Cyclohexene limonene

Die Xylol-sensibilisierte Bestrahlung von ( + )-l-Methyl-4-isopropcnyl-cyclohexen (Limonen) ftihrt in Methanol zu cis- und trans-4-Methoxy-4-methyl-l-isopropenyl-cyclohexan (28 bzw. 18% d.Th.)5. Das unumgesetzte Limonen wurde zu 84% racemisiert. 

Mit Palladium-Kohle und Cyclohexen, Limonen oder p-Menthen als Donatoren wird weder Cyclopentanon noch Heptanal reduziert. 

Synonyms Cajeputene Cinene Cyclohexene, 1-methyl-4-(1-methylethenyl)- Dipanol Dipentene (INCI) Inactive limonene 4-lsopropenyl-1-methyl-1-cyclohexene ( )-Limonene 1,8(9)-p-Menthadiene dl-p-Mentha-1,8-diene p-Mentha-1,8-diene ( )-1,8-p-Menthadiene 1-Methyl-4-isopropenylcyclohexene 1-Methyl-4-isopropenyl-1 -cyclohexene 1 -Methyl-4 (1-methylethenyl) cyclohexene Racemic limonene... 

The activity of the FePeCli6-S/tert-butyl hydroperoxide (TBHP) catalytic system was studied under mild reaction conditions for the synthesis of three a,p-unsaturated ketones 2-cyclohexen-l-one, carvone and veibenone by allylic oxidation of cyclohexene, hmonene, and a-pinene, respectively. Substrate conversions were higher than 80% and ketone yields decreased in the following order cyclohexen-1-one (47%), verbenone (22%), and carvone (12%). The large amount of oxidized sites of monoterpenes, especially limonene, may be the reason for the lower ketone yield obtained with this substrate. Additional tests snggested that molecular oxygen can act as co-oxidant and alcohol oxidation is an intermediate step in ketone formation. 

Lemon oil contains limonene or methyl-4-isopropenyl-l-cyclohexene, as shown in Fig. 7.4.2. 

Figure 12.13 Pyrogram of a natural rubber latex paint. Peak assignments 1, isoprene 2, toluene 3, xylene 4, 4 ethenyl 1,4 dimethyl cyclohexene 5, limonene 6, dehydro p cymene...

Synonym d-p-mentha-l,8,-diene, (R)-(+)-p-mentha-l,8-diene, (+)-l-methyl-4-(l-methylethenyl)cyclohexene, p-mentha-1,8-diene, carvene, cinene, citrene, cajeputene, kautschin Chemical Name dextro-limonene, (R)-(+)-limonene CAS Registry No 5989-27-5 Molecular Formula C10H16 Molecular Weight 136.234 Melting Point (°C) ... 

Thus, the oxidation potential of the former type of diene (limonene) is substantially the same as that of the corresponding monoolefin (1-Me-cyclohexene), whereas norbor-nadiene and bicyclo[2.2.2]octadiene show much lower oxidation potentials than those of norbornene and cyclohexene. 

RhCl(COD) 2] + Ph2P(CH2)2C0NHC(CH3)2CH2S03Li 1-hexene 1-octene cyclopentene cyclohexene cyclooctene carvone limonene... 

The liquid phase alkoxylation of limonene (3) with C4-C4 alcohols to 1-methyl-4-[a-alkoxy-isopropyl]-l-cyclohexene (5) was carried out both in batch and continuous fixed-bed reactor at 60 °C on various acidic catalysts (Scheme 3.1) [16]. The best yields were obtained in batch (85%) or continuous reactor (81%) using a /1-type zeolite with Si02/Al203 = 25. 

Limonene (10.128) is an analogue of 4-vinylcyclohexene, and, like the latter, it undergoes epoxidation of both the C(1)=C(2) and C(8)=C(9) bonds. Like in the dioxide 10.127, the two epoxide groups are hydrated at different rates by EH. Indeed, incubations in rat liver microsomes showed that hydrolysis of limonene 1,2-epoxide was 70 times slower than that of the 8,9-epoxide, a much larger difference than that observed for the dioxide 10.127 [192], Comparison of EH-catalyzed hydration of the four epoxy groups in 4-vinyl-cyclohexene and limonene confirmed that the relative rates decreased with increasing steric hindrance at these groups. 

