US3367972A - Selective hydrolysis of dialkyl ethers of protocatechuic aldehyde - Google Patents

Selective hydrolysis of dialkyl ethers of protocatechuic aldehyde Download PDF

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US3367972A
US3367972A US412302A US41230264A US3367972A US 3367972 A US3367972 A US 3367972A US 412302 A US412302 A US 412302A US 41230264 A US41230264 A US 41230264A US 3367972 A US3367972 A US 3367972A
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aldehyde
percent
isovanillin
hydrolysis
veratric
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Gitchel Wayne Benjamin
Pogainis Edmunds Modrins
Schoeffel Eugene Wilhelm
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STWB Inc
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Sterling Drug Inc
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Priority to SE13470/65A priority patent/SE321919B/xx
Priority to AT1006065A priority patent/AT262261B/de
Priority to CH1542565A priority patent/CH488643A/de
Priority to DEST24626A priority patent/DE1253697B/de
Priority to FI652736A priority patent/FI46498C/fi
Priority to NO160485A priority patent/NO116716B/no
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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C47/00—Compounds having —CHO groups
    • C07C47/52—Compounds having —CHO groups bound to carbon atoms of six—membered aromatic rings
    • C07C47/575—Compounds having —CHO groups bound to carbon atoms of six—membered aromatic rings containing ether groups, groups, groups, or groups
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S516/00—Colloid systems and wetting agents; subcombinations thereof; processes of
    • Y10S516/01—Wetting, emulsifying, dispersing, or stabilizing agents

