US2610193A - Cyclic organic compounds - Google Patents

Description

Patented Sept. 9, 1952 2,610,193 r a CYCLIC ORGANIC COMPOUNDS Richard R. Whetstone, Orinda, CaliL, assignor to Shell Development Company, San Francisco, Calif., a corporation of Delaware No Drawing. Application July 1, 1949, Serial No. 102,721

This invention relates to certain novel substituted compounds in the dihydropyran series of compounds, and to a method for their preparation; More particularly, the present invention relates to certain dihydropyran compounds having an oxymethyl group and a hydrocarbyl group directly attached to a single carbon atom of the dihydropyran ring, and to a method for their preparation from alpha-substituted alpha,betaolefinic aldehydes having a hydrocarbyl group substituted on the alpha carbon atom. Certain derivatives of the novel dihydropyran compounds, particularly the correspondingly substituted tetrahydropyran derivatives referred to hereinafter, also fall within the broader aspects of the present invention.

This application relates to subject matter divided from and is a continuation-in-part of my copending application Serial No. 713,455, filed December 2, 1946, Cyclic Organic Compounds, now U. S. Patent No. 2,479,283, issuing August 16, 1949.

The present application relates particularly to dihydropyran compounds having an oxymethyl group and a hydrocarbyl group directly substituted on the carbon atom in the No. 2 position of the dihydropyran ring and corresponding in structure to the structural formula Formula I in which R. represents a member of the class consisting of hydrogen, hydrocarbyl and acyl, R represents hydrocarbyl and R." represents one of the class consisting of hydrogen and hydrocarbyl. Substituted tetrahydropyran derivatives to which the invention relates in its generic aspects correspond in structure to the structural formula -HC/ (EH:

1120 o-cmon Formula II in which R, R and B" have their above significance. Reference will be made hereinafter to a number of specific compounds falling within the generic class of compounds provided by the present invention. Certain of the preferred mem- 16 Claims. (01. 260-333) bers of the class may be mentioned individually here; namely the dihydropyran derivatives 2,5- dimethyl 3,4-dihydro-1,2-pyran-2-methanol, 2- methyl-3,4-dihydro-1,2-pyran-2 methanol, and 2,5-dineo'pentyl-3,4dihydro-1,2-pyran-2-metha- 1101. As preferred compounds represented when R in the foregoing structural formulas represents acyl there may be particularly mentioned esters of lower alpha,alpha-olefinic carboxylic acids, especially the esters of acrylic and methaorylic acids with the dihydropyran methanols represented when R and R" represent lower alkyl groups, such as methyl or ethyl.

In the parent application acknowledged hereinabove, there are disclosed and claimed dihydropyran carbonylic compounds which may be characterized generically as having structures corresponding to the structuralformula H O CCR* Formula IV in which formulas R* represents a member of the class consisting of hydrogen, hydroxy, metaloxy and hydrocarbyloxy, R represents hydrocarbyl, and R" represents a member of the class consisting of hydrogen and hydrocarbyl.

In accordance with the inventions claimed in the aforesaid parent application and in the present application, it has been discovered unexpectedly that compounds of the present class: may be prepared in a highly efficient and effective manner by means of a process which comprises condensing at a suitable elevated temperature and in the presence of a suitable polymerization inhibitor an alpha,beta-unsaturated aldehyde having attached to the alpha carbon atom a hydrocarbyl group linked to said alpha carbon atom via a single bond. Products which may be prepared by such condensation of a1pha,betaolefinic aldehydes substituted on the alpha carbon atom by a hydrocarbyl group comprise compounds having structures defined by Formula III,

been expected that a1pha,beta-unsaturat.ed aliphatic aldehydes having no hydrogen atorn-v directly attached to the alpha carbon atom. would readily undergo condensation reactions of the type of reaction here involved. Unexpectedly", it;

4 chain or a cyclic hydrocarbon group containing one or more olefinic bonds, most desirably the group represented by R is one not readily hydrogenated, i. e., a saturated hydrocarbon group or an aromatic group. Cyclic groups which may be represented by B" may be either saturated cycloaliphatic 'orjaromatic, in'character or less desirably 'cyclo-olefinic in character. Representative unsaturated aldehydes corresponding to the foregoing formula and containing a cycloaliphatic group are alpha-cyclopentylacrolein, alpha-cyclohexylacrolein, alpha-(Z-ethylcyclohexyldacrolein, alpha (3 cyclohexylpropyl) acrolein, and homologs and analogs thereof. As unsaturated aldehydes containing an aromatic group there may be mentioned, for example,

has been discovered that the alpha,beta-unsaturated aldehydes of the present class, not only undergo such condensation reaction in the pres-- ence of a polymerization inhibitor, such as hyylic compounds, and with greater efficiencyand economy of operation, than have been attained in the case of certain related alpha,beta-unsaturated aldehydes heretofore employed. The products that may be prepared by aprocess compris ing such condensation. of the present classof alpha,beta-unsaturated aldehydes possess unique and unexpected properties that distinguish them in several respectsfrom compounds heretofore known, and. that-render them of corresponding advantage in the arts, r

The unsaturated aldehydes which may be employed in accordance with the process of f the present invention for the production of valuable new oxymethyl-substituted hydropyran compounds are those unsaturated aldehydes that have an olefinic bond in the alpha, beta position relative to the carbonyl group and that have attached to the alpha, carbon atom a singly bonded hydrooarbyl group. The advantages of the invention are most effectively realized by application in the process of those unsaturated aldehydes having structures corresponding to the formula RD oHi=c :cHo

Formula V wherein R signifies a hydrocarbyl group. The hydrocarbyl group may be. either an open chain hydrocarbon group or a cyclic group, such as a cyclic non-aromatic hydrocarbon group or an aromatic hydrocarbon group. It is particularly p-referredto employ those aldehydes whereinthe hydrocarbon group substitutedon the alpha carbon atom is an alkyl group, preferably one containing from one to 10 carbon atomsinclusive.

