Saturday, February 29, 2020

Covalent bond-definition-examples-formation energy and types

BY P GHOSH Covalent bond-definition-examples-formation energy and types , HOME

Covalent bond definition in chemistry

When a chemical bond is formed between two similar or different atoms by sharing of one or more electrons pairs by them to gain the more stable nearest inert gas electronic configuration , then the bond is called covalent bond . It is also called molecular bond.

Chemical bonding-definition-examples and importance in chemistry

BY P GHOSH Chemical bonding-definition-examples and importance in chemistry , HOME

Chemical bonding definition in chemistry

The force of attraction, through which two or more atoms of similar or different elements, are connected to form basic or compound molecule or ion , that force of attraction is called chemical bonding .

Benzoic acid-boiling point-strength-more acidic than acetic acid.

BY P GHOSH Benzoic acid-boiling point-strength-more acidic than acetic acid. , HOME

Benzoic acid boiling point explanation.

Oxygen is more electronegative than hydrogen. So, O – H bond of benzoic acid is polar in nature .

As a result, benzoic acid forms inter-molecular hydrogen bond. To break this large number of inter-molecular hydrogen bond , a great amount energy is required.

Benzene to benzoic acid-Gattermann-Koch reaction

BY P GHOSH Benzene to benzoic acid-Gattermann-Koch reaction , HOME

Benzene to benzoic acid change

There are different way for the preparation of benzoic acid from benzene molecule . The well known process is, involving Friedel craft’s alkylation or acylation reaction.

Benzoic acid can be prepared from benzene molecule , converting it first methyl benzene or toluene by Friedel craft’s alkylation reaction.

In the second step, oxidation of this toluene molecule by potassium permanganate followed by acidic hydrolysis ,produced the expected benzoic acid .

There are many other methods for the preparation of benzoic acid from benzene molecule.

For example , benzoic acid can be prepared from benzene , converting it Grignard reagent’s .

In the first step, benzene reacts with bromine in presence of iron catalyst , it form bromo benzene .

This bromo benzene reacts with metallic magnesium in dry ether medium , changed into Grignard reagent , phenyl magnesium bromide .

Finally, phenyl magnesium bromide reacts with carbon dioxide followed by hydrolysis , gives the expected product , benzoic acid .

Again , benzoic acid can be prepared from benzene , converting it acetophenone in the first step by Friedel craft acylation .

Then ,in the second step,this aceto phenone under goes haloform reaction, that is chloroform reaction to produce chloroform and sodium benzoate .

The acidic hydrolysis of this sodium benzoate gives benzoic acid .

One more change of benzene to benzoic acid through nitration of benzene . Nitration of benzene, followed by reduction , gives aniline .

This aniline under goes diazotization reaction to form diazonium salt .

On sand meyer’s reaction of diazonium salt in presence of CuCN / KCN , gives cyano benzene , which on acidic hydrolysis finally produce benzoic acid .

Gattermann-Koch reaction .

Besides the above reactions, the another most important name reaction ,Gattermann-Koch aldehyde synthesis ,through which benzoic acid may be prepared .

When a mixture of carbon monoxide and hydrogen chloride is passed through benzene

solution in presence of anhydrous AlCl₃ and little amount of Cu₂Cl₂ catalyst , then benzaldehyde is obtained as the main product .

This reaction is known as Gattermann-Koch aldehyde synthesis .The solvent used in this reaction is nitrobenzene or ether .

On oxidization of this benzaldehyde by oxidizing agent ,the expected benzoic acid is obtained .

Summary:

Benzene to benzoic acid-Gattermann-Koch reaction.

Benzene to benzoic acid change .

Why phenol is acidic in nature ?

Phenol is acidic in nature-phenol to salicylic acid and benzene change .

BY P GHOSH HOME , ORGANIC

Why phenol is acidic in nature ?

The acidity of phenols arises due to its ability to lose proton to form phenoxide ions. In case of phenol molecule, the –OH group is directly attached to the sp2 hybridized carbon atom of aromatic phenyl ring .

Due to – R effect of phenyl ring , the lone pair electron on ‘O’-atom takes part in the resonance with the pi electron of benzene ring .

As a result , the oxygen atom gets partially positive charge . Hence , oxygen atom attract the O – H bonded electron towards itself .

Consequently, O –H bond becomes more polar and easily break to release proton in aqueous solution along with phenoxide anion .

Now this phenoxide ion formed is stabilized by the delocalization of negative charge due to the resonance with the pi electron of benzene ring.

It has been experimentally found that phenoxide ion has greater stability than phenols .

Because in case of phenol charge separation takes place during resonance. But in case of phenoxide anion no such charge separation take place .

For the above two reason phenol is acidic in nature . The acidic properties of phenol is also supported by its pKa value .

The pKa value of phenol molecule is 9.98 . That is phenol is weak acid .

Phenol to salicylic acid change

Phenol can be changed into salicylic acid by Reimer-Tiemann reaction . This is a chemical reaction in organic chemistry by which ortho hydroxyl benzaldehyde as well as ortho hydroxyl benzoic acid (salicylic acid ) is obtained from phenol .

When the reaction is carried out in presence of chloroform and NaOH , the product is ortho hydroxyl benzaldehyde .

But if this reaction is carried out in presence of carbon tetra chloride and NaOH base under 338 K – 348 K temperature , the product is ortho hydroxyl benzoic acid or salicylic acid .

In first step , the inter mediate product is sodium 2-oxidobenzoate which on

hydrolysis by dilute HCl , the expected salicylic acid is produced . The reaction is shown below .

Phenol to benzene change

Phenol can be changed into benzene by reduction . When phenol is heated in the presence of strong reducing agent , it changed into benzene .

Zinc metal ( dust ) is used as reducing agent . In this reaction , phenol reduced by Zn-metal and gets converted into benzene along with ZnO as side product

The reaction of phenol to benzene changed is shown below .

Summary :

Why phenol is acidic in nature ?
Phenol to salicylic acid change
Phenol to benzene change

What is Ditte's reaction in halogen chemistry-Click here .