DE2556161A1 - PROCESS FOR OXIDATING PRIMARY ALLYL AND BENZYL ALCOHOLS - Google Patents

Description

Process for the oxidation of primary allyl and benzyl alcohol

The present invention relates to the Dppenauer oxidation of primary alcohols to their corresponding aldehydes. The invention is particularly applicable on the Dppenauer Üxidation 2-substituted, 3-substituted and 3,3-disubstituted allyl alcohol and benzyl alcohol.

The invention is mainly illustrated here using the example of Dppenauer oxidation of Geraniol (trans) and IMerol (eis) OjV-Dimethyl ^ jS-actadien-i-ol), one 3,3-disubstituted allyl alcohol, to citral (3,7-dimethyl-2,6-odadienal) described. With regard to the 2-substituted allylic alcohols, the allylic Double bond can be acyclic, exocyclic or endocyclic.

An example of a cyclic allyl alcohol which is implemented according to the invention is Perillylalkohal (1-hydroxymethyl-if-isDpropenylcyclohexen). An example of a benzylic alcohol to be reacted according to the invention is benzyl alcohol.

Citral, which is a mixture of Citral-a (Geranial) and Citral-b (Netal),

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provides an extremely versatile and useful interconnection in the Synthesis of numerous products. The synthesis ηη * θ of ions and methyl ions starts with citral. It can be used directly under condensation with acetone Pseudo-jonon are implemented, which in turn converts into - and ß-ionon can be. The latter connection is the key interconnection in the manufacture of Uitamin A. Pseudojonon can be used in the manufacture van V / itamin E. Citral has many other possible uses on, for example in synthetic fragrances.

The Dppenauer oxidation of secondary alcohols to ketones is an applicable one and well-known textbook reaction. The oxidation is generally carried out in the presence of an aluminum catalyst, such as aluminum tert. butoxide or aluminum isopropoxide, using a large excess Acetone as a hydrogen acceptor. The general applicability of this reaction however, it is limited to secondary alcohols.

As in Organic Reactions , Vol. UI, Hap. 5, under "The Oppenauer Oxidation", pp. 222-223, reported by Carl Djerassi, John Wiley and Sons Inc., 1951, the Oppenauer reaction, with the exception of exceptional cases, has not been used as a preparative method for oxidation until recently primary alcohols have been applied to aldehydes, since the aldehydes condense with the hydrogen acceptor.

As Djerassi points out, experimental modifications are made to the usual Oppenauer procedure necessary. This includes the use of valuable or difficult to obtain hydrogen acceptors, the use of stoichiometric amounts Catalyst and distillation of the product when it has been formed.

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The methods are expensive, and become difficult to perform on a large scale only used when no other method is available.

The Djerassx article from "Organic Reactions" is included here as a reference.

Previous observations on the oxidation of primary alcohols such as geraniol and Nerol, with acetone as the hydrogen acceptor, show that the aldehydes produced subject to a subsequent aldol condensation reaction with the acetone and in fact only a small amount of aldehyde (citral) can be obtained. Even though the end product of the aldol condensation of citral is pseudojonon two main problems prevented this reaction from being technical Manufacture of pseudo-jonon was applied. One problem is that the aldol condensation reaction produces water as a by-product, which hydrolyzes and consumes the aluminum catalyst.

The B requires nearly stoichiometric amounts of the aluminum catalyst as opposed to catalytic amounts; see p. 22k in Djerassi, above. In addition, the hydrolyzed catalyst is in the form of a gel-like precipitate, which is difficult to remove and also gives rise to mechanical problems when carrying out the oxidation reaction. Furthermore, large amounts of solvent are required in order to dissolve the correspondingly large amounts of catalyst used in the oxidation reaction. A second disadvantage is that if the reaction is carried out up to a high conversion, the yield can decrease.

