Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C29/00—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring
  • C07C29/132—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring by reduction of an oxygen containing functional group
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C29/00—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C29/00—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring
  • C07C29/60—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring by elimination of -OH groups, e.g. by dehydration
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C31/00—Saturated compounds having hydroxy or O-metal groups bound to acyclic carbon atoms
  • C07C31/18—Polyhydroxylic acyclic alcohols
  • C07C31/20—Dihydroxylic alcohols
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C45/00—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds
  • C07C45/002—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by dehydrogenation
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C45/00—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds
  • C07C45/61—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by reactions not involving the formation of >C = O groups
  • C07C45/65—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by reactions not involving the formation of >C = O groups by splitting-off hydrogen atoms or functional groups; by hydrogenolysis of functional groups
  • C07C45/66—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by reactions not involving the formation of >C = O groups by splitting-off hydrogen atoms or functional groups; by hydrogenolysis of functional groups by dehydration

Definitions

• citronellal and citron-' ellol which compounds are not only valuable as constituents of flavor and perfume compositions, but are also valuable as intermediates for synthesis of many other compounds useful as flavors and perfumes.
• citronellal is converted to menthol and hydroxycitronellal.
• Citronellol is esterified with the lower carboxylic acids to produce esters valuable in formulating perfumery products.
• Alphaand beta-pinenes are readily available from domestic turpentines and can be hydrogenated to pinane.
• Pinane yields 2,6-dimethyl-2,7octadiene or pyrolysis; Pines, ]'.A.C.S., 76, 4412 (1954).
• This acyclic diene can be converted to 2,6-dimethyl-7-octene-2-yl compounds according to the methods described in Serial No. 576,795, filed April 9, 1956, now US. Patent No. 2,902,510.
• These 2,6-dimethyl-7-octene-Z-yl compounds can be converted to 7,8-epoxy-2,6-dimethyl-octan-Z-yl compounds by methods described in Serial No. 576,794, filed April 9, 1956, now US. Patent No. 2,902,495.
• Another object is to provide a method for producing citronellal, hydroxycitronellal, citronellol, hydroxycitronellol, isomers thereof and esters and ethers of the alcohols.
• a further object is to provide a method for converting certain alcohol derivatives of 2,6-dimethyl-octane to the corresponding carbonyl analogues.
• An additional object is to convert citronellol and hydroxycitronellol into the corresponding aldehyde.
• Still another object is to convert 7,8-epoxy-2,6-dimethyl-octane-Z-ol into hydroxycitronellol and citronellol.
• 7,8epoxy-2,6-dimethyl-octan-2- 01 can be hydrogenated to produce 2,6-dimethyl-octane- 2,8-diol, which can be dehydrogenated to produce hydroxy dihydrocitronellal, commonly referred to as hydroxycitronellal, or alternatively it can be selectively dehydrated to produce citronellol, 2,6-dimethyl-2-octen-8- 01, which, in turn, can be dehydrogenated to produce citronellal.
• cobalt or nickel catalysts suitably of the Raney type, to secure highest conversions to the 2,8-diol.
• Other hydrogenation catalysts including copper chromite, palladium, etc., can be employed, but result in production of larger proportions of the less widely useful 2,7-diol.
• Hydrogen pressures are not critical though pressures of 500 to 1000 p.s.i,g. are economic to attain and are satisfactory as to rate of hydrogenation.
• the temperature of hydrogenation is not very critical, but temperatures of to C. have been found satisfactory with cobalt and nickel catalysts, while palladium can be used at ambient temperatures.
• the 7,8-epoxy2,6-dimethyl-octan- 2-ol is relatively viscous, and it is possible to increase the rate of hydrogenation through use of an inert solvent such as methanol and at the same time achieve higher yields of the desired 2,8-diol.
• the product can be fractionated, if desired, by distillation, preferably at reduced pressure, to obtain pure fractions of the 2,7-diol and the 2,8-diol.