" Representative unsaturated aldehydes which may be employed according to the invention for the preparation of the novel compounds of the invention include the alpha-alkyl acroleins, such as. alpha methylacrolein, alpha ethylacrolein, alpha propylacrolein, alpha isopropylacrolein, the alpha-butylacroleins, the alpha-pentyle acroleins, the alphaehexylacroleins, the alphaheptylacroleins, and homologous and analogous unsaturatedaldehydes having an alkyl group attached to the carbon atom in the alpha. position. Althoughthere may be employed unsaturated aldehydes corresponding to the immediately foregoing formula when R" signifies an open alpha-phenylacrolein, alpha-tolylacrolein, alphabenzylacrolein, alpha (2 phenylethyDacrolein and homologs and analogs thereof corresponding to the immediately foregoing structural formula.

The. hydrocarbon group that may be represented by R in the foregoing formula may be either substituted or unsubstituted provided the substituent groups thereon, if any, are non-reactive under the conditions employed in the present process and are not in a position in the molecule such that they would affect unfavorably the reactivity of the molecule. as. a whole inits'application in the present process. Substituent groups which thus may be present include, for example, halogen, carbonitrile, ethereal oxygen, etc. r

When a single unsaturated aldehyde of the foregoing class is employed in the process of the invention, the product obtained .by con.- densation thereof is a dihydropyranco-mpound corresponding in structure to structural Formula III, when R" and R" represent the same. substituent grouping, i. e., both R and R represent the same hydrocarbyl group, and.R* represents the hydrogen atom. When there isv employed instead of a single unsaturated aldehyde of". the foregoing formula a mixture of two or more unsaturated aldehydes havingtstructures repre sented by the formula, thereiareobtained compounds corresponding in structure to Formula III, when R and R represent different-1 substituent groups within the defined classes of substituent groups, 11* again representing hydrogen. When, instead of a mixture of two or more aldehydes corresponding to the foregoing formula, there is employed a mixture comprising, for example, acrolein and an aldehyde of the foregoing formula, there are obtained in excellent yields compounds corresponding in structure to Formula III, when R and RN again represent different groupsor atomsbut one. of R and R represents hydrogen. In this case, R again represents hydrogen. The condensa tion according to the process of dissimilar alpha,beta-unsaturated aldehydesfat least one of which corresponds in structure to Formula V, provides a highly eiiicient method of preparaldehydes. Although highly advantageousiresults may be obtained when acrolein is employed as the second unsaturated aldehyde, it is preferred that both 01 the unsaturated aldehydes be: members of the herein definedclass...

According to theprocess of the. present in vention, one or a mixture of aplurality of unsaturatedaldehydes as defined aboveis condensed at an elevated temperature in'thepresence of a suitable polymerization inhibitor to produce dihydropyran compounds correspond.- ing to Formula III, when R* irepresents-hy-r drogen. As the polymerization inhibitor, there maybe employed any suitable compound or material of the class known to the art as anti oxidants or polymerizationinhibitors, which is inert under the existing conditions with respect to reaction with the unsaturated aldehyde or aldehydes and the products of the. condensation reaction. Polymerization inhibitors which may be employed according to the invention include, for example, quinones, amines, phenolic compounds, nitro-aryl compounds, mercaptans, and the like. Hydroquinone is highly efiective. Compounds which may be employed in place of hydroquinone include benzoguinone, naphthoquinone, phenol, the cresols, a naphthol, a xylenol, thymol, catechol, eugenol, resorcinol, pyrogallol, orcinol, guaiacol, nitrobenzene, di *nitrobenzene, a nitrophenol, anitrosophenol or the like. Inorganic inhibitors which may be employed include, for instance, halogens, copper and alloys thereof, sulfur, selenium, and tellurium. Inorganic elementssuch as the foregoing also may be present in combined form in organic molecules, as in polysulfides, thioacids, selenoacidaetc. I l