A replacement of the Ufassstoffakzeptoren, so by cyclohexanone, that less

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strongly subject to aldol condensation, instead of acetone the aldehyde yield may be to enhance. However, relatively high reaction temperatures are required when using ketones as hydrogen acceptors of oxidation up to high degrees of conversion used in a reasonable time.

However, high temperatures would be disadvantageous in the case of heat-sensitive aldehydes like citral, as it enables self-condensation at high temperatures are. In addition, other ketonic hydrogen acceptors pose problems the accessibility or smaller equilibrium constants, with the latter If a large excess of hydrogen acceptor is necessary, what Difficulties in the subsequent isolation of the product with it brings.

Djerassi states the following on p. 23o: Until recently we are Aldehydes have so far only rarely been used as hydrogen acceptors. Aide- | Hyde are traditionally difficult to manufacture products that are unstable

and are subject to side reactions. The use of an aldehyde as a reactant or hydrogen acceptor means the same problems, he is alike unstable. and is subject to side reactions. In the case of the Oppenauer oxidation

he can handle both aldol and table-cup condensation reactions

are subject to, both with themselves and with the Oppenauer oxidation product.

Adkins et al. (e.g., Adkins et al., 3rd Amer . Chem. 5oc, 71, pp. 3622-3629) a number of studies have been carried out to determine the apparent oxidation potentials of various compounds, mainly ketones, although conclusions are drawn that a high oxidation

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potential is desirable, a relatively low potential (as explained by Djerassi on p. 22B) compensated for by using a large excess of hydrogen acceptor; other factors, such as rate of response and potential for weaving reactions, may be a exercise more control.

For example, acetone has a relatively low oxidation potential, however, it is inexpensive and can be used in large excess. Cyclohexanone on the other hand has a higher oxidation potential, but in comparative tests carried out with this compound, the Oxidation of geraniol only to a 15% conversion to citral.

According to the invention it has now surprisingly been found that furfural a unexpectedly superior oxidizing agent or an extremely suitable one hydrogen acceptor for the conversion of primary allylic or allyl alcohols and benzylic or benzyl alcohol to their corresponding Al-

I dehyden represents. |

The primary alcohols to be reacted according to the invention include allylic or AllylalkDhole, which are at least in the 2-position with a hydrocarbon radical are substituted; allylic or allyl alcohol which are substituted in the 3-position, or 3,3-disubstituted allyl alcohols; and benzylic or benzyl alcohol.

The allylic double bond can in the case of the 2-substituted allyl alcohols be acyclic, exocyclic or endacyclic; the 3-position can be unsubstituted, be monosubstituted or disubstituted.

In the case of the Oppenauer oxidation υοπ geraniol and (\ leral, the oxidation can occur through the following equation can be reproduced:

■ furfural ■ _; ;

CHQ aluminum catalyst

The conversion of a 2-substituted alcohol proceeds as follows:

CHO

Aluminum catalyst

λ ■ - ;. - '■ · ■ ".'-'
■ '', / ■■ '". · ^: Perillyl
aldehyde _: Uv o ' ■. " - '■>' ·: ■, ' '"
>;; · ■■ ^; '' S: ·;
, -ivfft: ■■ '"' ■ -"'
-. :>, - t · ■■ , HS ■ .. .. *: "... / ClKOH
0, ^e.g.

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ORIGINAL INSPECTED

The implementation of it & rd according to the invention under mild Oppenauer oxidation conditions * operations carried out in the presence of an aluminum catalyst, among such Furfural is not subject to the table cup co-reaction, like many other aldehydes.

In addition, furfural, which has no oirPratansn , is not an aldol condenser

sation with the aldehyde product, for example Gitral, subjected to such as Acetone. Therefore, the amount of aluminum catalyst required to react; is required, greatly reduced to catalytic amounts, with which the accompanying j mechanical and pollution problems are eliminated and the frfcaia-

ί lyser costs are reduced. * j

Surprisingly, the reaction of furfural with substituted primary allylic or allyl alcohols, such as nerol and geraniol and perillyl alcohol, and a high reaction rate even with primary benzyl alcohols on what the implementation of the reaction under the very mild reaction conditions allowed. This is important for heat sensitive compounds like citral. In particular, under the mild reaction conditions, which are used according to the invention, citral, perillylaldehyde and other aldehydes no aldol self-condensation. In the mild conditions of the According to the invention, there are also no noticeable side reactions.

