US2773895A

US2773895A - Preparation of alpha, omega-glycol esters

Info

Publication number: US2773895A
Application number: US383685A
Authority: US
Inventors: Seaver A Ballard; Richard R Whetstone
Original assignee: Shell Development Co
Current assignee: Shell Development Co
Priority date: 1953-10-01
Filing date: 1953-10-01
Publication date: 1956-12-11
Anticipated expiration: 1973-12-11

Description

United States Patent PREPARATION OF ALPHA, ONIEGA-GLYCOL ESTERS Seaver A. Ballard and Richard R. Whetstone, Orinda, Califi, assignors to Shell Development Company, Emeryville, Califl, a corporation of Delaware No Drawing. Application October 1, 1953, Serial No. 383,685

Claims. (Cl. 260-491) This invention relates to a method of preparing diesters of alpha,omega-dihydroxyalkanes containing at least four carbon atoms. More particularly, the present invention relates to a preferred aspect to a method for the preparation of aliphatic carboxylic acid diesters of alpha,omegadihydroxyalkanes, i. e., of alkylene glycols, containing at least four carbon atoms. In another preferred aspect the invention pertains to a method of preparing aromatic esters of alpha,omega-dihydroxyalkanes containing at least four carbon atoms. In specific aspects the invention pertains to a method for the preparation of aliphatic carboxylic acid esters of hexamethylene glycol and, in a further specific aspect, to a method for the preparation of diesters of dialkyl-substituted 1,5-pentanediols.

Included in the process of the invention as its essential step is a method for the preparation of diesters of alpha,- omega-dihydroxyalkenes containing at least four carbon atoms, which unsamrated diesters may, if desired, be separated as useful products of the process, but which more desirably are hydrogenated to form the above esters of the corresponding alpha,omega-dihydroxyalkanes.

Broadly stated, the invention comprises subjecting to pyrolysis a triester of an alpha,beta,omega-trihydroxyalkane containing at least four carbon atoms, to form as the principal products of the pyrolysis treatment diesters of alpha,omega-dihydroxyalkenes containing the same number of carbon atoms, which diesters may be hydrogenated to form in excellent overall yield diesters of thedesired alpha,omega-dihydroxyalkane. The diesters of the alpha,omega-dihydroxyalkanes readily may be converted to the free glycols by methods that either are specifically known or will be apparent to those skilled in the art to which the invention pertains.

It has been proposed to prepare certain esters of unsaturated monohydric alcohols, e. g., of allyl alcohol and of the theoretical vinyl alcohol, by pyrolysis of diesters of alkylene glycols and by pyrolysis of monoesters of alkylene glycols. In both cases esters of dihydric alcohols are employed as the initial reactants, whereas we desire to produce esters of dihydric alcohols. It also is known that glycerides, such as fats, and lower glycerides, such as triacetin, may be pyrolyzed to form acrolein and, in some cases, ketene. Both of these products obviously are distinctly different from the products that are produced in accordance with the present invention.

It unexpectedly has been discovered in accordancewith the invention-that carboxylic acid triesters of alpha,beta,- omega-trihydroxyalkanes containing at least four carbon atoms may be pyrolyzed to form as the principal products of the pyrolysis carboxylic acid diesters of alpha,omegadihydroxyalkenes, in excellent yields and with a minimum of formation of undesirable by-products. It unexpectedly has been discovered further that the pyrolysis may be effected with a minimum of accompanying formation of esters of beta,omegaand/ or alpha,beta-dihydroxyalkenes, or products of their pyrolysis. The practical value of this latter feature of the invention will be readily apparent when the possible difliculty of separating into their pure components mixtures of such isomeric esters, or mixtures of the corresponding saturated glycols or diesters thereof, is considered.

It is preferred to employ in the process to which the invention relates esters of the hereinbefore and hereinafter disclosed alpha,beta,omega-trihydroxyalkanes with saturated fatty acids, such as the acetates, propionates, butyrates, valerates, caproates, oenanthoates, caprylates, pelargonates, caprates, and homologous esters, the formates being less desirable. There also may be employed in the process an ester of an alpha,beta,omega-trihydroxyalkane with an unsaturated fatty acid containing one, two, or even more non-aromatic carbon-to-carbon multiple bonds, or esters wherein the acyloxy groups are derived from aromatic carboxylic acids, such as benzoic acid, toluic acid, and n-butylbenzoic and xylic acids. In accordance with the invention, the most favorable results in the matter' of yield of the desired products and in the overall eflicacy of the process are obtained when the triester that is employed is one which the acyloxy groups are derived from a saturated aliphatic monocarboxylic acid containing from 2 to about 8 carbon atoms. The process is particularly effective when there are employed the triacetates of the above-defined trihydric alcohols.