The amount of polymerization inhibitor that is employed is a minor amount sufiicient to inhibit or to prevent the formation of higher polymeric products of reaction under the conditions of reaction. The exact amount that is most suitable depends upon the particular polymerization inhibitor employed, the conditions under which the reaction is efiected, the particular reactants involved and similar factors. Frequently, only a trace of polymerization inhibitor is necessary. Generally speaking, amounts of polymerization inhibitor of from about 0.01,to about by weight of the unsaturated aldehyde or aldehydes are effective. Amounts of hydroquinone, for example, of from about 0.025 to about 2% are particularly effective. I The condensation of the unsaturated aldehyde may be effected in the presence of asuitable inert organic solvent, if desired, although particularly advantageous results have been obtained byconducting the condensation in the absenceof any added solvent. As the solvent, there may be employed an aromatic hydrocarbon, such as benzene, toluene, xylene, ethylbenzene, or mix-. tures of aromatic hydrocarbons; an aliphatic hydrocarbon such as octane, a nonane, or. other aliphatic hydrocarbons that are liquid ,under the conditions employed; an ether, such as dig ethyl ether, dipropyl ether,.diisoamyl ether; a heterocyclic compound, such as dioxane, furan, etc.; 'and the like. Mixtures of solvents maybe employed if desired. Benzene is particularly satisfactory as the solvent if. one is employed. There may be employedupto about 10 parts of solvent per part of aldehyde, preferablyup to about 2 parts of solvent per part of aldehyde. I Dihydropyran carboxaldehydes according .to Formula III may be prepared by heating the olefinic aliphatic aldehyde of the present, class,

nickel, chromium, etc. vessel generally is preferable because of possible: catalytic effects of metallic impurities in promoting side-reactions, extensive polymeriza- 6 or mixture of olefinic aldehydes comprising ran aldehyde of the present class, at an elevated temperature under suflicient pressure to. main! tain the reaction mixture'in the liquid state. Temperatures of from about 50 C. to about 240 C. maybe used, in general, although at times either somewhathigher or somewhatlower temperatures may be employed satisfactorily. I The preferred range of temperature depends in part upon the particular unsaturated aldehyde used. Temperatures from about C. to about 240 0., preferably from about C. to about 200 (2., generally are employed. Temperatures sufficiently high to promote excessive decomposition of reactants or reaction. products should be avoided. The reaction preferably is effected under superatmospheric pressure, although with higher boiling reactants and reaction prod-I- u'cts, atmospheric or lower pressures maybe employed. In any case, however, the pressure is maintained at or above the total vapor pressure'of the reaction mixture at the. tempera.- ture of reaction. Pressures sufficient to maintain the liquid state and from atmospheric pres.- sure up to about 3000 pounds per squarewinch thus may be employed. Preferably, the pressure is maintained between about 500 pounds per square inch and about 2000 pounds .per

square inch. If superatmospheric, the pressure conveniently may be. autogenous as in a closed reaction vessel, or it may be applied by introduc-'- tion of a suitable inert gas such as nitrogen, carbon dioxide, methane, ethane, propane-etc mm the reaction vessel. Oxygen desirably is excluded from the reaction vessel; I z.

The reaction time may be varied over relatively wide limits. Higher temperatures ofreaction generally enable the use of shorter reaction times. Reaction times of from about ,4; hour or less to 24 hoursor more have been employed. Underthe optimum conditions of reaction, satisfactory completion of the reaction ordinarily is obtained with a reaction time of from about /4 hour to about 2 hours. l r

The process of the invention may be executed either batchwise, intermittently, or continuously- For batchwise operatiomthe polymerization inhibitor and the organic solvent, if one is employed, may be mixed with the unsaturated aldehyde reactant or reactants, and the resultant mixture heated to a suitable temperature and under pressure adequate to maintain theliquid phase, for a time suflicient to complete the re: action. The reaction preferably is ,carriedout F in a reaction vessel which may be, either glass lined or constructed of stainless steel, iron, ,carhon-steel, or alloys of metals such as copper, A glass-lined reaction tion, etc. In continuous operations, particular advantages are realized by efiecting; the reaction reaction tube maintained at a temperature with- 'innthe, range of suitable reaction temperatures,

the dimensions of the tube and the rate of flow of the reactant stream being so correlated as to obtain adequate residence time of the reaction mixture at the reaction-temperature. It

willbe appreciated, however, that the process is not limited according to the particular@aipricarboxaldehydes paratus that is employed, and a wide variety of equipment apparent to those skilled in the art may be used with advantageous results. After completion of the reaction, the substituted dihydropyran-2-carboxaldehydes provided thereby may be recovered from the reaction mixture in any suitable way desired. Fractional distillation under reduced pressure is eminently satisfactory as a method of recovery. Other methods, such as treatment with selective solvents, may be employed. If desired, any unreacted aldehyde or aldehydes may be separated from the reactionmixture and recycled through the process. 1 The solvent, if one is employed, likewise may be reused. As recovered, at least those products formed from the lower molecular weight unsaturated aldehydesv are liquid, highboiling materials. They may be'further purifled;-if desired, by redistillation or by any other suitable means either chemical orphysical. Products which may be prepared according to the present process from a single unsaturated aldehyde of the herein defined class comprise those compounds having apparent structures definedby'Formula 'III when signifies hydrogen and R. and R both represent for example, methyl, ethyl, propyl, isopropyl, butyl, hexyl, or the like, or cyclic groups such as phenyl, xylyl, tolyl, cyelohexyl, ,cyclopentyl. phenethyl, cyclohexylmethyl, methyl-cyclohexyl, Z-cyclohexylpropyl, or homologous ,or analogous groups. a