The reaction according to the invention also happens to have a high equilibrium constant, so that it leads to high conversion and high yields of aldehyde without using a large excess of furfural.

In the oxidation of Eeraniol and Nerol, the citral reaction product is quick to gain and sufficiently pure so that it can be used for most purposes

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can be used without detergent. In this regard, furfuryl alcohol indicates which is also a product of the oxidation reaction, one proportionate low boiling point, which makes it suitable for separation from citral and recovery by distillation allowed.

It is a very valuable product that is priced around 1d% above furfural is and is suitable for the production of certain resins, whereby the invention Process is technically even more advantageous.

: A particular advantage of the invention is that the citral reaction. j product is sufficiently pure that it can be used in the manufacture of

"j

Pseudo-jonon can be used. This is done in the presence of j Acetone according to the following equation:

O):

mmmmmmmi

This reaction with citral can take place after separation from the others Reaction products of equation (1) or, alternatively, in a single pot process, in which acetone and a base are added directly to the reaction mixture of equation (1).

It is preferred to react furfural and alcohol in a molar ratio from furfural to primary allylic or allyl alcohol from about 1: 1o to about 1o: 1. A preferred range is about 1: 2 up to about 3: 1 and leads to high yields of the desired products

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ORIGINAL INSPECTED

without excess amounts of unreacted starting materials. That special The ratio chosen, however, depends on the desired end products. When producing νση PseudDjonon, furfural is also subject to aldol condensation, so that it is desirable to have a molar ratio of furfural to ileral / geraniol on the order of about 3: ^ to use the need the separation of the unreacted furfural before conversion of the citral into Avoid pseudo-jonon. On the other hand, if you can isolate Citral wishes a relatively large molar ratio of furfural to i \ lerol / geraniol on the order of 2: 1 used to maximize conversion.

Preferably, a catalytic amount of about 1 to 15 mole percent, based on the weight of primary alcohol employed, of an aluminum catalyst such as aluminum isopropoxide is used, although this depends in part on the amount of water present in the reaction mixture. ^!

The use of less than 2 mol% catalyst is possible if extreme |

Care is taken with regard to the water content. Other factors that dictate the amount of catalyst used include the desired rate of reaction, the amount of acid present in the reaction mixture and the amount of water or acid generated in the course of the reaction. The general rule for nerol / geraniol is that about 5 mol% of catalyst, based on the neral / geraniol used, results in optimal reaction conditions and action, e.g. equilibrium in 2 to 3 hours at about £ fO ^D C.

Any aluminum alkoxide or aluminum aryl oxide catalyst suitable for a Dppenauer reaction is suitable, such as aluminum tert-butoxide, AlCt-DC, Hg) - ,,

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can be used. Aluminum sap oxide is preferred because of its cost advantages and has the advantage of accessibility, although some furfural is consumed by oxidation of the isopropoxide to acetone.

In this regard, in the aforementioned literature from Organic Reactions, Vol. VI, Ξ. 209 (Djerassi) and also in Physical Organic Chemistry) by Hine reports that the actual active catalyst in the oxidation is an aluminum alkoxide, which is generated in situ , and to that extent depends on the reactants and conditions. It is usually produced by adding aluminum isopropoxide, aluminum tertiary butoxide, or aluminum phenoxide.

It can also be generated in- situ by adding an alkylaluminum compound such as triisobutylaluminum (Djerassi also has a number of others

: suitable connections on). These connections, although normally

called the catalysts, only the source of the aluminum alkali

j represents oxides.

