3,7-Dimethylocta-2,6-Dienal

OccurrenceReported found in apricot, clary sage, ginger, grape, grapefruit, lemon, lime, mandarin, orange, raspberry, tamarind, tangerine, tea and tomato.

UsesCitral is a liquid flavoring agent, light yellow in color with a citrus odor. it occurs in lemon and lemongrass oils. it is usually obtained from citral-containing oils by chemical means but may also be pre- pared synthetically. it is soluble in fixed oils, mineral oil, and pro- pylene glycol. it is moderately stable and should be stored in glass, tin, or resin-lined containers. it is used in flavors for lemon with applications in candy, baked goods, and ice cream at 20–40 ppm. it is also termed 2,6-dimethyl-octadian-2-6-al-8.

UsesCitral is an anti-microbial agent found in plants with antibacterial activity against some food pathogens. It is also a fragrance compound with a distinct lemon scent.

Usescitral is a naturally occurring aroma compound used to provide a lemon-type fragrance. Citral is a constituent of lemon oil, lemongrass oil, lime oil, ginger oil, verbena oil, and other plant-derived C essential oils.

General DescriptionA clear yellow colored liquid with a lemon-like odor. Less dense than water and insoluble in water. Toxic by ingestion. Used to make other chemicals.

PreparationSince citral is used in bulk as a starting material for the synthesis of vitamin A, it is produced industrially on a large scale. Smaller quantities are also isolated from essential oils. 1) Isolation from essential oils: Citral is isolated by distillation from lemongrass oil and from L. cubeba oil. It is the main component of these oils. 2) Synthesis from geraniol: Currently, the most important synthetic procedures are vapor-phase dehydrogenation and oxidation of geraniol or geraniol–nerol mixtures. Catalytic dehydrogenation under reduced pressure using copper catalysts is preferred. 3) Synthesis from dehydrolinalool: Dehydrolinalool is produced on a large scale from 6-methyl-5-hepten-2-one and acetylene and can be isomerized to citral in high yield by a number of catalysts. Preferred catalysts include organic orthovanadates, organic trisilyl oxyvanadates, and vanadium catalysts with silanols added to the reaction system. 4) Synthesis from isobutene and formaldehyde: 3-Methyl-3-buten-l-ol, obtained from isobutene and formaldehyde, isomerizes to form 3-methyl- 2-buten-lol. However, it is also converted into 3-methyl-2-butenal by dehydrogenation and subsequent isomerization. Under azeotropic conditions in the presence of nitric acid, 3-methyl-2-buten-l-ol and 3-methyl-2-butenal form an acetal (shown as follows), which eliminates one molecule of 3-methyl-2-buten-l-ol at higher temperatures. The intermediate enol ether undergoes Claisen rearrangement followed by Cope rearrangement to give citral in excellent yield: Today, this route is performed on a very large industrial scale in a continuous reactive distillation process.