Sciencemadness Discussion Board - 2-octanol

2-octanol

Magpie - 4-11-2015 at 11:05

Introduction
7.6g of 2-octanol was prepared by pyrolysis of castor oil using NaOH. The synthesis was a 1/6 scale version of the method of Vasishtha et al (ref 1) combined with a modified equipment arrangement described in the OrgSyn procedure for methyl-n-hexylcarbinol (ref 2). 22.9g of sebacic acid was recovered as a by-product. This is reported in a separate thread (ref 3).

Reagents & Equipment Set-Up
The OrgSyn procedure highly recommended the use of a copper pyrolysis vessel. In copper I was limited to a 500ml RBF. Due to the necessarily small scale of my procedure I had to prepare 5 batches.

25g of castor oil (Rite-Aid) was first saponified with 3.3g of NaOH in 75ml of water. To this was added 0.25g of red lead, 66.7g of Up & Up (Target) “heavy duty” mineral oil, and an additional 16.7g of NaOH. This was placed in the copper RBF. A magnetic stir bar was added and the RBF placed on an electric heating mantle. The RBF was equipped with a Claisen adapter to allow pot temperature measurement by thermocouple and a condenser assembly. The condenser assembly consisted of a vertical West condenser, a U-tube, and a vertical Graham condenser as shown below. The West condenser was equipped for steam heating; the Graham condenser was cooled with ice-water.

Procedure
The pot was insulated with a fiberglass blanket and heated. The West condenser was left unheated until ~55ml of water condensate had collected in a graduated cylinder receiver. At this point a trace of 2-octanol could be detected in the condensate. Pot temperature at this point was about 180°C. The receiver was then changed to a 125ml separatory funnel and steam heat was applied to the jacket of the West condenser. Heating was continued until no more 2-octanol came over. The final temperature in the pot had risen to about 325°C.

Preliminary water removal

Pyrolysis collecting 2-octanol

Workup
The pot residue contained a sebacic acid by-product. The workup of this is described in reference 3. The combined distillate of crude 2-octanol was 40ml for the 5 batches and is shown in the picture below drying over K2CO3.

crude 2-octanol

The crude 2-octanol was placed in a 100ml RBF for fractional distillation using a Hempel column packed with glass shards (bp 178.5°C per Wiki). This column had to be abandoned due to flooding.

Hempel column flooding

A Vigreux column was then tried. This worked well until about half way through the distillation. Then the column flooded due to severe foaming. I tried many things to get rid of the foam: (1) added magnetic stirring, (2) removed boiling stones, (3) tar removal using activated carbon, (4) added a few drops of baby Simethecone (Safeway), a polydimethylsiloxane, and (5) add a few drops of DOT5 silicone brake fluid (a diorganopolysiloxane). Nothing worked except the DOT5 silicone oil. It stabilized the foam but did not prevent its formation. The presence of a layer of foam (~7mm) was enough to prevent evaporation of the 2-octanol and hence prevent distillation. The results were: (1)10ml light forerun (bp<170°C), (2) 20ml of middle cut (bp 170-176°C), and (3) 8ml of dark amber pot residue.

The middle cut was placed in a 50ml RBF and redistilled. There was a forerun of about 5ml that boiled at 170-175°C, probably mostly 2-octanone (bp =172.9°C). The remainder of the distillate (6.6g) came over at 175-176°C and was taken as 2-octanol per OrgSyn. There was only a slight bit of tar as pot residue. There was no foaming during the distillation.

The forerun was combined with the forerun of the first distillation. This 13ml was distilled using a 25ml pot. 1 additional gram of 2-octanol was recovered boiling at 175-176°C. Again there was no foaming and only a slight bit of tar.

Results
The yield of 2-octanol was 7.6g for a %yield of 23.8%.

Discussion
The %yield of this synthesis is disappointing. Vasishtha (ref 1) claims a yield of 70.1%. OrgSyn (ref 2) claims yields of 40-42%. Discussed below are some factors that may have contributed to my low yield.

a. Tar & Foaming
Much time was spent trying to distill the crude distillate because of foaming. To get the distillate to rise to the top of a 20cm fractionation column required a lot of heat: 80% setting on the mantle and heavy insulation of the pot and column. This degraded the distillate as I could see it becoming progressively darker. If a vacuum distillation could be used this should greatly reduce tar formation. I found it ironic that in my search for an antifoam I learned that 2-octanol itself is an antifoam for some applications. Indeed, in the absence of the tar there was no foaming problem. When cleaning the glassware I found it difficult to form suds with liquid detergent, confirming that 2-octanol is an antifoam.