ι. ■ -

Therefore, the selection of the aluminum source is largely based on convenience. In the present description, the term "Oppenauer Oxi

dation catalyst "include all of the above compounds.

Alcohols of category 3-substituted and 3,3- to be reacted according to the invention; disubstituted can be represented by the following formula: i

R.
\

C = CH - CH ₂ OH

R.
in which substitution by one or more aliphatic or aromatic

1

see groups present. According to a preferred embodiment of the invention the allyl alcohol on carbon number 3 is disubstituted with aliphatic groups. Representative compounds of this class are Nerol / GeraniDl (above), farnesol (3, 7, 11-trimethyl-2,6,1o-dodecatrien-1-al), prenol (3-methyl-2-buten-1-ol) and vitamin A alcohol.

In a further class of compounds that can be used according to the invention, the allyl alcohol is on carbon IVr. 3 substituted with an aryl group. Re-; Cinnamyl alcohol (C _C H _C CH = CHCH “DH) and several aromatic polyhydroxycarbinol compounds such as coniferylal-! alcohol

Another third class of compounds for implementation in accordance with the present invention Invention are 3-substituted allyl alcohol, in which substitution by a single aliphatic group is present. A representative example within the group is 2-hexen-1-ol.

Structural formulas of representative alcohols are shown below:

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fNSPECTED

OH

Farnesol

2-hexen-l-ol

JH-CH-CH ₂ OH

OH

• PreivoV

Representative alcohols that are in the 2-position with a hydrocarbon radical
are substituted, or benzyl alcohol, which are implemented according to the invention
are the following:

■■ *

• ■ .Γν & Ί- · ■■ -

V CH ₂ OH

ί ¹ ; - '. # ■

^ ■! ΙιΜΡΐ ^ ν, χ.

CH ₂ OH

Methallyl alcohol perillyl alcohol

Benzyl alcohol

It can be seen that the above alcohols have a hydrocarbon substitution in
2-position, ie ß-position to the carbinal hydroxyl radical have in common. They can '· optionally substituted in the 3-position or unsubstituted, ^tjobei: Substitution may be present with an aliphatic or aromatic radical. '·.

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ORIGINAL IMSPECTCO

Further representative Bezylic alcohols for the purposes of the invention are polyhydric polyhydroxy compounds such as saligenin (o-HOCLH, Cl-LOH), p-hydroxybenzyl alcohol (P-HDC.-H, Q-LOH) and uanilly alcohol (<> (., 4-dihydroxy- 3-methoxytoluene) In the present description, the term "benzyl alcohol or benzylic alcohol" defines aromatic hydroxymethyl compounds.

An example of another cyclic allyl alcohol in which the allyl ical double bond is endocyclic, Mertenol represents:

CU ₂ OH

Other primary alcohols that can be converted according to the invention, are obvious for the professional.

The following examples are presented to illustrate the invention and its practice explain, but in no way limit them. In this description, all percentages and parts relate to weight and all Temperatures in degrees Celsius, unless otherwise stated.

example 1

This example illustrates the oxidation of geraniol / IMerol to citral using furfural as a hydrogen acceptor according to the concept of the present invention. A flask was filled with 1oao g of freshly distilled geraniol / fvierol (in a ratio of 6α: ί + ο) and 475 g of distilled furfural to achieve a molar ratio of furfural to IMerol / geraniol of about 5: k

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to submit. The mixture was ^{heated to 35 °} C. and a solution of 5 g of aluminum isopropoxide (5% by weight of the added nerol / geraninl) in iodine g of toluene was added. The TdIudI can be omitted if one preloads the catalyst in the geranin / IMerol.

Heating was discontinued and the mixture at ambient temperature for about 3 hours touched. The implementation was mildly exothermic. The mixture was purified by gas-liquid chromatography using a 1.22 m Carbowax column analyzed by tetradecene as an internal standard.