In the execution of the process of the invention, the

ICC

aforesaid triester of an alpha,beta,omega-trihydroxyalkane is heated to a temperature sufficiently elevated to effect the desired pyrolytic decomposition, but not so high that undesired generalized decomposition of the organic materials that are present occurs. Temperatures of at least 300 C. may be employed in accordance with the invention. Temperatures of at least about 350 C. preferably are employed. Considerably higher temperatures may be employed, if desired, up to about 650 C. Within the indicated range of temperatures, the Optimum temperature range depends inter alia upon the particular triester that is employed in the process and upon the residence time of the triester at the pyrolysis temperature. Lower residence times may be employed at the higher temperatures, and, conversely, longer residence times may be employed at the lower temperatures. When the pyof the invention is executed in a continuous manner, as"

by passing a stream of the triester into and through a reaction zone heated to the desired reaction temperature, the residence time at the pyrolysis temperature is determined by the liquid hourly space velocity, which is the rate at which the triester, measured in the liquid state, is

passed into and through the reaction zone. In quantitative terms, the liquid hourly space velocity is equal to the volume of the triester measured in the liquid state, passed through a unit volume of the reaction space per hour. The liquid hourly space velocity that is employed in the execution of the process of the invention may be varied within relatively wide limits, provided that under the existing conditions of temperature, presence or absence of catalysts, etc., it is such that practicable conversions of the triester to the desired products are obtained, without excessive generalized thermal decomposition of the organic materials that are present. Generally speaking, liquid hourly space velocities within the range of fromabout .1 hr.- to about hr? will be found to be suitable. The optimum value, or range of values, of the liquid hourly conditions under which the process is'exec'uted." ForeX- ample, at temperatures of from about 400 C. to about 550; C. liquid hourly space velocities of from about .5 hrr' to about 5 hrf frequently may be employedwith particular advantage. At other temperatures, somewhat different liquid hourly space velocities may be particularly advantageous.

Although the residence time'(or the liquid hourly space velocity in the case of continuous operations); in conjunction with the pyrolysis temperature, may be employed as an expression of the severity of thepyrolytic treatment, it isparticularly convenient; to define and to measure the 1 several conditions of the pyrolysis in terms of the proper! tion-of the initialamount of the triesterthat is-converted to othepproducts. We have found that particularly-ta vorableresults may be obtained in the practiceoftheprocess of the invention when the selected conditions are such'that relatively highconve rsionszof the initialtriester to other products are obtained. ,For' example, highly-far vorable results are obtained in the practiceof theinvention' when the conditions oi temper -ature residence time; and the;,l il e,;are'such that from about'SS 'to' about 85 of the tri esteris converted to other products,- the balance being unchanged; Conditions 'whichflead to lower total conversions, say down to about 10% of the triester; may be employed, although in such cases the amount of the desired products that "may be" obtained from 'a given amount of the triesterper pass is correspondingly-less:

The process of the present'iuvention may be executed in either a continuous, an intermittent, or a batchwise man ner,;continuousjoperations beingmost efficacious.-- One"- particularly efiective manner of operation comprises-pass ing a stream of the liquid triester of the alpha-betapmegatrihydroxyallcene through a zone,-as an elongated reaction zone, that-is heated to the pyrolysis temperature, at a rate that is correlated with the temperature to provide'thedesired percentage conversion of the triester to other prod ucts. The reaction 'Zonepreferably is defined by an elongated reaction tube which may be heated either internally or externally by suitable heating means. The" pyrolysis tube should be constructed of a suitable thermally and' chemically. resistant material, such asglass, nickel, stain-' less steel, Monel metal, or other resistant metals or'alloys of metals, quartz, porcelain, or the like. The pyrolysis tube'lrnay be otherwise empty, or the tube maybe packed' I withinert or catalytically active solids which favor the'de' siredpyrolyticdecompositions. Inert solids servepri marily to assist transfer of heat tothe triesterand main ,tenance of the temperature at the desiredvalue," and their presence thereby-may desirably increase the :overall etfec in the reaction tube include, for example; glass, silica; iron;

stainless steel, silicon carbide; carbomlaluminumt oxide;-;-.

ceramic ,materials, e; g.,; porcelaimand "thetlikez The salts'such as acidiccalcium and/or silicon phosphates;

and the like, Because of theunexpectedlyhigh-yields "of? the desired products that have been obtained in the herein'" described non-catalytic pyrolysis of the stated triesters; aii'da because of the possibility that-the presence ofcatalytic ally activemat'erials'may reduce the advantageously high'yields the vapor state, e. g., in a continuous process, it may be desirable'to provide a'preheate'r o'r suitable vaporize'r'i'ro convert the liquid triester to the vapor state. 'The vaporous ester may be diluted with an inert diluent gas, such as nitrogen, methane, or the like. Alternatively, the triester in the liquid state frequently maybe fed directly into the heated reaction zone and its volatilization and pyrolysis efiecte'd simultaneously. If the reaction zoneis defined as by an elongated heated reaction tube through which the triester'is passed, the intial portion of the'tube may serve as a preheater, or vapori'zen'the vaporous triester being subjected to further pyrolysis in the remaining portion of the reaction tube. The pressure most conveniently-may be maintained at or about atmospheric pressure. However, the invention is not limited to the use of atmospheric pressure, and pressures either above or'below atmospheric pressures may be employed if desirable.