• the 2,6-dimethyl-octan-2,8-diol can be selectively de hydrated by boiling with relatively strong aqueous acids. Such treatment results in removal of the tertiary hydroxyl group with formation of unsaturation involving the number 2 carbon atom.
• the dehydration is accomplished under conditions that favor the removal of the monohydric alcohol from the dehydrating reagent as it is produced, it will be rich in 2,6-dimethyl-l-octene-8-ol, acitronellol, but if this dehydration product is permitted to remain in contact with the acid for some time, then isomerization of the double bond from the 1-position to the 2-position occurs and the final product of the dehydration-isomerization is fl-citronellol, the predominate form found in natural oils.
• the identity of the mineral acid is not critical, that is, sulfuric or oxalic can be employed but phosphoric acid is satisfactory, cheap and is a relatively non-corrosive acid which is quite satisfactory.
• the phosphoric acid concentration is not critical, but we prefer to employ about to 35% concentrations, since use of more dilute acid causes a drop in the rate of dehydration and more concentrated acids may cause ether and polymer formation.
• Temperatures required for dehydration are not critical, but it is convenient to employ the temperature corresponding to refluxing at atmospheric pressure of the particular acid and concentration of choice. This will ordinarily involve temperatures of 100 to 130 C. Those skilled in the art will appreciate that superatmospheric pressures, higher temperatures, and weaker or more dilute acids could be used, but that such conditions would be less economic to achieve and would result in little or no change in yield of product since use of the simple preferred conditions results in almost quantitative yields.
• Example 8 Simple acid dehydration can be conducted as shown in Example 8 to obtain citronellol rich in the alpha form, whereas Example 3 provides details for production of citronellol almost exclusively in the beta form.
• Example 9 An alternate method for dehydration of the 2,8-diol and one capable of giving very high yields of the alpha form of citronellol is described in Example 9.
• the lower carboxylic acid ester of alpha-citronellol is desired, it is convenient to reflux the acid anyhdride with the 2,8-diol whereby the tertiary hydroxyl is lost with formation of a double bond at the 1-2 position, and the primary hydroxyl group at the 8-position is esterified.
• High yields of alpha-citronellol esters are so produced and are valuable as ingredients of perfume compositions.
• To obtain pure alpha-citronellol it is necessary only to saponify such esters and purify the alcohol by distillation.
• An alternate to this procedure is to esterify the 2,8-diol with an anhydride such as acetic anhydride at lower temperatures, say, room temperature and in the presence of a catalyst such as phosphoric acid to produce the diester of the 2,8-diol.
• the diester can be purified by conventional methods or can simply be heated to reflux whereby the elements of acetic or other acid is lost from the tertiary position, but the primary ester linkage is stable.
• This selective pyrolysis of the diester takes place readily at 150 to 225 C. and the operation can be conducted under a fractionating column so that the carboxylic acid and the mono ester are removed as formed by pyrolysis.
• esters including the esters of phthalic and azclaic acids, have little or no odor value but are valuable as fixatives and plasticizers for cellulose esters and for vinyl resins.
• 7,8-epoxy-2,6-dimethyl-octane-2-ol can also be employed in the practice of certain aspects of my present invention. These equivalents are those 7,8-epoxy-2,6-dimethyl-octane-2-yl compounds which can be readily hydrogenated to the corresponding 2,6-dimethyl-octane-8-ol-2-yl compounds and include the lower alkyl ethers and esters of 7,8-epoxy- 2,6-dimethyl-octane-2-ol which can be produced by the methods disclosed in copending application Serial No. 576,794.
• 7,8-epoxy-2,G-dimethyl-octane-Z-yl acetate can be hydrogenated to produce a mixture of 2,6-dimethyloctane-8-ol-2 yl acetate, and 2,6-dimethyl-octane-7-ol-2- yl acetate.
• These can be saponified readily to the glycols which are then further processed to citronellol, citronellal and hydroxycitronellal.
