what is the mechanism of darzen reaction .
c6H5_ch=o+cH2_cooH gives c6H5cHocHcoonegative

Are you sure this is the right reaction? Wikipedia says that:


The Darzens reaction (also known as the Darzens condensation or glycidic ester condensation) is the chemical reaction of a ketone or aldehyde with an α-haloester to form an α,β-epoxy ester, also called a "glycidic ester".

But I don't find any halogen nor ester in the molecules you mentioned, but a carboxylic acid.

Darzens reaction - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Darzens_reaction#Reaction_mechanism)

Your reaction is not readable. "CH2COOH is not a compound -- what else is on Carbon number 2? Your product, "C6H5cHocHcoonegative" is incorrectly capitalized and seems to be missing some of the atoms in the compound. Do yourself a favor by taking the time to present the question in a form that we can understand. Unknown008 is correct - this doesn't have the correct reactants or product for the "Darzens glycidic ester condensation" as you have shown them.
But I think I can see what your are trying to do. You have omitted the halogen and the ester group from the second reactant, it should be ClCH2COOC2H5 (ethyl chloroacetate). You need a base (sodium ethoxide) to remove H+ from the ester to make the enolate anion. This condenses with benzaldehyde to give the alkoxide ion. This intermediate would be C6H5CHO(-)CHClCOOC2H5. The alkoxide ion displaces the Cl- ion to form the epoxide (the glycidic ester). This is very difficult to show by typing the structures like this. The epoxide does not show up clearly.
Correct your reactants, use the correct catalyst and redraw your product and you will have the correctly formatted Darzens condensation. It must be in your Organic textbook.

Thanks i will check in my text book .
But what is the meaning of condensation here?

Sorry I have typed wrong .
The reaction is C6H5CHO+ClCH2COOH gives C6H5CHOCHCOOnegative
Alfa chloro epoxide
This reaction is in +nce of OHnegative dilute

What is the meaning of condensation here?

In the presence of \text{OH}^-, a molecule of water, \text{H_2O} is formed. The formation of this molecule is why this reaction is called a condensation reaction.

Also, there is the mechanism on the link I gave you. Did you check it out?

1. The \text{OH}^- will attack the H bonded to the C which is itself bonded to the Cl and forms a carbanion.
2. This carbanion acts as a nucleophile and attacks the C doubly bonded to O in the benzaldehyde, making one electron in the double bond to go to the oxygen atom and make it negatively charged.
3. The negatively charged oxygen then gets bonded to the next carbon atom, while the C-Cl bond breaks through an SN2 mechanism.

In a CONDENSATION reaction two miolecules join to form a new compound, accompanied by the elimination of another small molecule. If H2O is the byproduct it is easy to see why it's called a condensation. When the ester attacks benzaldehyde as in the reaction you cite the first product may be the alcohol in which you have completed an ADDITION reaction. Then, dehydration gives the more stable unsaturated ester as the final product. This is a Claisen-Schmidt reaction.
In the Darzens condensation you MUST use the ester, not the carboxylic acid. The carboxylate anion cannot stabalize the enolate anion. Once you have the enolate anion, a Claisen condensation reaction takes place (look that up in your text). You will see that a PAIR of electrons adds to the carbonyl carbon. As Unknown008 told you, the resulting alkoxide anion then displaces Cl- from the adjacent carbon resulting in the formation of the epoxide. As strained as the three membered ring is, it is formed very fast because of the proximity of the nucleolphile and the electrophillic carbon.

Thanks.it means when H2O will form then condensation must had happen ,is I'm right??

THANKU

thanks.it means when H2O will form then condensation must had happen ,is i m right???????????

Um... not really. A condensation reaction is one where the reactants react together forming another compound and a little molecule. This molecule can be water, HCl, etc.

O kkkkkkkkkkk THANKU