The pyrolysis of carboxylic acid triesters of alpha,beta,- omega-trihydroxyalkanes containing at least four carbon I atoms in'accordance with the processof-the invention has beenfound toj'form products comprising principallydiesters=of unsaturated diols, which diols contain the samenumber" of carbon atoms as the .t'rihydroxyalkane from which the initial triesters were derived, accompanied by only minor amounts of products of other possible rea'ctions. In fact, the'only other products of pyrolysis which 1 have been detected have been relativelysmall amounts of 1 esters-of diolefinic monohydric alcohols which easily may be separated, as by fractional distillation, from the aforesaid esters of unsaturated diols. These esters of diolefinic monohydric alcohols maybe recovered as useful products, or they may be hydrogenated .to the corre-"" sponding 'saturatedmonoesters, which also are useful compounds.

The-mixture leaving the. pyrolysis zone comprises an 1 amountwofthcarboxylic acid from which'the acyl groups tof the triester subjected to pyrolysis were derived and-"one or'more diesters of unsaturated diols asthe principal'produ'cts -ofthe pyrolysis. The carboxylic acid, whichprefe'rably is a' lower saturated aliphatic monocar boxylic'acidt'may be removed or recovered from the mix'- ture' of'productsin any suitable manner; The entire mixii turez' thuS m-ay becooled to' about ordinary room temper-' aturesas by passing it through'a suitable heat exchanger tiveness of theprocess: Inert solids which may bezpresent' in heat exchange with. water, air, or other coolant, and ii the carboxylic acid "thereafter "removed as by distillation. Ari'otherconveni'ent method'of removing "the carboxylic acid by-productis tosubject the'mixture'as itleavesthe pyrolysis: zoneito-a stripping treatment, at a temperaturesuflicien'tly elevated to volatilize-the carboxylic acidbut" not the esters'that are present.- Ofcourse,'other' methods of removing the carboxylicacid by productmay be em plo'yedy'if desired, as by'extractiomwith a selective solveh (e. g: "WBitCIgiiffllfi carb'oxylic acidiis water soluble) an'd .l the'like' Y arboxylicac'id diesters of the-unsaturated diols are desired as the ultimate products, they may be recov xered fromi therproducts of pyrolysis and purified as-by fractional-distillationof theester-containiug portion of the by promoting other, undesired reactions,.it'ispreferred' to executethe'proc'ess in the absence of added ca'talystsxx Inert substances, such as the inert solids referred to above;

are not regarded as catalysts.

The process of theinvention may be executed with the carboxylic acid ester of the alpha,beta,omega trihy'droxy'- alkanein either the liquid phase or in' the-vapor. phases; When the operations are carriedoutiwith the-.triesterfin...

.process'may be subjected' t'otheihydrogenation'treatmeht,-

reaction products; any'unconverted t'rie'sterof the alpha','--: beta,omega trihydroxyallcane also being separated at this": I time ifdesired; The unconve'rted triestermay berecycledthrough the pyrolysis step oftheprocesses WithtreSh-feed in orderrto=increasekthe"overall3 conversion of trie'st'e Whemth'e-processoftheinventionis directed ferrediembodiin'ent'to the' preparation of esters v omegaidihydroxyalkanes, e.,: of alkylene' 'glyco'ls, coutainiug'at le'ast four" carbonatoms, the dies tersfof' un saturated diols whichare'formedby the pyrolysis are liy drogenated byitreatment with molecular hydrogen inthe presencerof 'a hydrogenationcatalyst to saturate the-ole finic:b.onds 'that are'presentin the molecule. The' eh-tir mixture-"that isFproduced in the pyrolysisfstep' of the although-i preferably the carboxylic acicl -by produet offavored by fractionating the pyrolysis products only to such an extent that substantial separation of the above stated fraction is achieved. The fraction may contain varying amounts of possible side-products of the pyrolysis, depending upon the efficiency of the fractionation, the presence of such side-products during the hydrogenation treatment not being detrimental.