Definitions

  • Alkyl vanillins e.g., ethyl vanillin, are produced by selectively hydrolyzing a dialkyl ether of protocatechuic aldehyde with concentrated sulfuric acid, to a 4-monoether; re-alkylating to another dialkyl ether and selectively hydrolyzing that dialkyl ether under basic conditions at a temperature above 200 C. to a 3-rnono-ether.
  • This invention relates to chemical processes comprising the selective hydrolysis of alkyl aryl ethers, more particularly to processes comprising the selective hydrolysis of dialkyl ethers of protocatechuic aldehyde, and process'es utilizing this selective hydrolysis, including those for the production of ethylvanillin, i.e., bourbonal (3-ethoxy- 4-hydroxybenzaldehyde)
  • the invention sought to be patented resides in the concept of converting vanillin to ethylvanillin, in the concept of converting veratric aldehyde to a 3-alkoXy-4-hydroxybenzaldehyde in which the alkoxy group has at least 2 carbon atoms by selectively hydrolyzing veratric aldehyde to isovanillin with concentrated mineral acid, alkylating the isovanillin to 3 alkoxy 4 methoxybenzaldehyde in which the alkoxy group is higher than methoxy and selectively hydrolyzing the 3-al
  • ethylvanillin now commands a higher price than vanillin, i.e., up to about 4 times the price of vanillin. Therefore, it is desirable commercially to have a process which can inexpensively convert vanillin to ethylvanillin.
  • a process for converting vanillin to ethylvanillin is disclosed in US. Patent 2,878,292. This process involves as its first step the hydrolysis of vanillin to protocatechuic aldehyde.
  • protocatechuic aldehyde production from vanillin in high yield is not readily achieved. Only by the use of specialized reagents and conditions is a good yield achieved, The thus-produced protocatechuic aldehyde can selectively be alkylated to ethyl vanillin in only 77 percent yield. The latter patent states higher yields can be obtained if the by-products are recycled.
  • the process of this invention the use of the relatively labile protocatechuic aldehyde as an intermediate and specialized ether cleavage reagents is avoided by first alkylating the vanillin to veratric aldehyde and converting the veratric aldehyde to ethyl or other alkyl vanillin. If desired, the process can start with isovanillin, a compound "ice which up to now had little utility, thus eliminating the first of the selective ether cleavage steps.
  • veratric aldehyde is selectively hydrolyzed in high yield to isovanillin with concentrated mineral acid.
  • the thus-produced isovanillin is alkylated to S-ethoxyor other desired 3-alkoxy-4-methoxy-benzaldehyde, which is then selectively hydrolyzed under alkaline conditions at elevated temperature and pressure to the corresponding 3-alkoxy-4-hydroxy-benzaldehyde.
  • German Patent 622,966 discloses the conversion of isovanillin to ethylvanillin via the mixed. diether of protocatechuic aldehyde using glacial acetic acid and 48 percent HBr as the hydrolytic agent.
  • these materials are unpleasant and relatively expensive hydrolytic agents compared With the alkaline hydrolytic agents of this invention and the selectivity is poor.
  • Alkaline hydrolyzing agents have been used to remove the readily cleaved benzyl group from 3-methoxy-4-benzyloxybenzaldehyde. See US. Patents 487,204, 545,099 and 561,077. They have not been used to selectively cleave in high yield the 4-ethers of a 3,4-dialkyl diether of protocatechuic aldehyde.
  • the process involves two selective hydrolysis steps, higher over-all yields can be achieved than by a complete hydrolysis followed by monoalkylation or followed by dialkylation and the same type selective hydrolysis.
  • veratric aldehyde can be prepared from sources other than vanillin
  • the process of this invention employs veratric aldehyde as starting material.
  • vanillin is converted to ethylvanillin.
  • novel selective hydrolysis steps developed for use in the conversion of veratric aldehyde to eth-yl vanillin have independent utility in the preparation of 3-monoand 4-mono-ethers of protocatechuic aldehyde, which monoethers are useful as intermediates in the production of a variety of chemical compounds.
  • Sulfuric acid is generally regarded as not a suitable agent for the cleavage of ether groups in labile compounds. See Burwell, Chemical Reviews, vol. 54, page 615 (1954). Moreover, other strong acids have been used to selectively remove the 4-ether of veratric aldehyde. See German Patent 622,966. It is therefore surprising this preferred acidic hydrolyzing agent selectively cleaves the 3- ether of veratric aldehyde to give very good yields of isovanillin, calculated on veratric aldehyde consumed, under the conditions employed.
