3-Methyl-l-cyclohexene

Cyclohexene, l-methyl-4-(l-methylethenyI)-) to (Cyclohexane, 1-methoxy-l-methyl-4-(l-ethenyl-l-methyl-)... 

Tocopherol was effective and ascorbic acid ineffective in the protection of citrus oils evaluated by aroma (13). In a typical study, 5 g of orange oil was oxidized in 75-mL open brown bottles at 45°C and was evaluated by a panel after 6 d, at which time it was ranked as off-odor, "terpeney. The peroxide value of the initial oil was zero the oxidized material had a PV of 100. As a result, days to reach 100 PV was used as an endpoint. Comparative antioxidant effects on a number of citrus oils and on D-limonene [cyclohexene, l-methyl-4-(l-methylethenyl)-(R)-5989-27-5] are presented in Table X. BHA is the most active while AP has no activity alone but does synergize with tocopherol. 

Cyclohexene, l-methyl-4-( 1 -methyl-ethenyl)- [138-86-3], 56, 106 2-Cyclohexene-1-carboxylic acid, 2-... 

A.46) Cyclohexene, l-methyl-4-(l-methylethenyl)-, 4-isopropenyl-l-methyl-1-cyclohexene, p-mentha-1,8-diene, limonene, dipentene [138-86-3] ( )- [7705-14-8] ( )-(/ )- [5989-27-5]... 

Cyclohexene, l-methyl-4-(methylethylidene)- jterpinolene 172a 174a, 174b, 603, 3370... 

The rate of transfer hydrogenation also varies markedly with donor structure. For cyclohexene, 1 -methylcyclohexene, l-methyl-4-isopropyl-cyclohexene,and l-methyl-4-f-butyIcycIohexene as donor in the above hydrogenations, after 1 min the reduction was 11, 78, 99, and 99% complete, respectively (97). 

Triethyl- and triphenylphosphine have been used for deoxygenation not only of hydroperoxides to alcohols but also of dialkyl peroxides to ethers, of diacyl peroxides to acid anhydrides, of peroxy acids and their esters to acids or esters, respectively, and of endoperoxides to oxides [290] in good to excellent yields. The deoxygenation of ascaridole to l-methyl-4-isopropyl-l,4-oxido-2-cyclohexene [290] was later challenged the product is claimed to be p-cymene instead [668]). 

C H3 >=N-OH Na[BHJ/NiCl2 -6H20/C3OH - 30° 1 h Na[BH4]/Mo03/CH30H 0° - lh 3-Amino-4-methyl-1 -iso-propyl-cyclohexan (2-A mino-menthan) 6-Amino-l-methyl-4-iso-propyl-cyclohexen 90 90 5 5... 

E-1,2-Dichlorovinyl)-4-methyl-2-cyclohexen-l-one 2-Cyclohexen-l-one, 4-(l,2-dichloroethenyl)-4-methyl- (10) (73843-27-3)... 

FEMA No. 2249 fevo-Carvone l-l-Methyl-4-isopropenyl-6-cyclohexen-2-one... 

Among the hydroformylated l-methyl-4-[alpha-alkoxy-isopropyl]-l-cyclohexenes, i.e. 8-methoxy-p-menthan-2-carboxyaldehyde, the methyl ether 36 (Eq. 15.3.4) smells mangofruit-like and might be used as a perfumery material. The ethyl derivative has a green citrous fragrance, the propyl one has a fresh grass flavour and the butyl one smells woody. 

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). 

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. 

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... 

The addition of methanol to alpha-pinene in the presence of the above mentioned beta zeolite as catalyst in the batch reactor results in the cleavage of the cyclobutane ring and yields l-methyl-4-[alpha-methoxy-isopropyl]-l-cyclohexene (alpha-terpinyl methyl ether) as the main reaction product. The most common by-products to be found are isomerization compounds like camphene, limonene and terpinolene, and several bicyclic and double addition products, e.g. endo- or exo-methylbomylether, endo- or exo-methylfenchylether and cis- or trans-1,8-dimethoxy-p-menthane. 

The influence of temperature has been investigated within the range from 25 °C to 80 °C. The optimum temperature for alpha-pinene methoxylation has been found at 40 °C at a reaction time of 5 h. At this temperature, the highest selectivity obtained over beta zeolite is about 54% at 92% conversion. A temperature above 40 °C gives significant reduction in selectivity due to occurrence of consecutive reactions or decomposition of l-methyl-4-[alpha-methoxy-isopropyl]-l -cyclohexene and other side reactions at even shorter reaction times. A lower temperature causes a drop of the alpha-pinene conversion. However, this can be compensated by a longer reaction time (59). The dependencies of temperature and reaction time are consistent with the above observations for limonene methoxylation. However selectivities up to 98% are obtained for limonene methoxylation, whereas the highest selectivity achieved for methoxylation of alpha-pinene amounts to 54%. On account of the above mentioned additional formation of various bicyclic addition products, the selectivities for all methoxy compounds increase to about 80%. This indicates that for the production of l-methyl-4-[alpha-methoxy-isopropyl]-l-cyclohexene beta zeolite is more selective for the addition of methanol to limonene than to alpha-pinene. The activity of the catalyst, however, is nearly the same for both reactions. 

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