The present work has been supported by Vicerrector&#237;a de Investigaci&#243;n y Estudios de Posgrado from BUAP, Divulgation of Science, and Projects No. REOY-NAT14, 15, 16-G. HEAS-NAT17. RMG thanks CONACyT (Mexico) for scholarship 417887.

1. Reaction
<ol>
	<li>Place in a fume hood an opened round 100 mL flask with 0.5 mol (29.8 mL) glacial acetic acid and add 0.051 mol (5.82 mL) of 3,5-dimethylpyridine and 5 mL of H2O2 (35%). Keep the mixture reaction under constant magnetic stirring, at an inner temperature of 80 &#176;C for 5 h.</li>
	<li>After the reaction time, cool the flask to 24 &#176;C with ice (do not expose the acetic acid gases to the ice), and plug it to a high vacuum distillation unit for 90-120 min to remove excess ac...

<ol>
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Org. Chem. 82 (4), 2059-2066 (2017).</li><li>Merino Garc&#237;a, M. R., R&#237;os-Merino, F. J., Bern&#232;s, S., Reyes-Ortega, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Crystal+structure+of+3,5-dimethylpyridine+N-oxide+dihydrate.">Crystal structure of 3,5-dimethylpyridine N-oxide dihydrate.</a> Acta Cryst. 72 (12), 1687-1690 (2016).</li><li>Sarma, R., Karmakar, A., Baruah, J. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=N-Oxides+in+Metal-Containing+Multicomponent+Molecular+Complexes.">N-Oxides in Metal-Containing Multicomponent Molecular Complexes.</a> Inorg. 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W., Singh, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Facile+One-Step+Synthesis+of+C-Arylnitrones+Using+Dimethyldioxirane.">A Facile One-Step Synthesis of C-Arylnitrones Using Dimethyldioxirane.</a> J.Org.Chem. 55 (9), 2954-2957 (1990).</li><li>Kim, S. W., Um, T., Shin, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Br&#248;nsted+acid-catalyzed+&#945;-halogenation+of+ynamides+from+halogenated+solvents+and+pyridine-N-oxides.">Br&#248;nsted acid-catalyzed &#945;-halogenation of ynamides from halogenated solvents and pyridine-N-oxides.</a> Chem. Commun. 53 (18), 2733-2736 (2017).</li><li>Campeau, L., Rousseaux, R., Fagnou, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+solution+to+the+2-pyridyl+organometallic+cross-coupling+problem:+regioselective+catalytic+direct+arylation+of+pyridine+N-oxides.">A solution to the 2-pyridyl organometallic cross-coupling problem: regioselective catalytic direct arylation of pyridine N-oxides.</a> J. Am. Chem. Soc. 127 (51), 18020-18021 (2005).</li><li>Gang, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Metal-free+methylation+of+a+pyridine+N-oxide+C-H+bond+by+using+peroxides.">Metal-free methylation of a pyridine N-oxide C-H bond by using peroxides.</a> Org. Biomol. Chem. 13 (46), 11184-11188 (2015).</li><li>May, D., Nyman, M. J., Hampden-Smith, E. N., Duesler, <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis,+characterization,+and+reactivity+of+group+12+metal+thiocarboxylates+M(SOCR)2Lut2[M)+Cd,+Zn;+R+)+CH3,+C(CH3)3;+Lut+)+3,5-Dimethylpyridine+(Lutidine)].">Synthesis, characterization, and reactivity of group 12 metal thiocarboxylates M(SOCR)2Lut2[M) Cd, Zn; R ) CH3, C(CH3)3; Lut ) 3,5-Dimethylpyridine (Lutidine)].</a> Inorg. Chem. 36 (10), 2218-2224 (1997).</li><li>Cho, S. H., Hwang, S. J., Chang, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Palladium-Catalyzed+C-H+Functionalization+of+Pyridine+N-Oxides:+Highly+Selective+Alkenylation+and+Direct+Arylation+with+Unactivated+Arenes.">Palladium-Catalyzed C-H Functionalization of Pyridine N-Oxides: Highly Selective Alkenylation and Direct Arylation with Unactivated Arenes.</a> J. Am. Chem. Soc. 130 (29), 9254-9256 (2008).</li><li>Ide, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spin-crossover+between+high-spin+(S+=+5/2)+and+low-spin+(S+=+1/2)+states+in+six-coordinate+iron(III)+porphyrin+complexes+having+two+pyridine-N.+oxide+derivatives.">Spin-crossover between high-spin (S = 5/2) and low-spin (S = 1/2) states in six-coordinate iron(III) porphyrin complexes having two pyridine-N. oxide derivatives.</a> Dalton Trans. 46 (1), 242-249 (2017).</li><li>Drago, R. 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M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Crystal+structure+refinement+with+SHELXL.">Crystal structure refinement with SHELXL.</a> Acta Cryst. 71 (1), 3-8 (2015).</li><li>Sheldrick, G. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+short+history+of+SHELX.">A short history of SHELX.</a> Acta Cryst. 64 (1), 112-122 (2008).</li><li>Macrae, C. F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mercury+CSD+2.0+-+new+features+for+the+visualization+and+investigation+of+crystal+structures.">Mercury CSD 2.0 - new features for the visualization and investigation of crystal structures.</a> J. Appl. Cryst. 41 (2), 466-470 (2008).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> ChemBioDraw Ultra 13. , (2013).</li></ol>

