Citronellal Sigma is the main component of citronella oil, which naturally exists in essential oils such as lemon eucalyptus oil and citronella oil, with the content reaching 75% to 80% and 30% to 40%, respectively. This product is insoluble in water and glycerin, soluble in ethanol and oil, slightly soluble in propylene glycol. A strong, fresh, green citrus-like, slightly woody aroma. Unstable on exposure to air, sunlight and contact with alkalis. Citronellal can form binary azeotropes with nitrobenzene, m-cresol, ethylene glycol, benzyl alcohol, acetophenone, etc. Partially decomposed into isopulegol at 350 ℃, and stored in the air not only to obtain isopulegol, but also partially oxidized to (+)-citronellic acid, and formed peroxide, which can be inhibited by adding hydroquinone, It is oxidized with silver oxide in ammonia water to obtain citronellic acid, and catalyzed by platinum black in 75% ethanol to obtain 2,6-dimethyloctanal. At room temperature, it can be catalyzed by nickel to obtain (+)-citronellol or (+) – Dihydrocitronellol; Grignard reaction can also occur.
Citronellal Sigma can be obtained from the oxidation or catalytic dehydrogenation of citronellol, and can also be obtained from the catalytic hydrogenation of citral. Citronellal isolated from natural essential oils is optically active due to the presence of an asymmetric carbon atom in the molecule of citronellal. However, citronellal obtained from the hydrogenation of citral is a racemate and has no optical activity.
D-citronellal Sigma mainly exists in Java citronella oil (containing 30% to 40%), and L-citronellal mainly exists in lemon eucalyptus oil (containing 65% to 80%). There are two production methods: one is to vacuum distill crude aldehyde from essential oil, and then add and refine it with sodium bisulfite. Another method is the oxidation of citronellol. Due to the strong aroma of citronellal and its unstable chemical properties, it is only used in low-grade lilac, lily of the valley and other cosmetics and mosquito coils. Citronellal is mainly used in soap and cosmetic essence formulations, and the dosage is within 10%. IFRA has no restrictions.
At present, the number of Citronellal Sigma that is directly used as a fragrance in China is not much, and a large amount of Citronellal Sigma is used to synthesize hydroxycitronellal and L-menthol and other more widely used fragrances.