Trying the baby Simethicone was ill-advised. Although it is a polydimethylsiloxane it is in an aqueous dispersion and therefore was not compatible with the fatty 2-octanol.

b. Equipment Configuration
Both the Vasishtha and OrgSyn procedures specified a pyroysis equipment configuration in which condensate water would be returned to the pot. I did mimic the OrgSyn configuration, in a modified way, but did not provide for condensate return to the pot. It was never clear to me why this water return was necessary. Perhaps this was a way to extend the time of pyrolysis. Vasishtha specified a time of 5 hours, and OrgSyn specified a time of 48 to 72 hours! However, my yield of sebacic acid was 84.3% for the last two batches whereas that for Vasishtha was 72.5%. Based on this I conclude that my pyrolyses were complete even though my average pyrolysis time was only 2.3 hours.

References
1.”Sebacic Acid and 2-Octanol from Castor Oil,” by A.K. Vasishtha et al, Journal of American Oil Chemists, vol 67, no. 5, May 1990. http://www.sciencemadness.org/talk/viewthread.php?tid=62326&...
2. “Methyl-n-hexylcarbinol (2-octanol),” by Roger Adams et al, Organic Syntheses, Coll. Vol. 1, p.366 (1941). http://www.orgsyn.org/Result.aspx
3. http://www.sciencemadness.org/talk/viewthread.php?tid=64038#...

Comments, questions, and suggestions are welcomed.

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clearly_not_atara - 4-11-2015 at 13:31

Quote:

It was never clear to me why this water return was necessary. Perhaps this was a way to extend the time of pyrolysis.

Pyrolysis is weird. Water could have participated in the reaction; one possible mechanism assumes that C12-OH is oxidized and undergoes an ene reaction with C9=C10 so that C9 bonds to oxygen, then that ether must be cleaved, which probably involves water somehow.

I wouldn't change a procedure unless I thought I knew what it was doing. Furfural from corn cobs or some shit, do it by the book.

[Edited on 4-11-2015 by clearly_not_atara]

[Edited on 4-11-2015 by clearly_not_atara]

Magpie - 4-11-2015 at 14:42

Perhaps the water was intended to provide steam distillation of the 2-octanol.

AvBaeyer - 4-11-2015 at 19:10

Magpie,

What's the mechanism of the reaction that you show in your graphic? It's quite a strange/interesting redox reaction as the double bond is cleaved to give you the two products. Can't say that I have ever seen anything like this (though I have not looked either).

And, as usual, an excellent presentation.

AvB

Magpie - 4-11-2015 at 20:25

Thank you, AvB. A proposed mechanism is shown on the 3rd page of the Vasishtha reference. The link in reference 1 will take you to p. 9 in References. Scroll down over half way and you will see Solo's link to the article. In summary:

1. dehydrogenation of ricinoleic acid
2. isomerization of the ß, gamma - keto acid
3. retro-aldol fission to 2-octanol & sebacic acid

I'm sure you will understand this much better than I do.

Aqua-regia - 5-11-2015 at 01:40

Hey Magpie,

this is a good patway to get this alcohol. I like it. Do you have some similar methode to get pentanol?

Magpie - 5-11-2015 at 06:54

Quote: Originally posted by Aqua-regia

...Do you have some similar methode to get pentanol?

Not offhand. I think the double bond and the hydroxyl group in the ricinoleic acid makes this synthesis possible. I have also wondered if other fatty acids might have these functional groups.
As you know fatty acids are easily attainable through saponification of agriculturally derived oils.

Aqua-regia - 5-11-2015 at 07:08

Ok this is evidence, but i thought not this castor oil as starting material, I asked some similar pyrolysis methode from other plant oil.

Magpie - 6-11-2015 at 12:04

I redistilled the forerun and obtained 5.9g of liquid boiling at 172-174°C. Assuming this to be mostly 2-octanone (bp 172.9°C) I reacted a portion of it with semicarbazide to form 2-octanone semicarbazone. This, shown below, had a mp =123°C in agreement with the literature value (Brewster).

[Edited on 7-11-2015 by Magpie]

Darkstar - 9-11-2015 at 23:45

Quote: Originally posted by Magpie

Thank you, AvB. A proposed mechanism is shown on the 3rd page of the Vasishtha reference. The link in reference 1 will take you to p. 9 in References. Scroll down over half way and you will see Solo's link to the article. In summary:

1. dehydrogenation of ricinoleic acid
2. isomerization of the ß, gamma - keto acid
3. retro-aldol fission to 2-octanol & sebacic acid

I'm sure you will understand this much better than I do.

