions of the dilute acid to alcohol may be used.

The mixture of alcohol and aqueous acid solution is heated in a suitable rearranging zone at a temperature sufficiently high to effect the desired degree of rearrangement but below that temperature at which substantial formation of undesirable reaction products is encountered. The temperature at which the mixture is heated will vary with the nature of the alcohols to be rearranged. The mixture may be heated at its boiling temperature at the operating pressure. In the rearrangement of crotyl alcohol and methyl vinyl carbinol excellent results have been obtained by heating the rearranging mixtures at about 96 C,

Pressures inexcess of atmospheric pressure may suitablybeused tomaintain all or a part ofthe reactants in the liquid hase during the rearrang ingT-process. Any suitable type of still, fractionator, heating coil or the like, or a combination of any two or,more of these, may be used as the rearranging Zone. Whatever thetype f rearranging zone and operating conditions used, the time of contact of the alcohol and rearranging medium is controlled to obtain an optimum yield of the desired isomeric al o ol it a m imumo d s r b e la -product formation and should preferably not exceed the minimum time requiredto attain equilibrium for a given dilute acid. concentration. In the batchwise rearrangement of, crotyl alcohol or methyl vinyl carbinol in an aqueous solution of 0.5% to 4% sulfuric acid at the atmospheric boile ingtemperature of the reaction mixture, the time of contact will be limited so as not to exceed, for example, a period of time. increasing progressively with acid concentration used, from about hours for a 0.5% acid concentration to about 40 minutes for a 4% acid concentration. Although batch or intermittent modes of operation may, if desired, be resorted to, it is preferred to carry out the. process of the invention in any suitable continuous manner to reduce to a minimum the time of contact of the alcohols with the acid solution.

The alcohol to be rearranged may be charged in continuous stream into a still in vapor communication with a fractionating zone. A dilute aqueous acid solution, for example, a dilutesul- 'furic acid solution having a hydrogen ion concentration within the above-prescribed limits, is maintained within the still. The alcohol to be rearranged is introduced continuously into the acid solution at a rate which will assure the maintenance of a ratio of alcohol to acid solution within the prescribed limits. The liquid in the still is maintained at a temperature sufliciently high to effect the desired rearrangement and cause the passage of vapors comprising reaction products to an intermediate part of the fractionating zone. The desired isomeric alcohol is removed from the fractionating zone as a final product. Material comprising unconverted alcohol is returned continuously from the fractionator to the still.

The water azeotrope of methyl vinyl carbinol boils at 86.8 C. whereas the water azeotrope of crotyl alcohol boils at 942 C. Therefore, in rearranging either crotyl alcohol or methyl vinyl carbinol, the desired isomeric alcohol may be separated from the reaction mixture as the water azeotrope substantially as rapidly as it is formed therein. When the isomeric alcohol is removed from the rearranging zone as the Water azeotrope, sufficient water is continuously added to the still to maintain the desired hydrogen ion concentration of the rearranging mixture.

It is to be understood that the invention is not limited in its application to processes to which but a single alcohol is charged. It is equally applicable to the processing of a mixture comprising, for example, two isomeric forms of a single alcohol to thereby obtain an increase in the proportion of the desired isomer in the resulting mixture or to convert all of one isomer to the corresponding isomeric form. The process of the invention is applicable, for example, .to the rearrangement of 2 methyl butene-l-ol-3 and2 methyl butene-Z-ol-l. 1

CH2=C|LCHOH-CBa 5:; onion-(hearing CH3 I Ha which alcohols are obtained as a mixture by hy- 'drolysisof the products obtained in the:chlorina-' tion-of tertiary .amylene, and the conversion. of which mixture to a product consisting ofa single one of the two isomer-shy method availableheretofore is difficult and uneconomical. The invention may alsoabe applied to, mixture comprising two or. more homologues of. an unsaturated alcohol, or comprising two or more entirely different unsaturated: alcohols, capabl of undergoing rearrangemenhto therebyobtain a desiredmixture containing .an increased proportion ofdesired isomers.

. Example I About 50 parts by volume of crotyl alcohol were mixed withfabout 500 parts by volume of a, 1%

aqueous sulfuric acid solution and the mixture- Methyl vinyl carbinol 61.1 56.3 Orotyl alcohol 33.5 38.0 Ethers 5. 4 -5. 7

Example II About 50 parts by volume of methyl vinyl carbinol were mixed with about 500 parts by volume of a 1% aqueous sulfuric acid solution and heated at a temperature of 92 C. for approximately 5 hours in a still equipped with a reflux condenser returning all condensate to the still. The mol per cent composition of the alcohols and ethers separated from the reaction products was-found to be as follows:

Crotyl alc h l 24.7 Methyl vinyl carbinol 7 .0 Ethers 4.3

Example III An initial charge consisting of 2.1 liters of a mixture .of 1% aqueous sulfuric acid and crotyl alcohol in the proportion of 0.556 mol of crotyl alcohol per liter of aqueous sulfuric acid was heated in a still provided with a reflux condenser. The liquid in the still was maintained at a temperature of 955 C. and'the stillhead at about 89 C. The methyl vinyl carbinol formed was removed as rapidly as formed overheadfrom the fractionator as the water azeotrope containing 24.8% water. Crotyl alcohol wa continuously added to the flask to maintain the concentration of 0.556 mol of crotyl alcohol per liter of aqueous acid. A total of 2.655 mols of crotyl alcohol were added continuously to the liquid in the flask durfractionator. Less'than 4% of the crotyl alcohol charged was converted to ethersand only traces of glycols were formed. 1

We claim as our invention:

1. A process for rearranging crotyl alcohol to methyl vinyl carbinol which comprises heating crotyl alcohol with an aqueous solution of 1% to 2.5% sulfuric acid at about the atmospheric boiling temperature of the reaction mixture, and continuously distilling methyl vinyl carbinol from the reaction mixture substantially as soon as it is formed therein.

2. A process for rearranging 'crotyl alcohol to methyl vinyl carbinol which comprises heating crotyl alcohol with an aqueous solution of 0.5% to 4% sulfuric acid, and continuously distilling methyl vinyl carbinol from the reaction mixture substantially as soon as it is formed therein.

3. A process for effecting the rearrangement of crotyl alcohol to methyl vinyl carbinol which comprises heating crotyl alcohol with an aqueous acid solution having a pH of from 1.23 to 0.57, and continuously distilling methyl vinyl carbinol from the reactionmixture substantially as soon as it is formed therein.

4. A process for effecting the rearrangement of an aliphatic unsaturated primary monohydric alcohol containing at least four carbon atoms and