Whentwo unsaturated aldehydes are employed in the presentprocess, there may be obtained products comprising substituted dihydropyran corresponding in apparent structure to Formula III when R and-R" differ from each otherv For example, when an aldehyde of the present class is reacted with acrolein, there may be obtained as products'compounds cor'respondingin apparent structure to Formula III when oneof R and R" represents hydrogen and the other represents, for example, methyl as in the products prepared by reaction of methacrolein with acrolein, ethyl as in the products prepared by reaction of alpha-ethylacrolein with acrolein, and the like. When, as in a preferred case, there are employed two unsaturated aldehydes-both of which are of the hereindefined class, there may be obtained as products dihydropyran carboxaldehydes corresponding in apparent structure to Formula III when R and R both represent hydrocarbyl but differ from each other. Representative of these products are the-compounds wherein R and R represent, both respectively and inversely, methyl and ethyl asiir'the'reactionproducts of methacrolein and ethacrolein, methyl and isopropyl asin the reaction products of 'methacrolein and "alpha-isopropylacrolein, and analogous products of'the reaction of analogous pairs of aldehydes of the present class. Mixtures of more than two aldehydes comprising at least one aldehyde of the present class of aldehydes may be employed, if desired, although preferably a maximum of two aldehydes is employed in order to facilitate separation and/or recovery of any products that maybe desired in a relatively pure form. It unexpectedly has been discovered in accordance with the present invention that substituted dihydropyran aldehydes corresponding in structure to Formula III may be converted to substituted dihydropyran oxymethyl compounds represented by Formula I by treatment of the substituted dihydropyran aldehydes corresponding to Formula III with a strong alkali, such as a caustic alkali, to cause intermolecular oxidative-reductive reaction resulting in the formation. from two molecules of the dihydropyran aldehyde of one molecule of the corresponding dihydropyran methanol and one molecule of the corresponding dihydropyran 'carboxylic acid. Ordinarily, yields of the dihydropyran oxymethyl compound in excess of of-theory may be obtained; Suitable alkalies which may be employed include,'for example, sodium'hydroxide, potassium hydroxide, lithium'hydroxide, and the like. The desired reaction may be accomplished by treating the dihydropyran carboxaldehyde with the alkali, pref,- erably in the form of a concentrated aqueous solution. There preferably is employed an aqueous solution of a caustic alkali or a mixture of caustic alkalies having a'concentr-ation of from about 20% toabout 50% by weight. Temperatures of from about 15 C. to about 0., preferably from about 40 C. to 80 0., desirably are employed." Amounts of the caustic alkali upwards from about 0.2 mole per mole of the dihydropyran carboxaldehyde may be employed. Preferably there are employed between about 0.5 and about 5 moles of caustic alkali per mole of the dihydropyran carboxaldehyde. Reaction may be effected by mixing the solution of caustic, alkali with the dihydropyran carboxaldehyde as by gradually adding the caustic soluticnto the aldehyde with agitation. The reaction ordinarily will be conducted in a suitable reaction vessel equipped with means for controlling the temperature, such as a-jackete d vessel or a vessel equipped with internally located cooling coils. The reaction time required may vary from a few minutes to several hours, depending upon the reactants involved and the conditions of the reaction. When the alkali solution has been slowly added to the dihydropyran carboxaldehyde, the reaction frequently will be substantially completed by the time the alkali has been added.

After completion of the reaction, the oxymethyl dihydropyran compound may be recovered from the reaction mixture according to any appropriate method. Ordinarily it will be separated from the alkali salt of the dihydropyran carboxylic acid formed as a by-product by treatment of the crude reaction mixture with a selective solvent. The crude mixture thus may be treated with water to dissolve the carboxylic acid salt. The oxymethyl dihydropyran compound may be recovered from the water-insoluble residue as by fractional distillation, steam' distillation, extraction by treatment with an organic solvent or other suitable methods. 7 The aqueous'solution of the alkali salt of the dihydropyran carboxylic acid may be extracted by treatment with an organic solvent to recover any oxymethyl dihydropyran compound dissolved or dispersed therein. In other cases, the crude reaction mixture may be extractedby treat ment with a water-immiscible organic solvent,

such as a hydrocarbon solvent, to extract theoxy methyl dihydropyran compound and the desired product may be recovered from the extract by suitable methods, such as fractional distillation.

In accordance with the invention, oxymethyl hydropyran compounds corresponding in structure to Formulas I and II maybe prepared by hydrogenation of dihydropyran aldehydes corresponding in. structure to Formula'III, by treatment with molecular hydrogen in the presence of a hydrogenation catalyst. As the catalyst, any suitable metal or compound of a metal falling within the class known to the art as hydrogenation catalysts, may be employed. Representa- 9 tivemetals and compoundsof metals falling within this class are, for example; nickel, siron', cobalt, copper, silver, molybdenum, tungsten, vanadium, platinum, paladium, gold, tin, and the like, and compounds thereof, such as the ,catalytically active oxides, etcx Mixtures. or alloys of suitable metals maybe employed ashydrogenation. cat

