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I'm designing an experiment to extract the amygdalin from apricot leaves and kernels. I want to steam the kernels and leaves, grind them, add water and then filter it using a filter paper. Then transfer the solution to a separatory funnel, add dichloromethane (DCM), shake and collect the bottom DCM layer that I'm hoping would contain the amygdalin.

This is the process I used for extracting caffeine from coffee beans and it worked because caffeine is much more soluble in DCM than in water. However, I'm not sure about the solubility of glycosides and whether this process would even work or not which is why I'm making this post.

How soluble are glycosides in DCM, is it enough to make this work? If not, what other solvents do you recommend?

Also, how can I increase the efficiency of this process in general? I've been thinking of using vacuum filtration, but I'm not sure. Tell me what you think.

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Anybody with glycoside isolation from bio-matrices would tell you that your plan is not going to work. Amygdalin is classified as a cyanogenic glycoside because it contains nitrile moiety. It is contained in the seeds of bitter almond, apricot, apple, black cherry, peach, plum, etc. Amygdalin was first isolated in 1830 from bitter almond seeds (Prunus dulcis) by French chemists, Pierre-Jean Robiquet and Antoine Boutron-Charlard. Traditionally, the extraction method of the chemical ingredients in the medicinal materials is decoction in boiling water, which was the method French chemists has used to isolate amygdalin. Presently, it has been isolated using several other methods and its structure has been characterized by several groups around the world.

Amygdalin can be dissolved in water and ethanol easily. Solubility of amygdalin in water and ethanol is $\pu{83 g/L}$ and $\pu{1 g/L}$, respectively (Ref.1). Ref.1 described the isolation of amygdalin from plum seeds for the first time, has used ethanol to extract soluble compounds, and finally, used diethyl ether to isolate amygdalin from the complex ethanol extraction mixture. Before extract, the plant material was dried to the moisture content of 6% in a dark place and then ground in a blender to obtain a fine powder with average particle size of $\pu{0.3 mm}$. The ethanol extraction and diethyl ether isolation procedure used in Ref.1 have been described as follows:

The powdered solid plant material ($\pu{2.0 g}$) was transferred into the Plant material (2 g) was transferred into the $100$-$\pu{mL}$ round bottom flask and treated with exactly defined volume of ethanol. The extractions at higher temperatures were carried out under reflux, while the extractions at lower temperatures were carried out in closed vessels. The system temperature was maintained using a water bath. After extraction, the extract was separated from the solid plant material by filtering process. Plant extracts were evaporated in rotary evaporator under reduced pressure to remove the solvent, and then stored in desiccator until it reached the constant mass. After addition of diethyl ether ($\pu{10 mL}$) to the complex extraction mixture, amygdalin was precipitated, while fatty compounds were dissolved. The dissolved fatty compounds were removed by decanting process. The solid phase was dried at $\pu{30 °C}$ in order to remove the residual solvent. In this way, the sample was prepared for determination of its purity using HPLC analysis and structural characterization by FT-IR, UV, and MS methods.

The effect of extraction time ($\pu{10–120 min}$), ethanol concentration ($20–100\%,\: v/v$), solid-to-liquid ratio ($1: 5\: – 1: 25,\: m/v$) and extraction temperature ($\pu{22–78°C}$) on the content of amygdalin in the dried extract has been studied. As a result, the optimal conditions were achieved: The extraction time of $\pu{120 min}$; $100\% \:(v/v)$ ethanol; solid-to-liquid ratio of $1:25\: (m/v)$; and extraction temperature of $\pu{34.4°C}$. The optimal yield of $\pu{25.30 g}$ of amygdalin content in the extracts per $\pu{100 g}$ of dried extract was reported.

Reference:

  1. Ivan M. Savic, Vesna D. Nikolic, Ivana M. Savic-Gajic, Ljubisa B. Nikolic, Svetlana R. Ibric, Dragoljub G. Gajic, “Optimization of technological procedure for amygdalin isolation from plum seeds (Pruni domesticae semen),” Frontiers in Plant Science 2015, 6, Article 276 (11 pages) (DOI: 10.3389/fpls.2015.00276).
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  • $\begingroup$ I understand that your answer explains what has been done before, but you don't mention what is wrong with DCM as a precipitant. $\endgroup$ – Buck Thorn Jun 9 at 10:00
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    $\begingroup$ If amygdalin is 80-times more soluble in water than in ethanol, do you think it would be soluble in dichloromethane? The OP envisons extrcting with DCM (like caffeine), not precipitating. But you are right, the solubility of amygdalin in DCM is not addressed in this answer. @BuckThorn $\endgroup$ – Karsten Theis Jun 9 at 16:18
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    $\begingroup$ Ok, then I misunderstood how the DCM was to be used. I thought it might be used to precipitate amigdalin. $\endgroup$ – Buck Thorn Jun 9 at 17:29
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    $\begingroup$ @Buck Thorn: Karsten Theis was right on spot answering your question. DCM may be good enough to precipitate amigdalin, but not for solvent extraction. I'd even use ethyl acetate instead of DCM for environmental concern. When you look at solubility difference of amigdalin in water and ethanol, it is obvious that it won't dissolve in DCM preferably, because hydroxy group interactions are seemingly playing important role here. $\endgroup$ – Mathew Mahindaratne Jun 9 at 20:12
  • $\begingroup$ Thanks for the very helpful comment $\endgroup$ – queenslyr Jun 11 at 22:01

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