  • a molar excess of mineral acid preferably sulfuric acid
  • mineral acid preferably sulfuric acid
  • a 3:1 ratio yield of isovanillin drops.
  • 11:1 ratio there is no advantage in yield.
  • the molar ratio of mineral acid to H O employed in the reaction is important and should beat least 2:1, e.g., from about 2:1 to 10:1, preferably about 2:1 to 8:1, most preferably about 4: 1.
  • sulfuric acid of a concentration of about 92 to 98 percent, more preferably 94 to 96 percent, is used.
  • the preferred reaction temperature is about 60 to 105 0, preferably 70100 C., e.g., about 80 to 95 C.
  • the optimum reaction time at any selected reaction conditions is determined by the products produced. If 10 percent or more protocatechuic aldehyde is obtained under the selected reaction conditions, lower temperatures should be used. If the yield of isovanillin is lower than optimum, longer reaction times and/ or temperatures can be employed. At 60 up to 24 hours may be required; at 70 about 26 hours is usually required; at 105, 30-90 minutes or less sufiices. At optimum temperature, about 1 to 3 hours is the optimum reaction time.
  • the ratio of isovanillin to vanillin produced varies from about 5:1 to 15:1 with the higher ratios generally being obtained at the lower hydrolysis temperatures.
  • the optimum balance between yields and conversion rate is realized at about a 50 to 60 percent conversion.
  • the thus-produced isovanillin preferably can be isolated by diluting the reaction mass with water, preferably to a 30-50 percent H 50 concentration, extracting the organics from the aqueous mixture with solvent, extracting the products from the solvent extract with water at a pH above 9, and then lowering of the aqueous extract to a pH between 8 and 9, most preferably about 8.3 to selectively precipitate the isovanillin.
  • the diluted acid can, if desired, be re-used by reconstituting with S0 or fuming sulfuric acid.
  • Any organic solvent system which is not miscible in the diluted acid and in which the isovanillin is soluble can be used as the extraction solvent.
  • a mixture of ethylene dichloride and chloroform or carbon tetrachloride, a mixture of 'butanol and a non-polar solvent, e.g., benzene, toluene or xylene, diethylether, bromobenzene, etc. can be used.
  • a 30:70 to 10:90 by volume mixture works very well with butanol and toluene.
  • reaction mixture can first be neutralized, e.g., with caustic, potash, lime, calcium carbonate, caustic soda, to a pH above 9, extracted with solvent and then the pH lowered to between 8 and 9 to precipitate the isovanillin.
  • This sulfuric acid selective hydrolysis is also well suited for the conversion of other 3,4-diethers of protocatechuic aldehyde in which the alkoxy groups are the same or different and are, e.g., methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, octoxy, nonoxy, and cycloalkoxy including cyclopentoxy and cyclohexoxy, preferably those containing 1-8 carbon atoms and those in which the 4- alkoxy group contains at least the number of carbon atoms of the 3-alkoxy group and desirably more, to produce the corresponding 4-monoether.
  • the 3-ether is the 3-methyl ether.
  • the process can also be used to produce 4-allyl and other alkenyl, 4-5- hydroxyethyl and other functionally substituted alkyl, 4- phenyl and other aryl 4-mono-ethers of protocatechuic aldehyde, which compounds are useful as intermediates in the production of diverse pharmaceutical and polymer chemicals and as plasticizers and antioxidants for plastic films.
  • Examples of such starting compounds are 3-ethoxy-, 3-n-propoxy, 3-butoxy, 3-pentoXy-, 3-hexoxy-, 3-heptoxy, 3-octoxy-, 3-phenoxy-, and 3-cyclo-hexoXy-4-methoxybenzaldehyde, which can be prepared by the appropriate 3-alkylation of isovanillin, and the corresponding higher '4-alkyl homologues, e.g., 3-cyclohexoxy-4-ethoxy-benzaldehyde and 3,4-diethoxybenzaldehyde, which can be prepared by appropriate alkylation of a 3-alkoxy-4-hydroxybenzaldehyde or 3-hydroxy-4-alkoxy-benzaldehyde.
  • Ethyl chloride is an ideal alkylating agent although diethyl sulfate, ethyl iodide, ethyl bromide, etc., can also be used.
  • alkyl ethers of 28 carbon atoms e.g., propyl, ispropyl, 'butyl
  • the corresponding alkyl chloride, bromide or iodide can be used.
  • alkyl or, if desired, aryl, alkaryl, alkenyl, cycloalkyl, or cycloalkenyl ether can be employed. Conditions as vigorous as those described in US. 2,878,292 and even more so can be used. The product can be isolated in the same manner as veratric aldehyde.