alysts. Mixtures of suitable compounds ,ofmetals may. also be employed. ,Itsurprisingly has been discoveredthat the formylgroup: of the hereindescribed dihydropyran .aldehydes may, be preferentially converted to an oxymethyljorinethylol groupwhile avoiding substantial saturation of the multiple bond of the heterocyclic ring by conducting the hydrogenation in the presenceparticularly of base metal hydrogenation catalysts at-an elevated temperature and under a superatmospheric pressure, of hydrogen. By employingmore severe conditions of hydrogenation, that is higher temperatures and higher pressures of; hydrogena tion, saturation of the heterocyclic ring to produce oxymethyl tetrahydropyran compounds corresponding to Formula-II. also may be attained. Although the hydrogenpressures may be ,varied widely, hydrogen pressures of from about 50 pounds per square inch to about 10,0Q pounds pensquare inch ordinarily will be employed, apre ferred range being hydrogen pressures of from about 50d pounds per squareinchtoabout 2 500 pounds per square inch, Temperatures offrom about 20 C; to about 150 C. ordinarily will be employed, althoughitemperatures as high as 250 C. may be operable. 'For, the preparation of (11'', hydropyran oxymethyl compounds according to Formula I, it is particularly preferred? to employ a nickel hydrogenationcatalys't, such as the well known Raney nickel catalyst, and to conduct the hydrogenation at temperatures preferably within the range of from about 25 C. to about 75 C. and at hydrogen pressures of from about 500 pounds per square inch to about 2000 pounds per square inch. For the preparation of tetrahydro pyran oxymethyl compounds according to Formula II by hydrogenation in the presence of Bailey nickel of dihydropyran aldehydes accordmg: to Formula III, "hydrogen-pressures of from about 500 to: about 2000 pounds persquare inch and temperaturesfromabout C. to about 140 Cia're' preferred, I 'Ihe hydrogenation may be effected according to any suitable method, as continuously, intermittently, or batchwise. Thematerial tobe hydrogenated may, if desired, be dispersed or dissolved ina suitable organic solvent such as anydrocarbon; an ether, an alcohol, etc. Amounts of thesolvent from about part to; about 5 "parts by weight per part or the dihydropyran aldehyde ordinarily are satisfactory, After completion of the hydrogenation, the catalyst may be removed by filtration or other effective means and the re-f sulta'ntmixturesepafated into its components by fractionaldistillationiby treatment with selective s'olvents, or mother suitable ways. f 'Tetrahydropyran oxymethyl compounds according-to Formula II may be prepared by hydrogenation of corresponding dihydropyran oxymethyl compounds according to Formula I,

Representative substituted dihydropyran methanols embraced within the invention include, among others, the following: 2-methy1-3,4-dihydro-LZ-pyran-Z-methanol; 2,5 dimethyl-3A-dihydr -t vra et a l 2-, t la3e e h d 19,:L r yr nr han i.2 d am-ter s- IQ= y an 2 :meth 2 -d s pr pyle3i dihydro-l,2-pyran 2-methanol; 2 -isobutyl-5 -eth- 2,5 diphenfyl-BAi-dihydro-l,2-pyran-2 methanol, 2,5 dicyclohexyl-3,4rdihydroa1,2epyran-2 meth anol, 2,5 -dioctyl-3A-dihydro-1,2-pyran:2-meth+;

anol, and 2,5-dimethoxyphenyl 3,4-dihydro-1,2 pyran-Z-methanol. -1 Particularly, valuable and preferred are the substituted 3,l,-.-dihydro-l,2 pyran-Z-methanols which are described'by FQrmula I and which contain like lower alkylsubstituents in the 2 and 5 positions of the dihydropyranring; 1 Corresponding tetrahydropyran oxymethyl compounds are ,asll follows: 1 2-methyltetrahydropyran-2-methanol, 2,5-dimethyltetrahydropyran 2 methanol, 2 ethyltetrahydropyran-2, meth-i anol, 2,5- diethyltetrahydropyran 2 -"methanol,

2,5-diisopropyltetrahydropyran-2emethanol, 2-. I isobutyl- 5 -ethyltetrahydropyran- 2 -methanol,'

