How to Get Leaf Alcohol?2022-09-28

----Method for synthesizing leaf alcohol.

1. Extracted from natural plants
Leaf alcohol is present in almost all green plants. But its presence was not detected in tea oil until 1895.
In 1917, it was found that leaf alcohol exists in Japanese peppermint oil, and its structure was roughly determined. Stoll and Rouve determined that the structure of leaf alcohol was cis-3-hexen-l-ol.
Later, leaf alcohol was found in many higher plants one after another. The content of leaf alcohol in the leaf oil of acacia and mulberry can reach 50%, and that in green tea is nearly 30%.
The natural extraction method of leaf alcohol can be isolated and extracted from these plants, mainly extracted from essential oils, and then purified by reacting with the corresponding phthalates or allophanates, and the obtained cis isomer accounts for 95%.
Essential oils extracted from plants are themselves limited in number and often contain a wide variety of compounds. Therefore, it is very difficult to extract and separate a specific compound (such as leaf alcohol), and the extraction yield is also very small.
Obviously, extracting leaf alcohol directly from natural plants cannot satisfy the demand for leaf alcohol, which is also extremely uneconomical in practice.
2. Chemical synthesis
Chemical synthesis is currently the main method for the preparation of leaf alcohol. Dozens of chemical synthesis methods have been published in the literature, and several have been industrialized.
Looking at many chemical synthesis methods, the key to the synthesis of leaf alcohol is how to introduce 3-cis double bond in high yield and stereoselectivity. There are five main methods for introducing 3-cis double bonds:
(1) The catalytic hydrogenation of 3-hexyn-1-ol, which is one of the most important methods for preparing leaf alcohol;
(2) The selective reduction of conjugated hexadienols. Conjugated diene raw materials are easy to obtain, and conjugated diene alcohols can be obtained by using acetaldehyde-crotonaldehyde, sorbic acid, and vinyl acetylene as raw materials;
(3) The reductive ring opening of 3-chloro-2-ethyltetrahydrofuran. In 1987, Ding Xinteng et al. synthesized leaf alcohol from 2-ethyl-3-chlorotetrahydrofuran, a derivative of tetrahydrofuran;
(4) The conversion of cis olefin derivatives. This method is easy to obtain raw materials and has few synthesis steps;
(5) To use the Witting reaction. The method has mild reaction conditions, short synthetic route, high yield and easy-to-obtain raw materials.