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Author: Subject: Synthesis of Ethyl ß-Naphtholate (Nerolin)
Magpie
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[*] posted on 10-2-2013 at 17:17
Synthesis of Ethyl ß-Naphtholate (Nerolin)


A. Introduction
This procedure is for the preparation of nerolin, a perfume, and scent fixative. It is an alkyl aryl ether and is prepared here using the Williamson ether synthesis.

ß-naphthol, a weak acid, reacts with potassium hydroxide to form potassium ß-naphtholate:

chempic.bmp - 133kB

The ß-naphtholate anion then reacts with ethyl iodide by an SN2 mechanism to give ethyl ß-naphtholate:

2ndeqn.bmp - 146kB

B. Reagents
8g of potassium hydroxide (corrosive!)
6mL of ethyl iodide
10g of ß-naphthol
100mL of methanol (anhydrous)

CAUTION: methanol is highly flammable, and poisonous


reagents for Nerolin.JPG - 106kB
reagents

C. Equipment
250mL RBF
condenser (cold water cooled)
heating mantle
magnetic stirrer (optional)
600mL beaker
7cm Buchner funnel
suction flask
vacuum source
25mL Erlenmeyer flask

D. Procedure
Set up the 250mL RBF and condenser for reflux as shown in the photo below. The use of magnetic stirring is optional. However, it assists in mixing the reactants prior to boiling, and mitigates the mild bumping that occurs in the latter part of the reflux period.

2 hour reflux for Nerolin.JPG - 84kB
2 hour reflux

Place the methanol, ß-naphthol, KOH, and ethyl iodide in the 250mL RBF. Heat to boiling and reflux for 1.5 to 2 hours.

E. Workup
Fill the 600mL beaker to the 300mL mark with cracked ice. Then pour the hot reaction product onto the ice and stir well. The nerolin will precipitate as shown in the photo below:

Nerolin precipitated by pouring on ice.JPG - 76kB
precipitated nerolin on ice

When the ice has melted collect the nerolin by vacuum filtration using the Buchner funnel. Crude nerolin (~5g) is shown in the photo below:

crude Nerolin.JPG - 98kB
crude nerolin

Recrystallize the nerolin from methanol. You should get some glistening pure white plates as shown in the photo below:

purefied nerolin.JPG - 117kB
recrystallized nerolin

F. Results
The recrystallized nerolin shown above had a melting point of 36°C. The literature value is 37-38 °C. My yield was only 0.32g.

G. Discussion
Nerolin is used in perfumery and as a fixative in soaps. Fixatives reduce the evaporation rate of other added volatile scents.

One source of the discoloration in the crude nerolin was likely the homemade ß-naphthol, as it is also off-color. During the recrystallization there was a large amount of contamination that precipitated out first. I carefully removed the upper crystals which looked to be quite pure as shown in the photo above. I then attempted to harvest more pure crystals from the heavy residue but was not successful.

I’m not sure why the yield of nerolin is so low. Perhaps steric hindrance plays a part as the ß-naphtholate anion is quite bulky. I should also mention that I accidentally used 150mL of the solvent methanol instead of 100mL, which would reduce the concentration of the reactants.

This is a simple procedure and you are rewarded with a most delightful smelling compound. It smells so good you will not want to wash it off your hands. I detect notes of vanilla and citrus.

H. Reference
This procedure is a 2X scale paraphrase of a college hand-out obtained in 2003.





















The single most important condition for a successful synthesis is good mixing - Nicodem
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Hexavalent
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[*] posted on 11-2-2013 at 14:22


Excellent work and write-up Magpie, as usual.

Do you have any future plans for your nerolin? Perhaps cleavage with a hydrohalic acid to give an alkyl halide and an alcohol? Or even chlorination to give the alpha-chloroether? Good luck with your future work, I look forward to reading about more of your experiments.




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[*] posted on 11-2-2013 at 15:31


Thanks, Hexavalent. No, I have no further plans for the nerolin.



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[*] posted on 11-2-2013 at 21:07


I wish there was a like function like facebook has just to show interest in threads where my post really wouldn't be of any real value. Either way always a pleasure Magpie.




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[*] posted on 11-2-2013 at 21:39


Thank you Sedit - very kind of you.



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[*] posted on 12-2-2013 at 17:40


Could ethyl bromide be used in place of the ethyl iodide as long as its in the same stoichiometric amounts? As i cannot obtain the chemicals to make ethyl iodide or buy but i could make ethyl bromide with a raid of thr local pool store.
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[*] posted on 12-2-2013 at 19:41


Quote: Originally posted by reckless explosive  
Could ethyl bromide be used in place of the ethyl iodide as long as its in the same stoichiometric amounts?


See the 2 posts of Nicodem in this thread:

http://www.sciencemadness.org/talk/viewthread.php?tid=11663&...




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[*] posted on 13-2-2013 at 17:58


For people interested in how to synthesize ß-naphthol, there is some information that might prove useful in this thread:

http://www.sciencemadness.org/talk/viewthread.php?tid=11663

Is that how you made your ß-naphthol Magpie?




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[*] posted on 13-2-2013 at 19:18


Quote: Originally posted by sbbspartan  

Is that how you made your ß-naphthol Magpie?


Yes, I describe my preparation down farther in that same thread.

Maybe some don't know that 2-naphthol = beta-naphthol. That's IUPAC nomenclature vs the common name, I believe.