2,5-di t-butyltetrahydropyran-2-methanol, 2,5- dineopentyltetrahydropyran-2-methanol, 2,5,- di'. phenyltetrahydropyran-2-methanol, 2,5-dicyclo hexyltetrahydropyran-2-methanol', 1 2,5-diocty1-. tetrahydropyran-2-methanol, and 2,5-dimethoxyphenyltetrahydropyran-2emethanol. .Particularly valuable are the substituted, tetrahydropyram Z-methanols which contain like lower alkyl substituents in the 2, and 5 positions and are represented. in structure by Formula ,II. Esters of the foregoing and the analogous and homologous clihydropyran and tetrahydropyran meth'anols with carboxylic'or other acids may be prepared according to known procedures, for ex: ample,.by reaction betweenthe dihydropyran or tetrahydropyran methanol and the .acid. anhydride, or theacid chloride, the acidanhydride being preferred. The estersof the alcohols: of the invention with acids. such as acetic. acid, pro-. pionic acid, butyric. acid, caproic'acid,;lauric acid, ,stearic acid, benzoic acid, ,naphthoicxacid, acrylic acid, 1methacrylic acid,y crotonic :acid, pelargonic acid, octenoic acid, 1,3-butadiene-lcarboxylic acid, oleic, acid, succinic 'acid, adipic acid, glutaric acid, rchlorobenzoic acid, 9 betaethoxypropionic, acid, and like carboxylic .acids are included withinthe invention. For. many purposes, the esters in which the acyl radicalderived from the carboxylic acid contains, in addition to the carbonyl oxygen atom, only atoms of. carbon and of hydrogen are particularly preferred. Representative esters of the'invention are: 2.5. .-.'.dimethyl 3 ,4 dihydro 1,2 pyran-2- methanol acetate; -2,5-dimethyl-3,4-dihydro-L2- pyran-2-methanol isob'utyrate, 2,5-dimethyl-3A- dihydro 1,2 pyrana- 2 I-=methanol acrylate, 2 methyl-3l4-dihydro-1,2-pyran-2-benzoate, 2,5-dia ethyl-3,41-dihydro-L2-pyran#2-methano1 laurate, 2,5-dimethy1 3,4 dihydro-1,2-pyran-2 methanol phthalate, 2,5 dineopentyl-3,4--dihydro 1,2-pyran-2-methanol oleate, 2,5-dineopenty1-3,4-dihydro-1,2-pyran stearate', 2-methyl-5-ethyl--3,4-dihydro-1,2-py'ran crotonate, 2,5-diisopropyl- 3A-dihydro-lg pyran zkmethanol furoate," z' isopropy l-gb b f' fd h q e- P he meth acrylatej The corresponding; compounds saturated in the pyran'ring may bepreparedf] Ethers of the novel dihydropyran andtetrahydropyran methanols, which ethers are represented by Formulas I and II, respectively, when R represents a hydrocarbon group which may be substituted, include the ethers with monohydric and dihydric alcohols, such as the methyl, ethyl, propy is ro benzyl, y o xy bh h vinyl, allyl crotyl, imethallyl, 2- ethoxyethy1 ,and

' improved polymers.

3-hydroxypro'pyl ethers and homologs and ana-, logs thereof.

Representative ethers included by the invention are as follows: 1,2-pyran-2-methyl ethyl' ether, 2,5-dimethyl- 3,4 dihydro 1,2 pyran 2 methyl propyl ether, 2- methyl 3,4 dihydro 1,2 pyra-n- 2 methyl chloroethyl ether, 2,5 diisopropyl-3,4-dihydro-1,2-pyran-2-methyl ethoxyethyl ether, 2,5 dibutyl 3,4 dihydro 1,2 pyran 2- methyl phenyl ether, 2,5-dimethyl-3,4-dihydro- 1,2-pyran-2-methyl naphthyl ether, 2,5-dineopentyl -3,4- dihydro -1,2- pyran -2- methyl allyl ether, 2 methyl-5-ethyl3,4-dihydro-1,2-pyran- Z-methyl methallyl ether and 2,5-dibutyl-3,4-dihydro-1,2-pyran-2-methyl lauryl' ether. The corresponding tetrahydropyran ethers may be prepared and are embraced by the generic invention.

The novel heterocylic alcohols to which the invention relates are of value as special solvents, plasticizers and as chemical intermediates. The alcohols are of interest as raw materials for the preparation of useful amines obtainable by replacement of the hydroxyl group by an amino nitrogen atom which may be, for example, unsubstituted or Which may have one or both of the hydrogen atoms replaced by an alkyl, aryl, alkaryl, or olefinic group. Ethers of the new alcohols, for example, with lower monohydric saturated aliphatic alcohols, are of particular interest as special solvents. The ethers with higher alcohols, for example, the ethers with alcoholsof the aliphatic type containing from to 18 carbon atoms are of potential value as plasticizers and as softening agents, for example, in the treatmentof leather. Esters of the novel alcohols with alpha-methylene carboxylic acids, par- 2,5-dimethyl-3,4-dihydro-.

ticularly of the aliphatic type, are useful as resin intermediates from which there may be prepared Esters of the novel alcohols with saturated aliphatic carboxylic acids may be employed as plasticizers, as special solvents, and as chemical intermediates.

vThe following examples will serve to illustrate certain specific embodiments of the present invention. w

Example] Preparation 0 2,5 dimethyl-.S'A-dihydro-LZ- pig ran 2 carboscaldehyde. Methacrolein con taining 1% by weight of'added hydroquinone was dissolved in an equal weight of benzene and-the solution was heated at 170 C. for 3 hours under the autogenous pressure-in a glass lined reaction vessel. Upon fractional distillation of the resulting mixture, 2,5-dimethyl-3,4-dihydro-1,2- pyran-Z-carboxaldehyde was recovered as a.'frac-. tion boiling at101 C. to 101.4 C. under a pressure of 90 millimetersof mercury. Conversion, 77%, yield, 94%. The product was found to have a refractive index 5 of 1.4537. Itwas found to contain 68.43% carbon and 8.66% hydrogen compared to theoretical values of 68.54% carbon and 8.63% hydrogen. The structure formula for 2,5 dimethyl 3,4-dihydro-1,2-pyran- 2-carboxaldehyde is g o CEO The compound which is referred to as 2,5 dimethyl-BA-dihydro-1,2-pyran 2 carboxaldehyde may also be named as 2,5-dimethyl2- formyl-2,3-dihydropyran.