  • the hydrolysis reaction is conducted at between about 200 and 325, preferably from 240-300 and most preferably from 250-275 C.
  • the lower limit is determined by hydrolysis rate and the upper limit by loss of selectivity and decomposition of the products.
  • Sufficient pressure is employed to prevent substantial volatilization of the water. About 5 to 50 p.s.i.g. above the steam pressure produced at the selected temperature suflices.
  • any alkaline material or mixtures of alkaline materials which will provide an alkaline pH at the reaction temperature can be used in the hydrolysis, e.g., the alkalimetal hydroxides, preferably sodium or potassium hydroxide, the alkali-metal carbonates, preferably sodium carbonate, the alkali-metal carbonates, preferably sodium bicarbonate, the alkali-metal sulfites, lime, calcium carbonate, trisodium phosphate, etc.
  • a reducing agent e.g., one to two moles of sodium sulfite or sodium bisulfite per mole of aldehyde in the reaction mixture, increases yields.
  • the alkali-metal hydroxides, carbonates and bicarbonates, alone or in mixture with an alkali-metal sulfite or bisulfite, are the preferred hydrolyzing agents.
  • the molar ratio of hydrolyzing agent to 3-alkoxy-4- methoxy-benzaldehyde has a significant effect upon the yield of protocatechuic aldehyde 3-mono-ether obtained. Desirably, no more than a 1:1 molar ratio of hydrolyzing agent to aldehyde is employed although ratios as high as 4:1 are operable. At a pH above 11, e.g,. using an alkalimetal hydroxide, from about 0.5 to 1.05 moles hydrolyzing agent to aldehyde is preferably employed.
  • the alkaline hydrolysis of a 3-alkoxy-4-methoxybenzaldehyde provides very high ratios of 3-mono-etherto 4-mono-ether.
  • the pressure of the reducing agent maintains at a minimum the production of undesired byproducts.
  • the reaction product can be isolated by lowering the pH of the reaction mixture to less than 9, preferably about 8.3, and extraction with solvent, e.g., ethylene dichloride or one of the solvents described above for the isolation of the isovanillin.
  • solvent e.g., ethylene dichloride or one of the solvents described above for the isolation of the isovanillin.
  • the solvent can then be removed by distillation and the 3-alkyl mono-ether of protocatechuic aldehyde purified, if desired, by fractional crystallization.
  • a mixture of methanol and water is an excellent purification solvent for ethyl vanillin.
  • This alkaline selective hydrolysis is also useful for the conversion of 3,4-diethers of protocatechuic aldehyde in which the alkoxy groups are the same or different, e.g., methoxy, ethoxy, isopropoxy, n-butoxy, octoxy, nonoxy, and cycloalkoxy including cyclopentoxy and cyclohexoxy,
  • the 4-ether is the methyl ether. It can also be used to produce 3-allyl and other alkenyl, 3-6-hydroxy and other functionally substituted alkyl, and 3-phenyl and other aryl monoethers of protocatechuic aldehyde, which compounds are useful as flavorings, odorants, oil antifoaming agents, plasticizers and antioxidants for plastic films, intermediates, e.g., by conversion of the aldehyde group to the corresponding acid esters which have preservative and disinfectant activity, and conversion to the hydrazones thereof which have herbicidal activity.
  • Examples of such starting compounds are 3-ethoxy-, B-n-propoxy, 3-butoxy, 3-pentoxy-, 3-hexoxy-, 3-heptoXy-, 3-octoxy, 3-phenoxy-, and 3-cyclohexoXy-4-methoxy-benzaldehyde, which can be prepared by the appropriate 3-alkylation of isovanillin, and the corresponding higher 4-alkyl homologues, e.g., 3-cyc1ohexoxy- 4 ethoxy benzaldehyde and 3,4 diethoxybenzaldehyde, which can be prepared by appropriate alkylation of a 3-alkoxy-4-hydroxybenzaldehyde or 3-hydroxy-4-alkoxybenzal-dehyde.
  • n and m are integers from 1 to 8 and, when the hydrolysis is acidic, m is equal to or greater than n and is preferably 1 and, when the hydrolysis is alkaline, n is equal to or greater than m and is preferably at least 2.
  • 3-ethoxy-4-methoxy-, 3-octyloxy-4-methoxy, 3,4-diethoxy-, 3-ethoxy-4-propoxy, 3,4-dipropoxyand 3,4-dioctyloXy-protocatechuic aldehyde are selectively hydrolyzed, respectively, to A-methoxy-, 4-methoxy-, 4-ethoxy-, 4-propoxy-, 4-propoxy and 4-octyloxy-protocatechuic aldehyde.
  • Example 2 Alkalz'n e hydrolysis of 3-eth0xy-4-meth0xybenzaldehyde t ethylvanillin
  • 17.8 g. (0.1 mole) of 3-ethoxy-4- methoxy-benzaldehyde, 300 cc. of 0.5 M aqueous Na SO and 100 cc. of 1.0 M NaOH were heated in an evacuated sealed nickel bomb in a 450 C. salt bath under the conditions shown in Table III.