The retro-aldol fission step gives methyl hexyl ketone and 10-oxodecanoic acid, not 2-octanol and sebacic acid. It's the subsequent reduction of methyl hexyl ketone by the H₂ produced in the first step that gives 2-octanol, and the oxidation of 10-oxodecanoic acid that gives sebacic acid; however, the 10-oxodecanoic acid can also be reduced by H₂ as well to give 10-hydroxydecanoic acid, which seems to be the point of adding the Pb₃O₄ so that oxidation is favored. Based on the mechanism suggested in the Vasishtha reference, I imagine the reaction looks something like this:

mechy.bmp - 2.2MB

The Volatile Chemist - 10-11-2015 at 16:13

If this actually works, this is a great prep!I suppose there is no way to guarantee the isomer of 2-octanol that is produced [or does the melting point mach only with the 2- isomer?].

Ozone - 10-11-2015 at 16:51

2-octanol is a liquid at room temperature. You could look at BP (178.5°C relative to 1-octanol at 195°C ), though. Many of the other isomers, however, have similar BPs, so GC would probably be the only way to go. I'd run this on a wax column.

O3

The Volatile Chemist - 10-11-2015 at 17:37

Interesting. Though the fact that it wa not n-octanol was determined by the oxidation since it obviously made a ketone, not an aldehyde.

AvBaeyer - 10-11-2015 at 18:40

Darkstar,

Thanks for the explanation. I completely missed the addition of red lead in the reaction in Magpie's write up. Knowing that red lead is present helps clarify the seemingly strange redox reactions going on. Nice post!

AvB

The Volatile Chemist - 11-11-2015 at 17:58

Splicing the nonoleic acid using potassium permanganate and aliquat 336 would give interesting compounds (albeit, rather profitless ones). I think they would be separable with distillation, though it'd be close. How feasible would that be?

Darkstar - 12-11-2015 at 06:00

Quote: Originally posted by AvBaeyer

Darkstar,

Thanks for the explanation. I completely missed the addition of red lead in the reaction in Magpie's write up. Knowing that red lead is present helps clarify the seemingly strange redox reactions going on. Nice post!

AvB

Yeah, the reaction Magpie originally depicted in the image threw me for a loop too. There should have been a water on the reactant side and no H₂ on the product side. After dehydrogenation and isomerization of ricinoleic acid, water adds to the α,β-unsaturated ketone to give an aldol that undergoes retro-aldol fission to give the corresponding enolate and aldehdye. The enolate is then protonated to give a ketone (2-octanone) which gets reduced to 2-octanol by the H₂ generated in the dehydrogenation step. The aldehyde (10-oxodecanoic acid) is then either oxidized to sebacic acid or reduced by H₂ to 10-hydroxydecanoic acid. It is certainly an interesting reaction.

I don't blame Magpie, though. The mechanism in the reference is sort of hard to follow. For those who don't have access to the References section, here's the mechanism proposed in the Vasishtha reference (and what my mechanism above is based on):

Quote: Originally posted by The Volatile Chemist

Interesting. Though the fact that it wa not n-octanol was determined by the oxidation since it obviously made a ketone, not an aldehyde.

The ketone in the forerun was unreacted 2-octanone (methyl hexyl ketone), not 2-octanol that got oxidized back to a ketone at some point. Like I said above, it's 2-octanone that results from the retro-aldol fission step that must then get reduced by H₂ to the secondary alcohol. I think the reason Magpie got such high yields of sebacic acid but such low yields of 2-octanol was due to incomplete reduction. Maybe it had something to do with him altering the procedure (water return)? No protons for the enolate ions to grab and thus no ketones to be reduced to 2-octanol?

Dr.Bob - 12-11-2015 at 08:08

That is an interesting mechanism, I think it would have gotten a low grade in my advanced organic class, but it is hard to argue against empirical evidence that something skin that that happens, given the final products. Perhaps the lead acts as some sort of redox cycler in the shuttle of the hydrogen back and forth, it may even be a sort of transfer hydrogenation. It might be that conducting the reaction in a more sealed container would help keep the hydrogen so that it can be recycled, or even adding another reductant than can generate hydrogen, such as ammonium formate, hydrazine, or a THP compound, or another of the classic transfer H sources. Also wonder if Pd would catalyze the reaction as well or better. But it clearly works to some degree. The use of a copper vessel also might be a way to get traces of Pt/Pd/Ag into the reaction, as most copper has traces of it, and at higher temps, traces of those might be dissolves. Just look at "Pd free cross couplings" to find similar examples of very small traces of transition metals having a huge effect.

Magpie - 12-11-2015 at 09:39

Quote: Originally posted by Darkstar

Yeah, the reaction Magpie originally depicted in the image threw me for a loop too. There should have been a water on the reactant side and no H₂ on the product side. ....