Table 1

Analysis of the reactant product Wt% link 1, dS Furfural 3d, 19th Furfuryl alcohol 15.31 Neral 24.7a Geranial 7, SB IMerol 11.7a Geranial

Weight (g) 17.3
if 89, a 2kB, ο

1B9.6

Conversion of furfural 95.7 %

Weight yield to furfuryl alcohol 1o5.2 %

conversion of geraniol / IMeral 65.2%

Weight yield to citral 3k, 5%

Example 2

This example illustrates the course of the oxidation reaction as a function of

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Time and shows that the oxidation of neral / geraniol to citral is essentially until equilibrium is reached under very mild conditions and use of furfural can be done.

The oxidation was carried out at room temperature and the equilibrium was established reached in about 5 hours. The waste ratio of furfural to IMerol / geranial at the beginning it was about 5: 3. Aluminum isopropoxide catalyst was in a Amount of 1o wt .-%, based on the weight of the IMerol / geraniol used, used. Product analyzes were carried out by gas-liquid chromatography using an internal standard.

Table II

Time
Hour conversion
of furfural
(%) Yield too
Furfurylal
alcohol (%) Conversion of
IMerol etc. (%) Yield too
Citral (%) 0: 1o 9.56 99.97 17.59 1oo, o2 1:11 44.22 99.78 65.72 χ 2:26 6o, 6o 1do, 73 85.19 9B, 67 4:38 63, o3 99, o9 9o, 46 97, o8 5: 4a 63.2o
κ no analysis 1o1.54 91.44 96.47

It can be seen from the above data that conversions even at room temperature of about 85% of the nerol / geraniol to citral in one proportion short time (2:26 hours) can be achieved and with these degrees of conversion Citral yields of about 98% are available.

Even if the conversion is increased to about 90%, the decrease is from

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Yield (percent yield of citral produced) low. Tests show that the yield losses over a 24-hour period at room temperature are less than 5% , the yields always being in the range of 95-98 % . The main impurities are believed to be isocitrals. The purity of the product obtained, even if the reaction proceeds to equilibrium, makes it suitable for use in the production of pseudo-jonone.

Example 3

This example illustrates the balance on the side of oxidation from IMerol using furfural clearly from citral and furfuryl alcohol lies. This allows the conversion to expediently up to a high degree of conversion (e.g. 95% either IMerol or furfural) without using to carry out a large excess of a reactant.

A number of tests have been carried out with different molar ratios of furfural and IMerol. The same oxidation conditions were used in each test, namely room temperature, 10 % aluminum isopropoxide and atmospheric pressure. The results are given in Table II.

Table III

Molar ratio conversion of conversion of the

^ i ^ Furfurals of NerDls

2: k 97.9 kk, p

3 '. h 95.2 68, ο k ι h 87.2 79, if 5: k 81.2 89.6 6: 4 71, o 93, o

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Table III continued

7: if SdΛ%, 2

8: if 53, Β 97.6 1o: if Wi, 2 98.2

The conversion of furfural is slightly higher than what you can get from the crowd of the converted f \ ierol would expect. The discrepancy goes to a certain extent Oxidation of isopropyl alcohol (from aluminum isopropoxide) back to acetone. This reaction is much slower than the oxidation of the ftlerol or geraniDl and is only noticeable when the nerol or geraniol oxidation occurs Equilibrium reached.

Example k

A conversion of furfural to furfuryl alcohol of more than 90 % is desirable if the crude citral product is to be converted directly to pseudojanon without purifying the citral. The presence of furfuryl alcohol and unreacted IMeral and geraniol do not interfere with the reaction.

A small amount of furfurylidene acetone is produced during the pseudo-jonon reaction formed from unreacted furfural, but this affects production and not obtaining the pseudo-jonon.

In this example, 39o g of crude citral from Example 1 (i.e. the reaction product of Example 1 without purification) with 165o g of 9a% acetone under Use of 100 ml of 10% strength aqueous sodium hydroxide as a catalyst let react. Only 1.06% by weight of furfural was present in the reaction mixture.