Example II Preparation of Z-methyl 3,4 dihydro 1,2- m/ran-2-carboxaldehyde.A mixture of '1700 parts of methacrolein and acrolein present in'a 1:2.6 molar ratio containing 1% of hydroquinone was passed in a continuous stream through a stainless steel tube having a free space of 185 cubic centimeters at a flow rate of 1.85 volumes of feed per hour per volume under a pressure of 620 to 720 pounds per square inch. Prior to introduction into the reactor, the stream was preheated to 210 C. and a reactor temperature of 210 C. was maintained by externally located electrical heaters. The reactor effluent was collected and distilled. A fraction boiling between 78 C. at millimeters mercury pressure and 584 C. at 16 millimeters mercury pressure was separated in the amount of 502 parts. By redistillation of this fraction there was obtained 330 parts of 2-methyl-3,4-dihydro-1,2-pyran-2-carboxaldehyde boiling at 844 C. to 85.5 C. under a pressure of 90 millimeters of mercury and having a refractive index of 1.455 to 1.456. The semicarbazone of the 2-methyl-3,4-dihydro-1,2 pyran-z-carboxaldehyde was prepared and after recrystallization was found to contain 22.3% nitrogen and 51.9% carbon. Theory for v C'sHisOzNs 22.9% nitrogen and 52.4 carbon. The struc-,

CHO

Example III Preparation of 2,5-dimethyl3,4-dihydr0-1,2- pyran-Z-methanoL-One hundred seventy-nine parts of sodium hydroxide in the form of a 40% aqueous solution was added in hour to 300 parts of 2,5-dimethyl-3,4-dihydro-1,2- yran-2- carboxaldehyde while the mixture was held {by cooling at 40-50 C. The nearly solid resulting mixture was diluted with 300 parts of water and extracted with portions of diethyl ether totalling 1000 parts. The combined ether extract was dried and distilled. After separation of the ether, parts of 2,5-dimethyl-3,4-dihydro-1,2-pyran- 2-methanol. distilling at 75.8-79.6 C. under a pressure of 7-8 millimeters of mercury wererecovered. The refractive index of the 2,5-dimethyl-3,4-dihydro-1,2-pyran-2-methanol was found to be 1.4733. The product was found to contain 67.53% carbon and 9.90% hydrogen compared to calculated values of 67.57% carbon and 9.92% hydrogen; The structural formula for 2,5-dimethyl-3,4-dihydro-1,2-pyran-2-methanol is The compound which is referred" to as 2,5-dimethyl-3,4-dihydro-1,2-pyran-2-methanol may also be assigned the name 2,5-dimethyl-2-h'ydroxymethyl-2,3--dihydropyranL Example IV Preparation 1 of Z-methyl 3,4 e dihydro-1,2- pyran 2 methanoZ.-2-methyl-3,4-dihydro-1,2- pyran-2-carboxaldehyde was treated with sodium hydroxide according to the method of Example III. 2-methyl3,4-dihydro-1,2-pyran-2-methanol wasseparated from the resulting mixture by extraction with diethyl ether and distillation of the dried extract. 2-methyl-3,4-dihydro-1,2-pyranq 2-methanol was found to have a boiling. point of 75 C, under 10 millimeters mercury pressure and a refractive index of 1.4752. Analysis verified the empirical formula 071-11202 for the product. The structural formula for 2-methyl-3,4-dihydro-1,2- pyran-z-methanol is Example V Preparation of 2,S-dimethyltetrahydroprjran-Z- methanoZ.--To 187 parts of 2,5-dimethyl-3,4- dihydro-1,2-pyran-2-carboxaldehyde there were added 10 parts of Raney nickel. catalyst. The mixture was hydrogenated by treatment with molecular hydrogen under a pressure of 800 to 1700 pounds per square inch at a temperature of 100 C. to 125 C'. After 22 hours no further hydrogen was absorbed. The catalyst wasremoved by filtration and the filtrate distilled in vacuo. There were obtained 156.5 parts of 2,5- dimethyltetrahydropyran 2 methanol distilling at 82.8-83.6 C. under 10 millimeters mercury pressure. The product was found to contain 66.57% carbon, 11.20% hydrogen and to have a hydroxyl titre of 0.688 equivalent per 100 grams compared to calculated values of 66.63% carbon, 11.18% hydrogen and 0.694 equivalent of hydroxyl per 100 grams. The structural formula for 2,5- dimethyltetrahydro-2-methanol is HaC-HC C'Hz 112C C-CHs 0 onion Example VI Preparation of 2,5-dimethyl-3,4-dihydro-1,2- pyran-.Z-methanol and 2,5-dimethyltetrahydropyran-Z-methanol.0ne mole of 2,5-dimethyl- 3,4-dihydro 1,2 pyran 2 carboxaldehyde was treated with hydrogen under a pressure of 1000 pounds per square inch at 25 C. to 55 C. for 14 hours in the presence of by weight of Raney nickel catalyst. The products of the hydrogenation were separated by distillation of the filtered mixture. 2,5-dimethyl-3,4-dihydro-1,2- pyran-2-methanol and 2,5-dimethyltetrahydropyran-Z-methanol were obtained.