The hydrogenation of the fraction comprising essentially .the carboxylic acid diesters of the unsaturated diols may be effected by. subjecting the fraction to the action of molecular hydrogen in the presence of a hydrogenation catalyst under conditions which favor the reduction of olefinic bonds to saturated carbon-to-carbon bonds. As the hydrogenation catalyst there may be employed any of the metals, or compounds of metals, or mixtures thereof, customarily referred to in the art and employed as hydrogenation catalysts. Suitable metals which may be employed as the hydrogenation catalyst include, for example, Ni, V, Pd, Pt, Cu, Cr, Fe, Co, Ru, Mo, W, Ir, Ru, Ag, and suitable compounds thereof, such as oxides and sulfides thereof. It is preferred to employ the base metal hydrogenation catalysts because they have been found .to have a desirably high degree of efiicacy and because they am easily and economically prepared. Nickel catalysts, such as .the Well-known catalyst referred to in the art as Raney nickel catalysts, are particularly desirable. In place of the Raney nickel catalyst, there may be employed nickel catalysts that have been prepared, for example, by .thermal decomposition of suitable compounds of nickel, by mechanical subdivision of massive nickel, by

. electrodeposition, or according :to other known methods.

Catalytically active compounds of metals which may be employed as the hydrogenation catalyst include, among others, copper chromite, copper oxide, molybdenum oxide,

'mixtures of oxides of copper and of molybdenum, tungsten sulfide, and tungsten-nickel sulfide. The catalyst may be employed in the finely divided state and suspended in .the fraction to be hydrogenated, or it may be carried on "an inert or catalytical-ly active supporting material, such as' carbon, pumice, silica, clay, alumina, ktieselguhr, or the like.

In the hydrogenation step of the process of the invention, the carboxylic acid esters of the unsaturated diols are subjected to the action of the molecular hydrogen at an elevated temperature and under superatmospheric pressures of hydrogen in the presence of the hydrogenation catalyst. Amounts of the catalyst from about 1% to about 20% by weight of the fraction that is to be hydrogenated are generally satisfactory, although either 300 C. may be employed during the hydrogenation treatment, a preferred range being from about 50 C. to about 150 C. Hydrogen pressures of from about 250 pounds per square inch upwards are suitable. There is no known upper limit to the pressures of hydrogen that may be employed, although for practical reasons :it-rarely is desirable or necessary to employ hydrogen ipressures' above-about 10,000 pounds per square inch.

vents, and the like.

A preferred range of hydrogen pressures is from about 500 pounds per square inch to about 5000 poundsper square inch. f

The carboxylic acid diesters of unsaturated diols that are produced by the pyrolysis step of the process, or a fraction of the pyrolysis products comprising the same, may be hydrogenated by exposing them to the action of hydrogen gas under the aforesaid conditions of temperature and pressure of hydrogen gas in the presence of the hydrogenation catalyst until absorption of hydrogen is essentially complete. It has been discovered that the theoretically calculated amounts of hydrogen based on the degree of unsaturation of the fraction that is to be hydrogenated, may be absorbed. The absorption of hydrogen may be determined by measuring in any suitable known manner the amount of hydrogen that is absorbed. Alternatively, the hydrogenation may be continued until absorption of hydrogen ceases. The hydrogenation treatment ofthe invention may be carried out in either a continuous, an intermittent, or a batchwise manner. Any suitable apparatus of the character customarily employed for hydrogenation reactions may be employed.

The hydrogenation step of the process of the invention may be effected in the presence or absence of a suitable solvent, such as an inert organic solvent. Suitable organic solvents include, for example, saturated hydrocarbon solvents, ethers, esters,'alcohols, aromatic hydrocarbon solvents, halogen-containing hydrocarbon sol- When a solvent is employed it may be used in an amount ranging up to.90% by weight or more of the reaction mixture. The carboxylic acid diesters of unsaturated glycols that are produced by the pyrolysis step of the process thus can be effectively hydrogenated in the form of a 10% to 40% by weight solution in a saturated hydrocarbon or other suitable solvent. However, the presence of an inert solvent during the hydrogenation treatment is not a prerequisite to its successful practice, and, thereof, the invention also includes such hydrogenation when no solvent is. adde to the reaction mixture. 1

After completion of the hydrogenation step of the process, the desired carboxylic acid diester of the alpha, omega-alkanediol may be recovered from the mixture in any suitable manner. The catalyst, if suspended in the mixture, may be removed by filtration, centrifuga tion, or in equivalent ways. The solvent, if one is present, may be removed by evaporation, distillation, or the like, and the products of the hydrogenation thereafter separated in any effective manner, fractional distillation, as under reduced pressure, being preferred. It was a quite unexpected result of the present process-that the principal, and frequently the only diester present in appreciable quantities, is the carboxylic ester of the alpha,omega-dihydroxyalkane containing the same number of carbon atoms in the molecule (exclusive of the acyloxy groups) as the triester that was subjected to the pyrolysis. No significant quantities of the possible isomeric esters of beta,omegaand/or alpha,beta-dihydroxyalkanes have been found. There may be present, in minor amounts that may be influenced by the efliciency of the fractionation of the products of the pyrolysis step of the process, the corresponding carboxylic acid alkyl ester, presumably formed by saturation of the aforementioned esters of diolefinic monohydric alcohols. Since these products ordinarily have substantially different boiling points, they may be easily separated during purification of the hydrogenation products.