Here's a quote from Organic Syntheses procedure for methyl-n-hexylcarbinol (2-octanol):

Quote:

The container is now fitted with an efficient reflux condenser, and it is then heated over a ring burner as long as hydrogen is evolved. The heating is regulated to produce a fairly rapid evolution of gas as shown by leading a tube from the top of the condenser into a small beaker of water. The time required for the complete evolution of the hydrogen is about nine to ten hours.

I do remember some gas bubbling (evolution) during the synthesis. I must have had the outlet of the Graham condenser submerged in the receiver.

Darkstar - 12-11-2015 at 10:56

I just mean for a balanced reaction is all. One ricinoleic acid molecule gives one H₂ molecule and then reacts with two hydroxide ions and one water molecule to give one 2-octanone molecule and one 10-oxodecanoic acid molecule. The 2-octanone then reacts with the H₂ to give 2-octanol, and the 10-oxodecanoic acid gets oxidized to sebacic acid. So something like this:

ricinoleic acid + 2 NaOH + H₂O + heat → 2-octanol + sebacic acid

The H₂ is both formed as well as consumed during the reaction itself, so it's technically neither a starting reactant nor a final product. In practice hydrogen will certainly evolve since not all of it is going to react with 2-octanone or 10-oxodecanoic acid. Again, I just meant for a balanced equation. It's definitely an interesting reaction to say the least, and I must say that this was a wonderful write-up. I just wanted to help clarify what the Vasishtha reference suggests since there was clearly some interest in this rather strange reaction mechanism.

Magpie - 12-11-2015 at 11:15

But my reaction is balanced and the product is sodium sebacate, not sebacic acid. Only after the addition of HCl does one aquire sebacic acid.

I made an error in portraying the ricinoleic acid as some readers may have noticed. The -OH and the double bond need to be moved one carbon to the right.

[Edited on 12-11-2015 by Magpie]

Darkstar - 12-11-2015 at 12:26

If you noticed, I never bothered to show sebacic acid as sodium sebacate in my mechanism either. (and neither did the Vasishtha reference) Yes, it will be deprotonated under such basic conditions; however, my main point was to show the part of the reaction that we are actually concerned with. I wanted to show two things: that water does participate in the reaction according to the Vasishtha reference, and that H₂ is generated in situ and then consumed and not a product. How you want to treat the NaOH and water on either side is up to you. If you look at the mechanism, hydroxide actually gets regenerated in the pyrolysis part of the reaction and isn't technically consumed.

By balanced I really just mean that you don't have one mole of ricinoleic acid somehow generating two moles of H₂ like in the original image. Because if H₂ were to evolve like in your original image, there wouldn't have been any 2-octanol--it would've been 2-octanone. This started when you said:

Quote:

3. retro-aldol fission to 2-octanol & sebacic acid

I initially just wanted to point out that there is one last step that you missed, which is the reduction of 2-octanone (which is what the retro-aldol fission gives) to 2-octanol by H₂, which is probably the most interesting part of this reaction to begin with. I hope I have not caused too much confusion.

[Edited on 11-12-2015 by Darkstar]

Magpie - 12-11-2015 at 14:57

Thanks for your insights and interest, Darkstar.

I have some disappointing, although not totally surprising, lab results to report. It seems that my putative 2-octanol is 2-octanone. Looking back, my first clue was the low boiling point of 175-176°C. The bp for 2-octanol is 178.5°C.

Yesterday I attempted to make 2-octyl hydrogen phthalate. This failed. Today I tested my putative 2-octanol with (1) Na and (2) with acetyl chloride. The Na did produce a bubbling (H2) but not profusely. Acetyl chloride produced no reaction. Then I reacted some with semicarbazide and produced a nice mass of crystals looking just like the 2-octanone semicarbazone that I made before.

So, I will try this synthesis again. I will be trying to avoid conditions such as overheating that would promote oxidation of the 2-octanol.

gdflp - 12-11-2015 at 17:05

Do you have any of the 2-octanone left? If so, you might be able to recover some 2-octanol by reduction with aluminum isopropoxide or sodium borohydride.

Magpie - 12-11-2015 at 17:14

I don't have those reagents, but thanks. I want to get the castor oil procedure to work. I've invested a lot of time and effort in it.

AvBaeyer - 12-11-2015 at 18:53

Magpie,

The fact that you isolated 2-octanone is interesting in its own right. Be that as it may, thanks again for the great write up and the instigation of some interesting discussion. Even old timers like me can still learn new things.

AvB

Darkstar - 14-11-2015 at 00:54

Quote: Originally posted by Magpie

So, I will try this synthesis again. I will be trying to avoid conditions such as overheating that would promote oxidation of the 2-octanol.