• glycol mono esters can also be dehydrogenated with copper chromite as described herein, although some splitting of acetic acid from the 2-position may take place whereby a mixture of citronellal and 2-acetoxy-dihydrocitronellal is produced.
• the mono esters can also be treated with phosphoric acid as disclosed herein, whereby acetic acid is split out at the 2-position, thus producing alphaand beta-citronellol.
• 2-methoxy-7,8-epoxy-2,6-dimethyl-octane yields on hydrogenation, as described herein, a mixture of 2-methoxy-2,6dimethyl-ootane-7-ol and 2-methoxy-2,6-dimethyl-octanc-8-ol.
• these mono ethers yield methanol and the corresponding unsaturated secondary and primary alcohols, respectively, and rich or poor in unsaturation at the 1-position depending on duration of the acid treatment.
• the 2-methoxy-2,6-dimethyloctane-8-ol will yield Z-methoxy-Z,6-dimethyl-octane-8- al on dehydrogenation with copper chromite.
• Some methanol may be split out during the dehydrogenation so that more or less citronellal will also be produced.
• liquid phase dehydrogenation whereby-the alcohol and a copper bearing catalyst are mixed and. heated to cause dehydrogenation while the dehydrogenation products, aldehyde and hydrogen, are being removed by distillation substantially at the rate at which they are being formed so that the aldehyde is not subjected to long contact with hot catalyst.
• Suitable dehydrogenation catalysts are copper chromite, copper powder, cuprous oxide, cupric oxide and, in general, those copper compounds which yield copper readily on heating in the presence of organic material such as copper basic carbonate, etc.
• Other catalysts such as nickel and cobalt can also be used, but to no particular advantage, and in the case of citronellol these cause not only formation of aldehyde but also cause some hydrogenation of the double bond involving the number two carbon atom to produce 2,6-dimethyl-octane-8-al, dihydrocitronellal.
• the copper bearing catalyst can be of mixed type, such as results from mixing solutions of copper, manganese, silver, etc., and adding a precipitant such as an alkali or alkali earth hydroxide or carbonate.
• a precipitant such as an alkali or alkali earth hydroxide or carbonate.
• the 2,6-dimethyl-octane-Z,8-diol or the citronellol is placed in a vessel preferably equipped with an agitator and a fractionating column for operation at reduced pressure.
• a suitable vacuum is applied so that the aldehyde and hydrogen are removed from contact with the catalyst as they are formed and so that thetemperature in the vessel is such that a suitable reaction rate is maintained;
• dehydrogenating the citr nellols In dehydrogenating the citr nellols.
• the vapors leaving the pot were rich in citronellol, but the alcohol was returned to the stillpot as reflux and the aldehyde was removed at the head of the fractionating equipment as, say, 90% or higher purity aldehyde.
• Optimum temperatures and pressures may vary somewhat due to catalyst concentration, catalyst activity, efiiciency and size of the fractionating column, etc., but can be readily determined for any specific set of conditions.
• the dehydrogenation vessel can be fed continuously with catalyst and primary alcohol with only occasional shutdowns to remove spent catalyst and the traces of polymeric materials formed.
• the secondary alcohols, 2,6-dimethyl-octane-2,7-diol and 2,6-dimethyl-(l or 2)-octene-7-ols can be similarly dehydrogenated to the corresponding 2,6-dimethyl-octane- 2-ol-7-one and 2,6-dimethyl-(1 or 2)-octene-7-ones and to the extent to which these secondary alcohols may be present in the primary alcohol fractions subjected to dehydrogenation, the ketones will also be produced and appear as impurities in the crude aldehyde.
• the crude mixture resulting from hydrogenation can be dehydrated and dehydrogenated and the purified products can be isolated by fractional distillation or by other means such as bisulfite formation in the case of the aldehydes.
• optical rotations shown in the examples are those obtained by converting optically pure l-pinane to 7,8-epoXy-2,6-dimethyl-octane-Z-ol according to copending applications Serial Nos. 576,794 and 576,795, and
• the epoxide, B.P. 121 C. at 10 mm., D 0.9531, N 1.4476, is slightly dextro rotatory when prepared from pure l-pinane and shows +0.95 (10 cm. tube).