[Edited on 14-2-2013 by Magpie]

[Edited on 14-2-2013 by Magpie]




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[*] posted on 14-2-2013 at 06:22


Funny, I didn't even realize the thread you listed was the same one I was looking at. :)

You use the same source of methanol as I do too. I like HEET, it's easy to get and cheap...

Good prep!




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[*] posted on 25-10-2013 at 19:23


I too, recently finished the preparation of 2-ethoxynaphthalene via a slightly alternate procedure (that I more or less made up entirely as modifications of this prep). Instead of KOH, I elected to use sodium methoxide produced freshly as base. My starting 2-naphthol was somewhat less pure than Magpie's, melting from 118-120C (uncorr, lit. value 123C). This is pictured below.



A 250ml RBF was charged with a stirbar and 75ml of methanol (HEET, distilled to remove the fraction of a percent of oily high-boiling material). 1.33g (0.058mol) of fresh sodium, cut into thin sticks to speed reaction was added and stirring started. The methanol became quite warm as the sodium rapidly dissolved to an ever-so-slightly hazy solution of NaOMe in methanol.



7.21g (0.050mol) of the aforementioned (and pictured) mostly-pure 2-naphthol was added to this methoxide solution, rapidly dissolving to a dark brown solution. A liebig condenser was placed atop the RBF as a reflux condenser. After stirring for ~5 minutes, 10.92g (0.10mol) of Ethyl Bromide (I don't reccomend this. Just get some iodide. The reflux period is way too long with bromide unless you're making mol quantities.) was poured down the condenser into the reaction mixture, and the condenser was topped with a CaCl2 drying tube.

Very gentle reflux was maintained for 26 hours (arbitrary, based on the advice of Nicodem in the 2-naphthol thread, I did not have TLC plates to monitor with) The reaction mixture remained at ~50C during the entire period and at no time was the condenser permitted to rise above 20C through addition of ice to the recirculating water bath. The color of the reaction mixture lightened over the reflux period, but remained brown.



The reaction mixture was then brought to a vigorous boil for 5 minutes with the condenser removed in order to expel excess EtBr and any ethereal byproducts. The hot reaction mixture was poured into 300ml of ice water containing 2g of NaOH to help dissolve any unreacted naphthol. Initially, the mixture was a milky off-white suspension, but with stirring the 2-naphthol slowly "curdled" and sank to the bottom of the beaker leaving a cloudy, but decidedly translucent supernatant.



This solid was vacuum filtered and washed with 100ml of distilled water. It is highly hydrophobic. Air is drawn through the solid for some time and it dries fairly easily, providing 7.41g of crude 2-ethoxynaphthalene as a tan powder (86% yield).

An attempt was made to purify this material by recrystallization from dry methanol, which failed. 90% methanol, 10% water was then tried, which also gave a dark brown oil. I ended up reprecipitating with icewater, but the emulsion did not "curdle" like the first time and it remained white and milky with some chunks of tan material at the bottom. An attempt at vacuum filtration did not separate the emulsion and the medium frit plate plugged completely after a portion of "milk" was drawn through. DCM was added to the emulsion and stirred vigorously, but the "milk" remained. It was found that adding a few grams of NaCl caused the emulsion to break and the aqueous phase to clear. The DCM phase was boiled down, transferred to a 50ml RBF with stirbar and completely stripped of DCM under vacuum.

Disregard the above italics if repeating this preparation and simply transfer the crude 2-ethoxynaphthalene to a 50ml RBF with a small stirbar. The crude material is vacuum distilled with a short path stillhead. An air condenser is suitable for this scale, but ~40C water should be used for any larger amount.



The bulk of the material passes over at 170C (~30torr) with some forerun in the 160C range and is collected as a very slightly yellow oil that freezes in the reciever to a crystalline solid. Yield is 6.31g (73% yield from 2-naphthol, 85% recovery) of 2-ethoxynaphthalene as a white crystalline solid melting at 33-34C (uncorr. lit, 36-37C).



It has a powerful scent reminiscent of a more floral, sweeter version of methyl benzoate that is otherwise hard to put a finger on. At extremely high concentrations (nose right up to the bottle) it seems to have a disagreeable fecal smell. This could be impurity, but it would not surprise me seeing as how indole, which is floral at low concentrations is fecal at any decent concentration. Nerolin may activate the same receptors, but with different affinities.

It might be possible to properly recrystallize the material at this point and improve the m.p, but I'm sick of working with it after the first recrystallization failures.

[Edited on 10-26-13 by UnintentionalChaos]




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[*] posted on 26-10-2013 at 03:09


Nice work as always Magpie I love reading your experimental procedures.
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[*] posted on 26-10-2013 at 05:22


Nice work, both of you!

Question: Why the specific warning for methanol? I'd be more weary of exposure to alkylbromides and iodides.




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[*] posted on 26-10-2013 at 16:49


Quote: Originally posted by vulture  

Question: Why the specific warning for methanol? I'd be more weary of exposure to alkylbromides and iodides.


No reason other than I am aware of the hazards of methanol. Not so much those for the halides. Thanks for the warning.

I think this is an interesting comparison of the results for two slightly different procedures by two different experimenters. Oil-outs are a bitch and I think one is wise to go to distillation when they are encountered.

I placed my nerolin on a watch glass in my glassware cabinet. I am pleased by its pleasant smell every time I open the cabinet .




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