I think your main culprit was just lack of 2-octanone reduction, not so much 2-octanol oxidation. In fact, I wouldn't be surprised if you never actually produced 2-octanol to begin with. When you attempt the synthesis again, try to stick as closely to the procedure as possible. Like clearly_not_atara said, it's generally not a good idea to make alterations to a known procedure unless you're 100% sure you know exactly how the reaction works. The lack of water return may very well have been one of the key reasons your synthesis failed. You must assume that everything in the procedure was done for a reason. And as I demonstrated in my mechanism, water does take part in the reaction. It is necessary for both the formation of the aldol, as well as the protonation of the enolate to give 2-octanone.

Also, as suggested by Dr.Bob, conducting the reaction in a more tightly sealed vessel next time might also give better results. As I've mentioned numerous times, the reduction of 2-octanone by H₂ is how the 2-octanol is produced. I can't stress enough how critical this part of the reaction is. Without this step, there can be no 2-octanol in the first place! Try to keep the 2-octanone in contact with the hydrogen gas for as long as possible. This is also why it's probably a good idea to extend the reaction time for as long as possible as well.

Ask yourself this: if the pyroysis of ricinoleic acid went to completion for both of you, how is it that the Vasishtha reference somehow got a higher yield of 2-octanol than you, but a lower yield of sebacic acid? The most likely answer? Their reaction time was more than twice as long as yours. This means their 2-octanone had much more time to be reduced to 2-octanol by H₂, and, consequently, some of their 10-oxodecanoic acid to be reduced to 10-hydroxydecanoic acid as well. (hence the lower yield of sebacic acid)

And lastly, if you have any more 2-octanone leftover from your first attempt, maybe add it to the reaction vessel next time as well. More 2-octanone around means more opportunities to be reduced to 2-octanol and thus better yields. Even though in theory there's only enough H₂ to reduce just the 2-octanone generated in that specific reaction since they react in a 1:1 molar ratio, in practice the reduction will be far from 100% efficient, and there will inevitably be a lot of H₂ that ends up evolving as hydrogen gas. So hopefully all that extra 2-octanone can react with some of the H₂ that would have otherwise been wasted.

[Edited on 11-14-2015 by Darkstar]

byko3y - 14-11-2015 at 05:39

In this procedure 2-octanone is reduced to 2-octanol via Meerwein-Ponndorf-Verley reduction (alcoholate + alcohol), AFAIK. There's no way hydrogen can become active in the reaction.

AvBaeyer - 14-11-2015 at 19:01

I agree with byko3y. Once H2 is formed it is useless in this reaction. There appears to be no way that it can be "reactivated" as a reducing agent, particularly since the reaction is vented. The reduction must occur through some sort of hydride transfer such as the M-P-V reaction that byko3y mentions or some other sort of hydride shift. Perhaps the red lead is playing a redox role by shifting between oxidation levels and facilitating the reduction via electron transfer.

AvB

Darkstar - 14-11-2015 at 20:34

I am wondering if it's possible that H₂ activation could be affected by the copper vessel somehow? Perhaps in the manner that Dr. Bob suggested? I have no problem accepting an MPV-style reduction involving a hydride shift, but I'm still curious as to why Magpie didn't get any 2-octanol in his first attempt.

[Edited on 11-15-2015 by Darkstar]

Dr.Bob - 15-11-2015 at 05:26

Perhaps adding some isopropanol to the reaction might help drive the reaction then. I was figuring that any hydrogen reduction had to be using the lead as the transition metal, which is likely reduced and would then act catalytically on the ketone. I agree that hydrogen itself won't likely reduce the ketone just by itself in that situation. The need for lead and a copper vessel suggests that you might even make some small amount of a more complex metal complex in situ. I was just trying to think of ways to help the reaction. Would adding a small amount of copper dust allow the reaction to proceed in a glass vessel?

AvBaeyer - 15-11-2015 at 16:20

Here is a recent abstract though it also invokes microwave chemistry, for what it is worth:

Obtaining 2-Octanol, 2-Octanone, and Sebacic Acid from Castor Oil by Microwave-Induced Alkali Fusion

Nezihe Azcan * and Elif Demirel
Anadolu University, Faculty of Engineering and Architecture, Department of Chemical Engineering, 26470 Eskisehir, Turkey

Ind. Eng. Chem. Res., 2008, 47 (6), pp 1774–1778
DOI: 10.1021/ie071345u
Publication Date (Web): February 21, 2008
Copyright © 2008 American Chemical Society

