9.4.7.4 Alcohol Extraction Overview

Ethanol is one of the oldest solvents used to extract cannabis concentrates and due to its heavily taxed cost and hit and miss availability around at least the US, Isopropanol has gained popularity.

Ethanol and Isopropanol moledules

FDA classifies both solvents as Class III, but also classifies Ethanol as GRAS, or Generally Regarded As Safe.

Both have dielectric indexes above 15, so are polar solvents, with Ispropanol at 18.3 and Ethanol at 24.5.  That means they will have an affinity for other polar molecules like chlorophyll, and the anthocyanin plant color pigments, and some for the carotene, but are not as prone to extract the non polar plant waxes.

They are both also 100% miscible with water, so will extract both water and water soluble components. 

Here is how their dielectric constants compare to a few other select solvents:

NO

Solvent

Dielectric Index

1

Water

80.1

2

Glycerin

42.5

3

Methanol          

32.7

4

Ethanol

24.5

5

Ethyl Acetate

22.3

6

Diethyl Ether

22.1

7

Acetone

20.7

8

Propanol

20.1

9

MEK

18.4

10

Isopropanol

18.3

11

DiMethyl Ether

7.23

12

Acetic Acid

6.2

13

Cotton seed oil

3.1

14

Olive oil

3.1

15

Peanut oil

3.0

16

Sesame oil

3.0

17

Grape seed oil

2.9

18

Refined Coconut oil

2.9

19

Almond Oil

2.8

20

Heptane

1.92

21

Hexane

1.89

22

Pentane

1.84

23

CO2

1.6

24

Propane

1.6

25

Butane

1.4

          Dielectric Index of various hydrocarbons

https://www.organicdivision.org/orig/organic_solvents.html

http://www.engineeringtoolbox.com/liquid-dielectric-constants-d_1263.html

https://www.kabusa.com/Dilectric-Constants.pdf

While some applications call for full plant extraction, not all do.  For instance, Chlorophyll in high concentration causes severe gastric distress in some folks when used orally, and chlorophyll, carotene, and anthocyanins add harshness to vaporization products. 

Chlorophyll is a C-55 sized molecule, and its head is actually similar in structure to human blood hemoglobin, but chlorophyll has a magnesium ion in its head and hemoglobin has iron.  Its formula is C55-H72-O5-N4-Mg, so in addition to Carbon and Hydrogen, it also has Oxygen and Nitrogen, as well as the magnesium ion in its head.

Its breakdown byproduct is Pheophytin, which is the identical molecule without the positively charged Magnesium in the head and is dark blue in color, which may appear black in solution.

 

 

Pheophytin molecule

 

Human hemoglobin versus plant chlorophyll

Chlorophyll is highly soluble in alcohol, and insoluble in Alkanes, as well as being technically insoluble in water, but because of the charge on one end, can be transported by water in the form of micelles.

Micelles are formed with molecules like Chlorophyll with a charged hydrophylic, and a non polar hydrophobic tail, when the tails clump together with the heads facing out.

Molecules clumping into Micelle

Micelle

Anthocyanins are water soluble plant pigments known as polyphenols, which is a subgroup of flavonoids.   They are also highly soluble in alcohol, but mostly insoluble in non polar solvents.

They are C-15 to C-17 sized molecules, with a positive charge enabling them to absorb light, and thus produce colors, typically ranging from red (pink) through purple, to blue.

Excluding chlorophyll green, along with the carotenoids they produce most of the bright colors in the plant world. 

The water soluble pigments are found in the sap in the epidermal tissues of the flowers and fruit.     They are also plant sugars, with the sugar linked to the C3 position as 3-monoglycosides, or to the C3 and C5 positions as diglycosides.

 

Carotene is Chlorophyll's partner in photosynthesis and is a double bonded Alkene terpenoid, with a chemical formula of C40-H56.  It is insoluble in water and highly soluble in non polar solvents like the Alkanes, but only marginally so in Ethanol.

It is yellow to red in color and not readily broken down using UV.  It is in fact the fall colors you see after the chlorophyll has gone away.  As you can see there are no other atoms besides hydrogen and carbon, so breakdown products are typically CO2.

 

b-Carotene molecule

Plant waxes are in the C-30/34 sized molecules, but are relatively nonpolar, so are more of an issue when doing non polar extractions using alkane hydrocarbons.

Most of the plant wax comes from the plant surfaces, where they protect the plant from the environment and from dehydration, as well as provide UV protection, but some come from the trichome caps themselves.

These epicuticular plant waxes are mixtures of long-chain aliphatic hydrocarbons, consisting of alkanes, alkyl esters, fatty acids, alcohols, diols, ketones, and aldehydes.

I haven't run across a diagram of the cannabis plant wax molecular structure, but here is a picture of wax molecules in general, with cannabis waxes ostensibly closest to the Carnauba.

 

Wax molecules

 Soooo, besides our coveted C10 through C-22 target elements, those are the other key players, begging the question of how you extract them, while avoiding the non target elements above as much as possible?

The answer is subzero temperatures.  At subzero temperatures the water is frozen, tying up the water and water solubles like the anthocyanins, and it slows down extraction of all the molecules, but slows down extraction of the longer chain molecules more than the shorter ones.

With the water frozen, the water soluble chlorophyll binding proteins (WSCBP) also keep the chlorophyll in place, so it can't be transported as micelles.

How cold do you need to be  to keep these three unwanted guests out of the extract?  Again, it depends on the process, but for instance QWET is routinely done successfully at -18C/0F, while some process take it to -50C/-46F.

We go into the specific parameters under the different process headings, but while alcohols do an excellent job of harvesting the essential oils, they must also be removed afterwards and both their relatively high boiling point and affinity for some of the essential oil constituents make holding on to the monoterpenes problematic during purging.  Alcohol extractions are therefore typically not as aromatic as LPG extractions, and are typically smoother to vaporize.

We get our 190 proof Ethanol from the liquor stores, but in those locations that it isn't available, it can be ordered on line and shipped to you.

If you live on the East coast, check out  http://www.winechateau.com/

For West coasters, try http://organicalcohol.com/store/

Locally 99% Isopropyl alcohol is available from Safeway pharmacy, and at places like American Scientific, or from Fryes for cleaning circuit boards.


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