PURPLE?!?!

Hmm, here’s a quick little puzzle that I’m in the middle of solving. If anyone knows the answer, feel free to let me know.

Attempting to make the acid chloride of 2-picolinic acid by SOCl2. In dichloromethane, combined ~5g of 2-picolinic acid with a slight excess of SOCl2 (~1.2:1), refluxed for ~20 minutes, removed solvent, set it aside. The initial solid was tan-brown. After a few days, it was dark. Massively dark. And green-blue, as far as the eye can tell. After a week, it’s bone dry and still massively dark. A rough yield of around 6g. So it picked up some mass…

Solubility testing… Very soluble in water, forms a deep purple solution. Soluble in methanol, solution is a bit more blue. Very slightly soluble in chloroform, purple solution. Very slightly soluble in acetonitrile, greenish leaning toward blue solution.

NMR (in D2O)… Four clean aromatic signals, consistent with the 4 protons of an ortho-substituted pyridine ring, nothing else.

20140204nmrpurple01

UV-Vis (in water)… Peak at ~540nm, shoulder at ~650nm. Strong peak at ~260nm.

20140204uvvis01 20140204uvvis02

This has not been exhaustively lit searched yet, but the intensity of the color of the product is intriguing AND a ~20% mass increase makes it a fun little puzzle. We will be exploring more…

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N-4-phenyl picolinamide – Feb 10-Feb18 update

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TLC of KG04 together with reagents, phenylisocyanate, picolini acid, and diisopropylethylamine in ethylacetate/hexane eluent.

(Left, TLC in 1:9 ratio, center 2:3 ratio, right 2:3 ratio with components diluted)

The product KG04 was dissolved in acetone (not the one from the wash bottle), and TLC of of it was taken together with phenylisocyanate, picolini acid, and diisopropylethylamine in ethylacetate/hexane as eluent in the ratio of 1:9 (1.0mL ethylacetate and 9.0mL hexane). As seen in the picture (left), not much movement of the molecules were observed. Hence, new eluent for TLC was prepared with ethylacetate:hexane ratio of 1:2 (5mL and 10mL respectively). As seen in the middle of the picture, the result was better, but still not clear distinction, so another TLC was run will similar eluent, but this time the samples with diluted with acetone. The right TLC plate in the picture shows the result.

It is clear that the product does contain some picolinic acid and phenylisocyanate, but another method to analyse the product is required for detailed understanding.

Chemical dip method was done on the TLC plate, but no new spots were formed.

Characterizing N-4-phenyl picolinamide

he NMR spectrum of KG01 and KG02 were taken. The products were insoluble in CDCl3, so acetone was used as a solvent for obtaining NMR spectrum.

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ImageFrom the graphs it is clear that both, KG01 and KG02, are same product. However, clearly the products are not the ones we expected as the number of peaks are too few for N-4-phenyl picolinamide molecule. One of the possibilities is that since water was involved in the reaction (which I accidentally added in place of acetone), the N-4-phenyl picolinamide could have broken down into picolinic acid and aniline. The picolinic acid could have been washed away with water leaving aniline, so there is a probability that the spectrum is of aniline, and it does seem consistent; aniline has 4 different hydrogen environment, there are 4 major peaks with two triplet and a doublet.

N-4-phenyl picolinamide -Gurung

In this experiment, we are trying to create one branched, N-4-phenyl picolinamide molecules from the reaction between picolinic acid and pheylisocyanate in presence of amine, diisopropylethylamine and solvent DMF, under standard conditions.

Reactant:

Reactant Used Ratio
Picolinic acid 0.932g 1.5
Phenylisocyanate 0.548ml 1
N,N-diisopropylethylamine 1.76ml 2

Synthesis:

Reactant Used Ratio
Picolinic acid 0.936g 1.5
Phenylisocyanate 0.550ml 1
N,N-diisopropylethylamine 1.757ml 2
DMF (Solvent) 245.40ml

Observation:

10th Sept 2012

Picolinic acid was dissolved in DMF, the resulting solution was colorless solution, followed by addition of isocyanate, which turned the solution to yellow, then we added the amine N,N-diisopropylethylamine, which did no visual change to the solution. The solution was left to mix overnight.

Added at 15:20

17th Sept 2012

Under vacuum, attempt was made to remove the solvent, DMF, from the solution, but since it took long time, it was left to evaporate in air overnight.

Started at 17:45

19th Sept 2012

After two days all the solvent had already evaporated, leaving pale while/yellow sold at the flask.

Image

24th Sept,2012

The solid was to be dissolved in methanol for TLC, but unfortunately an error was made where I added water instead of methanol. Then, I added methanol on the solution so that it was 50/50 water and methanol and proceeded with heating the solution. On heating all the solid particles dissolved.

The solution was then put in ice to induce crystallization. Few crystals were formed. After that, the crystallization was done under vacuum. The solid collected in the filter paper was labelled KG01.

Formation of crystals were also observed in the filtrate, so we proceeded to crystallize the solute from the filtrate under vacuum in second erlenmeyer flask, and the crystal obtained was labelled KG02.

25th Sept,2012

To test where the crystals were expected products or not, their melting ranges were taken and was found to be 228-234oC for both KG01 and KG02, which is pretty high than of N-4-phenyl picolinamide,72.6-74.0oC (ref. Sasaki, Crich.) we are trying to synthesize. This is also intriguing because none of the reactants also have such high melting range.

Chemical Melting point/range (oC)
Picolinic acid 137
Phenylisocyanate -30
N,N-Diisopropylethelamine <-50

source: MSDS sheet, http://www.sciencelab.com

Hoping that the expected products were still in the filtrate obtained from crystallization, I initiated evaporation of liquid to in air obtain the solid product (along with other possible impurities.)

3rd Sept,2012

All the liquid had evaporated leaving pale white/yellow solid similar to the one obtained at 19th Sept 2012.

The solid was dissolved in methanol, giving orange solution, and TLC test was conducted with solvent of 95% dichloromethane and 5% methanol.

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The sample does contain mixture of particles.

By looking at Dr Bodwin’s similar experiment and TLC of his sample in similar solvent,

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it’s reasonable to say the product is between the two reactants (bottom two in the plate), and it seems acetone (the top one), can get ride of those two reactants leaving the product.

Right now what we have left to do is to separate the product and find out it’s structure, and possibly of also KG01 and KG02.