Abstract

In this study, the effect of microwave irradiation on alkali fusion of castor oil was investigated using different NaOH/oil ratios (8:15, 12:15, and 14:15), reaction temperatures (473, 493, 503, 513, and 523 K), and reaction times (15, 20, 25, and 30 min) in order to obtain oleochemicals (2-octanol, 2-octanone, and sebacic acid) in the presence of 1% catalyst (Pb3O4) by weight (w/w). The yields of 2-octanol (4.4−62.6%), 2-octanone (1.6−37.4%), and sebacic acid (9.1−76.2%) were obtained according to reaction conditions. Maximum yields of oleochemicals were obtained using methylated then presaponified castor oil (sodium ricinoleate), 14/15 NaOH/oil ratio at temperature 513 K and 20 min reaction time. 2-Octanol, 2-octanone, and sebacic acid were determined by GC and GC/MS analysis, and purity of sebacic acid (98.7%) was further assessed by its acid value (444) and melting point (406.5 K). Reaction time compared to conventional heating was dramatically decreased by microwave heating system from 5 h reaction time to 20 min.

It appears that the mix of products is condition dependent but we would need to see the actual data to evaluate same. I would hazard a guess that microwave conditions would produce the same product profile as regular thermal conditions.

AvB

Magpie - 15-11-2015 at 20:47

I had picked up that paper at the library yesterday, AvB, but had forgotten to look at it - thanks for the reminder. Here it is:
Attachment: 2-octanol & sebacic acid from castor oil by microwave.pdf (194kB)
This file has been downloaded 516 times

AvBaeyer - 15-11-2015 at 20:52

Magpie,

Thanks for the download. I will take a look.

AvB

gsd - 16-11-2015 at 22:55

Magpie,

This paper could be of some help to you for whatever it is worth.

gsd

Attachment: Chemical derivatives of castor oil.pdf (743kB)
This file has been downloaded 553 times

Magpie - 17-11-2015 at 09:18

Thanks gsd. That is a very comprehensive coverage of a much researched raw material.

I'm glad I was never required to drink castor oil!

I always wondered what the Castrol motor oil was all about. I read that it contains castor oil which at the time it was invented provided superior lubricating properties for auto racing.

The Volatile Chemist - 19-11-2015 at 10:24

Nice article. Will make good reading tonight

Magpie - 26-11-2015 at 18:24

After learning in the above experiments that I’ve been making 2-octanone rather than 2-octanol I began trying to improve my use of the Vasishtha procedure.

Batch # 6 (1/6 scale). This attempt added distillate water recycling to the pyrolysis pot, as did Vasishtha. This produced a large volume of cloudy distillate: ~45 ml. It did clear up when dried with K2CO3 overnight. However, when I attempted to fractionally distill it using a Vigreux column I had to abort due to severe foaming. I suspected that the pyrolysis distillate was contaminated with light components from the mineral oil.

Vacuum Distillation of Mineral Oil. Convinced that my mineral oil was too light (Vasishtha specified a bp of at least 380°C) I attempted to vacuum distill my oil at 1mmHg, discarding anything coming over at <198°C. Due to severe bumping, even with an ebulliator tube, this was aborted.

Batch #7 (1/6 scale). Paraffin wax is a mixture of alkanes with bp >350°C. Therefore I attempted to substitute paraffin wax for mineral oil in the Vasishtha procedure, again with distillate water recycle. But bits of wax were forming in the condenser so this attempt was also aborted.

At this juncture I decided to switch from the Vasishtha procedure to the OrgSyn (B) procedure.

Batch #8 (0.011 scale). The OrgSyn (B) procedure also uses distillate water recycle. Again I used my copper 500ml RBF as pot. The distillate was captured using a downward sloping condenser. This distillate was slowly reintroduced to the pot using a P-E funnel located in the short neck of a Claisen adapter. Not too long into the pyrolysis severe foaming overflowed and plugged the condenser. This attempt was aborted.

Batch #9 (0.0055 scale). OrgSyn cautions that there must be sufficient freeboard in the pot due to foaming. Therefore the batch size from above was cut in half. The quantities used were: castor oil, 65.1g; NaOH, 16g; water 32 ml. The components were mixed to saponify the oil prior to transfer to the pot. I recommend that the transfer be made before the oil turns into the hard curd shown below.

saponified castor oil curd

The same distillate water recycle system was used as in batch #8, as shown in the pictures below.

OrgSyn (B) apparatus

distillate water recycle apparatus.jpg - 59kB

distillate water recycle apparatus

Once 10 ml of water had accumulated in the separatory funnel it was drawn off and transferred to the P-E funnel. From there it was reintroduced to the pot drop-by-drop. There was no foaming problem. The electric mantle heat was set at 65% with the pot and Claisen insulated with fiberglass blankets. Stirring was done using a magnetic stirrer. The putative 2-octanol (oil) and water co-distilled, separating in the condenser. After setting overnight in the separatory funnel the oil and water layers separated nicely as shown in the picture below.

distillate receiver for 2-octanol.jpg - 61kB

distillate receiver

The yield was ~ 9 ml of crude oil, which is about a 26% yield.