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hold which resulted in a 95.7% conversion of furfural to furfuryl alcohol according to the reaction of equation (1). The pseudo-jonon reaction represented by the above equation (2) was carried out by stirring at ko to 43 ^{° C. for 2.5 hours.}

The product was neutralized with 20 ml of acetic acid and the acetone at atmospheric pressure and a pot temperature of 100 C fee-fe. The aluminum connections were extracted with dilute sulfuric acid, followed by extraction with saturated sodium carbonate. The product was then at distilled about 1 torr. Analyzes showed a 105% by weight yield of pseudo-yonDn , based on the nerol / geraniol consumed, before the last distillation and a 10% wt. yield after distillation.

The fractionation of the furfuryl alcohol from pseudojonone should give a theoretical yield of 113 g of furfuryl alcohol (based on a 96% conversion of the furfural). Analyzes by means of gas-liquid chromatography showed 106.3 g of furfuryl alcohol before the last distillation and 95.1 g after the last distillation for an isolated weight yield from furfural of 82 %. A recovery of over 96 % is possible, which increases the economy of the process according to the invention.

Example 5

This example illustrates the principles of the invention in the Dppenauer oxidation a hemiterpene alcohol and in particular the oxidation of prenol (3-Methy1-2-buten-1-01) to Prenal. Prenol is a commercially available, Product obtained by the catalytic hydration of isoprene in glacial acetic acid to give prenyl acetate which is then rapidly hydrolyzed to alcohol.

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It can also be made directly from dimethylvinylcarbinol with dilute sulfuric acid getting produced. Prenal is a suitable synthetic fragrance Product that gives off a fragrant raspberry scent.

The conversion from Prenol to Prenal can be shown by the following equation will:

₀ , -CHO

^ Furfural _: Prenal

\: i . '·.!'. v ^; - ^v . · '".". ■;': · Furfuryl alcohol

A flask was filled with 2.6 g of aluminum isopropoxide and 21.5 g of prenol and the contents were stirred for 15 minutes; h, B g (2 equivalents) of furfural was then added giving a molar ratio of 1: 2o catalyst to prenol and about 2: 1 for furfural to prenol. The mixture was then allowed to react with stirring at room temperature. Gas-liquid chromatography analyzes indicated about 70 % conversion after 3 hours. Continuing the reaction overnight resulted in a 98 % conversion to Prenal.

Example 6

This example explains the application of the inventive concept for the oxidation of 2-hexen-1-ol.

A reaction vessel was filled with 5.0 g of trans- 2-hexen-1-ol, 5 g of furfural and 2 ml of a 20% solution of aluminum isopropoxide in toluene. The mixture was allowed to react at room temperature for 16 hours. Gas-liquid chromatographic analyzes showed a furfural conversion of 73 % to furfuryl alcohol

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ORIGINAL WSPEGTED

and a conversion of hexenol to trans- 2-hexenol of 71 % . Only trace amounts of by-products were observed, which accounted for less than 2% of the crude product.

Example 7

In this example, Farnesol is the substrate. A reaction vessel was filled with k, k g of farnesol (a mixture of 4 isomers of 3,7,11-trimethyl ~ 2,6-1o-dodecatriene-1-als), 1.9 g of furfural and 1 ml of a 20% solution charged by aluminum isopropoxide in toluene. The Bemisch was Ik hours at room temperature allowed to react.

Gas-liquid chromatography analyzes indicated a conversion of furfural to furfuryl alcohol of 78 % and a comparable conversion of farnesol to farnesal. (Partial peak overlap of some of the Farnesol and Farnesal isomers prevented a precise analysis of the conversion of farnesol to farnesal from being carried out). The only by-products observed were about 5%, which are believed to be isofarnesals.

Example B.