All authors declare no conflict of interest.

The protocol presented here is a conventional method to link an oxygen atom to the nitrogen atom of the 3,5-lutidine as a functionalization method of substrates. This technique is also well established to yield X-ray suitable dehydrated crystals (Figure 5, pictures taken with a DSC-HX300 Cyber-shot Sony camera). As far as we are concerned, not many reports have described the production of such crystals16. Many compounds grow ideal crystals for X-ray analysis when they are chelated...

Nowadays, scientists around the globe have been investing resources into the development of new synthetic routes for the functionalization of aromatic groups, which are known for low reactivity front to addition reactions1,2,3. Pyridine, where a nitrogen atom substitutes a carbon atom, presents a similar chemical reactivity to analogue rings composed solely of carbon atoms3, and it usually undergoes a substitution mechanism rather than addition. N-oxides are distinctive by the presence of a donor bond between nitrogen and oxygen formed by the overlap of the nonbonding electron pair on the nitrogen with an empty orbital on the oxygen atom3. Particularly, pyridine N-oxides are Lewis bases, because their N-O moiety may act as an electron donor, and they may combine with Lewis acids forming the corresponding Lewis acid-base pairs. This property has an essential chemical consequence, because it can increase the nucleophilicity of the Lewis acids towards potential electrophiles and thus allow them to react under conditions where normally the reaction would not occur. Probably the most frequent use of such compounds is in various oxidation reactions where they act as oxidants4. Pyridine N-oxides and many of their ring-functionalized derivatives are recurrent molecules of biologically active and pharmacological agents5, and a clear spatial distribution by different spectroscopic tools has been established for some of them6,7. In research on attaching different groups to the pyridine ring, scientists have tested various methodologies to produce an easy and conventional method, since isoxazolines requires a catalytic amount of base such as DBU in boiling xylene to form 6-substituted-2-aminopyridine N-oxides8,9. A variety of pyridine derivatives were converted into their corresponding N-oxides in the presence of a catalytic amount of manganese tetrakis(2,6-diclorophenyl)porphyrin and ammonium acetate in CH2Cl2/CH3CN8,10. Other pyridines are oxidized to their oxides using H2O2 in the presence of catalytic amounts of methyltrioxorhenium8,11, or by the addition of excess dimethyldioxirane in CH2Cl2 at 0 &#176;C, which leads to the corresponding N-oxides8,12,13,14. Bis(trimethylsilyl)peroxide in the presence of trioxorhenium in CH2Cl2 has been used for the synthesis of pyridine N-oxides8,11. The synthesis of aminopyridine N-oxides involving acylation using Caro&#39;s acid (peroxomonosulfuric acid) has also been reported8. Nevertheless, the methodology reported here, and which uses part of the methodology reported by Ochiai1, provides very good results with the use of cheaper and accessible reagents, H2O2 and glacial acetic acid. This practice is more suitable for use in large scale preparations that act on tertiary amines, it produces good yields in a reaction that only requires 30% hydrogen peroxide and glacial acetic acid in a temperature between 70-80 &#176;C, and it uses a purification process that is available in most synthesis laboratories like distillation, without the use of catalyst or more expensive reagents1. The literature reports that other methodologies also frequently involve time frames from 10-24 h and temperatures above 100 &#176;C 4,8, and the yield of well-formed crystals for X-ray analyses is rarely reported.
Reactively, various N-oxide derivates are used to adequately activate the lutidine ring, in either a nucleophilic or electrophilic way. The nucleophilic or electrophilic factor is affected by the substituents. With the pyridine ring being the electron-withdrawing groups, the main factor is the nucleophilic characteristic1. The free N-oxide compounds are rarely isolated as suitable crystals for X-ray analysis due to the delocalized charge in the aromatic ring. However, the solvation factor is critical to stabilize the negative density of the oxygen15.