• EXAMPLE 1 One thousand grams of 7,8-epoxy-2,6-dimethyl-octane- 2-ol was hydrogenated in the presence of 50 grams of Raney nickel catalyst and 300 ml. of methanol at C. under a hydrogen pressure of 5001000 p.s.i.g. and until absorption of hydrogen had about ceased. The amount of hydrogen absorbed amounted to about 1.05 moles per mole of epoxide. The hydrogenation product was filtered to remove catalyst and was fractionated by distillation. Infrared spectro-analysis of the fractions indicated that the hydrogenation product was 24% 2,6-dimethyl-octane-Z-ol, B.P.
• the distillate was taken deFermmed from the mt'enslty of Charactenstlc off at 100 at Such a rate that the head temperature mlnal methylene absorption at 11.2 1 in the infrared specstayed between 138 and 140 C.
• the reaction was comtrumpleted in 12 to 16 hours.
• One hundred ninety grams of 0 EXAMPLE 9 distillate was recovered.
• the distillate was 95-97% B- O citronellal and 3-5% B-citronellol as determined by com- To 250 grams of acetlc anhydnde i 140445 paring its physical properties B'PMO mm.
• Infrared spectroanalysis of the distilfractlongtlon of thls f Smce 'cmonenol bolls late showed that it was 90-95% fi-citronellal and 510% about 2 below F'cltroneuol at 10 rum-Pressurefl-citronellol.
• Infrared spcctroanalysis of the oil remain- Refluxmg the "fltronellgl huIs W1th an aqueous ing in the stillpot showed that it was 9598% B-citronellol 25% 3 4 Solutlon changed It to fi' and 25% fi-citronellal.
• EXAMPLE 10 A portion of crude 70-80% alpha-citronellol Produced Two hundred. grams of 2,6-dimethyl-octane-2, 8-diol as in Example 9 is treated with 5% of its Weight of copand 10 grams of copper chromite (Harshaws CU- 1106 per chromite and the mixture is heated to boiling at 100 P) were heated in the stillpot of an efiicient fractionating mm. absolute pressure. The flask containing the reagents column. The distillate was taken on at 10 mm. presis surmounted y an eflicient ting column.
• octane-Z-ol is dehydrogenated using 20 grams copper chromite and at a pressure of 10 mm. absolute.
• the distillate is collected keeping the column head temperature below 133 C. by adjusting the reflux ratio so that glycols are returned to the stillpot for further contact with catalyst while lower boiling products, chiefly hydroxycitronellal and 2,6-dimethyl-octane-7-one-2-ol, are removed from the head of the column.
• additional crude glycol mixture containing 1% copper chromite suspended in it is added to the stillpotat about the same rate as distillate is removed from the head.
• Five hundred grams of the glycol mixture containing 5 grams catalyst is added over a period of about 30 hours, at which time only about 75 grams of unreacted glycol mixture remains in the stillpot.
• the dehydrogenation step can be carried out on either the glycol or the octenol.
• the tertiary ester or ether can be subjected to any of the treatments shown for the tertiary alcohol.
• the process which comprises hydrogenating 7,8- epoxy-2,6-dimethyl-octane-2-ol to convert the epoxy group into a hydroxyl group attached to one of the carbon atoms originally involved in the oxirane ring, and thereafter subjecting a glycol so formed to a dehydration to remove the elements of water from the number 2 and an adjacent carbon atom and to a dehydrogenation to convert the other hydroxyl group to a carbonyl group whereby there is produced an oxo-substituted dimethyloctene in which the oxo group is attached to a carbon atom originally involved in the oxirane ring and in which the double bond involves the number 2 carbon atom.

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• 1957
  • 1957-05-13 US US658515A patent/US3028431A/en not_active Expired - Lifetime
• 1958
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