A reaction vessel was charged with 2.6 g of cinnamyl alcohol, 2.0 g of furfural and 1.0 ml of a 20% strength solution of aluminum isopropoxide in toluene. The solution was allowed to react for 16 hours at room temperature. Gas-liquid chromatography analyzes indicated a conversion of furfural to furfuryl alcohol of 82% and a conversion of cinnamyl alcohol to cinnamaldehyde of 85 % . Less than about 2 % by-products were determined.

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Example 9

This example illustrates the advantages of the invention using furfural in comparison to the use of other oxygen acceptors, namely Cyclohexanone and benzaldehyde. The comparative reactions were among the same Conditions with equal equivalents of hydrogen acceptor, substrate and Catalyst carried out.

With benzaldehyde: A flask was filled with 3.1 g geraniol, 0.25 g aluminum isopropoxide and 2.1 q (1 equivalent) benzaldehyde charged, the contents for 16 hours Stirred at ambient temperature. Gas-liquid chromatography analyzes only cried a 5% conversion of geraniol to citral.

With cyclohexanone: A flask was filled with 3.1 g of geraniol, q, 25 g of aluminum isopropoxide and 1.9 η (1 equivalent) cyclqhexanone charged, the content 16 hours stirred at ambient temperature. Gas-liquid chromatography analyzes indicated only a 15% iqe Urnuandluno in citral.

With furfural: A flask was filled with 3.1 g geraniol, 0.25 q aluminum isopropoxide and 1.9 g (1 equivalent) of furfural charged, the contents for 16 hours Stirred at ambient temperature. Gas-liquid chromatography analyzes showed a 79% conversion of geraniol to citral.

Example 1o

In this example comparative tests with furfural and isobutyraldehyde! described, which has a higher oxidation potential under the same conditions . shows. j

l - I

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Two halves were each with a solution of 1.5 g of aluminum isopropoxide filled in 1d g geranial. There were 1.5 equivalents of furfural in one calving and added 1.5 equivalents of isabutyraldehyde in the other. Both were calving Let react for 20 hours at ambient temperature. Gas-liquid chromatography analyzes gave the following results:

Hydrogen acceptor% geranial% yield

consumed to citral

Furfural 94, ο % 98 + %

Isabutyraldehyde 78.2 % 88.1%

Example 11

This example illustrates the use of triisabutylaluminum under Production of the aluminum alkoxide catalyst. Calving was done with 8a g of neral and charged 1a ml of a 25% Läsuna van triisabutylaluminum in toluene.

39 g (α, 75 equivalents) of furfural were added to the solution and the solution was allowed to react for 18 hours at ambient temperature. Gas-liquid chromatography analyzes showed that G9 % of the nerol had been consumed to obtain citral in a yield of 9B + %.

Example 12

This example illustrates the oxidation of perillyl alcohol to perillyl aldehyde. A flask was filled with 100 ml of toluene and 16 g of furfural and under reflux to remove any water present using an azoetraper Distillation heated.

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The solution was then cooled to room temperature and 50 g of perillyl alcohol and 2.5 g of aluminum oxide were added. The solution was then heated ^{to 75 ° C. for 3 hours.} Gas-liquid chromatography analyzes indicated a degree of conversion of more than 90% to perillylaldehyde.

Example 13

This example illustrates the principles according to the invention in the Oppenauer oxidation of benzyl alkali to benzaldehyde. A half-tube equipped with a Dean-Stark trap was filled with 32.5 g (0.3 times) of benzyl alcohol and 3a ml of toluene and heated under reflux to remove any water contained by azeotropic distillation. The solution was cooled to room temperature and 28.8 g (α, 3 moles) of furfural and 2, α g of Cd, d1 moles) of aluminum isoprap hydroxide were added. _;

The mixture was stirred at ambient temperature; samples were taken at intervals for gas-liquid chromatography analyzes. After 5 hours, 61.5 % of the enzyl alcohol had been converted to benzaldehyde and 68.3 % furfural to furfuryl alcohol. After 72 hours the conversion to benzaldehyde had increased to 63.9 % and to furfuryl alcohol to 74.5 % . Heine by-products derived from benzyl alcohol or furfural could be determined by gas-liquid chromatography.