<table border="0" cellpadding="0" cellspacing="0" style="width:725px;" width="725">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">3,5-lutidine</td>
			<td style="width:228px;">Sigma-Aldrich</td>
			<td style="width:119px;">L4206-500ML</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Glacial acetic acid</td>
			<td>Fermont</td>
			<td>3015</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Hidrogen peroxide (35%)</td>
			<td>Sigma-Aldrich</td>
			<td>349887-500ML</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">Na2CO3 anhydrous</td>
			<td>Productos Qu&#237;micos Monterrey</td>
			<td>1792</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">Na2SO4 anhydrous</td>
			<td>Alfa reactivos</td>
			<td>25051-C</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">CHCl3</td>
			<td>Fermont</td>
			<td>6205</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Ethyl eter</td>
			<td>Mercury Chemist</td>
			<td>QME0309</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Distilled water</td>
			<td>Comercializadora Qu&#237;mica Poblana</td>
			<td>not-existent</td>
			<td></td>
		</tr>
	</tbody>
</table>

syntheses, crystallization, and spectroscopic characterization of 3,5-lutidine n-oxide dehydrate

The synthesis of 3,5-lutidine N-oxide dehydrate, 1, was achieved in the synthesis route of 2-amino-pyridine-3,5-dicarboxylic acid. Ochiai first used the methodology for non-substituted pyridines in 1957 in a 12 h process, but no X-ray suitable crystals were obtained. The substituted ring used in the methodology presented here clearly influenced the addition of water molecules into the asymmetric unit, which confers a different nucleophilic strength in 1. The X-ray suitable crystal compound 1 was possible due to the stabilization of the negative charge in the oxygen by the presence of two water molecules where the hydrogen atoms donate positive charge into the ring; such water molecules serve well to construct a supramolecular interaction. The hydrated molecules may be possible for the alkaline system that is reached by adjusting the pH to 10. Importantly, the double methyl substituted ring and a reaction time of 5 h, makes it a more versatile method and with wider chemical applications for future ring insertions.

The protocol is essentially an extension of Ochiai&#39;s technique1. However, lower temperature and less time are applied. This simple method can be used to obtain a versatile ligand, which is a substituted pyridine N-oxide derivate. To confirm the formation of 1, NMR 1H and 13C analysis are preferred to test the effectiveness of the procedure.
The chemical ...

Watch this Scientific Journal Video about Syntheses, Crystallization, and Spectroscopic Characterization of 3,5-Lutidine N-Oxide Dehydrate at JoVE.com

Syntheses, Crystallization, and Spectroscopic Characterization of 3,5-Lutidine N-Oxide Dehydrate

Herein, we report the synthesis and crystallization of 3,5-lutidine N-oxide dehydrate by a simple protocol that differs from the classical synthesis of pyridine N-oxide. This protocol utilizes different starting material and involves less reaction time to yield a new solvated supramolecular structure, which crystallizes under slow evaporation.

Syntheses, Crystallization, and Spectroscopic Characterization of 3,5-Lutidine N-Oxide Dehydrate

The synthesis of 3,5-lutidine N-oxide dehydrate, 1, was achieved in the synthesis route of 2-amino-pyridine-3,5-dicarboxylic acid. Ochiai first used the ...

