Sciencemadness Discussion Board - Synthesis of longer chain tertiary alcohols

Synthesis of longer chain tertiary alcohols

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aga - 26-12-2015 at 09:08

10ml α-pinene
20ml 15 v/v% H₂SO₄
125ml acetone

were mixed in a 250ml RBF and setup for reflux with stirring in an oil bath on a hotplate.

The mixture was held at between 85 and 90 C for 3.5 hours.

Boiling did not occur until 84 C, and the acetone was seen refluxing below the 1st bulb of the Allihn condenser at all times

(maybe the temperature can be raised to speed up the process).

After the 3.5 hours refluxing, the mixture remained a clear colourless liquid.

After briefly cooling in a water bath it became cloudy.

15 w% NaOH soloution was added in 1ml portions to the liquid with stirring to achieve a pH of 7~8. The amount added was 26ml.

The pH was tested by using half a pH strip on the end of tweezers to dip into the RBF.

Despite stirring, it was noted that there was a pH ~6 Upper layer in the liquid, as sampling required the pH strip to be immersed to a depth of at least 3mm before the end of the strip showed any colour change.

After adding the NaOH, a large amount of white precipitate had formed, and the mixture had an oily upper layer.

The RBF was then setup for simple distillation to remove the bulk of the acetone, again in an oil bath on a hotplate with stirring.
(i find that stirring when distilling this kind of stuff eliminates bumping altogether)

After 25 minutes of distillation the vapour temperature began to climb, and the liquid in the boiling pot was showing phase separation, so the distillation was stopped.

The residue in the RBF had become orange/brown in colour, with a small yet obvious oily upper layer.

The white precipitate had disappeared altogether.

The RBF was cooled in a water bath, then the contents transferred to a 100ml separatory funnel and left to stand for 5 minutes.

The lower aqueous layer was drained into a 100ml beaker.

After draining the lower layer, a very small third reddish layer was seen and drained off into a test tube.

Finally the upper (product) layer was drained into a 25ml RBF.

Total 'product' weight was 1.72g, although some of the red residue can be seen in the product.

[Edited on 26-12-2015 by aga]

blogfast25 - 26-12-2015 at 10:06

Very nicely executed, aga.

The "large amount of white precipitate" I suspect was Na₂SO₄, with the acetone acting as anti-solvent. When removing the acetone that Na₂SO₄ then redissolved in the watery phase.

Mystery: the formation of reddish precipitate during the distilling off the acetone.

A bit disappointing: the small yield.

Encouraging: the formation of an organic layer during refluxing. It clearly shows some transformation of raw material.

Before anything else, any solids in the crude product will have to be removed before we attempt any further work-up. Perhaps filtration on a mini-funnel with a high porosity filter medium?

For any follow-ups it would be wise to separate the organic and watery/acetone phases after the addition of the NaOH. I hadn't anticipated phase separation at that point. (The acetone could then be recovered from the watery/acetone mixture.)

Ideas/suggestions for purification remain welcome. My idea was thermal crystallisation from a water/EtOH mixture.

[Edited on 26-12-2015 by blogfast25]

aga - 26-12-2015 at 11:06

Quote: Originally posted by blogfast25

For any follow-ups it would be wise to separate the organic and watery/acetone phases after the addition of the NaOH.

That did occur to me, just there was no room in the procedure for it.

The upper layer was quite large at that point - larger than the post-acetone-distillation upper layer.

I have a suspicion that the acetone removal might be avoided altogether with a little bit more 'salting out', perhaps with K₂CO₃

Quote: Originally posted by blogfast25

Before anything else, any solids in the crude product will have to be removed

There are no solids i can see in the product.

The red stuff is also a liquid, although imiscible with the product

[Edited on 26-12-2015 by aga]

gdflp - 26-12-2015 at 11:40

Quote: Originally posted by blogfast25

Ideas/suggestions for purification remain welcome. My idea was thermal crystallisation from a water/EtOH mixture.

Formation of a solid derivative, followed by recrystallization and decomposition would probably work quite well; especially on the small amounts which aga has. Solid esters should work , as they allow for easy recovery of the alcohol through saponification. The only issue is that the required reagents aren't necessarily the easiest to obtain, unless aga has some 3,5-dinitrobenzoyl chloride laying around.

In this particular case however, the benzoate ester is almost certainly a solid as well so benzoyl chloride could be substituted. Still not the easiest to obtain, but worst comes to worst, a straight fischer esterification with benzoic acid would probably work instead at the cost of a slightly lower yield.

aga - 26-12-2015 at 13:06

Got some sodium benzoate if that helps.

Edit:

Might be a good idea to redo the whole thing and grab the stuff that separated after neutralising the acid.

[Edited on 26-12-2015 by aga]

gdflp - 26-12-2015 at 13:22

Great, conversion to benzoic acid is as easy as dissolving in water and acidifying with an acid of your choice.

Would you happen to have any S2Cl2 still? If so, you can reflux it with benzoic acid to form benzoyl chloride which can then be distilled off and used to directly react with the alcohol.

Remember, this is more involved then the crystallization from aq. EtOH, so I would call this more of a fallback idea if that doesn't work.

aga - 26-12-2015 at 13:39

Quote: Originally posted by gdflp

Great, conversion to benzoic acid is as easy as dissolving in water and acidifying with an acid of your choice.

Would you happen to have any S2Cl2 still?

Happily Not !

S2Cl2 eats everything i put it in, including glass *

It can easily be made, so no difficulty in having some - briefly - if you have a reaction scheme in mind that needs it.

* it did not 'eat' glass, just that sulphur deposits stuck the stopper so hard that the rbf and glass stopper broke when i wanted to get it out.

[Edited on 26-12-2015 by aga]

aga - 26-12-2015 at 13:51

Hold on a sec.

Would directly chlorinating the sodium benzoate not give NaCl and benzoyl chloride ?

gdflp - 26-12-2015 at 14:04

Unfortunately, no. There's an extra oxygen that you made disappear.

If you don't have any on hand, I don't think that the slight increase in yield is worth making it. As I said, I would try blogfast's idea first as long as he has some sort of reference to back it up. I'm not sure how he wants you to crystallize it since it melts at ~ -36°C.

aga - 26-12-2015 at 14:10

Ok.

We will have to await the Master's pronouncement then.

(Damn. I like making S₂Cl₂ - such an Interactive synthesis)

Meanwhile i think Plan B should be to grab that pile of stuff that floats after adding the acid neutralising agent.

blogfast25 - 26-12-2015 at 16:09

Synthesis of longer chain tertiary alcohols

Bloggers returns to the lab (slowly!)

Strange Results

Esterification of a t-alcohol (carbinol) with benzoyl chloride

Eeek ! Polymer !