Цитрал

Химические свойства

Citral occurs as (2Z)- and (2E)-isomers (citral a and b, respectively) analogous to the corresponding alcohols, geraniol and nerol: geranial (citral a), bp2.7 kPa 118–119 °C, d20 0.8888, n20 D 1.4898; neral (citral b), bp2.7 kPa 120 °C, d20 0.8869, n20 D 1.4869. Natural citral is nearly always a mixture of the two isomers. It occurs in lemongrass oil (up to 85%), in Litsea cubeba oil (up to 75%), and in small amounts inmany other essential oils. The citrals are colorless to slightly yellowish liquids, with an odor reminiscent of lemon.
Since citral is an α,β-unsaturated aldehyde with an additional double bond, it is highly reactive and may undergo reactions such as cyclization and polymerization. Geraniol, citronellol, and 3,7-dimethyloctan-l-ol can be obtained from citral by stepwise hydrogenation. Citral can be converted into a number of addition compounds; the (Z)- and (E)-isomers can be separated via the hydrogen sulfite addition compounds.The condensation of citral with active methylene groups is used on an industrial scale in the synthesis of pseudoionones, which are starting materials for ionones and vitamins.

Вхождение

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

Использование

Citral 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.

Определение

Commercial material is a mixture of α and β isomers.

Общее описание

A 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.

Реакции воздуха и воды

Insoluble in water.

Профиль реактивности

Citral is an aldehyde. Aldehydes are frequently involved in self-condensation or polymerization reactions. These reactions are exothermic; they are often catalyzed by acid. Aldehydes are readily oxidized to give carboxylic acids. Flammable and/or toxic gases are generated by the combination of aldehydes with azo, diazo compounds, dithiocarbamates, nitrides, and strong reducing agents. Aldehydes can react with air to give first peroxo acids, and ultimately carboxylic acids. These autoxidation reactions are activated by light, catalyzed by salts of transition metals, and are autocatalytic (catalyzed by the products of the reaction). The addition of stabilizers (antioxidants) to shipments of aldehydes retards autoxidation. Citral can react with alkalis and strong acids. Citral can readily isomerize.

Опасность

Questionable carcinogen.

Пожароопасность

Citral is combustible.

Контактные аллергены

Citral is an aldehyde fragrance and flavoring ingredient, a blend of isomers cis (Neral) and trans (geranial). As a fragrance allergen, citral has to be mentioned by name in cosmetics within the EU.

Профиль безопасности

Moderately toxic by intraperitoneal route. Mildly toxic by ingestion. Experimental reproductive effects. A severe human and experimental skin irritant. Mutation data reported. Combustible liquid. When heated to decomposition it emits acrid smoke and irritating fumes.