9.4.9.1 Pentane, Hexane, and Heptane simple Alkanes

 Simple Alkane MSDS Sheets & Properties:

The simple Alkanes most often involved in cannabis extraction are n-Propane, n-Butane, Isobutane, n-Pentane, n-Hexane. and n-Heptane.

Their MSDS and. Gov sheets are as follows:

1.0       n-Heptane:  http://www.sciencelab.com/msds.php?msdsId=9924237

            1.1       https://pubchem.ncbi.nlm.nih.gov/compound/heptane

2.0       n-Hexane: http://www.sciencelab.com/msds.php?msdsId=9927187

            2.1   https://pubchem.ncbi.nlm.nih.gov/compound/hexane 

3.0       n-Pentane: http://www.sciencelab.com/msds.php?msdsId=9927384

            3.1   https://pubchem.ncbi.nlm.nih.gov/compound/pentane

4.0       Misc:   https://www.sciencelab.com/msdsList.php

5.0  GRAS Data: https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?fr=182.20

Diones and long term chronic exposure

While Heptane and Pentane are Class III solvents, Hexane is a Class II because our livers turn Hexane and Heptane into 2.5 Diones, and Hexane 2.5 Dione is a known carcinogen.

Chronic exposure less than PEL to Hexane, has also been demonstrated to cause neurological and organ damage.

Here is a link to the CDC toxicology profile for n-Hexane:   https://www.atsdr.cdc.gov/toxprofiles/tp113.pdf 

Here is a link to the EPA study on chronic effects of Hexane exposure:  https://www.epa.gov/sites/production/files/2016-09/documents/hexane.pdf

Here is the Nationl Library of Medicine study: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4751449/

 FDA Standards for Residual Solvents

1.0  FDA Q-3 Guidelines to Industry: https://www.fda.gov/downloads/drugs/guidances/ucm073395.pdf

 2.0  Regulatory Information:  https://www.fda.gov/downloads/Drugs/GuidanceComplianceRegulatoryInformation/Guidances/UCM073403.pdf

 3.0  GRAS Subtances:  https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?fr=182.20

4.0  Propane Gras:  https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?fr=184.1655

5.0  Butane GRAS:  https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?fr=184.1165

Extracting with the simple Alkanes

The non polar simple Alkanes Pentane, Hexane, and Heptane are highly forgiving when used for extraction, as compared to extracting with polar solvents like the alcohols.   Besides their low polarity, they also have extremely low water solubility, so not prone to pick up water or water solubles.

They are however highly flammable so extractions should either be done outdoors in a well ventilated area, or in a NEMA 7, Class I, Div I or II extraction booth especially engineered for the purpose, with ventilation capable of maintaining any vapors below 10% of LEL.

If you treat it like gasoline, you won't be far off.

No

Alkane

BP

VP

DI

H2O Sol

LEL

HEL

Odor Thresh

1

Pentane

36C/97F

420mm/Hg

1.8

40mg/L

1.4%

7.8%

2.2 ppm

2

Hexane

69C/156F

120mm/Hg

2.0

9.5mg/L

1.2%

7.4%

6.4 ppm

3

Heptane

98C/208F

37.5mm/Hg

1.9

3.4mg/L

1.1%

6.7 %

0.2 ppm

 All three of them smell more or less like gasoline, and human odor threshold for them is relative low, so not hard to note their residuals in medications far below their FDA limits.  Hexane is a Class II solvent, so has the lowest allowable at 290 ppm.

As non polar solvents, they do not extract the water solubles or the chlorophyll, but they do extract the plant waxes and the carotene.  Extraction levels of both can be reduced by dropping the temperatures to subzero, but for full plant extracts, they all three work well in a soxhlet extractor.

As the Alkane chain gets longer, the water solubility drops, which is a good thing, but getting rid of them after extraction without losing monoterpenes gets harder, because of their higher boiling points.  Typically for highly aromatic concentrates, an even lower boiling point Alkane would be used, such as Butane or Propane.

Of the three, in most cases I would choose to work with Pentane, simply because it does the job, is a Class III solvent, and is easiest to get rid of afterwards, due not only to its lowest boiling point, but because of its high vapor pressure at even ambient.

It would also be my choice for soxhlet extraction vis a vis an alcohol, because it won't pick up as many non targeted constituents like chlorophyll even at boiling temperatures.

Perhaps the simplest and most straightforward way to extract with these three simple Alkanes, is simply soak a jar of material in the solvent.  It can be done at ambient temperature and timing is not as critical as with alcohol.  I've soaked overnight without issues.

They don't extract much chlorophyll or water soluble anthocanins, but do extract the plant waxes and carotene.

Here is a jar ready for extraction using HPLC grade of Hexane.

Hexane and jar of material to be extracted

We typically dump the jar of material into a chinoise strainer to remove the gross material and follow it up with filtration through a commercial coffee filter.

 

Commercial coffee filter and Chinos strainer

Most of the color that you see below comes from C-40 carotene and light transmission is blocked by the plant waxes, to further darken it.

 

Conical coffee filter

 Because of their low polarity, they can also be used to soxhlet extract using either soxhlet glassware or a soxhlet extractor like the ISO-3 and 4, or the Extract Craft Turbo.  The latter three are also capable of reflux distillation an recovery.

The Alkanes can be easily recovered in a conventional still, or can be evaporated away with a fan.

 

Purging with forced air

Here is a simple glass soxhlet extractor, with an Allihn condenser providing the reflux.  The solution is boiled in the lower flask and rises to the condenser, where it is returned to a liquid and allowed to rainfall down through the soxhlet containing the plant material between the boiling flask and Allihin:

 

Allihin Condenser

 


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