Auf analoge Weise erhalt man aus z. B. 6-Acetoxy-l, 8-menthadien 6-Amino-1,8-menthadien (6-Amino-4-isopropenyl-l-methyl-cyclohexen 6-Amino-limonen) in 84%iger Ausbeute1. Bei einer Variante der letzteren Reaktion wird ein Phosphorsaure-(4-acetoxy-2-butenyl-ester) zunachst mit 2-Methyl-piperidin umgesetzt und dann in der obigen Weise weiter verfahren man erhalt auf diese Weise 4-Amino-I-(2-methyl-piperidino)-2-buten in 84% Ausbeute1 ... 

Figure 5.7. There are many examples now known of the synthesis of NPs via matrix pathways (see also Figure 9.3). However, a nice example of the benefit of such flexibility was revealed when a mutant of spearmint that had smelled more like peppermint was studied.A comparison of the terpenes in both plants revealed that the single gene mutation had not resulted in a single chemical change but multiple changes, in the mutant plant, a hydroxyl group was added to the 3-position of the cyclohexene ring of limonene while the wild-type hydroxylated the 6-position. Some of the other wild-type tailoring enzymes in the mutant did not discriminate fully between the 3- and 6-hydroxylated products so a new family of NPs were produced which gave the mutant plant an odour of peppermint.

In the essential oil, apart from cuminaldehyde, perilla aldehyde (4-(l-methyl-ethenyl)-l-cyclohexene-l-carboxaldehyde), cumin alcohol or 4-isopropylbenzyl alcohol, a-pinene and /3-pinene (21%), dipentene, p-cymene, /3-phellandrene and limonene (Fig. 11.1) have been reported by Baser et al. (1992). 

Limonene (+ )- -Mentha-1,8-diene (8) Cyclohexene, l-methyl-4-(l-methylethenyl)- (9) (5989-27-5)... 

The zeolite-catalyzed alkoxylation of limonene (53, 54) and alpha-pinene (55, 56) over acid-treated mordenite, clinoptilolite and ferrierite as catalysts has already been reported in the literature. The best results were obtained for methoxylation of limonene in the presence of a clinoptilolite-type zeolite (60% yield). The alkoxylation of alpha-pinene with methanol in the presence of mordenite also achieved the highest yields of 66% for l-methyl-4-[alpha-methoxy-isopropyl]-l-cyclohexene. Syntheses of l-methyl-4-[alpha-alkoxy-isopropyl]-l-cyclohexenes via zeolite-catalyzed alkoxylation of other terpenes were reported in a review paper (57). 

Methanol reacts with limonene over acidic catalysts in a batch reactor to 1-methyl-4-[alpha-methoxy-isopropyl]-l -cyclohexene (alpha-terpinyl methyl ether) as the main reaction product (see Eq. 15.3.3 R- = CH3-). Besides the desired methoxylation, isomerisation reactions leading to terpinolene and traces of alpha-and gamma-terpinene can be observed. Furthermore, the addition of methanol to the methylterpinylether leads to the undesired cis- or trans-1,8-dimethoxy-p-menthane. The amount of unidentified products does not exceed 1%. At high temperatures and long reaction times the reverse reaction of the alpha-terpinyl methyl ether and the other addition products to limonene and its isomers can be observed. The reaction scheme of the alkoxylation oflimonene is illustrated in Equation 15.3.5. 

The reaction pathway is identical to that of alpha-pinene alkoxylation except no bicyclic compounds are formed. As mentioned in the literature (53, 54), alkoxylation of limonene to l-methyl-4-[alpha-alkoxy-isopropyl]-l-cyclohexene can be carried out only in the presence of acidic catalysts. After a catalyst screening using various zeolitic and non-zeolitic acid heterogeneous catalysts, we found that beta zeolite is the best candidate. 

Addition of methanol to limonene in the presence of a beta zeolite produces the highest selectivity to l-methyl-4-[alpha-methoxy-isopropyl]-l-cyclohexene of about 93% at 91% conversion. Surprisingly, the highest yield of about 85% has been obtained at room temperature. The other zeolites and solid acids applied for the alkoxylation of limonene reveal considerably lower conversion and selectivity. 

It is interesting to note that the destruction of the structure of beta zeolite by treatment with strong acids or high temperature leads to a complete deactivation of the catalyst for limonene alkoxylation. By using a higher reaction temperature only isomerisation and polymerisation products have been obtained. 1-methyl-4-[alpha-methoxy-isopropyl]-1 -cyclohexene or other addition products cannot be found. 

The chosen mass ratio between methanol and limonene of 2 1 is advantageous, because the feedstock and the products are well dissolved at this concentration. However, the excess of methanol can react with l-methyl-4-[alpha-methoxy-isopropyl]- -cyclohexene to cis- or trans-1,8-dimcthoxy-p-menthane in a... 

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