The overall goal of this methodology is to synthesize suitable X-ray monocrystals of 3, 5-lutidine N-oxide dehydrate in shorter reaction time using inexpensive and easy-accessible reagents to yield a novel solvated supramolecular structure. This method can help answer key questions in the synthetic organic and inorganic chemistry field such as how to synthesize noble aromatic compounds, and et-see-cic compounds and perioding dare-ee-batics. The main advantage of this technique is that it uses solvents and materials that are more accessible and generally found in a research laboratory.We first have the idea for this method when we were in search of an optimal route to obtain 3, 5-lutidine N-oxide as an intermediate of 2-aminopyridine-3, 5-dicarboxylic acid. First, place on open 100 milliliter round bottom flask containing a magnetic stir bar on a magnetic stir plate in a fume hood. Add 29.8 milliliters of glacial acetic acid, 5.82 milliliters of 3, 5-dimethylpyridine and five milliliters of 35%hydrogen peroxide to the flask.Stir the reaction mixture at an inner temperature of 80 degrees Celsius for five hours. After the reaction is complete cool the flask to 24 degrees Celsius with ice. Once cooled, connect the flask to a high-vacuum distillation unit for 90 to 120 minutes to remove excess acetic acid.Following this, add 10 milliliters of distilled water to the flask, and concentrate the mixture to remove trace acetic acid. Dissolve the isolated viscous and transparent product in 20 milliliters of distilled water. Then use a potentiometer to adjust the pH to 10 with sodium carbonate.Next, carefully add the solution to a 250 milliliter separation funnel. Extract the solution five times with 250 milliliters of chloroform. Recover the product containing organic layer and dry it over sodium sulfate for a maximum of 30 minutes.After filtering off the sodium sulfate remove the solvent under reduced pressure with a high-vacuum distillation unit to afford of a very hygroscopic, clear, beige, crystalline powder. Now, dissolve 4.3 grams of the crystalline powder in 50 milliliters of cold HPLC grade diethyl ether. Vacuum filter the solution to remove any trace of solid starting material or dust.Then pour the filtrate into a glass Petrie dish and store at four degrees Celsius to slowly evaporate the solvent. After two days, check that clear, colorless crystals are obtained. Then measure the melting point, which should be in the range of 310 to 311 Kelvin.Next, isolate the 3, 5-lutidine N-oxide dehydrate crystals by decantation for X-ray analysis. Finally, dissolve 0.01 grams of the 3, 5-lutidine N-oxide dehydrate crystals in 0.4 milliliters of deuterated chloroform for proton and carbon NMR analysis. The signal at 2.28 ppm in the proton NMR spectrum of 3, 5-lutidine N-oxide dehydrate corresponds to the six equivalent hydrogen atoms of the two methyl groups in the three and five positions.The signals at 7.9 ppm and 6.9 ppm represent protons C and A respectively. These hydrogens are at the higher frequency than the methyl hydrogens because they are closer to the electron-withdrawing oxygen atom. In the carbon spectrum of 3, 5-lutidine N-oxide dehydrate the signals for the carbons closer to the oxygen atom show frequency separation between their signals of 1300 hertz and 200 hertz.The methyl carbons do not show any change. The ORTEP diagram shows two molecules of water surrounding the asymmetric 3, 5-lutidine N-oxide dehydrate which are believed to stabilize the N-O bond. There is a significant stabilizing Pi type O-N back donation reflected in a calculated bond order higher than one and number of electron lone pairs on the oxygen atom lower than 36.While attempting this procedure it's important to remember that this protocol uses solvents and materials that are easily obtainable and generally found in any research laboratory.

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8.3K visualizações.  Benemérita Universidad Autónoma de Puebla. The overall goal of this methodology is to synthesize suitable X-ray monocrystals of 3, 5-lutidine N-oxide dehydrate in shorter reaction time using inexpensive and easy-accessible reagents to yield a novel solvated supramolecular structure. This method can help answer key questions in the synthetic organic and inorganic chemistry field such as how to synthesize noble aromatic compounds, and et-see-cic compounds and perioding dare-ee-batics. The main advantage of this technique is that it uses...