The process of the invention is particularly valuable for the preparation of carboxylic acid diesters of 1,6- hexanediol, from carboxylic acid triesters of 1,2,6-hexanetriol, the lower saturated aliphatic monocarboxylic acid esters preferably being employed. When a triester of 1,2,6-hexanetriol, e. g., the triacetate, is subjected to pyrolysis in accordance with the process of the invention, the principal product has been found to be a com- 7 plei mixture oresters ofi (3s mono-olefinic' diols with the *carbox ylici' acid,- possibly: with very :minor amounts of esters of Ca diolefinic monohydric alcohols.- There'also is'ronae'd the-carboxylic' acid from which 'the'acy'l groups "of'the triester'were derived. There-alsomaybe-present varyin'g' 'amonnts of unreacted 1-,2,6-hexanetriol 'trie'ster. In thec'ase' "ofthei lower saturated aliphatic mono'carbox ylic acid'e'sters of 1,2;6-hexan'etriol the pyrolysis-may be' -efie'c'tedadvantageously at fromabout *350"- (2. to about 500" C. and at a 'resid'ence time or liquid h ourly spac'e'velocity of from about 0.5 to about 2.5 hr.

The rhixture produced by the pyrolysis may be separated by"fractional' distillation so as to recover a-fractioriihavi'ng an increased content of"-the diesters 'of Ca fr-loin) oletinic dihydric=alcohols; and also if desired to I about 110 C.'under 3 mm.-Hg pressure, or overan *equivalent'temperature range under'other pressures, may be separated as'the fraction'rich in hexenylenediacetates. Of course,the esters of other carboxylic' acids may distill oVer a'SOmeWhat 'ditferent range of temperatures.

"The fraction-rich in hexenylene diesters may. be hydro- :genated under hydrogenation conditions which have been refer'-red" to hereinbefore, to-saturate the olefinicbonds. "'After' completion of the hydro'genation,- -any -minor amounts of other products may be separated 'frorn the :die'ster of l,6 hexanediol that is formed as the principal product, as by fractional distillation of the products of hydrogenation; If the free hexamethylene glycol rather th'anits' diester is desired as the ultimate product, the ester may be saponified according many of the methods that are known in the art to obtain the desired glycol.

When"reference-is made'herein to alpha, beta, omegat1ihydroXy-alkanes containing at least four carbon atoms, and-totheiresters, it is intended to refer to those saturated aliphatic triols which'cont'ain two primary alcoholic -hy droxyl g'rotips'anda third alcoholic hydroxyl group all bonded to separatecarbon atomsin a chain of at least "fourcarbonatoms, two of the 'hydroxyl' groups being attached to adjacent carbon atoms. Regarding the vicinal -hydroxyl groups' as attached to the'alpha and thebeta carbon atoms; the second terminalhydroxyl group, -i. e., the one' at the terminal, or the omega; carbon atom, may be separated from the beta carbon atom' by two or more carbon atoms. We preferably-employ triestersof alpha, -betapmega trihydroxyalkanes in which th'eomega carbon 1 atom-is separated-from thebeta carbon atom by not more "that 'about 5 atoms of 'carbon. T he carbonatoms in this smear-grou er four ormorecarbon atoms may be unst'ibstituted,- or'they' may be'substituted by one or'more groups. It is'preferred toernploy esters of alpha, -betaomega trihydroxyalkanes "which contain -not over l out 16 carbo'n'atom's', e'ir'clusiye of the'carbo'n atoms in the acyl groups.

