Haloform reaction

Haloform reaction

Aldehydes and ketones having at least one methyl group linked to the carbonyl carbon atom (methyl ketones) and secondary methyl carbinols with halogen are oxidised by sodium hypohalite to sodium salts of corresponding carboxylic acids having one carbon atom less than that of carbonyl compound. The methyl group is converted to haloform. This oxidation does not affect a carbon-carbon double bond, if present in the molecule.
Haloform reaction is specific for methyl ketones and alcohols oxidisable to methyl ketones .Thus haloform reaction constitutes a classical test for methyl ketones and methyl carbinols.

Haloform reaction

The reaction is carried out by dissolving  the compound in dioxane and first adding dilute sodium hydroxide and then a slight excess of iodine in potassium iodide solution.this is the followed by slight warming and finally adding water. If the compound contains the acetyl group , iodoform is precipitated out. when a ketone is treated with sodium hypoiodite solution , iodoform and sodium salt of carboxylic acid is formed.

Mechanism of Haloform reaction

Haloform reaction

Some Other Important Reactions

Diels Alder Reaction

The [4+2] cycloaddition reaction between a conjugated diene (4π- lectron system) and a compound containing a double or triple bond, called the dienophile (2π-electron  system) to form an adduct is known as Diels-Alder Reaction named after the two german chemists, who recieved the noble prize for chemistry in 1950. In this reaction a 1,3-diene reacts with a dienophile to form a six membered ring  with a double bond. A typical example is the reaction between butadiene and ethylene by heating both the components alone or in an inert solvent. Similarly, another simplest example is the reaction between butadiene and acetylene.
Diels Alder reaction In Diels Alder reaction two new -bonds are formed at the expense of two -bonds in the starting materials.

Stereochemistry
The reaction is highly stereospecific and used for the synthesis of a variety of products, having different types of structures. For example,dimethyl maleate (1, a cis dieenophile) reacts with butadiene to give cis-dimethyl 1,2,3,6-tetrahydrophthalate (2).However, dimethyl fumerate (3, a trans dienophile) on reaction with butadiene gives corresponding trans product, trans-dimethyl 1,2,3,6-tetrahydrophthalate,(4).
Diels Alder reaction

Dienes can exist in a cisoid and transoid conformation and only the cisoid form undergoes this reaction.if the diene is looked into the transoid conformation, as in (5), the reaction does not take place.
Diels Alder reaction

Mechanism
it is believed that the thermal Diels-Alder reaction is a concerted addition. in the cyclic transition state, the bond-formation and bond-breaking takes place simultaneously, but may not to the same extent. Such a mechanism is known as retarted concerted mechanism.
Diels Alder reaction


Some Other important Reactions

Cannizzaro Reaction

Clemmensen Reduction

Etard Reactions