  • the reaction mixture was at a temperature at which reaction occurs at asubstantially rapid. rate (225 and. d above) for only about 2.5 of the 4.5 minutes during which the mixture was heated. This is equivalent to about 1.5 to 2 minutes holding time at 290298 C. in a continuous reactor.
  • 3,4-diethoxy-, 3-propoXy-4-methoxy-, 3-propoxy-4-ethoxy-, 3,4-dipropoxy, 3- octyloxy-4-methoxyand 3,4-dioctyloxy-protocatechuic aldehyde are selectively hydrolyzed, respectively, to ethylvanillin, propylvanillin, propylvanillin, propylvanillin, octylvanillin and octylvanillin.
  • Table IV shows runs similar to those of Example 2 in which reactants at the indicated concentrations were reacted at various temperatures and times. Runs 8 to 16 were continuous runs in which the reactants were passed for the indicated times through a heated tubular reactor. Run 8 illustrates the adverse effect upon yield of molar ratios of NaOHzEMB in excess of about 1:1. Table V gives in more detail the reaction conditions employed in sodium hydroxide (34.9 percent by weight). The temperature rises to about 107 C. Regulate addition rate so as to maintain the reaction temperature at 107 C. during the additions. Time of addition is about 100 minutes. Ex-
  • vanillin is converted to ethylvanillin with 3-meth0xy-4-eth0xy benzzaldehyde and 3,4-diethoxy-benzaldehyde as intermediates.
  • vanillin is converted to the 3-phenyl, 3-cyclohexyl, 3-propyl, 3- 21121, B-n-hexyl, and other 3-ethers of protocatechuic alde- What is claimed is:
  • a process for converting a 3-monoether of protocatechuic aldehyde to another 3-monoether which comprises the steps of (a) alkylating a 3-alkyl rnonoether of protocatechuic aldehyde containing from l-8 carbon atoms with an alkylating agent to produce the 3,4-diether of protocatechuic aldehyde in which the alkoxy groups each contain from 1-8 carbon atoms and the 4-alkoxy group contains at least the number of carbon atoms of the 3-alkoxy group,
  • step (d) is selected from the group consisting of alkali-metal hydroxides, alkali-metal carbonates and alkali-metal bicarbonates.
  • step (d) comprises an alkali metal salt of a reducing acid.
  • step (dl) there is present about a molar equivalent of sodium hydroxide and at least a molar equivalent of sodium sulfite, each calculated on the aldehyde, and a reaction temperature between about 240-3 00 C. is employed.
  • step (a) is a methylating agent and in step (d) an ethylating agent.
  • a process for producing from veratric aldehyde an alkyl vanillin of the formula wherein n is an integer from 2 to 8 which comprises the steps of (a) selectively hydrolyzing veratric aldehyde with 92-98 percent sulfuric acid in a molar ratio of acid to veratric aldehyde of at least 3:1 and at a temperature between about and C. to produce isovanillin, (b) alkylating the thus-produced isovanillin with an alkylating agent to produce a diether of protocatechuic aldehyde of the formula wherein n has the value given above, and
  • a process for producing ethylvanillin from veratric aldehyde which comprises the steps of (a) selectively hydrolyzing the veratric aldehyde with 92-98 percent sulfuric acid at a temperature between about 80 and 95 C. to produce isovanillin,
  • a process for the selective hydrolysis of a 3,4-di- 75 alkyldiether of protocatechuic aldehyde in which each alkoxy group contains 1-8 carbon atoms and the 4-alkoxy group contains at least the number of carbon atoms of the '3alkoxy group, to produce the 4-monoether as the major product which comprises heating the diether with 92-98 percent sulfuric acid in a molar ratio of acid to said diether of at least 3:1 at a temperature between about 60 and 110 C.
  • reaction temperature is between about 80 and 95 C.
  • a process for the selective hydrolysis of veratric aldehyde to produce isovanillin which comprises contacting veratric aldehyde with 9496 percent sulfuric acid, in an H SO IV61atI'lC aldehyde molar ratio of from 4:1 to 11:1 at a temperature between about 8095 C.
  • a process for the selective hydrolysis of a 3,4-dialkyl diether of protocatechuic aldehyde to produce the corresponding 3-monoether as the major product which comprises hydrolyzing the diether with an aqueous alkaline hydrolyzing agent at a pH of at least 11 under pressure at a temperature above 200 C.
  • hydrolyzing agent is selected from the group consisting of alkali-metal hydroxides, alkali-metal carbonates and alkali-metal bicarbonates.
  • a process for the selective hydrolysis of 3-ethoxy- 4-methoxybenzaldehyde to ethylvanillin which comprises hydrolyzing the diether with about a molar equivalent of aqueous sodium hydroxide and at least a molar equivalent of sodium sulfite under pressure at a temperature between about 240 and 300 C.

