Citronellal

• Rhodinal
• 3,7- dimethyl- 6- octen- 1-al

Colorless liquid with a fruity odor

Liquid

0.85 g · cm -3

208 ° C

Insoluble in water

1,451

Attention

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Citronellal, also Rhodinal ( emphasis respectively on the final syllable: citronellal, Rhodinal ) is a clear, viscous liquid. Is a monoterpene aldehyde.

Occurrence

(R ) -citronellal is mainly found in citrus plants and citronella. The oil of the leaves of the lemon contains 25000-89000 ppm, the fruit of lime about 140 and the fruits of the commons juniper about 160 ppm ( R) - citronellal. ( S)- citronellal, with about 80% of the main component of the essential oil of the leaves of kaffir lime.

Production and representation

Citronellal can be prepared from pinene from. β -pinene is umformiert at temperatures above 500 ° C in the myrcene. Myrcene reacts with diethylamine and butyllithium. The resulting chelate reacts to N, N- diethyl geranylamine, which is rearranged to a specific catalyst for (3R) -1E -1 -diethylamino- 3 ,7 -dimethyl-1 ,6-octadiene. This is hydrolyzed to citronellal.

The heterogeneously catalysed hydrogenation of citral in the presence of palladium catalysts usually leads with Citronellal as an intermediate stage for Dihydrocitronellal. In the presence of ionic liquids based on imidazolium nitrilfunktionalisierten, the second hydrogenation step can be suppressed, and as citronellal can be obtained as main product.

Properties

The liquid boils at a standard pressure of 101.3 kilopascals at about 208 ° C. The density is about 0.85 g · cm -3. It is readily soluble in ethanol, in water and glycerol, however, hardly. The molar mass is 154.25 g · mol -1. The flash point is 78 ° C.

Use

It is itself used as a starting material for the synthesis of (1R, 3R, 4S ) - (- )-menthol. This forms, first with a zinc bromide chelate is converted into isopulegol which is then hydrogenated to menthol. It is also used for the preparation of hydroxycitronellal, to which it can react in the presence of water.

It is used in cheap perfumes, for perfuming cigarettes and as an insect repellent fabric ( repellent).

By condensation with 5-n- pentyl- 1 ,3-cyclohexanedione followed by a Diels -Alder reaction can not occur in nature cannabinoid Hexahydrocannabinol ( HHM), its (R ) - epimer is comparable active as the Δ ⁸ -tetrahydrocannabinol ( Δ ⁸ -THC ) ( which is contained in contrast to Δ9 -THC only in small amounts in cannabis), can be synthesized stereoselectively.