What is a Cannizzaro reaction?
What is a Cannizzaro reaction?
The Cannizzaro reaction, named after its discoverer Stanislao Cannizzaro, is a chemical process in which two molecules of a non-enolizable aldehyde are disproportionated by a base to yield a primary alcohol and a carboxylic acid.
Cannizzaro achieved this transition for the first time in 1853, when he produced benzyl alcohol and potassium benzoate by treating benzaldehyde with potash (potassium carbonate). More generally, the reaction will be done using sodium or potassium hydroxide, which gives the Carboxylic acid product sodium or potassium carboxylate salt:
2 C6H5CHO + KOH → C6H5CH2OH + C6H5COOK
This procedure involves a redox reaction which transfers hydrides from one molecule of the substrate to another: one aldehyde is oxidized to create acid and the other to form alcohol.
Mechanism of the reaction:
The reaction includes the replacement of the nucleophilic acyl with an aldehyde, with a second step being taken by the exit group. First, carbonyl is attacked by hydroxide. The resultant tetrahedral collapses, re-forms carbonyl to attack another carbonyl and transmit hydride. The acid and the alcohol ions created a proton replacement in the last stage of the reaction. The aldehyde initially produces a doubly charged anion in the presence of a very high base concentration from which a hydroid ion is transferred to the second aldehyde molecule for carboxylate and alcohol ions. The alcoholic ion then obtains a solvent proton.
In total, the response follows kinetics of the third order. The aldehyde is second order, the base is first order:
At very high base a second path (k’) becomes significant that is second order in base:
The k’ route involves a response between the double-charged anion (RCHO22−) and the aldehyde. The direct transfer of hydride ion is clear from the conclusion that, when the reaction occurs with D2O, no deuterium is included in the recovered alcohol connected to α-carbon.
Aldehydes which have alpha-hydrogen atoms are deprotonated and lead to enolates and potential aldol reactions due to the extremely alkaline reactions. The process generates just 50% alcohol and carboxylic acid under optimum circumstances (it takes two aldehydes to produce one acid and one alcohol). In order to prevent low yields, the crossed-cannizzaro reaction is popular in conjunction with a more useful chemistry and uses sacrificial aldehyde. In this variant, the reduction agent is formaldehyde, oxidized to sodium and reduced into alcohol by the other aldehyde chemical.
Carboxylic acid: Carboxylic Acid, one of the organic compounds classes in which a carbon (C) atom is connected to a double bond oxygen (O) atom, and to one single bond hydroxyl (-OH). A fourth bond connects the carbon atom to an atom of hydrogen (H) or to certain other univalent combinations. This group is so-called “carboxyl” (COOH) due to carbonyl (C=O) and hydroxyl.In nature, carboxylic acids are common. The fatty acids are glyceride components, which are fat in turn. The major metabolic products that occur in most living cells are hydroxyl acids, such as lactic acid (found in sour-milk products) and citric acid (found in citrus fruits). Proteins consist of amino acids and carboxylic acids as well.
Properties of Carboxylic acid:
- The main characteristic of and responsible for naming carboxylic acids is their acidity. An acid is a chemical that gives H+(a proton) to a second molecule, called a base. It is a hydrogen ion. It is claimed to be much more powerful acid than most classes, however it is considerably weaker than the main mineral acids – sulphuric (H2SO4), nitric (HNO3) and hydrochloric. Carboxylic acids are also stated to be much more easily (HCl).
- Carboxylic acids are comparable in water solubility to alcohols, aldehydes and ketones. Acids of less than 5 carbons dissolve into water; those of a greater molecular weight are insoluble because they are hydrophobic in the bigger hydrocarbon section.
- The boiling temperatures of carboxylic acids are significantly highe than those of a molecular-balanced hydrocarbon, alcohol, and aldehyde or ketone. Although both have almost uniform molecular weights, formic acid boils at 101 °C (214 °F), much more than the ethanol (ethyl alcohol) boiling point, C2H5OH boils at 78,5 °C (173 °F). The distinction is that two carboxylic acid molecules create two hydrogen bonds (two alcohol molecules can only form one).
Applications of Carboxylic acid:
There are several applications for Carboxylic acid derivatives. For example, formic acid is the simplest carboxylic acid in the textile processing and as an acid reducing agent in addition to its function as a disinfectant. In cellulose plastics and esters, acetate acid is often utilized. Acetic acid is used to produce aspirin, salicylic acid ester. In the production of soaps, cosmetics, medicines, buckets and protective coatings, palmitic acid and stearic acid are essential. In rubber production, stearic acid is also utilized. In the synthesis of polymers (long-chain molecules) called acrylic acid, acrylic acid is used as a species.Methacrylic acid is an ester and a Lucite polymer. The production of soap, detergents and textile is based on oleic acid.