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Hydrogen peroxide H 2 O 2 is commonly known as hydrogen peroxide , and commercially available reagents are generally 30% aqueous solutions
.
H 2 O 2 is used as a bleaching agent in industry , and a 3% aqueous solution is used as a bactericide in medicine
.
1.
Preparation of hydrogen peroxide
In the laboratory, H 2 O 2 is prepared by the reaction of peroxide and cold dilute sulfuric acid , namely
BaO 2 +H 2 SO 4 =BaSO 4 +H 2 O 2
The industrial production of hydrogen peroxide mainly uses electrochemical oxidation, ethyl anthraquinone and isopropanol oxidation
.
1) Electrochemical oxidation method
Hydrogen peroxide is prepared by electrolysis-hydrolysis method
.
Using platinum as an electrode, electrolyze saturated NH 4 HSO 4 solution to obtain (NH 4 ) 2 S 2 O 8
.
The (NH 4 ) 2 S 2 O 8 produced by electrolysis is hydrolyzed in dilute sulfuric acid to obtain H 2 O 2 , and the produced NH 4 HSO 4 can be recycled
.
(NH 4 ) 2 S 2 O 8 +2H 2 O=2NH 4 HSO 4 +H 2 O 2
2) Ethyl anthraquinone method
Under the action of a catalyst, 2-ethylanthraquinone is reduced with hydrogen using alcohol as a solvent to obtain 2-ethylanthraquinol
.
Oxidation of ethyl anthracenol with oxygen in the air obtains H 2 O 2 and ethyl anthracene aldehyde
.
H 2 +O 2 =H 2 O 2
3) Isopropanol oxidation method
Under heating and pressurizing conditions, isopropanol undergoes multi-step air oxidation to generate acetone and hydrogen peroxide
.
CH 3 CH(OH)CH 3 +O 2 =CH 3 COCH 3 +H 2 O 2
2.
The structure of hydrogen peroxide
There is a peroxy chain -OO- in the hydrogen peroxide molecule, and each oxygen atom is bonded to a hydrogen atom
.
The four atoms are not on the same straight line, nor are they coplanar
.
The O in the H 2 O 2 molecule adopts sp3 unequal hybridization.
The hybrid orbital containing a single electron forms a σ bond with the H atom and another O atom.
The repulsive effect of the lone electron pair makes the HO-O bond angle 94.
Figure 11-3 Schematic diagram of the molecular structure of H 2 O 2
3.
The properties of hydrogen peroxide
Pure H 2 O 2 is a light blue viscous liquid with a polarity (dipole moment 1.
57D) close to H 2 O (dipole moment 1.
85D)
.
H 2 O 2 intermolecular There is a strong association with the ratio of water, H 2 O 2 having a boiling point (150.
2 deg.
1) Acid
H 2 O 2 is a weak dibasic acid
The acidity is weaker than HCN
.
But its concentrated solution can react with strong alkali to generate peroxide, such as Na 2 O 2 , CaO 2 , BaO 2 and so on
.
H 2 O 2 +Ba(OH) 2 =BaO 2 +2H 2 O
2) Redox
The oxidation number of O in H 2 O 2 molecules is -1.
Therefore, H 2 O 2 has both oxidizing properties and reducing properties
.
H 2 O 2 is a strong oxidant in both acidic and alkaline solutions
.
The paint of the oil painting contains white PbSO 4 , which will react with the H 2 S in the air to generate black PbS and darken the oil painting if it is left for a long time
.
It can be whitened by carefully brushing with dilute H 2 O 2
.
PbS+4H 2 O 2 =PbSO 4 +4H 2 O
It can be seen from the element potential diagram that H 2 O 2 exhibits reducibility when it interacts with a stronger oxidant
.
Stronger reducibility under alkaline conditions
In the reaction, the only oxidation products and reduction products of H 2 O 2 are H 2 O and O 2 , so H 2 O 2 is an ideal green redox reagent, but the cost is higher
.
It can also be seen from the element potential diagram that H 2 O 2 is unstable in both acidic and alkaline media, and is easy to disproportionate and decompose
.
2H 2 O 2 =O 2 +2H 2 O
At room temperature, the decomposition rate of pure H 2 O 2 is not fast, but the decomposition reaction will accelerate when the temperature is increased and impurities are present
.
For example, H 2 O 2 contained a small amount of Mn 2+ when
Of MnO 2 + 4H + + 2E - = Mn 2+ + H 2 O E [Theta] A = 1.
23V
The Mn 2+ in the system will be oxidized by H 2 O 2 to generate MnO 2
H 2 O 2 +Mn 2+ =MnO 2 +2H + ①
The generated MnO2 can be reduced to Mn2+ by H2O2
MnO 2 +H 2 O 2 +2H + =Mn 2+ +O 2 +2H 2 O ②
Obviously, the total result of the two reactions ① and ② is the disproportionation and decomposition of H 2 O 2
.
2H 2 O 2 =O 2 +2H 2 O
Many substances are catalysts for the disproportionation and decomposition of H 2 O 2 , such as Mn 2+ , MnO 2 , Fe 2+ , Fe 3+ , I 2, etc.
Light, acid, and alkali can also accelerate the decomposition rate of H 2 O 2
.
In order to prevent H 2 O 2 decomposition, generally H 2 O 2 contained in brown bottles (alkaline glass surface to promote H 2 O 2 decomposition) or packed with black paper to prevent light to promote decomposition, sometimes adding some Na 2 SnO 3 (the colloid produced by hydrolysis can adsorb metal impurities) or a compounding agent to inhibit the catalysis of impurities on the decomposition of H 2 O 2
.
3) Peroxy chain transfer reaction
Add H 2 O 2 to the acidic K 2 Cr 2 O 7 solution , and blue CrO 5 is formed .
Cr 2 O 7 2- +4H 2 O 2 +2H + =2CrO 5 +5H 2 O
This is a typical peroxy chain transfer reaction
.
CrO 5 is unstable and decomposes quickly
.
4CrO 5 +12H + =4Cr 3+ +6H 2 O+7O 2
Adding organic solvents such as ether or amyl alcohol , CrO 5 enters the organic layer and decomposes more slowly
.
The single-bonded oxygen of vanadate can also be replaced by a peroxy chain, resulting in a peroxy chain transfer reaction
.
VO 4 3- +2H 2 O 2 =VO 2 (O 2 ) 2 3- +2H 2 O
The reaction of TiO 2+ with H 2 O 2 in a strong acid medium can also be regarded as a coordination reaction of H 2 O 2
.
TiO 2+ +2H 2 O 2 =[TiO(H 2 O 2 ) 2 ] 2+
These reaction products have specific colors and can be used for qualitative and quantitative analysis of related ions
.