Representative alpha, beta,omega-trihydroxyalkanes, carboxylic acid esters of which may be converted by the process of the invention to esters of alphapmega tlihydroxyalkanes include in addition to 1,2,6'hexanetriol, -l ,'2 ;4-butanetriol, l-,2,5-pentane'triol, and carboxylic acid esters of analogous and homologous; alpha,beta,omegatrihy'droxyalkanes. Generally: speaking; the esters of -alpha;beta,omega trihydroxyalkanes1 which we mayemploy inithe process or the invention-have structuresnac- --cording--to the-formula V -Robo-onz-(onon on onrooon irrwhich n represents an integral number, preferablyone not=greater than 5, and R represents a monovalenthydro- --carbon group containing up to 18 carbon atoms, preter- -ablyan alkyl group, such as a loweralkyl group. We also may employ esters of alpha,beta,omega-trihydroxyalkanescorres'ponding to theabove formula when one or -m01e of the hydrogen atoms in the: formula have been :replaced by an alkyl group, preferably a lower 'tilkyl group, such as corresponding esters-of 2,5-dimethyl-1-,2 ,6- hexanetriol, l Z-methyl-1,2,6-heXanetriol, 2,5-diisobutyl- -1;2,6-hexanetriol, 2,4-dimethyl-1,2,5 pentanetriol, and the like, the preferredcsters of such: alkyl-substituted alpha,beta,omega-trihydroxyalkanes' being the :esters .of such al'pha,beta,omega trihydroxyalkanes having not 1 more than two alkyl substituentgroups 1 replacing hydrogen atoms in the foregoing formula. -'From thettriesters of the unsubstituted alpha,beta,omcga-trihydroxyalkanes and'l'ower aliphatic monocarboxylic acids containing at 'least four-carbon atoms there are obtainedconesponding estersof alpha,omega-dihydroxyalkanes with t1ower aliphatit:mono'carboxylic acids containing at :least "four carbon-atoms. These products correspond to :the struc- RCOO-CH2'--( CH2) i1'-CH2CH2OOCR in which t re resents an integral number not g'reatefthan 5 "and RCOOrepr'esents theac'yloxy group of La'l'o'wer 'aliphatic"mo'nocarb'oxylic acid containing at'leastffour carbon atoms. Illustrative ofthese'are 1,6 hexanediol -dibutyrate, l,5-penta'nediol dicapr'ylate, and l,5 -pent anediol'dicaproate. From 'este'rsof alkyl-substituted alpha,-

' beta,omega?trihydroxyalkanes there are, obtained ia'ccordin'g"to"the pr'ocess of'the invention esters of'branch'ed' chain alpha,omega-glycols having structures corresponding to the formula RCOOCH2'(CH2) 1z-CH2'CH2OOC in'which n represents an integral number not "greater than 5 and RCOO represents the acyloxy group of an acid selected'from 'the group consisting of lower'aliphatic, monoca'rboxylic acids and aromatic monocarb'oxylic acids, wherein a hydrogen atomon a beta carbon'atom 'is repla'cedby a lower alkyl' group and from nonetoone,

inclusive, hydrogen atom on a different "non-terminal carbon atom of the linear carbon chain isireplacediby'a' 'dim'ethyl-l',6 '-hexanediol dib'u'tyrate. The novel esters are useful 'i'nter'aliaas plasticizers for polyvinyl chloride. 1-.

' The followinge'xample's' will :illustrate some ;of the possible s ecifie'embodiments of the, invention. 'lt'will'lbe understood that 'the examples are intended only 'tobe illustrative of the invention that is defined more broadly in the appended claims. In the examples, the partsare "by weight.

ExampIe I A vertically {positioned cylindrical reaction? tribee'onst'ructed of nickeland having a diameter 015L625 inch 'afid alength of 42 inches, was filled with S to 14 inesh silicon carbide chips. The top of the tube was"closed*from" the atmosphere and was provided with an inlet through which liquid feed'could be'supplie'd in measured quantities. The

; lowerend of the tube was connected through a short watenjacketed condenser to a suitable --receiving: flask for :efiiuent from: the reaction tube The reaction tubeftwss surrounded: by :-'::thehndstaaea11y ontm1lect e'lectl ieal heater's which were regulated with the aid of a thermocouple placed in the interior of the reaction tube.

The reaction tube and its contents were heated to 450 C. Liquid 1,2,6-hexanetriol triacetate then was fed into the top of the reaction tube onto the heated silicon carbide chips at a liquid hourly space velocity of 1.47 hrr' the velocity being calculated on the basis of the free space in the packed tube. The liquid product issued from the v bottom of the tube and was collected in the receiving flask.

When 215 parts of 1,2,6-hexanetriol triacetate had been 'fed to the pyrolysis tube, 200 parts of liquid products had collected in the receiving flask. The liquid crude product thus obtained was fractionally distilled under reduced pressure. A fraction distilling from 56.5 C to 62.2 C. under 100 mm. Hg pressure was collected and found to be composed primarily of acetic acid. After distillation of a second fraction, distilling from 42 C. to 89 C. under 3 mm. Hg pressure, there was collected a fraction distilling from 89 C. under 3 mm. Hg pressure to 115 C. under less than 1 mm. Hg pressure, amounting to 81 parts and consisting predominantly of diacetates of nonvinylic hexenediols. Fifty-one parts of unreacted 1,2,6- hexanetriol triacetate were separated as a fraction distilling at 115 C. to 116 C. under less than 1 mm. Hg pressure. Seven parts of residue remained in the still kettle.

