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Author: Subject: Collidine vs Pyridine
numos
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[*] posted on 24-1-2016 at 13:02
Collidine vs Pyridine


I am nearly done with my Rubrene synthesis, and have just finished recrystallizing a nice crop of triarylpropargyl alcohol, synthesis found here:
http://www.sciencemadness.org/talk/viewthread.php?tid=23112

The next step requires chlorination with Thionyl chloride, and although I have some, it was brought to my attention that this route sucks and is prone to crystallization problems.
plastics provided this method which should be much more reliable:
Quote: Originally posted by plastics  

Synthesis of rubrene from 1,1,3 triphenylprop-2-yn-1-ol

1,1,3-triphenylprop-2-yn-1-ol 2g 4g 6g 8g 10g
Dichloromethane (39.4 °C) 15ml 30ml 45ml 60ml 75ml
Triethylamine 1.1ml 2.2ml 3.3ml 4.4ml 5.5ml
Methanesulphonyl chloride (161 °C) 1.2ml 2.4ml 3.6ml 4.8ml 6.0ml
Collidine (171 – 172 °C) 1ml 2ml 3ml 4ml 5ml
Xylene (140 °C)

2.0 g 1,1,3-triphenylprop-2-yn-1-ol is dissolved in 15 ml anhydrous dichloromethane under nitrogen and cooled to 0 °C
1.1 ml anhydrous triethylamine and 1.2ml methanesulphonyl chloride were added and the mixture stirred for 1 hour at 0 °C, then allowed to warm to room temperature
The mixture was heated at reflux to distil off the dichloromethane which was gradually replaced with xylene
The solution was heated and on reaching 80 °C 1ml collidine added dropwise
Reaction temperature raised to 95 °C and held at this temperature for 7 hours
Mixture allowed to cool to room temperature and the precipitate collected by filtration
The red soldid was recrystallized from ethanol to afford the desired product yield 0.76 g (46%)


Paper found here:
http://www.sciencemadness.org/talk/files.php?pid=430392&...

Everything is good, except I don't have Collidine. I don't want to drop $50+ on Sigma Aldrich, and I haven't found an easy synthesis of Collidine. I read the article above, but either I missed something, or I don't have the required background to understand what's happening. (Likely the latter)

Can someone please explain the mechanism behind this reaction, specifically the role of Collidine. Collidine refers to a variety of trimethylpyridines and I'm curious because it is rather similar to Pyridine, and I'm hoping to be able to substitute it.




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byko3y
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[*] posted on 25-1-2016 at 06:59


Collidine here is a 2,x,6-pyridine, and it plays a role on non-nucleophilic base for condensation reaction. Pyridine won't work for that.
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DJF90
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[*] posted on 25-1-2016 at 07:12


2,6-Lutidine might work as a drop-in replacement.
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chemrox
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[*] posted on 25-1-2016 at 09:07


which collidine? or do you care?



"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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UC235
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[*] posted on 25-1-2016 at 11:16


If you have some ethyl acetoacetate, you can make a 2,6-dimethylpyridine via Hantzsch pyridine synthesis.
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Dr.Bob
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[*] posted on 25-1-2016 at 11:55


Collidine is most often referring to the 2, 4, 6 compound, if not specified. I would think based on the prep, that 2,6-dimethylpyridine would work OK, and maybe even pyridine, there might be some change, but I don't see anything that discusses the role of the collidine other than as a non-reactive base, and thus substitution might well work. The generic scheme just says base in that step. I have even substituted DMAP for pyridine and other pyridine bases in many cases with equal or better yields, since it is not nearly as smelly as pyridine, and is more basic, but in this case, I would not try that to start with.
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byko3y
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[*] posted on 25-1-2016 at 18:41


Dr.Bob, DMAP is more similar to pyridine than collidine/lutidine is. E.g. Dakin-West reaction gives lower yields when using pyridine as acylation catalyst.
Although, the OP's reaction is performed using tertiary alkyl halide, which is a weak alkylation agent by itself, so pyridine might work there, but I don't know whether there are no other possible electrophilic alkylators. Or probably reaction needs a protected pyridine ring, otherwise cyclization will happen.
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numos
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[*] posted on 25-1-2016 at 21:13


This is what I was hoping for
Quote: Originally posted by Dr.Bob  
I don't see anything that discusses the role of the collidine other than as a non-reactive base, and thus substitution might well work. The generic scheme just says base in that step.


This is what I was afraid of
Quote: Originally posted by byko3y  
Or probably reaction needs a protected pyridine ring, otherwise cyclization will happen.


It wouldn't even be a problem, I could just test it, but I have enough of the triphenyl propargyl alcohol to do one run.

The procedure only says "collidine" not specifying which isomer, so I'm hoping that's simply what they had on hand, or was easier to use. Judging from the responses, it seems the collidine is not a direct reactant (that sounds so incorrect, sorry) and pyridine would have the same affect, but in addition may influence the reaction negatively - so it will still work but I should expect my yield to take a hit?




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[*] posted on 25-1-2016 at 22:06


Quote: Originally posted by numos  

It wouldn't even be a problem, I could just test it, but I have enough of the triphenyl propargyl alcohol to do one run.



When you say one run, you mean on 2 g scale following the procedure Plastics had provided? Why not test the reaction on 50 to 100 mg scale...then if it works you can scale up, and if it doesn't then you've not burned all your material and can trial several other conditions.
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DrMethyl
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[*] posted on 27-1-2016 at 13:34


hello, I've used collidine to trap methyl iodide. Collidine is more basic and nucleophile because of the electron-releasing alkyl group.

I don't know this reaction but maybe it can be replaced by something like DBU (?)
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