Example 14

A Holben was filled with 3.1 g (20 millimoles) of 2,6-dimethyl-2,7-octadien-1-al, 0.3 g (1.5 millimoles) of aluminum isopropoxide and 2.0 g (21 millimoles) of furfural charged, the contents were stirred for 16 hours at ambient temperature,

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-Zk-

Analyzes of the product by means of vapor phase chromatography showed a 95% conversion of the starting alcohol to 2,6-dimethyl-2,7-actadienal at.

Dr Ro/ho

G09851 / 1123

Claims (1)

Claims Process for the Oppenauer oxidation of primary Alcohols from the group of the primary allylic bzu. AllylalkDhole that are substituted at least in the 2-position by a hydrocarbon radical and in which the allylic double bond is acyclic, exocyclic or end-cyclic is; primary benzylic bzuj. Benzyl alcohol and 3-substituted and 3,3-disubstituted allyl alcohols to the corresponding aldehydes in the presence of a Dppenauer oxidation catalyst and hydrogen acceptor under Oppenauer-Oxidationsbedinqunqen, characterized in that furfural is used as a hydrogen acceptor and a reaction product mixed forms which contains the aldehyde corresponding to the primary alcohol and furfuryl alcohol as a by-product. 2. l / experience according to claim 1, characterized in that that a molar ratio of furfural to primary alcohol in the range of about 1o: 1 to 1: 1o is used. 3. The method according to claim 2, characterized in that there is a molar ratio of furfural to primary alcohol in the range from 3: 1 to 1: 2 used. 4. The method according to any one of claims 1 to 3, characterized in that an allyl alcohol is used as the primary alcohol, which is substituted with aliphatic or aromatic groups. 609851/1123 5. Uerfahren according to claim h, characterized in that IMerol / geraniol (3,7-dimethyl-2,6-octadien-1-ol) is used as the allyl alcohol, this reaction product mixture containing citral. 6. Uerfahren according to claim 5, characterized in that the citral reaction product under an aldol condensation Reaction with a ketone and a base without added purification is subjected. 7. Uerfahren according to claim 6, characterized in that the ketone used is acetone and the aldol condensation product Is pseudojonon, where a molar ratio of furfural to (\ Ierol / Geraniol used at greater than about 1: 1. 8. Uerfahren according to claim k, characterized in that the allyl alcohol prenol (3-methyl-2-buten-1-ol) is oxidized to prenal. 9. Uerfahren according to claim k, characterized in that the allyl alcohol farnesol (3,7,11-trimethy1-2,6,1o-dodecatriene-1-Dl) is oxidized to farnesal. 10. Uerfahren according to any one of claims 1 to 3, characterized in that a Uertreter monosubstituted with an aromatic group is used as the allyl alcohol. 11. Uerfahren according to claim 1o, characterized 609851/1 123 draws that the allyl alcohol used is cinnamyl alcohol (C ₆ H ₅ CH = CHCH ₂ DH). 12. The method according to any one of claims 1 to 3, characterized in that the allyl alcohol is one with an aliphatic Group monosubstituted representatives used. 13. The method according to claim 12, characterized in that the allyl alcohol is 2-hexen-1-ol. Iff. Method according to one of Claims 1 to 3, characterized in that the primary alcohol used is Perilly! alcohol (1-hydroxymethyl-4-isopropenylcyclohexene) used. 15. The method according to any one of claims 1 to 3, characterized in that the primary alcohol used is benzyl alcohol. 16. The method according to any one of claims 1 to 3, characterized in that the alcohol used is Methally! alcohol. j 17. The method according to any one of claims 1 to 3, characterized in that the alcohol 2, G-dimethyl-2,7-octadien-1-al ; used. : 18. The method according to any one of claims 1 to 3, j characterized in that the alcohol used is Myrtenol. 609851/1123