The procedure for batch #9 will be repeated until at least 40 ml of oil have been acquired. Then I will fractionally distill it to hopefully obtain the pure 2-octanol.

Pumukli - 27-11-2015 at 07:19

Very good!

Btw. isn't 2-octanone a useful compound? If you made it rather than the 2-octanol at first then that procedure might also be worth optimizing.

Magpie - 27-11-2015 at 09:13

Thank you. Yes, the 2-octanone and sebacic acid have been saved for possible future use. At this time I will leave the optimization to others.

Such research can be very time and material intensive.

I'm only hoping that what I have is 2-octanol. Its smell is encouraging, ie, it's more oily and less pungent than the 2-octanone.

I wasn't sure I could even make 2-octanol by the OrgSyn procedure at such a small scale as 0.0055.

The Volatile Chemist - 28-11-2015 at 09:35

Be sure to do a second writeup when you're done; I've had a hard time following what actually works, and what is produced, but this certainly looks like an interesting and doable reaction.

Magpie - 1-12-2015 at 17:06

This is a continuation of the above described synthesis of 2-octanol using the OrgSyn (B) procedure at 0.0055 scale.

After 5 batches the combined putative 2-octanol amounted to about 48 ml. This was dried over K2CO3 overnight. Today it was fractionally distilled.

A 100ml pot with electric heating mantle and a Vigreux column was used for the distillation. The pot and column were fully insulated with Al foil and fiberglass blankets. No water was used in the condenser; it was set up as a contingency.

$fractional distillation of 2-octanol.jpg - 69kB$
distillation of 2-octanol

Because of the high boiling point (lit: 178.5°C) a setting of 90% was required on the mantle. The liquid boiled evenly and steadily with no foam or bumping. I took the heat up gradually and was concerned that I would generate tar when I found that a setting of 90% was required.

When sufficient heat was present the 2-octanol came over steadily at about 2d/s at a distillate temperature of 174-178.5°C per the literature range. Most came over at 177-178°C.

2-octanol distillate temperature.jpg - 49kB

2-octanol distillate temperature

The product was perfectly clear, as shown below:

2-octanol in receiver

The pot residue was only slightly discolored:

2-octanol pot residue

qualitative test results

1. A BB sized piece of sodium was placed in a ml of the 2-octanol. Profuse generation of H2 bubbles resulted.

2. Some acetyl chloride was added to a ml of 2-octanol. The smell of an ester was produced, ie, octyl acetate.

Both of the above tests are positive for an alcohol.

Discussion
Although my yield for the OrgSyn (B) procedure at my tiny scale was poor the product is of high quality. I now doubt that I would even have had to distill it let alone fractionally distill it. I had given some thought to vacuum distilling (bp 86°C @ 20mmHg) due to concern over product deterioration at the high bp. I decided against this for several reasons: (1) bumping might have been a real problem, (2) it's hard to keep the pressure right where you want it, so the bp is lost as an indication of quality, (3) it's risky from a safety standpoint, and (4) it's more trouble to set up.

Questions, comments, and suggestions are welcomed.

[Edited on 2-12-2015 by Magpie]

The Volatile Chemist - 2-12-2015 at 12:31

You test the alcohol for aldehydes and carboxylic acids and the like? Just to see if any impurities existed.

Magpie - 2-12-2015 at 12:42

No. The boiling point, color, and smell are all indicative of good purity. Even Sigma-Aldrich only offers 99% purity.

It would be nice to be able to check the refractive index but I don't have the instrument.

The Volatile Chemist - 2-12-2015 at 13:04

Great. Nice work.

Pumukli - 4-12-2015 at 10:41

Arggh, just the usual Magpie quality work - which makes me envious more and more. (I'm still in the "gathering equipment and reagents" stage.) :-)

Good to know that even without vacuum you got a good looking (smelling?) product and little discoloration in the boiler flask.

I understand that you don't have (yet) a GC or NMR in your home but maybe a quick TLC run would also confirm the purity of the product. (Can anyone reasonably expect more than one spot on TLC if the product is say 97%+ pure? Depends on the impurities I know, but would anyone expect anything in this particular case?)

2-octylhydrogenphthalate

Magpie - 11-12-2015 at 15:19

2-octylhydrogenphthalate was made using phthalic anhydride (PAN) and some of the 2-octanol synthesized above.