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US412302A 1964-11-19 1964-11-19 Selective hydrolysis of dialkyl ethers of protocatechuic aldehyde Expired - Lifetime US3367972A (en)

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Application Number Priority Date Filing Date Title
US412302A US3367972A (en) 1964-11-19 1964-11-19 Selective hydrolysis of dialkyl ethers of protocatechuic aldehyde
SE13470/65A SE321919B (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) 1964-11-19 1965-10-18
AT1006065A AT262261B (de) 1964-11-19 1965-11-08 Verfahren zur Herstellung von 4-Monoalkyläthern des Protocatechualdehyds
CH1542565A CH488643A (de) 1964-11-19 1965-11-09 Verfahren zur Herstellung von 3-Alkoxy-4-hydroxy-benzaldehyden
DEST24626A DE1253697B (de) 1964-11-19 1965-11-11 Verfahren zur Herstellung von 3-Alkoxy-4-hydroxy-benzaldehyden
FI652736A FI46498C (fi) 1964-11-19 1965-11-15 Tapa valmistaa protokatekualdehydin 4-monoalkyylieettereitä.
NO160485A NO116716B (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) 1964-11-19 1965-11-16

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CH (1) CH488643A (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
DE (1) DE1253697B (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
FI (1) FI46498C (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
NO (1) NO116716B (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4453004A (en) * 1982-04-01 1984-06-05 International Telephone And Telegraph Corporation Process for the alkylation of phenolic compounds
US4473713A (en) * 1981-09-29 1984-09-25 Rhone-Poulenc Specialites Chimiques Hydrolysis of aryl-aliphatic ethers
FR2725982A1 (fr) * 1994-10-24 1996-04-26 Rhone Poulenc Chimie Procede de preparation d'isovanilline
EP0758639A1 (en) * 1995-08-11 1997-02-19 Ube Industries, Ltd. Process for preparing isovanillin

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE622966C (de) * 1932-09-09 1935-12-10 Boehringer & Soehne Gmbh Verfahren zur UEberfuehrung von Isovanillin in 4-Oxy-3-aethoxybenzaldehyd
US3007968A (en) * 1957-07-25 1961-11-07 Monsanto Chemicals Etherification of hydroxy aromatic aldehydes

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE622966C (de) * 1932-09-09 1935-12-10 Boehringer & Soehne Gmbh Verfahren zur UEberfuehrung von Isovanillin in 4-Oxy-3-aethoxybenzaldehyd
US3007968A (en) * 1957-07-25 1961-11-07 Monsanto Chemicals Etherification of hydroxy aromatic aldehydes

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4473713A (en) * 1981-09-29 1984-09-25 Rhone-Poulenc Specialites Chimiques Hydrolysis of aryl-aliphatic ethers
US4453004A (en) * 1982-04-01 1984-06-05 International Telephone And Telegraph Corporation Process for the alkylation of phenolic compounds
FR2725982A1 (fr) * 1994-10-24 1996-04-26 Rhone Poulenc Chimie Procede de preparation d'isovanilline
EP0709361A1 (fr) * 1994-10-24 1996-05-01 Rhone-Poulenc Chimie Procédé de préparation d'isovanilline
US5648552A (en) * 1994-10-24 1997-07-15 Rhone-Poulenc Chimie Process for the preparation of isovanillin
US5786516A (en) * 1994-10-24 1998-07-28 Rhone-Poulenc Chimie Process for the preparation of isovanillin
EP0758639A1 (en) * 1995-08-11 1997-02-19 Ube Industries, Ltd. Process for preparing isovanillin

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SE321919B (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) 1970-03-23
DE1253697B (de) 1967-11-09
AT262261B (de) 1968-06-10
FI46498C (fi) 1973-04-10
NO116716B (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) 1969-05-12
CH488643A (de) 1970-04-15
FI46498B (fi) 1973-01-02

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