A solution of 22 parts of the fraction consisting predominantly of hexenediol diacetates dissolved in 78 parts of isooctane was placed in a hydrogenation bomb with 2 parts of Raney nickel hydrogenation catalyst. The mixture was subjected at 100 C. to the action of hydrogen gas under a pressure of 1400 pounds per square inch until hydrogen absorption ceased. The catalyst was removed by filtration and the filtrate was distilled. There were recovered 14.9 parts of hexamethylene glycol diacetate disstilling at 103.5 C. to 106 C. under 3 mm. Hg pressure.

The hexamethylene glycol diacetate was dissolved in 30 parts of anhydrous methanol containing 0.25 part of sodium, and methyl alcohol-methyl acetate azeotrope was distilled from the mixture until the theoretically calculated amount of methyl acetate was removed. The alkali was removed by passing carbon dioxide into the residual solution and filtering off the precipitate. The filtrate was dis tilled, with collection of 7 parts of hexamethylene glycol at 110 C. to 122 C. under 4 mm. Hg pressure. The hexamethylene glycol melted at 36 C. to 38 C. both alone and when mixed with a sample of glycol prepared by another method and melting at the same temperature.

Example II The tripropionate of 1,2,6-hexanetriol is pyrolyzed according to the method of the preceding example. The resulting mixed liquid products are fractionally distilled and a fraction comprising predominantly dipropionates of non-vinylic hexenediols is collected separately. This fraction is dissolved in about twice its weight of isooctane. The resulting solution is hydrogenated over copper chromite by treatment with gaseous hydrogen under a pressure of about 2000 pounds per square inch at a temperature of about 150 C. until absorption of hydrogen ceases. After separation of the catalyst the resulting solution is fractionated by distillation under reduced pressure, the fraction comprising the dipropionate of hexamethylene glycol being collected separately. The dipropionate of hexamethylene glycol distills at about 106 C. under 2 mm. Hg pressure.

Example III A fraction consisting predominantly of diacetates of 'nonvinylic hexenediols, prepared as in Example I, is hydrogenated in the form of a 25% by weight solution in isooctane in the presence of copper chromite and under a .hydrogen pressure of about 2000 pounds per square inch .and at about 150 C. The diacetate of hexamethylene glycol is recovered from the products of the hydrogeiia tion according to the procedure illustrated in Example I.

Example IV Forty-one parts of 2,5-dimethyl-1,2,6-hexanetriol"are acetylated by treatment with acetic anhydride in the presence of acetic acid and after standing over night themixture is rapidly distilled to recover the acetate estei. Tlie drogenation of this mixture over Raney nickel catalyst at 7 about C. under about 1200 pounds per square inch hydrogen pressure and fractionally distilling the products of the hydrogenation.

2,5dimethyl-1,2,6-hexanetriol used in this example can be prepared from 2,5-dimethyl-3,4-dihydro-1,2-pyran-2- 3 carboxaldehyde by hydrogenation at C. to C.

in aqueous ethanol or other aqueous solvent in the presence of acid and a hydrogenation catalyst, such as Raney nickel catalyst.

This application is a continuation-in-part of copending application Serial No. 207,865, filed January 25, 1951 now abandoned, which in turn was filed as a continuationin-part of application Serial No. 769,066, filed August 16, 1947, now abandoned.

We claim as our invention:

vinylic 1,6-hexenediols, which comprises pyrolyzing by heating at a temperature within the range of from about 300 C. to about 65 0 C. the triacetate of 1,2,6-hexanetriol and recovering from the products of the pyrolysis a dirange of from about 300 C. to about 650 C., a lower fatty acid triester of 1,2,6-hexanetriol and recovering from the products of the pyrolysis a lower fatty acid diester of a non-vinylic 1,6-hexenediol.

3. A process for the preparation of lower fatty acid diesters of non-vinylic 1,6-hexenediols, which comprises passing a lower fatty acid triester of 1,2,6-hexanetriol through a plyrolysis zone heated to within the range of from about 400 C. to about 550 C. at a liquid hourly space velocity of from about .5 hr." to about 5 hr.- whereby said triester is pyrolyzed to the lower fatty acid and lower fatty acid diesters of non-vinylic 1,6-hexenediols.

4. A process for the preparation of diacetates of nonvinylic alpha,omega-alkenediols, which comprises pyrolyzing by heating within the range of from about 300 C. to about 650 C. a triester having the formula in which n represents an integral number not greater than 5.