Reaction of 2-octanol with phthalic anhydride

I found 2 procedures for this synthesis, ie, that in Vogel, and that in OrgSyn (ref 1). I chose the OrgSyn procedure as it had the easiest workup. The only potential downside to the OrgSyn procedure is the required reaction time of 12-15hrs. However, by using a PID controller to keep an oil bath at a constant 110°C this required no attention.

I had several failures before discovering that my PAN was bad. Most likely it was instead phthalic acid (PA). So I painstakingly made 6g of PAN wool by gathering it as it sublimed from PA heated to 185°C. I have posted a warning concerning this in Prepublication following my procedure for converting PA to PAN. PA can be easily distinguished from PAN using chloroform (see Brewster, p. 119, forum library).

Procedure
5.3g (0.0405 mole) of 2-octanol was placed in a 25ml RBF. To this was added 6.0g of PAN wool (0.0405 mole). PAN wool is voluminous and had to be stuffed into the flask as shown in the picture below:

25 ml RBF with 2-octanol and phthalic anhydride.jpg - 51kB

25ml RBF with 2-octanol and phthalic anhydride

The RBF was closed with a glass stopper and placed in the silicone oil bath on a magnetic stirrer-hotplate. The oil was stirred magnetically; the oil temperature was maintained at 110°C using the PID controller and a TC.

After about 3 hours most of the PAN had dissolved/reacted as shown in the picture below:

phthalic anhydride remaining at 3hrs.jpg - 57kB

phthalic anhydride remaining after 3hrs

After 15hrs the product was poured into 342ml of water containing 6.1g of anhydrous Na2CO3. This formed the sodium salt. OrgSyn stated that if the salt solution is hazy it is because of 2-octanone contamination. As you can see it is perfectly clear:

Na 2-octylphthalate solution

About 20ml of 6M HCl was then added to make the solution distinctly acid (est. pH 3-4). This formed the 2-octylhydrogenphthalate. At first a fair amount of oil formed, floating on the surface. I left the lab to research what I might do to crystallize the oil. I could find no help. However, by the time I got back to the lab about 1/2hr later the oil had disappeared turning into floating white solids, as shown below:

2-octylhydrogenphthalate

The solids were caught on a 7cm Buchner funnel, ground in a mortar with water, sucked dry, washed with water, sucked dry again, then placed in a desiccator to dry.

The yield of crude product was near quantitative. Its melting point was found to be 46-47°C, even after washes with 95% ethanol and ether (OrgSyn value: 55°C). I chose not to recrystalize it from glacial acetic acid or petroleum ether. OrgSyn recommended this if highly pure material is required.

reference
1. Organic Syntheses, "D,L-s-octylhydrogenphthalate"

Comments, questions, and recommendations are welcomed.

[Edited on 11-12-2015 by Magpie]

[Edited on 11-12-2015 by Magpie]

[Edited on 12-12-2015 by Magpie]

[Edited on 12-12-2015 by Magpie]

[Edited on 12-12-2015 by Magpie]

Magpie - 13-12-2015 at 13:41

The OrgSyn reference in the above post should be:

"d- and l-OCTANOL-2"

The Volatile Chemist - 14-12-2015 at 15:32

Nice final product. T'would be a nice collectable. Are the melting points of phthalates very variable with minor impurities?

Magpie - 14-12-2015 at 20:59

2-octanol is racemic. The reason I made the ester was to allow separation of the enantiomers. But first I have to react it with a compound that yields enantiomers having different solubilities.

Contaminants lower the melting point. How much depends on the molality of the contaminants. If you want to know more about this research colligative properties.

All these edits mean I am a little rusty on my nomenclature.

[Edited on 15-12-2015 by Magpie]

[Edited on 15-12-2015 by Magpie]

[Edited on 15-12-2015 by Magpie]

[Edited on 15-12-2015 by Magpie]

Magpie - 4-1-2016 at 13:20

A value of 1.4225 was obtained for the refractive index of my synthesized 2-octanol. The value found on Wiki is 1.426.

It could likely be purified by fractional distillation.

edit: "A typical laboratory refractometer can determine the refractive index of a sample to a precision of ± 0.0002. However, small amounts of impurities can cause significant changes in the refractive index of a substance. Thus, unless you have rigorously purified your compound, a good rule of thumb is that anything within ± 0.002 of the literature value is a satisfactory match."

source: hanson@ups.edu

I don't think I really have my refractometer adjusted optimally yet as it is showing some chromatic aberration (color dispersion) in the viewing field. I just bought it off eBay with no operating manual and I'm just learning to use it. It is an Atago (Japan) analog Abbé type manufactured ca 1963.

[Edited on 5-1-2016 by Magpie]

[Edited on 5-1-2016 by Magpie]