Leaf alcohol exists in mostly all eco-friendly plants, as well as the supposed icon of the “environment-friendly” of plants is shown in the smell of fallen leave alcohol. Although leaf alcohol has been a web link in the human food web because human background, its presence was not detected in camellia oil until 1895. In 1917, it was uncovered that leaf alcohol existed in Japanese pepper mint oil, and its structure was roughly established. Stoll and Rouve determined that the structure of leaf alcohol was cis-3-hexen-l-ol. Leaf alcohol was also discovered in the fermentation of black tea around 1920, and also around 1930, Japanese chemical workers additionally located it in the fresh leaves of tea. Fallen leave alcohol has been located in lots of greater plants, such as jasmine huge flower, jasmine small blossom, mint, citronella, viola, tomato, tea, thyme, mangosteen, geranium, poultry mulberry, strawberry, grape, kiwi, Pomelo, raspberry, sweet-scented osmanthus, jasmine, violet leaves, red clover, radish, raspberry and also black grasshopper, and so on. The content of fallen leave alcohol in the fallen leave oil of acacia and also mulberry can get to 50%, as well as almost 30% in environment-friendly tea. The natural extraction approach of leaf alcohol can be separated as well as drawn out from these plants, mainly removed from important oils, and after that cleansed by responding with equivalent phthalates or allophanates, and the gotten cis-isomer make up 95%. Essential oils extracted from plants are themselves limited in quantity, and vital oils frequently consist of a variety of substances. Therefore, it is very tough to extract and also separate a certain particular substance (such as fallen leave alcohol), as well as the yield of extraction is also extremely tiny. Clearly, drawing out fallen leave alcohol straight from all-natural plants can not satisfy the demand for leaf alcohol, which is also extremely uneconomical in practice.
Chemical synthesis is presently the main method for producing leaf alcohol. Lots of chemical synthesis approaches have been published in the literary works, as well as several of them have been industrialized. Looking at many chemical synthesis approaches, the secret to the synthesis of fallen leave alcohol is just how to introduce 3-cis double bonds with high return and stereoselectivity. There are 5 major approaches for presenting 3-cis double bonds: one is the catalytic hydrogenation of 3-hexyn-1-ol; the other is the discerning decrease of conjugated hexadienol; the 3rd is 3-chloro-2-ethane The reduction ring-opening of tetrahydrofuran; the 4th is the conversion of cis-olefin by-products; the 5th is making use of Witting response. Different synthetic methods are introduced below.
1) Selective hydrogenation of 3-hexyn-1-ol
The response of 3-hexyn-1-ol with hydrogen in the existence of Lindlar driver can hydrogenate alkynes to remain in the olefin stage and obtain the cis setup. This technique is just one of one of the most crucial approaches for preparing fallen leave alcohol. Amongst them, Japan has made an innovation on this course, which has been applied to commercial production. They used the fundamental basic materials butyne or butadiene in petrochemical products as well as ethylene oxide to prepare the vital intermediate 3-hexyn-1-ol in steel sodium and also liquid ammonia, and after that controlled catalytic hydrogenation to get leaf alcohol. Under the artificial path:
2) Careful catalytic hydrogenation of conjugated diene alcohols: Conjugated diene raw materials are fairly very easy to obtain, as well as conjugated dienols can be obtained from acetaldehyde-crotonaldehyde, sorbic acid, and plastic acetylene. The trick is to find a suitable catalyst to manage 1,4-hydrogenation to get cis-configuration olefins. In 1982, Japanese researchers discovered that when Cr( C0) 6 or Cr( C0) 3 aryl composite stimulants were used, anti- and anti-conjugated dienes could be precisely hydrogenated, and also cis- configured alkenes. Specifically, such as the aldol condensation of acetaldehyde and also crotonaldehyde under the catalysis of phosphoric acid, adhered to by decrease with salt borohydride to acquire (E, E) -2,4- hexadien-1-alcohol, the last uses Cr( CO) 6 as Catalyst, selective 1,4-hydrogenation in methanol to obtain leaf alcohol, the product material is more than 98%, and also the return is about 90%. The response formula is as adheres to:
3) Reductive ring opening of 2-ethyl-3-chlorotetrahydrofuran – tetrahydrofuran method
In 1987, Ding Xinteng and others synthesized fallen leave alcohol by using tetrahydrofuran derivative 2-ethyl-3-chlorotetrahydrofuran as basic material. The synthetic course is as complies with:
This route utilizes magnesium to open up the ring of 2-ethyl-3-chlorotetrahydrofuran, as well as in the resulting product, the cis-isomer (leaf alcohol) represent 85%, and the trans-isomer make
up 15%; The ring-opening of base-3-chlorotetrahydrofuran, in the item, fallen leave alcohol represent 51%, as well as trans isomer accounts for 49%. In order to further rise the return of fallen leave alcohol, You Tianba et al. have actually boosted the above-mentioned process route. The mix of cis as well as trans isomers manufactured according to the above path is converted into 3-hexyn-1-ol, and after that catalytically hydrogenated to get the product, wherein the fallen leave alcohol content gets to 95%.
4) Conversion of cis-olefin derivatives
Leaf alcohol can additionally be prepared by first making a cis-configured double bond, and after that carrying out a conversion approach. An important instance of this is the development of a cis dual bond by means of the Diels-Alder reaction of 1,3-pentadiene with formaldehyde, followed by reductive cleavage with lithium-ethylamine. The raw products of this approach are simple to acquire, as well as the synthesis steps are couple of. The yield in the very first step is 51.5%, the overall return is 43%, as well as the cis isomer (leaf alcohol) > 92% in the acquired item. The synthetic path is as complies with:
5) Witting reaction-3-chloropropanol-triphenylphosphine-propionaldehyde approach
The technique has mild response conditions, short artificial path, high yield and easy-to-obtain resources. In this kind of response, the visibility or absence of the salts in the response solvent and also the solvent has a better influence on the ratio of cis-trans isomers in the product, so picking a suitable solvent and also eliminating the salts in the solvent contribute to boosting the return of phytol. return. Since the prep work of witting reagent is tough as well as it is challenging to divide from the item, this technique is tough to industrialize. Someone bonded the witting reagent to the polymer backbone to prepare a polymer witting reagent for the response, and attained great results.