5. A process for the preparation of monocarboxylic acid diesters of non-vinylic alpha,omega-alkenediols, which comprises pyrolyzing by heating within the range of from about 300 C. to about 650 C. a triester having the formula 0 O C R RC 0 O-CHr-(OHz) n-OH-CHz-O O C R in which each RCOO represents the acyloxy group of a lower fatty acid and n represents an integral number not greater than 5.

6. A process for the production of a monocarboxylic acid diester of hexamethylene glycol, which comprises pyrolyzing by heating within the range of from about 300 C. to about 650 C. a lower fatty acid triester of 1. A process for the preparation of diacetates of nonv a ran e atmospheric pressure an at an elevated temperature in the presence of a hydrogenation" -catalyst to produce a lower iatty acid ;di esten rot hexamethylene glycol, a

7.7.- A. process; r fiOIrf the. production ..of 1monocarboxylici id fi estfi al m t en sel whish sm se py q i h tins w n n esq IQmb 300 rcflto' aoouts650? C'. analkanetriol triestershaying,

inssvh ijchtelach ,RCOQ; represents. the; acylogry, group of a,

logy tiattyacid land In representsanflintegral' number 'not omega-alkanediols and hydrogenating thespyrolysis .prod1 uctrbyaction thereon of molecular hydrogen Zunder'. supep,

atmosphericpressurerandsat elevated temperatures in the 7 .20 carboxylic, acid, diester of'the' polymethylene fglycoljhav r pres er'lce'bfr a hydrogenationrcatalyst to produce .a mono:

ing jth'efs'arne number. of carbon atoms as' saidualkanetriol. i

SWA process for theprcparation of a monocarbbxylic acid di'ester of a polymethylene glycol, which comprises hydrogenating in the presence of a hydrogenation cata-Q lyst .at a temperature and u'nder a pressure-of hydrogen conducive to hydrogenating reactions va product'pro ducedv 9: A process for the preparation of *a' monocarboxylicg'j acid -diester of' liexamethylene glycol which comprises hyclrogen-ating in the presence of a hydrogenation catalyst" aka-temperature within the ran'ge-of from about '40" C." to "aboutBOO" C." 'an'd'under' a pressure of hydrogen of 12 Q-abQ F -PP fl 'WI qua n h. t tbels 9,0 PoundS Pas u e n h m re r d b P r l attemperatures: withinthe range of from about 300i.

toab outjojfi" C. of a fatty-acid trie ster-of a 1-,2 ,6-h exane- V triol and comprisingnatleastmone-rfatty:acid diesterot a;

non-vinylic l ,6 -hexenediol..

10.7 A process for the preparation of amonocarboxylic, acid diester. .of .a non-yinylic: alpha,ornega-alkenediol,s

which comprises 5 :pyrolyz ing a triester selected from vthe. group consisting of (a) triesters of trihydroxyalkanesw in which eachR represents a; hydrocarbon group rcontaine ing' up to 18 carbon atoms and n represents an integral number not, greater vthanS, and] (b)i'fth ose alkyl-s ubjstii I tuted triesters of alphagbeta',omegadrihydroiiyalkanes,

whichralkyl-substituted triesters arereprefsented by then:

foregoing formula When/the hydrogen atom on the fb eta w carbon atom is replaced by ar lower alkyl vgro'u p and j.

from none to one, inclusive,-hydro'gen atom on a difi ent non-terminal carbon-atom of the 'linean'carbo n?chain} ofvthe residue of the unsubstituted alphaibeta-dmega trihydroxyalkane is replaced tbya lower alkylg'roup as the only additional 'substituent and R and n' aredefined as hereinbefore; i

References-Cited'in the -file' of' this'patent UNITEDWSTATESOPATENTS 2,122,812 21 GrolL et aL; \,Ju1y;5, 1938:: 2,251,983', Chitwood Aug'. 12,;194'l i 2,700,656. Emerson etal ;.Jan'.s.,25, 1955 OTHER REFERENCES Frankei CA 3 0,,1740 ,(1936) Goldfarbd CAQ33, 4599x1939 Schniepp et-'al.: J. A..C. S; 67, 5456j(19 ).4 Bried et 211.: .Ind. EngnChemL3 9f, 484,9.l (..1947). Linduska et alJChem. Abst...41(19 .47,) 3580/2;

Wagner and 200k: Synthetic .Or g anic.,Chem. .Wiley

Claims

10. A PROCESS FOR THE PREPARATION OF A MONOCARBOXYLIC ACID DIESTER OF A NON-VINYLIC ALPHA,OMEGA-ALKENEDIOL, WHICH COMPRISES PYROLYZING A TRIESTER SELECTED FROM THE GROUP CONSISTING OF (A) TRIESTERS OF TRIHYDROXYALKANES HAVING THE FORMULA