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I'm not an expert teacher or lecturer of chemistry. I was only a student from SMA NEGERI 15 SURABAYA who had been one of the Bronze Medalist Participants of Olimpiade Sains Nasional X (2011) of Chemistry In Manado, North Sulawesi, 11 - 16 September 2011 and graduated in 2012. Now, I'm studying at Universitas Airlangga in Surabaya, Indonesia. I do love chemistry and I would like to help them who had difficulties in studying chemistry. That's why, please understand me if you found some misconcepts in my entries. Suggestions are always necessary in order to develop this blog. And I'm sorry because my English isn't so well.

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Tuesday, January 01, 2013

Synthesis of 2,4-dimethyl-3,5-dicarboethoxypyrrole

In organic chemistry, this compound is popular enough to be synthesized. The procedure are written as follows:

In a 3-l. three-necked, round-bottomed flask, fitted with a liquid-sealed mechanical stirrer and dropping funnel, are placed 390 g. (3 moles) of ethyl acetoacetate and 900 cc. of glacial acetic acid. The solution is cooled in an efficient freezing mixture to 5°, and a cold solution of 107 g. (1.47 moles) of 95 per cent sodium nitrite in 150 cc. of water is added dropwise with vigorous stirring at such a rate that the temperature remains between 5° and 7°. With efficient cooling about one-half hour is required to add the nitrite. The mixture is stirred for one-half hour longer and then allowed to stand for four hours, during which time it warms up to room temperature.
The separatory funnel is replaced by a wide-bore condenser, and the third neck of the flask is fitted with a stopper. The solution is stirred and portions of 196 g. (3 gram atoms) of zinc dust are added quickly through the third neck of the flask until the liquid boils and then frequently enough to keep it boiling. After the addition has been completed, the mixture is heated by a burner and refluxed for one hour. While still hot the contents of the flask are decanted from the remaining zinc into a crock containing 10 l. of water which is being vigorously stirred. The zinc residue is washed with two 50-cc. portions of hot glacial acetic acid which are also decanted into the water. After standing overnight, the crude product is filtered by suction, washed on the filter with two 500-cc. portions of water, and dried in air to constant weight. The yield is 205–230 g. (57–64 per cent of the theoretical amount) of material melting at 126–130°. On recrystallizing a 50-g. portion from 100 cc. of 95 per cent alcohol and washing twice with 20-cc. portions of cold alcohol, there is obtained 38.5 g. of pale yellow crystals melting at 136–137° .

Here's the mechanism:
1. Step One. Oxime Forming

HNO2 which is formed by the in situ reaction of NaNO2 and HCl at 0 oC reacts with the alpha hydrogen to form Nitrosonium Ion (NO+). Nitrosonium ion will be attacked by ethylacetoacetate in concerted way. See the mechanism as follows:

The nitrosonyl group will resonance to form oxime which is a more stable group.

2. Step Two: Reduction of Oxime to Form Amine
You have to know that this is not Clemmensen Reduction, it's just a usual reduction.
3. Step Three: Forming the Target Compound

Another ethylacetoacetate will be attacked (Nucleophilic addition and Elimination) by the compound.

Finally, the compound above arrange itself to form the target compound (controlled by reaction environment).

Glacial Acetic Acid act as catalyst and solvent in this reaction. The heat we use will release H2O compound to form 2,4-dimethyl-3,5-dicarboxyethoxypyrrole.

Total Reaction:

This mechanism is approved by a Strata 2 student.
Thank You


Clayden. Advanced in Organic Chemistry.
Fessenden. Organic Chemistry Ed. 3rd


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