In this reaction two carbonyl compounds containing a hydrogen condense in the presence of a base to give ß hydroxy carbonyl compound. This is the characteristic reaction for carbonyl compounds containing a hydrogen and hence formaldehyde and benzaldehyde will not give aldol condensation. This reaction indicates the acidic nature of hydrogen at alpha position in the carbonyl compound. For example acetaldehyde undergoes aldol condensation to give ß hydroxy butanaldehyde which on dehydration gives crotanaldehyde
This method is excellent synthetic way to prepare unsaturated aldehydes and acids. If we take a mixture of acetone and acetaldehyde we will get a condensation product between acetone and acetaldehyde in which the acetone will lose the alpha hydrogen easily to give the product.
This mechanism involves formation of carboxylate ion by losing alpha acidic hydrogen and attack of the nucleophile to another carbonyl compound. This is the condensation type reaction.
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In this reaction carbonyl compounds without hydrogen at a carbon undergo disproportion
to give alcohol and salt of carboxylic acid in the presence of a base. This is the characteristic reaction for compounds without hydrogen at alpha carbon.
Hence acetaldehyde and propanaldehyde will not undergo cannizzaro reaction. For example formaldehyde undergoes disproportion in the presence of base to give methyl alcohol and sodium formate.
2HCHO$\to$CH3OH + HCOONa
If we take formaldehyde and benzaldehyde the major products are methyl alcohol and benzoic acid.
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It is the reaction where two ester molecules condense in the presence of base to give condensed ester with alcohol. This is also another type of carbon-carbon bond formation reaction
. In this reaction instead of two ester molecules we can condense ester with another carbonyl compound like acetaldehyde and acetone also. For example two ethyl acetate molecules condense together to give ethyl acetoacetate and ethanol. This is a type of condensation reaction.
CH3-CH2-O-CO-CH3 + CH3-CH2-O-CO-CH3 → CH3-CH2-O-CO-CH2-CO-CH3 + CH3-CH2-OH
In this reduction an acyl chloride is reduced to aldehyde in the presence of Palladium and Barium sulphate as catalytic poison
. The purpose of Barium sulphate is reduce to effectiveness of palladium or otherwise the aldehyde thus formed will be directly reduced to alcohol.
This is the effective way to convert acyl chloride to aldehyde. For example Banzoyl chloride is reduced to benzaldehyde.
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Here the carbonyl compounds like aldehydes and ketones are directly reduced to alkane in the presence of hydrazine
in a suitable base like sodium ethoxide or sodium hydroxide.
The mechanism involves formation of hydrazone followed by deprotonation and evolution of nitrogen gives the desired alkane. For example acetone on Wolf-Kishner reduction gives propane.
It is the effective way to prepare the primary amines. Here the pthalimide is converted to N-methyl pthalimide which on further base hydrolysis gives the primary amine. The complete process involves the following steps.
This method will not work in case of aromatic amines like aniline as the halogen bond cannot be easily broken from benzene ring.
- Converting pthalimide to potassium pthalimide.
- Converting potassium pthalimide to N-methyl pthalimide.
- Hydrolysis of N-methyl pthalimide to give desired primary amine.
In this example on treating methyl iodide with pthalimide in the presence of base we will get methyl amine.
This is the characteristic reaction of primary amines. Primary amines on reacting with chloroform and potassium hydroxide form iso-cyanides a foul smell gas which is often used to identify primary amine group in an organic compound. Secondary and tertiary amines will not give this test.For example aniline on carbyl amine reaction gives phenyl iso-cyanide.
C6H5NH2 + CHCl3 + KOH → C6H5NC + 3KCl + 3H2O
Here the carbonyl compounds are reduced to alkanes in the presence of Zinc amalgam in hydrochloric acid
. This method is particularly effective for aryl-alkyl ketones and the substrate should not be acid sensitive. For example aceto phenone on clemmensen reduction gives ethyl benzene.
Acetone will give the test result to the moderate extend and on reduction it will give propane.
CH3-CO-CH3 → CH3-CH2-CH3
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Some Points about Lucas Test:
- This is the effective test to distinguish the primary, secondary and tertiary alcohols.
- Anhydrous zinc chloride in concentrated hydrochloric acid is called as Lucas reagent.
- Alcohols on reacting with Lucas reagent give alkyl halides due to which a turbidity develops.
- The turbidity will develop in according to the rate of the reaction.
Tertiary alcohols will undergo the reaction much more faster and turbidity will develop immediately.
Secondary alcohols will undergo the reaction at moderate rates and turbidity will develop after 2-3 minutes.
CH3-CH(OH)-CH3 +HCl $\to$ CH3-CH(Cl)-CH3 + H2O
Primary alcohols will not undergo the reaction at normal conditions so the turbidity will develop only on heating.
CH3-CH2-OH + HCl $\to$ CH3-CH2-Cl + H2O
By this we can differentiate primary, secondary and tertiary alcohols.
This is the characteristic reaction of primary amines. Primary amines on reactive with carbon disulphide in the presence of mercuric chloride to give iso-thiocyanates.
CH3-NH2 + CS2 + HgCl2 → CH3-S-CN + HgS + HCl
This test is also used to distinguish the primary amines from other amino groups. This is called as mustard oil reaction because the iso-thiocyanates are active ingredients of mustard oil.
Organic chemistry reactions are different from inorganic chemistry reactions as the core principle will guide the mechanism of the reaction and the products.For example hydrocarbons on combustion give carbon dioxide and water. This is applicable to all hydrocarbons in complete combustion. So any one can easily say that Methane on combustion will give carbon dioxide and water.
CH4 + 2O2 → CO2 + 2H2O
Named organic chemistry reactions were discovered pathways by many scientists over the course of time. They are named after the scientist who discovered the pathway. For example Claisen reaction is named after the scientist Claisen who discovered that esters can be condensed to give condensed products at slightly different conditions.
Some named reactions are named after the reactants, intermediates or products of the reaction. For example Gabriel-pthalimide synthesis uses pthalimide as an intermediate.
Organic chemistry mechanism is the detailed pathway of an organic chemistry reaction. It shows the intermediates formed during a organic chemistry reaction which can be isolated by adding suitable reagents.Similarly it explains the transition state through which a reactant is converted into product. The mechanism is useful in assisting to derive the rate expression and to determine the kinetically controlled and thermodynamically controlled products.
The strategic application of named reaction is their innovativeness that expand the scope of organic chemistry to new pathways and mechanisms. The organic chemistry field is expanding every day with the invention of new method of synthesis and new compounds. This provides more and more interest in the field for research and development.
The following are some of the named reactions in organic synthesis.
- Aldol condensation.
- Friedal-craft reaction.
- Cannizaro reaction.
- Rosamund reduction.
- Lucas test.
- Victor-meyer test
- Gabriel Pthalimide synthesis.
- Clemmenson reduction.
- Wolf-Kishner reduction.
- Claisen reaction.
Organic chemistry reactions can be classified as following.
- Oxidation reaction.
- Reduction reaction.
- Hydrolysis reaction.
- Hydration reaction.
- Dehydration reaction.
- Condensation reaction.
- Polymerization reaction.
- Substitution reaction.
- Addition reaction.
- Elimination reaction.