14 Example VII 2-methyZ-3,4-dihpdro 1,2 pyran-z-methanoi acetate.--2-methyl 3,4 dihydro 1,2 pyran-2- methanol acetate, which may be prepared by esterification of 2-methyl-3,4-dihydro-1,2-pyran- 2-methanol by treatment with, for example, acetic anhydride, has been prepared and found to have the following characteristics:

Boiling point (1 millimeter mercury pressure) C'.. 60-63 Refractive index (n 1- 1.457 Specific gravity (20/4) 1.049

Ewample VIII Preparation of 2,5-dineopentyl 3,4 dihydro- LZ-pyran 2-carboxaldehyde.--Alpha-neopenty1 acrolein was condensed according to the method illustrated in Examples I and II by heating in a stainless steel bomb for one hour at 165-190 C. Crude 2,5-dineopentyl-3,4-dihydro-1,2-pyran-2 carboxaldehyde was recovered by rapid distillation of the resulting mixture with collection of the fraction distilling between 98 C. and C. at about 1 millimeter of mercury pressure. lBy redistillation of this fraction there was obtained purified 2,5-dineopentyl 3,4-dihydro-1;2-pyran- 2-earboxaldehyde distilling at 91.4-91.6 C; under a maximum pressure of 1 millimeter of mercury. Analyses of the purified product were as follows: 76.1% carbon, 11.2% hydrogen and 0.41 equivalent carbonyl per 100 grams were found compared to calculated values of 76.2% carbon, 11.2% hydrogen and 0.40 equivalent carbonyl per 100 grams.

Example IX Preparation of 2,5-dineopentyl 3,4 dihydro- 1,Z-pyran-Z-methanol.-Ninety-two parts of 2,5- dineopentyl-3,4-dihydro-1,2-pyran-2-carboxaldehyde were dissolved in 100 parts of methanol and placed with 9 parts of Raney nickel hydrogenation catalyst in a hydrogenation bomb. The mixture was hydrogenated at C. under 700 to 1200 pounds per square inchhydrogen pressure. Distillation of the filtered solution iledto the separ'ationof 36 parts of product distilling at -135 C. under 2 millimeters mercury'pressure. 2,5-dineopentyl-3,4-dihydro-1,2-pyran-2- methanol has the structure H2 CIEHB /C\ CHa-CCH (I? (3H1 CH: HO O-GHIOH The structural formula of 2,5-dineopentyl-3,4- dihydro-1,2-pyran-2-carboxaldehyde is The claimed invention is: 1. As a new chemical compound, a member of the class consisting of (1) the dihydropyran de- 15" rivatives having structures corresponding to the formula I v H2 when R. represents one oi the class consisting of hydrogen, hydrocarbyl, and acyl residues of carboxylic acids, R represents hydrocarbyl, and R" represents one of the class consisting of hydrogen and hydrocarbyl, and (2) the tetrahydropyran derivatives having structures corresponding to the formula when}: represents one of the class consisting of hydrogen, hydrocarbyl, and acyl residues of carboxylic acids, R represents hydrocarbyl, and R" represents one of the class consisting of hydrogen and hydrocarbyl. V I

2.-'As new chemical compounds dihydropyran derivatives having structures corresponding to the formula in'which R, and R. represent like alkyl groups.

3. 2,5-dimethyl-3,4-dihydro-1,2-pyran-2-methanol.

4. 2,5-dimethyltetrahydropyran-2-methanol. 5. 2,5-dialkylteterahydropyran-2-methanol.

6. An ester of an unsubstituted aliphatic mono-i carboxylic acid and a 2,5-dialkyltetrahydropyran- Z-methanol.

'7. An ester of an unsubstituted aliphatic carboxylic acid and a 2,5-dialkyl-3,4-dihydro-L2 pyran-Z-methanol. I H V v 8. An ester of an unsubstituted aliphatic carb'oxylic acid and 2,5-dimethy1-3,4-dihydro-1,2- pyran 2-methano1.

16 V 9.;An ester of an unsubstituted aliphatic carboxylic acid and 2,5-dimethyltetrahydropyran 2- methanol. l V l 10. The process of preparing 2,5 dimethyl-2-' hydroxymethyl-2,3-dihydropyran which comprises reacting one mole of 2,5-dimethyl-2 formyl-2,3-dihydropyran with one mole of hydrogen in the presence-of a hydrogenation catalyst.

11. The process of claim 10 in which the catalyst is a' 'copper-containing hydrogenation catalyst.-

1 2'. The process of claim 10 in which the catalyst is a nickel hydrogenation catalyst;

13. A process for the preparation of i2,5-dimethyl-3,4 dihydro-l,2-pyran-2-methano1 by hydrogenation of 2,5dimethyl-3,4 -'dihydro-1-,2 pyr-an-2-carboxaldehyde which comprises hydro genating said 2,5 dimethyl 3,4 dihydro-1,2- pyran-2-carboxaldehyde by treatment with hydrogen gas at a pressure-of from about 500 pounds per square inch to about 10,000-pounds per square inch at a temperature from about 20 C. to about 150 C. in the presence of Raney nickel hydrolyst is a nickel hydrogenation catalyst.

V RICHARD R. WHETSTONE.

REFERENCES CITED The following references are of record in the file of this patent: g

. FOREIGN PATENTS Number Country 7 Date I 913941 France June '11, 1946

Claims (1)

1. AS A NEW CHEMICAL COMPOUND, A MEMBER OF THE CLASS CONSISTING OF (1) THE DIHYDROPYRAN DERIVATIVES HAVING STRUCTURES CORRESPONDING TO THE FORMULA