Synthesis mechanism of ethyl acetate
Ethyl acetate is a common ester compound in organic chemistry. Its synthesis mechanism is very interesting and contains many chemical principles.

1. Classic synthesis pathway - esterification reaction
1. ** Reactants and conditions **
It is common to synthesize ethyl acetate by esterification reaction of acetic acid and ethanol under the catalysis of concentrated sulfuric acid. Concentrated sulfuric acid acts as both a catalyst and a water-absorbing agent in this reaction. Acetic acid ($CH_3COOH $) and ethanol ($C_2H_5OH $) are used as reactants. In the molecular structure, acetic acid contains carboxyl ($-COOH $) and ethanol contains hydroxyl ($-OH $).
2. ** Reaction Mechanism **
First, concentrated sulfuric acid provides protons ($H ^ + $), and the carbonyl oxygen atom in the carboxyl group of acetate has a lone pair of electrons, which easily binds protons, so that the positive electricity of the carboxyl carbon atom is enhanced. Subsequently, the hydroxyl oxygen atom of ethanol attacks the positively charged carbon atom in the carboxyl group with its lone pair of electrons to form a tetrahedral intermediate. This intermediate is unstable, proton transfer occurs, and then a molecule of water is removed to form a positive carbon ion. Finally, the positive carbon ion loses a proton, forming ethyl acetate ($CH_3COOC_2H_5 $). The whole reaction process can be expressed as: $CH_3COOH + C_2H_5OH\ underset {\ Delta} {\ overset {H_2SO_4} {\ rightleftharpoons}} CH_3COOC_2H_5 + H_2O $. This reaction is a reversible reaction. In order to improve the yield of ethyl acetate, the equilibrium can be moved forward by increasing the concentration of the reactants or removing the products (such as water) in time.

Second, other synthesis methods and mechanisms
1. ** Acetaldehyde acetation **
With acetaldehyde ($CH_3CHO $) as the raw material, under the action of a specific catalyst, the condensation reaction of two molecules of acetaldehyde occurs first. The α-hydrogen atom of the molecule acetaldehyde (the hydrogen on the carbon atom connected to the carbonyl group) is affected by the electron-absorbing action of the carbonyl group and has a certain acidity. Under the action of the alkali catalyst, it leaves to form carbon negative ions. This negative carbon ion attacks the carbonyl carbon atom of another molecule of acetaldehyde, and a nucleophilic addition reaction occurs to generate β-hydroxybutyraldehyde. Then, β-hydroxybutyraldehyde undergoes a dehydration reaction under heating and catalyst action to generate crotonaldehyde ($CH_3CH = CHCHO $). Crotonaldehyde is further hydroreduced to obtain butanol. Butanol is then oxidized to form butyric acid, and butyric acid and ethanol are esterified under acid catalysis, and finally ethyl acetate is formed. Although this process has many steps, it provides an alternative path for the synthesis of ethyl acetate.
2. ** Ethylene Addition Method **
Ethylene ($CH_2 = CH_2 $) and acetic acid can directly undergo an addition reaction in the presence of a catalyst to synthesize ethyl acetate. The carbon-carbon double bond in the ethylene molecule has high reactivity. Under the action of the catalyst, the double bond is opened, and the carbon atom at one end is combined with the hydroxyl oxygen atom in the carboxyl group of acetic acid, and the carbon atom at the other end is connected with the carbonyl carbon atom in the carboxyl group to directly form ethyl acetate. This method has high atomic utilization and is in line with the concept of green chemistry.

In short, the synthesis mechanism of ethyl acetate is diverse, and different methods have their own advantages and disadvantages. In actual production, the appropriate synthesis path needs to be selected according to specific needs and conditions.